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Fault-induced perturbed stress fields and associated tensile and compressive deformation at fault tips in the ice shell of Europa: implications for fault mechanics
Abstract
Secondary fractures at the tips of strike-slip faults are common in the ice shell of Europa. Large magnitude perturbed stress fields must therefore be considered to be a viable driving mechanism for the development of part of the fracture sequence. Fault motions produce extensional and compressional quadrants around the fault tips. Theoretically, these quadrants can be associated with tensile and compressive deformational features (i.e. cracks and anti-cracks), respectively. Accordingly, we describe examples of both types of deformation at fault tips on Europa in the form of extensional tailcracks and compressional anti-cracks. The characteristics of these features with respect to the plane of the fault create a fingerprint for the mechanics of fault slip accumulation when compared with linear elastic fracture mechanics (LEFM) models of perturbed stress fields around fault tips. Tailcrack kink angles and curving geometry can be used to determine whether opening accompanies sliding motion. Kink angles in the 50 70° range are common along strike-slip faults that resemble ridges, and indicate that little to no opening accompanied sliding. In contrast, tailcrack kink angles are closer to 30° for strike-slip faults that resemble bands, with tailcrack curvatures opposite to ridge-like fault examples, indicating that these faults undergo significant dilation and infill during fault slip episodes. Anti-cracks, which may result from compression and volume reduction of porous near-surface ice, have geometries that further constrain fault motion history, corroborating the results of tailcrack analysis. The angular separation between anti-cracks and tailcracks are similar to LEFM predictions, indicating the absence of cohesive end-zones near the tips of Europan faults, hence suggesting homogeneous frictional properties along the fault length. Tailcrack analysis can be applied to the interpretation of cycloidal ridges: chains of arcuate cracks on Europa that are separated by sharp kinks called cusps. Cusp angles are reminiscent of tailcrack kink angles along ridge-like strike-slip faults. Cycloid growth in a temporally variable tidal stress field ultimately resolves shear stresses onto the near-tip region of a growing cycloid segment. Thus, resultant slip and associated tailcrack development may be the driving force behind the initiation of the succeeding arcuate segment, hence facilitating the ongoing propagation of the cycloid chain.
... identifiable as tailcracks, curved secondary tension fractures generated at the tip of slipping interfaces and faults. Tailcracks oriented clockwise from the tip indicate dextral shearing, while those oriented counterclockwise from the tip indicate sinistral shearing (Kattenhorn, 2004;Kattenhorn & Marshall, 2006). In the present case, tailcracks are formed at an angle of 70.5° in a clockwise orientation with respect to the strike of the fault and therefore indicate a right-lateral relative movement for their parent feature (Kattenhorn, 2004;Prockter et al., 2000). ...
... The identification of strike-slip faults on Europa has also revealed that certain fractures in the ice shell are not primarily caused by global tidal stresses but rather by lateral motions along strike-slip faults. These curved secondary tension fractures are termed tailcracks (see Section 3) yet sometimes also indicated as wing cracks, kinks, or horsetail fractures (Kattenhorn, 2004;Kattenhorn & Marshall, 2006;Prockter et al., 2000). Agenor Linea, a prominent bright band located in Europa's southern hemisphere (Figure 1), extends for approximately 1,500 km. ...
... This distinctive feature has experienced significant offset, with displacements reaching up to 20 km, and its current configuration may have been influenced by a complex history involving both strike-slip and dilational motion (Hoyer et al., 2014;Prockter et al., 2000). At its eastern tip, Agenor Linea displays a distinctive feature of at least six pronounced, curved trough-like tailcracks extending toward the southern direction, indicating right-lateral strike-slip motion (Kattenhorn, 2004;Kattenhorn & Marshall, 2006;Prockter et al., 2000). In Figure 3, some of the numbered (1-4) linear features bordering and intersecting Thrace Macula are the southern continuation of these tailcracks, which demonstrates their strike-slip origin. ...
Chaos terrains are geologically young and extensively disrupted surface features of Europa, thought to be an expression of the subsurface ocean interacting with the surface. The most prominent examples of this terrain on Europa are Conamara Chaos, and Thera and Thrace Maculae, all prime targets for the upcoming JUICE and Europa Clipper missions to assess the astrobiological potential of Europa. Of the three features, Thrace Macula is currently the least studied and understood. It intersects both Agenor Linea to the north and Libya Linea to the south, two important regional‐scale bands whose interaction with Thrace is yet to be fully unraveled, especially in terms of their relative ages of emplacement and activity. Using Galileo Solid State Imager data and Digital Terrain Models, we conducted detailed structural mapping and terrain analysis to develop a novel hypothesis on the mechanisms involved in the study area. We find that Thrace Macula is bordered along most sides by preexisting strike‐slip faults that have constrained its emplacement and areal distribution. We determine a sequence of events in the area involving the formation of Agenor Linea, followed by that of Libya Linea first and Thrace Macula later, and ultimately by strike‐slip tectonic activity likely driven by Libya Linea, that displaced a portion of Thrace Macula. Therefore, Thrace's subsurface material, uprising along faults postdating its formation, represents the freshest possible that could be sampled by future spacecraft in this region, a major consideration for the upcoming Europa Clipper mission.
... The term is used for topographic features that occur on extraterrestrial planetary surfaces, whose exact origin is uncertain, although they are thought to be the result of predominantly extensional tectonic processes (Schenk et al., 2020). Considering their morphologies as troughs not exhibiting raised rims along their flanks, fossae represent the most primitive (in terms of fracture development) and commonly youngest type of fractures on Europa's surface (Kattenhorn & Marshall, 2006). ...
... Since it crosscuts all other mapped units and therefore postdates them, the FU is interpreted as the youngest unit in this area. In terms of fracture development, considering their morphologies as troughs not exhibiting raised rims along their flanks, fossae represent the most primitive and commonly youngest type of fractures on Europa's surface (Kattenhorn & Marshall, 2006). ...
... along large faults (Hoppa, 1999;Sarid, 2002). However, this model is not necessarily compatible with all fault slip sense characteristics on Europa (Kattenhorn, 2004); it does not account for the whole range of fault morphologies, nor does it consider fault slip behavior and related deformation such as secondary fracturing (e.g., tailcracks and anti-cracks, Kattenhorn & Marshall, 2006). In response to the shear motion, the perturbed stress field at the tip of the fault is in fact both greater in magnitude and different in principal stress orientations to the remote (far-field) stress that caused the fault to slip. ...
Faults and fractures may emplace fresh material onto Europa's surface, originating from shallow reservoirs within the ice shell or directly from the subsurface ocean. Ménec Fossae is a region of particular interest as it displays the interaction of several geological features, including bands, double ridges, chaotic terrains, and fossae, within a relatively small area. These features might affect the emplacement of buried material and subsequent exposure of fresh volatiles, prime targets for the upcoming JUICE and Europa Clipper missions in order to assess Europa's astrobiological potential. Previous studies have already revealed that a deep central trough is present at Ménec Fossae, flanked by several subparallel minor troughs and by a few asymmetrical scarps with lobate planforms. The presence of such features has motivated this study, given its potential to provide clear indications on the tectonic regime involved. Through detailed geomorphological‐structural mapping using Galileo Solid State Imager data and terrain analysis on Digital Terrain Models, we could develop a novel hypothesis on the formation mechanisms that might have been involved in the study area. We propose that Ménec Fossae has been shaped by transtensional (strike‐slip with an extensional component) tectonic activity, as indicated by the orientation and relationship of the tectonic features present. Likely, such transtensional tectonism occurred above or associated with shallow subsurface water, consistent with the overall morphology and topography of the study area and the presence of chaotic terrains and double ridges. These results strengthen the case for widely distributed shallow water reservoirs within Europa's ice shell.
... Tensile wing cracks, also known as pinnate joints [1], tension gashes [2] or tail cracks, are opening-mode fractures, which may either appear as a single out-of-plane crack initiated from or around flaw tips (Figures 1, 4) or appearing as multiple subparallel fractures (Figures 5,6) with tapered tips branching out from the ends of flaws along the slipping flaw interfaces [3,4]. Their occurrence is agreed to be related to the sliding along pre-existing flaws (faults) [5]. ...
... They are commonly spaced a few centimeters apart and are also inclined at an angle with the pre-existing flaw/joint [7]. However, long single tensile wing cracks and horsetails extending up to several kilometers have also been reported [4,9] as shown in Figure 7. The development of horsetail fractures is favored by the variations in frictional strength along pre-existing flaws, which produces a slip gradient. ...
... In addition to the tensile wing cracks, which develop from the extensional quadrant of the pre-existing sliding flaws (Figure 10), anticracks are also another common feature initiated from the pre-existing flaws, but in the compressional quadrant [2,4,17,18]. The anticracks originate at stress concentrations and propagate through the rock (Figure 11), and occasionally appear as discrete solution surfaces (stylolites). ...
This paper briefly reviews the literature on the general crack formation mechanisms and the typical occurrence of crack coalescence in natural rocks, but with no particular reference to specific locations or geologic settings. The field occurrences of tensile wing cracks, horsetail cracks, anticracks and shear cracks, as well as their coalescence are described. In contrast to the tensile wing cracks which develop in the tensile quadrant, anticracks develop from the pre-existing discontinuities in the compressive quadrant. The discussion will be illustrated with plenty of field examples, supplemented by a review of commonly used terminologies.
... Nonetheless, some dilational bands are more rhomboidal where they occur in extensional stepover zones (i.e., pull-aparts) along strike-slip faults (see section 2.3.3) such as Astypalaea Linea in the southern antijovian region Kattenhorn, 2004a) and wedge-shaped bands in Argadnel Regio (Schulson, 2002;Kattenhorn and Marshall, 2006), implying a localized tectonic phenomenon. ...
... Although cycloidal ridges are more common, relatively younger cycloidal fractures have also been identified (e.g., Marshall and Kattenhorn, 2005), indicating that cycloid development has persisted until at least geologically recent times. (3) Tailcracks emanate from the tips of strike-slip faults (Fig. 7b) and represent brittle accommodation of fault motion in the tensile quadrant of a fault tip (Schulson, 2002;Kattenhorn, 2004a;Kattenhorn and Marshall, 2006). Also referred to as horsetail splays or wing cracks in terrestrial analogs, they have been recognized in many locations on Europa such as the impressive example at the southeast end of Agenor Linea Kattenhorn, 2004a). ...
... Strike-slip fault driven convergence is suggested to have occurred in the marginal blocks alongside Astypalaea Linea (Mével and Mercier, 2002), resulting in up to 55% contraction along numerous distributed ridge-like crenulations (perhaps a related contractional mechanism to convergence bands). Evidence for strike-slip fault-related convergence bands is also presented by Kattenhorn and Marshall (2006), who characterize compressive stress concentrations in the tip regions of strike-slip faults in Argadnel Regio (see section 2.3.3). ...
Europa has experienced significant tectonic disruption over its visible history. The descrip- tion, interpretation, and modeling of tectonic features imaged by the Voyager and Galileo mis- sions have resulted in significant developments in four key areas addressed in this chapter: (1) The characteristics and formation mechanisms of the various types of tectonic features; (2) the driving force behind the tectonics; (3) the geological evolution of its surface; and (4) the ques- tion of ongoing tectonics. We elaborate upon these themes, focusing on the following elements: (1) The prevalence of global tension, combined with the inherent weakness of ice, has resulted in a wealth of extensional tectonic features. Crustal convergence features are less obvious but are seemingly necessary for a balanced surface area budget in light of the large amount of ex- tension. Strike-slip faults are relatively common but may not imply primary compressive shear failure, as the constantly changing nature of the tidal stress field likely promotes shearing re- activation of preexisting cracks. Frictional shearing and heating thus contributed to the mor- phologic and mechanical evolution of tectonic features. (2) Many fracture patterns can be correlated with theoretical stress fields induced by diurnal tidal forcing and long-term effects of nonsynchronous rotation of the icy shell; however, these driving mechanisms alone prob- ably cannot explain all fracturing. Additional sources of stress may have been associated with orbital evolution, polar wander, finite obliquity, ice shell thickening, endogenic forcing by convection and diapirism, and secondary effects driven by strike-slip faulting and plate flex- ure. (3) Tectonic resurfacing has dominated the ~40–90 m.y. of visible geological history. A gradual decrease in tectonic activity through time coincided with an increase in cryomagmatism and thermal convection in the icy shell, implying shell thickening. Hence, tectonic resurfacing gave way to cryomagmatic resurfacing through the development of broad areas of crustal dis- ruption called chaos. (4) There is no definitive evidence for active tectonics; however, some tectonic features have been noted to postdate chaos. A thickening icy shell equates to a de- creased tidal response in the underlying ocean, but stresses associated with icy shell expansion may still sufficiently augment the contemporary tidal stress state to allow active tectonics.
... In the northern hemisphere, displacement is predominantly sinistral (left-lateral) whereas in the southern hemisphere it is dextral (right-lateral), although variability within 40°latitude of the equator appears dependent on the fault orientation and longitude. In the absence of offset indicators, secondary fractures such as tailcracks at the tips of strike-slip faults can be used to determine slip sense (Kattenhorn, 2004;Kattenhorn and Marshall, 2006). ...
... It is comprised of two arcuate segments (concave south) joined at a cusp, all of which appear to have been subsequently dilated by $3 km (Fig. 2c). From the eastern terminus, six tailcracks extend from the tip of the band toward the SE in a horsetail complex (Prockter et al., 2000b;Kattenhorn, 2004;Kattenhorn and Marshall, 2006). These arcuate cracks (black in Fig. 2b) are distinctly cuspate and thus have the appearance of cycloids (Hoppa et al., 1999b), implying that they grew relatively rapidly under the driving force of the combined diurnal tidal stress field and the fault-tip perturbed stress field (Kattenhorn and Marshall, 2006). ...
... From the eastern terminus, six tailcracks extend from the tip of the band toward the SE in a horsetail complex (Prockter et al., 2000b;Kattenhorn, 2004;Kattenhorn and Marshall, 2006). These arcuate cracks (black in Fig. 2b) are distinctly cuspate and thus have the appearance of cycloids (Hoppa et al., 1999b), implying that they grew relatively rapidly under the driving force of the combined diurnal tidal stress field and the fault-tip perturbed stress field (Kattenhorn and Marshall, 2006). Their presence at the tip of Agenor has been previously explained as being indicative of a stress concentration related to dextral motion and dilation along Agenor (Kattenhorn, 2004). ...
... In the northern hemisphere, displacement is predominantly sinistral (left-lateral) whereas in the southern hemisphere it is dextral (right-lateral), although variability within 40°latitude of the equator appears dependent on the fault orientation and longitude. In the absence of offset indicators, secondary fractures such as tailcracks at the tips of strike-slip faults can be used to determine slip sense (Kattenhorn, 2004;Kattenhorn and Marshall, 2006). ...
... It is comprised of two arcuate segments (concave south) joined at a cusp, all of which appear to have been subsequently dilated by $3 km (Fig. 2c). From the eastern terminus, six tailcracks extend from the tip of the band toward the SE in a horsetail complex (Prockter et al., 2000b;Kattenhorn, 2004;Kattenhorn and Marshall, 2006). These arcuate cracks (black in Fig. 2b) are distinctly cuspate and thus have the appearance of cycloids (Hoppa et al., 1999b), implying that they grew relatively rapidly under the driving force of the combined diurnal tidal stress field and the fault-tip perturbed stress field (Kattenhorn and Marshall, 2006). ...
... From the eastern terminus, six tailcracks extend from the tip of the band toward the SE in a horsetail complex (Prockter et al., 2000b;Kattenhorn, 2004;Kattenhorn and Marshall, 2006). These arcuate cracks (black in Fig. 2b) are distinctly cuspate and thus have the appearance of cycloids (Hoppa et al., 1999b), implying that they grew relatively rapidly under the driving force of the combined diurnal tidal stress field and the fault-tip perturbed stress field (Kattenhorn and Marshall, 2006). Their presence at the tip of Agenor has been previously explained as being indicative of a stress concentration related to dextral motion and dilation along Agenor (Kattenhorn, 2004). ...
Agenor Linea formed in at least three stages under different stress
conditions. The first two stages were dilational; the third stage
dextral transtension.
... [2] Splay faults that form "damage zones" around fault tips have been documented at scales ranging from laboratory experiments to involving the entire crust [Kim et al., 2004;Kim and Sanderson, 2006]. At the tips of mode II (strike-slip) cracks or faults, the local perturbation of the main stress field causes these splay faults to occupy three distinct domains dominated respectively by shear, contractional and extensional structures (Figure 1) [Rispoli, 1981;Pollard and Segall, 1987;Willemse and Pollard, 1998;Kattenhorn and Marshall, 2006]. In front of the main fault tip, shear stresses dominate to form diverging strike-slip branch faults that splay off the main fault tip [e.g., Kim et al., 2004;Kim and Sanderson, 2006]. ...
... In front of the main fault tip, shear stresses dominate to form diverging strike-slip branch faults that splay off the main fault tip [e.g., Kim et al., 2004;Kim and Sanderson, 2006]. The extensional domain on one side of the fault tip is characterized by "wing-tip" extensional cracks or normal faults that splay outward from the main fault with a characteristic~70.5 angle for a pure strike-slip fault, but away from the main fault the splay faults gradually rotate to be parallel to the direction of the principal compressive stress [Willemse and Pollard, 1998;Kattenhorn and Marshall, 2006]. Contractional structures in the dilational quadrant, if present, trend perpendicular to the extensional structures and the principal compressive stress direction. ...
... In the compressional quadrant on the other side of the main fault, thrust faults or solution features extend outward from the main fault. These thrust faults have a characteristic take-off angle of~70.5 from the main fault and gradually rotate to become perpendicular to the direction of principal compressive stress [Willemse and Pollard, 1998;Kattenhorn and Marshall, 2006]. Splay faults comprising damage zones around fault tips are well documented at outcrop scale [e.g., Rispoli, 1981;Cruikshank et al., 1991;McGrath and Davison, 1995;Kim et al., 2003Kim et al., , 2004, and published examples of large splay faults include crustal-scale fault systems [Kim et al., 2004;Kim and Sanderson, 2006] and fractures along strike-slip faults on the ice shell of Jupiter's moon Europa [Kattenhorn and Marshall, 2006]. ...
The Yakima Folds (YF) comprise anticlines above reverse faults cutting
flows of the Miocene Columbia River Basalt Group of central Washington
State. The YF are bisected by the ~1100-km-long Olympic-Wallowa
Lineament (OWL), which is an alignment of topographic features including
known faults. There is considerable debate about the origin and
earthquake potential of both the YF and OWL, which lie near six major
dams and a large nuclear waste storage site. Here I show that the trends
of the faults forming the YF relative to the OWL match remarkably well
the trends of the principal stress directions at the end of a vertical
strike-slip fault. This comparison and the termination of some YF
against the OWL are consistent with the YF initially forming as splay
faults caused by an along-strike decrease in the amount of strike-slip
on the OWL. The hypothesis is that the YF faults initially developed as
splay faults in the early to mid Miocene under NNW-oriented principal
compressive stress, but the anticlines subsequently grew with thrust
motion after the principal compressive stress direction rotated to N-S
or NNE after the mid-Miocene. A seismic profile across one of the YF
anticlines shows folding at about 7 km depth, indicating deformation of
sub-basalt strata. The seismic profile and the hypothesized relationship
between the YF and the OWL suggest that the structures are connected in
the middle or lower crust, and that the faults forming the YF are
large-scale splay faults associated with a major strike-slip fault
system.
... Thrust faults have been identified on Mercury, Venus, the Moon, and Mars (e.g., Suppe and Connors, 1992;Williams et al., 1994;Solomon et al., 2008; and chapters in this volume). Strike-slip faults have been identified on Mars (e.g., Schultz, 1989;Okubo and Schultz, 2006b;Andrews-Hanna et al., 2008) and on the icy satellite Europa that shows large lateral displacements, such as those found at terrestrial transform plate boundaries (Schenk and McKinnon, 1989;Kattenhorn and Marshall, 2006). Individual dilatant cracks (joints) and deformation bands Fossen et al., 2007) have both been identified on Mars (Okubo and McEwen, 2007;Okubo et al., 2008a) and perhaps Europa (Aydin, 2006), and the presence of subsurface igneous dikes has been inferred on Mars from surface topographic data . ...
... The analyses of fault populations began with Earth examples, so the first salient works and main references cited here are for terrestrial fault systems. The characteristics and processes of fault system development (e.g., McGill and Stromquist, 1979;Davison, 1994) described in this section are observed as well in planetary fault systems (e.g., Muehlberger, 1974;Lucchitta, 1976;Sharpton and Head, 1988;Banerdt et al., 1992;McGill, 1993;Schultz and Fori, 1996;Mège and Masson, 1996;Schultz, 1991Schultz, , 1997Schultz, , 1999Schultz, , 2000aKoenig and Aydin, 1998;Mangold et al., 1998;Watters et al., 1998;Wilkins and Schultz, 2003;Schultz, 2003, 2006b;Hauber and Kronberg, 2005;Kattenhorn and Marshall, 2006;Kiefer and Swafford, 2006;Knapmeyer et al., 2006), although the rheologies and characteristics of the lithospheric strength envelopes for those bodies differ in detail from those for the Earth (see Kohlstedt and Mackwell,Chapter 9). ...
This book describes the tectonic landforms resulting from major internal and external forces acting on the outer layers of solid bodies throughout the Solar System. It presents a detailed survey of tectonic structures at a range of length scales found on Mercury, Venus, the Moon, Mars, the outer planet satellites, and asteroids. A diverse range of models for the sources of tectonic stresses acting on silicate and icy crusts is outlined, comparing processes acting throughout the Solar System. Rheological and mechanical properties of planetary crusts and lithospheres are discussed to understand how and why tectonic stresses manifest themselves differently on various bodies. Results from fault population data are assessed in detail. The book provides methods for mapping and analysing planetary tectonic features, and is illustrated with diagrams and spectacular images returned by manned and robotic spacecraft. It forms an essential reference for researchers and students in planetary geology and tectonics.
... Argadnel Regio, a region of intense deformation located ~400 km to the north of Agenor Linea and spanning ~800 km in latitude (2.0°S to 27.8°S) and ~2,000 km in longitude (114.7°E to 183.6°E), is typified by an intertwined network of low albedo bands, double ridges, chaos terrain, and evidence of potential cryovolcanism with little to no vertical relief ( Figure 5A) (Smith et al., 1979;Schenk and McKinnon, 1989;Sullivan et al., 1997Kattenhorn and Marshall, 2006;Prockter et al., 2017;Melton, 2018). The tectonic deformation that characterizes Argadnel Regio is not only extremely unique to this region of Europa, but makes Europa itself unique as this style of deformation has not been described anywhere else in the solar system. ...
... (Prockter et al., 2002). In eastern Argadnel, the dilation of numerous right-lateral strike-slip faults has formed wedged-shaped bands (Zimmerman and Kattenhorn, 2020), some of which resemble tailcracks (Kattenhorn and Marshall, 2006). In western Argadnel, circular rafts of terrain are encircled by band-like material. ...
Europa, Jupiter's fourth-largest moon, has an anomalously young surface age (~40–90 million years old), and an extensively fractured surface. Conventional models for tectonic features on Europa have invoked global-scale tidal forcings (e.g., diurnal forcing, obliquity, nonsynchronous rotation, and true polar wander) as the mechanisms responsible for fracturing the icy shell. In an attempt to examine the complex history of deformation on Europa in the context of global tidal stress models, I examined a multitude of tectonic feature types, orientations, and ages across a broad region of Europa's anti-jovian hemisphere encompassing Argadnel Regio, a complex region of deformation consisting of an intertwining network of low albedo bands and ridges, and Agenor Linea, a ~1,500 km long band-like strike-slip fault. After mapping geologic feature types, orientations, and ages and comparing my observations with global tidal stress models, I found that Europa's oldest fractures (two sets of intersecting ridges oriented NE-SW and NW-SE) most closely align with the predicted stresses from two separate episodes of ~45° and ~15° of true polar wander. Dilational bands located to the north of Argadnel Regio that dilated pre-existing cycloids in a north-south extensional direction align more closely with a global stress field that would have been produced by a more recent stage of nonsynchronous rotation. While these models accounted for fracture sets in Europa's oldest terrain and younger dilated cycloids, many young tectonic features are not consistent with the predictions of true polar wander or nonsynchronous rotation stress fields, such as: 1) ~700–km-long, right-stepping én echelon bands with sigmoidal geometries within Argadnel Regio that are consistent with broadly-distributed, left-lateral shearing, 2) left-stepping én echelon bands younger than the ~700 km long sigmoidal bands that are consistent with right-lateral shearing, 3) clockwise rotations of circular rafts of material within Argadnel Regio also consistent with right-lateral shearing, and 4) bands (~5 km wide, ~10 km long) oriented ~045° and located ~100 km south of Agenor Linea that are consistent with left-lateral shearing of Agenor Linea and which pre-dates more recent right-lateral shearing of Agenor Linea. While these observations do not align with stresses from global tidal forcing, previous studies based on numerical and physical models have proposed plate tectonics as a potential mechanism responsible for fracturing and resurfacing Europa's icy crust. However, observational evidence (e.g., geologic evidence of translation or rotation across plate boundaries or broadly distributed lateral shearing within plates) is necessary to confirm the existence of plate tectonics on Europa. After extensively mapping bands, ridges, and other tectonic features across Argadnel Regio and Agenor Linea, I assert that young tectonic features align better with broadly distributed lateral shearing, a necessary component of plate tectonics, than with global tidal stress models. The misalignment of tectonic features with conventional global-tidal stress models, in addition to the presence of tectonic features resembling artifacts of broad-scale lateral shearing, suggests that deformation on Europa may need to be re-evaluated under a plate-tectonic paradigm in combination with global tidal stress models, occurring as contemporaneous processes. Plate tectonics would not only help explain complex deformation on Europa but would also provide a mechanism for recycling Europa's icy crust and maintaining the moon's young surface age.
... Thrust faults have been identified on Mercury, Venus, the Moon, and Mars (e.g., Suppe and Connors, 1992;Williams et al., 1994;Solomon et al., 2008; and chapters in this volume). Strike-slip faults have been identified on Mars (e.g., Schultz, 1989;Okubo and Schultz, 2006b;Andrews-Hanna et al., 2008) and on the icy satellite Europa that shows large lateral displacements, such as those found at terrestrial transform plate boundaries (Schenk and McKinnon, 1989;Kattenhorn and Marshall, 2006). Individual dilatant cracks (joints) and deformation bands Fossen et al., 2007) have both been identified on Mars (Okubo and McEwen, 2007;Okubo et al., 2008a) and perhaps Europa (Aydin, 2006), and the presence of subsurface igneous dikes has been inferred on Mars from surface topographic data . ...
... The analyses of fault populations began with Earth examples, so the first salient works and main references cited here are for terrestrial fault systems. The characteristics and processes of fault system development (e.g., McGill and Stromquist, 1979;Davison, 1994) described in this section are observed as well in planetary fault systems (e.g., Muehlberger, 1974;Lucchitta, 1976;Sharpton and Head, 1988;Banerdt et al., 1992;McGill, 1993;Schultz and Fori, 1996;Mège and Masson, 1996;Schultz, 1991Schultz, , 1997Schultz, , 1999Schultz, , 2000aKoenig and Aydin, 1998;Mangold et al., 1998;Watters et al., 1998;Wilkins and Schultz, 2003;Schultz, 2003, 2006b;Hauber and Kronberg, 2005;Kattenhorn and Marshall, 2006;Kiefer and Swafford, 2006;Knapmeyer et al., 2006), although the rheologies and characteristics of the lithospheric strength envelopes for those bodies differ in detail from those for the Earth (see Kohlstedt and Mackwell,Chapter 9). ...
... To date, considerable efforts have been made to study the fault activity and the geostress in various regions [20][21][22][23]. The Qinghai-Tibet Plateau is the largest plateau in the world, with multiple active fault zones within its interior. ...
The construction of infrastructure projects such as the Sichuan–Tibet Railway and western cascade hydropower stations has led to the increasing development of ultra-long and deeply buried tunnels in an environment characterized by highly active neotectonic movement, which affects the sustainable development of ecological civilization in Tibet. However, the effects of faults resulting from tectonic activity on the distribution of geostress fields have not been systematically studied. This research focuses on the development characteristics and basic type of the Zhuka fault near the RM hydropower station, aiming to analyze the phenomenon of geostress concentration in the study area. Field investigations have revealed significant high-geostress damage on the downstream slope of the lower dam site, situated on the hanging wall of the Zhuka fault. The results indicate a correlation between these high-geostress phenomena and the Zhuka fault, suggesting the concentration of geostress within a certain range on the hanging wall and outside of the fault zone. Stress concentration primarily depends on the characteristics of fault thrusting and fault morphology. The left-lateral strike-slip and thrusting process of the Zhuka fault, combined with NNW-directed tectonic compression stress and sudden changes in fault strike, contribute to geostress concentration within a specific range of the fault hanging wall. The observed high-geostress damage to the hard rock on the valley slope results from the combined effect of construction stress concentration and fourth-order valley incision stress concentration, which influences site selection for the RM hydropower station, thereby highlighting the role of geostress concentration outside the fault zone in engineering practice. This study provides valuable insights into geostress concentration and its implications for sustainable development in the Sichuan–Tibet region.
... This lineament has the 305 morphological characteristics of a ridge and the structures formed at its southern tip are 306 identifiable as tailcracks, curved secondary tension fractures generated at the tip of slipping 307 interfaces and faults. Tailcracks oriented clockwise from the tip indicate dextral shearing, while 308 those oriented counterclockwise from the tip indicate sinistral shearing (Kattenhorn, 2004; 309 Kattenhorn & Marshall, 2006). In the present case, tailcracks are formed at an angle of 70.5° in a 310 clockwise orientation with respect to the strike of the fault and therefore indicate a right-lateral 311 relative movement for their parent feature (Kattenhorn, 2004;. ...
Chaos terrains are geologically young and extensively disrupted surface features of Europa, thought to be an expression of the subsurface ocean interacting with the surface. The most prominent examples of this terrain on Europa are Conamara Chaos, and Thera and Thrace Maculae, all prime targets for the upcoming JUICE and Europa Clipper missions to assess the astrobiological potential of Europa. Of the three features, Thrace Macula is currently the least studied and understood. It intersects both Agenor Linea to the north and Libya Linea to the south, two important regional-scale bands whose interaction with Thrace is yet to be fully unraveled, especially in terms of their relative ages of emplacement and activity. Through detailed structural mapping using Galileo Solid State Imager data and terrain analysis on Digital Terrain Models, we here develop a novel hypothesis on the mechanisms that have been involved in the study area. We find that Thrace Macula is bordered along most sides by preexisting strike-slip faults that have constrained its emplacement and areal distribution. We determine a sequence of events in the area involving the formation of Agenor Linea, followed by that of Libya Linea first and Thrace Macula later, and ultimately by strike-slip tectonic activity driven by Libya Linea and displacing a portion of Thrace Macula. Therefore, Thrace’s subsurface material, uprising along faults postdating its formation, likely represents the freshest possible that could be sampled by future spacecraft in this region, a major consideration for the upcoming Europa Clipper mission.
... Soren (2010) studied that on a pit slope of 48°, if there is a fault with an initial factor of safety greater than 1.2, the safety factor falls below one. You et al. (2019) studied openpit mine slope stability due to three faults, whereas Kattenhorn and Marshall (2006) investigated tectonic structures effects on slope stability. The slope's safety factor decreased as faults were introduced and high stress concentration areas were observed at fault ends. ...
Mining operations can have a significant impact on the stability of the surrounding area. One example is the Medapalli open pit coal mine in southern India. The mine is a large excavation working at a depth of 165 m that can reach up to 200 m. The western side highwall has locked-up coal reserves in the mine, but concerns about the geologically disturbed regions have resulted in complications and significant challenges. Surface tension cracks around the excavation became visible in 2018, prompting intensive monitoring, protective measures, and numerous geotechnical analyses. The area, however, has a rich tectonic history, with faults interacting with soil movements. Proper geotechnical investigations were used in this work to analyse the stability of the highwall due to faults' effects on the area's reaction due to mining operations. The findings in the study highlighted the significance of flaws in the ground movement due to improper design of the highwall fault interaction area. The presence of the fault increases the likelihood of tensile cracks and subsidence at the highwall's surface level, significantly worsening the mining activities in the area. The analysis reveals that complex geological features, such as the presence of faults roughly parallel to the highwall slope profile, can exacerbate the mining operations in the surrounding environment. The recommended slope design with protective measures towards the west side disturbed highwall area helps safely excavate the western side highwall locked-up coal reserves in the Medapalli open pit mine.
... With the development of computer hardware and software, numerical simulation methods have been increasingly widely used in the study of tectonic stress because of the shorter research periods required, more intuitive research results, and less limited field environment. At present, numerical simulation methods of coal and rock mass have been widely used in the study of the stress fields at fault tips [25][26][27][28] and fault group [29], stability analysis of surrounding rock near faults [30][31][32][33][34][35][36], influence mechanism of fault parameters on the degree of disturbance to the stress field [37][38][39], etc. ...
To quantitatively describe the distribution characteristics of stress field of coal rock in fault area, a finite element model was established to study the influence mechanisms of different fault parameters on the stress distribution characteristics of coal rock and a prediction model of the tectonic stress field of a fault-containing coal rock was established based on the numerical simulations. The numerical simulation results show that the coal rock in the hanging wall of a normal fault forms an area of disturbance significantly larger than that in the footwall of the normal fault and reverse fault. With the increase in fault throw, the stress concentration factor and fault influence range decrease in both the normal and reverse fault scenarios. Additionally, for both the normal and reverse fault scenarios, with the increase in fault dip angle, the coal rock stress concentration zone gradually collapses to the fault plane and the stress concentration coefficient gradually increases due to the reduction in the area of pressure relief. The prediction model of the tectonic stress field can better describe the quantitative relationship between the fault parameters and the stress of coal rock, which can provide guidance for the excavation design of mining engineering and early warning for possible coal and gas outburst disasters.
... One region where faults developed at a high angle to the principal displacement zone that are not necessarily R′ shears, is at the horsetail tip regions of strike-slip faults and in the soft-linked stepping geometries between overlapping fault tips (e.g. Granier 1985;Hempton and Neher 1986;Sylvester 1988;Cowan 1990;Willemse and Pollard 1998;Kattenhorn and Marshall 2006;Kim and Sanderson 2006). The fault patterns of the Moattama Basin look compatible with a horsetail geometry, but this implies the Sagaing Fault terminates in the basin, for example like the relationship of the Mae Ping Corti and Dooley (2015), 15 mm displacement, (c) sandbox model, Dooley and McClay (1997), 10 cm displacement). ...
The Sagaing Fault (SF), one of the world's most active strike-slip faults, defines a plate boundary on the eastern West Burma Block margin, from the Andaman Spreading centre, northwards for >1600 km to the eastern Himalayas. In the Northern Andaman Sea the SF traverses the Late Miocene-Recent Moattama Basin. There, 2D and 3D seismic reflection data shows highly unusual fault patterns, that overall resemble a giant (area >33,000 km ² ) horsetail structure. A horsetail pattern typically implies loss of displacement at a fault tip, which is potentially incompatible with the SF forming a transform margin. In the thinner, northern part of the Late Miocene-Recent basin three branches of the SF can be identified. These become lost in the thickest (>7km), central part of the basin, and two branches emerge to the south where the basin thins. The fault patterns are interpreted to represent a previously unknown interaction of thin- and thick-skinned styles, where relatively shallow detached structures and sediment loading have interacted with basement-involved strike-slip faults that form a releasing bend geometry at the basement level. The Moattama Basin demonstrates how very thick sedimentary basins can produce fault patterns that differ from classic structural models.
... Field observations and laboratory experiments show how deformation can become more localized toward macroscopic failure in the laboratory, and with increasing total slip and slip-rate along faults in the field (e.g., Segall and Pollard, 1983;Chen and Spetzler, 1993;Bergbauer and Martel, 1999;Ben-Zion and Sammis, 2003;Schubnel et al., 2003;Kattenhorn and Marshall, 2006;De Joussineau et al., 2007;Moir et al., 2010;Zhao et al., 2018;Kandula et al., 2019;Renard et al., 2019a;Renard et al., 2019b;McBeck et al., 2020a;McBeck et al., 2020b). Locations of acoustic emissions (AEs) captured during rock deformation experiments under triaxial compression loading suggest that the AEs localize from a diffuse cloud to a narrower zone with increasing deformation (Lockner et al., 1991;Aben et al., 2019). ...
We quantify the spatial distribution of fracture networks throughout six in situ X-ray tomography triaxial compression experiments on crystalline rocks at confining stresses of 5–35 MPa in order to quantify how fracture development controls the final macroscopic failure of the rock, a process analogous to those that control geohazards such as earthquakes and landslides. Tracking the proportion of the cumulative volume of fractures with volumes >90th percentile to the total fracture volume, ∑ v 90 / v t o t indicates that the fracture networks tend to increase in localization toward these largest fractures for up to 80% of the applied differential stress. The evolution of this metric also matches the evolution of the Gini coefficient, which measures the deviation of a population from uniformity. These results are consistent with observations of localizing low magnitude seismicity before large earthquakes in southern California. In both this analysis and the present work, phases of delocalization interrupt the general increase in localization preceding catastrophic failure, indicating that delocalization does not necessarily indicate a reduction of seismic hazard. However, the proportion of the maximum fracture volume to the total fracture volume does not increase monotonically. Experiments with higher confining stress tend to experience greater localization. To further quantify localization, we compare the geometry of the largest fractures, with volumes >90th percentile, to the best fit plane through these fractures immediately preceding failure. The r ² scores and the mean distance of the fractures to the plane indicate greater localization in monzonite than in granite. The smaller mean mineral diameter and lower confining stress in the granite experiments may contribute to this result. Tracking these various metrics of localization reveals a close association between macroscopic yielding and the acceleration of fracture network localization. Near yielding, ∑ v 90 / v t o t and the Gini coefficient increase while the mean distance to the final failure plane decreases. Macroscopic yielding thus occurs when the rate of fracture network localization increases.
... Field observations and laboratory experiments show how deformation can become more localized toward macroscopic failure in the laboratory, and with increasing total slip and slip-rate along faults in the field (e.g., Segall and Pollard, 1983;Chen and Spetzler, 1993;Bergbauer and Martel, 1999;Ben-Zion and Sammis, 2003;Schubnel et al., 2003;Kattenhorn and Marshall, 2006;De Joussineau et al., 2007;Moir et al., 2010;Zhao et al., 2018;Kandula et al., 2019;Renard et al., 2019a;Renard et al., 2019b;McBeck et al., 2020a;McBeck et al., 2020b). Locations of acoustic emissions (AEs) captured during rock deformation experiments under triaxial compression loading suggest that the AEs localize from a diffuse cloud to a narrower zone with increasing deformation (Lockner et al., 1991;Aben et al., 2019). ...
... They showed that faults significantly modified the stresses and the deformations of the soil. Kattenhorn and Marshall (2006) studied the consequences of tectonic structures on slope stability, and You et al. (2019) studied the effect of three faults on an open-pit mine's slope stability. They concluded that the safety factor of the slope decreased with the introduction of the faults and noticed that higher stress concentration areas were created at the ends of the faults. ...
Mining operations can drastically affect
the stability of nearby areas. A representative case for
this has been the Mavropigi mine, a part of an open-pit
lignite mining complex in northwestern Greece.
Mavropigi is a vast excavation that has reached
150 m depth and has posed severe challenges and
stability issues that caused problems in the area. In
2010, noteworthy surface tension cracks appeared
near the excavation, leading to extensive monitoring
and countermeasures, while various studies were
conducted. The present work aims to revisit the case
study of Mavropigi from a different than the previous
perspectives. Previous studies were based only on
continuum approaches, thus understating or ignoring
the effect of discontinuities. Nevertheless, the area has
an intense tectonic past and faults that interact with
soil movements. In this work, advanced, discontinuous
numerical modelling through the distinct element
method was used to understand better the role of slopefault
interaction in the case study of Mavropigi and
assess the faults’ effect on the area’s response. The
results emphasised the influence of faults on ground
movements. The fault’s existence increases the impact
of the mine operations on the surrounding area
significantly and intensifies the possibility of structural
damage in nearby constructions. The analysis confirms
that the open-pit mine’s effect on the surrounding
area can be amplified under complex geological
conditions, in this case, the presence of faults nearly
parallel to the slope inclination.
... They showed that faults significantly modified the stresses and the deformations of the soil. Kattenhorn and Marshall (2006) studied the consequences of tectonic structures on slope stability, and You et al. (2019) studied the effect of three faults on an open-pit mine's slope stability. They concluded that the safety factor of the slope decreased with the introduction of the faults and noticed that higher stress concentration areas were created at the ends of the faults. ...
Mining operations can drastically affect the stability of nearby areas. A representative case for this has been the Mavropigi mine, a part of an open-pit lignite mining complex in northwestern Greece. Mavropigi is a vast excavation that has reached 150 m depth and has posed severe challenges and stability issues that caused problems in the area. In 2010, noteworthy surface tension cracks appeared near the excavation, leading to extensive monitoring and countermeasures, while various studies were conducted. The present work aims to revisit the case study of Mavropigi from a different than the previous perspectives. Previous studies were based only on continuum approaches, thus understating or ignoring the effect of discontinuities. Nevertheless, the area has an intense tectonic past and faults that interact with soil movements. In this work, advanced, discontinuous numerical modelling through the distinct element method was used to understand better the role of slope-fault interaction in the case study of Mavropigi and assess the faults’ effect on the area’s response. The results emphasised the influence of faults on ground movements. The fault’s existence increases the impact of the mine operations on the surrounding area significantly and intensifies the possibility of structural damage in nearby constructions. The analysis confirms that the open-pit mine’s effect on the surrounding area can be amplified under complex geological conditions, in this case, the presence of faults nearly parallel to the slope inclination.
... The formation of wing cracks is an interesting phenomenon that has been found in a wide range of earth and planetary science phenomena. For example, secondary cracks have been observed on opposite ends of a fault, as a result of the faulting process [81][82][83][84][85][86], associated with splitting, exfoliation, and rock burst [12], and have also been observed at the tip of strike-slip faults in the ice shell of Europa, Jupiter's moon [87]. While these initial static measurements allowed interesting observations, they did not allow to capture the evolution of dynamic ruptures. ...
The last few decades have seen great achievements in dynamic fracture mechanics. Yet, it was not possible to experimentally quantify the full-field behavior of dynamic fractures, until very recently. Here, we review our recent work on the full-field quantification of the temporal evolution of dynamic shear ruptures. Our newly developed approach based on digital image correlation combined with ultrahigh-speed photography has revolutionized the capabilities of measuring highly transient phenomena and enabled addressing key questions of rupture dynamics. Recent milestones include the visualization of the complete displacement, particle velocity, strain, stress and strain rate fields near growing ruptures, capturing the evolution of dynamic friction during individual rupture growth, and the detailed study of rupture speed limits. For example, dynamic friction has been the biggest unknown controlling how frictional ruptures develop but it has been impossible, until now, to measure dynamic friction during spontaneous rupture propagation and to understand its dependence on other quantities. Our recent measurements allow, by simultaneously tracking tractions and sliding speeds on the rupturing interface, to disentangle its complex dependence on the slip, slip velocity, and on their history. In another application, we have uncovered new phenomena that could not be detected with previous methods, such as the formation of pressure shock fronts associated with “supersonic” propagation of shear ruptures in viscoelastic materials where the wave speeds are shown to depend strongly on the strain rate.
... 13). The measured value of horizontal angle of 49 º between the fault tip and the orientation of direction of the recent riverbed in the entry area of gorge I indicates anti-crack, mixed-mode I-II, and concomitant sliding and opening according to Kattenhorn et al. (2006) (fig. 14). ...
My thesis based on the neotectonic uplifting of Visočica and Bjelašnica MTS in Central Dianrides as the result of the remote stress which is a promontor the Adria plate. This remote horizontal compresive stress directly influenced on the joint development and fault activity which resulted intensive exodinamic processes of geomorphic reshaping eleven Rakitnica Inner Gorges.
... The formation of wing cracks is an interesting phenomenon that has been found in a wide range of earth and planetary science phenomena. For example, secondary cracks have been observed on opposite ends of a fault, as a result of the faulting process [81][82][83][84][85][86], associated with splitting, exfoliation, and rock burst [12], and have also been observed at the tip of strike-slip faults in the ice shell of Europa, Jupiter's moon [87]. While these initial static measurements allowed interesting observations, they did not allow to capture the evolution of dynamic ruptures. ...
The last few decades have seen great achievements in dynamic fracture mechanics. Yet, it was not possible to experimentally quantify the full-field behavior of dynamic fractures, until very recently. Here, we review our recent work on the full-field quantification of the temporal evolution of dynamic shear ruptures. Our newly developed approach based on digital image correlation combined with ultrahigh-speed photography has revolutionized the capabilities of measuring highly transient phenomena and enabled addressing key questions of rupture dynamics. Recent milestones include the visualization of the complete displacement, particle velocity, strain, stress and strain rate fields near growing ruptures, capturing the evolution of dynamic friction during individual rupture growth, and the detailed study of rupture speed limits. For example, dynamic friction has been the biggest unknown controlling how frictional ruptures develop but it has been impossible, until now, to measure dynamic friction during spontaneous rupture propagation and to understand its dependence on other quantities. Our recent measurements allow, by simultaneously tracking tractions and sliding speeds on the rupturing interface, to disentangle its complex dependence on the slip, slip velocity, and on their history. In another application, we have uncovered new phenomena that could not be detected with previous methods, such as the formation of pressure shock fronts associated with "supersonic" propagation of shear ruptures in viscoelastic materials where the wave speeds are shown to depend strongly on the strain rate.
... The crustal stress field induced by tectonic loading may be generally invariant with the depth in regions away from the plate boundaries. Crustal and tectonic structures may cause a local variation in the stress field (e.g., Homberg et al., 1997;Kattenhorn and Marshall, 2006). The stress perturbation induces earthquakes in different faulting types in small regions, which is obvious in the subduction zones (Fig. 11). ...
Seismic activity and focal mechanisms are governed by the effective stress field that is a combined result of regional tectonic processes and local stress perturbation. This study investigates the regional variation in the stress field in the eastern continental margin of the Eurasian plate around the Korean Peninsula and Japanese islands using a damped stress inversion technique based on the focal mechanism solutions of regional earthquakes. The dominant compressional stress is directed ENE-WSW around the Korean Peninsula and eastern China, E-W at the central East Sea and northern and southern Japan, NW-SE at central Japan, and N-S around the northern Nankai trough. The dominant compression direction changes rapidly in the East Sea and Japanese islands, which may be due to the combined effects of tectonic loading in the subduction zones off the Japanese islands and the India-Eurasia plate boundary. The crustal stress fields around the subduction zones off the Japanese islands present characteristic depth-dependent orientations. The orientations of the largest horizontal stress components, σH, in the subduction zones are subparallel with the plate convergence directions at shallow depths. The σH orientations are observed to rotate clockwise with the depth owing to slab subduction and lithospheric deformation. The regional stress field around the Japanese islands was perturbed temporally by the 2011 M9.0 Tohoku-Oki megathrust earthquake. The regional stress field was recovered in a couple of years. The stress field and tectonic structures are mutually affected, causing stress field distortion and a localized mixture of earthquakes in different faulting types.
... Europa: Secondary fractures (most in the form of tailcracks) at the tips of strike-slip faults. Propagation of chain-forming ▶ cycloidal ridges may be driven by slip and associated tailcrack development (Kattenhorn 2004;Kattenhorn and Marshall 2006;Fig. 4). ...
... The measured value of horizontal angle of 49 º between the fault tip and the orientation of direction of the recent riverbed in the entry area of gorge I indicates anticrack, mixed-mode I-II, and concomitant sliding and opening according to Kattenhorn et al. (2006) (fig. 14). ...
This research analyses the genesis of eleven inner gorges that morphologically constitute the lower parts of the Rakitnica Canyon Valley in the Central Dinarides of Bosnia and Herzegovina. The spatial distribution of these 300 m deep fluviokarstic landforms, geomorphically reshaped in a thick, brittle Triassic dolomite and limestone, is directly related to contractional restraining bends of right lateral strike-slip faults. The origin and development of most of the Rakitnica's inner gorges was tectonically directed and controlled by pre-existing subvertical tensional gashes, which is confirmed on the basis of their close position to parent dextral strike-slip faults, orientation of its direction, the sigmoidal shape of the gorge's riverbed and hackles on the lower, intact sides of longer gorges. The morpho-evolution of these narrowest parts of the canyon valley, from Upper Pleistocene to recent time, is characterized by simultaneous transpressional uplifting of the terrain and fluvial downcutting across secondary joint fractures mode I opening.
... Development of tailcracks (tensile wing cracks) in the extensional quadrants and anticracks in the compressional quadrants in response to a far field major principal stress σ 1 . The right-lateral sense of shearing is indicated by the central arrow pair (Kattenhorn & Marshall, 2006). resembled the incipient development of anti-wing cracks, was indicated by an arrow pair with asterisks. ...
Various crack types have been reported to initiate from a pre-existing flaw in rocks under compression. In addition to the most commonly observed tensile wing cracks, anti-wing cracks propagating in an opposite direction to that of the tensile wing cracks are also observed in the field and in the laboratory testing. Although a substantial portion of the anti-wing crack path was observed to be associated with tensile cracking, signs of shearing such as the production of shearing dust were identified adjacent to the flaw tip in experimental studies. The objective of this paper is to numerically study the cracking processes involved in the anti-wing crack formation and compare it with those in the tensile wing crack formation. The numerical analysis was performed by a dynamic analysis software by incorporating the static damping technique to achieve a quasi-static loading condition. The numerical study revealed that for the anti-wing crack, the initiated crack segment adjacent to the flaw tip is "shear" in nature, while the remaining segment is "tensile" in nature.
... This appears to hold even in complex collision zones (Molnar & Tapponnier 1975). Andersonian-type structures have even been observed extraterrestrially in ice tectonics on the Jovian moon, Europa (Kattenhorn & Marshall 2006). Anderson's three fundamental classes of fault also account for a high proportion of seismologically determined focal mechanisms. ...
Geologists have long grappled with understanding the mechanical origins of rock deformation. Stress
regimes control the nucleation, growth and reactivation of faults and fractures; induce seismic activity;
affect the transport of magma; and modulate structural permeability, thereby influencing the redistribution
of hydrothermal and hydrocarbon fluids. Experimentalists endeavour to recreate deformation structures
observed in nature under controlled stress conditions. Earth scientists studying earthquakes will attempt
to monitor or deduce stress changes in the Earth as it actively deforms. All are building upon the pioneering
research and concepts of Ernest Masson Anderson, dating back to the start of the twentieth century. This
volume celebrates Anderson’s legacy, with 14 original research papers that examine faulting and seismic
hazard; structural inheritance; the role of local and regional stress fields; low angle faults and the role of
pore fluids; supplemented by reviews of Andersonian approaches and a reprint of his classic paper of 1905.
... Strike-slip faults are found on other planetary bodies as well as on Earth and Venus, such as Mars (Schultz 1989;Bistacchi et al. 2004;Anguita et al. 2006;Okubo & Schultz 2006;Borraccini et al. 2007;Yin 2012), Mercury (Massironi et al. 2012(Massironi et al. , 2014, Jupiter's moons Europa Tufts et al. 1999;Kattenhorn 2004;Aydin 2006;Kattenhorn & Marshall 2006), Io (Bunte et al. 2010) and Ganymede (Pappalardo & Collins 2005), and Saturn's moon Enceladus (Smith-Konter & Pappalardo 2008;Patthoff & Kattenhorn 2011). Arguments that formation of strike-slip faults implies the existence of rigid plates and, hence, modern plate tectonic processes (Pohn & Schaber 1992;Sleep 1994;Yin 2012) are clearly refuted by Fernández et al. (2010). ...
Regional shear zones are interpreted from Bouguer gravity data over northern polar to low southern latitudes of Venus. Offset and deflection of horizontal gravity gradient edges (‘worms’) and lineaments interpreted from displacement of Bouguer anomalies portray crustal
structures, the geometry of which resembles both regional transcurrent shear zones bounding or
cross-cutting cratons and fracture zones in oceanic crust on Earth. High Bouguer anomalies and thinned crust comparable to the Mid-Continent Rift in North America suggest underplating of denser, mantle-derived mafic material beneath extended crust in Sedna and Guinevere planitia
on Venus. These rifts are partitioned by transfer faults and flank a zone of mantle upwelling
(Eistla Regio) between colinear hot, upwelling mantle plumes. Data support the northward drift and indentation of Lakshmi Planum in western Ishtar Terra and .1000 km of transcurrent displacement between Ovda and Thetis regiones. Large displacements of areas of continent-like crust on Venus are interpreted to result from mantle tractions and pressure acting against their deep lithospheric mantle ‘keels’ commensurate with extension in adjacent rifts. Displacements of Lakshmi Planum and Ovda and Thetis regiones on Venus, a planet without plate tectonics, cannot be attributed to plate boundary forces (i.e. ridge push and slab pull). Results therefore suggest that a similar, subduction-free geodynamic model may explain deformation features in Archaean greenstone terrains on Earth. Continent-like ‘drift’ on Venus also resembles models for the late Cenozoic–Recent Earth, where westward translation of the Americas and northward displacement of India are interpreted as being driven by mantle flow tractions on the keels of their Precambrian cratons.
... Secondary crack extension has not only been observed in geological phenomena but also in planetary science. For example, wing cracks at the tips of strikeslip faults have been observed on the ice shell of Jupiter's moon, Europa [59]. ...
Mapping full-field displacement and strain changes on the Earth’s surface following an earthquake is of paramount importance to enhance our understanding of earthquake mechanics. Currently, aerial and satellite images taken pre- and post-earthquake can be processed with sub-pixel correlation algorithms to infer the co-seismic ground deformations (e.g., [1, 2]). However, the interpretation of this data is not straightforward due to the inherent complexity of natural faults and deformation fields. To gain understanding into rupture mechanics and to help interpret complex rupture features occurring in nature, we develop a laboratory earthquake setup capable of reproducing displacement and strain maps similar to those obtained in the field, while maintaining enough simplicity so that clear conclusions can be drawn. Earthquakes are mimicked in the laboratory by dynamic rupture propagating along an inclined frictional interface formed by two Homalite plates under compression (e.g., [3]). In our study, the interface is partially glued, in order to confine the rupture before it reaches the ends of the specimen. The specimens are painted with a speckle pattern to provide the surface with characteristic features for image matching. Images of the specimens are taken before and after dynamic rupture with a 4 Megapixels resolution CCD camera. The digital images are analyzed with two software packages for sub-pixel correlation: VIC-2D (Correlated Solutions Inc.) and COSI-Corr [1]. Both VIC-2D and COSI-Corr are able to characterize the full-field static displacement of the experimentally produced dynamic shear ruptures. The correlation analysis performed with either software clearly shows (i) the relative displacement (slip) along the frictional interface, (ii) the rupture arrest on the glued boundaries, and (iii) the presence of wing cracks. The obtained displacement measurements are converted to strains, using non-local de-noising techniques; stresses are obtained by introducing Homalite’s constitutive properties. This study is a first step towards using the digital image correlation method in combination with high-speed photography to capture the highly transient phenomena involved in dynamic rupture.
... LEFM is suitable because rocks in the upper crust, such as those exposed in the Pinto Ridge area, appear to behave in an elastic manner (i.e., stress is directly proportional to strain) on short time scales (e.g., Pollard and Segall, 1987). LEFMbased models have been applied to every style of fracturing on Earth (e.g., Jaeger and Cook, 1976;Pollard and Segall, 1987), as well as faulting on other planetary bodies (Koenig and Aydin, 1998;Schulson, 2002;Buczkowski and Cooke, 2004;Kattenhorn, 2004;Goudy et al., 2005;Kattenhorn and Marshall, 2006). Such studies have demonstrated that the initiation orientations and propagation paths of secondary fractures are explicitly determined by the sense of motion along the primary fault and the resultant perturbed stress fi eld (Fig. 7). ...
The hypothesized presence of a detachment underlying the Lake Mead region has created a dichotomy in the interpretations of the roles of strike-slip faults of the Lake Mead fault system in accommodating regional deformation. Our detailed field mapping reveals a previously unnamed left-lateral strike-slip segment of the Lake Mead fault system and a dense cluster of dominantly west-dipping and related normal faults located near Pinto Ridge. We suggest that the strike-slip fault that we refer to as the Pinto Ridge fault: (1) was kinematically related to the Bitter Spring Valley fault; (2) was responsible for the creation of the normal fault cluster at Pinto Ridge; and (3) utilized these normal faults as linking structures between separate strike-slip fault segments to create a longer, through-going fault. Results from numerical models demonstrate that the observed location and curving strike patterns of the normal fault cluster are consistent with the faults having formed as secondary structures as the result of the perturbed stress field around the slipping Pinto Ridge fault, regardless of whether or not the Pinto Ridge fault merges into a regional detachment at depth. Calculations of mechanical efficiency of various normal fault geometries within extending terranes suggest that a preferred west dip of normal faults likely reflects a west-dipping anisotropy at depth, such as a detachment. The apparent terminations of numerous strike-slip faults of the Lake Mead fault system into west-dipping normal faults suggest that a west-dipping detachment may be regionally coherent.
... Evidence of strike-slip faulting has also been recognized on Mars (e.g. Schultz 1989;Bistacchi et al. 2004;Okubo & Schultz 2006;Borraccini et al. 2007;Andrews-Hanna et al. 2008;Yin 2012), Venus (Koenig & Aydin 1998), Europa Hoppa et al. 1999;Kattenhorn 2004;Kattenhorn & Marshall 2006;Aydin 2006) and Enceladus (Patthoff & Kattenhorn 2011). ...
At a global scale, Mercury is dominated by contractional features manifested as lobate scarps, wrinkle ridges and high-relief ridges. Here, we show that some of these features are associ- ated with strike-slip kinematic indicators, which we identified using flyby and orbital Mercury Dual Imaging System (MDIS) data and digital terrain models. We recognize oblique-shear kinematics along lobate scarps and high-relief ridges by means of (1) map geometries of fault patterns (frontal thrusts bordered by lateral ramps, strike-slip duplexes, restraining bends); (2) structural morphologies indicating lateral shearing (en echelon folding, pop-ups, pull-aparts); and (3) esti- mates of offsets based on displaced crater rims and differences in elevation between pop-up struc- tures and pull-apart basins and their surroundings. Transpressional faults, documented across a wide range of latitudes, are found associated with reactivated rims of ancient buried basins and, in most cases, linked to frontal thrusts as lateral ramps hundreds of kilometres long. This latter observation suggests stable directions of tectonic transport over wide regions of Mercury’s surface. In contrast, global cooling would imply an overall isotropic contraction with limited pro- cesses of lateral shearing induced by pre-existent lithospheric heterogeneities. Mantle convection therefore may have played an important role during the tectonic evolution of Mercury.
... Major faults with larger shear offset (throw) usually exhibit a more continuous fault plane (up to several kilometers); segments are longer with fewer relay zones (Wesnousky, 1988;Stirling et al., 1996;De Joussineau and Aydin, 2009a,b). Field observations (Kattenhorn and Marshall, 2006;De Joussineau and Aydin, 2007) and numerical model simulations of fault growth (Moir et al., 2009) have shown that fractures within the damage zone also evolve from this linkage process, increasing fracture connectivity and connected fracture length. Jafari and Babadagli (2009) showed that fracture length is one of the most critical parameters, which, along with fracture density and the presence of multiple sets of fractures, influences the fracture-network connectivity and (thus) the equivalent fracture-network permeability. ...
... Others factors more related to the geometry and behaviour of the fault surface also seem to be very influential, as the 3-D geometry of the faults (e.g. Segall and Pollard, 1980;King et al., 1994;Willemse, 1997;Maerten et al., 2002;Bourne and Willemse, 2001), its spatial/temporal evolution (Willson et al., 2007;Lunn et al., 2008;Moir et al., 2009), and fault opening (Kattenhorn and Marshall, 2006). Therefore, any analysis of fault zones that aims to estimate the role of fault friction on the stress field, or in contrast to determine the state of friction from stresses analysis, must know any of these factors that can perturb the local stress field. ...
Fault friction is a parameter that is difficult to assess along fault zones since its determination depends on the knowledge of any factor controlling the state of stress around faults. In brittle homogeneous rocks, a limited number of these factors, such as the shape of the fault surface, the vicinity of fault tips or the remote stress ratio, are crucial to constrain for this determination. In this paper, we propose to analyse a field example in which all these properties are met and where the nature of the slipped structure suggest differences in static friction. We compare the orientations of branching fractures at strike-slip relay zones between en echelon stylolites and en echelon joints both reactivated in shear. The field data are compared with both photoelastic and 3-D numerical models that consider the remote stress conditions and the role of the geometry of the strike-slip segments. Based on field observations, these analyses quantitatively demonstrate the significant role of fault friction on the local stress field orientation and subsequent fracture formation. This work points out that estimations of fault friction based on analyses of fracture patterns or in situ stresses must be accompanied with a thorough investigation of the 3-D fault shape, its segmentation and the remote stress state.
Horsetailing is an important feature to identify the strike‐slip structure and indicates the movement mode of the fault. However, the formation mechanism of horsetailing in the extensional regime remains unclear. In this study, the formation process of horsetailing is reproduced through physical experiment, simulating the Linnan sag in the extensional regime. The results of the physical experiment demonstrates that the formation of the horsetailing in the extensional regime requires two phases of non‐coaxial stretching plus the segment of the principal fault. The stretching distance in the early phase is slightly smaller than that in the middle‐late phase. The segment point of the principal fault is only the intersection of the horsetailing structure and the principal fault. The horsetailing formed in the extensional regime is different from that in the strike‐slip regime. For the formation of structure, the principal fault is dip‐slip in the early phase and then becomes an oblique‐slip in the middle‐late phase, and the horsetailing is composed of the middle‐late new tensile faults. The fault properties of the horsetailing in the extensional regime has important guiding significance for the longitudinal fluid migration along the fault in petroliferous basins.
This book describes the tectonic landforms resulting from major internal and external forces acting on the outer layers of solid bodies throughout the Solar System. It presents a detailed survey of tectonic structures at a range of length scales found on Mercury, Venus, the Moon, Mars, the outer planet satellites, and asteroids. A diverse range of models for the sources of tectonic stresses acting on silicate and icy crusts is outlined, comparing processes acting throughout the Solar System. Rheological and mechanical properties of planetary crusts and lithospheres are discussed to understand how and why tectonic stresses manifest themselves differently on various bodies. Results from fault population data are assessed in detail. The book provides methods for mapping and analysing planetary tectonic features, and is illustrated with diagrams and spectacular images returned by manned and robotic spacecraft. It forms an essential reference for researchers and students in planetary geology and tectonics.
This book describes the tectonic landforms resulting from major internal and external forces acting on the outer layers of solid bodies throughout the Solar System. It presents a detailed survey of tectonic structures at a range of length scales found on Mercury, Venus, the Moon, Mars, the outer planet satellites, and asteroids. A diverse range of models for the sources of tectonic stresses acting on silicate and icy crusts is outlined, comparing processes acting throughout the Solar System. Rheological and mechanical properties of planetary crusts and lithospheres are discussed to understand how and why tectonic stresses manifest themselves differently on various bodies. Results from fault population data are assessed in detail. The book provides methods for mapping and analysing planetary tectonic features, and is illustrated with diagrams and spectacular images returned by manned and robotic spacecraft. It forms an essential reference for researchers and students in planetary geology and tectonics.
This book describes the tectonic landforms resulting from major internal and external forces acting on the outer layers of solid bodies throughout the Solar System. It presents a detailed survey of tectonic structures at a range of length scales found on Mercury, Venus, the Moon, Mars, the outer planet satellites, and asteroids. A diverse range of models for the sources of tectonic stresses acting on silicate and icy crusts is outlined, comparing processes acting throughout the Solar System. Rheological and mechanical properties of planetary crusts and lithospheres are discussed to understand how and why tectonic stresses manifest themselves differently on various bodies. Results from fault population data are assessed in detail. The book provides methods for mapping and analysing planetary tectonic features, and is illustrated with diagrams and spectacular images returned by manned and robotic spacecraft. It forms an essential reference for researchers and students in planetary geology and tectonics.
This book describes the tectonic landforms resulting from major internal and external forces acting on the outer layers of solid bodies throughout the Solar System. It presents a detailed survey of tectonic structures at a range of length scales found on Mercury, Venus, the Moon, Mars, the outer planet satellites, and asteroids. A diverse range of models for the sources of tectonic stresses acting on silicate and icy crusts is outlined, comparing processes acting throughout the Solar System. Rheological and mechanical properties of planetary crusts and lithospheres are discussed to understand how and why tectonic stresses manifest themselves differently on various bodies. Results from fault population data are assessed in detail. The book provides methods for mapping and analysing planetary tectonic features, and is illustrated with diagrams and spectacular images returned by manned and robotic spacecraft. It forms an essential reference for researchers and students in planetary geology and tectonics.
Large-scale discontinuities can significantly affect the mechanical properties of rock masses. However, the tensile behavior of rock discontinuities is often less investigated. To study the statistical characteristics of failure strength and fracture characteristics of rock discontinuities, Brazilian disc tests were conducted on limestone specimens with a single natural discontinuity at different load-discontinuity angles (β). In this study, β=0° and β=90° correspond to the discontinuity parallel and perpendicular to loading direction, respectively. The results show that Brazilian failure strength (BFS) can reasonably represent the tensile strength of rock with discontinuities, by comparing the BFS and tensile stress in the disc center at peak force. The two-parameter Weibull distribution can capture the statistical BFS characteristics of rock discontinuities parallel to loading direction (β=0°) and at different load-discontinuity angles (β≠0°). All specimens with discontinuity at different load-discontinuity angles show more plastic deformational behaviour than intact rock specimen. With increasing β, the mean BFS of limestone with discontinuity increases before reaching a plateau at β=45°. The single plane of weakness theory best explains the BFS of fractured limestone with β. Only a specific segment of pre-existing rock discontinuity could affect the fracture process. When β=0°, interfacial cracks and alternative cracks formed. When β≠0°, mixed failure mode with shear and tensile failure occurred, particularly when β=30° and β=60°. The findings can contribute to better understanding the failure and fracture characteristics of rock with discontinuities, particularly the interaction of pre-existing discontinuities with stress-induced fracturing.
The transition from stable to unstable fracture propagation occurs when fractures begin to interact and link. Thus, fracture network coalescence controls how rocks and engineered structures fail. To constrain the factors that influence localization in shear zones under brittle conditions, we build discrete element method models with a rough fault embedded in a shear zone. We add varying numbers of diffuse, randomly-placed weaknesses to examine the influence of diffuse damage on fracture network localization. The number of weaknesses controls the localization behavior of the fault network and the final fault geometry. We quantify localization using the Gini coefficient of the fracture volume, which measures the nonuniformity in a population. Each model generally increases in localization toward failure. However, models with more diffuse damage experience delocalization phases that are superimposed on the overall trend of increasing localization. The observed link between delocalization and host rock damage may help explain the varying localization of low magnitude seismicity in southern California. Models with more diffuse damage produce more complex fault geometries comprised of several parallel strands of wing cracks. The propagation of these wing cracks reduces the shear stress acting on the model boundaries, indicating that this fracture development increases the mechanical efficiency of the system.
Cambridge Core - Structural Geology, Tectonics and Geodynamics - Geologic Fracture Mechanics - by Richard A. Schultz
The paper summarizes the results of long-term field research in the dynamics of the Baikal ice cover as a multiscale block medium similar to the lithosphere in structure, rheology, and seismotectonic features. The analysis covers data on deformation, seismicity, and contact interaction modes as well as on meteorological factors responsible for dynamic fracture of ice plates and strong ice shocks with earthquake-like vibrations. Similarity between seismic features in ice interface zones and zones of tectonic subduction, collision, and shear is discussed. Reasoning from dynamic analogies and similarities of destruction processes in the ice and lithosphere, the research data can help solving fundamental and applied problems, particularly those of earthquake prediction and assessment of contact interactions between lithospheric plates in fault zones.
Strike-slip faulting is typically characterized by lateral offsets on icy satellites of the outer solar system. However, strike-slip faults on Enceladus lack these typical lateral offsets and instead are marked by the presence of tailcracks or en echelon cracks. These features are used here to develop the first near-global distribution of strike-slip faults on Enceladus. Strike-slip faults on Enceladus fall into three broad categories: tectonic terrain boundaries, reactivated linear features, and primary strike-slip faults. All three types of strike-slip faults are found predominantly, or within close proximity to, the antipodal cratered terrains on the Saturnian and anti-Saturnian hemispheres. Stress modeling suggests that strike-slip faulting on Enceladus is not controlled by nonsynchronous rotation, as on Europa, suggesting a fundamentally different process driving Enceladus's strike-slip faulting. The motion along strike-slip faults at tectonic terrain boundaries suggests large-scale northward migration of the ice shell on the leading hemisphere of Enceladus, occurring perpendicular to the opening direction of the tiger stripes in the south polar terrain.
Chaos terrains are among the most prominent landforms of Europa, and are generally among the youngest features recorded on the surface. Chaos units were formed by to endogenic activity, maybe related to solid-state convection and thermal diapirism in the ice shell, perhaps aided by melting of salt-rich ice bodies below the surface. In this work, we analyze the different units of chaotic terrain in a portion of Argadnel Regio, a region located on the anti-Jovian hemisphere of Europa, and their possible timing in the general stratigraphic framework of this satellite. Two different chaos units can be differentiated, based on surface texture, morphology, and cross-cutting relationships with other units, and from interpretations based on pre-existing surface restoration through elimination of a low albedo band. The existence of two stratigraphically different chaos units implies that conditions for chaos formation occurred during more than a single discreet time on Europa, at least in Argadnel Regio, and perhaps in other places. The existence of older chaos units on Europa might be related to convective episodes possibly favored by local conditions in the icy shell, such as variations in grain size, abundance of non-water ice-components, or regional thickness of the brittle lithosphere or the entire ice shell.
Based on the issues of roof collapse in fault zones, roof elastic thick outrigger mechanical models in normal fault zone and reverse fault zone are established; the roof stress distribution law is researched; and the roof collapse mechanisms under different roof pressures, different support strengths, different span-depth ratios, etc. are analyzed according to the Mohr-Coulomb failure criterion. Theoretical analysis shows that the maximum effective shear stress of roof thick outrigger increases with the growth of span-depth ratio; and it presents three different kinds of fracture modes with the increasing of span-depth ratio; support strength should be enhanced in the roadway crossed faults; surface protection effect should be enhanced near normal fault plane. According to the theoretical analysis, pressure relief anchor box beam support system is put forward to apply to fault zones, by which roof is supported opportunely and forcefully; and the effect of first anti-pressure, then pressure relief, at last anti-pressure is implemented; and the support system works effectively; the self-bearing ability of surrounding rock is put into full play. The mechanism research conclusion is applied to the support scheme in similar fault zones of the mine; and it prevents roof collapse accidents effectively, so as to prove that the conclusion of theoretical analysis is correct.
Preamble This report serves as the final technical report for the above mentioned project. The grant period began on January, 1,2002 and finished on June 3 0 ~ , 2004. The project personnel consisted of the PI, a co-investigator who served in an advisory capacity, and two full-time graduate students who completed MS thesis projects funded by the grant. The project ultimately led to the development of 6 full-length papers (1 published, 1 in press, 2 acceptedin revision, and 2 in preparation), 9 conference presentations with abstracts, and 1 invited seminar presentation at the Lunar and Planetary Institute in Houston, Texas. The success of the project, as outlined below, has enabled the strengthening of the planetary geoscience research program in the Department of Geological Sciences at the University of Idaho. I have successfully competed for two additional grant awards through the NASA-Idaho Space Grant Consortium and NASA-EPSCoR, and have developed national recognition through collaborations and interactions with numerous peer researchers. Furthermore, my planetary geoscience research program now attracts several graduate student applicants per year and has acquired two additional current graduate students working on research projects (one as an MS thesis and one as a PhD dissertation). A follow-up grant proposal is pending at NASA PG&G.
The exploration of the outer solar system in the last decades revealed
an exotic icy world with surfaces showing the most diverse geology,
sometimes exceptional to these icy bodies due to the peculiar rheology
of ice. Each of these icy bodies exhibits unique characteristics and its
own fascinating geological history - formed by the competition of
external and internal forces.
Shear sliding along a fault plane leading crack propagation can be classified as a strike-slip fault movement. The cracks propagated from the extensional quadrant or compressional quadrant of fault is named wing crack and anti-wing crack, respectively. This paper focuses on the experimental study on nucleation and growth of anti-wing crack from a surface flaw under biaxial compression. Four observation systems were used including multi channel digital strain gauge (MCDSG), video camera, digital speckle correlation method (DSCM) and acoustic emission (AE). In this study, two types of anti-wing crack development were found which was not reported by the previous studies. One of the crack types was formed by the growth of petal cracks extending from the interior of the specimen to the surface, whiles the other crack type was formed by the growth of tensile cracks from the specimen surface extending into the interior of the rock. Both types of anti-wing crack are the mixed mode pattern of tensile and compressive crack. Furthermore, the growth behavior of wing crack and anti-wing crack can be explained by the result of strain record. The result of this study provides more knowledge and understanding on the crack development of the strike-slip fault.
The mechanics of deformation in multilayer flexures is analysed by comparing field observations of joint clusters from the East Kaibab Monocline, Utah with fracture patterns produced in analytical and numerical experiments. Dune boundaries (bedding planes) were mapped through the thickness of the aeolian Navajo Formation, and the occurrence of joints related to dune boundary slip and fold curvature was documented. Slip along dune boundaries, as evidenced by joint clusters oblique to bedding, occurs along the steep limb of the fold and in the middle of the Navajo. Joints perpendicular to bedding and parallel to the fold axis occur near the synclinal hinge. Numerical experiments examine a layer flexed to match the Navajo at Hackberry Canyon with both uniform and observed distribution of dune boundaries. Within the numerical experiments, horizontal frictional interfaces slip within the centre of the layers where dips are steepest, and opening-mode fractures related to curvature form within the anticlinal and synclinal hinges of the fold. Thus, the first-order numerical results match field observations. This study illustrates the important roles of mechanical stratigraphy and interlayer slip in multilayered folding and the contribution of bedding-plane faults and fold curvature in the production of joint clusters.
The deformation associated with several small, brittle faults was investigated on both microscopic and macroscopic scales. While the dominant macroscopic structures are solution cleavage planes and secondary shear fractures, the dominant microscopic deformation structures are healed tensile microfractures. The fault-related microfractures display densities and orientations distinct from the background microfracture population. These densities and orientations are consistent with formation within the altered stress fields of propagating shear fracture tips. This microfracture population is used to define the fault process zone associated with growth of the macroscopic fault plane. Process zone microfractures show logarithmic density increases with proximity to the fault, a constant maximum density that is independent of fault length, and orientations which can be used to infer the direction of propagation of the fault plane. The width of the process zone scales linearly with fault length with a proportionality constant of the order of 10-2.
We propose that discrete solution surfaces originate at stress concentrations and propagate through rock as anticracks. As material is dissolved and removed, the anticrack walls move toward each other; stress and displacement fields are identical to those for the conventional opening crack, but with a change of sign. Observations of entire traces of solution surfaces are consistent with the anticrack concept: (1) the surfaces are bounded in extent; (2) the dissolved thickness varies from a maximum near the center to zero at the tips; and (3) the maximum dissolved thickness is proportional to the length of the surface. Local dissolution and in-plane propagation are suggested by the large isotropic compressive stress at the anticrack tip. Propagating solution surfaces will interact to form a regular array corresponding to some bulk strain rate. Anticracks may also interact with opening and shear cracks; observations of interacting solution surfaces, veins, and faults illustrate these configurations. Intersecting arrays of cracks, anticracks, and shear cracks operate to yield a mode of bulk deformation similar to diffusion-accommodated grain-boundary sliding in polycrystalline solids. *Present address: Center for Tectonophysics, Texas A&M University, College Station, Texas 77843
Normal faults growing in the Earth's crust are subject to the effects of an increasing frictional resistance to slip caused by the increasing lithostatic load with depth. We use three-dimensional (3-D) boundary element method numerical models to evaluate these effects on planar normal faults with variable elliptical tip line shapes in an elastic solid. As a result of increasing friction with depth, normal fault slip maxima for a single slip event are skewed away from the fault center toward the upper fault tip. There is a correspondingly greater propagation tendency at the upper tip. However, the tall faults that would result from such a propagation tendency are generally not observed in nature. We show how mechanical interaction between laterally stepping fault segments significantly competes with the lithostatic loading effect in the evolution of a normal fault system, promoting lateral propagation and possibly segment linkage. Resultant composite faults are wider than they are tall, resembling both 3-D seismic data interpretations and previously documented characteristics of normal fault systems. However, this effect may be greatly complemented by the influence of a heterogeneous stratigraphy, which can control fault nucleation depth and inhibit fault propagation across the mechanical layering. Our models demonstrate that although lithostatic loading may be an important control on fault evolution in relatively homogeneous rocks, the contribution of lithologic influences and mechanical interaction between closely spaced, laterally stepping faults may predominate in determining the slip behavior and propagation tendency of normal faults in the Earth's crust.
Uniaxial compression of plates of brittle materials containing pre-existing planar cracks oriented at certain angles with respect to the direction of overall compression has revealed that the relative frictional sliding of the faces of the pre-existing cracks may produce, at their tips, tension cracks which deviate at sharp angles from the sliding plane. These tension cracks then continue to grow in a stable manner with increasing axial compression, curving toward an orientation parallel to the direction of axial compression. Within the framework of linear fracture mechanics, the out-of-plane extension of a pre-existing straight crack, induced by overall far-field compression, is analyzed, and various parameters which characterize the growth process are quantified. It is shown analytically that, for a wide range of pre-existing crack orientations, the out-of-plane crack extension initiates at an angle close to 70o from the direction of the pre-existing crack; the exact value of this angle, of course, depends on the friction factor and the orientation of the pre-existing crack. It is found that the growth process is stable initially, but the rate of increase of the length of the extended portion with respect to the increasing axial compression dramatically increases after a certain extension length is attained, and in fact, this length becomes unbounded if a small lateral tension also exists. -Authors
Chaotic terrain on Europa is interpreted to be the result of the breakup of brittle surface materials over a mobile substrate. Two end-member models have been proposed for the mobile substrate: a liquid water ocean or solid warm ductile ice. Direct contact between the brittle surface ice and an underlying ocean might be accomplished by melting through Europa's ice shell, but plausible sources of thermal energy are insufficient to locally melt through the ice shell. We calculate that a liquid or partially liquid substrate is probably necessary for tilted blocks to be observed, challenging a solid-state model. We propose that a model in which chaos areas on Europa formed over bodies of melt or partial melt within the ice shell may be the best match to observational and thermal constraints. Such bodies of melt within the ice shell may be triggered by warm diapirs of relatively clean ice that partially melted an overlying layer of lower melting temperature, such as ice contaminated with salts.
Agenor Linea is a ~1500 km long, ~20-30 km wide geologically young zone
of deformation on Jupiter's icy moon, Europa. On the basis of recent
Galileo high-resolution images, we interpret Agenor Linea as a
strike-slip zone formed in three stages by a combination of lithospheric
separation, extension, and dextral horizontal shear. Agenor Linea
exhibits excellent examples of strike-slip duplexes in an icy
lithosphere, unobscured by vegetation and unaltered by erosion.
Galileo data enable the major geological units, structures, and surface features to be identified on Europa. These include five primary units (plains, chaos, band, ridge, and crater materials) and their subunits, along with various tectonic structures such as faults. Plains units are the most widespread. Ridged plains material spans a wide range of geological ages, including the oldest recognizable features on Europa, and appears to represent a style of tectonic resurfacing, rather than cryovolcanism. Smooth plains material typically embays other terrains and units, possibly as a type of fluid emplacement, and is among the youngest material units observed. At global scales, plains are typically mapped as undifferentiated plains material, although in some areas differences can be discerned in the near infrared which might be related to differences in ice grain size. Chaos material is composed of plains and other preexisting materials that have been severely disrupted by inferred internal activity; chaos is characterized by blocks of icy material set in a hummocky matrix. Band material is arrayed in linear, curvilinear, wedge-shaped, or cuspate zones with contrasting albedo and surface textures with respect to the surrounding terrain. Bilateral symmetry observed in some bands and the relationships with the surrounding units suggest that band material forms by the lithosphere fracturing, spreading apart, and infilling with material derived from the subsurface. Ridge material is mapped as a unit on local and some regional maps but shown with symbols at global scales. Ridge material includes single ridges, doublet ridges, and ridge complexes. Ridge materials are considered to represent tectonic processes, possibly accompanied by the extrusion or intrusion of subsurface materials, such as diapirs. The tectonic processes might be related to tidal flexing of the icy lithosphere on diurnal or longer timescales. Crater materials include various interior (smooth central, rough inner, and annular massif) and exterior (continuous ejecta) subunits. Structural features and landforms are shown with conventional symbols. Type localities for the units are identified, along with suggestions for portraying the features on geological maps, including colors and letter abbreviations for material units. Implementing these suggestions by the planetary mapping community would facilitate comparisons of maps for different parts of Europa and contribute to an eventual global synthesis of its complex geology. On the basis of initial mapping results, a stratigraphic sequence is suggested in which ridged plains form the oldest unit on Europa, followed by development of band material and individual ridges. Band materials tend to be somewhat older than ridges, but in many areas the two units formed simultaneously. Similarly, the formation of most chaos follows the development of ridged plains; although chaos is among the youngest materials on Europa, some chaos units might have formed contemporaneously
1] Global stress models for Europa are unable to readily explain the orientations of lineae in the equatorial region of Europa's trailing hemisphere if lineae originate as tension cracks. Our analysis of two equatorial, trailing regions reveals that lineae are predominantly oriented NE and NW, and E-W lineae are rare, contrary to predictions of stress and formation models. The measured orientations are consistent with an origin by shear failure. The studied regions are located near the point of maximum differential stress and minimum surface tensile stresses, where shear faulting may surmount tension fracturing. Several types of lineae are recognized; their relative abundance is inferred to have changed with time, consistent with formation models suggesting lineae evolve from simple troughs to complex ridges. The opening of crevasse-like tensile fractures is not required for generation of all lineae; the observations are consistent with ridge formation models where troughs (formed in tension or shear) experience shear heating from tidal deformation, allowing warm ice to buoyantly uplift, creating ridges. The stratigraphic relationships indicate the following: ridged plains formed first, followed by continued formation of a wide range of lineae, and lastly emplacement of lenticulae and continued linea formation. This sequence is consistent with an early thin, brittle lithosphere that thickened with time and was subject to repetitive diurnal tides during $30°–90° of nonsynchronous rotation. Ultimately, the thickened shell underwent thermally induced solid-state convection, producing lenticulae. The young surface age of Europa implies that this entire stratigraphic sequence was emplaced in the geologically recent past.
Opening-mode splay fractures have been observed within clusters near fault tips. The spatial distribution of splay fractures along faults influences fluid flow and lends insight into the mechanical processes of faulting. Slip gradients along faults produce stress concentrations which promote the development of opening-mode splay fractures along faults. Since the slip distribution depends on the distribution of frictional strength along faults, spatial variations in the frictional properties may influence fracture localization. Variations in friction coefficient along faults can reduce the stress singularities at fault tips and promote the development of multiple fractures inwards from the fault tips. The conditions that promote splay crack localization are examined using analytical and numerical fault models. Single splay fractures develop at locations of abrupt friction coefficient change and/or at fault tips when the frictign coefficient near the tips is less than a critical value. Fault models with linearly increasing friction coefficient toward the fault tip promote the development of multiple splay fractures within broad zones near the tip.
Fracture mechanics theory and field observations together indicate that the shear stress on many faults is non-uniform when they slip. If the shear stress were uniform, then: (a) a physically implausible singular stress concentration theoretically would develop at a fault end; and (b) a single curved ‘tail fracture’ should open up at the end of every fault trace, intersecting the fault at approximately 70 °. Tail fractures along many small faults instead range in number, commonly form behind fault trace ends, have nearly straight traces and intersect a fault at angles less than 50 °. A ‘cohesive zone’, in which the shear stress is elevated near the fault end, can eliminate the stress singularity and can account for the observed orientation, shape, and distribution of tail fractures. Cohesive zones also should cause a fault to bend. If the cohesive zone shear stress were uniform, then the distance from the fault end to the bend gives the cohesive zone length. The nearly straight traces of the tail fractures and the small bends observed near some fault ends implies that the faults slipped with low stress drops, less than 10% of the ambient fault-parallel shear stress.
The growth of cracks in photoelastic material and glass under compression is being studied as part of an investigation of brittle fracture of rock. In compression the most severely stressed crack is inclined at about 30° to the axis of compression. Such cracks, when either isolated or placed in an array, grow along a curved path which becomes parallel with the direction of compression. When this direction is attained, growth stops, unless applied compression is increased considerably. Cracks in certain en échelon arrays start to grow at much smaller applied stress than that required to enlarge an isolated crack.
Sedimentary rocks intruded by Tertiary mafic dikes on the Colorado Plateau typically display systematic dike-parallel joints. These closely spaced joints occur only near dikes, their spacing commonly increasing with distance from the dike contacts. Igneous breccias along some of these joints indicate that the joints are not younger than the dikes and, therefore, did not form during cooling. Field relations are best explained if the joints form in host rocks beyond the dike tip, becoming juxtaposed against the dike with continued propagation: an interpretation supported by previously reported descriptions of ground surface cracks formed near eruptive fissures and of microcracks formed near the tips of larger extension cracks during laboratory experiments. Tensile stress generated by magmatic pressure is sufficient to fracture host rocks beyond dike tips. The tensile maxima are located on either side of the dike plane, beyond the tip. The stresses increase in magnitude closer to the tip, thus explaining the greater abundance of joints near the dike plane. Noting that dikes may parallel regional joint sets, we contrast (1) emplacement along older joints oriented arbitrarily with respect to the principal stress directions acting at the time of intrusion and (2) emplacement along self-generated fractures propagated in a plane perpendicular to the least compressive stress direction. Magma can invade along older joints if magmatic pressure exceeds the horizontal stress acting across the joint plane. This situation is most common if the horizontal principal stress difference is small compared to the magmatic driving pressure or if joints are nearly perpendicular to the direction of least compressive regional stress. Magma must advance by filling self-generated fractures if older, suitably oriented, joints are absent.
We performed a nearest neighbor spacing distance analysis of chaos and lenticulae on Europa and found a dominant spacing of 16 - 36 km exists, suggesting a convecting layer 7 - 18 km thick.
Vertical joints in Devonian clastic sedimentary rocks of the Finger Lakes area of New York State are ornamented with arrays of fringe cracks that reveal the complex deformational history of the Appalachian plateau detachment sheet during the Alleghanian orogeny. Three types of fringe cracks were mapped: gradual twist hackles, abrupt twist hackles, and kinks. Gradual twist hackles are curviplanar en echelon fringe cracks that propagate with an overall vertical direction within the bed hosting the parent crack and are found in all clastic lithologies of the detachment sheet. Abrupt twist hackles propagate as planar features in thick shale beds above or below the siltstone beds hosting parent joints. Kinks propagate horizontally as planar surfaces from the tips of parent joints in siltstone beds. The breakdown of the parent joint into either gradual or abrupt twist hackles depends on the orientation and magnitude of the remote stress field, internal fluid pressure, and the elastic properties of the bed. The twist angle of gradual twist hackles is larger in coarser clastic beds, indicating that stress and internal pressure are more important parameters than elastic properties in controlling breakdown. Assuming that the vertical stress axis (S(v)) equals 78 MPa at 3 km burial depth, the difference in twist angle between sandstone and shale beds is used to estimate the maximum horizontal stress difference in the shale beds as S(H) - S(h) ~ 2.5 MPa when S(H) - S(h) ~ 12 MPa in sandstone beds. The twist angle of the fringe cracks and the abutting relationships of parent joints give an indication of the overall change in stress field orientation within the detachment sheet during Alleghanian tectonics. These parent joints indicate a regional clockwise stress rotation of Alleghanian age concordant with the twist angle of fringe cracks throughout the western part of the study area. A counterclockwise twist angle in the eastern portion indicates a local stress attributed to drag where no salt was available to detach the eastern edge of the plateau sheet. The clockwise change in stress orientation is consistent with the rotation in stress orientation found in the anthracite belt of the Pennsylvania Valley and Ridge, but is opposite to the sense of rotation in the southwestern portion of the detachment sheet (western Pennsylvania and West Virginia). The two regional rotation domains are separated by the Juniata culmination.
Observations of brittle fractures in the granite of the Massif de la
Borne as well as in other rocks allow us to discuss the different
hypotheses regarding the origin of faults. It seems that all faults
originate by shear along a preexisting plane which can be an important
fracture (joint, former fault) or a microflaw (pore, grain boundary).
The shear on the plane gives rise to an array of en echelon cracks that
makes the rock less resistant and permits the lengthening of the fault.
We also found an arrangement of "horsetail" fractures damping the
movements on the faults. We then propose a pattern for the development
of the faults. They originate on preexisting plane and propagate by
initiating en echelon cracks. The movements are damped by horsetails
which permit, by faults connection in relays, the creation of larger
faults.
Field observations of two overlapping normal faults and associated deformation document features common to many normal-fault relay zones: a topographic ramp between the fault segments, tapering slip on the faults as they enter the overlap zone, and associated fracturing, especially at the top of the ramp. These observations motivate numerical modeling of the development of a relay zone. A three-dimensional boundary element method numerical model, using simple fault-plane geometries, material properties, and boundary conditions, reproduces the principal characteristics of the observed fault scarps. The model, with overlapping, semicircular fault segments under orthogonal extension, produces a region of high Coulomb shear stress in the relay zone that would favor fault linkage at the center to upper relay ramp. If the fault height is increased, the magnitude of the stresses in the relay zone increases, but the position of the anticipated linkage does not change. The amount of fault overlap changes the magnitude of the Coulomb stress in the relay zone: the greatest potential for fault linkage occurs with the closest underlapping fault tips. Ultimately, the mechanical interaction between segments of a developing normal-fault system promote the development of connected, zigzagging fault scarps.
This is an advanced text for higher degree materials science students and researchers concerned with the strength of highly brittle covalent–ionic solids, principally ceramics. It is a reconstructed and greatly expanded edition of a book first published in 1975. The book presents a unified continuum, microstructural and atomistic treatment of modern day fracture mechanics from a materials perspective. Particular attention is directed to the basic elements of bonding and microstructure that govern the intrinsic toughness of ceramics. These elements hold the key to the future of ceramics as high-technology materials - to make brittle solids strong, we must first understand what makes them weak. The underlying theme of the book is the fundamental Griffith energy-balance concept of crack propagation. The early chapters develop fracture mechanics from the traditional continuum perspective, with attention to linear and nonlinear crack-tip fields, equilibrium and non-equilibrium crack states. It then describes the atomic structure of sharp cracks, the topical subject of crack-microstructure interactions in ceramics, with special focus on the concepts of crack-tip shielding and crack-resistance curves, and finally deals with indentation fracture, flaws, and structural reliability.
Spectacular rock fins on the flanks of Salt Valley anticline in southeast Utah are formed by erosion along zones of joints. Within a rock fin, arches form where intense fracturing is localized. Fracture localization is controlled by shear displacement along existing horizontal or vertical discontinuities. Horizontal discontinuities may be shale layers, shale lenses, or bedding planes, whereas vertical discontinuities are usually preexisting joint segments. The roof and overall shape of an arch is controlled by existing shale layers, interfaces between sandstones of different properties, or secondary fractures due to shear on vertical joints. Joints that bound rock fins are related to the formation of the diapir-cored Salt Valley anticline. Shear displacement along existing discontinuities, which localizes intense fracturing, is probably related to the growth of Salt Valley anticline and its subsequent collapse due to dissolution of the anticlines salt core. 31 refs., 11 figs.
The orientations, locations, sizes, and relative abundances of secondary fractures observed along small natural faults can be accounted for by a three-dimensional elastic model. Secondary fractures along small subvertical left-lateral strike-slip faults in massive granitic rock of the Sierra Nevada of California (1) consistently strike 25ø+10 ø counterclockwise from their host faults and dip at angles greater than 80ø; (2) generally are absent along the central portions of the fault traces; (3) are numerous near the ends of some fault traces but absent along others; and (4) in rare cases form echelon arrays either centered along a fault trace or just past the fault trace ends. These observations are consistent with secondary fractures that nucleated near the perimeter of an elliptical fault along a "cohesive rim" of high slip resistance and propagated in three dimensions normal to the local most tensile stress. The fracture orientations relative to the faults reflect small stress drops during slip on the faults. The observations and model together have direct implications for how faults grow and conduct fluids. Secondary fractures are likely to be larger at the ends of small strike-slip faults rather than at their tops and bottoms. As a result, if strike-slip faults grow in an unrestricted manner, they are more likely to be linked end-to-end rather than top- to-bottom, especially where slip is small. Hydraulic conductivity is likely to be enhanced at the linkages between faults, so highly conductive regions along linked strike-slip faults are more likely to be vertical rather than horizontal.
The crack extension in a large plate subjected to general plane loading is examined theoretically and experimentally. It is found that under skew-symmetric plane loading of brittle materials the “sliding” or the crack extension in its own plane does not take place, instead crack grows in the direction approximately 70 deg from the plane of the crack. This is very nearly the direction perpendicular to the maximum tangential stress at the crack tip, which is 70.5 deg. The hypothesis that the crack will grow in the direction perpendicular to the largest tension at the crack tip seems to be verified also by cracked plates under combined tension and shear. In spite of the fact that “sliding” and “tearing” modes of crack extension do not take place in brittle materials it is shown that one can still talk about critical stress intensity factors in plane shear and transverse bending of plates. It is also shown that, in general plane loading, the fracture criterion in terms of stress intensity factors is an ellipse.
Opening-mode splay fractures have been observed within clusters near fault tips. The spatial distribution of splay fractures along faults influences fluid flow and lends insight into the mechanical processes of faulting. Slip gradients along faults produce stress concentrations which promote the development of opening-mode splay fractures along faults. Since the slip distribution depends on the distribution of frictional strength along faults, spatial variations in the frictional properties may influence fracture localization. Variations in friction coefficient along faults can reduce the stress singularities at fault tips and promote the development of multiple fractures inwards from the fault tips. The conditions that promote splay crack localization are examined using analytical and numerical fault models. Single splay fractures develop at locations of abrupt friction coefficient change and/or at fault tips when the friction coefficient near the tips is less than a critical value. Fault models with linearly increasing friction coefficient toward the fault tip promote the development of multiple splay fractures within broad zones near the tip.
Sliding along a preexisting flaw can result in the formation of tensile cracks where stresses concentrate near the flaw tips. These tensile cracks are referred to as wing cracks and are generally oriented oblique to the preexisting flaw. Previous studies based on linear elastic fracture mechanics (LEFM) showed that the kink angle depends on the ratio of normal to shear loading on the flaw. We present analytical solutions for cohesive end zone (CEZ) flaw models and find that the relationship between kink angle and load differs significantly from that for LEFM flaws. Furthermore, the remote flaw-parallel normal stress may significantly reduce or increase the kink angle, especially for CEZ flaws with large end zones. These results suggest that multiple interpretations are possible for some measured kink angles. In some materials, solution surfaces may form at the tip of the sliding flaw. By considering the angle between wing cracks and solution surfaces it is possible to determine whether the LEFM or CEZ model is more appropriate and thus to provide a better constrained interpretation of the boundary conditions that accompanied sliding. For some CEZ flaws the stress state in the cohesive end zone is nearly homogeneous, possibly promoting formation of arrays of opening mode cracks and solution surfaces that together form a shear zone. The CEZ flaw model can explain some orientations and patterns of cracks and solution surfaces commonly observed along natural faults that cannot be accounted for with the LEFM model.
This study investigates the reasons for the superimposition of several maximum principal stress directions (σ1) in the same area, and examines the contrast between unperturbed areas (stable direction of σ1) and perturbed areas (changing σ1 direction). We studied mesoscale structures on a 1000 m2 continuous limestone exposure near a regional scale strike-slip fault. Local σ1 directions were deduced from a high concentration of minor strike-slip faults, extension fractures and stylolites formed during the Pyrenean shortening in Languedoc, France. Most of the stylolites were formed in a stress field which was homogeneous on the exposure scale. This was followed by the reactivation of pre-existing extension fractures as strike-slip faults whose activity determined stress perturbations. A very heterogeneous stress field was produced leading to the formation of new localized stylolites and extension fractures, especially at fault terminations and at oversteps. Thus the final pattern shows the superimposition of all these structures. Reactivation of structures was caused by slight temporal changes in the orientation and intensity of the stress field produced by the nearby regional strike-slip faults. Our study suggests that the origin of stress deviations or superimpositions cannot be explained by random measurements of σ1. It is essential to be able to synthesize the fault pattern and the stress trajectories which it determines, and to do this, a very high density or a selection of data from mesoscale structures is needed.
A Barenblatt model that treats fracture resistance as an internal
cohesive stress acting at the crack tip is used to investigate the
effect of confining pressure on rock tensile failure. For a propagating
dike, the near-tip stress field is dominated by the large suction acting
within a small (about several meter) cavity at the tip generated by
viscous flow of magma within the dike. Perturbations to the ambient
stress are on the order of the cavity suction and act over regions on
the order of the cavity length. The tip cavity pressure may be
maintained by exsolution of magmatic volatiles or by influx of host rock
pore fluids; inelastic deformation is enhanced by the latter. Because
the tip cavity grows with dike size, the energy consumed by rock
fracture also increases with dike size and is potentially as significant
for large dikes as for small dikes.
Topography of chaos is variable and frequently elevated above
surrounding plains, supporting diapiric models for their origin.
Astypalaea Linea, a lineament in the extreme southern hemisphere of
Europa, has been found to be a global-scale strike-slip fault, based on
a palinspastic reconstruction of landscape on reprojected Voyager 2
images. The fault accommodates 35 km of right-lateral offset and extends
at least 810 km - a length comparable to the San Andreas Fault in
California. It exhibits familiar strike-slip features including braids
and pull-aparts. Straight segments of the fault are concentric about an
Euler pole provisionally located at (-48deg , 247.25deg W). Spanning
over 29deg from (-60deg ,191deg W) to (-78.5deg , 268.5deg W) Astypalaea
Linea is the longest strike-slip fault yet identified on Europa. The
fault is consistent with differential stress magnitudes and stress
directions predicted for high Europan latitudes due to possible non-
synchronous rotation (tidal bulge in its present location) (Greenberg
and Weidenschilling, 1984; Helfenstein and Parmentier, 1985). Extension
on neighboring gray band Thynia Linea matches the same stress field
(Pappalardo and Sullivan, 1996); thus, Astypalaea Linea and Thynia Linea
may be part of a south polar deformation zone which acts as a
"structural set" (Lucchitta and Soderblom, 1982). Analogous structures
may exist at the Europan north pole, although factors such as a possible
global structural dichotomy (Lucchitta and Soderblom, 1981) may affect
their occurrence. Lateral crustal motion, as implied by the fault, is
consistent with a subsurface viscous horizon structurally decoupling the
outer layer of the icy Jovian satellite from its interior (e.g. Schenk
and McKinnon, 1989).
Although a single model currently exists to explain the development of curved Europan cycloids, there have been no systematic studies of the range of morphologies and quantifiable geometric parameters of cycloidal features. We address variations in geometry along individual cycloid segments, characterizing differences in cusp styles and angles, and addressing the morphologic aspects of cycloid segments and cusps. In so doing, we illustrate how geometric and morphologic evidence imply a formation mechanism that differs from the existing model in several aspects. The current model states that cycloids are initiated as tensile fractures that grow in a curved path in response to rotating diurnal tidal stresses on Europa. However, the geometry of a cycloid cusp necessitates that shear stress was resolved onto the existing cycloid segment by the rotating diurnal stresses at the instant of cusp formation. Furthermore, we observe that cycloid cusps have a strikingly similar geometry to tailcracks that developed at the tips of many ridge-like strike-slip faults on Europa in response to shearing at the fault tip. We suggest that this similarity in geometries can be attributed to an identical formation mechanism whereby cycloid cusps form by a tailcracking process. We therefore present a revised, mechanically-based model for cycloid formation that retains the basic premise that crack growth is governed by diurnal stresses, but describes the development of cycloid cusps in response to resolved shear stresses at the tips of existing cycloid segments. The ratio of normal to shear stress at the time of tailcrack formation dictates the cusp angle and, over longer time periods, influences the morphologic evolution of the cycloid segment as it is repeatedly reworked by tidal stresses.
Estimates of the thickness of the ice shell of Europa range from 30 km. The higher values are generally assumed to be estimates of the entire ice shell thickness, which may include a lower ductile layer of ice, whereas many of the smaller thickness estimates are based on analyses that only consider that portion of the ice layer that behaves elastically at a particular strain rate. One example of the latter is flexure analysis, in which the elastic ice layer is modeled as a plate or sphere that is flexed under the weight of a surface load. We present calculations based on flexure analysis in which we model the elastic ice layer as flexing under a line-load caused by ridges. We use precisely located, parallel flanking cracks as indicators of the location of greatest tensile stress induced by flexure. Our elastic thickness results are spatially variable: ˜500 2200 m (two sites) and ˜200 1000 m (one site). Thorough analysis of Europan flexure studies performed by various researchers shows that the type of model selected causes the greatest variability in the thickness results, followed by the choice of Young's modulus, which is poorly constrained for the Europan ice shell. Comparing our results to those of previously published flexure analyses for Europa, we infer spatial variability in the elastic ice thickness (at the time of load emplacement), with smooth bands having the thinnest elastic ice thickness of all areas studied. Because analysis of flexure-induced fracturing can only reveal the elastic thickness at the time of load emplacement, calculated thickness variability between features having different ages may also reflect a temporal variability in the thickness of Europa's ice shell.
[1] We suggest that a crack that developed into a wedge-shaped band within the icy crust of Europa (at ∼28°S, 170°W [see Schenk and McKinnon, 1989, Figure 4; Prockter et al., 1999, Figure 1]) originated under an applied compressive stress through the operation of a frictional sliding mechanism. We analyze this suggestion using a scale-independent, sliding crack model and obtain an estimate of the maximum compressive stress to initiate the crack that compares reasonably well with earlier estimates [Helfenstein and Parmentier, 1985; McEwen, 1986; Greenberg et al., 1998] of Europan crustal stresses that are based upon elastic deformation of a shell. We then show through an application of both power law dislocation creep and diffusion creep that colder, near-surface Europan ice appears to be capable of supporting the deduced stresses with little relaxation over a period from 104 to 105 years.
The most recent visible tectonic features in the Astypalaea region in the southern hemisphere of Europa are a set of cycloidal ridges, three of which have cross-cutting relationships that define a time sequence for their formation. The longitudes at which each of these features formed, which may be different from the current location due to rotation of Europa, are constrained by models of their formation. Reconciling the time sequence with the inferred longitudes of formation appears to require that
The tectonics of Europa, one of Jupiter's moons, are complex. This satellite probably hosts a subsurface water ocean, but the thickness of the outer ice crust is poorly constrained and the episodic presence of liquid water at the surface is debated. We argue that some surface features of Europa are formed by soft ice that is heated by viscous dissipation of tidal motion along faults, and do not depend on a shallow ocean. Our model suggests that transient pockets of liquid water or brine could form at shallow depths in the crust.
The northern leading hemisphere of Europa was imaged at regional mapping resolution (~230 m/pixel) by the Galileo spacecraft SSI camera. We produced geologic maps from a regional-scale mosaic and a high resolution inset of this region. Twelve geologic units were sufficient to produce correlative geologic maps at both regional and local scales. Stratigraphic relationships indicate four major episodes in the geologic history of this area: The first episode includes background plains formation and modification, followed by a second period of extensive lineament formation. The third episode included extensive chaotic disruption of the surface at low and middle latitudes. The final episode includes the formation of new sets of ridges and bands, especially at high latitudes. The low crater density indicates that all these episodes in Europa's geologic history are geologically recent. The latitudinal distribution of chaos areas broadly matches that of areas of crustal thinning from models of tidal heating. We show that stress directions rotated clockwise with time, which is consistent with predictions from global stress models involving tidal deformation and nonsynchronous rotation of Europa's crust. On the basis of the change in lineament orientation with time, the reconstructed longitudinal positions of the studied area indicate that Europa's crust completed a full rotation relative to the tidally deformed interior.
Study of four different regions on Europa imaged by the Galileo spacecraft during its first 15 orbi