C. Collettini's research while affiliated with Sapienza University of Rome and other places

Publications (155)

Article
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Fault stability is inherently linked to the frictional and healing properties of fault rocks and associated fabrics. Their complex interaction controls how the stored elastic energy is dissipated, that is, through creep or seismic motion. In this work, we focus on the relevance of fault fabrics in controlling the reactivation and slip behavior of d...
Article
Crustal seismicity is in general confined within the seismogenic layer, which is bounded at depth by processes related to the brittle-ductile transition (BDT) and in the shallow region by fault zone consolidation state and mineralogy. In the past 10-15 years, high resolution seismological and geodetic data have shown that faulting within and around...
Preprint
Analysis of seismicity can illuminate active fault zone structures but also pervasive deformation occurring within large volumes of the seismogenic zone. Here we show that, for the M w 6.5 2016–2017 Central Italy seismic sequence, seismicity not only localizes along SW-dipping normal faults, but also occurs within larger volumes of Triassic Evapori...
Article
We performed a suite of experiments aimed at examining the frictional properties of unaltered basalts at conditions considered to be representative of slip at shallow depths in volcano-tectonic environments and in-situ geo-energy basaltic sites. Scientific drilling and field studies on exhumed subsurface faults and fractures analogues suggest that,...
Article
The presence of weak phyllosilicates in mature carbonate fault zones has been invoked to explain weak faults. However, the relation between frictional strength, fault stability, mineralogical composition, and fabric of fault gouge, composed of strong and weak minerals, is poorly constrained. We used a biaxial apparatus to systematically shear diffe...
Article
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Understanding the physical mechanisms at the origin of slow-slip events has been proven a very challenging task. In particular, little is known on the role of fault heterogeneity during slow slip. In this study, we provide evidences that fault fabric controls slip velocity time histories during slow-slip events generated in the laboratory. We perfo...
Article
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Abstract Tectonic faults typically break in a single rupture mode within the range of styles from slow slip to dynamic earthquake failure. However, in increasingly well‐documented instances, the same fault segment fails in both slow and fast modes within a short period, as in the sequences that culminated in the 2011 Mw = 9.0 Tohoku‐Oki, Japan, and...
Article
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On natural faults that host repeating slip events, the inter‐event loading time is quite large compared to the slip event duration. Since most friction studies focus on steady‐state frictional behavior, the fault loading phase is not typically examined. Here, we employ a method specifically designed to evaluate fault strength evolution during activ...
Article
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Understanding the factors controlling fracture frequency distribution can greatly improve the assessment of fluid circulation in fault damage zones, with evident implications for fault mechanics, hydrogeology and hydrocarbon exploration. This is particularly important for relay zones that are usually characterized by strong damage and structural co...
Presentation
Fractures constitute the main pathway for fluids in fault damage zones hosted in low-porosity rocks. Understanding the factors controlling fracture distribution is hence fundamental to better assess fluids circulation in fault damage zones, with evident implications for fault mechanics, hydrogeology and hydrocarbon exploration. Being usually charac...
Article
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Giant rockslides are widespread and sensitive to hydrological forcing, especially in climate change scenarios. They creep slowly for centuries and then can fail catastrophically posing major threats to society. However, the mechanisms regulating the slow-to-fast transition toward their catastrophic collapse remain elusive. We couple laboratory expe...
Presentation
Fracture distribution controls fluids circulation in fault damage zones, with evident implications for fault mechanics, hydrogeology and hydrocarbon exploration. Being usually characterized by a strong damage and structural complexity, this is of particularly importance for relay zones. We investigated the fracture distribution within a portion of...
Article
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Minor fault geometry and kinematics within relay ramps is strongly related to the stress field perturbations that can be produced when two major fault segments overlap and interact. Here we integrate classical fieldwork and interpretation of a virtual outcrop to investigate the geometry and kinematics of subsidiary faults within a relay ramp along...
Article
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Pore fluid overpressures in active fault systems can drive fluid flow and cause fault weakening and seismicity. In return, deformation accommodated by different modes of failure (e.g. brittle vs. ductile) also affects fault zone permeability and, hence, fluid flow and pore fluid pressure distribution. Current numerical simulation techniques model h...
Article
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Empirical scaling relationships between fault or slip dimensions and earthquake magnitudes are often used to assess the maximum possible earthquake magnitude of a territory. Upon the assumption of the reactivability of any fault, the earthquake magnitudes derived from the surface fault length (FLEM) are compared at the national scale in Italy again...
Article
Some faults are considered strong because their strength is consistent with the Coulomb criterion under Byerlee’s friction, 0.6 <μ <0.85. In marked contrast, numerous studies have documented significant fault weakening induced by fluid-assisted reaction softening that generally takes place during the long-term evolution of the fault. Reaction softe...
Presentation
A multiscale geometrical and kinematic characterization of fault zones is the starting point to understand fault mechanics, in particular that of potentially seismogenic faults. Fieldwork and seismological studies can provide pictures and kinematic characterization of faults at sub-regional scale (i.e. tens of kilometers). Until the advent of Digit...
Article
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Faults in the brittle crust constitute preexisting weakness zones that can be reactivated depending on their friction, orientation within the local stress field, and stress field magnitude. Analytical approaches to evaluate the potential for fault reactivation are generally based on the assumption that faults are ideal planes characterized by zero...
Article
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Faults can slip seismically or aseismically depending on their hydromechanical properties, which can be measured in the laboratory. Here, we demonstrate that fault slip induced by fluid injection in a natural fault at the decametric scale is quantitatively consistent with fault slip and frictional properties measured in the laboratory. The increase...
Article
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Fluid overpressure is one of the primary mechanisms for triggering tectonic fault slip and human-induced seismicity. This mechanism is appealing because fluid overpressure reduces the effective normal stress, hence favoring fault reactivation. However, upon fault reactivation models of earthquake nucleation suggest that increased fluid pressure sho...
Presentation
A fault zone is composed of one or multiple fault cores, which are located within a complex network of fractures and secondary slip surfaces (i.e., the damage zone) that determine the mechanical behaviour. For example, fractures within the damage zone control fluid circulation and have a strong impact on the elastic properties of the host rock. Fur...
Data
Table contains normal stress vs. shear stress data measured in friction experiments carried out in direct shear configuration on serpentine rock powders. Details of experimental procedure and data analysis in the linked publication. Column 1: Normal Stress (MPa) during steady-state sliding of serpentine. Other columns: Shear Stress (MPa) measured...
Article
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The Hikurangi subduction zone hosts shallow slow-slip events, possibly extending to the seafloor. The mechanisms allowing for this behavior are poorly understood but are likely a function of the frictional properties of the downgoing seafloor sediments. We conducted friction experiments at a large range of effective stresses, temperatures, and velo...
Article
Serpentines are common minerals in several major tectonic faults in a variety of geodynamic settings and have variable frictional strength and complex deformation processes. Here we present friction experiments carried out on a suite of serpentine samples that include veins of antigorite, lizardite, and fibrous serpentine (chrysotile and polygonal...
Article
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Serpentinites play a key role in controlling fault rheology in a wide range of geodynamic settings, from oceanic and continental rift zones to subduction zones. In this paper, we provide a summary of the most common deformation mechanisms and frictional strengths of serpentine minerals and serpentinites. We focus on deformation mechanisms in retrog...
Article
One of the major challenges regarding the disposal of radioactive waste in geological formations is to ensure isolation of radioactive contamination from the environment and the population. Shales are suitable candidates as geological barriers. However, the presence of tectonic faults within clay formations put the long-term safety of geological re...
Article
A great number of earthquakes occur within thick carbonate sequences in the shallow crust. At the same time, carbonate fault rocks exhumed from a depth < 6 km (i.e., from seismogenic depths) exhibit the coexistence of structures related to brittle (i.e., cataclasis) and ductile deformation processes (i.e., pressure-solution and granular plasticity)...
Article
The kaolinite-bearing Opalinus Clay (OPA) is the host-rock proposed in Switzerland for disposal of radioactive waste. However, the presence of tectonic faults intersecting the OPA formation put the long-term safety performance of the underground repository into question due to the possibility of earthquakes triggered by fault instability. In this p...
Presentation
The characterization of frictional properties and deformation mechanisms of carbonate–bearing normal faults is fundamental to characterize reservoir development and seismic hazard. We conducted 24 experiments on simulated calcite fault gouges made of powdered Carrara Marble. Experiments have been performed at room temperature with a biaxial apparat...
Article
It is widely recognized that the significant increase of M > 3.0 earthquakes in Western Canada and the Central United States is related to underground fluid injection. Following injection, fluid overpressure lubricates the fault and reduces the effective normal stress that holds the fault in place, promoting slip. Although, this basic physical mech...
Article
Large normal faults are frequently reactivated as high-angle reverse faults during basin inversion. Elevated fluid pressure is commonly invoked to explain high-angle reverse slip. Analogue and numerical modeling have demonstrated that frictional weakening may also promote high-angle reverse slip, but there are currently no frictional strength measu...
Article
The physical characterization of carbonate–bearing normal faults is fundamental for resource development and seismic hazard. Here we report laboratory measurements of density, porosity, Vp, Vs, elastic moduli and permeability for a range of effective confining pressures (0.1-100 MPa), conducted on samples representing different structural domains o...
Article
Surface geometry is an essential component in faulting and earthquake dynamics, yet its evolution and interrelationship with friction are poorly understood. The geometric characteristics of smooth fault surfaces are herein investigated by combining direct shear experiment results with statistical analysis of the surface topography. Ground limestone...
Article
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Graphitization, or the progressive maturation of carbonaceous material, is considered an irreversible process. Thus, the degree of graphite crystallinity, or its structural order, has been calibrated as an indicator of the peak metamorphic temperatures experienced by the host rocks. However, discrepancies between temperatures indicated by graphite...
Article
We studied the frictional behaviour and deformation products of large (20 cm × 20 cm bare surfaces) experimental limestone faults. We sheared samples in a direct shear configuration, with an imposed normal force of 40–200 kN and shear velocity of 10 μm/s. The steady-state shearing of these surfaces yielded a coefficient of friction 0.7<μ<1 (average...
Article
Laboratory and theoretical studies provide insight into the mechanisms that control earthquake nucleation, when fault slip velocity is slow (< 0 .001 cm/s), and dynamic rupture when fault slip rates exceed centimeters per second. The application of these results to tectonic faults requires information about fabric evolution with shear and its impac...
Article
The physical mechanisms governing slow earthquakes remain unknown, as does the relationship between slow and regular earthquakes. To investigate the mechanism(s) of slow earthquakes and related quasi-dynamic modes of fault slip we performed laboratory experiments on simulated fault gouge in the double direct shear configuration. We reproduced the f...
Article
Sealing layers are often represented by sedimentary sequences characterized by alternating strong and weak lithologies. When involved in faulting processes, these mechanically heterogeneous multilayers develop complex fault geometries. Here we investigate fault initiation and evolution within a mechanical multilayer by integrating field observation...
Article
The Northern Apennines of Italy is a unique area to study active crustal processes due to the availability of high-resolution subsurface geology (deep borehole and seismic profiles) and seismicity (back-ground and seismic sequences) data. In this work we have investigated the relationship between crustal structures and lithologies, rheological prof...
Article
Temporal changes in seismic velocity during the earthquake cycle have the potential to illuminate physical processes associated with fault weakening and connections between the range of fault slip behaviours including slow earthquakes, tremor and low-frequency earthquakes. Laboratory and theoretical studies predict changes in seismic velocity befor...
Article
Full-text available
Fluid overpressure is one of the primary mechanisms for tectonic fault slip, because fluids lubricate the fault and fluid pressure reduces the effective normal stress that holds the fault in place. However, current models of earthquake nucleation, based on rate-and state-friction laws, imply that stable sliding is favoured by the increase of pore f...
Article
The presence of calcite in and near faults, as the dominant material, cement, or vein fill, indicates that the mechanical behaviour of carbonate-dominated material likely plays an important role in shallow- and mid-crustal faulting. To better understand the behaviour of calcite, under loading conditions relevant to earthquake nucleation, we sheared...
Article
Recent friction experiments carried out under upper crustal P-T conditions have shown that microstructures typical of high temperature creep develop in the slip zone of experimental faults. These mechanisms are more commonly thought to control aseismic viscous flow and shear zone strength in the lower crust/upper mantle. In this study, displacement...
Article
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The strength, shape, and ultimately seismic behavior of many thin-skinned fold and thrust belts, including marine accretionary wedges, are strongly controlled by large-scale faults that develop from weak, clay-rich sedimentary horizons (decollements). The increase of temperature with depth along clay-rich faults promotes the so-called smectite-illi...
Article
The impact of heat, readily provided by magma, circulating hot fluids, or rapid fault slip on carbonate substrata is an important factor in determining the flank stability of volcanoes and the mechanical behavior of faults in areas where carbonate lithologies are prevalent. The mineralogy and mechanical properties of carbonate rocks are demonstrabl...
Article
Faults involving phyllosilicates appear weak when compared to the laboratory-derived strength of most crustal rocks. Amongst phyllosilicates, talc, with very low friction, is one of the weakest minerals involved in various tectonic settings. As the presence of talc has been recently documented in carbonate faults, we performed laboratory friction e...
Article
Observations from deep boreholes at several locations worldwide, laboratory measurements of frictional strength on quartzo-feldspathic materials and earthquake focal mechanisms indicate that crustal faults are strong (apparent friction μ≥0.6). However, friction experiments on phyllosilicate-rich rocks and some geophysical data have demonstrated tha...
Poster
Opalinus Clay formation (OPA) is an indurated shale under study in the context of geological deep disposal of nuclear waste in Switzerland. We will study the frictional properties of fault zones in OPA to evaluate the long-term safety performance of the repository. A better understanding of fault stability and possible related leakages are the main...
Article
The understanding of fault-slip behaviour in carbonates has an important societal impact due to the widespread occurrence and propagation of earthquakes in these rocks. Fault rock variations in carbonates are systematically controlled by the lithology of the faulted protolith: cataclasis and hydraulic fracturing with evidence of past seismic slip c...
Article
Observations of heterogeneous and complex fault slip are often attributed to the complexity of fault structure and/or spatial heterogeneity of fault frictional behavior. Such complex slip patterns have been observed for earthquakes on normal faults throughout central Italy, where many of the Mw 6 to 7 earthquakes in the Apennines nucleate at depths...
Article
Full-text available
The availability of multidisciplinary and high-resolution data is a fundamental requirement to understand the physics of earthquakes and faulting. We present the Alto Tiberina Near Fault Observatory (TABOO), a research infrastructure devoted to studying preparatory processes, slow and fast deformation along a fault system located in the upper Tiber...
Article
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The characterization of fault zone structure and its evolution is essential for understanding earthquake mechanics and rupture evolution. Most of our knowledge about fault structure is derived from field studies of ancient faults. By using earthquake locations, we reconstruct the complex structure of a normal fault at a resolution directly comparab...
Article
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As part of an interdisciplinary research project, funded by the European Research Council and addressing the mechanics of weak faults, we drilled three 200–250 m-deep boreholes and installed an array of seismometers. The array augments TABOO (The AltotiBerina near fault ObservatOry), a scientific infrastructure managed by the Italian National Insti...
Article
We have investigated mineralogy and micro/nanostructures of pressure solution seams in four different carbonatic faults with kilometric displacement, cropping out in the Northern Apennines, Italy. Disregarding the different protoliths and deformation conditions, the stylolite-filling material has almost constant mineralogical characteristics, being...
Article
The Zuccale fault is a regional, low-angle, normal fault, exposed on the Isle of Elba in central Italy that accommodated a total shear displacement of 6–8 km. The fault zone structure and fault rocks formed at <8 km crustal depth. The present-day fault structure is the final product of several deformation processes superposed during the fault histo...
Article
The link between actual fault rock/structures and multi-mode slip behavior of faults, such as earthquakes, tremors, creep and others is controversial. We addressed this topic for carbonate-hosted, mature faults carrying out field and microstructural analyses and performing friction experiments on three thrusts exposed in the Umbria-Marche Apennines...