Richard W. Allmendinger

• PhD
• Professor (Full) at Cornell University

The youngest and best exposed Iron Oxide Cu–Au (IOCG) deposits currently recognized are found in the coastal belt of the Andes. Their formation has been attributed to back-arc extension or transtension associated with the convergent Andean margin. Here we document transpressional deformation synchronous with Cu mineralization in the Candelaria-Punt...

Regions of sparse exposure challenge geologic mappers because of limited information available on the underlying structure and continuity of the map units. We introduce here a little-known technique for post-processing bare earth digital terrain models (DTMs) that can dramatically improve knowledge of the underlying structure in covered areas. Text...

GMDE is a program, available on the desktop for Apple Macintosh, Microsoft Windows, and Linux platforms and in a mobile version for iOS, that enables geologists to extract quantitative structural information from geologic maps and satellite images. The program facilitates the digitizing of strikes and dips or calculating them from three-point probl...

Multiple factors affecting boulder weathering: Case of Chuculay Boulder Field in the Atacama Desert, northern Chile

Geoscience is an inherently interdisciplinary endeavor, and one of the most interdisciplinary geosciences is tectonics. Embracing experimental, observational, and theoretical perspectives, tectonics focuses on the interactions among various components of Earth and planetary systems as they evolve over many spatial and temporal dimensions. Many of t...

Smart phones are equipped with numerous sensors that enable orientation data collection for structural geology at a rate up to an order of magnitude faster than traditional analog compasses. The rapidity of measurement enables field structural geologists, for the first time, to enjoy the benefits of data redundancy and quantitative uncertainty esti...

The 2014 MW = 8.1 Iquique (Pisagua), Chile earthquake sequence ruptured a segment of the Nazca-South America subduction zone that last hosted a great earthquake in 1877. The sequence opened >3,700 surface cracks in the fore arc of decameter-scale length and millimeter-to centimeter-scale aperture. We use the strikes of measured cracks, inferred to...

The A.D. 2014 Pisagua earthquake sequence reactivated ancient surface cracks along the entire rupture length in the northern Chilean forearc. These subtle brittle strain features that are ~50 km above the subduction zone interface in the hyperarid Atacama Desert record deformation from the single earthquake sequence. In this study we document how a...

After 137 years without a great earthquake, the Mw 8.1 Pisagua event of 1 April 2014 occurred in the central portion of the southern Peru–northern Chile subduction zone. This megathrust earthquake was preceded by more than 2 weeks of foreshock activity migrating ∼3.5 km/ day toward the mainshock hypocenter. This foreshock sequence was triggered by...

We present new field structural data from the Chilean Coastal Cordillera located above the northern and central parts of the interplate contact ruptured by the A.D. 2010 Mw 8.8 Maule earthquake. The northern study area contains the northwest-striking Pichilemu normal fault, an intraplate structure reactivated after the megathrust event by crustal e...

The March 16–April 3, 2014 Pisagua earthquake sequence ruptured the middle part of the southern Peru-northern Chile seismic gap in the curved segment of the Andean subduction zone. The sequence began on March 16, with an Mw 6.7 earthquake that struck near the central section of the gap. A few hours after this initial event, intense seismic activity...

The Precordillera thrust belt of western Argentina is anomalously close, both horizontally and vertically, to the coeval subduction zone of the Nazca plate. The thin-skinned part of the belt has an unusually deep decollement that is well defined by industry seismic reflection and recent broadband experiments. New area and line-length balanced cross...

50 years after the great Alaskan earthquake, the Mw8.2 Pisagua earthquake filled in the center of the northern Chile seismic gap, part of the Nazca-South America plate boundary that had not experienced a great earthquake since 1877. The northern Chile margin bears several similarities to Cascadia: both are concave towards the subducting oceanic pla...

The last three great subduction earthquakes on Earth have demonstrated that slip activity at subduction zones seems to be related in two ways with the upper plate fault activity. The 2010 Mw 8.8 Maule Earthquake and the 2011 Mw 9.1 Tohoku-Oki Earthquake generated aftershocks in the upper plate compatible with the reactivation of normal faults. On t...

Over the past decade, the Isla Santa Maria (south-central Chile) has provided one of the most exquisitely detailed records of deformation and tectonically controlled sea-level change anywhere along the Andean margin ([Bookhagen et al., 2006][1]; [Melnick et al., 2006][2], [2009][3], [2012][4]).

Shortening from balanced cross sections is typically cited as a minimum estimate because of the uncertainty in the position of eroded hanging-wall cutoffs. We show here using area balancing that the single most significant source of error is that associated with the shape and thickness of the initial stratigraphic wedge involved in the deformation....

Earthquakes are accompanied by coseismic and post-seismic rebound: blocks of crust on either side of the fault spring back to their initial, undeformed configuration. This rebound is well documented by space geodetic data, such as the Global Positioning System. Thus, all earthquake-induced deformation of the crust is considered non-permanent and is...

[1] Geologists have long known that young normal faults are an important structural element of the Andean Coastal Cordillera, but their relationship to the subduction seismic cycle is still unclear. Some of the largest aftershocks of the 2010 Mw 8.8 Maule earthquake in central Chile were nucleated on upper plate normal faults, including the Mw 6.9...

[1] Geologists have long known that young normal faults are an important structural element of the Andean Coastal Cordillera, but their relationship to the subduction seismic cycle is still unclear. Some of the largest aftershocks of the 2010 Mw 8.8 Maule earthquake in central Chile were nucleated on upper plate normal faults, including the Mw 6.9...

State-of-the-art analysis of geological structures has become increasingly quantitative but traditionally, graphical methods are used in teaching. This innovative lab book provides a unified methodology for problem-solving in structural geology using linear algebra and computation. Assuming only limited mathematical training, the book begins with c...

The 2010 Mw 8.8 Maule subduction earthquake in south-central Chile is one of the best instrumentally recorded great seismic events in the world. Here, we explore the permanent geological deformation that accompanies the liberation of elastic strain energy during this type of megathrust earthquakes. Along the outer forearc (OF) of the south-central...

Balanced structural cross sections are models that are fit to incomplete data. The models are under-constrained with respect to any particular two-dimensional line-length model, but enough data generally exists to yield a well-constrained area balance solution. Furthermore, the area balance encompasses all possible line-length solutions. Therefore,...

Trishear is a kinematic model of fault-propagation folding in which the decrease in displacement along the fault is accommodated by deformation in a triangular shear zone radiating from the tip line. This model has garnered increasing acceptance, particularly for cases where parallel kink-fold models do not work (e.g., footwall synclines, lateral a...

Coseismic cracks preserved in the hyper-arid Atacama Desert of Northern Chile provide a unique record of the seismic history of the modern Andean forearc, which has generated the largest earthquakes on earth. Loveless et al. (2009) mapped more than 50,000 cracks on satellite imagery and, based on boundary element modeling, suggested that they indic...

The 2010 Maule earthquake was preceded by several decades of intense geological study of the Central and Southern Andes and 15 years of geodetic GPS monitoring of the South America-Nazca Plate boundary. With an excellent record of interseismic and coseismic deformation, and comprehensive description of upper plate regimes of shortening, vertical ax...

The extreme aridity of the northern Chilean Coastal Cordillera enables the complete preservation of permanent deformation related to the coupling between Nazca and South America. The region between Antofagasta and Arica is characterized by four types of Late Cenozoic structures: EW-striking reverse faults; ~NS-striking normal faults; sparse WNW and...

Despite its location in a convergent tectonic setting, the Coastal Cordillera of northern Chile between 21°S and 25°S is dominated by structures demonstrating extension in the direction of plate convergence. In some locations, however, normal faults have been reactivated as reverse faults, complicating the interpretation of long-term strain. In ord...

For geothermal to have a national impact as a major energy supplier in the U.S., deployment must eventually utilize lower grade hydrothermal or Enhanced Geothermal Systems (EGS) resources. In these locations the costs of drilling as a function of depth will limit produced fluids to lower temperatures. This limitation favors applications for direct...

Geodetic data from the Global Navigation Satellite System (GNSS), and from satellite interferometric radar (InSAR) are revolutionizing how we look at instantaneous tectonic deformation, but the significance for long-term finite strain in orogenic belts is less clear. We review two different ways of analyzing geodetic data: velocity gradient fields...

SSPX is a Macintosh, Cocoa/Universal application to compute strain from displacement/velocity data in two and three dimensions. SSPX solves small and large deformation problems, in either the undeformed (Lagrangian) or deformed (Eulerian) configuration. The program offers several options to compute strain: best fit for all or selected data, strain...

Understanding the long-term patterns of great earthquake rupture along a subduction zone provides a framework for assessing modern seismic hazard. However, evidence that can be used to infer the size and location of past earthquakes is typically erased by erosion after a few thousand years. Meter-scale cracks that cut the surface of coastal areas i...

A comparison of shortening directions calculated from GPS vectors and fault-slip data from the western Argentine Andes indicates that the two data sets, which describe deformation over significantly different temporal scales, are nearly indistinguishable when calculated at similar spatial scales. Campaign GPS vectors sample motion at the decadal sc...

Reverse faults in northern Chile have formed 20–300 m high scarps that contain open fractures which occur in a zone of 20–1600 m wide. Two-dimensional numerical models were used to explore the geometrical and mechanical parameters needed to produce extension within a bulk contractional regime. All of the mechanical models show the same structure as...

Overlying the only part of the South American continental crust that is in direct contact with the subducting Nazca Plate, the Coastal Cordillera of northern Chile and southern Peru should provide the most complete geological record of the coupling between the two plates. This record of coupling is exquisitely preserved in the hyperarid Atacama Des...

Unambiguous elastic rebound recorded by GPS data collected before and after major earthquakes has led to the conclusion that the majority of the tectonic signal captured by GPS is elastic and transitory. Elastic models used to understand plate kinematics commonly assume that the only heterogeneities in the earth are the discontinuities (i.e., fault...

Three plateaus, two collisional (Tibet & Anatolia) and one non-collisional (the Altiplano) have been analyzed by inverting campaign GPS velocities for the velocity gradient tensor. We use both distance weighted and nearest neighbor algorithms to produce smoothed regional maps of 2D strain and dilatation rate as well as vertical axis rotation rate....

Meter-scale surface cracks throughout the northern Chilean and southern Peruvian forearcs provide a long-term record of seismic segmentation along the Andean plate boundary. The cracks, mapped on high-resolution satellite imagery, show strong preferred orientations over large regions and the mean strikes of cracks vary systematically as a function...

Patterns of faulting in the northern Chilean forearc are consistent with modeled stress fields resulting from the subduction zone earthquake cycle. We define positive Coulomb stress change as encouraging normal faulting motion on steeply-dipping planes striking approximately parallel to the plate boundary, as shown by fault kinematic data collected...

We present the first numerical age constraint for young deformation of the Atacama Fault System (AFS) in northern Chile. The young activity of the AFS is expressed by several fault scarps which affects alluvial fan sediments of the eastern side of the Coastal Cordillera (23°30′–23°42′S). Detailed mapping of alluvial fans reveals a complex relations...

Global positioning system (GPS) data from the central Andes record vertical axis rotations that are consistently counterclockwise in Peru and Bolivia north of the bend in the mountain belt, and clockwise to the south in southern Bolivia, Argentina, and Chile. These geologically instantaneous rotations have the same sense as rotations that have accr...

Kinematic and mechanical modeling of the Rip Van Winkle (SE New York, USA) and La Zeta (SW Mendoza, Argentina) anticlines illustrate the influence of mechanical stratigraphy and initial stress state on the kinematics of fault propagation folding. In both anticlines, faults nucleating at distinct stratigraphic levels open upward into triangular zone...

This study addresses multiple controls on foreland-basin accommodation and contributes to enhanced understanding of the evolution of the northern Andes. The Middle Magdalena Valley Basin (MMVB), Eastern Cordillera, and Llanos Basin are part of a Late Cretaceous-Cenozoic foreland-basin system, east of the Colombian Central Cordillera. Mechanical mod...

Despite convergence across the strongly coupled seismogenic interface between the South American and Nazca plates, the dominant neotectonic signature in the forearc of northern Chile is arc-normal extension. We have used 1 m resolution IKONOS satellite imagery to map nearly 37,000 cracks over an area of 500 km2 near the Salar Grande (21°S). These f...

Development of the Colombian Middle Magdalena Valley Basin (MMVB) was determined by late Cretaceous-early Eocene uplift of the Central Cordillera to the west, and subsequent transferal of deformation to the Eastern Cordillera to the east. These phases are separated in the tectono-stratigraphic record by a major unconformity, the Middle Magdalena Va...

In the Central Andes, the frictional coupling between South America and the subducting Nazca Plate occurs beneath the Coastal Cordillera of northern Chile. One of the most distinctive characteristics of the Coastal Cordillera is a suite of EW topographic scarps located between 19° and 21.6°S latitude. These scarps are associated with predominantly...

Most structural/kinematic models are inherently two-dimensional; even several recent three-dimensional models are "pseudo-three-dimensional" in that they consist of a series of parallel two-dimensional cross sections. Lack of a true three-dimensional formulation hampers our abilities to simulate three-dimensional structures such as oblique- and str...

We have expanded previous trishear fault-propagation-fold forward models by allowing additional structural complexity in the form of multiple ramps and flats, variable propagation-to-slip ratio (P/S) and trishear angle, as well as multiple faults in a single section. The resulting forward models simulate characteristics of real structures very well...

The Coastal Cordillera of northern Chile is located in the hyperarid Atacama Desert and is situated over the interplate seismic zone of the Nazca-South America convergent plate boundary. The Coastal Cordillera is bounded to the west by a 1000 m high escarpment that plunges directly to the sea north of Iquique but to the south has a 1-5 km wide Plei...

▪ Abstract The enigma of continental plateaus formed in the absence of continental collision is embodied by the Altiplano-Puna, which stretches for 1800 km along the Central Andes and attains a width of 350–400 km. The plateau correlates spatially and temporally with Andean arc magmatism, but it was uplifted primarily because of crustal thickening...

The Maastrichtian-Cenozoic southern Middle Magdalena Valley Basin of Colombia contains a unique record of unconformities, strata, and structure, from which we extract the histories of exhumation of the Central Cordillera, to the west, and evolution of the Eastern Cordillera fold-and- thrust belt, to the east. This study integrates field-based analy...

Faults propagating through the Earth generate a wave of deformation ahead of their tip lines. We have modeled this process to understand the relationship between fold geometry and fault propagation. Using finite element modeling (FEM), we investigate the response of incompressible frictionless and frictional materials, and a compressible frictional...

Numerous analog models and some natural examples display smoothly curving backlimb fold hinges over sharp, angular bends in the underlying thrust surface. We present a new kinematic model that can reproduce this geometry by defining a triangular zone focused on the fault bend. The model presupposes incompressible flow in the triangular zone and mak...

Basement structures, to which trishear fault-propagation models have most successfully been applied, are commonly three-dimensional folds formed at the tip-line of a fault. We present here a ‘pseudo-3D’ trishear model in which various parameters are permitted to vary along strike and oblique-slip can be modeled. These variations may be combined in...

We present the GPS-derived velocity field from the south-central Andes mountains between 28 o and 36 oS. The GPS network covers the entire orogenic system from forearc to backarc and is especially dense over the active Precordillera fold and thrust belt in west-central Argentina. The study area coincides with the transition from flat to steeply dip...

[1] Abstract: We interpret the interseismic crustal velocity field of the central Andes using a simple three-plate model in which the Andean mountain belt is treated as a rigid microplate located between the Nazca and South American (SoAm) plates. We assume that the Euler vectors associated with these plates are strictly coaxial and that the surfac...

A general method for the derivation of velocity fields consistent with the basic kinematics of the trishear model of fault-propagation folding is given. We show that the fields can be written as explicit functions of position within the deformation zone. To demonstrate the approach, several different linear and non-linear velocity fields are derive...

The link between thin-skinned foreland shortening and thickening of the lower crust beneath the hinterlands of mountain belts has seldom been observed. We have reprocessed Yacimientos Petrolı́feros Fiscales (YPF S.A.) seismic reflection data from the Eastern Cordillera of the Central Andes at 22°S latitude using Vibroseis extended correlation; the...

A numerical grid search using the trishear kinematic model can be used to extract both slip and the distance that a fault tip line has propagated during growth of a fault-propagation fold. The propagation distance defines the initial position of the tip line at the onset of slip. In the Santa Fe Springs anticline of the Los Angeles basin, we show t...

The High Atlas Mountains of North Africa were formed over a major intracontinental rift system that had extended from what is now the Atlantic margin of Morocco to the Mediterranean coast of Tunisia. The Atlas rift system began in the Triassic and was active through the Jurassic. The inversion phase of the Atlas rift system began in the Early Creta...

Fault-propagation folds commonly display footwall synclines as well as changes in stratigraphic thickness and dip on their forelimbs, features that cannot easily be explained by simple parallel kink fold kinematics. An alternative kinematic model, trishear, can explain these observations, as well as a variety of other features which have long intri...

The NE-SW trending Middle Atlas Mountains of Morocco are obliquely oriented within the late Cenozoic regional stress field, resulting in deformation that is partitioned into strike-slip faulting and thrust-related folding. In the central Middle Atlas, thrusting is confined to a 20 km wide fold belt between two relatively rigid crustal blocks that a...

The Tectonic Evolution of the Atlas Mountains, Morocco BEAUCHAMP, WELDON, RICHARD W. ALLMENDINGER, MUAWIA BARAZANGI, AHMED DEMNAI, and MOHAMED EL ALJI The Atlas mountains of North Africa were formed by the reactivation of a major intracontinental rift system. This rift system extended from what is now the Atlantic margin of Morocco, to the Mediterr...

Okay, everyone who thinks that continuum mechanics makes inherently fascinating, light reading, raise your hands. Hmm, I thought so. Most geologists and not a few geophysicists view continuum mechanics almost as a necessary evil, somewhat akin to a bad tasting medicine, which will make us better scientists even though the process of acquiring that...

The enigma of continental plateaus formed in the absence of continental collision is embodied by the Altiplano-Puna, which stretches for 1800 km along the Central Andes and attains a width of 350–400 km. The plateau correlates spatially and temporally with Andean arc magmatism, but it was uplifted primarily because of crustal thickening produced by...