Blind Thrust Research Articles

The 26 November 2019 Durrës earthquake, Albania: coseismic displacements and occurrence of slow slip events in the year following the earthquake

SUMMARYOuter Albanides experienced a seismic sequence starting on 21 September 2019, with an Mw 5.6 earthquake, considered a foreshock, and culminated with the main shock on 26 November 2019, followed by a paramount aftershock activity. We propose a model for the coseismic slip distribution using InSAR, permanent, and campaign GNSS measurements. We tested two hypotheses: an earthquake on a thrust plane with the direction N160° and along with a back thrust. By varying the depth and dip angle for the first hypothesis and only the dip angle for the second hypothesis, we concluded the optimal solution is a blind thrust at a 15-km depth dipping eastward 40°, a maximum slip of 1.4 m and an Mw 6.38. A GNSS time-series obtained after 2020 shows two slow slip events (SSEs): the first one is 200 d after the main shock up to 26 d, and the second one is 300 d after the main shock up to 28 d. We tested three hypotheses: SSE along the basement thrust where the main shock has been localized, SSE along the flat formed by the detachment layer of the cover, and SSE along these two faults. We concluded that SSE occurred along the detachment layer or along the two faults.

Hundalee Fault, North Canterbury, New Zealand: late Quaternary activity and regional tectonics

ABSTRACT The Hundalee Fault forms part of the southeastern margin of the 2016 Kaikōura Earthquake rupture zone. Its late Quaternary activity and structural character may offer insights to fault interrelationships associated with the 2016 rupture. Mapping of the Hundalee Fault revealed several pre-existing fault scarps. Trenching of a scarp across a fluvial terrace together with radiocarbon dating shows the occurrence of at least two, probably three, surface ruptures since 3.5 ka. The scarp records about 2.5 m of reverse-sense vertical deformation, mostly folding, of which ∼0.6 m occurred in 2016, along with subordinate sinistral slip. Fluvial terrace ages inferred from geomorphological relationships, together with the trenching results, indicate a long-term vertical slip rate of 0.2–0.4 mm/yr since at least 30 ka. Geological data indicate a relatively recently surface emergence of the Hundalee Fault from beneath a fault propagation fold. The 2016 Hundalee Fault rupture is interpreted as a break-out from an extensive blind thrust fault, whose motion triggered predominantly contractional rupture of an array of steeper near-surface faults. The thrust is hypothesised as having provided linkage in the 2016 rupture between the predominantly strike-slip ruptures of The Humps Fault to the southwest and the Kekerengu Fault to the northeast.

Thrust faulting on Venus: Tectonic modeling of the Vedma Dorsa Ridge Belt

Radar images from the Magellan mission reveal compressional ridge belts transecting several low-lying plains on Venus, including Atalanta, Vinmara, Lavinia, and Rusalka/Llorona/Vellamo Planitiae. Vedma Dorsa is an ∼1800 km long ridge belt with 0.5–1 km of relief in Llorona/Vellamo Planitiae. We analyze sections of the ridge belt that have an asymmetric topographic cross section, indicative of deep thrust faulting and shallow folding as the dominant formation mechanisms. We perform elastic dislocation and Monte Carlo tectonic modeling of thrust faulting at several locations along Vedma Dorsa to constrain the fault displacement (D), depth of faulting (z), and fault dip (θ). We find that the models are consistent with blind thrust faulting and folding as the dominant mechanism for producing Vedma, with preferred fault parameters of D ∼ 1–2 km, z ∼ 10–25 km, and θ ∼ 25–30°. The results support an upper fault tip >3 km below the surface (blind fault), and a change in dip at depth. Our preferred models and the additional fault complexities supported at each site suggest that this section of Vedma is an intermediate structure between lobate scraps and fold and thrust belts, incorporating morphometric aspects from both classifications. Observations of terrestrial fault depths and the best-fitting depth of faulting from our models lead to an estimated heat flux of 16–39 mW m−2 at the time of Vedma Dorsa's formation, consistent with formation over a cold, downwelling region of the mantle.

Mechanism of Fault Terminations: Theory and Field Examples

ABSTRACT Contrary to the mechanism of initiation and growth of a fault that has been extensively addressed, the termination of the fault is poorly understood. It is generally believed that the major factors such as the zone of weakness, frictional homogeneity, rock tension, and the minor factors such as stress and gravity are responsible for the initiation and growth of faults, while the deficiency of these factors leads to the termination of a fault. A theory of fault-termination has been proposed by combining progressive deformation and branching (as observed on seismic data from the North Sea and Scotian basin) along with the hindrance, flanking, block rotation, enhanced mineralization, relaxation and cohesive strength. This model of progressive deformation during faulting is categorized into three zones: displacement zone in the beginning, displacement shear transition zone in the middle and the shear zone towards the termination. These well-patterned changes of progressive deformation include continuation of shearing beyond the tip line and converting brittle displacement deformation state into shearing displacement towards the termination. This mechanism also elucidates the deformation state for blind thrust, brittle-ductile transition zone within the crust, initiation of the reverse fault and deformation-stress relationship for faulting.

Late Pleistocene Slip Rate and 3D Geometry of the Mid-Channel Blind Thrust, Santa Barbara Channel, California, and Their Implications for Earthquake Hazards

ABSTRACTThe Mid-Channel fault is an active blind thrust overlain by a south-vergent anticline in the Santa Barbara channel of southern California. We use high-quality industry seismic reflection data to characterize the 3D geometry of the Mid-Channel fault, and define its lateral extent and interactions with other structures in the region. We use a detailed chronostratigraphic sequence of nine Pleistocene horizons ranging in age from 120 ka to 1.05 Ma to interpret the geometry and deformational history of the Mid-Channel anticline and blind thrust. These precisely dated horizons provide unique insights on the Pleistocene activity of the Mid-Channel fault because of the nearly complete preservation of sediment on the backlimb of the fold. Using a new method of relating structural relief of these horizons to slip on the underlying Mid-Channel fault, we calculate the faults late Pleistocene slip rate. Results indicate that the structure became active between 790 and 710 ka in the eastern part of the Channel and subsequently propagated west along strike. In the east, where the overlying anticline preserves a complete section of syntectonic growth strata, the Mid-Channel fault has a dip-slip rate of 1.8 mm/yr with a range of 1.6–2.1 mm/yr. Based on a map of total displacement, we infer that the maximum dip-slip rate on the Mid-Channel fault along strike is 2.1 ± 0.2 mm/yr, suggesting that it may accommodate about one-third of the observed geodetic contraction across the basin. We explore alternative ways that the fault may extend to depth and interact with surrounding structures, and consider the seismic hazard implications of these scenarios, including estimates of potential earthquake rupture areas, magnitudes, and average recurrence intervals.

Characterization of the shallow subsurface structure across the Carrascoy Fault System (SE Iberian Peninsula) using P-wave tomography and Multichannel Analysis of Surface Waves

The seismicity in the SE Iberian Peninsula is distributed parallel to the coast in a well-developed strike-slip fracture system known as the Eastern Betic Shear Zone (EBSZ). This work focuses on the characterization of the shallow subsurface structure of the Algezares-Casas Nuevas Fault, within the Carrascoy Fault System of the EBSZ. The Carrascoy Fault borders the Guadalentín Depression to the south, which is a densely populated area with extensive agricultural activity. Therefore, this faults system represents a seismic hazard with significant social and economic implications. We have constructed two velocity-depth models based on P-wave tomography and Multichannel Analysis of Surface Waves (MASW) acquired from seismic reflection data. The resulting velocity models have allowed us to interpret the first ~250m depth and have revealed: i) the thickness of the critical zone; ii) the geometry of the Algezares-Casas Nuevas Fault; iii) the depth of the Messinian/Tortonian contact and iv) the presence of blind thrusts and damage zones under the Guadalentín Depression. Our results have also helped us to estimate an apparent vertical slip rate of 0.66±0.06m/ky for the Algezares-Casas Nuevas Fault since 209.1±6.2ka. Our results provide a methodological and backflow protocol to study the shallow subsurface of active faults, complementing previous geological models based on paleoseismological trenches, and can be used to improve the seismic hazard assessment of tectonically active regions around the world.

Loa-Geo1: A field regional transect to unravel the structure of the western Central Andes

The structure of the Central Andes forearc of northern Chile has been an enigma for many years. Along this region, the preservation of a long pediplain constituted by gravels and unconsolidated sediments has hidden the structure of the region, making it difficult to understand its tectonic evolution. The traditional and regional-scale structural models are mainly supported by outcrop-scale and local observations. To unravel the structure of this Andes region, we carried out a regional-scale study based on local and regional observations, geological mapping, and the elaboration of local and regional balanced cross-sections, thereby illustrating the geometry and distribution of the first-order structural styles. We examined four specific sectors along a regional transect: the Loa and San Salvador rivers (parallel to each other), Sierra de Limón Verde, and Cerros de Tuina. Three structural styles were identified in the hybrid thick- and thin-skinned and doubly verging fold-and-thrust belt. These styles comprise partially inverted Permian to Jurassic normal faults, thick-skinned reverse faults affecting Paleozoic crystalline basement blocks, and shallow and thin-skinned fault-related folds. The shallow and thin-skinned fault-related folds usually result from the propagation of large, thick-skinned thrust ramps into stratigraphic successions. The restoration of a regionally balanced cross section constrained by field data and the previously interpreted two-dimensional (2-D) seismic profiles suggest that much of the crustal shortenings are accommodated by the reverse reactivation of Triassic and Jurassic normal faults bounding half-graben structures. It is also accommodated by blind thrust faults, whose geometry, kinematic, and depth are debatable. However, we have proposed a large, thick-skinned thrust ramp as the structure responsible for the greater shortening in the region, along which a significant thick- to thin-skinned transition occurs. The age of the synorogenic deposits identified here is unknown, specially those exposed at the Loa and San Salvador rives, however, the basal successions exposed at the Tuina sector reported Upper Cretaceous ages, thus suggesting that the orogeny in the forearc could have started during this time spam. Regional correlations with similar synorogenic deposits recognized in neighboring regions (e.g., Salar de Atacama Basin and Coastal Cordillera) also affirm an Upper Cretaceous–Paleocene age for the initiation of the crustal contraction in the region.

Episodic Deformation and Topographic Development Along the Santa Ynez River Fault: A Blind Thrust in the Western Transverse Ranges of California

AbstractThe Santa Ynez River fault is a blind thrust in the western Transverse Ranges fold and thrust belt of southern California. To evaluate the late Quaternary fault kinematics and landscape development, we used fluvial and marine terraces that intersect the fault as geomorphic markers of deformation. Field mapping, GIS analysis, elevation surveys, and radiocarbon and postIR‐IRSL luminescence dating of these terraces indicate an approximately 50 kyr episode of vertical displacement and folding across the fault during the late Pleistocene. Deformation of terraces began at approximately 85 ka following an extended period of tectonic quiescence and fluvial planation in the area. Multiple terrace levels ranging in age from 95.5 ± 11 to 43 ± 5 ka are lifted and folded across the fault with the amount of deformation decreasing with decreasing age. Terraces younger than approximately 35 ka show no evidence of folding or vertical displacement across the fault, indicating that the fault has not slipped in the past 35 kyr. Deformation of the terraces shows that the Santa Ynez River fault exhibited alternating episodes of activity and quiescence on a timescale of tens of thousands of years. This episodic nature cannot be attributed to directional growth of the fold and thrust belt, fault linkage, or long recurrence intervals and evidence of fault slip since Miocene time suggests the episodic activity is not restricted to late‐Quaternary time. This unusual episodic behavior may be due to surface deformation switching back and forth between different shallow structures in the mountain belt through time.

A Blind Thrust Fault Ruptured During the 10 October 2018 Situbondo, East Java, Indonesia, Earthquake Estimated Using GNSS Data

A Blind Thrust Fault Ruptured During the 10 October 2018 Situbondo, East Java, Indonesia, Earthquake Estimated Using GNSS Data

Origin of the Palos Verdes Restraining Bend and Its Implications for the 3D Geometry of the Fault and Earthquake Hazards in Los Angeles, California

ABSTRACT The Palos Verdes fault zone (PVFZ) extends across the southwestern Los Angeles basin and Inner Continental Borderland, California, and is considered capable of generating large (Mw>7), damaging earthquakes with short recurrence intervals. The 110 km long fault zone is composed of vertical and moderately dipping segments that accommodate oblique, right-lateral reverse displacement. Onshore, there is a counterclockwise reorientation in the PVFZ’s strike, which produces a major restraining bend that generates the Palos Verdes Peninsula. Here, we use well and seismic reflection data to develop kinematic models that show folding of the PVFZ by the Wilmington blind thrust led to formation of the restraining bend. North of the peninsula in Santa Monica Bay, debate persists over the extent, geometry, and activity of the PVFZ. Here, we analyze a dense grid of high-resolution seismic reflection data and present a new mapping of the Santa Monica Bay segment of the PVFZ, including multiple active splays (e.g., Redondo Canyon fault zone) that occur within a broad damage zone at the northern termination of the fault system. Based on these insights and prior studies, we develop a new, comprehensive 3D model of the PVFZ including its Santa Monica Bay, San Pedro Bay, and Lasuen Knoll segments. The sizes of these segments indicate that PVFZ is capable of larger events than previously reported—Mw 7.1–7.4 for single-segment ruptures and Mw 7.4–7.8 for multisegment ruptures. Based on a reported slip rate of 1.1–5.9 mm/yr, average recurrence intervals for these single- and multisegment rupture scenarios are 580–610 and 760–1170 yr, respectively.

Neotectonics of Turkey (Türkiye) and surrounding regions: a new perspective with block modelling

This paper aims to present a new neotectonic perspective concordant with the seismic activities in Turkey and surrounding regions. The neotectonic structures have been re-evaluated mainly by using focal mechanism solutions and high-resolution satellite (Google Earth) images. The Southeast Anatolian Wedge explains thrust/blind thrust and asymmetrical folding relationship in SE Turkey, Syria, and Northern Iraq. The neotectonic structures of the Turkish-Iranian Plateau are enlightened by the rhomboidal cell model which creates a base to determine multiple intersection points between the region-wide left- and right-lateral shear zones. The releasing stepover between the North Anatolian Fault Zone and Southeast Anatolian-Zagros Fault Zone plus their connections with the Northeast Anatolian Fault Zone and the East Anatolian Fault Zone are described in a more meaningful way with the Anatolian Diagonal concept. It also clarifies the role of left-lateral shear zone in the west-southwest movement of Anatolian plate and its relationship with the Aegean and Cyprus arcs. A neotectonic region under the influence of NW-SE contraction is determined between the North Anatolian, Eskişehir, and Kırıkkale-Erbaa fault zones in which the Elmadağ-Eldivan and Abdüsselam pinched crustal wedges and the Beypazarı Blind Thrust Zone are developed. A new route for the southern branch of the North Anatolian Fault Zone is determined between Bolu and Değirmenlik (Milos) Island in the Aegean Sea via Mudurnu, Bursa, Balıkesir, and İzmir. All main neotectonic structures mentioned in this paper are evaluated by the elastic dislocation modelling and new neotectonic provinces are suggested.

3D seismic reflection evidence of the blind thrust system in the northern Diyarbakır, southeast Turkey

3D seismic reflection evidence of the blind thrust system in the northern Diyarbakır, southeast Turkey

Quadratic Stress Drop Model of the 2013 Mw 6.6 Lushan Earthquake and Aftershocks Triggered by Blind Thrust Events

Quadratic Stress Drop Model of the 2013 Mw 6.6 Lushan Earthquake and Aftershocks Triggered by Blind Thrust Events

Structural geometry and kinematic history of the southern Kicking Horse Rim Cambrian carbonate platform: out-of-sequence thrust faulting in the southern Canadian Rocky Mountains

Abstract The structure of the southern Kicking Horse Rim Cambrian carbonate platform is spectacularly exposed in the Rocky Mountains southwest of Calgary, Alberta, Canada. Episodic uplift along the approximately 100 km long, north-northwest-trending Kicking Horse Rim during the middle and upper Cambrian controlled the position of the Cambrian carbonate platform to basin facies change. Extensive hydrothermal alteration, with local magnesite and/or Pb-Zn mineralization occurred along the west margin of the Rim. Spectacular slump scars, escarpments, megaconglomerates and slide masses locally mark the edge of the southern Kicking Horse Rim platform. Megaconglomerates form a unique and indisputable stratigraphic tie between the basin and platform and show that there is no stratigraphic gap or suture along this boundary. The change from carbonate- to shale-dominated lithologies resulted in a major change in structural style and the boundary between the Eastern and Western Main Ranges structural subprovinces. Serial and regional cross-sections across the area document the southward plunge of Kicking Horse Rim strata and the Eastern Main Ranges structural subprovince and show that this is due to underlying structure, and not stratigraphic thinning of the Cambrian carbonate platform. Prospective horizons for mineralization extend southward in the subsurface beyond their current southern limit of exposure. Kicking Horse Rim and associated Cambrian strata were carried northeastward along the Fatigue Thrust - blind thrust fault system. Because of a prominent hanging wall ramp through the entire Cambrian succession along the east side of the Kicking Horse Rim, the southern Kicking Horse Rim and Cambrian platform formed an asymmetric, east-facing anticline with a long gently-dipping west limb as they were uplifted and carried northeastward. In the northern part of the study area, displacement was along the Fatigue Thrust and the fault climbed through the Paleozoic section. In the south, most displacement on this fault system went into a blind detachment fault near the base of the thick basinal lower Ordovician section and overlying faulted detachment folds. The Simpson Pass Thrust truncated and overrode in its footwall the east-facing anticline and other structures developed in the hanging wall of the Fatigue Thrust. The Simpson Pass Thrust is out-of-sequence relative to the Fatigue Thrust and is one of the few larger displacement, out-of-sequence thrust faults recognized in the southern Canadian Rocky Mountains. Deformation of the Western Main Ranges and thrust faults near the Cambrian facies change occurred prior to the main motion along the Fatigue Thrust - blind thrust system. Motion on this thrust system, and the formation of faulted detachment folds that extend southward into the eastern part of the Porcupine Creek fan structure, occurred prior to motion on the Simpson Pass Thrust. Deformation of all these structures occurred during Jurassic–Early Cretaceous deformation most likely sometime prior to 125 Ma.

Fossil thermogenic hydrocarbon migration within the plumbing system of paleo-cold seeps in the Hikurangi subduction wedge (North Island, New Zealand)

In the Hikurangi subduction wedge (New Zealand), a strong relationship exists between tectonic structures and fluid migrations. In the study area, outcropping tubular carbonate concretions, corresponding to the shallow subsurface plumbing systems of paleo-cold seeps, are hosted by Miocene syn-subduction mudstones. New observations demonstrate the presence of migrated solid bitumen within the tubular concretions and in the fault gouge of a major fault zone. A multi-proxy approach was performed to determine the organic matter thermal maturity in the study area (organic matter petrography and solid bitumen reflectance (BR) Rr% (Rr: random reflectance)). We also used Rock-Eval pyrolysis, vitrinite reflectance (VR) Rr%, and clay mineral reaction progress (illite Kübler-Index and clay mineral paragenesis) to determine the diagenesis grade of the rocks. Low Tmax values and clay minerals indicate a thermally immature sedimentary cover. The main source rock of the region, the Waipawa Formation is locally thermally mature (VR = 0.86 Rr%) suggesting that tectonic thrust-sheet stacking isresponsible for a structural thickening causing local organic maturation. The seaward propagation of out-of-sequence thrusts at base of intra-slope basins could be responsible for the inititation of biogenic fluid flows sourced in the shallow sedimentary cover that is subjected to deformation above the blind thrusts, leading to the earlier generation of the first carbonate tubular concretions. With the continuation of blind thrusting, deep thermogenic fluids then migrated laterally through fault planes (primary migration) and finally vertically through the intrabasinal pre-existing tubular concretions (secondary migration). In this paper, solid bitumen is used for the identification of a fossil thermogenic fluid migration from the source rock, along faults and through tubular carbonate conduits within a subduction thrust-wedge. The study evidences a multi-genetic tubular concretion formation, related with the timing and style of the deformation, being therefore a potential reliable indicator for the evolution of tectonic activity.

Oblique Convergence Causes Both Thrust and Strike‐Slip Ruptures During the 2021 M 7.2 Haiti Earthquake

AbstractA devastating magnitude 7.2 earthquake struck Southern Haiti on 14 August 2021. The earthquake caused severe damage and over 2000 casualties. Resolving the earthquake rupture process can provide critical insights into hazard mitigation. Here we use integrated seismological analyses to obtain the rupture history of the 2021 earthquake. We find the earthquake first broke a blind thrust fault and then jumped to a disconnected strike‐slip fault. Neither of the fault configurations aligns with the left‐lateral tectonic boundary between the Caribbean and North American plates. The complex multi‐fault rupture may result from the oblique plate convergence in the region, so that the initial thrust rupture is due to the boundary‐normal compression and the following strike‐slip faulting originates from the Gonâve microplate block movement, orienting SW‐NE direction. The complex rupture development of the earthquake suggests that the regional deformation is accommodated by a network of segmented faults with diverse faulting conditions.

Revealing Geometry and Fault Interaction on a Complex Structural System Based on 3D P-Cable Data: The San Mateo and San Onofre Trends, Offshore Southern California

Deformation observed along the San Mateo (SMT) and San Onofre trends (SOT) in southern California has been explained by two opposing structural models, which have very different hazard implications for the coastal region. One model predicts that the deformation is transpressional in a predominantly right lateral fault system with left lateral step-overs. Conversely in the alternative model, the deformation is predicted to be compressional associated with a regional blind thrust that reactivated detachment faults along the continental margin. State-of-the-art 3D P-Cable seismic data were acquired to characterize the geometry and linkage of faults in the SMT and SOT. The new observations provide evidence that deformation along the slope is more consistent with step-over geometry than a regional blind thrust model. For example, regions in the SOT exhibit small scale compressional structures that deflect canyons along jogs in the fault segments across the slope. The deformation observed in the SMT along northwesterly trending faults has a mounded, bulbous character in the swath bathymetry data with steep slopes ( ∼ 25°) separating the toe of the slope and the basin floor. The faulting and folding in the SMT are very localized and occur where the faults trend more northwesterly (average trend ∼ 285°) with the deformation dying away both towards the north and east. In comparison, the SOT faults trend more northerly (average trend ∼ 345°). The boundary between these fault systems is abrupt and characterized by shorter faults that appear to be recording right lateral displacement and possibly accommodating the deformation between the two larger fault systems. Onlapping undeformed turbidite layers reveal that the deformation associated with both major fault systems may be inactive and radiocarbon dating suggests deformation ceased in the middle to late Pleistocene (between 184 and 368 kyr). In summary, our preferred conceptual model for tectonic deformation along the SMT and SOT is best explained by left lateral step-overs along the predominantly right lateral strike-slip fault systems.

Neotectonics of the Western Suleiman Fold Belt, Pakistan: Evidence for Bookshelf Faulting

The Suleiman Fold-Thrust Belt represents an active deformational front at the western margin of the Indian plate and has been a locus of major earthquakes. This study focuses on the western part of the Suleiman Fold-Thrust Belt that comprises two parallel NW–SE oriented faults: Harnai Fault and Karahi Fault. These faults have known thrust components; however, there remains uncertainty about the lateral component of motion. This work presents the new observation of surface deformation using the Small Baseline Subset (SBAS), Interferometric Synthetic Aperture Radar (InSAR) technique on Sentinel-1A datasets to decompose displacement into the vertical and horizontal components employing ascending and descending track geometries. The subsurface structural geometry of this area was assessed using 2D seismic and well data. In addition, geomorphic indices were calculated to assess the relative tectonic activity of the area. InSAR results show that the Karahi Fault has a ~15 mm right-lateral movement for descending and ~10 mm/for ascending path geometries. The Harnai Fault does not show any lateral movement. Seismic data are in agreement with the InSAR results suggesting that the Harnai Fault is a blind thrust. This work indicates that the block between these two faults displays a clockwise rotation that creates the “bookshelf model”.

Significant Seismic Risk Potential From Buried Faults Beneath Almaty City, Kazakhstan, Revealed From High‐Resolution Satellite DEMs

AbstractMajor faults of the Tien Shan, Central Asia, have long repeat times, but fail in large (7+) earthquakes. In addition, there may be smaller, buried faults off the major faults which are not properly characterized or even recognized as active. These all pose hazard to cities along the mountain range front such as Almaty, Kazakhstan. Here, we explore the seismic hazard and risk for Almaty from specific earthquake scenarios. We run three historical‐based earthquake scenarios (1887 Verny7.3, 1889 Chilik8.0 and 1911 Chon‐Kemin8.0) on the current population and four hypothetical scenarios for near‐field faulting. By making high‐resolution Digital Elevation Models (DEMs) from SPOT and Pleiades stereo optical satellite imagery, we identify fault splays near and under Almaty. We assess the feasibility of using DEMs to estimate city building heights, aiming to better constrain future exposure datasets. Both Pleiades and SPOT‐derived DEMs find accurate building heights of the majority of sampled buildings within error; Pleiades tri‐stereo estimates 80% of 15 building heights within one sigma and has the smallest average percentage difference to field‐measured heights (14%). A moderately sized6.5 earthquake rupture occurring on a blind thrust fault, under folding north of Almaty is the most damaging scenario explored here due to the modeled fault stretching under Almaty, with estimated 12,3005,000 completely damaged buildings, 4,1003,500 fatalities and an economic cost of 4,7002,700 Million US dollars (one sigma uncertainty). This highlights the importance of characterizing location, extent, geometry, and activity of small faults beneath cities.

A fast way to estimate the clay fabric from shale fragments. Key example from a strained thrust footwall (Pyrenees).

This paper presents a new approach based on Anisotropy of Magnetic Susceptibility, that aims to define the spatial evolution of deformation in shales through the analysis of non-oriented fragments. This technique facilitates and speeds up sampling and measurements, and consequently, hundreds of samples can be analyzed in a few weeks of work. The proposed procedure is here applied to a high-resolution study of deformation in the Eocene shales of the South Pyrenean basin. This study shows that it is possible to accurately measure small irregularly shaped fragments of a few grams. Scalar data that are not dependent on the orientation of the sample are studied. The magnetic fabrics indicate a deformation gradient in the foot-wall of a major thrust, for which a five-stage development is proposed. On the other hand, gradient heterogeneities reveal non-previously detected tectonic features, such as blind thrusts. This technique can be applied both to surface geology and cuttings from boreholes, and its sound results indicate that the study of the magnetic fabric is particularly sensitive and accurate for understanding the process and state of deformation in shales.