Dynamic stress field of a kinematic earthquake source model with k-squared slip distribution

Source models such as the k -squared stochastic source model with k -dependent rise time are able to reproduce source complexity commonly observed in earthquake slip inversions. An analysis of the dynamic stress field associated with the slip history prescribed in these kinematic models can indicate possible inconsistencies with physics of faulting. The static stress drop, the strength excess, the breakdown stress drop and critical slip weakening distance D _c distributions are determined in this study for the kinematic k -squared source model with k -dependent rise time. Several studied k -squared models are found to be consistent with the slip weakening friction law along a substantial part of the fault. A new quantity, the stress delay, is introduced to map areas where the yielding criterion of the slip weakening friction is violated. Hisada's slip velocity function is found to be more consistent with the source dynamics than Boxcar, Brune's and Dirac's slip velocity functions. Constant rupture velocities close to the Rayleigh velocity are inconsistent with the k -squared model, because they break the yielding criterion of the slip weakening friction law. The bimodal character of D _c / D _tot frequency–magnitude distribution was found. D _c approaches the final slip D _tot near the edge of both the fault and asperity. We emphasize that both filtering and smoothing routinely applied in slip inversions may have a strong effect on the space–time pattern of the inferred stress field, leading potentially to an oversimplified view of earthquake source dynamics.     

Quasi-static crack models and the frictional stress threshold criterion for slip arrest

Summary. Two-dimensional crack problems in elastic homogeneous isotropic media are considered which describe rupture over a fault surface characterized by non-uniform stress drop. Solutions can be found in which the stress field is finite at the crack tips and the rupture surface is not assigned a priori , but is part of the solution. These crack models are found to be consistent with the frictional stress threshold criterion for slip arrest over pre-existing fault surfaces. A crack is found to stop when its contribution to the stress field is opposite to the stress drop at the crack tips. The quasi-static propagation of a crack up to the arrest configuration is studied in terms of the minimum energy principle. The crack spontaneously propagates in such a way as to make the value of the stress intensity factor at one tip equal to the value at the other tip. Furthermore a tip propagating in a region with higher friction is found to move more slowly than the other tip propagating in a region with lower friction. Simple criteria for fracture arrest are derived, in terms of a properly averaged stress drop. Piecewise constant stress drop profiles are explicitly considered yielding a variety of solutions which can be applied to modelling asperities or barriers over a fault plane. The evaluation of the amount of the energy released during the quasi-static crack propagation shows that stopping phases cannot be efficiently radiated if the crack comes to rest in a low friction region.     

Along‐strike structural linkage and interaction in an active thrust fault system: A case study from the western Sichuan foreland basin,China

Along‐strike structural linkage and interaction between faults is common in various compressional settings worldwide. Understanding the kinematic history of fault interaction processes can provide important constraints on the geometry and evolution of the lateral growth of segmented faults in the fold‐and‐thrust belts, which are important to seismic hazard assessment and hydrocarbon trap development. In this study, we study lateral structural geometry (fault displacement and horizon shortening) of thrust fault linkages and interactions along the Qiongxi anticline in the western Sichuan foreland basin, China, using a high‐resolution 3D seismic reflection dataset. Seismic interpretation suggests that the Qiongxi anticline can be related to three west‐dipping, hard‐linked thrust fault segments that sole onto a regional shallow detachment. Results reveal that the lateral linkage of fault segments limited their development, affecting the along‐strike fault displacement distributions. A deficit between shortening and displacement is observed to increase in linkage zones where complex structural processes occur, such as fault surface bifurcation and secondary faulting, demonstrating the effect of fault linkage process on structural deformation within a thrust array. The distribution of the geometrical characteristics shows that thrust fault development in the area can be described by both the isolated fault model and the coherent fault model. Our measurements show that new fault surfaces bifurcate from the main thrust ramp, which influences both strain distribution in the relay zone and along‐strike fault slip distribution. This work fully describes the geometric and kinematic characteristics of lateral thrust fault linkage, and may provide insights into seismic interpretation strategies in other complex fault transfer zones.     

A crack model of creep processes on deep sections of faults

A crack model in antiplane shear configuration is shown representing creep processes interpreted in terms of 'viscous' deformation of a narrow plastic layer, characterized by inhomogeneous rheological properties, embedded within a homogeneous elastic medium. The evolution in time of slip and stress over the crack plane is studied through a truncated expansion in Chebyshev polynomials, and convergence is proved to be fast in the simple examples considered. Finite-stress solutions are found which are compatible with constitutive relations of elasto-plastic materials and furthermore these allow us to simulate creep propagation and stress transfer between locked and unlocked fault segments. This model provides a simple interpretation of the shallow depth of the seismogenic layer observed in several areas of the world and lends itself to modelling creep processes during either post-seismic rebound or pre-seismic stress buildup. Stress transfer is accomplished mostly by the slow extension of the creeping section. During a seismic cycle it is envisaged that different regimes dominate over deep, intermediate and shallow sections of faults: (i) slow pre-seismic stress build-up accompanied by creep and stress migration toward intermediate depths; (ii) brittle fracture over shallow and intermediate sections of faults; (iii) post-seismic rebound over intermediate and deep sections of faults. The present crack model, while providing finite-stress solutions, allows a better understanding of how stress may accommodate at different depths over a fault plane during a seismic cycle.     

Tectonic geomorphology of the Ash Hill fault, Panamint Valley, California

ABSTRACT
Panamint Valley, in eastern California, is an extensional basin currently bounded by active, dextral-normal oblique-slip faults. There is considerable debate over the tectonic and topographic evolution of the valley. The least-studied structure, the Ash Hill fault, runs for some 50 km along the valley's western edge, and active strands of the fault continue south into the neighbouring Slate Range. Vertical displacement on the fault is valley-side up, creating topography that conflicts with the gross morphology of the valley itself. We use this topography, along with kinematic and geological markers, to constrain the Quaternary slip rate and orientation of the Ash Hill fault. The fault offsets all but the active channel deposits in the valley, and slickenlines indicate a strike-slip to dip-slip ratio of 3.5:1. An offset volcanic unit dated at 4 Ma provides a minimum slip rate of 0.3±0.1 mm yr⁻¹, and a long-term strike-slip to dip-slip ratio of 5.2:1. Slip on the fault has warped a palaeolake shoreline within the valley. Simple elastic dislocation modelling of the vertical deformation of the shoreline suggests total fault slip of ≈60 m, valley-side up. The shoreline probably dates to 120–150 ka, implying a late Quaternary slip rate of 0.4–0.5 mm yr⁻¹. We suggest two possible mechanisms for the apparently anomalous slip behaviour of the Ash Hill fault. The fault may be a listric structure related to the proposed low-angle fault underlying Panamint Valley. Alternatively, the Ash Hill fault is a high-angle fault, implying that the valley is currently bounded by high-angle dextral-slip faults. Lack of detailed subsurface information precludes any knowledge of the true relationships between the presently active faults.     

Quantifying the slip rates, spatial distribution and evolution of active normal faults from geomorphic analysis: Field examples from an oblique-extensional graben, southern Turkey

Quantifying the extent to which geomorphic features can be used to extract tectonic signals is a key challenge in the Earth Sciences. Here we analyse the drainage patterns, geomorphic impact, and long profiles of bedrock rivers that drain across and around normal faults in a regionally significant oblique-extensional graben (Hatay Graben) in southern Turkey that has been mapped geologically, but for which there are poor constraints on the activity, slip rates and Plio–Pleistocene evolution of basin-bounding faults. We show that drainage in the Hatay Graben is strongly asymmetric, and by mapping the distribution of wind gaps, we are able to evaluate how the drainage network has evolved through time. By comparing the presence, size, and distribution of long profile convexities, we demonstrate that the northern margin of the graben is tectonically quiescent, whereas the southern margin is bounded by active faults. Our analysis suggests that rivers crossing these latter faults are undergoing a transient response to ongoing tectonic uplift, and this interpretation is supported by classic signals of transience such as gorge formation and hill slope rejuvenation within the convex reach. Additionally, we show that the height of long profile convexities varies systematically along the strike of the southern margin faults, and we argue that this effect is best explained if fault linkage has led to an increase in slip rate on the faults through time from  0.1 to 0.45 mm/yr. By measuring the average length of the original fault segments, we estimate the slip rate enhancement along the faults, and thus calculate the range of times for which fault acceleration could have occurred, given geological estimates of fault throw. These values are compared with the times and slip rates required to grow the documented long-profile convexities enabling us to quantify both the present-day slip rate on the fault (0.45 ± 0.05 mm/yr) and the timing of fault acceleration (1.4 ± 0.2 Ma). Our results have substantial implications for predicting earthquake hazard in this densely populated area (calculated potential M_w = 6.0–6.6), enable us to constrain the tectonic evolution of the graben through time, and more widely, demonstrate that geomorphic analysis can be used as an effective tool for estimating fault slip rates over time periods > 10⁶ years, even in the absence of direct geodetic constraints.     

Seismic reflection imaging of active offshore faults in the Gulf of Corinth: their seismotectonic significance

High resolution seismic reflection surveys over one of the most active and rapidly extending regions in the world, the Gulf of Corinth, have revealed that the gulf is a complex asymmetric graben whose geometry varies significantly along its length. A detailed map of the offshore faults in the gulf shows that a major fault system of nine distinct faults limits the basin to the south. The northern Gulf appears to be undergoing regional subsidence and is affected by an antithetic major fault system consisting of eight faults. All these major faults have been active during the Quaternary. Uplifted coastlines along their footwalls, growth fault patterns and thickening of sediment strata toward the fault planes indicate that some of these offshore faults on both sides of the graben are active up to present. Our data ground‐truth recent models and provides actual observations of the distribution of variable deformation rates in the Gulf of Corinth. Furthermore they suggest that the offshore faults should be taken into consideration in explaining the high extension rates and the uplift scenarios of the northern Peloponnesos coast. The observed coastal uplift appears to be the result of the cumulative effect of deformation accommodated by more than one fault and therefore, average uplift rates deduced from raised fossil shorelines, should be treated with caution when used to infer individual fault slip rates. Seismic reflection profiling is a vital tool in assessing seismic hazard and basin‐formation in areas of active extension.     

Transtensional fault-termination basins: an important basin type illustrated by the Pliocene San Jose Island basin and related basins in the southern Gulf of California, Mexico

Transtensional basins are sparsely described in the literature compared with other basin types. The oblique‐divergent plate boundary in the southern Gulf of California has many transtensional basins: we have studied those on San Jose island and two other transtensional basins in the region. One major type of transtensional basin common in the southern Gulf of California region is a fault‐termination basin formed where normal faults splay off of strike‐slip faults. These basins suggest a model for transtensional fault‐termination basins that includes traits that show a hybrid nature between classic rift and strike‐slip (pull‐apart) basins. The traits include combinations of oblique, strike‐slip and normal faults with common steps and bends, buttress unconformities between the fault steps and beyond the ends of faults, a common facies pattern of terrestrial strata changing upward and away from the faults into marine strata, small fault blocks within the basin that result in complex lateral facies relations, common Gilbert deltas, dramatic termination of the margin of the basin by means of fault reorganization and boundary faults dying and an overall short basin history (few million years). Similar transtensional fault‐termination basins are present in Death Valley and other parts of the Eastern California shear zone of the western United States, northern Aegean Sea and along ancient strike‐slip faults.     

Neotectonics and Quaternary geology of the Hunter Mountain fault zone and Saline Valley region,southeastern California

The Hunter Mountain fault zone strikes northwesterly, is right-lateral strike-slip, and kinematically links the northern Panamint Valley fault zone to the southern Saline Valley fault zone. The most recent displacement of the fault is recorded in the offset of Holocene deposits along the entire length of the fault zone. Right-lateral offsets of drainage channels within Grapevine Canyon reach up to 50 to 60 m. Initial incision of the offset channels is interpreted on the basis of geomorphic and climatic considerations to have occurred approximately 15 ka. The 50 to 60 m of offset during 15 ka corresponds to a right-lateral fault slip rate of 3.3–4.0 mm/year within Grapevine Canyon. Further to the north along the Nelson Range front, the fault is composed of two sub-parallel fault strands and the fault begins to show an increased normal component of motion. A channel margin that is incised into a Holocene surface that is between 10 and 128 ka in age is offset 16–20 m, which yields a broad minimum bound on the lateral slip rate of 0.125–2.0 mm/year. The best preserved single-event displacements recorded in Holocene deposits range from 1.5 to 2.5 m. In addition to faulting within Grapevine Canyon and the main rangefront fault along the southwest edge of Saline Valley, there also exist normal fault strands within the Valley that strike northeasterly and towards Eureka Valley. The northeasterly striking normal faults in the Valley appear to be actively transferring dextral slip from the Hunter Mountain fault zone north and east onto the Furnace Creek fault zone. Separations on northerly trending, normal faults within Saline Valley yield estimates of slip rates in the hundredths of millimeters per year.     

Miocene extensional basin development in the Betic Cordillera, SE Spain revealed through analysis of the Alhama de Murcia and Crevillente Faults

The Alhama de Murcia and Crevillente faults in the Betic Cordillera of southeast Spain form part of a network of prominent faults, bounding several of the late Tertiary and Quaternary intermontane basins. Current tectonic interpretations of these basins vary from late‐orogenic extensional structures to a pull‐apart origin associated with strike–slip movements along these prominent faults. A strike–slip origin of the basins, however, seems at variance both with recent structural studies of the underlying Betic basement and with the overall basin and fault geometry. We studied the structure and kinematics of the Alhama de Murcia and Crevillente faults as well as the internal structure of the late Miocene basin sediments, to elucidate possible relationships between the prominent faults and the adjacent basins. The structural data lead to the inevitable conclusion that the late Miocene basins developed as genuinely extensional basins, presumably associated with the thinning and exhumation of the underlying basement at that time. During the late Miocene, neither the Crevillente fault nor the Alhama de Murcia fault acted as strike–slip faults controlling basin development. Instead, parts of the Alhama de Murcia fault initiated as extensional normal faults, and reactivated as contraction faults during the latest Miocene–early Pliocene in response to continued African–European plate convergence. Both prominent faults presently act as reverse faults with a movement sense towards the southeast, which is clearly at variance with the commonly inferred dextral or sinistral strike–slip motions on these faults. We argue that the prominent faults form part of a larger scale zone of post‐Messinian shortening made up of SSE‐ and NNW‐directed reverse faults and NE to ENE‐trending folds including thrust‐related fault‐bend folds and fault‐propagation folds, transected and displaced by, respectively, WNW‐ and NNE‐trending, dextral and sinistral strike–slip (tear or transfer) faults.     

A multidisciplinary study of a slow-slipping fault for seismic hazard assessment: the example of the Middle Durance Fault (SE France)

Assessing seismic hazard in continental interiors is difficult because these regions are characterized by low strain rates and may be struck by infrequent destructive earthquakes. In this paper, we provide an example showing that interpretations of seismic cross sections combined with other kinds of studies such as analysis of microseismicity allow the whole seismogenic source area to be imaged in this type of region. The Middle Durance Fault (MDF) is an 80-km-long fault system located southeastern France that has a moderate but regular seismicity and some palaeoseismic evidence for larger events. It behaves as an oblique ramp with a left-lateral-reverse fault slip and has a low strain rate. MDF is one of the rare slow active fault system monitored by a dedicated dense velocimetric short period network. This study showed a fault system segmented in map and cross section views which consists of staircase basement faults topped by listric faults ramping off Triassic evaporitic beds. Seismic sections allowed the construction of a 3-D structural model used for accurate location of microseismicity. Southern part of MDF is mainly active in the sedimentary cover. In its northern part and in Alpine foreland, seismicity deeper than 8 km was also recorded meaning active faults within the crust cannot be excluded. Seismogenic potential of MDF was roughly assessed. Resulting source sizes and estimated slip rates imply that the magnitude upper limit ranges from 6.0 to 6.5 with a return period of a few thousand years. The present study shows that the coupling between 3-D fault geometry imaging and accurate location of microseismicity provides a robust approach to analyse active fault sources and consequently a more refined seismic hazard assessment.     

Late Quaternary activity of faults and recurrence interval of earthquakes in the eastern Hokuriku region, northern central Japan, on the basis of precise cryptotephra analysis of fluvial terrace sequences

About 2000 active faults are known to exist within the land area of Japan. Most of these active faults have deformed the topographic surfaces which were formed in the late Quaternary, including fluvial terraces; and the formative ages of these terraces are estimated mainly by tephrochronology. Fluvial terraces in the eastern Hokuriku region, comprising the Toyama, Tonami, and Kanazawa Plains, northern central Japan, are widely distributed and have been deformed by reverse active faults. The formative age of terraces in this area has not been reported, as volcanic ash deposits are rarely visible within terrace deposits and the overlying loamy soil, and outcrops of fluvial terraces are quite scarce in this area. In the present study, we carried out a drilling survey on these terraces to obtain samples of the overlying loamy soil and upper part of terrace deposits. From these samples, we extracted some well-known widespread volcanic ash, from which we were able to estimate the approximate age of the terraces and the vertical slip rate of the active faults. Late Quaternary fluvial terraces in eastern Hokuriku are divided into 12 levels: Terraces 1 to 12 in descending order. Widespread tephras such as the Kikai-Tozurahara Tephra (K-Tz: 95 ka) are contained in the lowest part of the loamy soil in Terrace 4 and the Daisen-Kurayoshi Pumice (DKP: 55 ka) is present in the lowest part of the loamy soil in Terrace 6. From the ages and the vertical displacements of the fluvial terraces, the late Quaternary average vertical slip rates of active faults in eastern Hokuriku are estimated to be 0.2–0.9 mm/year (Uozu fault), 0.1–0.4 mm/year (Kurehayama fault), 0.1–0.3 mm/year (Takashozu fault), 0.1–0.4 mm/year (Hohrinji fault), and 0.5–0.8 mm/year (Morimoto-Togashi fault). We also estimated the recurrence interval of earthquakes related to active faults from displacement per event and ages of terraces and no significant difference in vertical displacement per single earthquake for different active faults, and recurrence intervals tend to be inversely proportional to vertical displacement rates. This study demonstrates that a combination of drilling of loamy soil and precise cryptotephra analysis of fluvial terraces can be used to estimate the formative age of the terraces and the average slip rate of active faults in areas where volcanic ash deposits are rare.     

Detection of fluid migration pathways in seismic data: implications for fault seal analysis

A new and efficient method for fault seal analysis using seismic data is presented. It uses multiple seismic attributes and neural networks to enhance fluid migration pathways, including subtle features that are not detectable using single attributes only. The method may be used as a first estimate of fault seal or to calibrate results from other techniques. The results provide information about which faults and fault segments are sealing or leaking. Fluid flow along individual faults appears to be focused along zones of weakness, and fault seal research should thus be focused on finding such weak locations within fault zones, a task that is best done using three‐dimensional (3D) seismic data. Under certain conditions, it is suggested that fluids migrate along fault planes by a diapiric fluid flow mechanism. The results assist in calibrating the bulk hydraulic properties of faults and rock formations and can be used in basin modelling.     

Fault propagation and climatic control of sedimentation on the Ghoubbet Rift Floor: insights from the Tadjouraden cruise in the western Gulf of Aden

A detailed geophysical survey of the Ghoubbet Al Kharab (Djibouti) clarifies the small-scale morphology of the last submerged rift segment of the propagating Aden ridge before it enters the Afar depression. The bathymetry reveals a system of antithetic normal faults striking N130°E, roughly aligned with those active along the Asal rift. The 3.5 kHz sub-bottom profiler shows how the faults cut distinct layers within the recent, up to 60 m thick, sediment cover on the floor of the basin. A large volcanic structure, in the centre of the basin, the 'Ghoubbet' volcano, separates two sedimentary flats. The organization of volcanism and the planform of faulting, with en echelon subrifts along the entire Asal–Ghoubbet rift, appear to confirm the westward propagation of this segment of the plate boundary. Faults throughout the rift have been active continuously for the last 8400 yr, but certain sediment layers show different offsets. The varying offsets of these layers, dated from cores previously retrieved in the southern basin, imply Holocene vertical slip rates of 0.3–1.4 mm yr⁻¹ and indicate a major decrease in sedimentation rate after about 6000 yr BP, and a redistribution of sediments in the deepest troughs during the period that preceded that change.     

A Bayesian approach to estimating tectonic stress from seismological data

Earthquakes are conspicuous manifestations of tectonic stress, but the non-linear relationships between the stresses acting on a fault plane, its frictional slip, and the ensuing seismic radiation are such that a single earthquake by itself provides little information about the ambient state of stress. Moreover, observational uncertainties and inherent ambiguities in the nodal planes of earthquake focal mechanisms preclude straightforward inferences about stress being drawn on the basis of individual focal mechanism observations. However, by assuming that each earthquake in a small volume of the crust represents a single, uniform state of stress, the combined constraints imposed on that stress by a suite of focal mechanism observations can be estimated. Here, we outline a probabilistic (Bayesian) technique for estimating tectonic stress directions from primary seismological observations. The Bayesian formulation combines a geologically motivated prior model of the state of stress with an observation model that implements the physical relationship between the stresses acting on a fault and the resultant seismological observation. We show our Bayesian formulation to be equivalent to a well-known analytical solution for a single, errorless focal mechanism observation. The new approach has the distinct advantage, however, of including (1) multiple earthquakes, (2) fault plane ambiguities, (3) observational errors and (4) any prior knowledge of the stress field. Our approach, while computationally demanding in some cases, is intended to yield reliable tectonic stress estimates that can be confidently compared with other tectonic parameters, such as seismic anisotropy and geodetic strain rate observations, and used to investigate spatial and temporal variations in stress associated with major faults and coseismic stress perturbations.     

Earthquake mechanisms of the Adriatic Sea and Western Greece: implications for the oceanic subduction-continental collision transition

We present 21 focal solutions (magnitude > 5.5) reliably computed by body-wave modelling for the western Hellenic arc from Yugoslavia to the southern Peloponnese. Mechanisms located within the Aegean show normal faulting, the T-axis trending N-S in the centre and parallel to the active boundary in the external part. Mechanisms associated with the Keffalinia fault are consistent with dextral strike-slip motion. Reverse mechanisms located along the active boundary are remarkably consistent and do not depend on the nature of the active boundary (continental collision or oceanic subduction). The consistency in azimuth of the slip vectors and of the GPS velocity relative to Africa, all along the active boundary, suggests that the deformation is related to the same motion. The discrepancy between seismic-energy release and the amount of shortening confirms that the continental collision is achieved by seismic slip on faults but the oceanic subduction is partially aseismic. The northward decrease in velocity between continental collision and oceanic subduction suggests the continental collision to be a recent evolution of the active subduction.     

Late Quaternary kinematics of the Pallatanga strike-slip fault (Central Ecuador) from topographic measurements of displaced morphological features

The northeast-trending Pallatanga right-lateral strike-slip fault runs across the Western Cordillera connecting N50E-N70E trending normal faults in the Gulf of Guayaquil with N-S reverse faults in the Interandean Depression. Over most of its length, the fault trace has been partly obscured by erosional processes and can be inferred in the topography only at the large scale. Only the northern fault segment, which follows the upper Rio Pangor valley at elevations above 3600 m, is prominent in the morphology. Valleys and ridges cut and offset by the fault provide an outstanding record of right-lateral cumulative fault displacement. The fault geometry and kinematics of this particular fault segment can be determined from detailed topographic levellings. The fault strikes N30E and dips 75 to the NW. Depending on their size and nature, transverse morphological features such as tributaries of the Rio Pangor and intervening ridges, reveal right-lateral offsets which cluster around 27 ± 11m, 41.5 ± 4 m, 590 ± 65 m and 960 ± 70 m. The slip vector deduced from the short-term offsets shows a slight reverse component with a pitch of about 11.5 SW. The 41.5 ± 4 m displacements are assumed to be coeval with the last glacial termination, yielding a mean Holocene slip-rate of 2.9- 4.6 mm yr⁻¹. Assuming a uniform slip rate on the fault in the long term, the 27 m offset appears to correlate with an identified middle Holocene morphoclimatic event, and the long term offsets of 590 m and 960 m coincide with the glacial terminations at the beginning of the last two interglacial periods.     

Characterization of active fault scarps from LiDAR data: a case study from Central Apennines (Italy)

A high-resolution digital elevation model (DEM, 1 ms spacing) derived from an airborne light detection and ranging (LiDAR) campaign was used in an attempt to characterize the structural and erosive elements of the geometry of the Pettino fault, a seismogenic normal fault in Central Apennines (Italy). Four 90- to 280 m-long fault scarp segments were selected and the surface between the base and the top of the scarps was analyzed through the statistical analysis of the following DEM-derived parameters: altitude, height of the fault scarp, and distance along strike, slope, and aspect. The results identify slopes of up to 40° in faults lower reaches interpreted as fresh faces, 34° up the faces. The Pettino fault maximum long-term slip rate (0.6–1.1 mm/yr) was estimated from the scarp heights, which are up to 12–19 m in the selected four segments, and the age (ca. 18 ka) of the last glacial erosional phase in the area. The combined analysis of the DEM-derived parameters allows us to (a) define aspects of three-dimensional scarp geometry, (b) decipher its geomorphological significance, and (c) estimate the long-term slip rate.     

Example of a supradetachment basin within a pull-apart tectonic setting: Mormon Point, Death Valley, California

The geological features now exposed at Mormon Point, Death Valley, reveal processes of extension that continue to be active, but are concealed beneath the east side of Death Valley. Late Cenozoic sedimentary rocks at Mormon Point crop out in the hangingwall of the Mormon Point low-angle normal fault zone, a fault zone that formed within a releasing bend of the oblique-slip (right-normal slip) fault zone along the east side of Death Valley. The late Cenozoic sedimentary rocks were part of the valley when the low-angle fault zone was active, but during late Quaternary time they became part of the Black Mountains block and were uplifted. Rocks and structures exposed at Mormon Point are an example of the types of features developed in a releasing bend along the margins of a major pull-apart structure, and in this example they are very similar to features associated with regional detachment faults. The oldest sedimentary rocks in the hangingwall of the Mormon Point low-angle fault zone dip steeply to moderately east or north-east and were faulted and rotated in an extensional kinematic environment different from that recorded by rocks and structures associated with younger rocks in the hangingwall. Some of the younger parts of the late Cenozoic sedimentary rocks were deposited, faulted and rotated during movement on the Mormon Point low-angle normal fault. Progressively, strata are less faulted and less rotated. The Mormon Point low-angle normal fault has an irregular fault surface whose segments define intersections that plunge 18°-30°, N10°-40°W, with a maximum of 22°, N22°W that we interpret to be the general direction of slip. Thus, even though Death Valley trends north, movement on the faults responsible for its formation was at least locally north-northwest. Gouge and disrupted conglomerates along the faults are interpreted to have formed either as adjustments to accommodate space problems at the corners of blocks or along faults that bounded blocks during their displacement and rotation. The younger units of the late Cenozoic sedimentary rock sequence and the geomorphic surfaces developed on them are rarely faulted, not rotated, and overlap the Mormon Point low-angle faults. Active faults cut Holocene alluvium north of the late Cenozoic rocks and form the present boundary between Mormon Point and the Black Mountains. The distribution of active faults defines a releasing bend that mimics the older releasing bend formed by the Mormon Point low-angle fault zone. Rocks and structures similar to those exposed above the Mormon Point low-angle fault zone are probably forming today beneath the east side of Death Valley north-west of Mormon Point.     

Influence of oblique basement strike–slip faults on the Mesozoic evolution of the south-eastern segment of the Mid-Polish Trough

A series of analogue models are used to demonstrate how the multistage development of the Mid‐Polish Trough (MPT) could have been influenced by oblique basement strike–slip faults. Based on reinterpretation of palaeothickness, facies maps and published syntheses of the basin development, the following successive stages in the Mesozoic history of the south eastern part of the MPT were simulated in the models: (1) Oblique extension of the NW segment of the MPT connected with sinistral movement along the Holy Cross Fault (HCF, Early Triassic–latest Early Jurassic). (2) Oblique extension of both NW and SE segment of the MPT, parallel to the HCF (latest Early and Middle Jurassic). (3) Oblique extension of the SE segment of the MPT and much lesser extension of its NW segment connected with dextral movement along the HCF (Early Oxfordian–latest Early Kimmeridgian). (4) Oblique extension of the SE segment of the MPT and much lesser extension of its NW segment connected with dextral movement along the Zawiercie Fault (ZF, latest Early Kimmeridgian–Early Albian). (5) Oblique inversion of the NW segment of the MPT connected with dextral movement along the HCF (Early Albian–latest Cretaceous). (6) Oblique inversion of the SE segment of the MPT along the W–E direction (latest Cretaceous–Palaeogene). The different sense of movements of these two basement strike–slip faults (HCF and ZF) resulted in distinct segmentation of the basin and its SW margin by successive systems of extensional en‐echelon faults. The overall structure of this margin is controlled by the interference of the border normal faults with the en‐echelon fault systems related to successive stages of movement along the oblique strike–slip faults. This type of en‐echelon fault system is absent in the opposite NE‐margin of the basin, which was not affected by oblique strike–slip faults. The NE‐margin of the basin is outlined by a typical, steep and distinctly marked rift margin fault zone, dominated by normal and dip–slip/strike–slip faults parallel to its axis. Within the more extended segment of the basin, extensive intra‐rift faults and relay ramps develop, which produce topographic highs running across the basin. The change in the extension direction to less oblique relative to the basin axis resulted in restructuring of the fault systems. This change caused shifting of the basin depocentre to this margin. Diachronous inversion of the different segments of the basin in connection with movement along one of the oblique basement strike–slip faults resulted in formation of a pull‐apart sub‐basin in the uninverted SE‐segment of the basin. The results of the analogue models presented here inspire an overall kinematic model for the southeastern segment of the MPT as they provide a good explanation of the observed structures and the changes in the facies and palaeothickness patterns.