Fault Kinematics Research Articles

Logarithmic Model Joint Inversion Method for Coseismic and Postseismic Slip: Application to the 2017 Mw 7.3 Sarpol Zahāb Earthquake, Iran

AbstractInterferometric synthetic aperture radar (InSAR) has become an important technique for studying earthquake cycle deformation. However, due to the limited satellite revisit time, it is often difficult to fully separate coseismic and postseismic slip from InSAR data. Nevertheless, accurately estimating spatiotemporal coseismic and postseismic fault slip distribution models is important for quantifying earthquake slip, understanding the kinematics of seismogenic faulting, and evaluating seismic hazards. Here, we develop a logarithmic model‐based method (LogSIM) for the joint inversion of coseismic and postseismic fault slip using InSAR data from multiple platforms in different orbits. This method considers the nature of early postseismic slip following logarithmic decay. The coseismic slip, the decay time constant, and the decay amplitude of the logarithmic model can be jointly estimated from unwrapped interferograms without the need for InSAR time series calculations, thereby reducing the number of unknown parameters and stabilizing the inversion. The robustness of LogSIM is first validated with synthetic experiments. We then apply LogSIM to invert for the coseismic and postseismic slip models of the 2017 Mw 7.3 Sarpol Zahāb earthquake. We find that the maximum afterslip value and postseismic moment release during the first four months reported in previous studies are underestimated by ~26% and ~31%, respectively, due to the unavailability of the first five days of postseismic deformation. The estimated afterslip distribution spatially overlaps with the aftershocks in the updip region of the fault plane. LogSIM could potentially be extended to integrate different space geodetic data in earthquake cycle deformation modeling.

The kinematics of the Dasht-e Bayaz earthquake fault during Pliocene-Quaternary: Implications for the tectonics of eastern Central Iran

The Arabia - Eurasia convergence is accommodated across the Iranian plateau and surrounding mountain ranges. Strike-slip faults play significant roles in the current deformation of the Iranian plateau and were responsible for several moderate to large earthquakes, especially in east of Iran. The sinistral Dasht-e Bayaz fault shows conspicuous seismic and geological activities, while the role of the fault in the accommodation of active convergence is still debated. This paper focuses on the Pliocene-Quaternary to present-day states of stress in the region affected by the Dasht-e Bayaz fault. We applied the fault-slip inversion technique to both kinds of seismologic and geological fault slip data. The inversion results indicate a mean N045±5°E trending σ1 in the modern stress field, which agrees with the present-day tectonic regime (regional N050±05°E trending σ1) deduced from the inversion of earthquake focal mechanism data. The paleostress state is characterized by a N135±15°E trending regional mean σ1, with a transpressional stress regime; E-W faults of the region such as the Dasht-e Bayaz fault were reverse dextral in this paleostress field. We show that the shift in fault kinematics during the Pliocene-Quaternary times has not been restricted to northeastern parts of the Iranian plateau. The cross-cutting relationship between active N-S dextral and E-W sinistral faults indicates a crosswise to conjugate fault arrangement in the middle and the eastern end of the Dasht-e Bayaz fault. Integrating our results at a larger regional scale, we present a kinematic model in which the region between Lut and Kopeh Dagh is divided by the Doruneh fault into two tectonic domains. In the northern domain, active convergence is taken up by the extrusion of fault-bounded crustal blocks while, in the southern domain the convergence is accommodated through crosswise strike-slip faulting accompanied by reverse/thrust faulting in confining wedges.

Complex geometry and kinematics of subsidiary faults within a carbonate-hosted relay ramp

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 the Tre Monti normal fault in the Central Apennines. Although the Tre Monti fault strikes parallel to the regional extension (NE-SW) it shows predominant dip-slip kinematics, suggesting a NW-SE oriented extension acting at sub-regional scale (1–10 km). Conversely, the slickenlines collected on the front segment of the relay ramp highlight right-lateral kinematics. The subsidiary faults in the relay ramp show a complex geometry (variable attitudes) and slickenlines describe multiple kinematics (left-lateral, dip-slip, right-lateral), independently of their orientation. Our fault slip analysis indicates that a local stress field retrieved from the kinematic inversion of the slickenlines collected on the front segment, and likely promoted by the interaction between the overlapping fault segments that bound the relay zone, can explain most of the geometry and kinematics of the subsidiary faults. Further complexity is added by the temporal interaction with both the regional and sub-regional stress fields.

3-D slip analyses of listric faults with ideal geometries

Abstract Studying the kinematics of listric faults is of great importance in petroleum geology and seismicity. The deformation related to listric faults differ from the planar fault plane case. This study involves 3-D co-ordinate geometry with spherical co-ordinates to deduce the effective-slip ( e s ) and the net-slip ( n s ) of listric faults of three ideal geometries: spherical, paraboloid and ellipsoidal. We perform 3D slip analyses on two types of listric faults (Type-1 and 2). Previous authors have considered these shapes of fault planes in their modeling. Using these e s , one can track material points before and after faulting, similar to Mukherjee (2019) applied on translational faults with planar fault planes. The n s can be divided into a strike-slip ( s n s ) and a dip-slip component ( d n s ). This resolution being done on the listric fault plane itself, n s ≠ ( s n s 2 + d n s 2 ) 0.5 . This is unlike the planar fault plane case. The purpose of 3D-geometric analysis of listric faults could be, in long run, the restoration of rock blocks that underwent listric faulting.

A NW-striking dextral strike-slip fault at the eastern end of the Altyn Tagh fault and its tectonic implications for northeastward growth of the Tibetan Plateau

The eastern end of the Altyn Tagh fault connects the western Qilian Shan thrust belt and its foreland basin, the Hexi Corridor, which contains numerous active faults with various strikes and kinematics. Although understanding of the geometry and kinematics of these active faults is increasing, the deformation pattern since the late Quaternary in the western end of the Hexi Corridor remains controversial. Studying the geometry and kinematics of these faults provides great benefit for understanding regional deformation patterns. The North Kuantan Shan fault (NKTSF) is located at the eastern end of the Altyn Tagh fault and the western end of the Hexi Corridor. Remote sensing images and field investigations suggest that the NKTSF strikes NW and acts as a right-lateral strike-slip fault with a reverse component. Optically stimulated luminescence (OSL) data combined with vertical offsets of the fault scarp imply a range of vertical slip rates of 0.015–0.093 mm/a, and cosmogenic 10Be ages and displacements of river terrace risers suggest a range of horizontal slip rates of 0.25–0.71 mm/a. The geometry and kinematics of the NKTSF enable us to estimate the deformation pattern in the western Hexi Corridor, which indicates that this area is undergoing northeastward compression related to the northern Tibetan Plateau (Qilian Shan). Active faults in the region are driven by the northeastward push of the Tibetan Plateau rather than the eastward extension of the Altyn Tagh fault.

Unusual kinematics of the Papatea fault (2016 Kaikōura earthquake) suggest anelastic rupture.

A key paradigm in seismology is that earthquakes release elastic strain energy accumulated during an interseismic period on approximately planar faults. Earthquake slip models may be further informed by empirical relations such as slip to length. Here, we use differential lidar to demonstrate that the Papatea fault-a key element within the 2016 Mw 7.8 Kaikōura earthquake rupture-has a distinctly nonplanar geometry, far exceeded typical coseismic slip-to-length ratios, and defied Andersonian mechanics by slipping vertically at steep angles. Additionally, its surface deformation is poorly reproduced by elastic dislocation models, suggesting the Papatea fault did not release stored strain energy as typically assumed, perhaps explaining its seismic quiescence in back-projections. Instead, it slipped in response to neighboring fault movements, creating a localized space problem, accounting for its anelastic deformation field. Thus, modeling complex, multiple-fault earthquakes as slip on planar faults embedded in an elastic medium may not always be appropriate.

Gravitational and tectonic stress states within a deep-seated gravitational slope deformation near the seismogenic Periadriatic Line fault

The role of tectonic horizontal stresses in activating deep-seated gravitational slope deformations (DSGSD) has rarely been studied. We applied a new numerical technique for determining the present-day stress states within a large DSGSD, situated near the Periadriatic Line fault (PAL) in the Eastern Alps. The stress states were calculated from three-dimensional displacements of the sinistral Obir fault conjugated to the dextral PAL fault, which also forms the upper DSGSD detachment plane. The analysed fault displacements occurred in two distinct activity phases associated with the elastic rebound along (i) the Obir fault in the summer of 2014, and (ii) the core of the PAL fault in the winter of 2014/2015. These periods were synchronous with the periods of increased local seismicity. The results brought an insight into a possible causative link between horizontal tectonic stresses and DSGSDs activation. We observed, that transient dextral transpressions and dextral transtensions opposing to the general fault kinematics associated to the elastic rebound had a potential to destabilize the DSGSD at the micrometre level. The applied stress-tensor calculation, although restricted only to shallow near-surface conditions, is a reliable method that can reveal stress states almost in the real-time.

Pliocene-Quaternary fault kinematics in the Larderello geothermal area (Italy): Insights for the interpretation of the present stress field

In geothermal areas the evaluation of the active stress field from local earthquakes is generally contradictory, mainly suggesting normal to strike-slip tectonic regime. This feature has been investigated in the Larderello geothermal area comparing information from field data and focal mechanisms from the area of the Pliocene-Pleistocene Lago Basin, where the most effective exploitation occurs today. The methodology follows the classical approach of structural geology, inversion of kinematic data from slip-fault surfaces and comparison with focal mechanisms of local earthquakes. The results indicate strong similarities in the orientation of the main stress axes as obtained from paleo-stress analysis and double couple focal mechanisms solution, suggesting the same stress field since Pliocene, at least. The analysed structures are explained as part of the deformation developed within a NE-oriented transfer zone, and the Lago Basin is explained as a pull-apart basin. The transfer zone is characterised by the coeval activity of NE-striking left-lateral oblique- to strike-slip faults and by NW-striking normal faults, thus indicating a key for the understanding of the different focal mechanisms. Moreover, field data analysis indicates that both the NE- and NW-striking faults can be reactivated as normal faults dominantly, as also suggested by the local focal mechanisms. It is therefore concluded that the vertical movement is active when surface uplift, reasonably induced by heat flow, is more effective than crustal extension. Finally, the switch of the local intermediate stress axis from vertical to horizontal is considered a key-factor to channel deep geothermal fluids toward lateral structural traps.

Intracontinental deformation within the India-Eurasia oblique convergence zone: Case studies on the Nantinghe and Dayingjiang faults

AbstractThe most striking structural features in the interior of the Shan Plateau, southeast of the eastern Himalayan syntaxis, are a series of NE-trending faults that exhibit sinistral movement and an arcuate geometry. Their origin and tectonic evolution remain poorly understood. Furthermore, a switch in slip sense is recorded along many of these faults, but the timing of kinematic reversal is still unclear, hindering an understanding of the causal geodynamic mechanisms. We conducted an integrative study of apatite and zircon (U-Th)/He thermochronology, 40Ar/39Ar geochronology, and structural and geomorphic analysis to decipher the evolution of two major NE-trending faults: the Nantinghe and Dayingjiang faults. At least three deformation stages are identified within the Nantinghe fault zone, including top-to-the-SE/ESE thrusting, dextral ductile strike-slip shearing, and sinistral movement. Zircon and apatite (U-Th)/He data, collected from the northeastern terminus of the Nantinghe fault, reveal rapid cooling in the early Miocene. Combined with the 40Ar/39Ar data from sinistrally sheared mylonite, left-lateral movement on the Nantinghe fault is inferred to have initiated as early as ca. 20 Ma. The Dayingjiang fault reactivated as a sinistral brittle fault along the dextral Yingjiang shear zone. A two-stage thermal history is identified along the shear zone, with prominent cooling during dextral ductile shearing in the early- to mid-Miocene followed by a lower-magnitude cooling episode at ca. 11 Ma caused by sinistral transtension along the Dayingjiang fault. The evolution of the Nantinghe and Dayingjiang faults suggests that the NE-trending fault system in the Shan Plateau may have developed along preexisting structures and underwent diachronous slip-sense inversion in the late Cenozoic. The northward advance of the eastern Himalayan syntaxis caused a major change in both the regional stress field and fault geometries in the eastern India-Eurasia oblique convergence zone, contributing to the inversion of fault kinematics.

Active normal faulting along the Seerteng Shan, North China: Geometry and kinematics

Although rotation of fault blocks during seismic and long-term periods has long been recognized in extensional tectonic regimes, the geometry and kinematic behaviors of normal faults at outcrop scale have scarcely been investigated in sufficient detail. In this study, combining with the analysis of high-resolution topography acquired by small unmanned aerial vehicle (sUAV) using the structure-from-motion (SfM) technique, we present the results of our field observations on the structural characteristics of the Seertengshan Piedmont Fault (SPF), a major active normal fault bounding the northern margin of the Hetao Graben, North China. Although previous studies have reported the recent tectonic activity of this fault including timing of most recent earthquake, average slip rate and repeat time of paleo-earthquakes, few of them have focused on geometric patterns of the outcropping fault zones, which provide excellent outcrop-scale examples to investigating geometry and kinematics of active normal faults. Besides the observed prominent fault scarps indicative of recent tectonic activity along the SPF, outcrop observations indicate that in some cases both planar and curved normal faults are developed, forming complex fault zones. Sequential development of normal faults may have rotated the early-formed fault blocks, resulting in shallowly dipping faults and highly tilted strata. Collectively, structural similarities probably exit among normal faults at multiple spatial scales. We suggest that the results of this study are also helpful for a better understanding of structural development and evolution in other actively extending areas.

Fault kinematic and Plio-Quaternary paleostress evolution of the Bakırçay Basin, Western Turkey

ABSTRACT At the end of the Cenozoic, western Turkey was fragmented by intense intra-continental tectonic deformation resulting in the formation of two extensional areas: a transtensional pull-apart basin systems in the northwest, and graben systems in the central and southwest areas. The question of the connection of this Late Cenozoic extensional tectonics to plate kinematics has long been an issue of discussion. This study presents the results of the fault slip data collected in Bakırçay Basin in the west of Turkey and addresses changes in the direction of extensional stresses over the Plio-Quaternary. Field observations and quantitative analysis show that Bakırçay Basin is not a simple graben basin that has evolved during a single phase. It started as a graben basin with extensional regime in the Pliocene and was transformed into a pull-apart basin under the influence of transtensional forces during the Quaternary. A chronology of two successive extensional episodes has been established and provides reasoning to constrain the timing and location of subduction-related back-arc tectonics along the Aegean region and collision-related extrusion tectonics in Turkey. The first NW–SE trending extension occurred during the Pliocene extensional phase, characterized by slab rollback and progressive steepening of the northward subduction of the African plate under the Anatolian Plate. Western Turkey has been affected, during the Middle Quaternary, by regional subsidence, and the direction of extension changed to N–S, probably in relation with the propagation of the North Anatolian Fault System. Since the Late Quaternary, NE–SW extension dominates northwest Turkey and results in the formation and development of elongated transtensional basin systems. Counterclockwise rotation of Anatolian block which is bounded to the north by the right-lateral strike-slip North Anatolian Fault System, accompanies to this extensional phase.

The episodic rise, net growing rate and kinematics of radial faults of the Salinas de Oro diapir using paleoseismological techniques (NE Spain). Salt upwelling versus karstic subsidence

This paper explores the use of trenching and paleoseismological techniques to determine salt flow rates into a salt diapir for the first time in the literature. The Salinas de Oro diapir, located in the northern Spanish Pyrenees, is an oval-shaped Triassic-salt stock that extends vertically for ≫7 km down to the Paleozoic basement. Salt dissolution subsidence and diapir growth are coeval active processes. Karstification is responsible for the development of large sinkholes, a thick caprock and the monocline folding and ring faulting of the Cretaceous and Early Tertiary limestone rim. The evaporite karstic aquifer discharges high-concentration water of up to 137 g/l of total dissolved solids and a conductivity over 200 mS/cm into the Salado Creek, which drains the diapir top. The salinity monitoring of this drainage provides a maximum karstic surface lowering rate of around 2.8 mm/yr. Salt upwelling has caused the 150 m uplift of the annular limestone escarpment and the development of ≫3000 m long radial grabens with up to 90 m of vertical offset that disrupt drainages, displace Quaternary deposits and overprint concentric faults. The 260 cm drag folding of lacustrine facies exposed in a 42 m long and 6.5 m deep trench due to the creep motion of the western radial fault of Azanza Graben yielded a minimum short-term uplift slip rate of 1.75 mm/yr for the last 1485 years and provides a minimum salt supply rate of over 5 mm/yr considering karstification lowering. This value that is several hundred times higher than average, evidence the discontinuous growth of Salinas de Oro diapir.

Accommodation, slip inversion, and fault segmentation in a province-scale shear zone from high-resolution, densely spaced wide-aperture seismic profiling, Centennial Valley, MT, USA

We acquired a ~9-km long, high-resolution reflection seismic profile in the Centennial Valley, Montana, to better understand the kinematics of basin bounding faults and their role in accommodating proposed right-lateral shear in the Northern Basin and Range adjacent to the Yellowstone hotspot. In pursuing these goals, our findings have also shed light on the development of hanging wall stratigraphy and seismic hazards for this part of the SW Montana seismic belt. Here we present the profile and a working interpretation that identifies fault inversion, and an oblique, anticlinal accommodation zone linking the Centennial and Lima Reservoir faults in the Centennial Valley. These interpretations are consistent with seismicity and GPS-geodetically observed right-lateral shear aligned with the Centennial Valley north of the Yellowstone hotspot. Data were acquired using dense, wide-aperture arrays and illuminate the subsurface stratigraphy and faults down to ~1200 m, showing that the basin is a half-graben with a southern depocenter driven by the listric geometry of the north-dipping Centennial fault. Reflectors onlap basement highs with growth geometry against these faults. Our interpretation of a bright basal reflection as the Timber Hill Basalt (~6 Ma) or related flow, is consistent with a late Miocene – Pliocene inception of the basin proposed by other research. We also note a small inversion structure that we interpret as local evidence of transpression in the shear zone. This transpression is part of the accommodation zone and seismogenic faults including the Lima Reservoir fault that has well-expressed Holocene surface ruptures a few kilometres west of the seismic line along the northern edge of the Centennial basin.

Dextral, normal, and sinistral faulting across the eastern California shear zone–Mina deflection transition, California-Nevada, USA

AbstractStrike-slip faults commonly include extensional and contractional bends and stepovers, whereas rotational stepovers are less common. The Volcanic Tableland, Black Mountain, and River Spring areas (California and Nevada, USA) (hereafter referred to as the VBR region) straddle the transition from the dominantly NW-striking dextral faults that define the northwestern part of the eastern California shear zone into a rotational stepover characterized by dominantly NE-striking sinistral faults that define the southwestern Mina deflection. New detailed geologic mapping, structural studies, and 40Ar/39Ar geochronology across the VBR region allow us to calculate Pliocene to Pleistocene fault slip rates and test predictions for the kinematics of fault slip transfer into this rotational stepover. In the VBR, Mesozoic basement is nonconformably overlain by a Miocene sequence of rhyolite, dacite, and andesite volcanic rocks that yield 40Ar/39Ar ages between 22.878 ± 0.051 Ma and 11.399 ± 0.041 Ma. Miocene rocks are unconformably overlain by an extensive sequence of Pliocene basalt and andesite lava flows and cinder cones that yield 40Ar/39Ar ages between 3.606 ± 0.060 Ma and 2.996 ± 0.027 Ma. The Pliocene sequence is, in turn, unconformably overlain by Quaternary tuffs and sedimentary rocks. This sequence of rocks is cut by NS- to NW-striking normal faults across the Volcanic Tableland that transition northward into NS-striking normal faults across the Black Mountain area and that, in turn, transition northward into NW-striking dextral and NE-striking sinistral faults in the River Spring area. A range of geologic markers were used to measure offset across the faults in the VBR, and combined with the age of the markers, yield minimum ∼EW-extension rates of ∼0.5 mm/yr across the Volcanic Tableland and Black Mountain regions, and minimum NW-dextral slip and NE-sinistral slip rates of ∼0.7 and ∼0.3 mm/yr, respectively, across the River Spring region. In the River Spring area, our preferred minimum dextral slip and sinistral slip rates are 0.8–0.9 mm/yr and 0.7–0.9 mm/yr, respectively. We propose three kinematic fault slip models, two irrotational and one rotational, whereby the VBR region transfers a portion of dextral Owens Valley fault slip northwestward into the Mina deflection. In irrotational model 1, Owens Valley fault slip is partitioned into two components, one northeastward onto the White Mountain fault zone and one northwestward into the Volcanic Tableland. Slip from the two zones is then transferred northward into the southwestern Mina deflection. In irrotational model 2, Owens Valley fault slip is partitioned into three components, with the third component partitioned west-northwest onto the Sierra Nevada frontal fault zone. In the rotational model, predicted sinistral slip rates across the southwestern Mina deflection are at least 115% greater than our observed minimum slip rates, implying our minimum observed rates underestimate true sinistral slip rates. A comparison of summed geologic fault slip rates, parallel to motion of the Sierra Nevada block relative to the central Great Basin, from the Sierra Nevada northeastward across the VBR region and into western Nevada are the same as geodetic rates, if our assumptions about the geologic slip rate across the dextral White Mountain fault zone is correct.

Normal fault growth influenced by basement fabrics: The importance of preferential nucleation from pre‐existing structures

AbstractReactivation of pre‐existing intra‐basement structures can influence the evolution of rift basins, yet the detailed kinematic relationship between these structures and overlying rift‐related faults remains poorly understood. Understanding the kinematic as well as geometric relationship between intra‐basement structures and rift‐related fault networks is important, with the extension direction in many rifted provinces typically thought to lie normal to fault strike. We here investigate this problem using a borehole‐constrained, 3D seismic reflection dataset from the Taranaki Basin, offshore New Zealand. Excellent imaging of intra‐basement structures and a relatively weakly deformed, stratigraphically simple sedimentary cover allow us to: (a) identify a range of interaction styles between intra‐basement structures and overlying, Plio‐Pleistocene rift‐related normal faults; and (b) examine the cover fault kinematics associated with each interaction style. Some of the normal faults parallel and are physically connected to intra‐basement reflections, which are interpreted as mylonitic reverse faults formed during Mesozoic subduction and basement terrane accretion. These geometric relationships indicate pre‐existing intra‐basement structures locally controlled the position and attitude of Plio‐Pleistocene rift‐related normal faults. However, through detailed 3D kinematic analysis of selected normal faults, we show that: (a) normal faults only nucleated above intra‐basement structures that experienced late Miocene compressional reactivation, (b) despite playing an important role during subsequent rifting, intra‐basement structures have not been significantly extensionally reactivated, and (c) preferential nucleation and propagation of normal faults within late Miocene reverse faults and folds appears to be the key genetic relationship between contractionally reactivated intra‐basement structures and rift‐related normal faults. Our analysis shows that km‐scale, intra‐basement structures can control the nucleation and development of newly formed, rift‐related normal faults, most likely due to a local perturbation of the regional stress field. Because of this, simply inverting fault strike for causal extension direction may be incorrect, especially in provinces where pre‐existing, intra‐basement structures occur. We also show that a detailed kinematic analysis is key to deciphering the temporal as well as simply the spatial or geometric relationship between structures developed at multiple structural levels.

Strain variations in a seismogenic normal fault (Baza Sub-basin, Betic Chain): Insights from magnetic fabrics (AMS)

AMS and structural analysis are here applied to study the deformed zone associated with a large-scale, active normal fault in the central Betic Cordillera (Spain), namely the Baza fault system, to determine: i) the kinematics of structures and their relation with fault zone architecture and segmentation degree, ii) the correlation between deformational structures and the different types of magnetic fabrics and iii) the evolution of magnetic fabrics patterns, from sedimentary to shear-related, associated with normal faults. Five outcrops (969 samples) were analysed along the fault trace, which shows different degrees of segmentation along strike and strong localization of deformation along narrow fault zones. A first, main set of magnetic fabric data corroborates the normal kinematics of the Baza fault, showing magnetic lineations parallel to the dip-slip, transport direction. A second, secondary set of magnetic lineations, is parallel to the intersection lineation, and can be related to less intense deformation in the fault rocks. Furthermore, a detailed study (523 samples) of a trench excavated across the fault zone, where two fault splays tend to coalesce in a linkage relay zone indicates that i) lithology and distance to fault planes are two factors that control the development of extension-related magnetic fabrics in weakly deformed sediments, ii) the development of shear-related fabrics in fault zones entails the mechanical rotation of minerals, iii) different orientation of magnetic lineations are related to different intensity of bulk deformation and iv) magnetic lineation is useful to define local deviations of deformation axes produced by changes in the local extension direction (from fault-perpendicular to fault-parallel extension) in the linkage zone between adjacent fault splays.

Evidence for Deformation in the Cambrian‐Ordovician Warburton Basin and Implications for the Evolution of the Tasmanides (Eastern Australia)

AbstractThe Paleozoic tectonic history of the Tasmanides in eastern Australia was dominated by subduction‐related processes along the margin of eastern Gondwana. The earliest deformation event, Delamerian Orogeny, took place in the middle‐late Cambrian and is recorded in rocks within the Delamerian and Thomson orogens. The Cambrian‐Ordovician Warburton Basin covers the boundary between the Delamerian and Thomson Orogens, but very little is known about its origin and deformation history. Here we interpret geophysical data, including 2‐D seismic reflection transects, Bouguer gravity, and aeromagnetic data that provide new insights into the deformation in the eastern Warburton Basin and the kinematics of major faults. Our results show that curvilinear NE‐trending faults in the eastern Warburton Basin are basement reverse faults that experienced multiple phases of contractional deformation. Evidence for a syn‐kinematic Cambrian package (Kalladeina Formation) suggests that faulting commenced in response to the Delamerian Orogeny. A subsequent Early Devonian deformation in the eastern Warburton Basin is evident from K‐Ar geochronology of low‐grade (subgreenschist) metasedimentary rocks. We suggest that the NE‐trending Cambrian fold‐thrust belt within the eastern Warburton Basin marks the continuation of the curved Delamerian Orogen into the Thomson Orogen. This oroclinal structure may have developed in the Early Devonian in response to dextral transpression along the northern boundary of the Delamerian Orogen. Our results provide a demonstration for the complex interactions that can take place during the evolution of convergent plate boundaries, involving deformation in the fold‐thrust belt, development of sedimentary basins, and oroclinal bending.

The influence of mechanically weak layers in controlling fault kinematics and graben configurations: Examples from analog experiments and the Norwegian continental margin

Fault systems in extensional basins commonly display geometries that vary with depth, reflecting depth- and lithology-dependent mechanical strength. Using an experimental approach, we investigate this relationship by deploying physical analog models with stratified sequences consisting of brittle–ductile (sand–silicone polymer) sequences subject to single and polyphase deformation. The experiments were used as analogs for a sandstone sequence interlayered by beds of evaporates or overpressured or unconsolidated mudstone in nature (the latter being representative of decollement horizons). Experiments (series 1 [S1]) using homogeneous and stratified quartz and feldspar sand produced asymmetric, composite single grabens with diverse fault frequencies and fault styles for the graben margin faults. For the mechanically stratified experiments with one decollement level (series 2), contrasting graben configurations were produced, in that the lowermost sequence was characterized by graben geometries of similar type to that of the S1 experiments, whereas the sequence above the decollement was characterized by large fault blocks, delineated by steepened or oversteepened faults. The experiments with two decollements (series 3) were displayed similarly but included graben geometries that widened upward, with each level being characterized by independent fault systems. The results can be used to explain strata-bound fault patterns and depth-dependent extension as seen in several places along the Norwegian continental margin and elsewhere.

Geodetic Observations of the 2018 Mw 7.5 Sulawesi Earthquake and Its Implications for the Kinematics of the Palu Fault

AbstractThe ascending and descending interferometric synthetic aperture radar data are used to investigate the fault rupture and slip model of the 2018 Mw 7.5 Sulawesi, Indonesia, earthquake. The best fitting slip model indicates that this earthquake ruptured not only a segment extending the Palu fault to the north but also a northwestern segment offshore. The slip on the onshore fault is predominant left‐lateral strike slip. The slip on the offshore fault is dominated by normal faulting with a maximum slip of ~6.3 m. The newly discovered offshore normal faulting is likely to be the cause of the tsunami after the shock. Combined with previous geomorphic, tectonic, geodetic, and modeling studies, we suggest that the kinematics of the Palu fault maintained the same style of faulting from north to south, which resulted from an oblique extension occurred on an east dipping fault at depths. The deformation pattern of NW Sulawesi is dominated by this slip mechanism.

Effect of kinematic fault rupture process on tsunami propagation

The scope of this study is to investigate the effect of the kinematic rupture process on tsunami propagation and corresponding tsunami hazards in coastal regions. It is significant for the tsunageneric earthquakes of long fault length and subsequent long duration of the fault rupture in the strike direction. Most previous studies on the tsunami hazard assessments of the Manila Trench did not consider the effect of the rupture process of huge plates. The movements of the seabed near the earthquake source are calculated by Okada model. The free surface elevation triggered by the seafloor motion is modeled by the nonlinear shallow water equations. The 2004 Indian Ocean tsunami and the 2011 Japan Tohoku tsunami are used to validate the numerical model by comparing with measurement data. The numerical experiments of the tsunami propagation for the cases of different source rupture velocities in uniform depth and continental shelf are carried out to understand the mechanism of the changes of the tsunami arrival time and the tsunami amplitude due to the kinematic rupture process. Stimulated by the long duration of plate motion of 2004 Indian Ocean tsunami, we propose several typical patterns of the rupture process of the long fault of the Manila Trench and analyze quantitatively on the role of the uncertain rupture process of tectonics source in tsunami propagation in the South China Sea. Our results have highlighted that the slow rupture velocity will remarkable affect the tsunami arrival time and maximum amplitude in the South China Sea, comparing to the instantaneous rupture. It is suggested that the rupture process is essential for assessments of the tsunami hazards generated by submarine mass failure with extreme long earthquake rupture source.