Normal Slip Research Articles

Spatiotemporal Distribution of Afterslip following the 2014 Yutian Mw 6.9 Earthquake Using COSMO-SkyMed and Sentinel-1 InSAR Data

Spatiotemporal distribution of early afterslip is essential for seismic hazard evaluation and determination of fault friction properties. In this study, we used early post-seismic COSMO-SkyMed (19 February 2014–08 April 2014) and long-term Sentinel-1 (16 October 2014–17 June 2020) observations from multiple platforms over different periods to create a rate decay model driven by post-seismic afterslip. The combined observations provide full coverage of the post-seismic deformation following the 2014 Yutian Mw 6.9 earthquake that occurred at the southwestern end of the Altyn Tagh Fault. The observation and modeling results showed that post-seismic deformation was characterized by left-lateral strike-slip movement with minor normal slip, which was consistent with that of co-seismic rupture. The maximum early afterslip (7–55 days) was as large as approximately 0.09 m with a depth of 7 km in the west of co-seismic rupture, and the maximum long-term afterslip was about 0.24 m. The simulated post-seismic deformation caused by poroelastic rebound and viscoelastic relaxation suggests that the afterslip mechanism controls the post-seismic deformation. The coupling pattern of the aftershock and afterslip indicates that the aftershock was mainly caused by the afterslip. The post-seismic spatiotemporal features of the 2014 Yutian earthquake have significant implications for analyzing seismic hazards at the southwestern end of the Altyn Tagh Fault.

The 2020 Mw 6.5 Monte Cristo Range, Nevada, Earthquake: Anatomy of a Crossing-Fault Rupture through a Region of Highly Distributed Deformation

ABSTRACT The 15 May 2020 Mw 6.5 Monte Cristo Range earthquake (MCRE) in Nevada, United States, is the largest instrumental event in the Mina deflection—a zone of east-trending left-lateral faults accommodating a right step between northwest-trending right-lateral faults of the Walker Lane. The MCRE ruptured a highly distributed faulting area with muted geomorphic expressions, motivating us to characterize the behavior of an earthquake on a structurally immature fault system. Inverse modeling of Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS) displacements reveals left-lateral slip on an east-striking, eastern fault and left-lateral–normal slip on an east-northeast-striking, western fault. Unusually, the two faults cross one another and ruptured together in the mainshock. The maximum slip of 1 m occurs at 8–10 km depth, but less than 0.1 m of slip reaches the surficial model fault patches, yielding a pronounced shallow slip deficit (SSD) of 91%. Relocated hypocenters indicate that the mainshock initiated at 9 km depth and that aftershocks span depths of 1–11 km, constraining the local seismogenic thickness. Our new field observations of fracturing and pebble-clearing in the western MCRE characterize a third, shorter, northern fault that is at the resolution limit of the InSAR–GNSS modeling. The segmented and intersecting fault geometry, off-fault aftershocks with variable mechanisms, distributed surface fractures, limited long-term geomorphic offsets, and a 600–700 m (cumulative) bedrock offset are all characteristic of a structurally immature fault system. However, the large SSD is not unusual for an earthquake of this magnitude, and a larger compilation of InSAR models (28 Mw≥6.4 strike-slip events) shows that SSDs correlate with magnitude rather than structural maturity. This study demonstrates the importance of integrating geodesy, seismology, and field observations to capture the full complexity of large earthquakes, and further suggests that seismic hazard assessments in shattered crustal regions consider the potential for multi- and cross-fault rupture.

Finite-Source Model of the 8 July 2021 M 6.0 Antelope Valley, California, Earthquake

Abstract We present a finite-source coseismic slip model of the 2021 Mw 6.0 Antelope Valley earthquake based on the joint inversion of regional seismic waveforms, Interferometric Synthetic Aperture Radar (InSAR), and Global Navigation Satellite Systems data. The results show that the mainshock rupture was dominated by normal slip along a nearly north–south-trending fault dipping to the east. The rupture lasted for ∼10 s, with primarily unilateral propagation toward the south. Most coseismic slip is found to be within a depth range between 6 and 10 km, with apparently no slip reaching the surface. Surface projection of the modeled fault plane matches well with the southern extension of the previously mapped Slinkard Valley fault (SVF). Aftershocks one year after the mainshock are mostly distributed within a relatively narrow band of 2–3 km thickness around the up-dip portion of the inferred coseismic rupture plane. There is little aftershock activity below 10 km, suggesting a relatively shallow brittle-to-ductile transition in this area. Aftershocks are also clustered at shallow depth beneath several branches of the Antelope Valley faults to the east of the mainshock rupture, including the Mw 4.4 event on 27 August 2021, which produced clear coseismic surface deformation observed by InSAR. Most aftershocks, immediately up-dip of the coseismic rupture and to the east beneath the Antelope Valley faults, are in areas of substantial coseismic Coulomb stress increase, particularly when assuming that all faults in this area dip to the east. This suggests that like the SVF that hosted the mainshock, the Antelope Valley faults in this area also dip to the east. There is little to no postseismic deformation seen from InSAR observations ∼2 months after the mainshock. The lack of clear coseismic and postseismic slip on the shallow portion of the fault suggests the potential for future shallow seismic activity.

Formulation and Numerical Solution of the Stability Loss Problem of Elastic-Plastic Shells of Revolution with an Elastic Filler under Combined Axisymmetric and Torsional Loadings

A dynamic statement and a method for numerically solving the buckling problems of elastoplastic shells of revolution with filler in axisymmetric and non-axisymmetric shapes under quasi-static and dynamic loading are presented within the framework of two approaches. In the first approach, the problem of elastic-plastic deformation and buckling of shells of revolution with an elastic filler under combined axisymmetric loading with torsion is formulated in a two-dimensional (generalized axisymmetric) formulation based on the hypotheses of the shells theory of the Timoshenko type and the Winkler foundation. The constitutive relations are written in the cylindrical system of Euler coordinates. For each shell element, a local Lagrangian coordinate system is introduced. Kinematic relations are recorded in the current state metric. The distribution of the displacement velocity components over the shell thickness and strain rate tensors in the local basis is written as the sum of the momentless and moment components, which, in turn, are written as the sum of the symmetric and asymmetric parts in the local and in the general basis. The elastoplastic properties of the shell material are taken into account within the framework of the theory of flow with nonlinear isotropic hardening. To take into account non-axisymmetric forms of buckling, the desired functions (both displacements and forces, moments, contact pressure) are expanded into a Fourier series in the circumferential direction. The variational equations of shell motion are derived from the general equation of dynamics. The contact between the shell and the deformable filler is modeled based on the conditions of non-penetration along the normal and free slip along the tangent. The variational equations of shell dynamics for axisymmetric and nonaxisymmetric processes are interconnected through the physical relations of the theory of plasticity. They take into account large axisymmetric shape changes and the instantaneous stress-strain state of the shell. At the initial stage of the nonaxisymmetric buckling process, the deflections are small; therefore, the equations of nonaxisymmetric buckling are obtained as linearized with respect to nonaxisymmetric forms. To initiate nonaxisymmetric buckling modes, initial nonaxisymmetric deflections are introduced. To solve the defining system of equations, a finite-difference method and an explicit time integration scheme of the “cross” type are used. The second approach is based on continuum mechanics hypotheses and implemented in a three-dimensional setting. Both approaches make it possible to simulate the nonlinear subcritical deformation of shells of revolution with an elastic filler, to determine the ultimate (critical) loads in a wide range of loading rates, taking into account geometric shape imperfections, to study the processes of buckling in axisymmetric and non-axisymmetric shapes under dynamic and quasi-static complex loading by tension, compression, torsion, internal and external pressure. The results of numerical simulation are compared with experimental data on the torsion of steel cylindrical elastoplastic shells ( R / h = 1.45) with an elastic filler.

A Deeper Look Into the 2021 Tyrnavos Earthquake Sequence (TES) Reveals Coseismic Breaching of an Unrecognized Large‐Scale Fault Relay Zone in Continental Greece

AbstractLarge magnitude (Mw ∼ ≥6) earthquakes in extensional settings are often associated with simultaneous rupture of multiple normal faults as a result of static and/or dynamic stress transfer. Here, we report details of the coseismic breaching of a previously unrecognized large‐scale fault relay zone in central Greece, through three successive normal fault earthquakes of moderate magnitude (Mw 5.7–6.3) that occurred over a period of ∼10 days in March 2021. Specifically, joint analysis of InSAR, GNSS and seismological data, coupled with detailed field and digital fault mapping, reveals that the Tyrnavos Earthquake Sequence (TES) was accommodated at the northern end of a ∼100 km wide transfer structure, by faults largely unbroken during the Holocene. By contrast, the southern section of this relay zone appears to have accrued significant slip during Holocene. InSAR‐derived displacements agree with the loci of eight subtle, previously undetected, faults that accommodated coseismic and/or syn‐seismic normal fault slip during the TES. Kinematic modeling coupled with fault mapping suggests that all involved faults are interconnected at depth, with their conjugate fault‐intersections acting largely as barriers to coseismic rupture propagation. We also find that the TES mainshocks were characterized by unusually high (>6 MPa) stress‐drop values that scale inversely with rupture length and earthquake magnitude. These findings, collectively suggest that the TES propagated north‐westward to rupture increasingly stronger asperities at fault intersections, transferring slip between the tips of a well‐established, but previously unrecognized, relay structure. Fault relay zones may be prone to high stress‐drop earthquakes and associated elevated seismic hazard.

An uncertainty quantitative model of wellbore failure risk for underground gas storage in depleted gas reservoir during the construction process

The sensitivity of wellbore-wall failure risk under depleted formation-pressure coefficients and underground gas storage in depleted gas reservoirs during the construction process is quantitatively assessed, especially the failure risk of wellbore collapse and fracture in depleted reservoirs with ultralow formation-pressure coefficients, and to effectively guide safe construction. Based on the Mohr–Coulomb failure theory and multilevel confidence model, three typical in situ stress states (normal fault, slip fault, and reverse fault) are considered to establish an analytical model for wellbore-wall failure risk under different depleted reservoir pressure coefficients. Taking a depleted sandstone reservoir as the main reservoir for wellbore-wall stability analysis as an example, a wellbore-wall stability state visualization analysis model with three typical in situ stress states under arbitrary orientations and well deviation angles is obtained, and the uncertain probability distribution law of wellbore-wall collapse and fracture failure in a reservoir with an ultralow formation-pressure coefficient is constructed using a stochastic uncertainty simulation method with interval confidence. The distribution patterns of wellbore-wall stress fields and borehole safety density windows during the construction of depleted reservoirs are quantitatively analyzed. The results show that a safety density window with interval uncertainty estimates would be more intuitive for assessing the stability of the reservoir wellbore wall in a quantitative form, and it is observed that inclined well sections in depleted reservoirs typically have narrower safety density windows. In conclusion, the lower and upper limits of the safety density window in numerical examples are 1.4 to 1.6 g/cm3 (normal fault state), 1.2 to 1.5 g/cm3 (slip fault state), and 1.2 to 1.65 g/cm3 (reverse fault state), respectively. The research results can provide effective guidance for wellbore instability control, design, and construction of directional wells in depleted gas reservoirs.

Roles of Normal Stress, Roughness, and Slip Displacement in the Stability of Laboratory Fault in a Sandstone

Unstable slip of a fault block is considered to be the main cause of shallow earthquakes. However, the underlying mechanism of the stability-to-instability transition of faults has not been fully understood. Here, we used the stiffness ratio, which is the ratio between the shear stiffness of the fault subjected to direct shear and the critical stiffness to evaluate the fault stability degree from stable to unstable slip, and examined the effects of normal stress, roughness, and slip displacement on the fault stability. Our experimental results show that with the increase in slip displacement, the shear stiffness change in stable slip mainly includes four stages, namely “rapid increase–keep unchanged–slow increase–rapid decrease”, and unstable slip tends to occur in the last two stages. This process of shear stiffness change is accelerated by the increase in normal stress and the decrease in fault roughness. Our study reveals that fault stability over slip is mutually dictated by asperity interlocking and wear-induced gouge. Asperity interlocking controls fault stability when the gouge amount is low, whereas the fault gouge prevails with the increased wear of the fault surface since the gouge generated during slip can participate in the subsequent friction process. Thus, we infer that the stable–unstable transition of fault over slip is a spontaneous process due to the interplay of asperity interlocking and wear-induced gouge lubrication.

Present-day crustal strain and major fault slip rates in North China determined using GNSS observations

• A strain model and an elastic block model of North China were established. • The western Ordos and the northern North China exhibited larger strain rates. • The NNE- and NWW-trending faults showed dextral and sinistral slip respectively. • The fault deformation in North China was controlled by neighboring blocks. North China is characterized by numerous faults, where many earthquakes were recorded. However, the fault slip and crustal deformation mechanism underlying the effects of neighboring block motions remain poorly understood. In this study, we first constructed a strain model using global navigation satellite system (GNSS) velocities to analyze the relationship between seismicity and strain. We then constructed a block model based on the fault distribution and GNSS observations to obtain fault slip. The strain and fault slip rates were then used to determine the crustal deformation mechanism in North China. The strain model suggests the western border of the Ordos Block and the northern North China Plain had larger maximum shear strain rates. These areas are located in a transition between positive and negative dilatation rates, which indicate intense crustal deformation. Based on the block model, we found the NNE-trending faults were dominated by dextral slip. The northern and southern borders of the Ordos Block indicate left-lateral motion (0.4–2.5 mm/a), while its western and eastern margins exhibited right-lateral slip (1.0–3.0 mm/a). The periphery of the Ordos Block exhibited normal slip (0.2–3.2 mm/a), except at the southwestern tip. These results suggest that the eastward extrusion of the Tibetan Plateau caused left-lateral shear in North China, which led to sinistral slip of NNE-trending faults. The northward expansion of the northeastern Tibetan Plateau also contributes to sinistral slip along the northern and southern margins of the Ordos Block, as well as dextral slip along its western and eastern margins.

Weak catch bonds make strong networks.

Molecular catch bonds are ubiquitous in biology and essential for processes like leukocyte extravasion1 and cellular mechanosensing2. Unlike normal (slip) bonds, catch bonds strengthen under tension. The current paradigm is that this feature provides ’strength-on-demand’3, thus enabling cells to increase rigidity under stress1,4,5,6. However, catch bonds are often weaker than slip bonds because they have cryptic binding sites that are usually buried7,8. Here we show that catch bonds render reconstituted cytoskeletal actin networks stronger than slip bonds, even though the individual bonds are weaker. Simulations show that slip bonds remain trapped in stress-free areas, whereas weak binding allows catch bonds to mitigate crack initiation by moving to high-tension areas. This ‘dissociation-on-demand’ explains how cells combine mechanical strength with the adaptability required for shape change, and is relevant to diseases where catch bonding is compromised7,9, including focal segmental glomerulosclerosis10 caused by the α-actinin-4 mutant studied here. We surmise that catch bonds are key to creating life-like materials.

Source mechanism of the 2020 Mw 6.3 Nima earthquake derived from Bayesian inversions with InSAR observations: Insight into E-W extensional activity in the central Tibet

Normal faults and conjugate strike-slip faults have been considered to play an important role in response to the extension deformation of central Tibet. On 22 July 2020, a Mw 6.3 earthquake struck the Nima county, central Tibet, in China, which provides a rare opportunity to get insights into how the normal faults in central Tibet accommodates the east-west extension caused by the Indian-Eurasian convergence. In this study, the Sentinel-1 images are collected to measure the coseismic deformation associated with this 2020 event and image its slip distribution. To mitigate the atmospheric phase effects, the generic atmospheric correction online service (GACOS) model is used to correct the coseismic inteferograms. The final coseismic deformation results show mainly negative displacement with a maximum value of ∼ 30 cm in the line of sight (LOS) direction. After that, a Bayesian inversion method is used to invert the fault model. Our results reveal the optimal seismogenic fault of this event with a strike angle of 31.3°, a dip angle of 51.6°, and show that its slip distribution is dominated by normal slip with a maximum value of 2.55 m at a depth of 4.79–9.53 km, which suggest it’s a blind normal rupture with high east-trending dip angle. The total released geodetic moment is, equivalent to Mw 6.3. In addition, we analyze the Coulomb stress change due to the 2008 Gaize and this 2020 Nima events, suggesting the 2020 event should not be triggered by the 2008 event. Finally, we estimate an interseismic slip rate of 4.7±1.2 mm/yr on the Yibug Caka-RigainPun Co (YCRC) fault with published global navigation satellite system (GNSS) measurements. Given that these high frequent normal slip events but a low crustal extension rate of 4.7±1.2 mm/yr in this region, we speculate that the asthenosphere material upwelling should be also a possible reason for E-W extensional activities in central Tibet.

Frictional behavior of planar and rough granite fractures subjected to normal load oscillations of different amplitudes

The dynamic frictional behaviors of natural discontinuities (joints, fractures, faults) play an important role in geohazards assessment; however, the mechanisms of the dynamic fault weakening/strengthening are still unclear. In this paper, a dynamic shear box was used to perform direct shear tests on saw-cut (planar) and natural (rough) granite fractures, with different normal load oscillation amplitudes. Based on the recorded shear forces and normal displacements, the shear forces, apparent friction coefficients and normal displacements are found to change periodically with oscillated normal loads and are characterized by a series of time shifts. The observed changing patterns are similar for the rough and planar fractures. Compared with the test data under constant normal load (CNL), small/large normal load oscillation amplitude enhances/reduces the peak shear strength, with a critical point. The magnitude of critical normal load oscillation for the rough fractures is smaller than the planer fractures. The results imply that dynamic fault weakening/strengthening can be achieved by both normal load oscillation amplitudes and slip surface topography. The rough fractures with larger normal oscillation amplitude can easily cause frictional weakening under stress disturbance.

Transient evolution of permeability and friction in a slowly slipping fault activated by fluid pressurization

The mechanisms of permeability and friction evolution in a natural fault are investigated in situ. During three fluid injection experiments at different places in a fault zone, we measured simultaneously the fluid pressure, fault displacements and seismic activity. Changes in fault permeability and friction are then estimated concurrently. Results show that fault permeability increases up to 1.58 order of magnitude as a result of reducing effective normal stress and cumulative dilatant slip, and 19-to-60.8% of the enhancement occurs without seismic emissions. When modeling the fault displacement, we found that a rate-and-state friction and a permeability dependent on both slip and slip velocity together reasonably fit the fault-parallel and fault-normal displacements. This leads to the conclusion that the transient evolution of fault permeability and friction caused by a pressure perturbation exerts a potentially dominant control on fault stability during fluid flow.

22 years of satellite imagery reveal a major destabilization structure at Piton de la Fournaise

Volcanic activity can induce flank failure, sometimes generating large earthquakes and tsunamis. However, the failure structures have never been fully characterized and the failure mechanism is still debated. Magmatic activity is a possible trigger, either through fault slip, which might be induced by dyke intrusions, or through sill intrusions, which might be undergoing coeval normal displacements and slip. At the Piton de la Fournaise volcano, satellite imagery combined with inverse modeling highlights the pathways of 57 magmatic intrusions that took place between 1998 and 2020. We show that a major arcuate dyke intrusion zone is connected at depth to a sill intrusion zone, which becomes a fault zone towards the sea, forming a spoon-shaped structure. Some sills are affected by coeval normal displacement and seaward slip. Overall, the structure is characterized by a continuum of displacement from no slip, to sheared sills and finally pure slip. Repeated intrusions into this spoon-shaped structure could trigger catastrophic collapses.

Normal reactivation of the Main Central Thrust Zone in Sikkim Himalaya

• The Main Central Thrust Zone, Sikkim , was reactivated as a normal shear zone. • The normal shear zone is 2.5 km wide with >5 km normal movement. • Normal movement followed thrusting marking the start of doming in footwall. • Doming caused steepening and destabilization of the MCTZ and normal slip. The Main Central Thrust Zone (MCTZ) controlled the Miocene development of the Himalaya. Its kinematic evolution is key to understanding the orogeny. The MCTZ accommodated shortening of the Himalayan orogen and thrusted hot rocks of the Greater Himalayan Sequence over cooler ones of the Lesser Himalayan Sequence, giving rise to an inverted metamorphic sequence. In Sikkim, NE India, the transport direction during thrusting describes a broad curved pattern indicating complex kinematics. In this paper we document further complexities in the motion of the MCTZ in the NW section of the Tista Dome in Sikkim, that reveals that SE-directed thrusting, at 45° to the orogenic front, was reactivated by top-to-NW normal movement. This produced a 2.5 km-wide ductile shear zone that accommodated >5 km of normal dip-slip movement, where the inverted metamorphic sequence is preserved with minor retrogression. This change from reverse to normal ductile movement likely occurred in the early stages of doming at ∼12 Ma, following peak metamorphism at 13.8 Ma. We argue that normal movement relates to the abandonment of the MCTZ and movement transfer to the Ramgarh Thrust and/or the Main Boundary Thrust, structurally deeper in the system. This new thrust gave rise to a duplex system responsible for the growth of the Tista Dome from ∼12 Ma onwards causing steepening and destabilization of the MCTZ leading to stress relaxation and normal movement reactivation. This must have occurred in the early stages of doming because the rocks were still sufficiently hot to respond in a ductile fashion.

Experiment Program on Retrofitted Anchorage System under Impact Loads

This study aims to evaluate the strength and performance of retrofitted anchorage system in concrete under impact loads. A novel technique called “Post Installation of Supplementary Anchorage” (PISA) is introduced to retrofit five different configurations of rebar anchorage system used in concrete. The configurations of rebar are straight bar (A1), 90 degree bend (A2),180 degree hook (A3), single head (A4) and double head (A5) bars which was retrofitted by supplementary steel reinforcement. Direct tension pullout loads are applied on 60 anchorage specimens (each 30 of conventional and retrofitted) casted with M25 grade concrete. The boundaries of tested specimens were followed by strut-and-tie analogy. The rebar anchorage tested at 1.58, 1.52 impact factor using two different bars of 12mm and 16mm diameter respectively. The deterministic characteristics of test parameters are normal strength, bond strength, ductility, and slip of anchorage at ultimate load. The test variables are rebar configuration, size of anchored bar, and presence of supplementary steel. The results validated by nonlinear finite element based ANSYS modeling. A good agreement of results between experiment and model analysis was observed. Also a considerable improvement of nonlinear characteristics of retrofitted anchorage such as ultimate load (3%-6%), bond strength (1%-6%), ductility (3%-4%), concrete contribution (20%-32%), bar slip (8%-48%) and crack width (30%-42%) was obtained. This study promotes useful information to retrofit non-engineered anchorage system by PISA technique. Application of this technique may further extended to retrofit discrete regions of concrete elements such as bracket connection, corbel projection and beam-column joint subjected to impact loads.

Geologic map of central Panamint Range, California, USA

This detailed geologic map and supplemental digital data set1 examine and demonstrate the complex deformational history and reactivation relationships of the Panamint Range (California, USA), from active transtension of the Walker Lane belt, Miocene extension of the Basin and Range, to multiple Mesozoic events related to subduction, and Neoproterozoic extension. This collection of map data focuses on the geometry, kinematics, and relative timing of deformation to understand the deformation history and effects of structural reactivation. A minor portion of this geologic mapping data was presented in the analysis and figures of Andrew and Walker (2009). The Neogene extension and subsequent dextral transtension deformation has created a complex network of faults via partial reactivation of Mesozoic and Neoproterozoic structures. Structural data show oblique normal slip overprinting earlier normal slip along the western range flank fault of the western Panamint Range. Jurassic and Cretaceous deformation is localized along the western range on the Goldbug fault. The hanging wall of this fault preserves migmatitic fabrics and intense deformation due to Jurassic contraction. The Goldbug fault places Paleoproterozoic to Mesoproterozoic rocks over Neoproterozoic rocks. The Jurassic contraction has top-to-the-northeast relative transport and the more discrete Cretaceous thrust faulting has top-to-the-east transport. A set of Late Cretaceous plutonic rocks and mylonitic gneisses derived from them, occur along the Goldbug fault and demonstrate the reactivated nature of this fault in the Late Cretaceous. New data for the Butte Valley fault show that this fault cuts Late Jurassic plutonic rocks and has normal slip. The Butte Valley fault ends northward at the linked sinistral slip Warm Spring Canyon fault, which was previously interpreted to be an intrusive contact. A previously unrecognized rim syncline structure occurs along the boundary of the Late Jurassic Manly Peak quartz monzonite. Neoproterozoic deformation is difficult to discern due to the overprinting deformations. Numerous Neoproterozoic deformation-related mass wasting deposits can be seen within this formation, including a set of conspicuous allochthonous deposits and clasts of older Beck Spring Dolomite that appear to be frozen in the process of breaking away from intact, normal thickness beds in the Surprise–Happy Canyons divide. This detailed geologic mapping and collection of structural data for the rocks in the central Panamint Range were created using digital in-the-field geographic information systems software running on a field-hardened laptop computer combined with an earlier set of field data that were digitized into the digital georeferenced database. This map is a simplification of detailed geologic mapping data collected at 1:2000–1:6000 scales and reduced to 1:20000 scale. Structural data include kinematic and relative timing of deformation information.

Geologic map of southern Panamint Valley, southern Panamint Range, and central Slate Range, California, USA

Abstract This detailed geologic map and supplemental digital data set1 examine and demonstrate the complex deformational history and reactivation relationships of the southern Panamint Valley area (California, USA), from active transtension of the Walker Lane belt, Miocene extension of the Basin and Range, multiple Mesozoic events related to subduction, and Neoproterozoic extension. This collection of map data focuses on the geometry, kinematics, and relative timing of deformation to understand the deformation history and effects of structural reactivation. Andrew and Walker (2009) used these geologic mapping data to palinspastically restore the Fish Canyon area of the Slate Range to overlapping the western Panamint Range at Goler Wash. Neogene extension and subsequent dextral transtension has created a complex network of faults via partial reactivation of Mesozoic and Neoproterozoic structures and has separated the Slate Range from the Panamint Range. The Neogene fault system changes from south to north from dextral strike-slip along the southern Panamint Valley fault to oblique normal slip along the Emigrant fault at a triple junction with the sinistral-oblique normal Manly Pass fault. The Mesozoic deformation history is different in the two ranges across Panamint Valley. The Slate Range was the hanging wall to Jurassic and Cretaceous contractional deformation; this same deformation in the Panamint Range to the east was localized along the western range flank with the majority of the Panamint Range thus being in the footwall to Mesozoic contraction. The western Panamint Range preserves migmatitic fabrics and deformation due to Jurassic contraction and plutonism. The Goldbug fault, along the western Panamint Range, places Paleoproterozoic to Mesoproterozoic rocks over Neoproterozoic to Cretaceous rocks. Jurassic contraction has top-to-the-northeast relative transport and the more discrete Cretaceous thrust faulting in the Panamint Range has top-to-the-east transport. The Butte Valley fault, previously recognized farther north of the map area in the Panamint Range, cuts Late Jurassic rocks and structures. Neoproterozoic to Cambrian sedimentary rocks with top-to-the-northeast contractional deformation occur as relative down-dropped block exposed east of the Butte Valley fault. The Butte Valley fault continues southward and is then deflected by Late Cretaceous thrust faulting on the Goldbug fault. Neoproterozoic deformation is more difficult to discern but is hypothesized to relate to abundant olistostromes mapped within the Kingston Peak Formation in the Panamint Range (i.e., Prave, 1999). This detailed geologic mapping and collection of structural data for the rocks in the southern Panamint Valley area were created using digital in-the-field geographic information systems software running on a field-hardened laptop computer. This map is a simplification of detailed geologic mapping data collected at 1:6000 scales and reduced to 1:20000 scale. Structural data includes kinematic and relative timing of deformation information.

Field observations of surface ruptures accompanying a tsunami and supershear earthquake along a plate boundary strike-slip fault

AbstractStrike-slip earthquakes near major subduction zones have received less attention than thrust or reverse earthquakes in subduction zone areas. The occurrence of the 2018 Palu Mw 7.5 earthquake in eastern Indonesia provides an unprecedented opportunity to investigate the characteristics of one of these events. The Palu earthquake occurred on the left-lateral, north–south-striking Palu–Koro fault, which is the main plate boundary structure accommodating the convergence between blocks in a triple junction area. It excited a significant tsunami, which unusually is associated with strike-slip earthquakes, and also ruptured at a supershear speed, which is mostly observed on strike-slip faults in continents. Based on our fieldwork, we speculate that the normal slip component of the offshore rupture section in Palu bay on the middle segment probably favours tsunami genesis. Our field investigation has revealed evidence of a simple geometry as well as slip partitioning of dip-slip and strike-slip motion on two subparallel strands on the main segment, both of which may have contributed to the supershear of the rupture propagation. Instead of only a transtensive behaviour of the middle segment, our results also illustrate the transpressional property of the northern and southern rupture segments, which shows more complex behaviour than that of a common continental strike-slip fault.

An Overview of the Geological Control on Groundwater Potential in Lacamutu River, Alaua Kraik Area, Baucau Municipality, Timor-Leste

Timor island has a tropical climate with relatively little rainfall and surface water is often not available throughout the year with groundwater relied on to fulfill daily domestic necessities. Geological reconnaissance mapping, hydrogeological investigation, and resistivity survey were undertaken in this study to systematically understand the hydrogeologic system (e.g., aquifer system, hydrostratigraphic units, groundwater flow direction) and its potentiality for water supply to human consumption in Alaua Kraik area, Baucau Municipality, Timor-Leste. Res2DInv, Dips 5.1, Surfer 16, Global Mapper 13, and ArcGIS 10.6 software was used to create geological reconnaissance maps, resistivity interpretation profile lines, and a hydrostratigraphic model. Rainfall precipitation, rainfall intensity, maximum rate of runoff and infiltration data are also used to interpret the groundwater potential in the study area. Two rock units occur in the study area; permeable alluvial deposits which unconformable overlie impermeable interbedded red marl-chert and calcareous shale. Structurally the area comprises the Lacamutu anticline, thrust fault, left slip fault, and normal right slip fault. Resistivity lines indicate three (3) types of lithologies: alluvial deposit, an intercalated layer of red marl-chert, calcareous shale and wet calcareous shale. The alluvial deposit and red marl-chert layer intercalated with calcareous shale units are classified as a hydrostratigraphic unit of intergranular and localised aquifer systems with low productivity. The groundwater flows through the existing fractures of the shear joint and tends to flow towards the left slip fault plane zone from the North to South direction. Much of the rainwater in the study area is most likely intercepted, evaporated, and or transpiration as opposed to running off and infiltrating into the ground. The permeable and heavily fractured impermeable rock units in the study area have good porosity but low permeability and represent poor aquifers. The springs and Lacamutu River have low discharge and are generally dry in the dry season as it does not have an adequate aquifer that can accumulate and pass groundwater with significant volumes even if the rainfall in the study area is classified as moderate rainfall.

Kinematic Slip Model of the 2021 M 6.0 Antelope Valley, California, Earthquake

Abstract We present a kinematic slip model of the 8 July 2021 Antelope Valley earthquake from a finite-source inversion based on regional seismic waveforms and static offsets from Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR). Seismic waveforms are employed at 6 s dominant period out to 100 km from the epicenter, and the combined GPS and InSAR datasets cover the near field and far field out to ∼100 km and constrain the overall rupture size. The aftershock pattern defines a nearly north-striking, 50° east-dipping fault plane. We find a unilateral rupture along this fault plane propagating southward and updip with predominantly normal slip up to ∼1.5 m. The estimated seismic moment of 8.47×1017 N·m is equivalent to Mw 5.92. A finite-source inversion that retains seismic waveforms and GPS static offsets but omits InSAR range changes yields a seismic moment of 1.08×1018 N·m (Mw 5.99). Despite vigorous aftershock activity between 10 km and Earth’s surface, coseismic slip is concentrated in the depth interval 7–10 km.