Uniform Slip Research Articles

Characterizing and predicting the partial slip subjected to variable gradients of velocity and pressure in eccentric micro-scale Taylor–Couette flows

In the context of eccentric micro-scale Taylor–Couette flow, variations in localized flow scales result in a non-uniform fluid–solid interface slip state, distinct from the typically studied uniform slip velocity distribution. This study introduces a boundary condition definition method aimed at characterizing partial slip states, complemented by a coupled iterative analysis system tailored to address this complexity. Key contributions include the development of a method for calculating the limiting shear stress, which considers local velocity gradients and pressures. Validation demonstrates that the locally derived slip state aligns more closely with Knudsen number distributions of local flow scales compared to traditional uniform slip models, and exhibits greater consistency with experimentally measured pressure distributions. Additionally, the study reveals that eccentric Taylor–Couette flow, characterized by significant variations in local flow scales and strong self-induced pressure effects, leads to complex distributions of local pressure, velocity gradients, and differences in local slip velocities. Specifically, the non-uniform distribution of local pressure gradients due to eccentricity results in partial slip occurring predominantly on the rotor in regions with positive pressure gradients, and on the stator in regions with negative pressure gradients. Furthermore, the variation in gap height exerts a greater influence on local slip compared to rotational speed and eccentricity ratio. Under certain conditions influenced by pressure gradients, the slip velocity on the rotor may exceed its tangential speed.

A cryogenic incremental sheet forming process for improving the formability of AA6061 to reveal the dual enhancement effect and microstructure evolution mechanism

Based on the dual enhancement effect of hardening and plasticity in aluminum alloys at cryogenic temperatures, the cryogenic incremental sheet forming process is introduced in this paper for manufacturing complex components. Experimental results indicate that incremental sheet forming at cryogenic environments results in a remarkable enhancement of formability. The ultimate forming height of specimen at 113K presents an increase of 32.4% compared with the specimen at 295K. Meanwhile, it is confirmed that cryogenic conditions increase the work-hardening ability and reduce the microcrack generation on the specimen surface. Moreover, the mechanism of dual enhancement effect on 6061 alloy during cryogenic incremental forming was studied. At 295 K, the dislocation distribution was localized due to significant cross-slip in the specimens. It was also observed that dislocation entanglement occurred at grain boundaries, which tends to cause stress concentration and therefore reduced formability. In contrast, at 113 K, the decrease in stacking fault energy leads to suppression of cross-slip, and the uniform slip leads to a significant increase in dislocation density. As a result, the cryogenic temperature exhibits enhanced work-hardening ability and formability. The rolling texture evolves mainly along the α and β orientation lines during the forming process, the 295K specimen generates a large number of Goss textures in the final forming region due to the uneven deformation which makes it difficult for the texture to evolve further. In contrast, at 113 K the texture fully evolves and intersects in the Brass texture along the two orientation lines due to the enhanced formability.

Unlocking slip-mediated bending in multilayers: Efficient modeling and solutions with high precision and simplicity

This work introduces a novel approach to understanding the bending behavior of multilayer structures with weak interfaces. Despite the existence of various theoretical models, achieving high accuracy and computational efficiency remains a challenge. To address these limitations, we propose a Non-uniform Slip Model (NSM) governed by two essential dimensionless parameters: the number of layers and the shear factor. Utilizing the Semiparametric Hybrid Variational (SHV) method, we derive theoretical solutions that require less computational effort and offer enhanced accuracy. We further simplify the NSM through homogenization to the Uniform Slip Model (USM), yielding clear and concise analytical solutions for deflection curves and effective bending stiffness with high precision. The USM is also extended to account for nonlinear slipping interfaces with continuous shearing flow, providing an analytical stiffness expression that includes the bending angle. This extension explains the experimental observation of multilayered graphene’s bending stiffness, which decreases from cubic to linear with increasing number of layers due to continuous slip and dislocation between atomic layers. Our study delivers theoretical insights for analyzing slip-mediated bending in laminated materials, paving the way for the design and optimization of such structures.

Tsunami hazard assessment in the South China Sea based on geodetic locking of the Manila subduction zone

Abstract. This study provides a dataset and shows the spatial distribution of tsunami hazard in the South China Sea sourced from the Manila subduction zone. The plate motion data around the Manila subduction zone are used to invert the geodetic locking of the Manila subduction zone, further used to estimate the maximum possible magnitude and applied to obtain a more reliable tsunami hazard assessment. The spatial distribution of tsunami wave height with a 1000-year return period is shown, and several high-hazard areas in the South China Sea are pointed out. Uncertainties in the seismic source are explored, including the slip heterogeneity, the upper limit of seismic magnitude and segmentation. The impact of the locking distribution and randomness of slip on tsunami hazard assessment demonstrates that the traditional uniform slip assumption significantly underestimates the tsunami hazard. Moreover, the assessment results involving the effect of the locking distribution should be more realistic and show a larger tsunami height than when only considering the stochastic slip in most areas, which should prompt coastal management agencies to enhance tsunami prevention awareness.

The N-S direction strike-slip activities in the Pamir hinterland under oblique convergence: the 2015 and 2023 earthquakes

SUMMARY The prominent Pamir plateau holds considerable significance in comprehending the processes of Asian continental collisional orogeny. However, due to harsh natural conditions and low seismic activity within the Pamir hinterland, our understanding of this region remains deficient. Recent major events and the accumulation of geodetic observations present a rare opportunity for us to get insights into the tectonic activities and orogenic processes occurring in this region. First, employing Sentinel-1 and Advanced Land Observation Satellite (ALOS)-2 Synthetic Aperture Radar (SAR) images, we acquire coseismic displacements associated with the most recent earthquakes in 2015 and 2023. Subsequently, we conduct the source models inversion with the constraints of surface displacements based on a finite-fault model. Our results reveal displacements ranging from −0.8 to 0.8 m for the 2015 Mw 7.2 Tajik earthquake and −0.25 to 0.25 m for the 2023 Mw 6.9 Murghob event, respectively. The optimal three-segment model for the 2015 event ruptured a fault length of 89 km with a surface rupture extending 59 km along the Sarez–Karakul fault (SKF), characterized predominantly by left-lateral strike-slip motion, with a maximum slip of 3.5 m. Meanwhile, our preferred uniform slip model suggests that the 2023 event ruptured an unmapped fault in the southern Pamir region with a strike angle of 31° and a dip angle of 76.8°. The distributed slip model indicates that the 2023 event ruptured a fault length of 32 km, resulting in an 8 km surface rupture. This event is characterized by left-lateral strike slip, with a peak slip of 2.2 m. Secondly, the Coulomb stress calculations demonstrate that the 2023 event was impeded by the 2015 event. Finally, interseismic Global Positioning System data revel a relative motion of 3.4–5.7 mm yr−1 in the N-S component and 3.2–3.8 mm yr−1 in the E-W component along the SKF in the Pamir hinterland, respectively. These N-S direction strike-slip activities and slip behaviours support an ongoing strong shear and extension in the Pamir regime, which is a response to the oblique convergence between the Indian and Eurasian plates.

Stability of fluid flow in a porous medium with uniform cross-flow and velocity slip

This work examines the evolution of small perturbations in a plane Poiseuille flow through a porous medium bounded by porous walls implemented with the Brinkman flow model. The effect of uniform cross-flow across the channel along with slip imposed on the channel walls is examined for the associated fluid flow. The modified Orr–Sommerfeld equation for the flow system under consideration is derived and then solved numerically using Chebyshev spectral collocation method. The acquired sufficient conditions ensure that fluid motion will remain stable even when the flow system is widely perturbed. The linear stability characteristics and the onset of instability is discussed for a wide range of cross-flow Reynolds number, slip length and porosity parameter. The above mentioned flow parameters have a significant stabilizing effect on the fluid flow that is depicted with neutral stability curves, growth rate dispersion curves and eigenspectrums. Asymmetric slip allows the critical Reynolds number to increase rapidly when the upper channel wall experiences more slip than the lower.

Possible Maximum Earthquake Tsunami Along the South Coast of China Inferred From GPS‐Derived Surface Velocities

AbstractThis study aims to assess the tsunami hazard of the maximum possible earthquake along the south coast of China. GPS‐derived surface velocities around the Manila Trench have been used to clarify the active tectonics and estimate the seismic potential of Manila subduction, where catastrophic tsunamis may originate and cause devastating damage to the surrounding area of the South China Sea. Based on the maximum potential earthquake magnitude estimated from the accumulated seismic moment, more than 100,000 possible tsunami scenarios with varying epicenters have been simulated considering the slip heterogeneity. The impact of several uncertain parameters including the release period and release ratio of accumulated seismic moment are investigated, as well as some assumptions in the model of tsunami generation. Although different release conditions for accumulated seismic moment result in a significant impact on the value of tsunami height, similar trend in spatial distribution has been shown. The results show that the tsunami wave height along the south coast of China has an increasing trend from west to east, with the maximum tsunami wave height exceeding 10 m corresponding to the potential earthquake Mw = 9.1 with a 1,000‐year release period. The impact of fault slip heterogeneity on tsunami wave height is significant. Compared to uniform slip, considering stochastic slip will increase the average tsunami wave height by about 15%. Considering locking distribution will increase the average tsunami wave height by about 20%–30% and also increase the maximum tsunami wave height by about 60%–70%.

Complex Rupture Features and Triggering during the 2022 Chishang Earthquake Sequence in Eastern Taiwan Estimated by InSAR, GPS, Strong Motion, and Teleseismic Waveform Evidence

Abstract The most recent 2022 Chishang earthquake sequence broke a long-time seismic quiescence on the Central Range fault (CRF), attracting lots of attention to the seismic behaviors and fault interactions of the Longitudinal Valley zone (LVZ), eastern Taiwan orogeny. However, detailed rupture features of both the foreshock and mainshock are still scarce. Here, available static displacements (i.e., Interferometric Synthetic Aperture Radar [InSAR], Global Positioning System [GPS], and strong motion [SM]) and kinematic waveform evidence (i.e., high-frequency GPS, strong motion, and teleseismic data) are used to delineate the rupture behaviors of both the foreshock and mainshock in this sequence. Our results indicate that the static displacements derived from strong-motion sites rival the high precision of GPS observations, replenishing the near-field constraints on the hanging wall together with InSAR and GPS. The optimal uniform slip models exhibit that both the foreshock and mainshock generally ruptured the west-dipping CRF along the south-southwest-striking direction with a steep dip angle >65°. The slip distribution models revealed that the rupture of foreshock and mainshock nearly ruptured a total length of CRF within 65 km from the Guanshan to Ruisui at a depth of above 14 km, and their slips are concentrated within one asperity and two asperities, respectively. The spatial evolution of this sequence’s ruptures exhibits a discontinued and separated pattern, and is well consistent with the local seismicity. Considering that the mainshock was initialed in a weak slip and negative static Coulomb stress region caused by the foreshock, the 2022 sequence occurrence is in favor of a preslip triggering mechanism. The rupture region of the 2022 sequence filled the “seismic gap” along the western flank of the LVZ and will promote the potential seismic hazard in this region.

Investigation of Wear Rate of Passenger Airplanes Tyres During Landing

A real, functioning copy of one main landing gear wheel is used to show the landing impact of an aircraft. By minimizing abrasive sliding between aircraft tires and runway surfaces right after touchdown, this study seeks to identify possible tire-life improvements. An experimental investigation of size 22 X 5.5, type VII airplane tyres was conducted to evaluate the wear and related properties of temperature and friction caused while braking. One way to evaluate the tire's performance on surfaces with uniform slip ratios, including asphalt, concrete, and slurry seal, was to gear it up to the driving wheel of a ground vehicle. The range of slip ratios often attributed to an airplane's braking system was covered by the data gathered during dry runway operations. Our results show that cumulative tire wear is affected by runway surface features, increases with increasing slip ratio, and changes linearly with miles. The differing wear rates associated with the various surfaces may be used to rank runways based on tire wear.

Stepwise decrease in strike-slip rate along the eastern Altyn Tagh Fault and its relation to the Qilian Shan thrust system, northeastern Tibetan Plateau

As the northern boundary fault the Tibetan Plateau, the slip-rate decrease pattern of the eastern Altyn Tagh Fault (ATF) and its relation to the neighboring Qilian Shan thrust system remain unclear. In this study, high-resolution topographic data have been acquired by using the UAV-based LiDAR and Structure from Motion (SfM) technique. Using OSL dating ages obtained from terraces, we constrained the strike-slip rates at four locations along the eastern ATF, ranging from ∼7 mm/yr to ∼1 mm/yr. In combination with previous observations, a stepwise decrease pattern in strike-slip rate along the eastern ATF has been proposed in this study. To confirm this conclusion, sandbox experiments were conducted to simulate the simultaneous deformation involving the sinistral slip of the eastern ATF and the crustal shortening in the northeastern Tibetan Plateau. The role of ductile middle-lower crust was examined by comparative experiments (Models 1 and 2). In Model 1, without a ductile middle-lower crust, the wedge translated forward as a rigid block until reaching the frontal thrust, resulting in an almost uniform slip rate along the strike-slip fault. In Model 2, with a ductile middle-lower crust, the slip rate exhibited rapid decrease while passing each thrust belt, forming a stepwise decrease pattern rather than a gradient decrease; The compressional deformation was accommodated by a series of thrust belts that were active simultaneously, consistent with the late Quaternary simultaneous activity of the thrust belts within the Qilian Shan thrust system. Our modeling results suggested coupled growth between the eastern ATF and the Qilian Shan thrust system, and that a ductile middle-lower crust played important role in dispersing deformation into parallelly distributed thrust belts.

Adjoint Inversion of Near‐Field Pressure Gauge Recordings for Rapid and Accurate Tsunami Source Characterization

AbstractWe explore the potential of the adjoint‐state tsunami inversion method for rapid and accurate near‐field tsunami source characterization using S‐net, an array of ocean bottom pressure gauges. Compared to earthquake‐based methods, this method can obtain more accurate predictions for the initial water elevation of the tsunami source, including potential secondary sources, leading to accurate water height and wave run‐up predictions. Unlike finite‐fault tsunami source inversions, the adjoint method achieves high‐resolution results without requiring densely gridded Green's functions, reducing computation time. However, optimal results require a dense instrument network with sufficient azimuthal coverage. S‐net meets these requirements and reduces data collection time, facilitating the inversion and timely issuance of tsunami warnings. Since the method has not yet been applied to dense, near‐field data, we test it on synthetic waveforms of the 2011 Mw 9.0 Tohoku earthquake and tsunami, including triggered secondary sources. The results indicate that with a static source model without noise, using the first 5 min of the waveforms yields a favorable performance with an average accuracy score of 93%, and the largest error of predicted wave amplitudes ranges between −5.6 and 1.9 m. Using the first 20 min, secondary sources were clearly resolved. We also demonstrate the method's applicability using S‐net recordings of the 2016 Mw 6.9 Fukushima earthquake. The findings suggest that lower‐magnitude events require a longer waveform duration for accurate adjoint inversion. Moreover, the estimated stress drop obtained from inverting our obtained tsunami source, assuming uniform slip, aligns with estimations from recent studies.

Impact of Variable Fault Geometries and Slip Rates on Earthquake Catalogs From Physics‐Based Simulations of a Normal Fault

AbstractPhysics‐based earthquake simulators have been developed to overcome the relatively short duration and incompleteness of historical earthquake and paleoseismic records, respectively. These simulators have the potential to be a useful addition to seismic hazard assessment as they produce millions of synthetic earthquakes over thousands to millions of years using predefined fault geometries and slip rates. Due to the sparsity of fault data and the computational expense of the modeling, it is common to simplify earthquake simulator input parameters. Fault surfaces are typically characterized by simplified mapped traces and constant dip with depth, with slip rates that are often assumed to be uniform over the fault plane. This study uses the well‐defined 3D geometry of an active normal fault in offshore Aotearoa New Zealand, the Cape Egmont Fault, to demonstrate the impact of using nonuniform slip rates and nonplanar fault geometries on the resulting synthetic earthquakes from the earthquake simulator RSQSim. Adopting variable slip rates that decrease to zero along the fault tipline (rather than uniform slip rates) reduces unrealistically high nucleation rates of seismicity along fault edges. Introduction of complex 3D fault geometries, including fault segmentation and bends on kilometer scales, and variable slip rates produces less characteristic earthquake populations, increasing the number of M6‐7 moderate‐large magnitude events. Incorporation of variable fault geometries and slip rates in physics‐based simulators may modify the seismic hazards estimated from synthetic earthquake catalogs.

Interseismic slip rate and fault geometry along the northwest Himalaya

SUMMARY Geodetic networks enable us to investigate interseismic crustal deformation along the northwest Himalaya. Using 144 GNSS surface velocities and a Bayesian inversion model, we estimate the slip rate and fault geometry of the Main Himalayan Thrust (MHT) along six arc-normal transects in the northwest Himalaya. We consider that the fault plane consists of three sections along the décollement, namely the locking zone (0−12 km), the transition zone (10−22 km) and the creeping zone (≥22 km). The MHT is found to be completely locked from the surface down to an average depth of 6 ± 2 km. The locking-to-creeping transition zone along the décollement extends from the edge of the fully locked area to a deeper depth (14 ± 3 km) to the tip of the creeping zone of the MHT (17 ± 2 km) with a slip rate of 1.6 ± 0.9 to 3.7 ± 1.1 mm yr−1. Considering the range of uncertainties between 1−2 mm yr−1 for the GNSS velocities, the inverted slip rate along the transition zone of MHT turns out to be insignificant. Thus, the locking zone along the northwest Himalaya extends from the MFT to ∼111 ± 6 km in the north with a locking depth of ∼17 ± 2 km. The deeper part of the MHT is inferred to be creeping with an average slip rate of ∼19.1 ± 1.9 mm yr−1 along the northwest Himalaya. In addition, we have also illustrated a splay-fault model to account for the fault kinematics along the splay faults and the main décollement. The splay-fault model indicates a distributed slip rate at the locking-to-creeping transition zone and about ∼15 per cent smaller slip rate of the MHT than that of the single-fault model. Further, the checkerboard test and the uniform slip model exhibit the reliability of the current GNSS network and the inversion model (single- and splay-fault models). Overall, the updated fault kinematics inevitably contribute to the improvement of seismic hazard evaluation along the northwest Himalaya.

Effect of helium bubbles on the interface shear strength of copper/niobium multilayer

The influence of the helium bubble on the interfacial shear strength of copper/niobium multilayers and the corresponding deformation mechanisms are studied through molecular dynamics. Strong anisotropy of the shear strength is demonstrated, and the ratio of the highest strength to the lowest is approximately 4.3. The interface bubble leads to the dislocation emission under the shear along the high-strength directions and results in the severe decrease of the interface bearing capability, while the loss of the interface bearing is negligible for the case along the weak/medium-strength directions. The contradictory effects of the bubble on the interface shear strength under different shear directions are explained by the competition between the bubble-related dislocation emission and propagation and the regular uniform interface slip. For the shear along the high-strength direction, the interface could bear relatively high shear stress which is large enough to activate the dislocation from the bubble. Consequently, the corresponding deformations are dominated by the mechanism of bubble-related dislocation emission and its propagation. For the shear along the weak/medium-strength direction, the interface itself is sheared under relatively low shear stress before the effective nucleation of dislocation. Therefore, the corresponding deformation mechanism is controlled by the regular interface shear.

Hydrodynamics of a slip-stick sphere with a non-axisymmetric patch

We study the low Reynolds number hydrodynamics of a slip-stick sphere suspended in an arbitrary ambient Stokes flow, whose surface is partitioned into two regions with different slip lengths. The fore-aft symmetry of the sphere breaks due to the varied slip length over the surface, which causes translational and rotational motion of the slip-stick sphere. An analytical solution is developed using the double curl method to evaluate Faxén's formulae for the hydrodynamic drag and torque exerted on the slip-stick sphere for the sub-cases, namely, (a) cap/strip model and (b) patch model. Subsequently, we compute the flow field, velocity, and rotation rate, which strongly depend on the slip lengths and configuration of the patch. As a specific example, we consider the slip-stick sphere immersed in a Poiseuille flow. For the cap/strip model, we find an optimal configuration for which the velocity of the slip-stick sphere is maximum compared to the slip-stick sphere with uniform slip. We also find configurations for which the velocity is independent of the slip lengths. Subsequently, in the patch model, we obtain the optimal azimuthal angles for the maximum rotation rate of the slip-stick sphere. We observe near-field deviations in streamlines due to the heterogeneous nature of the surface of the slip-stick sphere. These findings help design efficient artificial passive swimmers with prescribed slip lengths.

Coseismic displacement fields and the slip mechanism of the 2021 Mw 6.7 Hovsgol earthquake in Mongolia constrained by Sentinel-1 and ALOS-2 InSAR

ABSTRACT On 11 January 2021, an Mw 6.7 earthquake, which involved a complex rupture mechanism, occurred in Lake Hovsgol, Mongolia. This study measured the earthquake’s 3-D coseismic surface displacement fields using interferometric synthetic aperture radar (InSAR) pairs of three radar look directions: Sentinel-1B from the descending path and Advanced Land Observing Satellite-2 from the ascending and descending paths. The three DInSARs showed that the maximum coseismic surface displacement appeared east of the Northern Hovsgol Fault (NHF), where the displacement components were 18 cm, 5 cm, and 33 cm in the east–west, north–south, and up–down directions, respectively (precision: 1.7 cm, 20.4 cm, and 5.2 cm). However, the 3-D displacements indicated that although the earthquake induced a combination of normal faulting with strike slip motions, the displacements in the north–south direction had very large uncertainty owing to the similar geometry of the InSARs in the descending path. Later, we performed inversions of the DInSAR-measured coseismic surface displacement fields in the line-of-sight direction, which assumes a fault plane’s uniform and distributed slips in analyzing the slip mechanism. We conducted slip distribution estimations on the ruptured fault plane in accordance with the optimal fault geometry and source parameters determined by the uniform slip model. Investigations revealed that, with a correlation of 95.3%, the simulated displacements from the best-fitted distributed slip model were consistent with the observed displacements from DInSARs. Besides, our slip distribution model showed two distinctive slip patches, which include differences in their magnitudes and directions on the fault plane. We also observed ruptured faults experiencing a predominant right-lateral strike slip with a significant dip slip, according to the slip distribution, which caused two distinct slips due to the dramatic bending of the fault strike. Then, by analyzing the Coulomb stress change, our findings proposed that the seismic risk potential of active faults in the Hovsgol Basin increased after the earthquake. Overall, the great potential of multi-track DInSAR observations in the identification of complex slip mechanisms was demonstrated.

Formability enhancement and deformation mechanism of 2195 Al Li alloy sheet in cryogenic forming

Cryogenic medium pressure forming is very suitable for producing thin-walled, complex-shaped aluminum alloy components. In order to evaluate the feasibility of the new forming process, an innovative cryogenic hydro-bulging method and corresponding device was developed to determine the cryogenic formability under biaxial tensile stress. An analysis of cryogenic biaxial stress-strain relations was conducted to quantify the strain hardening behavior. The deformation mechanisms at cryogenic temperature were investigated by analyzing microstructures. The limiting expansion ratio of the 2195 AlLi alloy solution-treated sheet at −196 °C increases to 38.7%, 95.5% more than that at 20 °C. The acquired cryogenic biaxial stress-strain curve demonstrates significantly enhanced strain hardening ability at −196 °C. The strain and thickness distribution are more uniform at −196 °C due to the increased cryogenic strain hardening ability. The enhanced cryogenic plasticity and strain hardening ability is caused by the formation of uniform high-density dislocations and dislocation cells at −196 °C, which is conducive to uniform dislocation slip and localized deformation suppression. It demonstrates cryogenic medium pressure forming is very suitable for manufacturing thin-walled complex-shaped aluminum alloy components due to its enhanced cryogenic biaxial formability.

Coseismic Gravity Changes and Crustal Deformation Induced by the 2018 Fiji Deep-Focus Earthquake Observed by GRACE and GRACE-FO Satellites

Earthquakes at depths of ≥300 km are generally called deep-focus earthquakes. Only two deep-focus earthquakes with Mw 8.0 or more have occurred in this century—the 2013 Okhotsk earthquake (Mw 8.3) and the 2018 Fiji earthquake (Mw 8.2) on 19 August 2018. However, the 2018 Fiji earthquake was only reported on seismographs, and the related crustal deformations were not observed by the Global Navigation Satellite System because the observation network did not exist around the epicenter. This study analyzed the time series of gravity data observed by the Gravity Recovery And Climate Experiment (GRACE) and its successor, GRACE Follow-On, and detected the spatial distribution of coseismic gravity changes mainly due to crustal deformation by the 2018 Fiji earthquake. The results in this study were not consistent with the numerical calculation of gravity changes when using the fault parameters estimated by the data of seismic waves. Thus, numerical calculations were used to construct a uniform slip rectangle fault model to explain coseismic gravity changes and provide a spatial distribution map of crustal deformation. However, this fault model is only based on gravity changes; thus, new research combining satellite gravimetry and seismic wave data will be necessary in the future.

A two-step inversion for fault frictional properties using a temporally varying afterslip model and its application to the 2019 Ridgecrest earthquake

The stress status and frictional parameters of a fault system control its slip behaviors over earthquake cycles. These parameters generally exhibit large spatial variations in a real fault system, and resolving such variations is of critical importance for realistic assessments of the seismic hazard. Slowly evolving afterslip reflects the slip response of a fault system to the coseismic stress loading, which is commonly observed following large earthquakes, thus providing information for constraining the fault stress and frictional parameters. In this study, we demonstrate that two independent and determinable frictional properties (i.e., σ(a−b) and Rinit=log⁡(vinit/v0), where σ, (a−b), vinit and v0 are the effective normal stress, velocity-dependence frictional parameters, initial slip velocity, and reference velocity, respectively) can be obtained from an afterslip evolution process. We propose a two-step strategy that uses the temporally segmented afterslip models to invert for the independent parameters. After validating the performance of our inversion procedure by synthetic tests, we apply it to the 2019 Ridgecrest earthquake afterslip process. Our results show that σ(a−b) in the main afterslip area is 0.2∼0.5 MPa. The spatial distribution of this parameter suggests a significant difference of pore pressure at the two ends of the coseismic rupture. The depth profile of the effective normal stress in the afterslip concentration area reveals that the pore fluid pressure is hydrostatic above 5 km depth and increases to lithostatic from 5 to 20 km, indicating a gradual permeability decrease in this depth range. Our analysis also shows that the afterslip models which assume a uniform slip evolution function cannot be directly used for the estimation of the frictional properties.

Are the earthquake locations reliable in caldera structures?

Increasing evidence suggests that non-planar faults have been activated during caldera collapse events linked to basaltic eruptions around the world. Despite advances in the description of the source location and processes, there is inconclusive evidence regarding the quality of the locations, both hypocentres and centroids, and their relationship with the geology and laboratory experiments. For example, trapdoor and piston collapses are not expected to activate faults within the caldera boundaries, unlike piecemeal or funnel collapses. Small earthquakes at ring faults present small rupture areas, hence, the curvature does not affect the location of the events and the source can be approximated as a planar fault. For larger events, the curvature becomes critical and the centroid migrates towards the centre of the ring while the arc rupture increases. Consequently, centroid locations within the caldera rims might be either real events in the corresponding location or an artefact due to the curvature of the source. In this work, I test the well-known equation of the centroid location at a ring fault with uniform slip and contrast it with a Gaussian-like distribution. Then, I perform numerical simulations assuming three cases of rupture velocity to compare hypocentre estimations with the analytical expressions for centroid location. For instance, hypocentres of an instantaneous rupture behave as the centroid of a uniform slip distribution, a 6 km/s rupture shows hypocentres congruent with the centroid of a Gaussian-like slip distribution, and finally, a 0.9vS rupture velocity shows the most likely locations at the rims but showing large uncertainty. I applied these results to two cases; hypocentres calculated at Bárðarbunga and centroids calculated for Sierra Negra caldera collapse earthquakes. By using this methodology, both cases give a first order approximation on the quantification of the artefact affecting locations due to curvature.