Slip Area Research Articles

Dynamics of ferromagnetic due to nonlinear thermal buoyancy when Cattaneo–Christov heat flux and magnetic dipole whose magnetic scalars are significant

The fluid flow and heat transfer characteristics under magnetic dipole with non-Fourier flux are useful in understanding practical significance for undersea applications, for example, managing transference and/or separation of the boundary layer above submerged blocks and in suppressing recirculating bubbles. The heat transfer features of a ferromagnetic fluid were numerically analyzed over an elastic elongating surface convectively heated. Over a flexible body at the boundary, a partial Casson slip is considered. To balance the heat transition, the radiative and non-Fourier flux are combined in the energy. Similarity modifications are utilized to transform the partial differential equations (PDEs) from linear momentum and traditional energy equations into ordinary differential equations (ODEs) that are nonlinear. By the shooting method, numerical solutions to these equations are obtained. The results of various related physical parameters are studied, including ferromagnetic activity, dimensionless velocity slip, Biot number, thermal radiation, thermal slip, temperature and velocity area instability. The surface friction and the number of Nusselt are also measured for and at separate embedded parameters.

Investigation of a relationship between twin-disc wear rates and the slipping contact area on R260 grade rail

Twin-disc tests present some limitations for wheel-rail wear characterization such as the obtained contact patch and the error for very low creepages. In this work, creepage phenomena are investigated ranging from 0.12% to 2.45%. To improve the fitting of experimental tests with the theoretical adhesion curve, a modification of the FASTSIM algorithm is proposed. A linear correlation has been found between wear and the slip area including the non-linear zone. Normalized weight losses and wear rates are similar for all tested creepages. Applying this relationship, identified for delaminative wear by surface and metallographic characterization, it is possible to calculate wear for low creepages at wheel-rail contact from twin-disc tests, which should be close to the saturation of the friction coefficient.

Optimization of boundary slip region on bearing sliders to improve tribological performance

This study aims at optimizing the boundary slip region on bearing sliders for improving tribological performance. Surface of the bearing slider are divided into a rectangular mesh, in which each rectangular grid is assumed to be local slip region or no-slip region, labeled as 1 or 0. Then, the Genetic algorithm is performed to optimize the shape and pattern of boundary slip area. Stepped trapezoid shapes of slip coverage area located in the inlet of the bearing slider are attained as the optimization result. The influences of convergent ratio, width and slip length on the optimization results are evaluated and discussed. Subsequently, corresponding experiments demonstrated the optimized boundary slip arrangement achieved relatively low friction coefficients.

The 30 October 2020, MW = 7.0, Samos earthquake: aftershock relocation, slip model, Coulomb stress evolution and estimation of shaking

We study the major MW = 7.0, 30 October 2020, Samos earthquake and its aftershocks, by calculating improved locations using differential travel times and waveform cross-correlations. We image the rupture of the mainshock using local strong motion data, and we examine the Coulomb stress evolution prior to the mainshock, as well as the coseismic stress changes. Lastly, we estimate the produced shaking using all the available information from strong motion data and testimonies. Earthquake relocations reveal the activation of the E-W oriented Kaystrios fault, in the North basin of Samos with a possible extension to the West. The kinematic rupture inversion suggests non-uniform bilateral rupture on a ∼60 km × ∼20 km fault area, with the main rupture propagating towards the West and maximum slip up to approximately 2.5 m. Improved locations of the aftershock sequence are anti-correlated with areas of maximum slip on the fault surface. Similarly, the Coulomb stress change calculations show that only off-fault earthquake clusters are located within lobes of increasing positive static stress changes. This observation is consistent with assuming a fault area of either uniform slip, or variable slip according to the obtained slip model. Both scenarios indicate typical stress patterns for a normal fault with E-W orientation, with stress lobes of positive ∆CFF increments expanding in E-W orientation. In the case of the variable slip model, both negative and positive stress changes show slightly larger values compared to the uniform slip model. Finally, Modified Mercalli Intensities based on the fault model obtained in this study indicate maximum intensity (VII +) along the northern coast of Samos Ιsland. Spectral acceleration values at 0.3 s period also demonstrate the damaging situation at Izmir.

The Promotion Mechanism of Frozen Stagnant Water on the Sliding in the Loess Landslide Zone of Heifangtai

Freeze-thaw cycles can significantly change the hydrologic and thermal state of slopes in cold regions and affect their stability. Landslides occur continuously in the slip area of seasonally frozen soil area during the freezing period. The freeze-thaw action and the difference in the characteristics of the underlying surface of the slope are important factors inducing landslides. Taking Heifangtai slope in Gansu Province as an example, the freezing-thawing characteristics of the slope surfaces under different underlying surface conditions were analyzed by field monitoring. A thermohydromechanical coupling model was established to reconstruct the frozen stagnant water process of the Heifangtai landslide zone, and the impact of freeze-thaw action on the loess landslide zone was studied. The results show that differences in the underlying surface led to different freezing-thawing characteristics between the unsaturated area and the groundwater overflow zone. During the freezing period, the soil freezing depth was greater, and the freezing duration was longer in the unsaturated area. The frozen stagnant water effect of the Heifangtai loess landslide zone is obvious. The maximum difference in the groundwater level between February and August could reach nearly 1 m. Meanwhile, the frozen stagnant water process of the Heifangtai landslide zone has a slip-promoting action on the slope. The factor of safety declined during the freezing period and increased during the thawing period. It reached a minimum of 1.42 in February.

The stabilizing effect of high pore-fluid pressure along subduction megathrust faults: Evidence from friction experiments on accretionary sediments from the Nankai Trough

Pore-fluid pressure is an important parameter in controlling fault mechanics as it lowers the effective normal stress, allowing fault slip at lower shear stress. It is also thought to influence the nature of fault slip, particularly in subduction zones where areas of slow slip have been linked to regions of elevated pore-fluid pressure. Despite the importance of pore-fluid pressure on fault mechanics, its role on controlling fault stability, which is determined by the friction rate parameter (a−b), is poorly constrained, particularly for fault materials from subduction zones. In the winter of 2018-19 the accretionary complex overlying the Nankai Trough subduction zone (SW Japan) was drilled as part of Integrated Ocean Drilling Program (IODP) Expedition 358. Here we test the frictional stability of the accretionary sediments recovered during the expedition by performing a series of velocity-stepping experiments on powdered samples (to simulate fault gouge) while systematically varying the pore-fluid pressure and effective normal stress conditions. The Nankai gouges, despite only containing 25% phyllosilicates, are strongly rate-strengthening and exhibit negative values for the rate-and-state parameter b. We find that for experiments where the effective normal stress is held constant and the pore-fluid pressure is increased the Nankai gouges become more rate-strengthening, and thus more stable (an increase in (a−b) of ∼6 × 10−5 MPa−1 with increasing pore-pressure). In contrast, when the pore-fluid pressure is held constant and the effective normal stress is varied, there is minimal effect on the frictional stability of the gouge. The increase in frictional stability of the gouge at elevated pore-fluid pressure is caused by an evolution in the rate-and-state parameter b, which becomes more negative at high pore-fluid pressure. These results have important implications for understanding the nature of slip in subduction zones and suggest the stabilizing effect of pore-fluid pressure could promote slow slip or aseismic creep on areas of the subduction interface that might otherwise experience earthquake rupture.

Shallow Slow Earthquake Episodes Near the Trench Axis off Costa Rica

AbstractSlow earthquakes are mainly distributed in regions surrounding seismogenic zones along the plate boundaries of subduction zones. In the Central American subduction zone, large regular interplate earthquakes with magnitudes of 7–8 occur repeatedly around the Nicoya Peninsula, in Costa Rica, and a tsunami earthquake occurred off Nicaragua, just north of Costa Rica, in 1992. To clarify the spatial distribution of various slip behaviors at the plate boundary, we detected and located very low frequency earthquakes (VLFEs) around the Nicoya Peninsula using a grid‐search matched‐filter technique with synthetic templates based on a regional three‐dimensional model. VLFEs were active in September 2004 and August 2005, mainly near the trench axis, updip of the seismogenic zone. The distribution of VLFEs overlapped with large slip areas of slow slip events. Low frequency tremor signals were also found in high‐frequency seismogram envelopes within the same time windows as detected VLFEs; thus, we also investigated the energy rates of tremors accompanied by VLFEs. The range of scaled energy, which is the ratio of the seismic energy rate of a tremor to the seismic moment rate of accompanying VLFE and related to the rupture process of seismic phenomena, was 10−9–10−8. The along‐dip separation of shallow slow and large earthquakes and the range of the scaled energy off Costa Rica are similar to those in shallow slow earthquakes in Nankai, which shares a similar thermal structure along the shallow plate boundary.

Asymmetric Brittle Deformation at the Pāpaku Fault, Hikurangi Subduction Margin, NZ, IODP Expedition 375

AbstractQuantifying fault damage zones provides a window into stress distribution and rheology around faults. International Ocean Discovery Program (IODP) Expeditions 372/375 drilled an active thrust splay fault within the Hikurangi subduction margin. The fault, which is hosted in Pleistocene clastic sediments, is surrounded by brittle fractures and faults as well as ductile deformation features. We find that fracture density in the damage zone enveloping the fault is asymmetric, with the hanging wall showing greater overall fracture density and at greater distances from the fault than the footwall. Furthermore, the peak in fracture density occurs within an area of mesoscale folding and localized slip in the hanging wall rather than adjacent to the main fault zone. We attribute the asymmetry in damage to disparate deformation histories between the hanging wall and footwall, greater ductile deformation within the footwall, and/or dynamic stress asymmetry around a propagating rupture. Damage asymmetry is common at shallow depths in subduction zones and influences the mechanical and hydrological properties of the fault, such as channelized fluid flow and fault stability. Finally, we demonstrate that subduction zone faults show similar damage‐displacement scaling as continental faults.

Revisiting the Source Rupture Process of the Mainshock of the 2016 Kumamoto Earthquake and Implications for the Generation of Near-Fault Ground Motions and Forward-Directivity Pulse

ABSTRACT Strong near-fault ground motions associated with the MJMA 7.3 mainshock of the 2016 Kumamoto, central Kyushu, Japan, earthquake sequence have received attention by seismological and engineering communities. In this study, the kinematic source rupture process was reanalyzed based on an improved approach for the representation of source faults. The slips at densely distributed point sources were defined via the bilinear interpolation of those at surrounding control points. The result shows that the rupture started on the Hinagu fault with a small initial rupture and propagated beyond the junction to the Futagawa fault. The rupture on the Futagawa fault mainly propagated up and northeastward. A large slip area with a peak slip of 4.9 m and peak slip velocity of 3.1 m/s was detected at depths ranging from 3 to 15 km in the central part of the Futagawa fault. This asperity spatially coincides with a body with moderate-seismic velocity (VP∼6 km/s) and low-seismic attenuation. The slips on the Futagawa fault have significant normal-slip components, whereas the slip vectors of the Hinagu fault represent almost pure right-lateral strike slip. The shallower part of the fault segments in the western Aso caldera is characterized by relatively large normal slips. The estimated slip-velocity functions at shallower depths (<3 km) are almost temporally symmetric and relatively long. The shallower portion of the source fault significantly contributes to the velocity and displacement waveforms at near-fault sites. On the contrary, the slip-velocity functions at deeper depths (>3 km) are temporally asymmetric and have a sharp peak. The simulation of the ground-motion evolution suggests that the lateral flow in the Aso Valley was primarily triggered by the strong forward-directivity pulse generated from the asperity on the Futagawa fault.

Geodetic Coupling Models as Constraints on Stochastic Earthquake Ruptures: An Example Application to PTHA in Cascadia

AbstractCurrent stochastic rupture modeling techniques do not consider the potential influence of inter‐seismic coupling, a first‐order property of a megathrust, which can show correlation between areas of high coupling and areas of greater slip as seen in recent large ruptures globally. Therefore, it is reasonable to assume that it should be considered as prior information in rupture modeling. Here, we first present a mathematical formalism to introduce coupling models as prior information into stochastic rupture modeling. We then focus on how introducing slip deficit information into the stochastic rupture models influences slip distributions for the Cascadia subduction zone (CSZ). We compare rupture models created with two end member models of coupling, one with a shallow coupling and another with coupling deeper downdip. We also discuss the comparison to models created without assuming knowledge of the coupling distribution except for variation in the downdip limit of slip. Variations occur and correlate well with areas with the largest differences in slip deficit rates. The ruptures are then used for regional probabilistic tsunami hazard assessment. Overall, the tsunami amplitudes generated are much more hazardous in the northern extent of the CSZ where differences in coupling distribution are more prevalent. Models obtained from assuming a shallower downdip limit have tsunami amplitudes more similar to those from the geodetic coupling models. Although uncertainties are present in the accuracy of coupling, imposing either constraint created different hazard estimations when compared to those where no prior coupling information was used.

Seismic Reflection Images of Possible Mantle-Fluid Conduits and Basal Erosion in the 2011 Tohoku Earthquake Rupture Area

Multi-channel seismic reflection and sub-bottom profiling data reveal landward-dipping normal faults as potential conduits for mantle-derived fluids in the coseismic slip area of the 2011 Tohoku earthquake (Mw9.0). Normal faults below the helium isotope anomaly sites appear to develop through the forearc crust (i.e., the seafloor sedimentary section and Cretaceous basement) and to evolve to lower dip angles as extension progresses deeper, potentially extending down to the mantle wedge, despite their intermittently continuous reflections. The faults are characterized by high-amplitude, reverse-polarity reflections within the Cretaceous basement. Moreover, deep extension of the faults connecting to a low-velocity region spreading from the Cretaceous basement into the mantle wedge across the forearc Moho suggests that the faults are overpressured by local filling with mantle-derived fluids. The locations of the normal faults are roughly consistent with aftershocks of the 2011 Tohoku earthquake, which show normal-faulting focal mechanisms. The 2011 Tohoku mainshock and subsequent aftershocks can lead the pre-existing normal faults to be reactive and more permeable so that locally trapped mantle fluids can migrate up to the seafloor through fault fracture zones. The reactivated normal faults may be an indicator of shallow coseismic slip to the trench. Locally elevated fluid pressures can decrease the effective normal stress for the fault plane, facilitating easier slip along the fault and local tsunami. The landward-dipping normal faults developing from the seafloor down into the Cretaceous basement are predominant in the middle slope region of the forearc. A possible shear zone with high-amplitude, reverse-polarity reflections above the plate interface, which is almost localized to the middle slope region, suggests more intense basal erosion of the overlying plate in that region.

Surface and subsurface analysis based on the geological structure and electrical resistivity Data in Gorontalo Outer Ring Road (GORR), Huidu Utara

Gorontalo is one of the areas prone to earthquakes because Gorontalo has a geological structure, which is a fault. This fault has a northwest-southeast direction that cuts across the Gorontalo City area and crosses Lake Limboto. The research objective is to determine the direction of subsurface geological structures and analyze the impact of geological structures on the GORR development infrastructure. The research method is divided into several stages, namely, the preparation phase, the stage of data collection and the stage of data processing and analysis. The preparatory phase includes literature studies and regional geological studies. The next step is data collection in the field including lithology, geomorphology and structural data. And finally, data processing and analysis uses several classifications. Based on surface data, there are several types of lithology such as tuff, clay, and limestone which have started to decay. Geological structure in the form of fault / normal fault with northwest-southeast direction is also found in the study area. Based on subsurface data there are three types of layers namely clay sand, alluvial, and sandstone which are determined based on the classification of rock and mineral resistivity. Subsurface data also shows faults, in the same direction. And based on the vertical resistivity cross section shows the slip area seen from the resistivity value of the layer above it has a lower value than the layer below, it is very possible for landslides because the layer is more easily eroded and flowed, plus supported by a fairly steep field and rainfall in the GORR Region high enough.

Geoelectric Method Application of Dipole-Dipole Configuration for Identification of Landslide Prone Areas in Poka Village, Ambon

Landslide disaster is one type of disaster that often occurs in Indonesia which causes many casualties and loss of property. Ambon City is an area with high potential for landslides. This is because Ambon City is an area with steep slopes and high rainfall, so a study is needed to overcome this as a disaster mitigation effort. This study aims to determine the area of landslide slip and direction of landslides as a basis for identifying landslide-prone areas using the dipole-dipole configuration geoelectric method. This research was conducted in Poka Village, Ambon City, Maluku Province. Geoelectric measurements using the AGI Ministing tool with data retrieval as much as 5 tracks. Based on the results of the analysis, it was found that the soil layer was dominated by clay and limestone. The reconstruction results show that the topography of the area is a slope with a slope of 45o-80o, and the slip plane has each path with a resistivity contrast of ± 25-60 Ωm at a depth of 5-15 meters, while the direction of the landslide is directed to the southeast.

Rupture Models of Recent Mw>7 Thrust Earthquakes in the Guerrero–Oaxaca Region of the Mexico Subduction Zone Using Teleseismic Body Waves

Abstract We invert the teleseismic broadband (1–60 s period) ground-displacement body waveforms recorded for the 1995 Mw 7.3 Copala, the 1996 Mw 7.1 Oaxaca, the 2012 Mw 7.5 Ometepec, and the 2018 Mw 7.2 Pinotepa Nacional thrust earthquakes in the Guerrero–Oaxaca portion of the Mexico subduction zone to derive the best-fit rupture models using a sampling procedure in which input fault parameters are selected from a prescribed range of values. More than 400 independent inversions are performed for each event using random combinations of strike, rake, dip, and hypocenter depth. Waveform fits are observed to be relatively insensitive to variations in strike, rake, and focal depth but show a distinct dependence on fault dip. The lowest residuals are limited to a dip interval of about ±3°, indicating that a relatively precise estimate of the fault dip is necessary for the optimal derivation of slip models using teleseismic body waves. The best-fit teleseismic source models obtained for the four events show varying degrees of spatial detail, with the 2012 and 2018 earthquakes exhibiting more separated slip along the fault than has been observed in rupture models derived using frequency bands covering longer periods. Areas of high-interplate slip for the four events do not overlap, suggesting an adjoining pattern of asperity zones that is consistent with prior observations in northwest Mexico and in the New Britain region of the South Pacific. Additional investigation of this type of asperity interaction for recurrent events would be beneficial, given the implications for estimating the size and location of future large subduction earthquakes.

Variations in the Characteristic Amplitude of Tectonic Tremor Induced by Long‐Term Slow Slip Events

AbstractLong‐term slow slip events (L‐SSEs) often excite short‐term slow slips events (S‐SSEs) and tectonic tremor in the zone of episodic tremor and slip (ETS). However, the factors controlling the occurrence of primary versus excited tremor events remain unclear. To elucidate these factors, we analyzed tectonic tremor events in and around the Bungo Channel (Nankai subduction zone), where L‐SSEs are known to excite tremor and S‐SSEs in the ETS zone. We focused on the spatial distribution of the characteristic amplitude (CA) of tremor, determined from the duration‐amplitude distributions of tremor events, as an indicator of the properties of the tremor source. CAs are large in L‐SSE slip areas and small in adjacent areas. The difference between CA values during tremor‐excitation periods (L‐SSEs) and the intervening periods (ΔCA) is positive in the slip area, negative in adjacent areas, and tends toward zero in the far field. We suggest that the heterogeneous distributions of CA and ΔCA reflect the heterogeneous effective strengths of tremor patches, which might be related to petrological properties, and stress and pore‐fluid pressure variations induced by L‐SSEs, respectively. The upward migration of fluid from the ETS zone along the plate interface might modulate the effective stress and strength states of tremor patches during L‐SSEs.

Simulation of near-fault ground strains and rotations from actual strike-slip earthquakes: case studies of the 2004Mw 6.0 Parkfield, the 1979Mw 6.5 Imperial Valley and the 1999Mw 7.5 Izmit earthquakes

SUMMARYPrevious studies have demonstrated that finite-fault simulations of actual or hypothetical earthquakes using deterministic, physics-based simulation techniques constitute an effective tool for characterizing near-fault ground strains and rotations in the low-frequency range. The characteristics of these motions are further investigated in this study by performing forward ground-motion simulations of three well-documented strike-slip earthquakes (i.e. 2004 Mw 6.0 Parkfield, 1979 Mw 6.5 Imperial Valley and 1999 Mw 7.5 Izmit) using models of the seismic source and crustal structure available in the literature. Time histories of ground strains and rotations are numerically generated at near-fault stations and at a dense grid of observation points extending over the causative fault. This is achieved by finite differencing translational motions simulated at very closely spaced stations using a kinematic modelling approach. The simulation results show that the three strike-slip earthquakes produce large-amplitude pulse-like shear strain and torsion in the forward direction of rupture propagation. The time histories of specific components of displacement gradient, strain and rotation at near-fault stations can be estimated from those of ground velocities using a phase velocity, whereas peak ground torsions in the near-fault region can be reasonably estimated from peak horizontal ground velocities using a scaling factor. However, both the phase velocity and the scaling factor exhibit significant variability in the near-fault region of the considered earthquakes. The concept of isochrones is also utilized to associate fault rupture characteristics with near-fault ground strains and rotations. The results indicate that the seismic energy radiated from the high-isochrone-velocity region of the fault—which encompasses areas of large slip locally driven by high stress drop—arrives at a near-fault station in a short time interval that coincides with the time window of the large-amplitude pulse-like shear strain and torsion.

An Improved Quadtree Sampling Method for InSAR Seismic Deformation Inversion

With the development of interferometric synthetic aperture radar (InSAR), the seismic deformation observation density increases sharply. Data down-sampling can effectively reduce the observation density and the computational cost for subsequent researches. Considering the saliency of the deformation field, we introduce a saliency-based quadtree algorithm for down-sampling (SQS). Three simulation experiments show that SQS can effectively distinguish the near-field and far-field deformation, as well as reduce the amount of observation, while keeping the detailed information of the main deformation near the fault. SQS can avoid the interference of far-field local deformation better than the traditional quadtree sampling algorithm (QS), thus obtaining better inversion results. We took the Dingri earthquake on 20 March 2020 as a case study to verify the advantages of SQS in dealing with real earthquake deformation. We obtained the co-seismic deformation from the ascending and descending Sentinel-1 for the Dingri earthquake, using QS and SQS for sampling and inversion separately. The results show the advantages of SQS in data volume reduction, observation distribution, anti-interference of local deformation, and inversion accuracy. Our preferred solution based on SQS shows that the Dingri earthquake was caused by a normal fault slip. The main slip area is 2–5.5 km deep with a maximum slip of 0.68 m. The estimated geodetic moment is 3.14 × 1017 Nm, corresponding to a magnitude of Mw5.63.

Nonlinear Interface Reduction for Time-Domain Analysis of Hurty/Craig-Bampton Superelements with Frictional Contact

Virtual prototyping in engineering design rely on modern numerical models of contacting structures with accurate resolution of interface mechanics, which strongly affect the system-level stiffness and energy dissipation due to frictional losses. High-fidelity modeling within the localized interfaces is required to resolve local quantities of interest that may drive design decisions. The high-resolution finite element meshes necessary to resolve inter-component stresses tend to be computationally expensive, particularly when the analyst is interested in response time histories. The Hurty/Craig-Bampton (HCB) transformation is a widely used method in structural dynamics for reducing the interior portion of a finite element model while having the ability to retain all nonlinear contact degrees of freedom (DOF) in physical coordinates. These models may still require many DOF to adequately resolve the kinematics of the interface, leading to inadequate reduction and computational savings. This study proposes a novel interface reduction method to overcome these challenges by means of system-level characteristic constraint (SCC) modes and properly orthogonal interface modal derivatives (POIMDs) for transient dynamic analyses. Both SCC modes and POIMDs are computed using the reduced HCB mass and stiffness matrices, which can be directly computed from many commercial finite element analysis software. Comparison of time history responses to an impulse-type load in a mechanical beam assembly indicate that the interface-reduced model correlates well with the HCB truth model. Localized features like slip and contact area are well-represented in the time domain when the beam assembly is loaded with a broadband excitation. The proposed method also yields reduced-order models with greater critical timestep lengths for explicit integration schemes.

Confirmation and Characterization of the Rupture Model of the 2017 Ms 7.0 Jiuzhaigou, China, Earthquake

AbstractOn 8 August 2017, an Ms 7.0 earthquake struck the Jiuzhaigou town, Sichuan Province, China, rupturing an unmapped fault, which is adjacent to the Maqu seismic gap in the Min Shan uplift zone in the easternmost part of the Bayan Har block. Having summarized the previous studies on the source of this earthquake, we confirmed the rupture model by jointly inverting the teleseismic P-wave and SH-wave data, Interferometric Synthetic Aperture Radar line-of-sight displacement data, and the near-field seismic and strong-motion data, a most complete dataset until now. The confirmation showed that a scalar seismic moment of 6.6×1018 N·m was released (corresponding to a moment magnitude of Mw 6.5), and 95% of the release occurred in the first 10 s. The slip area was composed of two asperities, with a horizontal extension of ∼20 km and a depth range of ∼2–15 km. A bilateral extending occurred at shallow depths, but the rupturing upward from deep depth dominated in the early time. The rupture process was found generally featuring the slip-pulse mode, which was related to the weak prestress condition. The aftershocks almost took place in gaps of the mainshock slip because of the coulomb stress change. Combining the aftershock relocations, aftershock focal mechanism solutions, and our confirmed rupture model, we suggest that the seismogenic fault was a northward extension of the mapped Huya fault. The occurrence of this earthquake made the Maqu seismic gap at a higher level of seismic risk, in addition to the moderate to high strain accumulation on the easternmost tip of the Kunlun fault system and the weak lower crust below.

Temporal Seismic Velocity Variations: Recovery Following From the 2019 Mw 7.1 Ridgecrest, California Earthquake

AbstractWe investigated seismic velocity changes (dv/v) associated with the 2019 Ridgecrest earthquake sequence with high‐frequency autocorrelations of ambient seismic noise data. Daily autocorrelation functions were computed for the entirety of 2019 and the first quarter of 2020 for broadband stations within the region, including the temporary broadband stations installed during the aftershock deployment. Travel time shifts in the daily autocorrelation functions, relative to the mean autocorrelation waveform, were computed to produce dv/v time series, which are sensitive to the evolving material properties of the shallow crust surrounding the Ridgecrest fault zone (RFZ). A short‐term velocity drop follows the Mw 7.1 earthquake at stations in the vicinity of the rupture surface, while those greater than 50 km away showed no such drop. The maximum, absolute changes in seismic velocity are proportional to the logarithm of distance from the fault rupture and to the peak dynamic strain experienced during the earthquake. Near the areas of the highest coseismic slip within the RFZ, seismic velocities recovered over 3 months. However, in the vicinity of the nearby Garlock fault, where triggered slip manifested, and north of the RFZ, seismic velocities recovered within a month. We interpret the seismic velocity changes and their recovery to be largely due to changes in the physical properties of the shallow crust, such as fault zone damage recovery caused by the earthquake rupture process and in response to the large dynamic stresses of passing seismic waves from the mainshock.