Slip Area Research Articles

Seismic Induced Ground Deformation and Ionospheric Perturbations of the 29 July 2021, Mw 8.2 Chignik Earthquake, Alaska

AbstractThe subsurface, surface, and ionospheric characteristics associated with the 29 July 2021 Mw 8.2 Chignik Earthquake are studied in detail using continuous Global Positioning System (cGPS) data over Alaska. The cGPS‐inverted coseismic displacements demonstrate that the slip is distributed along the rupture area northeast of the epicenter with a maximum coseismic slip of ∼3.85 m occurring at a depth of ∼24.25 km. The vertical surface displacement estimated from the coseismic slip exhibits a similar deformation pattern with a maximum uplift of ∼1.0 m over the highly slip area. The ionospheric electron density perturbations associated with the Chignik earthquake were investigated using cGPS‐derived Total Electron Content (TEC) data. Unlike the northeast‐directed coseismic rupture and surface uplift, the ionospheric imprints of this event are more dominant southwest of the epicenter. This study reveals that the Earth's magnetic field and the ionospheric background electron density significantly controlled the TEC perturbation orientation and amplitudes rather than the rupture propagation and coseismic uplift pattern.

Analytical study for prediction of stress distribution on orthodontic archwire considering short-term stress loss

This article proposes a method to predict the stress distributions on orthodontic archwires by considering the short-term stress losses. First, finite element (FE) analysis and numerical analysis using stress-loss formulations were performed. The FE models of the upper teeth and archwire were generated, and the initial stresses along the archwire were predicted from the FE model. The initial stresses on the wire were released in a relatively short amount of time due to shortening of the teeth, and slip and friction between the wire and brackets. Therefore, the formulations for the short-term stress losses were adopted from prestressed concrete design techniques and used to calculate the wire stress releases. To validate, loading tests and image processing were conducted, and the stresses were calculated from the deformations and curvatures of the loaded wire images. FE analyses without considering the stress losses predicted the stress distributions are unrealistically large; hence, including losses from elastic shortening, anchorage slip, and friction area could reduce the initial stresses by 16–34%. Comparing the average wire stress from FE analysis with image processing, a difference of only 0.82% was noted, which validates the method for predicting stress distribution using FE analysis and the method for stress loss calculations.

Continuous estimation of coseismic and early postseismic slip phenomena via the GNSS carrier phase to fault slip approach: a case study of the 2011 Tohoku-Oki sequence

The transition process from coseismic to early postseismic phenomena within a half-day remains a significant topic for understanding the slip budget and friction properties of the fault. However, the investigation of this phase has undergone limited advancement. This is mainly due to the lack of precision pertaining to the Global Navigation Satellite System (GNSS) analysis caused by difficulty of separation between fault slip and other unknown parameters such as tropospheric delay. Therefore, we propose an alternative approach (phase-to-slip; PTS) that detects fault slip directly from GNSS carrier phase variation without conventional positioning. Since the PTS simultaneously estimates fault slip and other unknowns, we can quantitatively evaluate their separation accuracy and contribution in the estimation. This study attempts to continuously estimate the coseismic and early postseismic slip of the 2011 Tohoku-Oki sequence using the PTS method. We analyzed 1-Hz carrier phase data for approximately 2 h before and after the mainshock origin (2011/03/11/05:46UTC). As a result, we successfully obtained the coseismic slip of the Mw9.0 mainshock and two major aftershocks in the off-Ibaraki (Mw7.8) and off Iwate (Mw7.4) regions. For all three events, the estimated slip distribution, equivalent moment magnitude, and calculated displacement field well agreed with those from the conventional positioning. Additionally, our results suggest postseismic slip mainly in the downdip area adjacent to the mainshock rupture. We obtained three major slip areas around the downdip region near Aomori, Iwate, and Miyagi. The estimated slip amount reaches approximately 0.1–0.2 m in 34 min immediately after the mainshock. The equivalent seismic moment of the slip areas near Iwate and Miyagi were approximately Mw7.4. This amount is similar or slightly greater than the estimations based on conventional positioning. Significant overlap is observed in the locations of the slip areas. In this manner, PTS continuously detected a series of coseismic and early postseismic slips with timescale ranging from a few minutes to an hour. Our results demonstrate the capability of the PTS method for broadband fault slip monitoring and its potential contribution to the investigation of early postseismic phenomena.

Temperature distribution for interplate seismic events in the southcentral Alaska subduction zone based on 3-D thermomechanical modeling

In the southcentral Alaska subduction zone, the Pacific plate and an oceanic plateau, known as the Yakutat terrane, are subducting at a convergence rate of ∼4.7 cm/yr in the direction of N21.5°W with respect to the current North American plate. We constructed a 3-D thermomechanical model to simulate the simultaneous subduction of the Pacific plate and Yakutat terrane. In the numerical simulation, the oceanic plate subducts along a 3-D geometry model obtained from the seismic data, with a spatiotemporally changing convergence rate that was provided based on the past plate motion model. Under these conditions, we obtained the time-dependent temperature and mantle flow velocity fields from 18 Ma to the present. As a result, we discovered that the interplate temperature for the source region of the 1964 Alaska earthquake with a coseismic slip larger than 2 m was estimated to be 155–323 °C at depths of approximately 10–20 km. We also estimated the temperature for the slip area with cumulative slip larger than 5 cm of the northeastern 2009–2013 long-term slow slip event (L-SSE) and the southwestern 2010–2012 L-SSE to be 337–570 °C and 300–381 °C, respectively. In the southcentral Alaska subduction zone, the temperature at the boundary between the downdip of the seismogenic zone and the updip of the L-SSEs is estimated to be approximately 350 °C, which is consistent with the temperature at the transition from frictional instability to stability at the plate boundary proposed in previous studies.

Poiseuille flow of a Bingham fluid in a channel with a superhydrophobic groovy wall

Plane Poiseuille flow of a Bingham fluid in a channel armed with a superhydrophobic (SH) lower wall is analysed via a semi-analytical model, accompanied by complementary direct numerical simulations (DNS). The SH surface represents a groovy structure with air trapped inside its cavities. Therefore, the fluid adjacent to the wall undergoes stick–slip conditions. The model is developed based on introducing infinitesimal wall-induced perturbations into the motion equations, followed by Fourier series expansions, and solving the resulting equations as a boundary value problem. The Navier slip law accounts for the slip at the liquid/air interface (assuming the Cassie state). The presented analysis is fairly comprehensive, covering the creeping and inertial regimes for thick channels (via the semi-analytical and DNS solutions). The main dimensionless numbers are the Reynolds ( $Re$ ), Bingham ( $Bi$ ) and slip ( $b$ ) numbers, as well as the groove periodicity length ( $\ell$ ) and the slip area fraction ( $\varphi$ ). By increasing $Bi$ , the perturbation and slip velocity fields grow. As $Re$ increases, the perturbation and slip velocity fields become asymmetric. For certain flow parameters, an unyielded plug zone may appear on the SH wall liquid/air interface, while its formation is accelerated by inertial effects. The results classify the regimes of creeping and inertial flows via predicting the onset of the unyielded plug zone formation at the SH wall.

Large extensional earthquakes push-up terrific amount of fluids

How large earthquakes are triggered is a key question in Earth science, and the role played by fluid pressure seems to be crucial. Nevertheless, evaluation of involved fluid volumes is seldom investigated, if not unaccounted for. Moreover, fluid flow along fault zones is a driving factor for seismicity migration, episodic heat and chemical transport. Here we show that time repeated (4D) seismic tomography resolves changes of Vp and Vp/Vs during the Mw6.2 2009 L’Aquila normal faulting sequence, that indicate a post-failure fluid migration from hypocentral depths to the surface, with a volume estimated between 5 and 100 × 106 m3 rising at rates up to 100 m/day. This amount inferred by tomograms is surprisingly consistent with the about 50 × 106 m3 surplus water volume additionally measured at spring discharge, spread in time and space along the 700 km2-wide regional carbonate fractured aquifer. Fluids were pushed-up within a huge volume across the fault and expelled from the area of large coseismic slip. Such quantities of fluids liberated during earthquakes add unprecedented constraints to the discussion on the role of fluids during and possibly before earthquake, as well as to the potential impact on the pristine high-quality drinkable groundwater, possibly affecting the biodiversity of groundwater dependent ecosystems too.

Simulation of great earthquakes along the Nankai Trough: reproduction of event history, slip areas of the Showa Tonankai and Nankai earthquakes, heterogeneous slip-deficit rates, and long-term slow slip events

Great earthquakes have occurred repeatedly along the Nankai Trough, but only for recent events are details known, such as rupture areas and time lags between paired events. It is meaningful for disaster prevention to consider in advance what kind of phenomena are likely after an earthquake that partially ruptures a seismogenic zone in this region. We constructed three-dimensional simulations to partially reproduce the spatial and temporal distribution of seismic or aseismic slip and the heterogeneous distribution of the slip-deficit rate beneath the seafloor on the plate boundary along the Nankai Trough. We found it necessary to assign spatial heterogeneity to two friction parameters, the effective normal stress and characteristic distance, based on a hierarchical asperity model. Our model produced many event pairs consisting of events east and west of Cape Shiono (Tokai/Tonankai and Nankai events, respectively), nearly all of them either simultaneous or separated by less than 3 years. The rupture areas of these event pairs were rich in variation, and even when the rupture areas were the same, the magnitudes and maximum displacements differed. The Tonankai earthquakes rarely occurred alone. Our model also simulated recurring long-term slow slip events in deeper parts of the seismogenic zone, and these events were caused by stress disturbance and heterogeneous stress distributions associated with non-ruptured portions of the seismogenic zone.Graphical

Stress Drop Estimates for Small to Moderate Earthquakes in Tohoku, Japan Considering Rupture Geometry, Speed, and Directivity

AbstractThis study develops a spectral ratio method to estimate the earthquake stress drop considering the rupture geometry, speed, and directivity. This spectral ratio method is applied to Mw 3.3–5.9 earthquakes in Fukushima and Ibaraki, Japan. A rectangular source model with a square rupture front and uniform slip distribution is used to fit spectral ratios stacked by station and wave type for multiple empirical Green's functions, and estimate the finite source properties. Comparing the rupture areas obtained by the spectral ratio method with the slip inversion results shows that our results from the spectral ratio method are associated with a localized area of large slip rather than the overall rupture area. Hence, the rupture area obtained from this spectral ratio method is inappropriate to calculate the average static stress drop. This study proposes a procedure to estimate the average stress drop for the entire rupture area and one for the localized area with large slip, using a source model with a single asperity and heterogeneous stress drop distribution. As a result, we obtained average static stress drops of 0.42–40.2 MPa with a median of 3.7 MPa. The local stress drop is 5.7 times larger than the average static stress drop. This study suggests that a compact area compared to the overall rupture area mainly controls the shape of a broadband seismic spectrum. Thus, we should consider the source heterogeneity in addition to the rupture geometry, speed, and directivity when estimating the stress drops from seismic spectra.

The 2021 Mw7.0 and Mw6.7 Miyagi‐Oki Earthquakes Nucleated in a Deep Seismic/Aseismic Transition Zone: Possible Effects of Transient Instability Due To the 2011 Tohoku Earthquake

AbstractIn March and May 2021, Mw7.0 and Mw6.7, respectively, deep interplate earthquakes occurred off Miyagi, Japan, near the downdip edge of the rupture area of the 2011 M9 Tohoku earthquake. We study the two Mw ∼ 7 earthquakes to investigate how a great (Mw ∼ 9) earthquake cycle impacts the generation of smaller (Mw7‐8) earthquakes in the deep seismic/aseismic transition zone. Our hypocenter relocation results show that many repeating earthquakes have emerged in the downdip area after the Tohoku earthquake. The March Mw7.0 event was initiated in the slip area of an emerging interplate repeating earthquake sequence, suggesting that the nucleation of the Mw7.0 event occurred in a conditionally stable area where only aseismic slip occurred before the Tohoku earthquake. Downdip high‐rate creep in the postseismic period is a probable reason for the temporal aseismic‐to‐seismic transition that allowed the occurrence of repeating earthquakes and the rupture initiation of the Mw7.0 earthquake. The May Mw6.7 earthquake originated in an area where earthquake activity was high locally, both before and after the Tohoku earthquake, and shear stress increased after the March event. This suggests that both frictional properties and shear stress change contributed to the rupture initiation. The slip inversion results indicate that these two Mw ∼ 7 earthquakes ruptured the western part of the 1978 Mw7.6 Miyagi‐Oki earthquake source area and loaded the eastern part. Continued monitoring of seismicity patterns, including possible updip expansion of the interplate seismicity, is essential to examine how strain energy, plate‐locking state, and creep evolve during the Mw9.0 earthquake cycle.

Rupture process of the 2020 Mw = 6.9 Samos, Greece earthquake on a segmented fault system constrained from seismic, geodetic, and tsunami observations

The seismic, geodetic, and tsunami observations are utilized to investigate the October 30th 2020 Samos, Greece earthquake. We adopt back projection (BP) and multi-point source (MPS) techniques to determine the rupture directivity and focal mechanism change of this event. Both methods reveal a unilateral rupture propagation to the west of the epicenter, and also resolve a changed focal mechanism. We use a two-segment-faults geometry to parameterize the fault model with strikes at 283° for the east segment and 250° for the west respectively, and conduct a finite fault inversion (FFI) combining seismic and geodetic observations. The kinematics results indicate the whole rupture process lasts about 25 s, yielding a total seismic moment of 3.16×1019 Nm (Mw = 6.9) with a peak moment rate reaching 3.1×1018 Nm/s around 10 s. The rupture is composed of two asperities separated by the junction of two fault planes. The main slip area, with maximum amplitude reaching three meters, distributes at a shallow depth and displays a complementary pattern with aftershocks. The slip in the first six seconds is dominated by a pure normal faulting mechanism, while the following rupture includes an additional strike-slip component. The change of focal mechanism reflects the tectonic transition from dilatation to lateral shearing, which is also evident in the aftershock mechanisms. The synthetic tsunami waves also well fit three tidal gauge observations. The coseismic Coulomb stress is calculated to analyze the relationship between the mainshock and aftershock evolution. The mechanism combination of two rupture epochs reflects the combination of shear and dilatational stress status and complicated fault system of the Samos source area.

Seismicity distribution in the Tonankai and Nankai seismogenic zones and its spatiotemporal relationship with interplate coupling and slow earthquakes

We conducted seismic tomography to estimate the seismic velocity structure and to evaluate the spatiotemporal distribution of interplate earthquakes of the Kii Peninsula, central Honshu, Japan, where the Tonankai and Nankai megathrusts are located. Microearthquakes were quantitatively detected by using the data from a cable-type seafloor seismic observation network, completed in 2015. Our velocity model was consistent with the previous 2-D active-source surveys, which reported the areal extent of key structures: a high-velocity zone beneath Cape Shionomisaki, a subducted seamount off Cape Muroto, and the subducted Paleo-Zenith Ridge. The absence of any other subducted seamount with the same or larger spatial scale, than the identified key structures, was confirmed. Our velocity model also revealed that there was not a simple relationship between areas of large coseismic slip or strong interplate coupling and areas of high velocity in the overriding plate. Relocated hypocenters widely ranged from the upper plate to within the slab, while the most active region was attributed to the oceanic crust in the aftershock region of 2004 off-Kii earthquake. Compared with the results from the land-based observation network, the accuracy of the focal depth estimation was substantially improved. Furthermore, we identified the seismic activity in the vicinity of the plate boundary and determined 14 locations for interplate seismicity areas. They were primarily distributed in the range of seismogenic zone temperature (150–350 °C) along the plate boundary and were located outside of the strong interplate coupling zone. Several active areas of interplate earthquakes exhibited clustered activity during the periods of slow-slip events, observed and accompanied with shallow very-low-frequency earthquakes. Thus, regular interplate microearthquakes became active at the plate boundary in the conjunction with slow slip. In summary, as regular earthquakes provide a more accurate source location than slow earthquakes and can detect events of smaller magnitude, monitoring such interplate earthquakes may reveal spatiotemporal variations in the stick–slip conditions on the plate boundary.

Icequake‐Magnitude Scaling Relationship Along a Rift Within the Ross Ice Shelf, Antarctica

AbstractFractures within ice shelves are zones of weakness, which can deform on timescales from seconds to decades. Icequakes produced during the fracturing process show a higher b‐value in the Gutenberg‐Richter scaling relationship than continental earthquakes. We investigate icequakes on the east side of rift WR4 in the Ross Ice Shelf, Antarctica. Our model suggests a maximum icequake slip depth that is ∼7.8 m below the rift mélange, where the slip area can only grow laterally along the fracture planes. We propose ductile deformation below this depth, potentially due to the saturation of unfrozen water. We use remote sensing and geodetic tools to quantify surface movement on different timescales and find that the majority of icequakes occur during falling tides. The total seismic moment is <1% of the estimated geodetic moment during a tidal cycle. This study demonstrates the feasibility of using seismology and geodesy to investigate ice rift zone rheology.

Effects of local microstructure on crack initiation in super martensitic stainless steel under very-high-cycle fatigue

Super martensitic stainless steel is known for its outstanding mechanical properties, which lead to its widely application in structural component bearing cyclic loadings. This study investigates the effect of local microstructure on the crack initiation behavior of a super martensitic stainless steel in the very high cycle fatigue (VHCF) regime. Results show that the non-inclusion-induced crack initiation is the dominating pattern of VHCF failure. Fatigue cracks initiate from the boundaries of the martensite lath due to the mode II cracking process, resulting in the formation of a slip area located at the core of the fine granular area (FGA). The size and the orientation of the martensite lath determine the morphology of the slip area but exert limited influence on the formation of the FGA at the fracture surface. These results may effectively improve the service safety and reliability of super martensitic stainless steel.

High-Frequency Rupture Processes of the 2014 Mw 8.2 Iquique and 2015 Mw 8.3 Illapel, Chile, Earthquakes Determined from Strong-Motion Recordings

ABSTRACT Strong-motion recordings of the 2014 Mw 8.2 Iquique and 2015 Mw 8.3 Illapel, Chile, earthquakes were analyzed to determine rupture propagation and the location, timing, and strength of subevents that produce most of the high-frequency (≥1 Hz) ground motions. A moving window,cross-correlation analysis of recordings from a local dense array, band-pass filtered at 1 Hz, directly shows that the Iquique earthquake ruptured to the southeast over a distance of about 60 km. Array analysis of lower frequency energy (0.03–0.1 Hz) indicates that it occurred updip of the high-frequency rupture. A methodology was developed for inverting the envelopes of acceleration records (1–5 Hz) to map high-frequency source factors on the rupture zone and was applied to the two earthquakes. Waveforms of Mw 6 earthquakes were used as empirical Green’s functions in the inversions. High-frequency subevents within the two Mw 8 earthquakes were located at depths ranging from 25 to 55 km and mostly occurred downdip of the peak slip of these earthquakes. Fourier spectral ratios of the Iquique mainshock with respect to Mw 5–6 aftershocks were fit to determine their stress drops. The stress drops were roughly constant from Mw 5 to 8 at 10–20 MPa. A compound rupture model is described in which subevents occur in areas of spatially heterogeneous strength and stress on the rupture, and produce the high-frequency radiated energy of the overall earthquake, but are not located in the areas of peak slip. The stress drop of the overall earthquake is shown to equal the root mean square stress drop of subevents averaged over the rupture area.

Impact of Ambiguity of Physical Properties of Three-Dimensional Crustal Structure Model on Coseismic Slip and Interseismic Slip Deficit in the Nankai Trough Region

Since huge earthquakes are expected along plate subduction zones such as the Japan Trench and Nankai Trough, the estimation of coseismic slip and interseismic slip deficit is essential for immediate response and preliminary measures to reduce damage. Recently, analysis considering the complex topography and underground structure of the plate subduction zone has been performed for improving the estimation performance. However, the three-dimensional (3D) crustal structural model needs to be improved continuously. In this paper, we obtained Green’s functions for 3D crustal structural models with ambiguity by 3D crustal deformation analysis, and the coseismic slip and interseismic slip deficit were estimated. Here we enabled the calculation of many Green’s functions with different physical properties of the 3D crustal structure by utilizing a GPU-based 3D crustal deformation analysis method that significantly reduces the analysis cost. The physical properties on the upper plate’s side, which are located above the plate boundary fault, were changed. We found no significant difference in the estimation performance, except for the upper crust, which most of the fault slip area is in contact with, in the case of coseismic slip estimation. In contrast, the coseismic slip estimation when the properties of the upper crust was changed had a significant error, and a negative slip was estimated at the deep part of the plate boundary where no slip was originally given.

Effect of presowing seed treatments on teak (Tectona grandis L. F) drupes dormancy and germination

Poor seed germination is a major issue in teak (Tectona grandis) propagation. Teak seed dormancy is thought to be the reason for delayed germination. So far, specific dormancy mechanisms have not yet been identified. In order to study the influence of presowing treatments on germination, seedling vigour, and biochemical attributes of fresh teak drupes collected from the seed production area of Top Slip in Tamil Nadu. The collected drupes were subjected to different presowing treatments viz., T1 - control, T2 - soaking and drying for 6 days, T3 – T18 (soaking and drying for 5 days + soaking in different concentrations of thiourea, potassium nitrate, hydrogen peroxide and calcium oxychloride for 12 hours). Treated drupes were placed for germination in earthen pots and kept in open sunlight. In parallel, true seeds extracted from untreated drupes were also subjected to germination under in vitro conditions as a check. A higher percentage of germination (40%) was recorded in true seeds under in vitro conditions when compared to the treated and untreated drupes under in vivo conditions. Among the treated drupes sown under in vivo conditions, the drupes given soaking + drying for 5 days + soaking in 2% calcium oxychloride (CaOCl2) recorded higher germination (17.16) with better seedling vigour. Analysis of teak true seeds and mesocarp extract in high-performance liquid chromatography showed that gibberellic acid was found only in true seeds, whereas the other compounds, viz., indole-3-acetic acid, indole butyric acid, abscisic acid and coumarin, were not present in the true seed or mesocarp.

Citizen seismology helps decipher the 2021 Haiti earthquake.

On 14 August 2021, the moment magnitude (Mw) 7.2 Nippes earthquake in Haiti occurred within the same fault zone as its devastating 2010 Mw 7.0 predecessor, but struck the country when field access was limited by insecurity and conventional seismometers from the national network were inoperative. A network of citizen seismometers installed in 2019 provided near-field data critical to rapidly understand the mechanism of the mainshock and monitor its aftershock sequence. Their real-time data defined two aftershock clusters that coincide with two areas of coseismic slip derived from inversions of conventional seismological and geodetic data. Machine learning applied to data from the citizen seismometer closest to the mainshock allows us to forecast aftershocks as accurately as with the network-derived catalog. This shows the utility of citizen science contributing to our understanding of a major earthquake.

Quantifying the Sensitivity of Microearthquake Slip Inversions to Station Distribution Using a Dense Nodal Array

ABSTRACT To investigate the sensitivity of slip inversions to station distribution and choice of empirical Green’s function (EGF), we examine three microearthquakes that occurred within the high-density LArge-n Seismic Survey in Oklahoma (LASSO) nodal seismic array. The LASSO array’s dense distribution of 1825 geophones provides an exceptional level of spatial and azimuthal coverage, allowing for more accurate inversions of slip than are possible with typical station distributions. The highly accurate slip inversions, in turn, allow for the exploration of the sensitivity of slip inversions to station distribution and parameter choices. We examine the effects of these choices using three well-recorded strike-slip microearthquakes (ML 1.7, 2.3, and 2.7) using an EGF method. From this analysis and the systematic testing of varied network arrangements, we find that station distributions that have uniform coverage of azimuth and distance can retrieve the overall pattern of slip, but the estimated amplitude of slip can vary by 30% for high-slip regions due to small variations in station location. In addition, we find that the distance range that accurately resolves the overall pattern of slip is the one that contains the takeoff angles of 45°–65°. Concerning azimuthal coverage, a network with >270° performs similarly to having complete coverage. The choice of EGF can shift the location of resolved areas of slip and their amplitude, depending on its similarity in location and radiation pattern to the target earthquake.

Coseismic and Postseismic Fault Kinematics of the July 22, 2020, Nima (Tibet) Ms6.6 Earthquake: Implications of the Forming Mechanism of the Active N‐S‐Trending Grabens in Qiangtang, Tibet

AbstractThe N‐S‐trending grabens, the most prominent active structures in the Tibetan plateau, contain important information about the evolution and deformation mechanism of the plateau. The Ms6.6 earthquake that occurred in Nima, Qiangtang on July 22, 2020, provides an opportunity to investigate the kinematics of the grabens. Here, we use field survey and interferometric synthetic aperture radar to study the structural style, coseismic and postseismic deformation, fault slip, and stress changes of the Nima earthquake. The N‐S‐trending Qomo Ri graben (QRG) and the normal faults on the east and west sides are kinematically correlated with the NE‐trending sinistral Jiangaizangbu River and West Yibug Caka faults. The QRG is characterized by an extensional strike‐slip duplex and negative flower structure. The maximum coseismic deformation of the Nima earthquake is 29.4 cm in the line‐of‐sight direction observed by Sentinel‐1 ascending images. The coseismic slip model demonstrates that the NE20–30°‐striking fault caused the Nima earthquake has a maximum slip of 1.39 m and a main slip area at 4–12 km depth. The seismological fault may transit from a moderately dipping normal fault near the surface to a steeper strike‐slip fault at depth. Obvious postseismic deformation was observed in the stress‐enhancement area. The afterslip model shows that the mainshock fault is correlated with parallel normal faults to its west. We infer that the QRG was formed by local E‐W‐trending extension at the joints of the left‐stepping sinistral fault system, and the active normal faulting in the Qiangtang block favors stress localization.

Predictive Simulation for Surface Fault Occurrence Using High-Performance Computing

Numerical simulations based on continuum mechanics are promising methods for the estimation of surface fault displacements. We developed a parallel finite element method program to perform such simulations and applied the program to reproduce the 2016 Kumamoto earthquake, where surface rupture was observed. We constructed an analysis model of the 5 × 5 × 1 km domain, including primary and secondary faults, and inputted the slip distribution of the primary fault, which was obtained through inversion analysis and the elastic theory of dislocation. The simulated slips on the surface were in good agreement with the observations. We then conducted a predictive simulation by inputting the slip distributions of the primary fault, which were determined using a strong ground motion prediction method for an earthquake with a specified source fault. In this simulation, no surface slip was induced in the sub-faults. A large surface slip area must be established near a sub-fault to induce the occurrence of a slip on the surface.