Deep Slip Research Articles

Scattered M3–4 Slip Bursts Within Creep Events on the San Andreas Fault

AbstractScientists have observed the surface expression of creep events along the San Andreas Fault since the 1960s. However, the evolution of slip at depth has been examined relatively little. So here we probe that deep slip by analyzing strain observations just before and during hours‐ to day‐long creep events at the northern end of the creeping section of the San Andreas Fault. We identify 71 strain offsets that are likely produced by few‐hour bursts of slip at depth. Then, we grid search to determine the location, depth, and magnitude of these slip bursts. We find that the slip bursts occur at a range of along‐strike locations, from 0 to 7 km away from the surface slip observations. Slip occurs at depths from 0 to 10 km; 42%–55% of the bursts are likely below 4 km depth. The bursts typically have moments equivalent to Mw 3.2–4.1 earthquakes. These findings suggest that creep events are not just small shallow events; they are relatively large events that nucleate at significant depths and could play a prominent role in the slip dynamics of the creeping section.

DIFFERENT-SCALE HETEROGENEITIES IN SEGMENTS OF SEISMOGENIC FAULTS AND THEIR INFLUENCE ON SLIP MODES

The paper presents some multidisciplinary research results on the structure of slip surfaces in segmented sections of tectonic faults in the Baikal region and Mongolia. The properties of subsurface (modern) and deep slip planes that came to the earth’s surface as a result of many-kilometer denudation in the upper part of the earth’s crust are studied at different levels-from macroscale to nanocrystals. Other types of heterogeneities characterizing the structure of fault slip zones are also considered. The presented data indicate a heterogeneous structure of tectonic faults. Their slip zones show both low friction in sections where strong mineral phases are replaced by weak minerals, and potentially unstable patches with high frictional resistance. The results obtained in a comprehensive study of geological conditions, under which different-scale heterogeneities emerge in exhumed fault segments, should be taken into account when developing rock mass models suitable for numerical simulation of earthquake preparation processes at the micro-, mesoand macroscales.

A New Method to Invert for Interseismic Deep Slip Along Closely Spaced Faults Using Surface Velocities and Subsurface Stressing‐Rate Tensors

AbstractInversions of interseismic geodetic surface velocities often cannot uniquely resolve the three‐dimensional slip‐rate distribution along closely spaced faults. Microseismic focal mechanisms reveal stress information at depth and may provide additional constraints for inversions that estimate slip rates. Here, we present a new inverse approach that utilizes both surface velocities and subsurface stressing‐rate tensors to constrain interseismic slip rates and activity of closely spaced faults. We assess the ability of the inverse approach to recover slip rate distributions from stressing‐rate tensors and surface velocities generated by two forward models: (a) a single strike‐slip fault model and (b) a complex southern San Andreas fault system (SAFS) model. The single fault model inversions reveal that a sparse array of regularly spaced stressing‐rate tensors can recover the forward model slip distribution better than surface velocity inversions alone. Because focal mechanism inversions currently provide normalized deviatoric stress tensors, we perform inversions for slip rate using full, deviatoric or normalized deviatoric forward‐model‐generated stressing‐rate tensors to assess the impact of removing stress magnitude from the constraining data. All the inversions, except for those that use normalized deviatoric stressing‐rate tensors, recover the forward model slip‐rate distribution well, even for the SAFS model. Jointly inverting stressing rate and velocity data best recovers the forward model slip‐rate distribution and may improve estimates of interseismic deep slip rates in regions of complex faulting, such as the southern SAFS; however, successful inversions of crustal data will require methods to estimate stressing‐rate magnitudes.

Understanding the Rupture Kinematics and Slip Model of the 2021 Mw 7.4 Maduo Earthquake: A Bilateral Event on Bifurcating Faults

AbstractWe image the rupture process of the 2021 Mw 7.4 Maduo, Tibet earthquake using slowness‐enhanced back‐projection (BP) and joint finite fault inversion, which combines teleseismic broadband body waves, long‐period (166–333 s) seismic waves, and 3D ground displacements from radar satellites. The results reveal a left‐lateral strike‐slip rupture, propagating bilaterally on a 160 km long north‐dipping sub‐vertical fault system that bifurcates near its east end. About 80% of the total seismic moment occurs on the asperities shallower than 10 km, with a peak slip of 5.7 m. To simultaneously match the observed long‐period seismic waves and static displacements, potential deep slip is required, despite a tradeoff with the rigidity of the shallow crust. The deep slip existence, local crustal rigidity, and synthetic long‐period Earth response for Tibet earthquakes thus deserve further investigation. The WNW branch ruptures ∼75 km at ∼2.7 km/s, while the ESE branch ruptures ∼85 km at ∼3 km/s, though super‐shear rupture propagation possibly occurs during the ESE propagation from 12 to 20 s. Synthetic BP tests confirm overall sub‐shear rupture speeds and reveal a previously undocumented limitation caused by the signal interference between two bilateral branches. The stress analysis on the forks of the fault demonstrates that the pre‐compression inclination, rupture speed, and branching angle could explain the branching behavior on the eastern fork.

Three-dimensional deformation velocity field and kinematic characteristic of the middle and east parts of Haiyuan fault zone from InSAR and GPS observations

Three-dimensional deformation velocity field can reveal fine characteristics of surface deformation, and provide data support for the research on crustal motion mechanism and seismic hazard. In this study, the ascending and descending InSAR deformation velocity fields in the middle and east parts of Haiyuan fault zone are firstly obtained with Sentinel-1A data and SBAS InSAR technology. Then, by combining with GPS observations, the three-dimensional deformation velocity field is extracted and analyzed. Finally, the locking depths and deep slip rates at different locations are inverted by using the classical two-dimensional screw dislocation model, and the maximum shear-strain rate is investigated. The results indicate that there are significant differences in the InSAR deformation velocity field between both sides of the middle and east parts of Haiyuan fault zone. The east–west deformation velocity field clearly reveals the left-lateral strike-slip characteristic of the fault zone. The northward movement gradually changes to southward movement from northwest to southeast. The vertical deformation velocity field displays significant differences on both sides of the section between MMSF and the middle of LHSF, and the middle and eastern of HYE fault. For LHSF, the locking depth and deep slip rate are 9.7 km and 4.9 mm/a; for HYW fault, they gradually decrease from west to east, with the locking depths of 6.4 km, 3.6 km and 3.2 km, respectively, and the deep slip rates of 5.5 mm/a, 4.2 mm/a and 3.8 mm/a, respectively; for HYM fault, they are 7 km and 4.7 mm/a; for HYE fault, they are 5.8 km and 3.6 mm/a. There are two obvious extreme regions of maximum shear-strain rate along the fault strike. This study can provide a reference for investigating the mechanism of regional uplift and extension and seismic hazard.

Holocene Slip Rate Along the Beng Co Fault and Dextral Strike‐Slip Extrusion of Central Eastern Tibet

AbstractThe dearth of quantitative studies of Holocene fault slip‐rates makes kinematic modeling of crustal deformation across SE Tibet debatable. The ∼230 km long, WNW‐striking, dextral Beng Co fault (BCF) is the most prominent strike‐slip fault of southern Tibet. Using new UAV topographic data and OSL/14C dating of geomorphic markers, we measure horizontal offsets and ages of fluvial terraces/fans and lacustrine shorelines at eight sites west and east of the Beng Lake pull‐apart. Along the eastern BCF's northern branch, our measurements at two different locations are consistent with offsets of ∼4.7 ± 1.1 and ∼8.7 ± 0.7 m during the past ∼3.1–3.6 and 3.6–5.2 ka, respectively. Along the southern branch, ∼25 ± 5 m of slip have accrued since ∼9 ka. The total Holocene slip‐rate across both faults (4.2–5.4 or 4.8 ± 0.5 mm/yr), consistent with GPS/InSAR values, implies that the BCF contributes significantly to the eastward extrusion of eastern‐central Tibet. This rate is slightly larger than the lower bound of the extension rate (∼6 ± 1.8 mm/yr) recently determined across the middle Gulu rift normal fault, which splays off southwards from the southeastern tip of the BCF's southern branch. Empirical relationships suggest that the reported ∼90 km length of theMw7.7, 1951 Beng Co earthquake surface rupture is too short, which implies that the eastern BCF is immature, or requires additional, partly deep slip, along other branches of the eastern BCF. That there is no field evidence of rupturing along the western BCF in the last ∼1,000 yr indicates that the Bange County area, west of Beng Co, may be at risk of anMw ≈ 7.4? event.

Resolving Shallow Moment Releases of Megathrust Earthquakes by Empirical Green’s Function‐Based Inversions: A New Approach for Tsunami Warning

AbstractTsunamis are secondary hazards generated by megathrust earthquakes, which are commonly related to coseismic slips occurring at shallow depths. Various methods were proposed to quickly predict tsunami excitations, while these methods mostly require specific observations or modeling techniques, which limits their application to global subduction zones. In this study, we propose an inversion technique that utilizes the water‐reverberation phases in teleseismic P coda waves to discriminate shallow and deep slips and adopts teleseismic empirical Green’s functions (EGFs) to enable rapid inversions. We developed an EGF extraction and interpolation method to construct Green’s functions. We apply this algorithm to seven megathrust earthquakes, which have been well studied and identified with or without significant shallow slips. In comparison with inversions performed with theoretical Green’s functions, the EGF‐based inversion technique is more effective in discriminating these two types of earthquakes. We propose a threshold to evaluate the percentage of shallow moment releases and found that the EGF‐based inversion result resembles that of joint inversion results. We also analyze the possibility to apply the EGF‐based inversion technique for tsunami warning purposes and infer that it serves as a promising algorithm to enable efficient tsunami early warning.

Insights into spatio-temporal slow slip events offshore the Boso Peninsula in central Japan during 2011–2019 using GPS data

Using Global Positioning System (GPS) coordinate time series, we detect three transient slow slip events (SSEs) offshore the Boso Peninsula in central Japan during 2011–2019. To extract the tiny SSE signals obscured by the significant post-seismic deformation after the 2011 MW9.0 Tohoku earthquake, we develop a new GPS coordinate time series processing software to obtain these SSE-induced deformations from high-noise GPS data. In addition, we apply the principal component analysis-based inversion method (PCAIM) to get the spatio-temporal slip distribution of the three SSEs. The spatio-temporal evolutions of these slips reveal that the nucleation styles are different. Compared to the 2011 and 2018 SSEs, the 2013–2014 SSE displays faster slip spatio-temporal variation, deeper slip, shorter slip duration, minor seismic moment, and lower maximum slip rate. The 2018 SSE exhibits the most significant seismic moment, the maximum slip, and the maximum slip rate of these three SSEs. The spatio-temporal variations of the 2011 SSE are the most complex, containing two acceleration and deceleration phases. The slip zone expanded along the eastern side of the Boso Peninsula in the acceleration phase and shrank back in the deceleration phase. Furthermore, the recurrence interval of SSEs spans from 2.2 to 4 years during 2011–2019, suggesting that the recurrence interval might become shorter and non-periodic due to the enormous earthquake. After the 2013–2014 SSE, the recurrence interval of the SSE gradually returns to normal. Thus, we can infer that the SSE may occur every 4–7 years after the 2018 SSE if there is no large earthquake.

Rescuing Behavioral Impairment after Doxorubicin Chemotherapy in Rats

Chemotherapy regimens have been extensively used for the treatment of various types of cancers. Despite the effectiveness of this treatment, clinical use of chemotherapeutic agents often produces negative side effects like deficits in cognition and memory, delayed processing speed, and executive function. This condition is widely recognized as chemotherapy‐induced cognitive impairment or “Chemo brain.” Our study aimed to identify the neurobiological mechanisms possibly responsible for this cognitive impairment. We examined the effects of chronic treatment with the chemotherapeutic drug Doxorubicin on cognitive impairment. Doxorubicin is a reactive oxygen species‐producing antineoplastic Anthracycline agent that adversely affects hippocampal neurogenesis, causes neuro‐inflammation, and induces apoptosis. Baseline activity data were collected and then twelve young female Long Evans hooded rats were randomly assigned to receive either Doxorubicin (6mg/kg) or 0.9% saline given intraperitoneally, once weekly for four weeks. After treatment, rats were assessed on the string‐pulling task, the bar walk test, and open field test. Two individuals blind to the treatment calculated the average time duration, number of attempts to pull the string, number of misses, total number of mouth contacts before and after treatment for the string‐pulling task, number of deep slips, slight slips, and the total number of slips for the bar walk test. Similarly, the number of entries to the center, number of entries to the corners, time spent at the center vs corner, and latency to first enter and exit the center was calculated for the open field test and compared between two groups. No significant differences were detected between Dox‐treated and Control rats on any measure, which suggests that the Dox‐treatment produced little or no significant peripheral neuropathy that disrupted performance on the motor tasks we used and did not induce significant anxiety in our rats. Immuno‐histochemical analyses of brain tissues is ongoing to examine markers of neurogenesis and neuro‐inflammation.

Deep fault slip characteristics in the Xianshuihe-Anninghe-Daliangshan Fault junction region (eastern Tibet) revealed by repeating micro-earthquakes

• 9 repeating earthquake sequences are identified in the Xianshuihe-Anninghe-Daliangshan Fault junction region in eastern Tibet . • The southern Xianshuihe Fault and the Gongyihai section of Daliangshan Fault is creeping, while the southern Anninghe Fault is locked. • The accumulated strain on the southern Anninghe Fault is large enough to form the next M7 earthquake. The Xianshuihe-Anninghe-Daliangshan Fault junction region in eastern Tibet marks the transition zone between the creeping Xianshuihe Fault and the locked Anninghe Fault. However, the role in slip partitioning of these three faults is unclear, mainly because the geodetic data lack the resolution to discriminate slip at depth. Repeating earthquakes, the seismic events rupture the same fault patch more than once, are recognized as the slip meters at depth and play an important role in the assessment of seismic hazard. In this study, repeating earthquakes in the Xianshuihe-Anninghe-Daliangshan Fault junction region are identified and the deep fault slip characteristics are investigated. First, a complete catalog (2013–2020) for the study region is achieved by using Matched Filter Technique detecting the continuous waveforms of the dense Xichang array. Second, waveform cross-correlation and double-difference location technologies are used to identify repeating earthquakes. Finally, by checking waveforms, focal depth and satellite images, mining expositions are excluded and 9 repeating earthquake sequences (RES) are obtained. RES indicate the deep slip at a rate of 8 mm/yr on the southern Xianshuihe Fault is partitioned to the northern Anninghe Fault and the Gongyihai section of Daliangshan Fault at rates of 1 mm/yr and 2–6 mm/yr, respectively. Aseismic slip on the southern Xianshuihe Fault and northern Anninghe Fault reach to 12 km depth. A large asperity on the Anninghe Fault from Liziping to Xichang is constrained by the back ground seismicity and the location of RES, which will form a M ∼ 7 potential earthquake when it ruptures.

Acceleration of Deep Slip Along the Longmenshan Fault Plane Before the 2008 M8.0 Wenchuan Earthquake

The first step toward earthquake forecasting is the identification of variables whose spatio-temporal variation can be connected with pre-seismic crustal deformation. Four periods of campaign Global Positioning System (GPS) observations around the Longmenshan fault zone (LFZ) provide important insights in crustal deformation and deep fault slip before the 2008 M8.0 Wenchuan earthquake. By using TDEFNODE to invert the coupling fraction and dynamic slip deficit rate of the Longmenshan fault plane before the Wenchuan earthquake, we show that under a background of strong coupling, the compressive slip deficit rate perpendicular to fault increased slightly at first and then decreased; a value of ∼1.5–3.6 mm/a along the central–southern segment from 1999 to 2001 increased to ∼1.9–3.9 mm/a from 2001 to 2004, and then decreased to ∼1.1–2.6 mm/a from 2004 to 2007. The dextral slip deficit rate parallel to fault was ∼6 mm/a from 1999 to 2004, before increasing significantly to ∼9.5 mm/a from 2004 to 2007, when the compressive slip deficit rate decreased. At the same time, large-scale GPS velocity profiles show that compressive shortening deformation in the Eastern Tibet Block, perpendicular to fault, increased slightly from 2001 to 2004, and then decreased from 2004 to 2007. Meanwhile, the dextral shear deformation parallel to fault near the LFZ increased significantly from 2004 to 2007. These findings are in good agreement with those calculated using repeating earthquake sequences, indicating that the deep slip rate of the Longmenshan fault plane may have accelerated several years before the Wenchuan earthquake. Our results demonstrate that GPS data can record pre-seismic preparatory processes, and have the potential for use in medium-term large earthquake forecasting.

The 2009 Ms 6.0 earthquake in Yao'an, Yunnan Province: Source constraints using relocated aftershocks and InSAR

An Ms 6.0 earthquake occurred in Yao'an County, Yunnan Province, on 9 June 2009. According to the results of relocated aftershocks, we find that the distribution of aftershocks has differences in the strike direction and depth in local areas. Therefore, the fault is divided into two segments. Combined with the surface deformation information obtained from InSAR Data as the constraint condition of the slip model, we inverse the three-dimensional coseismic slip distribution of the seismogenic fault of the Yao'an earthquake and discussed the influence of the Yao'an earthquake on the surrounding faults and the rupture direction of the event. The main research results are as follows: 1) we quickly obtain reasonable fault parameters, model, and slip distributions through relocated aftershocks and InSAR data, and the results obtained after inversion are consistent with the results of the geological structure and scholars' research. At the same time, the abnormal deep slip is found, which proves that there is a complex structure underground in the Yao'an area. 2) The results of static Coulomb stress change show that the aftershocks are basically distributed in the area where the static Coulomb stress increases. Faults with a relatively significant increase of Coulomb stress include the northwest section of Honghai Fault, the middle of Chenghai Fault, the middle of Hongge Fault, the middle of Nanhua-Chuxiong Fault, and the north of Yuanmou Fault. The future seismic risk of these faults should be considered. 3) The main direction of the Yao'an earthquake rupture is controlled by regional stress, and the abnormal rupture direction is affected by the complex underground structure.

Movement characteristics of a creeping slope influenced by river erosion and aggradation: Study of Xinwulü River in southeastern Taiwan

The average surface displacement rate of 0.1 m/year of the studied slope adjacent to the Xinwulü River has been measured over the past three decades. Damage to the retaining structures of a highway and tunnel through the slope has frequently been reported. Maintenance and reconstruction have been required at intervals of several to ten years. In this study, multi-temporal remote sensing images, site investigations, and ground and tunnel monitoring are interpreted to clarify the movement characteristics of the slope and the factors that affect them. The results of this study reveal that riverbed erosion and aggradation of the adjacent river dominate the movement characteristics of the slope. When the riverbed is low, the direction of slope movement ranges between that of the maximum slope gradient and the dip direction of foliation. Gravitational deformation, which is associated with a deep slip surface, is the main cause of movement; it is facilitated by gullies that develop upward from the sides of the Xinwulü River and the surrounding sliding masses. When the riverbed is high as a result of the aggradation of debris from upstream, the slope moves in the direction of the maximum gradient. Water washes out the slope toe, which has a relatively low strength because it has previously been displaced. Slope collapses occur frequently along the river bank, and gullies actively grow upward, stimulating the movement of the sliding masses with a shallow slip surface. Furthermore, the cyclic erosion and aggradation of the river account for the formation of shallow and deep slip surfaces of 33 m and 90 m, respectively. The results of this study demonstrate the effects of riverbed erosion and aggradation on the creeping deformation and stability of the adjacent slope in the Xinwulü River region; this is valuable for formulating countermeasures to protect the study site and maintain the existing tunnel.

Distinct element modeling of deep underground slip failure of coal rock mass with weak interlayers

Distinct element modeling of deep underground slip failure of coal rock mass with weak interlayers

In Situ Observation of the Tensile Deformation and Fracture Behavior of Ti-5Al-5Mo-5V-1Cr-1Fe Alloy with Different Microstructures.

The plastic deformation processes and fracture behavior of a Ti–5Al–5Mo–5V–1Cr–1Fe alloy with bimodal and lamellar microstructures were studied by room-temperature tensile tests with in situ scanning electron microscopy (SEM) observations. The results indicate that a bimodal microstructure has a lower strength but higher ductility than a lamellar microstructure. For the bimodal microstructure, parallel, deep slip bands (SBs) are first noticed in the primary α (αp) phase lying at an angle of about 45° to the direction of the applied tension, while they are first observed in the coarse lath α (αL) phase or its interface at grain boundaries (GBs) for the lamellar microstructure. The β matrix undergoes larger plastic deformation than the αL phase in the bimodal microstructure before fracture. Microcracks are prone to nucleate at the αp/β interface and interconnect, finally causing the fracture of the bimodal microstructure. The plastic deformation is mainly restricted to within the coarse αL phase at GBs, which promotes the formation of microcracks and the intergranular fracture of the lamellar microstructure.

Complex Migration of Tremor Near Cholame, CA, Resolved by Seismic Array Analysis

AbstractTectonic tremor observed along the Cholame and Parkfield sections of the San Andreas Fault has previously been associated with transient slip beneath the seismogenic zone. To study tremor and associated Low Frequency Earthquakes (LFEs), we deployed three dense near‐fault seismic arrays for a period of 3 months in 2018. In early August 2018, the arrays recorded a strong 4‐day‐long deep transient that nucleated in Cholame and propagated toward the northwest. The initiation area is characterized by tremor that persists throughout the transient, while adjacent fault portions located to the northwest host more intermittent tremor. From the rate and location of tremor and LFEs, we infer a deep slip transient, whose along‐strike propagation velocity is ∼8 km/day. Secondary tremor fronts are observed to travel ahead of the main slow slip front at speeds that are times faster. These rapid migrations propagate in slow slip events (SSE) slip‐parallel direction, and are sometimes observed to back‐propagate into previously ruptured segments. High‐resolution images of secondary fronts obtained by using near‐fault borehole stations indicate the active tremor band takes the shape of a narrow strain pulse that is bounded from above by the lower edge of the seismogenic zone. We estimate the stress drops associated with the secondary slip fronts are of the order of a few kPa. Frequency‐dependent analysis suggests the tremor signal is coherent at frequencies as high as 16 Hz, and that the spatial distribution of high‐ and low‐frequency tremor radiators is sometimes complementary.

Effect of Nimodipine and Botulinum Toxin A on Peripheral Nerve Regeneration in Rats: A Pilot Study

BackgroundPeripheral nerve damage is a frequent problem, with an estimated 2.8%-5.0% of trauma admissions involving peripheral nerve injury. End-to-end, tension-free microsurgical repair (neurorrhaphy) is the current gold standard treatment for complete transection (neurotmesis). While neurorrhaphy reapproximates the nerve, it does not address the complex molecular regenerative process. Evidence suggests that botulinum toxin A (BTX) and nimodipine (NDP) may improve functional recovery, but mechanisms of action remain unknown. MethodsThis research investigates BTX and NDP for their novel capacity to improve neural regeneration in the setting of neurorrhaphy using a Lewis rat tibial nerve neurotmesis model. In a triple-masked, placebo-controlled, randomized study design, we compared functional (rotarod, horizontal ladder walk), electrophysiological (conduction velocity, duration), and stereological (axon count, density) outcomes of rats treated with: NDP+saline injection, BTX+NDP, Saline+placebo, and BTX+placebo. Additional controls included sham surgery +/- BTX. ResultsNDP+saline outperformed other treatment groups in the ladder walk. This group had the fewest deep slips (15.07% versus 30.77% in BTX+NDP, P = 0.122), and the most correct steps (70.53% versus 55.58% in BTX+NDP, P = 0.149) in functional testing. NDP+saline also had the fastest nerve conduction velocity (0.811m/s versus 0.598m/s in BTX+NDP, P = 0.126) among treatment groups. BTX+NDP had the highest axon count (10,012.36 versus 7,738.18 in NDP+Saline, P = 0.009). ConclusionThis study is the first to test NDP with BTX in a multimodal assessment of nerve recovery following neurotmesis and neurorrhaphy. NDP outperformed BTX+NDP functionally. Future work will focus on nimodipine in an effort to improve nerve recovery in trauma patients.

Experimental Study on Landslides in Terraced Fields in the Chinese Loessial Region under Extreme Rainfall

Due to the development of the scale of tractor-ploughed terraces, terraces have been increasing in number, while global climate change is causing frequent extreme rainfall events in the Loess Plateau, resulting in many terrace landslides. To study the mechanism and process of shallow landslides and deep slip surface of terraces induced by extreme rainfall in loess hill and gully area, we conducted a laboratory model test of a terrace under artificial rainfall and used the Swedish arc strip method. The research results are as follows. The mechanism of shallow landslides in terraces is rill erosion accelerating rainfall infiltration, suspending the slope, and increasing its bulk density. The destruction process of shallow landslides can be roughly divided into six processes, and the earth volume of the landslide is 0.24 m3. The mechanism of the deep sliding surface in terraces occurs under the combined action of water erosion and gravity erosion. The soil moisture content increases, which decreases the anti-sliding moment and increases the sliding moment, and the safety factor becomes less than the allowable limit for terraces. The deep sliding deformation area of the terrace was 0~1.0 m below the slope surface, slip surface radius was 1.43 m, the slip surface angle was 92°, and the deep sliding surface began to form earlier than terraced shallow landslides. The displacement of the characteristic points increased from the slope top, to the slope center, and to the slope foot, with maximum displacements of 40.3, 15.5, and 6.0 mm, respectively.

Geodetic Observation of Seismic Cycles before, during, and after the 2020 Monte Cristo Range, Nevada Earthquake

AbstractThe 15 May 2020, M 6.5 Monte Cristo Range, Nevada earthquake (MCE) occurred inside the footprint of the semicontinuous MAGNET and continuous Network of the Americas Global Positioning System (GPS) networks, which provide precise geodetic coverage in the western Great basin. The event occurred in the White Mountain seismic gap between twentieth century events in the eastern central Walker Lane, on an east-northeast extension of faults in the Candelaria Hills. The earthquake precipitated a rapid and sustained GPS field response, which is providing data on the MCE pre-, co-, and postseismic deformation. The response was especially rapid owing to ∼1 dozen MAGNET stations immediately surrounding the epicenter being fortuitously occupied with receivers at event time. Modeling the coseismic displacements suggests that the MCE offset was ∼1 m, greater than the individual observations of surface rupture, but consistent with the seismic moment. Although the epicenter is separated from most of the observed surface rupture by ∼10 km, the slip plane inferred from the GPS data spans the gap, suggesting deep slip continuity that tapered toward the surface, making the event partially blind. However, the range of magnitudes estimated from geologic, geodetic, and seismic data overlap in the range of Mw 6.3–6.4. Postseismic displacement over several months occurred in directions aligned with the coseismic displacement, suggesting afterslip of over 9% of the coseismic displacement, too large to be explained by aftershock seismicity, suggesting that most postseismic deformation was aseismic. The interseismic direction of no-length change was very closely aligned to the MCE slip azimuth, as expected for a strike-slip event. This alignment is sensitive to transient postseismic viscoelastic deformation from previous earthquakes in the western Great basin, which may have temporarily improved the alignment. Thus, these viscoelastic transients may have created conditions favoring the slip to occur on the MCE fault.

Driving stress and seismotectonic implications of the 2013 Mw5.8 Awaji Island earthquake, southwestern Japan, based on earthquake focal mechanisms before and after the mainshock

A driving stress of the Mw5.8 reverse-faulting Awaji Island earthquake (2013), southwest Japan, was investigated using focal mechanism solutions of earthquakes before and after the mainshock. The seismic records from regional high-sensitivity seismic stations were used. Further, the stress tensor inversion method was applied to infer the stress fields in the source region. The results of the stress tensor inversion and the slip tendency analysis revealed that the stress field within the source region deviates from the surrounding area, in which the stress field locally contains a reverse-faulting component with ENE–WSW compression. This local fluctuation in the stress field is key to producing reverse-faulting earthquakes. The existing knowledge on regional-scale stress (tens to hundreds of km) cannot predict the occurrence of the Awaji Island earthquake, emphasizing the importance of estimating local-scale (< tens of km) stress information. It is possible that the local-scale stress heterogeneity has been formed by local tectonic movement, i.e., the formation of flexures in combination with recurring deep aseismic slips. The coseismic Coulomb stress change, induced by the disastrous 1995 Mw6.9 Kobe earthquake, increased along the fault plane of the Awaji Island earthquake; however, the postseismic stress change was negative. We concluded that the gradual stress build-up, due to the interseismic plate locking along the Nankai trough, overcame the postseismic stress reduction in a few years, pushing the Awaji Island earthquake fault over its failure threshold in 2013. The observation that the earthquake occurred in response to the interseismic plate locking has an important implication in terms of seismotectonics in southwest Japan, facilitating further research on the causal relationship between the inland earthquake activity and the Nankai trough earthquake. Furthermore, this study highlighted that the dataset before the mainshock may not have sufficient information to reflect the stress field in the source region due to the lack of earthquakes in that region. This is because the earthquake fault is generally locked prior to the mainshock. Further research is needed for estimating the stress field in the vicinity of an earthquake fault via seismicity before the mainshock alone.