Coseismic Coulomb stress changes induced by a 2020-2021 M_(W)>7.0 Alaska earthquake sequence in and around the Shumagin gap and its influence on the Alaska-Aleutian subduction interface

Three M_(W)>7.0 earthquakes in 2020-2021 occurred in the Shumagin seismic gap and its adjacent area of the Alaska-Aleutian subduction zone,including the Mw7.8 Simeonof thrust earthquake on July 22,2020,the M_(W)7.6 Sand Point strike-slip earthquake on October 19,2020,and the M_(W)8.2 Chignik thrust earthquake on July 29,2021.The spatial and temporal proximity of these three earthquakes prompts us to probe stress-triggering effects among them.Here we examine the coseismic Coulomb stress change imparted by the three earthquakes and their influence on the subduction interface.Our results show that:(1)The Simeonof earthquake has strong loading effects on the subsequent Sand Point and Chignik earthquakes,with the Coulomb stress changes of 3.95 bars and 2.89 bars,respectively.The Coulomb stress change caused by the Sand Point earthquake at the hypocenter of the Chignik earthquake is merely around 0.01 bars,suggesting the negligible triggering effect on the latter earthquake;(2)The triggering effects of the Simeonof,Sand Point,and Chignik earthquakes on aftershocks within three months are not well pronounced because of the triggering rates of 38%,14%,and 43%respectively.Other factors may have played an important role in promoting the occurrence of these aftershocks,such as the roughness of the subduction interface,the complicated velocity structure of the lithosphere,and the heterogeneous prestress therein;(3)The three earthquakes caused remarkable coseismic Coulomb stress changes at the subduction interface nearby these mainshocks,with an average Coulomb stress change of 3.2 bars in the shallow region directly inwards the trench.

Investigation of Coulomb stress changes in south Tibet(central Himalayas) due to the 25th April 2015 M_W 7.8 Nepal earthquake using a Coulomb stress transfer model

After Mw 7.8 Nepal earthquake occurred, the rearrangement of stresses in the crust commonly leads to subsequent damaging earthquakes. We present the calculations of the coseismic stress changes that resulted from the 25th April event using models of regional faults designed according to south Tibet-Nepal structure, and show that some indicative significant stress increases. We calculate static stress changes caused by the displacement of a fault on which dislocations happen and an earthquake occurs. A Mw 7.3 earthquake broke on 12 May at a distance of - 130 km SEE of the Mw 7.8 earthquake, whose focus roughly located on high Coulomb stress change （CSC） site. Aftershocks （first 15 days after the mainshock） are associated with stress increase zone caused by the main rupture. We set receiver faults with specified strikes, dips, and rakes, on which the stresses imparted by the source fault are resolved. Four group normal faults to the north of the Nepal earthquake seismogenic fault were set as receiver faults and variant results followed. We provide a discussion on Coulomb stress transfer for the seismogenic fault, which is useful to identify potential future rupture zones.

Co-seismic Coulomb stress changes on the northern Tanlu fault zone caused by the Tohoku-Oki M_(W)9.0 earthquake

Based on the spherical earth dislocation theory and a fault slip model of the Tohoku-Oki M_(W)9.0 earthquake,the co-seismic Coulomb failure stress changes(ΔCFS)on the northern Tanlu fault zone at depths of 0–40 km are calculated.By comparing two sets of results from the spherical earth dislocation theory and the semi-infinite space one,the effect of earth curvature on the calculation results is analyzed quantitatively.First,we systematically summarize previous researches related to the northern Tanlu fault zone,divide the fault zone as detailed as possible,give the geometric parameters of each segment,and establish a segmented structural model of the northern Tanlu fault zone.Second,we calculate the Coulomb stress changes on the northern Tanlu fault zone by using the spherical earth dislocation theory.The result shows the Coulomb stress changes are no more than 0.003 MPa,which proves the great earthquake did not significantly change the stress state of the fault zone.Finally,we quantitatively analyze the disparities between the results of semi-infinite space dislocation theory and the spherical earth one.The average disparity between them is about 7.7%on the northern Tanlu fault zone and is 16.8%on the Fangzheng graben,the maximum disparity on this graben reaches up to 25.5%.It indicates that the effect of earth curvature can not be ignored.So it’s necessary to use the spherical earth dislocation theory instead of the semi-infinite space one to study the Coulomb stress change in the far field.

Coulomb stress changes due to the 2021 MS7.4 Maduo Earthquake and expected seismicity rate changes in the surroundings

On May 22 nd,2021,an MS7.4 earthquake occurred near the Maduo county of the Qinghai Province,China,within the Bayan Har Block.Seismic activities have been intense in this block,thus whether the Maduo Earthquake will bring subsequent seismic hazards to its surrounding regions raises wide concerns.In this paper,we first calculated the Coulomb failure stress changes caused by the Maduo Earthquake on nearby faults,and estimated how much these faults are brought closer or further from their next failures based on their stressing rates.Next,we combined the Coulomb failure stress changes with the rate-state frictional law to estimate the seismicity rate in the study region in the next decade.A declustered catalogue before the Maduo Earthquake was adopted to calculate background seismicity rate,and rate-state parameters are constrained by fault slip rates.Our results show that the Maduo Earthquake increases stress accumulations in the northwestern portion of the Qingshuihe fault(0.02 MPa at maximum),the two ends of the Kunlun Mountain Pass-Jiangcuo fault(0.01 MPa at maximum),and the northwestern portion of the Maduo-Gande fault(on average~0.09 MPa),and seismicity rates are expected to increase near these faults.What is especially worth noting is the seismic hazard in the region extending from the eastern end of the Kunlun Mountain Pass-Jiangcuo fault to the Maqin-Maqu seismic gap on the Eastern Kunlun fault,which is calculated to have experienced a maximum stress increase of 0.67 MPa after the Maduo Earthquake.On the other hand,stress accumulations are reduced in the southern end of the Elashan fault,the Eastern Kunlun fault segment to the west of Maduo,and the northwestern portion of the Dari fault.Seismic hazards are expected to be low in these regions.For the study region as a whole,the probability of an M≥6 earthquake taking place in the next decade is estimated to be 59%,about twice the value calculated for the time period before the Maduo Earthquake.

Finite element simulation of deformation and stress changes of Kalpin-Kemin fault system in the Southwest Tianshan Orogenic Belt

Under the shadow of the far-field effect of the India-Eurasia collision,the Tianshan orogenic belt underwent tectonic re-activation in the Cenozoic,accompanied by strong tectonic deformation and frequent large earthquakes.Bounded by two rigid cratonic blocks located in its north and south,a series of marginal foreland fold-and-thrust belts are developed within the Tianshan orogenic belt and continue to develop to the bilateral pull-apart basins.Meanwhile,the faults in the orogenic belt are reactivated.The deformation caused by thrust-related structure accounts for larger than 50%of the total convergence of the Tianshan Mountains,which results in the most active structure with large earthquakes in the Tianshan area.Therefore,it is of great significance to study the dynamic process of the newly generated and reactivated thrust-nappe structures in Tianshan orogen via numerical modeling.This paper selects a classical cross-section profile in the western segment of the Southwest Tianshan Mountains,which contains the Kalpin-Maidan-Nalati-Kemin fault system from the south to the north.We attempt to establish a two-dimensional plane strain,viscoelastic finite element model,by treating the regional faults as a whole fault system and considering the topography,fault geometry,and GPS data.The displacement and stress fields of the model are retrieved,the short-term cumulative deformation field of the overall fault system is analyzed,and the rate of Coulomb failure stress change of each fault is also considered.The results show that the deformation is concentrated in the middle and southern parts of the Southwest Tianshan Mountains.In contrast,the deformation of the Kemin fault in the north is relatively small.According to the Coulomb failure stress changes of these four faults and the historical earthquake catalog,the potential seismicity of each fault is qualitatively analyzed.Our preliminary results suggest that the possibility of large earthquake occurrence is higher in the Kalpin fault,Maidan fault,and Nalati fault but lower in the Kemin fault in the near future。

Monitoring the change in horizontal stress with multi-wave time-lapse seismic response based on nonlinear elasticity theory

Monitoring the change in horizontal stress from the geophysical data is a tough challenge, and it has a crucial impact on broad practical scenarios which involve reservoir exploration and development, carbon dioxide (CO_(2)) injection and storage, shallow surface prospecting and deep-earth structure description. The change in in-situ stress induced by hydrocarbon production and localized tectonic movements causes the changes in rock mechanic properties (e.g. wave velocities, density and anisotropy) and further causes the changes in seismic amplitudes, phases and travel times. In this study, the nonlinear elasticity theory that regards the rock skeleton (solid phase) and pore fluid as an effective whole is used to characterize the effect of horizontal principal stress on rock overall elastic properties and the stress-dependent anisotropy parameters are therefore formulated. Then the approximate P-wave, SV-wave and SH-wave angle-dependent reflection coefficient equations for the horizontal-stress-induced anisotropic media are proposed. It is shown that, on the different reflectors, the stress-induced relative changes in reflectivities (i.e., relative difference) of elastic parameters (i.e., P- and S-wave velocities and density) are much less than the changes in contrasts of anisotropy parameters. Therefore, the effects of stress change on the reflectivities of three elastic parameters are reasonably neglected to further propose an AVO inversion approach incorporating P-, SH- and SV-wave information to estimate the change in horizontal principal stress from the corresponding time-lapse seismic data. Compared with the existing methods, our method eliminates the need for man-made rock-physical or fitting parameters, providing more stable predictive power. 1D test illustrates that the estimated result from time-lapse P-wave reflection data shows the most reasonable agreement with the real model, while the estimated result from SH-wave reflection data shows the largest bias. 2D test illustrates the feasibility of the proposed inversion method for estimating the change in horizontal stress from P-wave time-lapse seismic data.

Advances in experiments and numerical simulations on the effects of stress perturbations on fault slip

Laboratory experiments and numerical simulations on rock friction perturbations,an important means for understanding the mechanism and influencing factors of stress-triggered earthquakes,are of great significance for studying earthquake mechanisms and earthquake hazard analysis.We reviews the experiments and numerical simulations on the effects of stress perturbations on fault slip,and the results show that stress perturbations can change fault stress and trigger earthquakes.The Coulomb failure criterion can shed light on some questions about stress-triggering earthquakes but cannot explain the time dependence of earthquake triggering nor be used to investigate the effect of heterogeneous stress perturbations.The amplitude and period are important factors affecting the correlation between stress perturbation and fault instability.The effect of the perturbation period on fault instability is still controversial,and the effect of the high-frequency perturbation on earthquakes may be underestimated.Normal and shear stress perturbation can trigger fault instability,but their effects on fault slip differ.It is necessary to distinguish whether the stress perturbation is dominated by shear or normal stress change when it triggers fault instability.Fault tectonic stress plays a decisive effect on the mode of fault instability and earthquake magnitude.Acoustic emission activity can reflect the changes in fault stress and the progression of fault nucleation,and identify the meta-instability stage and precursor of fault instability,providing a reference for earthquake prediction.

Stress triggering" between different rupture events in several earthquakes

Most strong earthquakes have complex rupture processes. As an approximation, each earthquake can be described as two or more subevents of rupture with time interval of several seconds to several days. In order to discuss the relationship between different subevents, we investigated the rupture process of the 1966 Xingtai, the 1976 Tangshan, the 1990 Gonghe and the 1996 Lijiang earthquake by calculating the static Coulomb failure stress changes produced by the first subevent. The calculation of static stress changes produced by fault slip is based on the formulation of Okada (1992). The result suggests that the static Coulomb failure stress changes (ΔCFS) produced by the first subevent have 'triggering' effect on the subsequent subevents which locate in the region where the Coulomb stress change produced by the first event is positive, with the order of magnitude 10-2 [similar to] 10-1 MPa.

Regional seismicity triggered by the M_s=7.8 Tangshan event on July 28, 1976 and the stati cstress field change

We studied the seismicity before and after the M_s=7.8 Tangshan event on July 28, 1976 (39°28'N, 1 18° 11'E) and the results show that in 3 regions outside of the source zone, seismicity rate increasing were observed, which was significant in 0.99 significance level using Z-statistic test and was proposed to be triggered by the M_s=7.8 Tangshan earthquake. The magnitude of the greatest triggered event was 5.5. The epicenter distances of these earthquakes were several ten kilometers to 300 km. The static stress change △CFS of Coulomb failure was calculated using an elastic dislocation model in half space and the △CFS on the major rupture directions in these three regions were positive.

Evolution of cumulative Coulomb failure stress in northeastern Qinghai-Xizang (Tibetan) Plateau and its effect on large earthquake occurrence

We simulate accumulative Coulomb failure stress change in a layered Maxwell viscoelastic media in the northeastern Qinghai-Xizang （Tibetan） Plateau since 1920. Lithospheric stress/strain evolution is assumed to be driven by dislocations of large earthquakes （M≥7.0） and secular tectonic loading. The earthquake rupture parameters such as the fault rupture length, width, and slip are either adopted from field investigations or estimated from their statistic relationships with the earthquake magnitudes and seismic moments. Our study shows that among 20 large earthquakes （M≥7.0） investigated, 17 occurred in areas where the Coulomb failure stress change is positive, with a triggering rate of 85%. This study provides essential data for the intermediate to long-term likelihood estimation of large earthquakes in the northeastern Tibetan Plateau.

Research on seismic stress triggering

This paper briefly reviews basic theory of seismic stress triggering. Recent development on seismic stress triggering has been reviewed in the views of seismic static and dynamic stress triggering, application of viscoelastic model in seismic stress triggering, the relation between earthquake triggering and volcanic eruption or explosion, other explanation of earthquake triggering, etc. And some suggestions for further study on seismic stress triggering in near future are given.

Failure time variation derived from R–S relation: the role of the static stress perturbation

In general, earthquake cycle related to earthquake faulting could include four major processes which could be described by （1） fault locking, （2） self-acceleration or nucleation （possible foreshocks）, （3） coseismic slip, and （4） post-stress relaxation and afterslip. A sudden static stress change/perturbation in the surrounding crust can advance/ delay the fault instability or failure time and modify earth- quake rates. Based on a simple one-dimensional spring-sli- der block model with the combination of rate-and-state- dependent friction relation, in this study, we have approxi- mately derived the simple analytical solutions of clock advance/delay of fault failures caused by a sudden static Coulomb stress change applied in the different temporal evolution periods during an earthquake faulting. The results have been used in the physics-based explanation of delayed characteristic earthquake in Parkfield region, California, in which the next characteristic earthquake of M 6.0 after 1966 occurred in 2004 instead of around 1988 according to its characteristic return period of 22 years. At the same time, the analytical solutions also indicate that the time advance/ delay in Coulomb stress change derived by the dislocation model has a certain limitation and fundamental flaw. Fur- thermore, we discussed the essential difference between rate- and state-variable constitutive （R-S） model and Coulomb stress model used commonly in current earthquake triggering study, and demonstrated that, in fact, the Coulomb stress model could be involved in the R-S model. The results, we have obtained in this study, could be used in the development of time-dependent fault interaction model and the probability calculation related to the time-dependent and renewal earthquake prediction model.

Finite element simulation of stress change for the M_(S)7.4 Madoi earthquake and implications for regional seismic hazards

On May 22,2021,the M_(S)7.4 earthquake occurred in Madoi County,Qinghai Province;it was another strong event that occurred within the Bayan Har block after the Dari M_(S)7.7 earthquake in 1947.An earthquake is bound to cast stress to the surrounding faults,thus affecting the regional seismic hazard.To understand these issues,a three-dimensional viscoelastic finite element model of the eastern Bayan Har block and its adjacent areas was constructed.Based on the co-seismic rupture model of the Madoi earthquake,we analyzed the co-and postseismic Coulomb stress change caused by the Madoi earthquake on the surrounding major faults.The results show that the Madoi earthquake caused significant co-seismic stress increases in the Tuosuo Lake and Maqin-Maqu segments of the East Kunlun fault(>10 kPa),which exceeded the proposed threshold of stress triggering.By integrating the accumulation rate of the inter-seismic tectonic stress,we conclude that the Madoi earthquake caused future strong earthquakes in the Tuosuo Lake and Maqin-Maqu segments of the East Kunlun fault to advance by 55.6-623 and 24.7-123 a,respectively.Combined with the influence of the Madoi earthquake and the elapsed time of the last strong earthquake,these two segments have approached or even exceeded the recurrence interval of the fault prescribed by previous research.In the future,it is necessary to focus greater attention on the seismic hazard of the Maqin-Maqu and Tuosuo Lake segments.This study provides a mechanical reference to understand the seismic hazard of the East Kunlun fault in the future,particularly to determine the seismic potential region.

Abiotic and Biotic Stresses and Changes in the Lignin Content and Composition in Plants

Lignin is a polymer of phenylpropanoid compounds formed through a complex biosynthesis route, represented by a metabolic grid for which most of the genes involved have been sequenced in several plants, mainly in the model-plants Arabidopsis thaliana and Populus. Plants are exposed to different stresses, which may change lignin content and composition. In many cases, particularly for plant-microbe interactions, this has been suggested as defence responses of plants to the stress. Thus, understanding how a stressor modulates expression of the genes related with lignin biosynthesis may allow us to develop study-models to increase our knowledge on the metabolic control of lignin deposition in the cell wall. This review focuses on recent literature reporting on the main types of abiotic and biotic stresses that alter the biosynthesis of lignin in plants.

Features of seismicity in Xinjiang and its possible reason after the Yutian M_S7.4 earthquake,2008

The paper discusses quantitatively the influence of the Yutian Ms7.4 earthquake of March 21, 2008 and Wuqia Ms6.9 earthquake of October 5, 2008 on regional seismicity in Xinjiang, and explains primarily the possible reason of earthquake activity feature in Xinjiang after the Yutian Ms7.4 earthquake by analyzing the static Coulomb failure stress change produced by the Yutian Ms7.4 earthquake and Wuqia Ms6.9 earth-quake, and the seismicity feature of Ms≥3 earthquakes in the positive Coulomb stress change region of Kashi-Wuqia joint region, the central segment of Tianshan Mountain and Kalpin block. The result shows that the Yutian Ms7.4 earthquake of March 21, 2008, may encourage the Wuqia Ms6.9 earth-quake of October 5, 2008, and the Yutian Ms7.4 earthquake and Wuqia Ms6.9 earthquake may change the seismicity state in the central segment of Tianshan Mountain, Kalpin block and Kashi-Wuqia joint region, and encourage the subsequent Ms≥3 earthquakes.

The Kangding earthquake swarm of November, 2014

There was an earthquake swarm of two major events of MS6.3 and MS5.8 on the Xianshuihe fault in November, 2014. The two major earthquakes are both strike-slip events with aftershock zone along NW direction.We have analyzed the characteristics of this earthquake sequence. The b value and the h value show the significant variations in different periods before and after the MS5.8earthquake. Based on the data of historical earthquakes, we also illustrated the moderate-strong seismic activity on the Xianshuihe fault. The Kangding earthquake swarm manifests the seismic activity on Xianshuihe fault may be in the late seismic active period. The occurrence of the Kangding earthquake may be an adjustment of the strong earthquakes on the Xianshuihe fault. The Coulomb failure stress changes caused by the historical earthquakes were also given in this article. The results indicate that the earthquake swarm was encouraged by the historical earthquakes since1893, especially by the MS7.5 Kangding earthquake in1955. The Coulomb failure stress changes also shows the subsequent MS5.8 earthquake was triggered by the MS6.3earthquake.

Earthquake triggering and delaying caused by fault interaction on Xianshuihe fault belt, southwestern China

The coseismic Coulomb stress change caused by fault interaction and its influences on the triggering and delaying of earthquake are briefly discussed. The Xianshuihe fault belt consists of Luhuo, Daofu, Kangding, Qianning and Ganzi fault. Luohuo (MS=7.6, 1973)-Kangding (MS=6.2, 1975)-Daofu (MS=6.9, 1981)-Ganzi (MS=6.0, 1982) earthquake is a seismic sequence continuous on the time axis with magnitude greater than 6.0. They occurred on the Luhuo, Kangding, Daofu and Ganzi fault, respectively. The coseismic Coulomb stress changes caused by each earthquake on its surrounding major faults and microcracks are calculated, and their effects on the triggering and delaying of the next earthquake and aftershocks are analyzed. It is shown that each earthquake of the sequence occurred on the fault segment with coseismic Coulomb stress increases caused by its predecessors, and most after-shocks are distributed along the microcracks with relatively larger coseismic Coulomb stress increases resulted from the main shock. With the fault interaction considered, the seismic potential of each segment along Xianshuihe fault belt is reassessed, and contrasted with those predicted results ignoring coseismic Coulomb stress change, the significance of fault interaction and its effect on triggering and delaying of earthquake are emphasized. It is con-cluded that fault interaction plays a very important role on seismic potential of Xianshuihe fault belt, and the maximal change of future earthquake probability on fault segment is up to 30.5%.

Focal depths and mechanisms of Tohoku-Oki aftershocks from teleseismic P wave modeling

Aftershocks of the 2011 Tohoku-Oki great earthquake have a wide range of focal depths and fault plane mechanisms. We constrain the focal depths and focal mechanisms of 69 aftershocks with Mw 〉 5.4 by modeling the waveforms of teleseismic P and its trailing near-surface reflections pP and sP. We find that the ＂thrust events＂ are within 10 krn from the plate interface. The dip angles of these thrust events increase with depth from ~ 5~ to ~ 25~. The ＂non-thrust events＂ vary from 60 km above to 40 km below the plate interface. Normal and strike-slip events within the overriding plate point to redistribution of stress following the primary great earthquake; however, due to the spatially variable stress change in the Tohoku-Oki earthquake, an understanding of how the mainshock affected the stresses that led to the aftershocks requires accurate knowledge of the aftershock location.

Quantitative analysis of the Nepal earthquake on 25 April, 2015 in the perspective of future earthquake hazard

The earthquake that occurred in Nepal on 25 April, 2015 was followed by about 256 aftershocks which continued for another 20-25 days. The Coulomb stress change due to the main shock has been estimated at depths 10 km, 15 km and 22 km which justify the occurrence of about 218 aftershocks of magnitudes 4 to 5 mostly at 10 km depth and the rest of magnitudes 5 to 7.3 mostly at 15-30 km depth. The western, southern and northern fringes of the fault plane that slipped on 25 April, 2015 show a high value of positive Coulomb stress change estimated at the above mentioned depths and yet these parts of the fault remained devoid of any aftershock epicentre and therefore must be treated as seats for possible future events. Co-seismic displacement of 5 GPS stations located in Nepal after the devastating earthquake of MwZ8 on 25 April, 2015 and its largest aftershock of MwZ3 on 12 May, 2015 have been separately estimated and analysed.