stress transfer and its implication for earthquake hazard on the kunlun fault tibet abstract the 1600 km long kunlun fault striking e w to wnw ese had long been recognized as one of the major left lateral strike slip faults bounding the tibetan plateau and ranked one of the most active faults in china continent during the past hundred years over twenty strong earthquakes occurred along and near the kunlun fault including six large earthquakes m 7 since some major highly populated and industrialized cities are close to the kunlun fault understanding of stress transfer and earthquakes migration along the kunlun fault is most important for assessing seismic hazard in this region in this study by integrating coseismic effect viscoelastic relaxation and tectonic loading we studied the evolution of the regional coulomb stress field by analyzing a sequence of strong earthquakes along the kunlun fault we studied the stress evolution over one century by analysing a sequence of five earthquakes m 7 that occurred along the kunlun fault since 1937 the model of dislocation sources embedded in a mixed elastic inelastic layered half space was used and the layered model and relevant parameters were constrained by seismic studies fault rupture locations and geometry as well as slip distribution of earthquakes were taken from field observations and seismic studies numerical results showed a good correlation between stress transfer accumulation and earthquakes occurrence all four studied earthquakes occurred after the 1937 tuosuo lake quake were encouraged by the preceding earthquakes with positive stress loading in subject to the choice of the earthquake source parameter two or three out of four events occurred in regions that experienced previous coseismic and postseismic stress changes of at least 0 01 mpa suggesting that earthquake triggering due to stress transfer has occurred along the kunlun fault the total stress change since 1937 of the kunlun fault region has lead to high levels of stress accumulated on the xidatan dongdatan segment and maqin maqu segment which have not experienced any significant large earthquake over at least several hundred or several thousand years the accumulated stress raises the potential earthquake hazard in these areas our study demonstrated the crucial importance of postseismic viscoelastic relaxation in the stress transfer and accumulation following large earthquakes

a multilayer model of time dependent deformation following an earthquake on a strike slip fault a multilayer half space model of the earth is used in finite element calculations of time dependent deformation and stress following an earthquake on an infinitely long strike slip fault the model involves shear properties of an elastic upper lithosphere a standard viscoelastic linear solid lower lithosphere a maxwell viscoelastic asthenosphere and an elastic mesosphere time dependent displacements strains and stresses are computed both at the surface of the earth and at depth the analysis includes both systematic variations of fault and layer depths and comparisons with simpler elastic lithosphere over viscoelastic asthenosphere calculations for conditions which may be appropriate for the earth the creep of both the lower lithosphere and the asthenosphere can contribute to the postseismic deformation the magnitude of the deformation is enhanced by a short distance between the bottom of the fault slip zone and the top of the creep layer but is less sensitive to the thickness of the creeping layer furthermore postseismic restressing is increased as the lower lithosphere becomes more viscoelastic but the tendency for the width of the restressed zone to grow with time is retarded

change in the probability for earthquakes in southern california due to the landers magnitude 7 3 earthquake the landers earthquake in june 1992 redistributed stress in southern california shutting off the production of small earthquakes in some regions while increasing the seismicity in neighboring regions up to the present this earthquake also changed the ratio of small to large events in favor of more small earthquakes within about 100 kilometers of the epicenter this implies that the probabilistic estimate for future earthquakes in southern california changed because of the landers earthquake the location of the strongest increase in probability for large earthquakes in southern california was the volume that subsequently produced the largest slip in the magnitude 7 1 hector mine earthquake of october 1999

stress sensitivity of fault seismicity a comparison between limited offset oblique and major strike slip faults we present a new three dimensional inventory of the southern san francisco bay area faults and use it to calculate stress applied principally by the 1989 m 7 1 loma prieta earthquake and to compare fault seismicity rates before and after 1989 the major high angle right lateral faults exhibit a different response to the stress change than do minor oblique right lateral thrust faults seismicity on oblique slip faults in the southern santa clara valley thrust belt increased where the faults were unclamped the strong dependence of seismicity change on normal stress change implies a high coefficient of static friction in contrast we observe that faults with significant offset 50 100 km behave differently microseismicity on the hayward fault diminished where right lateral shear stress was reduced and where it was unclamped by the loma prieta earthquake we observe a similar response on the san andreas fault zone in southern california after the landers earthquake sequence additionally the offshore san gregorio fault shows a seismicity rate increase where right lateral oblique shear stress was increased by the loma prieta earthquake despite also being clamped by it these responses are consistent with either a low coefficient of static friction or high pore fluid pressures within the fault zones we can explain the different behavior of the two styles of faults if those with large cumulative offset become impermeable through gouge buildup coseismically pressurized pore fluids could be trapped and negate imposed normal stress changes whereas in more limited offset faults fluids could rapidly escape the difference in behavior between minor and major faults may explain why frictional failure criteria that apply intermediate coefficients of static friction can be effective in describing the broad distributions of aftershocks that follow large earthquakes since many of these events occur both inside and outside major fault zones

effects of imparted coulomb stress changes in the seismicity and cluster of the december 2017 hojedk se iran triplet the hojedk area in the southeastern iran experienced three earthquakes during 12 days in december 2017 these events occurred in proximity to a region that has experienced several moderate and large events in the past in this paper the role of coulomb stress changes in occurrence of the hojedk cluster was investigated and also the produced stress changes due to these events on the surrounding and optimally oriented faults was calculated previous earthquakes events in the golbaf sirch region the shahdad slip and the dahuiyeh zarand earthquake imparted positive stress changes on the fault planes of the hojedk earthquakes especially on the ruptured plane of the first main shock the hojedk first main shock triggered the second one by imparting maximum stress changes of about 11 7 mpa on the fault plane of this event and these two events brought the third main shock to failure by producing more than 6 0 mpa stress changes on its ruptured plane among the major active faults in the surrounding area the middle part of the nayband fault northern part of the golbaf sirch fault and southern part of the kuhbanan fault received positive stress changes and southen parts of the ravar and all parts of the chatrud faults received negative stress changes due to the hojedk earthquakes furthermore our results for correlation between coulomb stress changes and seismicity distribution showed that following the dahuiyeh zarand earthquake the majority of the seismicity located on the positive stress area and coulomb stress changes have a controlling role on the spatial distribution of seismicity even after a decade the occurrence of the hojedk first main shock affects the spatial distribution of aftershocks until the occurrence of the next main hocks by triggering the next one the stress patterns change in the area and seismicity follows from the stress patterns of the last event

elastic and inelastic triggering of earthquakes in the north anatolian fault zone abstract deformation models used to explain the triggering mechanism often assume pure elastic behaviour for the crust and upper mantle in reality however the mantle and possibly the lower crust behave viscoelastically particularly over longer time scales consequently the stress field of an earthquake is in general time dependent in addition if the elastic stress increase were enough to trigger a later earthquake this triggered event should occur instantaneously and not many years after the triggering event hence it is appropriate to include inelastic behaviour when analysing stress transfer and earthquake interaction in this work we analyse a sequence of 10 magnitude m s 6 5 events along the north anatolian fault between 1939 and 1999 to study the evolution of the regional coulomb stress field we investigate the triggering of these events by stress transfer taking viscoelastic relaxation into account we evaluate the contribution of elastic stress changes of post seismic viscoelastic relaxation in the lower crust and mantle and of steady tectonic loading to the total coulomb stress field we analyse the evolution of stress in the region under study as well as on the rupture surfaces of the considered events and their epicentres we study the state of the coulomb stress field before the 1999 izmit and duzce earthquakes as well as in the marmara sea region in general the coulomb stress failure criterion offers a plausible explanation for the location of these events however we show that using a purely elastic model disregards an important part of the actual stress increase decrease in several cases post seismic relaxation effects are important and greater in magnitude than the stress changes due to steady tectonic loading consequently viscoelastic relaxation should be considered in any study dealing with coulomb stress changes according to our study and assuming that an important part of the rupture surface must be stressed for an earthquake to occur the most likely value for the viscosity of the lower crust or mantle in this region is 5 10 17 10 18 pa s our results cannot rule out the possibility of other time dependent processes involved in the triggering of the 1999 duzce event however the stress increase due to viscoelastic relaxation brought 22 of the 1999 duzce rupture area over the threshold value of c 0 01 mpa 0 1 bar and took the whole surface closer to failure by an average of 0 2 mpa finally we argue that the marmara sea region is currently being loaded with positive coulomb stresses at a much faster rate than would arise exclusively from steady tectonic loading on the north anatolian fault

new insights into the mechanism of postseismic stress relaxation exemplified by the 23 june 2001 mw 8 4 earthquake in southern peru 1 the 2001 mw 8 4 southern peru subduction earthquake marked the beginning of a transient postseismic surface motion in direction of the coseismic displacement at the permanent gps station arequipa in general this motion is assigned to afterslip our hypothesis is that the observed transient signal can be explained by stress relaxation processes in the overriding plate we use a 2d finite element model incorporating non linear viscoelastic maxwell rheology our model results indicate that coseismically induced stresses are relieved by viscoelastic stress relaxation in the lower crust the trenchward directed creep motion is transferred to the upper crust due to elastic coupling leading there to an instantaneous relief of elastic stresses in contrast to the existing conceptual models for stress relaxation which incorporate shear stresses we conclude that tensional elastic stresses throughout the crust and upper mantle are the main driving forces for the transient gps signal

uniform postglacial slip rate along the central 600 km of the kunlun fault tibet from 26al 10be and 14c dating of riser offsets and climatic origin of the regional morphology late pleistocene holocene sinistral slip rates on several segments of the kunlun fault in northeastern tibet have been determined these determinations are based on the measured displacement of alluvial surfaces whose surface ages were determined by cosmogenic 2 6 al and 1 0 be dating of quartz pebbles and by 1 4 c dating of charcoal in the west at three sites along the xidatan dongdatan segment of the fault near 94 e terrace riser offsets ranging from 24 to 110 m with cosmogenic ages ranging from 1800 to 8200 yr yield a mean left lateral slip rate of 11 7 1 5 mm yr 1 field observations indicate minimum offsets of 9 12 m this offset when combined with the long term slip rate indicates that great earthquakes m 8 rupture this segment of the fault with a recurrence interval of 800 1000 yr at two sites along the dongxi anyemaqin segment of the fault near 99 e terrace riser offsets ranging from 57 to 400 m with 1 4 c ages ranging from 5400 to 37 000 yr bp yield a minimum slip rate of 10 mm yr 1 at one site the 1937 january 7 m 7 5 and the penultimate earthquakes produced 4 m of left slip and 0 4 m of reverse slip the maximum recurrence interval of earthquakes with such characteristic slip is thus 400 yr farther east near 100 5 e along the maqen segment of the fault the 180 m offset of a lateral moraine emplaced between the last glacial maximum 20 ka and 11 100 yr bp yields a mean slip rate of 12 5 2 5 mm yr 1 the slip rates are constant within uncertainty throughout the 600 km of the kunlun fault that we studied the average slip rate is 11 5 2 0 mm yr 1 extrapolating this rate to the reminder of the fault we conclude that most 80 per cent of the 300 morphological offsets measured in the field or on spot satellite images post date the last glacial maximum most of the terraces we studied were deposited during the humid period of the early holocene optimum 9 5 ka the formation of younger terraces reflects late holocene climate change

uniform slip rate along the kunlun fault implications for seismic behaviour and large scale tectonics a long term slip rate is derived from concordant 10 be 26 al and 14 c dating of cumulativeoffse ts along much of the length of the kunlun fault values at 6 sites indi cateuniform slip 11 5 2 0 mm yr since 40 kyr bp this relatively high slip rate corresponds to a first order discon tinuity in the asian crustal velocity field m 8a nd m 7 5 earthquakes on 2 segments of the fault recur with charac teristic slip 10 2ma nd 4 4 0 4m ev e ry 850 and 420 yrs respectively

fault plane solutions of earthquakes and active tectonics of the tibetan plateau and its margins summary fault plane solutions of earthquakes within and on the margins of the tibetan plateau show diverse styles of faulting and deformation with thrust faulting and crustal shortening normal to the margins of the plateau and with normal and strike slip faulting resulting in roughly east west crustal extension within the plateau the direction of overthrusting of the himalaya onto the indian shield is radially outward varying from southwest in the western himalaya to south southeast in the east assuming that the indian shield behaves rigidly this requires a west northwest divergence of western tibet from southeastern tibet at a rate of 18 9 mm yr 1 comparable with the rate of convergence at the himalaya fault plane solutions of earthquakes in the southern portion of the tibet plateau consistently show large components of normal faulting on roughly north striking planes and corroborate such extension within the high plateau where elevations exceed 5000 m normal and strike slip faulting occur so that an overall east southeast west northwest extension of the region at about 10 mm yr 1 is partitioned into roughly equal parts of crustal thinning and north northeast south southwest crustal shortening about 5 mm yr 1 in general strike slip faulting characterizes solutions for earthquakes within eastern tibet where mean elevations drop below 4500 5000 m but the orientations of the strike slip faults vary across the region in central tibet left lateral slip occurs on planes trending roughly northeast but for earthquakes farther east the orientations of that plane become progressively east west and then southeast this variation in orientation implies a rotation of material along curved left lateral shear zones thus the eastward extrusion of tibet appears to be facilitated not only by rapid left lateral shear but also by large clockwise rotations of the material in eastern tibet the rate of eastward extrusion of material in eastern tibet relative to the tarim basin to its north is roughly 30 40 mm yr 1 fault plane solutions of earthquakes in the northern and eastern margins of tibet show large components of thrust faulting with the p axes oriented radially outward from the plateau and approximately perpendicular to the regional topographic contours of the plateau the orientation of this crustal shortening is northeast southwest on the northeastern margin east west on the eastern margin and northwest southeast in the longmenshan on the southeastern margin thus at least some of the extrusion of eastern tibet out of india s northward path into asia is absorbed by crustal shortening on the margins of the plateau the variation from normal faulting in the high tibetan plateau where elevations exceed 5000 m to dominantly strike slip faulting farther east where elevations are lower and then to thrust faulting on the margins of the plateau where elevations drop below 3000 m surely results at least in part from a decrease in the value of the vertical stress the magnitude of the east west compressive stress need not vary across the plateau

evidence of nonlinear elasticity of the crust from the mw7 6 manyi tibet earthquake satellite synthetic aperture radar sar interferometry shows that the magnitude 7 6 manyi earthquake of 8 november 1997 produced a 170 kilometer long surface break with up to 7 meters of left lateral slip reactivating a n76 e quaternary fault in western tibet the radar interferometric map reveals asymmetric along strike displacement profiles between the two sides of the surface rupture a pattern that cannot be explained with linear elastic theory this observation suggests that the elastic moduli of the crust in tension and in compression are different because of the presence of cracks in the crust at shallow depth a model indicates that a ratio of 2 between compressive and tensile elastic moduli can account for the observed asymmetry a ratio that is consistent with laboratory and borehole measurements

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

complex geometry and segmentation of the surface rupture associated with the 14 november 2001 great kunlun earthquake northern tibet china abstract the 14 november 2001 kunlun china earthquake with a moment magnitude m w 7 8 occurred along the kusai lake kunlun pass fault of the kunlun fault system we document the spatial distribution and geometry of surface rupture zone produced by this earthquake based on high resolution satellite landsat etm aster spot and ikonos images combined with field measurements our results show that the surface rupture zone can be divided into five segments according to the geometry of surface rupture including the sun lake buka daban hongshui river kusai lake hubei peak and kunlun pass segments from west to east these segments each 55 to 130 km long are separated by step overs the sun lake segment extends about 65 km with a strike of n45 75 w between 90 05 e 90 50 e along the previously unrecognized west sun lake fault a gap of about 30 km long exists between the sun lake and buka daban peak where no obvious surface ruptures can be observed either from the satellite images or field observations the buka daban hongshui river kusai lake hubei peak and kunlun pass segments run about 365 km striking n75 85 w along the southern slope of the kunlun mountains between 91 07 e 94 58 e this segmentation of the surface rupture is well correlated with the pattern of slip distribution measured in the field detailed mapping suggest that these five first order segments can be further separated into over 20 second order segments with a length of 10 30 km linked by smaller scale step overs or bends our result also shows that the total coseismic surface rupture length produced by the 2001 kunlun earthquake is about 430 km excluding the 30 km long gap which is the longest coseismic surface rupture for an intracontinental earthquake ever recorded finally we suggest a multiple bilateral rupture propagation model that shows the rupture process of the 2001 m w 7 8 earthquake is complex it consists of westward and eastward rupture propagations and interaction of these bilateral rupture processes

influence of static stress changes on earthquake locations in southern california earthquakes induce changes in static stress on neighbouring faults that may delay hasten or even trigger subsequent earthquakes1 10 the length of time over which such effects persist has a bearing on the potential contribution of stress analyses to earthquake hazard assessment but is presently unknown here we use an elastic half space model11 to estimate the static stress changes generated by damaging magnitude m 5 earthquakes in southern california over the past 26 years and to investigate the influence of these changes on subsequent earthquake activity we find that in the 1 5 year period following a m 5 earthquake any subsequent nearby m 5 earthquake almost always ruptures a fault that is loaded towards failure by the first earthquake after this period damaging earthquakes are equally likely to rupture loaded and relaxed faults our results suggest that there is a short period of time following a damaging earthquake in southern california in which simple coulomb failure stress models could be used to identify regions of increased seismic hazard

crustal deformation in the india eurasia collision zone from 25 years of gps measurements the india eurasia collision zone is the largest deforming region on the planet direct measurements of present day deformation from global positioning system gps have the potential to discriminate between competing models of continental tectonics but the increasing spatial resolution and accuracy of observations have only led to increasingly complex realizations of competing models here we present the most complete accurate and up to date velocity field for india eurasia available comprising 2576 velocities measured during 1991 2015 the core of our velocity field is from the crustal movement observation network of china i ii 27 continuous stations observed since 1999 56 campaign stations observed annually during 1998 2007 1000 campaign stations observed in 1999 2001 2004 and 2007 260 continuous stations operating since late 2010 and 2000 campaign stations observed in 2009 2011 2013 and 2015 we process these data and combine the solutions in a consistent reference frame with stations from the global strain rate model compilation then invert for continuous velocity and strain rate fields we update geodetic slip rates for the major faults some vary along strike and find that those along the major tibetan strike slip faults are in good agreement with recent geological estimates the velocity field shows several large undeforming areas strain focused around some major faults areas of diffuse strain and dilation of the high plateau we suggest that a new generation of dynamic models incorporating strength variations and strain weakening mechanisms is required to explain the key observations seismic hazard in much of the region is elevated not just near the major faults

quaternary and active faulting observed on the 1985 academia sinica royal society geotraverse of tibet active and recent faulting along the main north south road in tibet is dominated by normal faulting occurring on northerly trending planes and by strike slip faulting both of which reflect an east west extension of the plateau normal faulting is prevalent in the southern half of the plateau but we saw no evidence for any major graben in the northern half strike slip faulting on roughly easterly trending structures is m ore prevalent in the northern half but conjugate faulting with right lateral slip on northwesterly trending planes and left lateral slip on northeasterly trending planes is common in the southern half in two areas we also observed components of thrust faulting apparently in association with young strikeslip faulting our most important results are bounds on the rates of slip on the two main strands of the kunlun strike slip fault system which trends east w est through the kunlun range ground moraine containing boulders of pyroxenite is separated by 30 km from the nearest outcrop of such rock implying that amount of displacement in the last 1 5 to 3 m a therefore the average rate of slip during the quaternary period has been between 10 and 20 mm a with a likely value of 13 mm a abundant fresh tension cracks and mole tracks imply continued slip on the main strand the xidatan tuosuohu maqu fault and the likely occurrence of a major earthquake in the last few hundred years consistent offsets of gullies and dry stream channels of about 10 m may reflect slip of that amount during such an earthquake and possible multiple offsets at one site suggest that slip may occur by large displacements of 10 m during infrequent great earthquakes along the other strand the kunlun pass fault offsets of roughly 50 to 150 m of apparently post glacial valleys and of one glacier and its terminal moraine suggest a holocene rate of slip between 5 and 20 mm a and most likely about 10 mm a on this fault these rapid rates of displacement imply that tibet is being extruded rapidly eastward at a rate com parable to the rate at which india is penetrating into eurasia and therefore that at present a substantial fraction of this penetration is being absorbed by the eastward extrusion of tibet

mantle flow beneath a continental strike slip fault postseismic deformation after the 1999 hector mine earthquake two recent large earthquakes in the mojave desert california the magnitude 7 3 1992 landers and magnitude 7 1 1999 hector mine earthquakes have each been followed by elevated crustal strain rates over periods of months and years geodetic data collected after the hector mine earthquake exhibit a temporally decaying horizontal velocity field and a quadrant uplift pattern opposite to that expected for localized shear beneath the earthquake rupture we interpret the origin of this accelerated crustal deformation to be vigorous flow in the upper mantle in response to the stress changes generated by the earthquake our results suggest that transient flow in the upper mantle is a fundamental component of the earthquake cycle and that the lower crust is a coherent stress guide coupling the upper crust with the upper mantle

fault interaction and stress triggering of twentieth century earthquakes in mongolia 1 a cluster of exceptionally large earthquakes in the interior of asia occurred from 1905 to 1967 the 1905 m7 9 tsetserleg and m8 4 bolnai earthquakes the 1931 m8 0 fu yun earthquake the 1957 m8 1 gobi altai earthquake and the 1967 m7 1 mogod earthquake sequence each of the larger m 8 earthquakes involved strike slip faulting averaging more than 5 m and rupture lengths of several hundred kilometers available geologic data indicate that recurrence intervals on the major source faults are several thousands of years and distances of about 400 km separate the respective rupture areas we propose that the occurrences of these and many smaller earthquakes are related and controlled to a large extent by stress changes generated by the compounded static deformation of the preceding earthquakes and subsequent viscoelastic relaxation of the lower crust and upper mantle beneath mongolia we employ a spherically layered viscoelastic model constrained by the 1994 2002 gps velocity field in western mongolia vergnolle et al 2003 using the succession of twentieth century earthquakes as sources of deformation we then analyze the time dependent change in coulomb failure stress f at remote interaction distances static f values are small however modeled postseismic stress changes typically accumulate to several tenths of a bar over time intervals of decades almost all significant twentieth century regional earthquakes m 6 with well constrained fault geometry lie in positive f lobes of magnitude about 0 5 bar our results suggest that significant stress transfer is possible among continental faults separated by hundreds of kilometers and on timescales of decades

did the 2008 mw 7 9 wenchuan earthquake trigger the occurrence of the 2017 mw 6 5 jiuzhaigou earthquake in sichuan china

3d finite element modeling of earthquake interaction and stress accumulation on main active faults around the northeastern tibetan plateau edge in the past 100 years the northeastern tibetan plateau edge is an active tectonic region with crustal deformation featured mainly by thrust and strike slip faults in the past 100 years several strong earthquakes have occurred around this region associated with regional tectonic loading these strong earthquakes altered the stress buildup of active faults this in turn should affect the potential hazard of seismicity around the northeastern tibetan plateau here we developed a 3d viscoelastic finite element model to explore the stress accumulation along the main active faults during the past 100 years in this model rheological contrast of the crust and upper mantle between the tibetan plateau and its surrounding regions is approximated and regional tectonic loading is simplified from dense global positioning system measurements results show that after the 1920 m 8 7 haiyuan earthquake the succeeding ruptures both of thrusting and strike slipping events had received positive changes of coulomb failure stress among which the coseismic and the postseismic deformations from previous earthquake s contributed 36 80 this means that significant mechanical interactions existed between the active faults around northeastern tibet during the earthquake process even though they were separated by hundreds of kilometers numerical results also suggest that the 1954 m 7 2 shandan earthquake and the 1990 m 6 2 tianzhu earthquake could have been triggered because the coulomb failure stress received from coseismic and postseismic deformation of previous earthquakes around the epicenter of these two events reached 0 02 0 3 mpa after about 100 years of regional tectonic loading coseismic and postseismic deformations of past large earthquakes the coulomb failure stress along the northeastern segment of the altyn tagh fault the tianzhu segment of the haiyuan fault and the gulang fault has accumulated to 0 005 0 2 mpa therefore as previous studies mentioned for the tianzhu seismic gap these active faults should be carefully studied because of their potential earthquake hazard online material snapshots of coulomb failure stress changes

delayed triggering of the 1999 hector mine earthquake by viscoelastic stress transfer stress changes in the crust due to an earthquake can hasten the failure of neighbouring faults and induce earthquake sequences in some cases1 2 3 4 5 the 1999 hector mine earthquake in southern california magnitude 7 1 occurred only 20 km from and 7 years after the 1992 landers earthquake magnitude 7 3 this suggests that the hector mine earthquake was triggered in some fashion by the earlier event but uncertainties in the slip distribution and rock friction properties associated with the landers earthquake have led to widely varying estimates of both the magnitude and sign of the resulting stress change that would be induced at the location of the hector mine hypocentre with estimates varying from 1 4 bar ref 6 to 0 5 bar ref 7 more importantly coseismic stress changes alone cannot satisfactorily explain the delay of 7 years between the two events here we present the results of a three dimensional viscoelastic model that simulates stress transfer from the ductile lower crust and upper mantle to the brittle upper crust in the 7 years following the landers earthquake using viscoelastic parameters that can reproduce the observed horizontal surface deformation following the landers earthquake our calculations suggest that lower crustal or upper mantle flow can lead to postseismic stress increases of up to 1 2 bar at the location of the hector mine hypocentre during this time period contributing to the eventual occurrence of the 1999 hector mine earthquake these results attest to the importance of considering viscoelastic processes in the assessment of seismic hazard8 9 10 11

stress modulation of the seismic gap between the 2008 ms 8 0 wenchuan earthquake and the 2013 ms 7 0 lushan earthquake and implications for seismic hazard

coseismic deformation of the 2001 mw 7 8 kokoxili earthquake in tibet measured by synthetic aperture radar interferometry the 14 november 2001 m w 7 8 kokoxili earthquake ruptured more than 400 km of the westernmost stretch of the left lateral kunlun fault in northern tibet interferometric synthetic aperture radar data from descending orbits along four adjacent tracks covering almost the entire rupture and 1 m pixel ikonos satellite images are used to map the rupture geometry and the surface displacements produced by the event interferograms are then inverted to solve for coseismic slip on the fault at depth the radar data show that the rupture connected the heituo fault where the earthquake initiated to the main kunlun fault cutting across a pull apart trough in between the two strike slip faults the fault model includes two vertical sections extending to a depth of 20 km and discretized into 5 km 5 km patches using a nonnegative least squares method that includes an appropriate degree of smoothing we solve for the left lateral slip on each fault patch our solution shows that the largest slip occurred at depths between 0 and 5 km reaching 8 m in two areas 200 and 250 km east of the earthquake epicenter significant slip took place below 10 km at both ends of the rupture slip appears to have been highly variable along the fault defining six sections of major moment release these sections correspond to six subsegments of the kunlun fault system defined from the surface morphology of the fault this suggests that fault geometry exerted a predominant influence on controlling the rupture propagation

the role of triggering by static stress transfer during geothermal reservoir stimulation 1 during creation of an enhanced geothermal system massive fluid injections are conducted to induce fracture shear which generates reservoir permeability in this study we analyze coseismic static stress transfer caused by induced seismic events during a stimulation at the european research project at soultz sous forets alsace france for this purpose we developed an efficient method to calculate coseismic static stress changes from an elliptical slip distribution on a circular fracture using superposition of rectangular sources which enables us to apply an analytical solution for fast computation this method is applied on a data set of 715 focal mechanisms derived from seismic recordings of the stimulation of the well gpk2 to calculate temporal evolution of static stress transfer we find that the resulting structure of coseismic stress changes can be divided into three parts a quiet zone where no spreading of seismicity occurs an active zone within the created reservoir with ongoing fracturing and a process zone where the growth of the reservoir occurs static stress changes in the active zone are of the order of 1 mpa both positive and negative but may exceed this value considerably on a local scale analysis of stress changes from a cluster of events that occurred after shut in lets us conclude that triggering by coseismic static stress changes is possible for some events our analysis shows that triggering by static stress transfer plays a minor role for injection induced seismicity in a volumetric reservoir whereas it can be quite effective for rupture propagation along single large fault zones

simulating faults and plate boundaries with a transversely isotropic plasticity model abstract in mantle convection simulations dynamically evolving plate boundaries have for the most part been represented using an visco plastic flow law these systems develop fine scale localized weak shear band structures which are reminiscent of faults but it is a significant challenge to resolve the large and the emergent small scale behavior we address this issue of resolution by taking into account the observation that a rock element with embedded planar failure surfaces responds as a non linear transversely isotropic material with a weak orientation defined by the plane of the failure surface this approach partly accounts for the large scale behavior of fine scale systems of shear bands which we are not in a position to resolve explicitly we evaluate the capacity of this continuum approach to model plate boundaries specifically in the context of subduction models where the plate boundary interface has often been represented as a planar discontinuity we show that the inclusion of the transversely isotropic plasticity model for the plate boundary promotes asymmetric subduction from initiation a realistic evolution of the plate boundary interface and associated stresses is crucial to understanding inter plate coupling convergent margin driven topography and earthquakes

three dimensional finite element modeling of stress evolution around the xiaojiang fault system in the southeastern tibetan plateau during the past 500 years abstract the left lateral strike slip xiaojiang fault system is a main boundary between the southeastern tibetan plateau and the south china block and accumulates several large m 7 earthquakes in the past 500 years and a dozen of moderate 5 7 earthquake ruptures occurred in the past 500 years are simulated with split node technique in seismogenic upper crust we investigate the coulomb failure stress changes mainly on vertical planes parallel to the different strands of the xiaojiang fault system and at the epicenters of large m 7 earthquakes in the past 500 years and of moderate 5 7 earthquakes that occurred in the past 500 years both from their coseismic and postseismic effects among which the postseismic effect results in the stressing rate being obviously accelerated near epicenters of the large m 7 earthquakes after their occurrence thus the percentage of positive coulomb failure stress changes of 0 01 mpa at the epicenters increases from 37 to 50 for the large m 7 earthquakes and from 43 to 64 for the moderate 5

variations in locking along the east kunlun fault tibetan plateau china using gps and leveling data the east kunlun fault ekf is one of the largest and most active sinistral strike slip faults in the qinghai tibet plateau since 1900 many earthquakes of magnitude 7 have occurred in this region the maqin maqu segment mms a seismic gap underlying a densely populated zone is particularly important while the area has been extensively researched to assess seismic risk refined asperity geodetic imaging is deficient we combined multiple sets of gps and leveling observations to obtain spatial temporal distributions of locking along the ekf we delineated the probable asperity ranges according to the fault plane locking and the distribution of small earthquakes long term observations on gps velocity 1999 2013 and leveling 1970 2013 indicate that the dulan maduo segment dms of the ekf has a 140 km long strong coupling section and both the mms and the eastern ruoergai segments have a 40 km long locking range the 2013 2015 gps velocity observations show that from maqu to maqin the locked dms and mms lengths increased to 200 km and 240 km respectively while the locked eastern ruoergai segment decreased and migrated 60 km to the west this change in locking over time implies that the post seismic effects of surrounding earthquakes have had significant impacts on the ekf the locking area derived from 2015 to 2017 gps velocity shows a growing trend and indicates the connectedness between the two speculative asperities combining the distribution of historical earthquakes and the precision positioning of small earthquakes we conclude that the geodetic imaging of the ekf indicates that the mms and dms are high risk zones for destructive earthquakes

present day crustal deformation in china constrained by global positioning system measurements global positioning system gps measurements in china indicate that crustal shortening accommodates most of india s penetration into eurasia deformation within the tibetan plateau and its margins the himalaya the altyn tagh and the qilian shan absorbs more than 90 of the relative motion between the indian and eurasian plates internal shortening of the tibetan plateau itself accounts for more than one third of the total convergence however the tibetan plateau south of the kunlun and ganzi mani faults is moving eastward relative to both india and eurasia this movement is accommodated through rotation of material around the eastern syntaxis the north china and south china blocks east of the tibetan plateau move coherently east southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year respectively with respect to the stable eurasia

response of seismicity to coulomb stress triggers and shadows of the 1999 mw 7 6 chi chi taiwan earthquake 1 the correlation between static coulomb stress increases and aftershocks has thus far provided the strongest evidence that stress changes promote seismicity a correlation that the chi chi earthquake well exhibits several studies have deepened the argument by resolving stress changes on aftershock focal mechanisms which removes the assumption that the aftershocks are optimally oriented for failure here one compares the percentage of planes on which failure is promoted after the main shock relative to the percentage beforehand for chi chi we find a 28 increase for thrust and an 18 increase for strike slip mechanisms commensurate with increases reported for other large main shocks however perhaps the chief criticism of static stress triggering is the difficulty in observing predicted seismicity rate decreases in the stress shadows or sites of coulomb stress decrease detection of sustained drops in seismicity rate demands a long catalog with a low magnitude of completeness and a high seismicity rate conditions that are met at chi chi we find four lobes with statistically significant seismicity rate declines of 40 90 for 50 months and they coincide with the stress shadows calculated for strike slip faults the dominant faulting mechanism the rate drops are evident in uniform cell calculations 100 month time series and by visual inspection of the m 3 seismicity an additional reason why detection of such declines has proven so rare emerges from this study there is a widespread increase in seismicity rate during the first 3 months after chi chi and perhaps many other main shocks that might be associated with a different mechanism

post seismic motion following the 1997 manyi tibet earthquake insar observations and modelling summary on november 8 1997 a mw 7 6 earthquake occurred in the manyi region of northern tibet near the western end of the kunlun fault over 7 m of left lateral slip occurred on a 200 kmlong fault here we use insar observations of post seismic surface deformation following the manyi earthquake to investigate possible causal mechanisms time series of deformation are constructed from 26 interferograms covering the entire length of the fault for nearly 4 yr after the earthquake three different modelling approaches are used to try and understand the observed variations in surface displacement first order poroelastic models predict displacement fields which do not match those observed modelling of viscoelastic stress relaxation in a half space with standard linear solid rheology beneath an elastic lid provides a reasonable fit to the observations and demonstrates that two relaxation times are needed to characterize the post seismic transient the best fitting viscosity is 4 10 18 pa s and the fully relaxed shear modulus is 32 per cent of the purely elastic value a model with a maxwell viscoelastic halfspace underlying the lid cannot explain the observations at later times larger viscosities are required than at earlier times this increase in effective viscosity with time may be consistent with stress relaxation occurring in a power law rheology the time series are also inverted for distributed afterslip on an extension of the coseismic rupture along strike correlation of coseismic and post seismic slip maxima suggests that afterslip is a plausible mechanism the maximum slip in the afterslip model is 0 72 m after 3 yr and the equivalent moment release is approximately 20 per cent of the coseismic moment this study shows that it is possible to rule out certain mechanisms as the dominant post seismic process but with the current insar data set it is difficult to distinguish between other plausible options

storm time penetration to low latitudes of magnetospheric ionospheric convection and convection driven thermospheric winds from de 2 satellite measurements during two magnetic storms we show that i the magnetospheric convection driven east west ion flows of high velocities 1400 m s penetrate to magnetic latitudes as low as 30 with larger velocities 2000 3000 m s appearing at 45 50 latitudes and ii high velocity 300 640 m s thermospheric winds appear in association with the above ion flows the similarity of the latitude structures and time evolutions of the ion and neutral motions indicates that the zonal winds are driven by magnetospheric ionospheric convection through ion drag these velocities of the convection driven ion flows and winds at such low latitudes are much larger than those reported from observations or predicted by current models

global positioning system measurements from eastern tibet and their implications for india eurasia intercontinental deformation we present and interpret global positioning system gps measurements of crustal motions for the period 1991 1998 for a network encompassing the eastern part of the tibetan plateau and its foreland relative to a eurasian frame defined by minimizing the velocities of 16 gps stations in europe central asia and siberia stations within all parts of the plateau foreland in south china move 6 10 mm yr east southeast indicating that the eastward movement within the plateau is part of a broader eastward movement that involves the plateau and its eastern and northern foreland north of the plateau foreland stations move northeastward at 10 mm yr indicating that the northern boundary of the deformation zone lies north of the plateau with this realization of a eurasian frame the velocity of the gps station at bangalore in southern india implies that the northward motion of india is 5 12 mm yr slower than that predicted from the nuvel 1a plate reconstruction viewed relative to the south china block stations of the northeast plateau bounded on the north by the qilian shan and the altyn tagh fault move nne to ne with velocities ranging from 19 mm yr within the plateau to 5 11 mm yr in its foreland the altyn tagh fault shows left lateral slip of 10 mm yr at 95 e and shortening across the fault of 5 mm yr stations south and west of the xianshuihe xiaojiang fault system define a crustal fragment rotating clockwise at 10 mm yr relative to the south china block around the eastern himalayan syntaxis the gps measurements indicate no significant shortening 3 mm yr within the longmen shan of the central eastern plateau and its adjacent foreland although the longmen shan rise over 6 km in 100 km horizontal distance geological studies indicate that the deformational field was established diachronously in late miocene to pliocene time was characterized by no east west shortening of tibetan crust and has an inhomogeneous style of deformation resulting from a balance of different tectonic processes

the co seismic coulomb stress change and expected seismicity rate caused by 14 april 2010 ms 7 1 yushu china earthquake a moderate and widely felt earthquake of ms7 1 mw6 9 occurred on april 14 2010 in yushu district of qinghai province china which destroyed a large number of buildings and killed more than two thousand people the distribution of the aftershock sequence is sparse but with relatively large magnitudes ms6 3 and ms5 7 aftershocks were recorded strong aftershocks are still highly potential to occur in the near future therefore it is critical to delineate areas where potential aftershocks could occur based on static stress triggering theory we calculated the coseismic stress changes induced by the mainshock in yushu county and its surrounding regions by adopting elastic dislocation theory and a multilayered crustal model according to the rate and state variable friction law we calculated the expected seismicity rate and probability of occurrences of m 5 0 earthquake in the next ten years it is observed that the coulomb stress changes increase apparently on the segment of the wudaoliang qumalai fault the batang luoxu and dangjiang longbao segments of the ganzi yushu fault and the whole wulanwula lake yushu fault based on the theory of coulomb stress triggering the probability of earthquake occurrence on these faults would increase in the near future considering the historical seismicity the strain accumulation and the coulomb stress changes the probability of m 5 earthquake and m 6 earthquake occurrence in the entire study area in the next 10 years are 79 87 and 26 7 33 6 respectively actually a moderate earthquake of ms5 3 occurred to the northwest of the nangqian county on june 26 2011

gravitational viscoelastic postseismic relaxation on a layered spherical earth viscoelastic relaxation of a ductile asthenosphere underlying a purely elastic plate is a strong candidate process for explaining anomalous rates of crustal deformation observed following large earthquakes the nongravitational treatment of pollitz 1992 which is valid on a global scale and includes the effects of compressibility is here extended to permit the calculation of gravitational viscoelastic relaxation for a specified spherically layered viscoelastic rheology following an earthquake in an elastic layer the simple approximations we adopt make the resulting treatment particularly suitable for near field calculations for an asthenosphere with a maxwell rheology the effect of gravitational coupling is manifested only many relaxation times after the earthquake as obtained by previous investigators its effect is generally to speed up the long wavelength component of the relaxation process and attenuate the overall vertical displacement pattern several subtle features common to the relaxation behavior from several different fault types thrust rift and strike slip are identified the effect of gravitational coupling on horizontal displacements is consistent with flexure of the upper elastic plate driven by the corresponding effects on the vertical displacement stress diffusion away from the source region generally exhibits pulse like behavior which is dispersive in both space and time if the asthenosphere is confined to a relatively narrow channel then the dispersion branches governing relaxation are radically altered and stress diffusion effects far from the coseismic rupture zone exhibit a complicated time dependence reflecting the competing tendencies of toroidal and spheroidal mode relaxation

stress evolution on active faults in the southwestern yunnan region southeastern tibetan plateau and implications for seismic hazard abstract southwestern yunnan is expressed as a seismically active region bordering the southeastern tibetan plateau however the recent seismicity in this region has been relatively quiet considering some highly populated cities nearby and the historical record in this region understanding the stress changes on the main active faults is crucial for seismic hazard analysis in this study we calculated the co and post seismic coulomb failure stress change cfs on these faults caused by historical earthquakes in and around the region then by integrating the inter seismic tectonic loading estimated using a geodynamic model and gps data we analyzed the total stress change on all of these faults the results reveal that the cfs patterns caused by events on different segments of the sagaing fault vary the combined cfs increased on the middle segment of the longling lancang fault the heihe fault and the nantinghe fault among which the maximum change reached 3 5 kpa the great 1950 assam earthquake in the eastern himalayan syntax increased the cfs on almost all faults and the maximum change reached 20 kpa more importantly the cfs caused by earthquakes in the southwestern yunnan region was significantly larger than that caused by earthquakes in the surrounding region because of the geographical proximity the inter seismic tectonic stress loading rate reached 2 kpa yr 1 a significant total stress build up occurred on five segments distributed among four faults namely the nantinghe fault the longling lancang fault the heihe fault and the menglian fault making them possible candidates for the next major earthquake in this region

short and long term earthquake triggering along the strike slip kunlun fault china insights gained from the ms 8 1 kunlun earthquake and other modern large earthquakes abstract following the 2001 ms8 1 kunlun earthquake earthquake records of more than 10 years in addition to more than one century s records of large earthquakes provide us with a chance to examine short term days to a few years and long term years to decades seismic triggering following a magnitude 8 continental earthquake along a very long strike slip fault the kunlun fault system located in northern tibet china based on the calculations of coseismic coulomb stress changes cfs from the larger earthquake and post seismic stress changes due to viscoelastic stress relaxation in the lower crust and upper mantle we examined the temporal evolution of seismic triggering the etas epidemic type aftershocks sequence model shows that the seismic rate in the aftershock area over 10 years was higher than the background seismicity before the mainshock moreover we discuss long term years to decades triggering and the evolution of stress changes for the sequence of five large earthquakes of m 7 0 that ruptured the kunlun fault system since 1937 all subsequent events of m 7 0 occurred in the regions of positive accumulated cfs these results show that short term up to 200 days in our case triggering along the strike slip kunlun fault is governed by coseismic stress changes while long term triggering is somewhat due to post seismic coulomb stress changes resulting from viscoelastic relaxation

stress transferred by the 1995 mw 6 9 kobe japan shock effect on aftershocks and future earthquake probabilities the kobe earthquake struck at the edge of the densely populated osaka kyoto corridor in southwest japan we investigate how the earthquake transferred stress to nearby faults altering their proximity to failure and thus changing earthquake probabilities we find that relative to the pre kobe seismicity kobe aftershocks were concentrated in regions of calculated coulomb stress increase and less common in regions of stress decrease we quantify this relationship by forming the spatial correlation between the seismicity rate change and the coulomb stress change the correlation is significant for stress changes greater than 0 2 1 0 bars 0 02 0 1 mpa and the nonlinear dependence of seismicity rate change on stress change is compatible with a state and rate dependent formulation for earthquake occurrence we extend this analysis to future mainshocks by resolving the stress changes on major faults within 100 km of kobe and calculating the change in probability caused by these stress changes transient effects of the stress changes are incorporated by the state dependent constitutive relation which amplifies the permanent stress changes during the aftershock period earthquake probability framed in this manner is highly time dependent much more so than is assumed in current practice because the probabilities depend on several poorly known parameters of the major faults we estimate uncertainties of the probabilities by monte carlo simulation this enables us to include uncertainties on the elapsed time since the last earthquake the repeat time and its variability and the period of aftershock decay we estimate that a calculated 3 bar 0 3 mpa stress increase on the eastern section of the arima takatsuki tectonic line attl near kyoto causes fivefold increase in the 30 year probability of a subsequent large earthquake near kyoto a 2 bar 0 2 mpa stress decrease on the western section of the attl results in a reduction in probability by a factor of 140 to 2000 the probability of a mw 6 9 earthquake within 50 km of osaka during 1997 2007 is estimated to have risen from 5 6 before the kobe earthquake to 7 11 afterward during 1997 2027 it is estimated to have risen from 14 16 before kobe to 16 22

stress evolution and seismic hazard on the maqin maqu segment of east kunlun fault zone from co post and interseismic stress changes bin shan 1 2 xiong xiong 1 rongjiang wang 3 yong zheng1 and r b s yadav4 1state key laboratory of geodesy and earth s dynamics institute of geodesy and geophysics chinese academy of sciences wuhan 430077 china e mail binshan whigg ac cn 2australian research council centre of excellence for core to crust fluid systems gemoc department of earth and planetary sciences macquarie university sydney australia 3gfz german research centre for geosciences d 14473 potsdam germany 4department of geophysics kurukshetra university kurukshetra 136119 india

fault slip in the 1997 manyi tibet earthquake from linear elastic modelling of insar displacements summary the mw 7 6 1997 manyi earthquake occurred in an area of central northern tibet where sparse vegetation coverage and a lack of human habitation provide excellent conditions for interferometric synthetic aperture radar insar studies we use coseismic pairs of radar images acquired by the esa ers 2 satellite to construct interferograms of the surface displacement field due to the earthquake the location and extent of the coseismic fault rupture are mapped using a combination of optical satellite imagery high resolution digital topography interferometric correlation and azimuth offset measurements in so doing we are able to relate prominent geomorphic features in the fault zone to bends in the fault using elastic dislocation models consistent with this mapped fault trace we then test a range of fault geometries and slip conditions to find the combination which best explains the insar displacements our favoured model contains a reversal in fault dip approximately halfway along its length occurring at the location of a restraining bend slip on this model fault is heterogeneous with two areas of peak slip of 7 m or greater and components of dip slip displacement which vary significantly along strike the success of this model in fitting the data implies that an observed asymmetry in the coseismic interferograms can be explained in terms of the local fault geometry rather than by using non linear elastic rheologies as suggested by earlier authors

stress coupling between earthquakes in northwest turkey and the north aegean sea we have investigated the coulomb stress interactions of 29 earthquakes m s greater than or equal to 6 0 that have occurred in the region of northwest turkey and north aegean sea since 1912 of these events 23 may be related to earlier events and 16 are clearly related to earlier events all events after 1967 are related to previous events events in the early part of our time interval that show no correlation could be related to historical events as yet unidentified in some cases faults that have received a stress reduction from earlier events are prepared for an event by an earthquake occurring a few years before that creates a local coulomb stress rise thus regions of coulomb stress shadow can become regions where a damaging earthquake may occur the relation between smaller events and the coulomb stress distribution is less clear but may be related to poor data quality and practical limitations of our modeling technique nonetheless there are 4 times as many events per unit area in regions of enhanced stress than where stress is reduced we discuss the contemporary distribution of coulomb stress and argue that it is possible to identify the likely locations of future damaging earthquakes including identifying the most likely candidate faults

surface ruptures associated with the 1937 m 7 5 tuosuo lake and the 1963 m 7 0 alake lake earthquakes and the paleoseismicity along the tuosuo lake segment of the kunlun fault northern tibet examination of aerial photos taken in the late 1960s and field mapping allowed us to re evaluate the surface ruptures associated with the 1937 m 7 5 tuosuo lake and 1963 m 7 0 alake lake earthquakes along the tuosuo lake and alake lake segments central part of the kunlun fault individual ruptures can be distinguished by their freshness of surface expression slip distributions and surficial geometry they are separated by the geometrical bend that probably acts as an effective barrier to rupture propagation of these earthquakes the rupture 40 km long with 1 2 m left lateral slip of the 1963 alake lake earthquake occurred on the west of the bend whereas that of the 1937 tuosuo lake earthquake about 150 km long with 4 1 m mean left lateral offset occurred on the east of the bend the change of dip slip sense reflects the characteristics of jogs and bends along the segment boundaries systematically and progressively displaced terrace risers and gullies indicate repeated activity of the fault during the late quaternary five trenches excavated across the surface ruptures along the tuosuo lake segment reveal distinct indicators of paleoseismic events at least nine earthquakes are constrained in the holocene deposits and a 630 130 yr upper bound recurrence interval of large earthquakes in the past 2000 years is determined

evolution of stress in southern california for the past 200 years from coseismic postseismic and interseismic stress changes summary the seismicity of southern california results from stresses that arise from the relative motion of the pacific and north american plates being accommodated along the san andreas fault saf system and the eastern california shear zone ecsz here we calculate how the stress field in southern california has evolved over the past two centuries due to interseismic loading as inferred from current gps observations of surface velocities from redistributions of static stress induced by large m w 6 5 earthquakes since the 1812 wrightwood quake and postseismic viscoelastic relaxation associated with these events that serves to transfer coseismic stresses from the deep warm lower crust and upper mantle to the overlying seismogenic upper crust we calculate coulomb stress changes on vertical strike slip faults striking parallel to the saf and at the hypocenters on the rupture planes of all m w 6 events over the past two centuries our results suggest that the 1857 m w 8 2 fort tejon earthquake by far the largest event to have occurred in the region over the past two centuries had a profound influence on the state of stress in southern california during the 19th century inducing significant stress increases to the north parkfield region and adjoining creeping saf and south southern saf and san jacinto fault and stress relief across the southern ecsz these stress changes were then greatly magnified by postseismic relaxation through the early part of the 20th century slow interseismic build up of stress further loads all major strike slip faults and works to reload the areas of the ecsz where stress was relieved by the 1857 quake our calculations suggest that only 56 of hypocenters were pushed closer to failure by preceding coseismic stress changes suggesting that the occurrence of large earthquakes is not strongly determined by coseismic coulomb stress changes this percentage rises to 70 when postseismic stress changes are also considered our calculations demonstrate the importance of postseismic viscoelastic relaxation in the redistribution of stress following large earthquakes we find however that postseismic processes associated with events more than about a decade old are near completion and thus do not significantly influence the regional velocity field presently observed in southern california

focal depths and fault plane solutions of earthquakes under the tibetan plateau we compare synthetic and recorded p wave forms to place constraints on the focal depths and fault plane solutions of 16 crustal earthquakes beneath the highest parts 4000 m of the tibetan plateau fault plane solutions for all 16 events show combinations of normal and strike slip faulting with t axes oriented approximately east west none of these solutions show thrust faulting thus the data corroborate previous inferences that the active tectonics are dominated by east west extension focal depths for all 16 events are less than 15 km and appear to be between 5 and 10 km this style of deformation and these depths of faulting are similar to those in the basin and range province of the western united states two intermediate depth events below the crust of southern tibet also show primarily normal faulting with east west t axes the solution for one discussed by chen et al 1981 is unambiguous the solution for the other the event of august 1 1973 27 59 n 89 17 e 85 10 km mb 4 9 is less certain both apparently occurred in the mantle beneath a thick aseismic lower crust and their occurrence suggests that brittle deformation occurs there in response to a stress field similar to that operating at shallow depths beneath tibet

stress loading from viscous flow in the lower crust and triggering of aftershocks following the 1994 northridge california earthquake following the m w 6 7 northridge earthquake significant postseismic displacements were resolved with gps using a three dimensional viscoelastic model we suggest that this deformation is mainly driven by viscous flow in the lower crust such flow can transfer stress to the upper crust and load the rupture zone of the main shock at a decaying rate most aftershocks within the rupture zone especially those that occurred after the first several weeks of the main shock may have been triggered by continuous stress loading from viscous flow the long term decay time of aftershocks about 2 years approximately matches the decay of viscoelastic loading and thus is controlled by the viscosity of the lower crust our model provides a physical interpretation of the observed correlation between aftershock decay rate and surface heat flow

reevaluation of surface rupture parameters and faulting segmentation of the 2001 kunlunshan earthquake mw7 8 northern tibetan plateau china the 14 november 2001 m w 7 8 kunlunshan earthquake ruptured the westernmost part of the kunlun fault northern tibetan plateau the main segment affected by this event was the kusaihu segment field investigations allowed us to constrain the length the width and the coseismic horizontal displacement distribution of the kunlunshan earthquake rupture zone the mapped surface rupture zone starts from 90 257 e in the west and ends at 94 795 e in the east with a total length of 426 km it consists of three main sections the western strike slip section the transtensional section and the eastern strike slip section the rupture zone is oriented n100 10 e on average the distribution of the coseismic horizontal displacements is characterized by multiple peaks departing clearly from a general bell shaped distribution reassessment of the maximum coseismic horizontal left lateral displacement yields a value of 7 6 0 4 m at the site 35 767 n 93 323 e consistent with independent measurements derived from interferometric synthetic aperture radar and seismology from this site the horizontal displacement decreases unevenly to both the west and east coseismic vertical reverse displacement is also noted at the eastern end of the rupture but it remains much smaller than the horizontal component the width of the rupture zone varies from site to site from several meters to few kilometers the maximum width measured reaches 8 km along the yuxi feng subsection where a large number of shaking related cracks were well developed

rupture segmentation and process of the 2001 mw 7 8 central kunlun china earthquake field investigations allow us to constrain the coseismic surface rupture zone of 400 km with a strike slip up to 16 3 m associated with the 2001 m w 7 8 central kunlun earthquake that occurred along one of the western segments of the kunlun fault northern tibet the rupture zone may be divided into four segments based on the geological structures tectonic landform features spatial displacement distributions obtained from field observations and analysis of teleseismic waveforms the deformational characteristics of the surface ruptures and focal mechanism solutions reveal that the earthquake had a nearly pure strike slip mechanism the inversion results from seismic data show that the rupture started from the west near the epicentral area bilaterally and rapidly extended to the east in an unilateral manner for 380 km and that the largest slip region was limited in the subsegment 150 280 km east of the epicenter consistent with field observations the average stress drop is estimated to be 7 mpa in the area where the largest displacements occurred a value typical of intraplate earthquakes the geologic evidence and the inversion results from seismic data clearly show that temporal and spatial displacement distributions and the rupture process are restricted by the pre existing geological structures of the kunlun fault

stress triggering of the 1999 hector mine earthquake by transient deformation following the 1992 landers earthquake the m 7 3 june 28 1992 landers and m 7 1 october 16 1999 hector mine earthquakes california both right lateral strike slip events on nnw trending subvertical faults occurred in close proximity in space and time in a region where recurrence times for surface rupturing earthquakes are thousands of years this sug gests a causal role for the landers earthquake in triggering the hector mine earth quake previous modeling of the static stress change associated with the landers earthquake shows that the area of peak hector mine slip lies where the coulomb failure stress promoting right lateral strike slip failure was high but the nucleation point of the hector mine rupture was neutrally to weakly promoted depending on the assumed coefficient of friction possible explanations that could account for the 7 year delay between the two ruptures include background tectonic stressing dissi pation of fluid pressure gradients rate and state dependent friction effects and post landers viscoelastic relaxation of the lower crust and upper mantle by employing a viscoelastic model calibrated by geodetic data collected during the time period between the landers and hector mine events we calculate that postseismic relaxa tion produced a transient increase in coulomb failure stress of about 0 7 bars on the impending hector mine rupture surface the increase is greatest over the broad surface that includes the 1999 nucleation point and the site of peak slip further north since stress changes of magnitude greater than or equal to 0 1 bar are associated with documented causal fault interactions elsewhere viscoelastic relaxation likely con tributed to the triggering of the hector mine earthquake this interpretation relies on the assumption that the faults occupying the central mojave desert i e both the landers and hector mine rupturing faults were critically stressed just prior to the landers earthquake

broadband source modeling of the november 8 1997 tibet mw 7 5 earthquake and its tectonic implications we studied the source process of a large ms 7 9 intraplate earthquake that occurred on november 8 1997 at 1002 ut in a remote region of northern tibet we used four distinct methods to investigate the broadband source process and thereby better understand the tectonic implications of this event we relocated aftershocks using a master event technique and found that the distribution of aftershocks covers a region of 200 km in lateral extent we also employed a surface wave spectral inversion technique to estimate the mainshock moment depth centroid location and centroid time and utilized an empirical green s function technique to extract rupture directivity information and a detailed source time function from observed seismograms we also inverted body waves to estimate the moment release along the fault and the source time function the 1997 earthquake ruptured a strike slip fault that appears to be an extension or splay of the kun lun fault system this fault is one of the most seismically active strike slip faults within the tibetan plateau and has had events with surface wave magnitudes of 6 1 7 4 and 7 9 in this region since 1973 the rupture released most of the energy within the first 20 s and propagated bilaterally initially with the later rupture propagating westward for 20 30 s the absence of large aftershocks suggests that the earthquake efficiently released the stored strain comparing mainshock to the largest aftershock energy ratios for this event and other large strike slip events shows that faulting within the plateau has the characteristics of weak faults e g fracture zone faulting

evidence of power law flow in the mojave desert mantle studies of the earth s response to large earthquakes can be viewed as large rock deformation experiments in which sudden stress changes induce viscous flow in the lower crust and upper mantle that lead to observable postseismic surface deformation laboratory experiments suggest that viscous flow of deforming hot lithospheric rocks is characterized by a power law in which strain rate is proportional to stress raised to a power n refs 2 3 most geodynamic models of flow in the lower crust and upper mantle however resort to newtonian linear stress strain rate relations here we show that a power law model of viscous flow in the mantle with n 3 5 successfully explains the spatial and temporal evolution of transient surface deformation following the 1992 landers and 1999 hector mine earthquakes in southern california a power law rheology implies that viscosity varies spatially with stress causing localization of strain and varies temporally as stress evolves rendering newtonian models untenable our findings are consistent with laboratory derived flow law parameters for hot and wet olivine the most abundant mineral in the upper mantle and support the contention that at least beneath the mojave desert the upper mantle is weaker than the lower crust

coseismic postseismic and interseismic coulomb stress evolution along the himalayan main frontal thrust since 1803 the himalayan main frontal thrust is the most active fault in the himalayan subduction zone with a high degree of locking and a large thrust rate gaps on the himalayan main frontal thrust have been free of strong earthquakes for hundreds of years and the surrounding areas are densely populated so it is significant to study the evolution law and the current status of stress along the himalayan main frontal thrust based on a lithospheric viscoelastic layered medium model we analyzed the interseismic stress accumulation along the himalayan main frontal thrust and the coseismic and postseismic stress disturbance on the fault surface caused by nine mw 7 5 earthquakes since 1803 the results showed that the stress disturbance along the himalayan main frontal thrust caused by historical earthquakes have promoted most of the subsequent earthquakes but the coseismic and postseismic stress changes caused by the historical earthquakes on the faulty surface of subsequent earthquakes are not significant because of the long distance between strong earthquakes interseismic stress enhanced the stress level of the majority of fault planes in the study area and played a dominant role in the stress evolution and strong earthquake preparation along the himalayan main frontal thrust the recurrence interval of mw 7 5 7 9 earthquakes on the himalayan main frontal thrust is 70 250 years and the recurrence interval of mw 8 earthquakes which rupture the whole seismogenic layer may be longer than 500 years this agrees with historical seismic records the elapsed time of strong earthquakes in the four seismic gaps is between 460 and 915 years and the possibilities of mw 8 earthquakes in the future 10 years always exist including a probability of higher than 50 in three seismic gaps the peak of cumulative coulomb stress in the seismic gaps is more than 1 mpa and the seismic hazard on the himalayan main frontal thrust needs further attention

fundamentals of 3 d migration part 1 this is a tutorial on 3 d migration of seismic data subsurface geological features of interest in hydrocarbon exploration are three dimensional in nature examples are salt diapirs overthrust and folded belts major unconformities and deltaic sands the 2 d seismic section is a cross section of the 3 d seismic wave field it contains signals from all directions including out of plane of the profile sideswipe energy this sideswipe energy can only be handled by 3 d migration of 3 d seismic data

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

co seismic strike slip and rupture length produced by the 2001 ms 8 1 central kunlun earthquake field investigations show that the surface wave magnitude ms 8 1 central kunlun earthquake tibetan plateau of 14 november 2001 produced a nearly 400 kilometer long surface rupture zone with as much as 16 3 meters of left lateral strike slip along the active kunlun fault in northern tibet the rupture length and maximum displacement are the largest among the co seismic surface rupture zones reported on so far the strike slip motion and the large rupture length generated by the earthquake indicate that the kunlun fault partitions its deformation into an eastward extrusion of tibet to accommodate the continuing penetration of the indian plate into the eurasian plate

triggering of 1812 santa barbara earthquake by a great san andreas shock implications for future seismic hazards in southern california we study the evolution of the stress field over the last 200 years in southern california using the stress buildup associated with major faults and stress drops associated with great earthquakes in this report we calculate the change in the coulomb failure function cff associated with the great wrightwood earthquake of dec 8 1812 on the san andreas fault for the region near santa barbara that experienced a large shock 13 days later the rupture length constrained by paleoseismic data is used for the wrightwood earthquake of 1812 a uniform displacement of 3 5 m from the surface to seismogenic depths is assumed the geologic setting and focal mechanisms of earthquakes in the santa barbara region are dominated by thrust left lateral strike slip faulting and combinations of the two for our preferred rupture model of the earthquake of dec 8 the santa barbara shock of dec 21 1812 occurred in a region of 0 01 to 0 1 mpa cff for reasonable fault orientations indicating that it may have been advanced by years to decades and triggered by the great san andreas earthquake 13 days earlier we also calculate cff on typical kinds of faults in southern california for a future candidate great earthquake along the san bernardino and coachella valley segments of san andreas fault this earthquake produces large positive values of cff for shallow dipping thrust faults beneath the greater los angeles area and for nw trending right lateral strike slip faults in three regions this suggests that shocks of magnitude similar to the m 7 1 1812 santa barbara earthquake could be triggered by the next great event on the southern san andreas fault

new constraints on recent large earthquakes along the xidatan dongdatan segment of the kunlun fault western china field investigation and paleoseismic study constrain the offset and timing of recent large earthquakes on the xidatan dongdatan segment of the strike slip kunlun fault northern tibet displaced terrace risers and gullies preserved on the lowest and youngest terrace in the central part of the xidatan dongdatan valley indicate that the offset produced by the most recent earthquake is 3 6 m which is much smaller than what has been previously estimated however it is consistent with the slip of historical earthquakes along the kunlun fault and recent well recorded large earthquakes on other strike slip faults accumulated offsets on higher terraces indicate repeated seismic activity of the kunlun fault we assume a 150 20 km long surface rupture for the most recent event based on roughly continuous linear features on remote sensing images and distinct mole tracks in the field the lack of seismicity records in the region earlier than 100 years ago led us to carry out paleoseismic investigation samples collected from the faulted upper layer show that the most recent large event on the xidatan dongdatan segment is not older than 663 yr b p at least three prehistoric events are identified on the trench wall due to a lower constraint on the offset produced by the most recent earthquake it would be necessary to reevaluate the seismic behavior of the xidatan dongdatan segment

using geodetic data to calculate stress changes on faults in the tibetan plateau caused by the 2015 mw7 8 nepal earthquake abstract the 2015 m w 7 8 nepal earthquake occurred on the segment of the main himalayan thrust fault between the indian and eurasian plates and caused serious casualties this earthquake may produce a profound impact on the evolution of the tibetan plateau and have brought a stress loading to faults within the plateau in this paper a high resolution slip distribution of the 2015 nepal earthquake is inverted from the insar and gps data in the near field and is used to compute the evolution of the cumulative coulomb stress changes on faults in the earthquake prone zone in the tibetan plateau in the given reasonable parameters the calculated co and post seismic stress changes on faults do not exceed 1 0 kpa at the north of latitude 32 in the tibetan plateau the largest positive stress changes occur on the south tibet detachment fault and the magnitudes are much less than 100 kpa the estimated seismicity rate change on the segment of the south tibet detachment fault can be up to a level of two hundred thousandths this indicates that there is a high hazard of earthquake triggering in the south tibet detachment fault and its adjacent regions in the northern and eastern tibetan plateau the estimated seismicity rate changes are lower than a level of one thousandth however some faults with a relative high background seismicity rate such as the xianshuihe and longmenshan faults may have a high hazard of earthquake triggering in the future

indonesian earthquake earthquake risk from co seismic stress last year s indonesian earthquake has increased seismic hazard in the region the scale of death and destruction caused by the recent sumatra andaman islands earthquake and its tsunami has raised concerns that another earthquake might be triggered on the contiguous sunda trench subduction zone a new calculation of stress distribution here and on the neighbouring sumatra fault reveals stress build up on both structures severe enough to increase the already high earthquake hazard this finding makes the need for an indian ocean tsunami warning system all the more pressing following the massive loss of life caused by the sumatra andaman earthquake in indonesia and its tsunami the possibility of a triggered earthquake on the contiguous sunda trench subduction zone is a real concern we have calculated the distributions of co seismic stress on this zone as well as on the neighbouring vertical strike slip sumatra fault and find an increase in stress on both structures that significantly boosts the already considerable earthquake hazard posed by them in particular the increased potential for a large subduction zone event in this region with the concomitant risk of another tsunami makes the need for a tsunami warning system in the indian ocean all the more urgent

lower crustal relaxation beneath the tibetan plateau and qaidam basin following the 2001 kokoxili earthquake summary in 2001 november a magnitude 7 8 earthquake ruptured a 400 km long portion of the kunlun fault northeastern tibet in this study we analyse over five years of post seismic geodetic data and interpret the observed surface deformation in terms of stress relaxation in the thick tibetan lower crust we model gps time series first year and insar line of sight measurements years two to five and infer that the most likely mechanism of post seismic stress relaxation is time dependent distributed creep of viscoelastic material in the lower crust since a single relaxation time is not sufficient to model the observed deformation viscous flow is modelled by a lower crustal burgers rheology which has two material relaxation times the optimum model has a transient viscosity 9 1017 pa s steady state viscosity 1 1019 pa s and a ratio of long term to maxwell shear modulus of 2 3 this model gives a good fit to gps stations south of the kunlun fault while displacements at stations north of the fault are over predicted we attribute this asymmetry in the gps residual to lateral heterogeneity in rheological structure across the southern margin of the qaidam basin with thinner crust higher viscosities beneath the basin than beneath the tibetan plateau deep afterslip localized in a shear zone beneath the fault rupture gives a reasonable match to the observed insar data but the slip model does not fit the earlier gps data well we conclude that while some localized afterslip likely occurred during the early post seismic phase the bulk of the observed deformation signal is due to viscous flow in the lower crust to investigate regional variability in rheological structure we also analyse post seismic displacements following the 1997 manyi earthquake that occurred 250 km west of the kokoxili rupture we find that viscoelastic properties are the same as for the kokoxili area except for the transient viscosity which is 5 1017 pa s the viscosities estimated for the manyi and kokoxili areas are consistent with constraints obtained from other earthquakes in the northwest and south central parts of the tibetan plateau

slip rate on the kunlun fault at hongshui gou and recurrence time of great events comparable to the 14 11 2001 mw 7 9 kokoxili earthquake abstract a field study of the surface rupture of the 14 november 2001 mw 7 9 kokoxili or kunlun shan earthquake near hongshui gou 35 9 n 92 2 e a site with exceptional geomorphic offsets long identified on spot images yields bounds on this earthquake return time and on the slip rate along the kusai hu segment of the kunlun fault measurements of the sinistral coseismic and cumulative offsets of four distinct strath terrace risers and of rill channels incised in the adjacent fan bajada complemented by post earthquake metric resolution satellite image restoration are 3 0 5 m 6 1 m 31 2 m 63 5 m and 110 10 m the smallest offset is unambiguously that of the 14 11 2001 earthquake the 31 and 63 m riser offsets which have thermoluminescence ages of 2885 285 and 5960 450 yr respectively imply an average slip rate of 10 0 1 5 mm yr almost identical to that found 200 km eastwards in xidatan using 10 be cosmogenic dating of surface pebbles the repetitive seismic slip 3 m implies an average recurrence time of 300 50 yrs for earthquakes comparable to the 14 11 2001 event this new data increases the body of evidence suggestive of local characteristic slip during large earthquakes and firmly corroborates the millennial eastward extrusion rate 1 cm yr of north central tibet relative to the qaidam

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

coulomb stress evolution in northeastern caribbean over the past 250 years due to coseismic postseismic and interseismic deformation summary the northeastern caribbean region accommodates 20 mm yr 1 of oblique convergence between the north american and caribbean plates which is distributed between the subduction interface and major strike slip faults within the overriding plate as a result this heavily populated region has experienced eleven large m 7 0 earthquakes over the past 250 yr in an effort to improve our understanding of the location and timing of these earthquakes with an eye to understand where current seismic hazards may be greatest we calculate the evolution of coulomb stress on the major faults since 1751 due to coseismic postseismic and interseismic deformation our results quantify how earthquakes serve to relieve stress accumulated due to interseismic loading and how fault systems communicate with each other serving both to advance or retard subsequent events we find that the observed progressive westwards propagation of earthquakes on the septentrional and enriquillo strike slip faults and along the megathrust was encouraged by coseismic stress changes associated with prior earthquakes for the strike slip faults the loading of adjacent segments was further amplified by postseismic relaxation of a viscoelastic mantle in the decades following each event furthermore earthquakes on the septentrional fault relieve a small level of coulomb stress on the parallel enriquillo fault to the south and vice versa perhaps explaining anticorrelated timing of events on these respective fault systems the greatest net build up of coulomb stress changes over the past 250 yr occurs along the central and eastern segment of the septentrional and the bowin strike slip faults 65 71 w as no recent earthquake has relieved stress in these regions for oblique thrust faults net stress build up over the past 250 yr is the largest on the north american caribbean megathrust west of 70 5 w high coulomb stress has also developed east of 65 5 w where no historic events have been inferred to have relieved stress though uncertainties in fault slip rates from our block model associated with a lack of gps observations in this region may have led to an over estimation of stress changes

stress interactions within the strong earthquake sequence from 2001 to 2010 in the bayankala block of eastern tibet abstract four major earthquakes of m s 7 0 occurred in the tibetan plateau during the last decade they were the 2001 m s 8 1 kunlun mountains hoh xil earthquake in qinghai the 2008 m s 7 3 yutian earthquake in xinjiang the 2008 m s 8 0 wenchuan earthquake in sichuan and the 2010 m s 7 1 yushu earthquake in qinghai all four occurred in relative proximity to the bayankala block by the integration of coseismic effects and viscoelastic relaxations we studied the stress interactions among those four earthquakes then the epidemic type aftershock sequence etas model and stochastic declustering method were used to detect the local seismic signals of each succeeding major earthquake this analysis considered increases or decreases with the coulomb failure stress cfs variations induced by its preceding major earthquakes the results showed that the stress interactions among these four major earthquakes are too weak to trigger each other and that the preceding major earthquakes did not obviously impact the local seismicity of the succeeding major earthquakes it demonstrates that the occurrences of these four major earthquakes that clustered around the bayankala block might not have been caused by the triggering effects instead these might have resulted from the southeastward movement of the bayankala block which related to the compression and penetration of the indian australian plate into the eurasian plate

evolution of moderate seismicity in the san francisco bay region 1850 to 1993 seismicity changes related to the occurrence of large and great earthquakes the rate of seismic activity of moderate size m 5 5 earthquakes in the san francisco bay sfb region has varied considerably during the past 150 years as measured by the rate of seismic moment release seismic activity in the sfb region is observed to accelerate prior to m 7 0 earthquakes in 1868 1906 and 1989 and then to decelerate following them we examine these seismicity changes in the context of the evolution of the stress field in the sfb region as a result of strain accumulation and release using a model of dislocations in an elastic halfspace we use a coulomb failure function cff to take into account changes in both shear and normal stresses on potential failure planes of varying strike and dip in the sfb region we find that the occurrence of a large or great earthquake creates a stress shadow a region where the stress driving earthquake deformation is decreased interseismic strain accumulation acts to reverse this process gradually bringing faults in the sfb region out of the stress shadow of a previous large or great earthquake and back into a state where earthquake failure is possible as the stress shadow generated by a large or great earthquake disappears it migrates inward toward the fault associated with that large or great event the observed changes in the rate of occurrence of moderate earthquakes in the sfb region are broadly consistent with this model in detail the decrease in seismicity throughout most of the sfb region and a localized increase in the monterey bay region following the great 1906 earthquake is consistent with our predicted stress changes the timing and location of moderate size earthquakes when the rate of seismicity increases again in the 1950s is consistent with areas in which the 1906 stress shadow had been eliminated by strain accumulation in the sfb region those earthquakes that are most inconsistent with our stress evolution model including the 1911 earthquake southeast of san jose are found to occur in regions where dip slip faulting is common in addition to strike slip the 1906 earthquake brought that zone of dip slip faulting closer to failure suggesting that the 1911 event may have been a reverse faulting earthquake rather than a strike slip one similar to the 1984 morgan hill earthquake the occurrence of activity on faults very close to the san andreas such as the lake elsman earthquakes of 1988 and 1989 appear to be associated with the last disappearence of the stress shadow on the loma prieta segment of the san andreas fault thus events of that type may represent an intermediate term precursor to a large earthquake such as the 1989 loma prieta event much of the moderate size earthquake activity in the sfb region appears to be modulated in time by the buildup and release of stress in large and great earthquakes a tensorial approach to earthquake prediction i e taking into account changes in the components of the stress tensor has several advantages over examining scalar changes such as those in seismic activity and moment release rates this tensorial approach allows for both activation and quiescence but in different subregions prior to as well as after large earthquakes

coulomb stress evolution along xianshuihe xiaojiang fault system since 1713 and its interaction with wenchuan earthquake may 12 2008 abstract the curved left lateral strike slip xianshuihe xiaojiang fault system xxfs in southwestern china extends at least 1400 km in the eastern margin of the tibetan plateau fieldworks confirm that the xxfs is one of the longest and most seismically active faults in china the strain released by the slip motion on the xxfs is related to the convergence between the indian and eurasian plates the entire fault system has experienced at least 35 earthquakes of m 6 in the recent 300 years and almost all segments of the system have been the locus of major historical earthquakes since the xxfs region is heavily populated over 50 million people understanding the migration of the large earthquakes in space and time is of crucial importance for the seismic hazard assessment in this region we analyze a sequence of 25 earthquakes m 6 5 that occurred along the xxfs since 1713 and investigate their influence on the 2008 mw7 9 wenchuan earthquake occurred on the adjacent longmenshan fault in our analysis the relevant parameters for the earth crust are constrained by seismic studies the locations and geometries of the earthquake faults as well as the rupture distributions are taken from field observations and seismological studies results from the coulomb failure stress modeling indicate significant interactions among the earthquakes after the 1713 earthquake 19 out of 24 earthquakes occurred in the positive stress zone of the preceding earthquakes the other 5 earthquakes located in the area without significant stress changes induced by the preceding events in particular we can identify 4 visible earthquake gaps with increasing seismic hazard along the xxfs consistent with the findings from the paleo seismological studies the seismic activity and tectonic motion on the xxfs reduced the coulomb stress accumulation at the hypocenter of 2008 mw7 9 wenchuan earthquake implying that the wenchuan earthquake might not be triggered directly by the seismic activities on the xxfs on the other hand the coulomb failure stress induced by the wenchuan earthquake has increased in a region of 125 km long segment of the xxfs northwest of kangding city

stress evolution before and after the 2008 wenchuan china earthquake abstract we examine the distribution of coulomb stress before and following the m 7 9 wenchuan earthquake and model the time dependent components of the stress field into the future our modelling shows that the combined coseismic plus postseismic viscoelastic stress change due to the preceding large events m 6 7 at the hypocentral area of the wenchuan earthquake is negative which may have led to a delay on its occurrence between 16 and 95 yr depending on the rake of the rupture on the other hand coseismic stress modelling of the wenchuan earthquake shows strong interaction particularly with the faults close to its sw and ne ends such interactions have previously been shown to trigger further large earthquakes in addition redistribution of stresses due to continuing postseismic deformation will potentially increase the stress levels not only on these faults but also on the distant faults such as the xianshuihe kunlun and tazang faults postseismic viscoelastic stress load on these distant faults over the next 22 yr since the earthquake could be up to 2 5 times larger than that of the coseismic stress increase alone this would potentially advance these faults in their seismic cycle and thereby encourage future earthquakes resulting in clustering of large earthquakes in the region this behaviour however strongly depends on the stage that these faults are in their seismic cycle which is not known currently given the high density of population in the area with several cities chengdu guangyuan and hanzhong of more than 1 million inhabitants our results indicate a need for detailed paleoseismic studies to help elucidate the state of the stressed faults

stress changes induced by the 2008 mw7 9 wenchuan earthquake china abstract we invert the background stress fields of the longmenshan and its adjacent regions before and after the 2008 great wenchuan earthquake from focal mechanism data our results show that the stress orientations after the 2008 great wenchuan earthquake are more coherent than those before this event at the epicentral zone this result includes twofold implications one is that the wenchuan event altered the local stress field the other is that the strength of the wenchuan fault zone is very high and the characteristic of the seismogenic fault is consistent with the asperity model we also estimate the stress changes caused by the wenchuan event using an accurate source model and exhaustive receiver faults the stress changes of 10 kpa mainly occur in the nearby areas of the longriba east kunlun qingchuan lushan faults and the southeastern section of the xianshuihe fault indicating that there is high earthquake hazard in these areas the seismicity before and after the great wenchuan earthquake in the longmenshan and its adjacent regions shows that some subsequent earthquakes in the stress shadow area may be delayed and the 2013 lushan earthquake may be advanced

background and precursory seismicities along and surrounding the kunlun fault before the ms8 1 2001 kokoxili earthquake china abstract the ms8 1 kokoxili china earthquake on 14 november 2001 occurred on the western portion of the kunlun fault by analyzing data from geological surveys and records of historical and modern earthquakes we know that at least 8 ms6 9 8 1 earthquakes occurred along the kunlun fault from 1879 ad to 2000 ad the spatial arrangement of these ruptures indicates the existence of two rupture gaps the kokoxili and the maqu on the fault before 2001 the kokoxili gap and surrounding area experienced a long term seismicity quiescence of ms 5 earthquakes and developed the corresponding background seismic gap at least from 1966 to 2001 the 2001 kokoxili earthquake occurred on the kokoxili gap the maqu gap on the eastern portion of the kunlun fault was found to be a site where the seismicity rate of smaller earthquakes increased anomalously about 3 4 years before the kokoxili earthquake we analyze this anomalous increase in seismicity rate and conclude that it was a significant precursor of the kokoxili earthquake the cases in this study suggest that rupture gaps on a great inland strike slip fault zone could be sites of potentially major or great earthquakes or sites of precursory seismicities emerging prior to major or great earthquakes on the same fault zone

insight into the 2016 menyuan m w 5 9 earthquake with insar a blind reverse event promoted by historical earthquakes in 2016 the mw 5 9 menyuan earthquake occurred at the western end of the tianzhu seismic gap in the middle segment of the left lateral strike slip haiyuan fault system studying the focal mechanism of the menyuan earthquake and its correlation with historical seismicity is of great significance in understanding the tectonic style of the haiyuan fault system and assessing the tianzhu gap seismic risk using sentinel 1a radar imagery we obtain the coseismic deformation field of the menyuan earthquake in the los direction and invert the deformation field slip distribution model based on the interseismic deformation field reflected by gps data and the relocated results of aftershocks provided by previous studies we then analyze the seismogenic nodal plane of the menyuan earthquake and consider the west dipping model to be the most likely seismogenic solution the west dipping model indicates that the average slip of the menyuan earthquake is 0 41 m and the average rake angle is 68 with a magnitude of mw 5 905 considering the historical strong earthquakes and viscoelastic layered crust the results from coulomb failure stress modeling indicate that the coulomb stress loading caused by the historical strong events promoted the occurrence of the 2016 menyuan earthquake both the low seismicity within the tianzhu gap and the cluster phenomenon of medium earthquakes on the lao hu shan lhs and leng long ling lll faults have strong correlations with the stress change distribution resulting from the historical strong earthquakes a series of medium events occurring on the north side of the lll fault represented by the 2016 menyuan earthquake would raise the seismic risk on the western end of the tianzhu gap

the crustal viscosity gradient measured from post seismic deformation a case study of the 1997 manyi tibet earthquake abstract we here analyse an insar dataset which constrains the temporal and spatial distribution of post seismic ground displacement following the 1997 manyi tibet earthquake to estimate the depth variation of creep viscosity within the crust we use a method which depends on the detection and measurement of a systematic variation in post seismic relaxation rate with distance from the fault at a given distance the displacement rates may be compared with the prediction of a uniform viscosity model with apparent viscosity u the rate at which u decreases with distance from the fault is directly diagnostic of the parameter that controls the vertical gradient of viscosity in a stratified crust our best fit viscosity profile for manyi exponentially decreases from 1 2 10 21 pa s at the top of the visco elastic layer at 10 km to 1 6 10 18 pa s at the moho at 60 km the predicted temporal and spatial variations of post seismic displacements generally fit the observed post day 165 displacements within error if we assume that displacements pre day 165 are attributed to after slip on the fault within error the crustal viscosity at 10 km depth may range between 6 1 10 20 pa s and 1 4 10 22 pa s estimates of the maxwell time constant consistent with an inter seismic period of 500 1000 yr imply an effective elastic layer thickness of 20 km for best fit and upper bound viscosity solutions we also show that the estimated viscosity profile is broadly consistent with laboratory measurements of creep for crustal materials like quartzite and granite by deducing from our viscosity profile the ratio q n of activation energy to stress exponent at 45 81 kj mole thus providing a new link between laboratory scale measurements of creep deformation and viscosity measured from post seismic relaxation

isostatic gravity anomaly lithospheric scale density structure of the northern tibetan plateau and geodynamic causes for potassic lava eruption in neogene abstract this paper will help to further constrain geodynamic models for the evolution of northern tibet through two techniques that employ bouguer gravity anomaly data the first is isostatic correction of bouguer gravity anomalies and the second is 2 d density modeling along a profile at 88 5 e from 30 n to 37 n within the tibetan plateau areas dominated by volcanic rocks exhibit ultra low bouguer gravity anomalies and low isostatic residual anomalies the 2 d density structure beneath profile 88 5 e shows a giant upward dome distributed body of low density in the middle lower crust and mantle beneath the high to ultra potassic areas suggesting that the original middle and lower crusts were reformed and replaced extensively in the area based on existing regional geology and tectonics geochemical data from magmatic rocks and geophysical information this paper proposes that the sustained northward subduction of the indian plate has resulted in breaking off of the frontal margin of the asian lithospheric mantle subsequently the original lithosphere was reactivated by thermal tectonic changes high to ultra potassic volcanoes erupted extensively in the northern tibetan plateau during neogene and the plateau experienced rapid ne trending uplift

stress evolution and seismic hazard of the dead sea fault system abstract we calculated the stress evolution for the central part of the dead sea fault system 30 5 n 34 5 n from 551 to 2005 through modelling the static stress changes due to 14 historical earthquakes with m s 6 0 superimposed by tectonic loading from relative plate motion from the results of our numerical models we identified two segments with high positive changes in coulomb failure stress cfs exceeding 4 mpa a 90 km long segment of the jordan fault south of the sea of galilee and a 30 km long segment east of the dead sea these segments could result in m s 7 4 and m s 6 8 earthquakes respectively in contrast to similar stress evolution models of other continental transform faults our results support only partly the hypothesis that coseismically induced static stress changes control the spatial succession of earthquakes we calculated on each rupture plane the mean of cfs and the maximum cfs due to the stress changes of all preceding earthquakes the results of the calculated mean cfs values reveal that only 6 out of 13 earthquakes could have been triggered the subsequent earthquake from the analysis of the maximum cfs values we find that 8 out of 13 earthquakes could have triggered the subsequent earthquake since our model results are sensitive to location and magnitude of historical earthquakes and the tectonic loading rates of the fault segments we emphasize the need for further paleoseismological studies and current slip rate estimation from continuously observing gps arrays and geological investigations taking into account that six large cities beirut damascus haifa tel aviv amman and jerusalem are in close proximity with distances between 30 and 150 km to the jordan segment the seismic risk is probably higher than accounted before

average slip rate and recurrence interval of large magnitude earthquakes on the western segment of the strike slip kunlun fault northern tibet interpretations of satellite remote sensing images field and trench excavation investigations and radiocarbon dates constrain the holocene slip rate and average recurrence interval of large earthquakes on the western segment of the strike slip kunlun fault related with the 2001 m w 7 8 central kunlun earthquake northern tibet streams and gullies developed on the alluvial fans having an average 14 c age of 7000 years are sinistrally offset by up to 115 m along the kunlun fault this constrains a slip rate of 16 4 mm yr for the past 7000 years trenches and 14 c ages reveal that at least four seismic faulting events occurred in the past 6200 years and that the penultimate event prior to the 2001 m w 7 8 earthquake occurred during the past 400 years with an average left lateral offset of 4 5 m coupling the slip rate of 16 4 mm yr with the average offset of 4 5 m produced by individual large earthquakes it is estimated that the average recurrence interval of large earthquakes is 300 400 years on the western segment of the kunlun fault our results confirm that the kunlun fault plays an important role as a major strike slip fault in accommodating the horizontal eastward extrusion of tibet

joint estimation of afterslip rate and postseismic relaxation following the 1989 loma prieta earthquake global positioning system gps data from campaigns carried out over the 5 years following the 1989 loma prieta earthquake and leveling data measured in 1990 and 1992 define the postseismic velocity field around the loma prieta rupture zone subtraction of a background velocity field yields a residual velocity pattern which we interpret as the product of two physical processes 1 slow afterslip along distinct planes in the upper cru st and 2 viscoelastic relaxation of the lower crust and upper mantle biirgmann et al 1997 previously derived an afterslip model involving uniform afterslip on two optimally determined planes in cluding oblique reverse slip on the coseismic rupture and reverse slip on a shallow thrust fault to the northeast of the san andreas fault we further consider models of distributed slip on these two fault planes plus a viscoelastic relaxation pattern which depends on a suitable cose ismic rupture model and crust and mantle viscosities several fault models from the literature were considered for the 1989 coseismic rupture with nearly identical impact on the results simultaneous maximum likelihood inversion of the gps and leveling data for afterslip distri bution and viscosity yields the following results 1 a good fit to the data is obtained by smooth afterslip distributions without any viscoelastic relaxation being required 2 tangible broad scale viscoelastic relaxation of the lower crust and upper mantle are present in this data set at 97 confidence and a lower crustal viscosity of 1029 pa s is obtained however the viscosity of both the lower crust and upper mantle are poorly constrained 3 for a given misfit 20 less integrated afterslip and smoother afterslip distributions result when viscoelas tic relaxation is included 4 maximum slip rates on the slip distributed models are 3 5 crn yr the dominant patches estimated on the two planes fill in the entire depth range 4 13 km without significant overlap and deeper afterslip is not required the afterslip distribution on the coseismic rupture plane is strongly dominated by reverse slip immediately southeast of the main center of coseismic reverse slip