dynamic topography produced by lower crustal flow against rheological strength heterogeneities bordering the tibetan plateau summary dynamic stresses developed in the deep crust as a consequence of flow of weak lower crust may explain anomalously high topography and extensional structures localized along orogenic plateau margins with lubrication equations commonly used to describe viscous flow in a thin gap geometry we model dynamic stresses associated with the obstruction of lower crustal channel flow due to rheological heterogeneity dynamic stresses depend on the mean velocity u viscosity and channel thickness h uniquely through the term u h 2 these stresses are then applied to the base of an elastic upper crust and the deflection of the elastic layer is computed to yield the predicted dynamic topography we compare model calculations with observed topography of the eastern tibetan plateau margin where we interpret channel flow of the deep crust to be inhibited by the rigid sichuan basin model results suggest that as much 1500 m of dynamic topography across a region of several tens to a hundred kilometres wide may be produced for lower crustal material with a viscosity of 2 10 18 p asfl owing in a 15 km thick channel around a rigid cylindrical block at an average rate of 80 mm yr 1

role of initial stress rotations in rupture dynamics and ground motion a case study with implications for the wenchuan earthquake 1 motivated by observations in the 2008 mw 7 9 wenchuan earthquake we study effects of systematic changes in the principal stress orientation along the fault strike on rupture dynamics and ground motion using a 3 d finite element method based on anderson s theory of faulting we set up the initial stress field with rotations in stress orientations along strike for a dynamic rupture model of a shallow dipping fault we find that initial stress rotations along strike can cause dramatic changes in rupture speed and produce distinct patterns in slip distribution and peak ground motion when a mismatch unfavorable for faulting between fault geometry and initial stress orientations is encountered rupture can spontaneously stop some first order features in the wenchuan event may be partially caused by rotations in the principal stress orientation along strike such as the rupture arrest at the northeast end and two severe destruction zones in the observed seismic intensity distribution these results may have important implications for assessing seismic hazards imposed by faults with changes in the initial stress field along strike worldwide

the 2002 denali fault earthquake alaska a large magnitude slip partitioned event the mw moment magnitude 7 9 denali fault earthquake on 3 november 2002 was associated with 340 kilometers of surface rupture and was the largest strike slip earthquake in north america in almost 150 years it illuminates earthquake mechanics and hazards of large strike slip faults it began with thrusting on the previously unrecognized susitna glacier fault continued with right slip on the denali fault then took a right step and continued with right slip on the totschunda fault there is good correlation between geologically observed and geophysically inferred moment release the earthquake produced unusually strong distal effects in the rupture propagation direction including triggered seismicity

historical pattern and behavior of earthquake ruptures along the eastern boundary of the sichuan yunnan faulted block southwestern china abstract the eastern boundary of the sichuan yunnan faulted block in southwestern china which contains four major fault zones named xianshuihe anninghe zemuhe and xiaojiang behaves as a huge left lateral strike slip active fault system where the most frequent seismicity in continental china occurs to uncover the history of earthquake ruptures of this fault system we developed an empirical relation between rupture extent and seismic intensity distribution based on data of those earthquakes whose rupture extents and intensity distributions are well known through analyzing various types of data including distributions of damage or intensity of historical earthquakes as well as surface ruptures and aftershock zones of modern earthquakes we determined systematically the locations and spatial extents of ruptures for 36 main earthquakes and built up a spatial temporal pattern of the rupture history of the fault system for the last several hundred years the spatial temporal rupture pattern contains information of multi cycle and broad scale ruptures from which we find that for most fault segments scales of segment ruptures are time or cycle variable and only in two or three cases do scales of segment ruptures in successive cycles seem to be characteristic in infrequent cases several adjacent and connecting fault units may rupture simultaneously resulting in cascading ruptures triggering of ruptures is common along the fault system but differs in various periods even on a single fault zone triggered ruptures may not occur on fault segments adjacent to a preceding rupture of major earthquake but on other segments at some distance away from the preceding rupture implying that the rupture history determines whether a segment can be triggered or not recurrence intervals of major segment ruptures are longer on the anninghe and zemuhe fault zones and on the southernmost segment of the xiaojiang fault zone than that on the xianshuihe fault zone and the northern and middle segments of the xiaojiang fault zone probably due to the partitioning of slip along major and secondary faults and their complicated fault geometry four seismic gaps along the fault system are recognized where major earthquakes have been absent for a long time

crustal structure across longmenshan fault belt from passive source seismic profiling 1 we analyse receiver functions from 29 broad band seismographs along a 380 km profile across the longmenshan lms fault belt to determine crustal structure beneath the east tibetan margin and sichuan basin the moho deepens from about 50 km under songpan ganzi in east tibet to about 60 km beneath the lms and then shallows to about 35 km under the western sichuan basin the average crustal vp vs ratios vary in the range 1 75 1 88 under songpan ganzi in east tibet 1 8 2 0 under the lms and decrease systematically across the nw part of the sichuan basin to less than 1 70 a negative phase arrival above the moho under songpan ganzi and sichuan basin is interpreted as a ps conversion from the top of a low velocity layer in the lower crust the very high crustal vp vs ratio and negative polarity ps conversion at the top of lower crust in east tibet are inferred to be seismic signatures of a low viscosity channel in the eastern margin of the tibetan plateau the lateral variation of moho topography crustal vp vs ratio and negative polarity ps conversion at the top of the lower crust along the profile seem consistent with a model of lower crust flow or tectonic escape

rupture history of the 2013 mw 6 6 lushan earthquake constrained with local strong motion and teleseismic body and surface waves 1 the rupture history of the 20 april 2013 mw 6 6 lushan china earthquake is constrained by inverting waveforms of local strong motion teleseismic broadband body waves and long period surface waves this earthquake ruptured a blind thrust fault oriented n210 e along the longmenshan fault zone and dipping 40 to the nw the inverted slip distribution is heterogeneous dominated by a slip patch with a roughly right triangular shape which spans a depth range of 5 20 km and accounts for two thirds of the total seismic moment 8 9 1018 n m the rupture initiated roughly at the middle of the triangle s hypotenuse and during the first 4 s propagated mainly in along strike and downdip directions toward a peak slip of 1 2 m despite a large number of fatalities and economic loss the estimated static and apparent stress drops of the lushan earthquake are 1 5 mpa and 0 35 mpa considerably low with respect to other similar intraplate earthquakes

earthquake triggering along the xianshuihe fault zone of western sichuan china western sichuan is among the most seismically active regions in southwestern china and is characterized by frequent strong m 6 5 earthquakes mainly along the xianshuihe fault zone historical and instrumental seismicity show a temporal pattern of active periods separated by inactive ones while in space a remarkable epicenter migration has been observed during the last active period starting in 1893 the sinistral strike slip xianshuihe fault of 350 km total length was entirely broken with the epicenters of successive strong earthquakes migrating along its strike this pattern is investigated by resolving changes of coulomb failure function cff since 1893 and hence the evolution of the stress field in the area during the last 110 years coulomb stress changes were calculated assuming that earthquakes can be modeled as static dislocations in an elastic halfspace and taking into account both the coseismic slip in strong m 6 5 earthquakes and the slow tectonic stress buildup associated with major fault segments the stress change calculations were performed for faults of strike dip and rake appropriate to the strong events we evaluate whether these stress changes brought a given strong earthquake closer to or sent it farther from failure it was found that all strong earthquakes and moreover the majority of smaller events for which reliable fault plane solutions are available have occurred on stress enhanced fault segments providing a convincing case in which coulomb stress modeling gives insight into the temporal and spatial manifestation of seismic activity we extend the stress calculations to the year 2025 and provide an assessment for future seismic hazard by identifying the fault segments that are possible sites of future strong earthquakes

seismic signature of the collision between the east tibetan escape flow and the sichuan basin abstract gps displacement vectors show that the crust in east tibet is being squeezed in an easterly direction by the northward motion of the indian plate and the sichuan basin is resisting this stream and redirecting it mainly towards indochina the longmen shan containing the steepest rise to the high plateau anywhere in tibet results from the strong interaction between the east tibetan escape flow and the rigid yangtze block sichuan basin but the kinematics and dynamics of this interaction are still the subject of some debates we herein present results from a dense passive source seismic profile from the sichuan basin into eastern tibet in order to study the deep structure of this collision zone using p and s receiver function images we observe a sudden rise of the lithosphere asthenosphere boundary lab from 120 to 150 km beneath the sichuan basin and from 70 to 80 km beneath eastern tibet in contrast the depth of the crust mantle boundary moho increases from 36 to 40 km beneath the sichuan basin and from 55 to 60 km beneath eastern tibet the 410 km discontinuity is depressed below eastern tibet by about 30 km although the 660 remains at nearly the same depth throughout the lms from these observations we conclude that the mode of collision that occurs between tibet and the sichuan basin is very different to that found between india and tibet in southern tibet we observe in essence the subduction of the indian plate which penetrates northwards for several hundred kilometers under central tibet the very thin mantle part of the lithosphere beneath eastern tibet may indicate delamination or removal of the bottom of the lithosphere by hot asthenospheric escape flow this process leads to the exceptionally steep topography at the eastern tibetan margin as a result of gravitational buoyancy this view is supported by the very unusual depression of the 410 km discontinuity beneath eastern tibet which could be caused by the dynamics of the sub vertical downward asthenospheric flow

contemporary crustal deformation around the southeast borderland of the tibetan plateau 1 we derive a detailed horizontal velocity field for the southeast borderland of the tibetan plateau using gps data collected from the crustal motion observation network of china between 1998 and 2004 our results reveal a complex deformation field that indicates that the crust is fragmented into tectonic blocks of various sizes separated by strike slip and transtensional faults most notably the regional deformation includes 10 11 mm yr left slip across the xianshuihe fault 7 mm yr left slip across the anninghe zemuhe xiaojiang fault zone 2 mm yr right slip across a shear zone trending northwest near the southern segment of the lancang river fault and 3 mm yr left slip across the lijiang fault deformation along the southern segment of the red river fault appears not significant at present time the region south and west of the xianshuihexiaojiang fault system whose eastward motion is resisted by the stable south china block to the east turns from eastward to southward motion with respect to south china resulting in clockwise rotation of its internal subblocks active deformation is detected across two previously unknown deformation zones one is located 150 km northwest of and in parallel with the longmenshan fault with 4 6 mm yr right slip and another is continued south southwestward from the xiaojiang fault abutting the red river fault with 7 mm yr left slip while both of these zones are seismically active the exact locations of faults responsible for such deformation are yet to be mapped by field geology comparing our gps results with predictions of various models proposed for tibetan plateau deformation we find that the relatively small sizes of the inferred microblocks and their rotation pattern lend support to a model with a mechanically weak lower crust experiencing distributed deformation underlying a stronger highly fragmented upper crust

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

characterization of lacustrine mixed fine grained sedimentary rocks using coupled chemostratigraphic petrographic analysis a case study from a tight oil reservoir in the jimusar sag junggar basin abstract mixed deposits are sediments consisting of external clastic epiclastic or terrigenous intrabasinal components and pyroclastic components the mixture comprising variable amounts of the three components is defined as mixed sedimentary rocks the permian lucaogou formation p2l in the jimusar sag of the junggar basin is a promising tight oil target in western china the fine grained mixed sedimentary rocks of which are rich in organic matter om and two sweet spot intervals with relatively high porosity however the sediment composition provenance and deposition environmental settings have not been studied in detail in this study coupled chemostratigraphic petrographic analysis were used to reconstruct their depositional environments the results show that the fine grained sedimentary rocks have three major sediment sources external clastic input terrigenous clastics intrabasinal autochthonous to parautochthonous components carbonates siliceous skeletal debris and om and pyroclastic input main lithofacies include siltstone fine sandstone mudstone dolomite and tuffite the silt sandstones were mainly sourced from rocks with calc alkaline composition while the tuffaceous sedimentary rocks were sourced from high k calc alkaline rocks elemental proxies suggest that the carbonate rocks were generally deposited under warm and arid conditions whereas the fine grained clastic sediments were deposited under relatively humid conditions the muddy or silty tuffaceous mixed rocks were deposited under relatively reducing conditions compared with carbonates and sandstones variations of lithofacies and om accumulation of different intervals reflect changing deposition environmental settings and the frequently altered high toc content rocks and good reservoirs are benefit for tight oil formation the work may provide some useful insights and serve as a reference for studying other mixed fine grained sedimentary rocks and tight oil plays in similar lacustrine basins elsewhere

crustal rheological strength heterogeneities control the formation of continental plateau margins the margins bordering the tibetan plateau show two end member morphologies in topographic gradient steep margins and low gradient margins to investigate the formation mechanism of convergent intracontinental plateau margins we conduct 2d numerical experiments to simulate crustal deformation process across plateau margins our numerical experiments demonstrate that heterogeneities in crustal rheological strength control significantly the formation of plateau margins when subjected to crustal convergence a very steep margin is the result of crustal convergence between plateau with weak lower crust and foreland basin with strong lower crust by contrast a low gradient margin could result from crustal convergence between plateau and foreland with less strength contrast this finding suggests that the diversity in topographic gradient along the tibetan plateau borders reflects heterogeneities in crustal rheological strength across the plateau margins steep gradient at the margins indicate large crustal rheological strength contrasts between the weak ductile lower crust of the tibetan plateau and its strong surrounding foreland basins like the sichuan basin the tarim basin and the qaidam basin beneath these steep margins the horizontal flow of the tibetan ductile lower crust is inhibited and forced to extrude to support escarpments low gradient at the margins indicate less crustal strength variations between the plateau and outer forelands like at the northeastern and southeastern margins where they might be outlets for the weak ductile tibetan lower crust to flow away from the plateau

a review on active tectonics and deep crustal processes of the western sichuan region eastern margin of the tibetan plateau abstract one of remarkable geological and geomorphological features in continental china is the presence of a north south trending tectonic zone which separates the seismically active tibetan plateau to the west from the tectonically stable south china and ordos blocks to the east the zone also owns a name of north south seismic belt as a large number of great historical earthquakes occur on it the most recent one the 2008 wenchuan earthquake attests its recent tectonic activity in this review i take the western sichuan region as an example to probe the structural styles and kinematic pattern as well as deep geological process associated with tectonic deformation of the north south trending zone through integrated studies on active faults gps crustal deformation and geophysical structure we show that deformation in the western sichuan is governed by interactions among three crustal blocks songpan chuandian and south china of distinctive rheological properties under the tectonic framework that eastward growth of the soft eastern tibet is blocked by the hard lithosphere of the south china block the left lateral xianshuihe fault continues to the north south trending fault system without crustal shortening to form a bounding fault to limit the northern extend of the magnificent clockwise rotation of crustal material around the eastern himalaya syntax upper crust of the three blocks is dominated by brittle deformation whereas the ductile flow of lower crust would drag the brittle upper crustal blocks to move with respect to each other the relative motions among the brittle upper crustal blocks cause strain accumulations among their bounding faults to generate large earthquakes deformation of the western sichuan region can thus be described in terms of combined model of rigid block movement and continuous deformation we suggest this combined model can be applied to entire continental china

rupture process of the 2008 wenchuan china earthquake inferred from teleseismic waveform inversion and forward modeling of broadband seismic waves abstract we investigate the source process of the may 12 2008 wenchuan earthquake using teleseismic waveform data we divide the source area into southwestern and northeastern segments and estimate the probable dip angle for the northeastern fault segment by analyzing the waveform misfit of the inversion the results of the slip distribution indicate a thrust motion around the epicenter while a strike slip motion dominates from about 110 km northeast of the epicenter to the northeastern end of the fault the maximum slip and total seismic moments are estimated as being up to 11 0 m and 1 2 1021 n m mw 8 0 respectively additionally we simulate broadband seismic waves to verify our source model assuming realistic three dimensional earth structures and using the spectral element method the resulting synthetic waveforms agree well with the observed waveforms for both body and surface waves in the frequency range in the period from 20 to 150 s in our model comprising high angle strike slip mechanisms in the northeastern segment the misfits of the surface wave in the range from 60 to 500 s is systematically smaller than the corresponding values in other source models comprising thrust or low angle strike slip mechanisms the coulomb stress distribution in the northeastern segment computed by using our model indicates positive and large changes induced by the rupture in the southwestern segment we consider that the source fault of the 2008 wenchuan earthquake is composed of at least two main fault segments one with a low dip angle and the other with a high dip angle which are dominated by thrust and strike slip motions respectively we further consider that the rupture might transfer between these two faults during the mainshock

low seismicity in the bhutan himalaya and the stress shadow of the 1897 shillong plateau earthquake abstract the seismicity of the bhutan himalaya region is generally low as compared to its adjoining himalayan segments the topography in the region is slightly subdued and different from the neighbouring central nepal region low seismicity in the region may possibly be due to the postulated low convergence rate in the bhutan himalaya difference in subsurface structures or the aseismic nature of the region we suggest that the lower seismicity in the bhutan himalaya may also be due to stress change caused by the great 1897 shillong plateau earthquake as the low seismicity region of the bhutan himalaya coincides with the stress shadow of the earthquake

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

erosional control on the dynamics of low convergence rate continental plateau margins s u m m a r y over the last decade thermomechanical models have revealed the control of both tectonics and erosion on the morphology of continental plateaus margins however unravelling the specific effects of these two coupled processes has been difficult in practice here to assess the control of erosion we investigate the dynamics of the eastern and the northern borders of the tibetan plateau which are characterized by a low convergence rate and a steep topographic escarpment adjacent to the sichuan and tarim basins respectively thermomechanical modelling of continental lithosphere coupled with fluvial denudation reveals that important crustal deformation with large scale horizontal displacements can occur without any convergence as a response to mass transfer due to gravitational collapse and to erosional unloading these processes are sensitive to crustal structure geothermal gradient as well as surface erosion at a timescale of several million years our results suggest that this denudation triggered deformation exerts a primary control on the evolution of those plateau margins by counterbalancing the mass removal due to erosion and stabilizing the topographic escarpment this finding supports a possible explanation for the morphology of the longmen shan eastern tibet in which the paradoxical combination of persistent high topographic gradients close to the foreland and low convergence rates can be related to the influence of erosion on deformation patterns

stress shadow on the southwest portion of the longmen shan fault impacted the 2008 wenchuan earthquake rupture the 2008 wenchuan earthquake mw7 9 unilaterally ruptured the longmen shan fault lmsf along eastern tibet the earthquake rupture propagated about 270km northeastward whereas it propagated only about 20km southwestward along the strike of the fault although a significant attention has been paid to the question of predominantly unilateral propagation the primary reasons for this type of propagation remain unclear in this research we examined the change of coulomb stress along the lmsf caused by the historical earthquakes near and on the lmsf from 1725 to 2008 we found that the 14 preceding large earthquakes m6 5 on the xianshui he fault cast a stress shadow on the sw segment of the lmsf which was not activated by the 2008 wenchuan earthquake rupture the 1970 dayi earthquake on the sw segment of the lmsf contributed significantly to this stress shadow compared with the segment of the 2008 wenchuan earthquake rupture this stress shadow caused strong stress contrasts of 214 22 and 80kpa in the seismic gap of the very sw segment of the lmsf the rupture zone of the 2013 lushan earthquake and the seismic gap between the 2008 wenchuan and 2013 lushan earthquake ruptures respectively stress contrasts in these values were consistent with tectonic loading over 165 17 and 62years respectively by integrating an interseismic stress loading rate of 1 3kpa a we proposed that this stress shadow might have created a barrier at the sw segment preventing the earthquake rupture propagating southwestward

postseismic stress transfer explains time clustering of large earthquakes in mongolia abstract three m 8 earthquakes have occurred in mongolia during a 52 year period 1905 1957 since these earthquakes were well separated in space 400 km the coseismic stress change is far too low 0 001 bar to explain mutual earthquake triggering by contrast postseismic relaxation gradually causes a significant stress change 0 1 0 9 bar over large distances using a spring slider model to simulate earthquake interaction we find that viscoelastic stress transfer may be responsible for the earthquake time clustering observed in active tectonic areas therefore revealing postseismic strain by satellite geodesy and modeling earthquake clusters could improve our understanding of earthquake occurrence especially in zones where large earthquakes have already struck in past decades

beware of slowly slipping faults the fault zone that hosted the devastating wenchuan earthquake in 2008 had been assigned a moderate to low seismic hazard rating because it slips slowly in hindsight it seems that this type of fault is not necessarily innocuous

slip maxima at fault junctions and rupturing of barriers during the 2008 wenchuan earthquake the devastating wenchuan earthquake in 2008 struck along a fault zone that showed low rates of deformation analysis of gps and insar data suggests that as structural barriers failed during a single earthquake the rupture cascaded across multiple fault segments which may explain the high magnitude of the event

coseismic fault slip of the 2008 mw 7 9 wenchuan earthquake estimated from insar and gps measurements 1 we infer co seismic fault slip during the 2008 mw 7 9 wenchuan earthquake from interferometric synthetic aperture radar insar and gps observations of ground deformation we use alos palsar data from ascending orbits on six tracks and we do not use data that are strongly affected by ionospheric perturbations we use a fault model composed of three planar fault segments of the beichuan fault and one planar segment representing the parallel pengguan fault maximum thrust slip is up to 6 7 m near the surface and occurs in two locations near yingxiu in the south and beichuan in the center of the rupture maximum strike slip is over 4 m and occurs near pingtong and nanba along the northern end of the rupture we find that the ratio of coseismic thrust to strike slip on the beichuan fault decreases from 1 5 to 0 7 from the sw to the ne citation feng g e a hetland x ding z li and l zhang 2010 coseismic fault slip of the 2008 mw 7 9 wenchuan earthquake estimated from insar and gps measurements geophys res lett 37 l01302 doi 10 1029 2009gl041213

rupture of deep faults in the 2008 wenchuan earthquake and uplift of the longmen shan the longmen shan mountains rise up 6 000 m over a distance of just 100 km but the mechanisms driving formation of this striking topography are debated analyses of crustal movements during the 2008 wenchuan earthquake suggest that fault induced uplift plays a role in building the high topography

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

three dimensional velocity structure of crust and upper mantle in southwestern china and its tectonic implications using p and s arrival times from 4625 local and regional earthquakes recorded at 174 seismic stations and associated geophysical investigations this paper presents a three dimensional crustal and upper mantle velocity structure of southwestern china 21 34 n 97 105 e southwestern china lies in the transition zone between the uplifted tibetan plateau to the west and the yangtze continental platform to the east in the upper crust a positive velocity anomaly exists in the sichuan basin whereas a large scale negative velocity anomaly exists in the western sichuan plateau consistent with the upper crustal structure under the southern tibetan plateau the boundary between these two anomaly zones is the longmen shan fault the negative velocity anomalies at 50 km depth in the tengchong volcanic area and the panxi tectonic zone appear to be associated with temperature and composition variations in the upper mantle the red river fault is the boundary between the positive and negative velocity anomalies at 50 km depth the overall features of the crustal and the upper mantle structures in southwestern china are a low average velocity large crustal thickness variations the existence of a high conductivity layer in the crust or and upper mantle and a high heat flow value all these features are closely related to the collision between the indian and the asian plates

the response of creeping parts of the san andreas fault to earthquakes on nearby faults two examples rates of shallow slip on creeping sections of the san andreas fault have been perturbed on a number of occasions by earthquakes occurring on nearby faults one example of such perturbations occurred during the 26 january 1986 magnitude 5 3 tres pinos earthquake located about 10 km southeast of hollister california seven creepmeters on the san andreas fault showed creep steps either during or soon after the shock both left lateral ll and right lateral rl steps were observed a rectangular dislocation in an elastic half space was used to model the coseismic fault offset at the hypocenter for a model based on the preliminary focal mechanism the predicted changes in static shear stress on the plane of the san andreas fault agreed in sense ll or rl with the observed slip directions at all seven meters for a model based on a refined focal mechanism six of the seven meters showed the correct sense of motion two possible explanations for such coseismic and postseismic steps are 1 that slip was triggered by the earthquake shaking or 2 that slip occurred in response to the changes in static stress fields accompanying the earthquake in the tres pinos example the observed steps may have been of both the triggered and responsive kinds a second example is provided by the 2 may 1983 magnitude 6 7 coalinga earthquake which profoundly altered slip rates at five creepmeters on the san andreas fault for a period of months to years the xmm1 meter 9 km northwest of parkfield california recorded ll creep for more than a year after the event to simulate the temporal behavior of the xmm1 meter and to view the stress perturbation provided by the coalinga earthquake in the context of steady state deformation on the san andreas fault a simple time evolving dislocation model was constructed the model was driven by a single long vertical dislocation below 15 km in depth that was forced to slip at 35 mm yr in a rl sense a dislocation element placed in the seismogenic layer under xmm1 was given a finite breaking strength of sufficient magnitude to produce a parkfield like earthquake every 22 years when stress changes equivalent to a coalinga earthquake were superposed on the model running in a steady state mode the effect was to make a segment under xmm1 that could slip in a linear viscous fashion creep ll and to delay the onset of the next parkfield like earthquake by a year or more if static stress changes imposed by earthquakes off the san andreas can indeed advance or delay earthquakes on the san andreas by months or years then such changes must be considered in intermediate term prediction efforts

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

a global search for stress shadows 1 debate continues regarding the relative proportion of earthquakes triggered by passing seismic waves versus static stress changes from a main shock static stress changes are expected to have long term effects on earthquake probabilities whereas dynamic stress changes due to the passing of seismic waves should not both mechanisms are expected to raise seismicity rates in some areas but only static stress change calculations predict rate decrease shadows thus identification of post main shock earthquake suppression is diagnostic of a static stress change process we note that in principle static stress change theory predicts suppression of particular earthquake mechanisms in a shadow zone rather than an overall rate reduction a stress shadow can therefore be characterized by a change in the average earthquake focal mechanism before and after a main shock that results from suppression of a given mechanism type we examined average mechanisms from 2 radii and 5 year periods before and after 119 ms 7 main shock earthquakes drawn from the harvard centroid moment tensor cmt catalog significant average mechanism changes caused by earthquake suppression were found in only two cases however by stacking the data we were able to resolve statistically significant suppression of particular post main shock focal mechanisms this indicates that while static stress shadows are subtle they are indeed present in the global catalog

rupture complexity of the 1970 tonghai and 1973 luhuo earthquakes china from p wave inversion and relationship to surface faulting the source processes of the 4 january 1970 tonghai earthquake m s 7 5 and the 6 february 1973 luhuo earthquake m s 7 5 in southwestern china were investigated using an inversion technique on the very complex body waves the two earthquakes were associated with 48 and 90 km of surficial strike slip rupture respectively and the distribution of displacement with distance along the fault was well documented by field studies of both events the source process for both earthquakes comprised three to four subevents with different moments and rupture durations these calculated parameters agree well with the field observations and aftershock distributions particularly in the total rupture length and in the amount and asymmetry of fault displacements relative to the locations of the main epicenters

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

fem simulation of interseismic and coseismic deformation associated with the 2008 wenchuan earthquake abstract we make use of two step modeling to simulate inter and coseismic deformation within one seismic cycle by means of visco elastic finite element method fem the first step is to perform inversion to find the optimum modeling parameters by fitting the observed interseismic deformation then the model continues to produce a major seismic event to simulate the wenchuan earthquake the model results show that in order to fit the observed interseismic deformation it needs a soft lower crust and upper mantle beneath the eastern tibet and a very strong lithosphere of the sichuan basin the computed interseismic strain accumulation in the lower crust beneath the eastern tibet is much faster than that in the other regions especially the elastic strain energy density rate esed accumulates very rapidly in and around the longmen shan fault in the depth above 30 km that may explain why the great wenchuan earthquake occurs in the region of such a slow surface deformation rate simulations of coseismic processes reveal relationships among slip acceleration normal stress and shear stress changes on surface of the seismogenic fault coseismic slip appears to initiate in the gently dipping section of the fault but primary slips coseismic rupture on both gently dipping and steeply dipping sections take place simultaneously minor fault slip accelerations decrease normal stress on fault surface to reduce frictional strength of fault and in general increase shear stress on fault surface to enhance tectonic stress on the fault to drive the fault further slips both processes facilitate major slip or rupture on the listric reverse fault coseismic slip distribution also suggest that an important role of high angle listric reverse faulting is to transfer overwhelming horizontal deformation of the eastern tibet into significant vertical displacement in the longmen shan during the 2008 wenchuan earthquake

material contrast does not predict earthquake rupture propagation direction 1 earthquakes often occur on faults that juxtapose different rocks the result is rupture behavior that differs from that of an earthquake occurring on a fault in a homogeneous material previous 2d numerical simulations have studied simple cases of earthquake rupture propagation where there is a material contrast across a fault and have come to two different conclusions 1 earthquake rupture propagation direction can be predicted from the material contrast and 2 earthquake rupture propagation direction cannot be predicted from the material contrast in this paper we provide observational evidence from 70 years of earthquakes at parkfield ca and new 3d numerical simulations both the observations and the numerical simulations demonstrate that earthquake rupture propagation direction is unlikely to be predictable on the basis of a material contrast

effects of a low velocity zone on a dynamic rupture dynamic crack earthquake simulations generally assume that the crustal material surrounding faults is laterally homogeneous tomographic and near fault seismic studies indicate that the crust near faults is instead comprised of rocks of varying material velocities we have tested the effects of adding material velocity variation to simulations of spontaneously propagating earthquakes we used two dimensional plane strain conditions coupled with a slip weakening fracture criterion and examined earthquakes on faults that bisect finite width low velocity zones embedded in country rock and earthquakes on faults that bound two different velocity materials when a fault bisects a low velocity zone the normal stress remains unchanged but both the rupture velocity and slip velocity pulse shape are perturbed the presence of the low velocity zone induces high frequency oscillations in the slip function near the rupture front when the fault is on the edge of the low velocity zone the oscillations are more pronounced and repeated sticking and slipping can occur near the rupture front for the slip weakening velocity independent friction model however the temporary sticking does not lead to permanent arrest of slip and slip duration is still controlled by the overall rupture dimension when an earthquake ruptures a fault juxtaposing a lower velocity material against a higher velocity material the normal stress across the fault near the crack tip is perturbed the sign of the normal stress perturbation depends on the direction of rupture leading in some cases to a directional dependence of rupture velocity when slip is accompanied by stress reduction a positive feedback develops between the normal and shear stress changes as previously noted by andrews and ben zion 1997 resulting in an apparently unavoidable grid size dependence in computation of stress change near the rupture front numerical experiments indicate however that the rupture velocity is insensitive to this zone size dependence which is highly localized immediately behind the crack tip the factors controlling the rupture velocity in the simulations including directional dependence are further elucidated by a new analytical solution for rupture of an asperity on a frictionless interface

field study of a highly active fault zone the xianshuihe fault of southwestern china the xianshuihe fault of western sichuan province china is one of the world s most active faults having produced 4 earthquakes during this century of magnitude 7 along a 350 km length of the fault at least 8 such events have occurred since 1725 in the more limited 150 km long segment including luhuo and daofu major earthquakes in 1904 1923 1973 and 1981 m 7 7 7 6 6 9 were associated with overlapping surficial fault ruptures and with individual left lateral displacements as large as 3 6 m field studies indicate that this high degree of activity is typical of the fault s longer term history the holocene left lateral slip rate on the north western segment of the fault has been 15 5 mm yr decreasing to about 5 mm yr on its southeastern segment based on radiometrically dated offset stream channel and terrace deposits and on offset glacial moraines physiographic features of active faulting are fully as diagrammatic as those of california s san andreas fault mainly because of high altitude preservation and the absence of cultural modification on this eastern margin of the tibetan plateau detailed en echelon tensional and pushup features resulting from surface ruptures in 1973 1955 1923 and 1893 can still be recognized today and new data have been collected bearing on the offsets and fault rupture lengths during these and other events the locations and magnitudes of historic earthquakes suggest that the characteristic earthquake model may apply to the xianshuihe fault obvious geometric segmentation of the fault has controlled the initiation and termination of ruptures in some events whereas segmentation control for others remains obscure based on the historic record repeat times estimated from slip rates and current seismic gaps two segments are particularly likely sites for m 7 earthquakes in the near future the 65 km long segment between daofu and qianning and the 135 km long segment bracketing kangding continuing creep has been documented along some segments of the fault and this together with the high degree of activity and other unique attributes makes the xianshuihe fault one of the most promising sites in the world for earthquake prediction and hazard evaluation studies

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

coseismic slip distribution of the 2002 mw7 9 denali fault earthquake alaska determined from gps measurements 1 on 3 november 2002 an mw7 9 earthquake occurred in central alaska the earthquake ruptured portions of the susitna glacier denali and totschunda faults inversion of the gps measured displacement field indicates that the event was dominated by a complex right lateral strike slip rupture along the denali fault gps sites closest to the epicenter show the effect of thrust motion on the susitna glacier fault the preferred coseismic slip model with m w 7 8 indicates relatively low slip on the western part of the rupture and high slip from about 60 km east of the hypocenter extending to the junction of the denali and totschunda faults we find mostly shallow slip from the surface to 15 km depth but the inversion suggests one large deep slip patch about 110 km east of the hypocenter our model predicts surface slip in good agreement with surface geological observations where model resolution is good

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

bar morphology of dissipative beaches an empirical model this study of 150 examples of nearshore bar morphology along the highly dissipative beaches 33 of the southeast mediterranean shoreline employs 32 years of aerial photography and wave data aided by detailed short term field studies three major bar types were delineated non rhythmic parallel meandering bars inner single crescentic bars and double crescentic bars each of these bar families includes variations the bars were related to daily ship and shore wave data including wave spectra from the day of observation back to 60 days prior to the observation the increase in total bar occurrence during summer is related to crossing of a major wave energy threshold in the spring when significant wave heights 1 m sharply increase to 70 85 in april may the bar morphology wave comparisons further indicate that as the significant wave heights decrease and remain below 1 m non rhythmic bars form within 7 10 days single crescentic bars require 15 days and double crescentic bars require 20 30 days this adjustment period of the bars to wave power causes a delayed response which accounts for lack of coincidence between wave energy and bar occurrence the formation of the initial double crescentic bar and its transformation to the mature double crescentic type requires a short pulse of wave energy 0 5 h13 1 5 m some bar families occur throughout the year the aseasonal occurrence is best shown by the mature double crescentic type which apparently is the final stage in the crescenticbar development sequence however other bar families show a tendency for a seasonal distribution which reflects their sensitivity to wave energy inner single crescentic and initial double crescentic bars are largely restricted to the calmest wave months of may april to october november there is an antiphase relationship between the frequencies of non rhythmic and crescentic bars

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

variations in rupture speed slip amplitude and slip direction during the 2008 mw 7 9 wenchuan earthquake summary theoretical and observational evidence implies that variable rupture velocity may be associated with high fault slip and high moment release rates during earthquakes we investigate this relationship for the 2008 mw 7 9 wenchuan china earthquake which appears to have experienced a highly variable moment release rate we used an empirical green s function egf deconvolution analysis of teleseismic waveforms to retrieve the primary rupture characters for this event based on field observations and the deconvolved source time function from thrust and strike slip egfs we divided the ruptured fault into three segments allowing us to determine the spatial slip distribution with different average rupture velocities on each segment we deployed a grid search analysis in which we integrated the teleseismic waveform inversion and forward modelling of the regional surface wave to determine the optimum rupture speed in each fault segment our result shows that the 2008 wenchuan earthquake had slip amplitude direction and rupture velocity that were highly spatially variable the earthquake initially ruptured with nearly pure thrust motion and a slow rupture velocity of 1 7 km s 1 then the rupture speed increased up to 3 1 3 3 km s 1 and produced the largest slip on the second segment where two parallel faults ruptured simultaneously rupture velocity then slowed down to 2 5 2 9 km s 1 on the final segment which underwent primarily strike slip motion in total the fault extended 300 km with an average rupture speed in the range of 2 6 2 9 km s 1 the high rupture speed close to the shear wave velocity in the second segment may be related to the simultaneous rupture of the two parallel faults on well established pre existing structures the spatial distribution of rupture velocity and slip are likely related to the strongly rotational and 3 d deformation in the eastern tibetan plateau margin which leads to the heterogeneous stress field of the longmen shan region

how does crustal shortening contribute to the uplift of the eastern margin of the tibetan plateau the eastern margin of the tibetan plateau the longmen shan has triggered a vigorous debate to explain the uplift and maintaining of its steep and high topography several mechanical and kinematic models have been previously developed in order to investigate the tectonic and erosional control on the formation mechanism of the longmen shan but the contribution of crustal shortening has never been taken into account due to the lack of significant surface convergence rate about 3 mm a across the longmen shan range we investigate this question through 2d finite element modelling assuming visco elasticity rheology the numerical results are constrained with geological and geophysical observations across the longmen shan range we find that even low rate of crustal shortening contributes significantly to the uplift of the longmen shan this contribution has been greatly underestimated in previous studies the viscosity contrast between the tibetan plateau lower crust and the yangtze crust crucially controls the uplift of the longmen shan due to crustal shortening the ductile tibetan lower crust thickens to accommodate most of crust shortening as the eastward movement of the tibetan plateau is obstructed by the mechanical strong and stable yangtze craton the uplift rate contrast between the tibetan plateau and the sichuan causes a steep uplift rate gradient to produce and maintain the longmen shan steep and high topography in the time scale of several million years our results support a possible explanation for the paradox of the high topography and low convergence rate at the longmen shan range

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 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

stress accumulation and increased seismic risk in eastern turkey abstract unlike the north anatolian fault zone which has produced 11 large earthquakes since 1939 the east anatolian fault zone eafz has been relatively quiescent in the last century when compared to historical records and has therefore accumulated significant stresses along its length determination of the location and likely magnitude of a future probable earthquake along the eafz is of interest both because of this history of large earthquakes m 8 and the density of population in the area here we calculate stress evolution along the fault zone due to both seismic and tectonic loading since 1822 a sequence of 10 well constrained historical earthquakes is selected and the resulting stresses are calculated summed with tectonic loading stresses and resolved onto the mapped active faults we identify two areas of particular seismic risk one of which might be expected to yield a large event our results are sensitive to the previous history of large earthquakes in the region and indicate a need for detailed investigations to constrain the exact rupture geometries of previous earthquakes on these segments

crustal structures in the area of the 2008 sichuan earthquake from seismologic and gravimetric data abstract the 12 may 2008 the sichuan earthquake was one of the worst natural disasters in china here we present a detailed picture of the epicentral area inferred geophysical data based on the analysis of teleseismic data acquired by a dense seismic network we highlight an abrupt 20 km moho offset between the sichuan basin and the tibetan plateau and a horizontal discontinuity at 15 km depth which may connect with the ruptured zone of the 2008 event we obtain low mean crustal velocity ratios which suggest the absence of a thick and extensive zone of partial melt within the crust beneath the eastern part of the songpan garze terrane all our data support the idea that the longmen shan range mark a zone of active strain localization due to the rigid yangtze craton resisting eastward displacement of the tibetan plateau

coseismic slip model of the 2008 wenchuan earthquake derived from joint inversion of interferometric synthetic aperture radar gps and field data 1 we derived a coseismic slip model for the mw 7 9 2008 wenchuan earthquake on the basis of radar line of sight displacements from alos interferograms gps vectors and geological field data available interferometric synthetic aperture radar insar data provided a nearly complete coverage of the surface deformation along both ascending fine beam mode and descending orbits scansar to scansar mode the earthquake was modeled using four subfaults with variable geometry and dip to capture the simultaneous rupture of both the beichuan fault and the pengguan fault our model misfits show that the insar and gps data are highly compatible the combined inversion yields a 93 variance reduction the best fit model has fault planes that rotate from shallow dip in the south 35 to nearly vertical dip toward the north 70 our rupture model is complex with variations in both depth and rake along two major fault strands in the southern segment of the beichuan fault the slip is mostly thrust 13 m and occurred principally in the upper 10 km of the crust the rupture progressively transformed to right lateral strike slip as it propagated northeast with maximum offsets of 7 m our model suggests that most of the moment release was limited to the shallow part of the crust depth less than 10 km we did not find any shallow slip deficit in the slip depth distribution of this mixed mechanism earthquake aftershocks were primarily distributed below the section of the fault that ruptured coseismically

eastward expansion of the tibetan plateau by crustal flow and strain partitioning across faults the tibetan plateau is expanding eastwards but the modes of deformation are poorly understood high resolution seismic images from the region identify localized zones of weak crustal rocks as well as deep faults implying that deformation occurs through a combination of crustal flow and movement of rigid blocks of crust