shallow creep on the haiyuan fault gansu china revealed by sar interferometry interferometric synthetic aperture radar data are used to map the interseismic velocity field along the haiyuan fault system hfs at the north eastern boundary of the tibetan plateau two m 8 earthquakes ruptured the hfs in 1920 and 1927 but its 260 km long central section known as the tianzhu seismic gap remains unbroken since 1000 years the envisat sar data spanning the 2003 2009 period cover about 200 300 km2 along three descending and two ascending tracks interferograms are processed using an adapted version of roi pac the signal due to stratified atmospheric phase delay is empirically corrected together with orbital residuals mean line of sight velocity maps are computed using a constrained time series analysis after selection of interferograms with low atmospheric noise these maps show a dominant left lateral motion across the hfs and reveal a narrow 35 km long zone of high velocity gradient across the fault in between the tianzhu gap and the 1920 rupture we model the observed velocity field using a discretized fault creeping at shallow depth and a least squares inversion the inferred shallow slip rate distribution reveals aseismic slip in between two fully locked segments the average creep rate is 5 mm yr 1 comparable in magnitude with the estimated loading rate at depth suggesting no strain accumulation on this segment the modeled creep rate locally exceeds the long term rate reaching 8 mm yr 1 suggesting transient creep episodes the present study emphasizes the need for continuous monitoring of the surface velocity in the vicinity of major seismic gaps in terms of seismic hazard assessment

three dimensional dynamic simulation of the 1992 landers earthquake the 1992 landers california earthquake magnitude 7 3 was modeled as the propagation of a spontaneous rupture controlled by a realistic prestress distribution with the use of a three dimensional finite difference method the dynamic rupture reproduces the general slip pattern used to compute the initial stress distribution and generates near fault ground motions at the surface similar to observations the simulated rupture propagates on the fault along a complex path with highly variable speed and rise time changing the magnitude and pattern of the stress significantly the method provides the framework to estimate earthquake rupture parameters from recorded seismic and geodetic data

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

three dimensional nonplanar simulation of the 1992 landers earthquake 1 we have simulated the rupture process of the 1992 landers california earthquake using a realistic nonplanar fault geometry including fault bends and branches through a three dimensional boundary integral equation method considering an external loading system due to local tectonics as well as a nonplanar fault structure we could reproduce the characteristic features of this earthquake such as spontaneous rupture transfer between faults pattern of slip distribution and propagation of rupture front without assuming any laterally heterogeneous distribution of parameters we could also reproduce seismic waveforms near the faults especially in the forward direction of rupture propagation where rupture directivity controlled by rupture transfer between faults significantly affects ground motion

dynamic rupture simulation of the 2008 mw 7 9 wenchuan earthquake with heterogeneous initial stress the rupture process and tectonic surroundings of the 2008 wenchuan china earthquake are both complex in a way that might be related to the heterogeneous stress field of the longmen shan region in this study we construct dynamic models with heterogeneous initial stress to reproduce a kinematic inversion result by wen et al 2012 and investigate the physical mechanisms of the variable slip pattern and rupture velocity in this event the results show that for the 2008 wenchuan earthquake 1 the rupture behavior and slip pattern can be explained by heterogeneities in initial stress and 2 the variations of rupture velocity and ground motion pattern are strongly affected by both stress drop and fault strength our preferred dynamic model agrees with the kinematic model that the 2008 wenchuan earthquake initiated with a slow velocity in the southwest sped up in the segment with the largest slip and then slowed down for the remaining propagation to the northeast

millennial recurrence of large earthquakes on the haiyuan fault near songshan gansu province china the haiyuan fault is a major active left lateral fault along the northeast edge of the tibet qinghai plateau studying this fault is important in understanding current deformation of the plateau and the mechanics of continental deformation in general previous studies have mostly focused on the slip rate of the fault paleo seismic investigations on the fault are sparse and have been targeted mostly at the stretch of the fault that ruptured in the 1920 m 8 6 earthquake in ningxia province to investigate the millennial seismic history of the western haiyuan fault we opened two trenches in a small pull apart basin near songshan in gansu province the excavation exposes sedimentary layers of alternating colors dark brown silty to clayey deposit and light yellowish brown layers of coarser grained sandy deposit the main fault zone is readily recognizable by the disruption and tilting of the layers six paleoseismic events are identified and named ss1 through ss6 from youngest to oldest charcoal is abundant yet generally tiny in the shallowest parts of the trench exposures thirteen samples were dated to constrain the ages of paleoseismic events all six events have occurred during the past 3500 3900 years the horizontal offsets associated with these events are poorly known however events ss3 to ss6 appear to be large ones judging from comparison of vertical separations and widths of fault zones the youngest event ss1 instead seems to be a minor one probably the 1990 mw 5 8 earthquake thus four large events in 3500 3900 years would imply a re currence interval of about 1000 years three events ss2 to ss4 prior to 1990 occurred sometime during 1440 1640 a d shortly after 890 1000 a d and 0 410 a d re spectively we tentatively associate them with the 1514 a d 1092 a d and 143 or 374 a d historical earthquakes taking 10 2 m of slip for large events ss3 and ss4 comparable to the 1920 m 8 haiyuan earthquake their occurrence times would be consistent with the long term 12 4 mm yr estimate of lasserre et al 1999 however a more realistic evaluation of slip rate and its possible change with time requires a more rigorous determination of coseismic slip amounts of past earth quakes

rupture dynamics and ground motion from potential earthquakes around taiyuan china abstract using the curved grid finite difference method we develop dynamic spontaneous rupture models of earthquakes on the jiaocheng fault jf near taiyuan the capital and largest city of shanxi province in north china we then model the wave propagation and strong ground motion generated by these scenario earthquakes a map of the seismic hazard distribution for a potential m 7 5 earthquake is created based on dynamic rupture and true 3d modeling the tectonic initial stress fields derived from the inversion of focal mechanisms of historical earthquakes a nonplanar fault and a rough surface are considered in the dynamic rupture simulation based on the geological structure of the taiyuan basin normal faulting with a dipping angle of 60 is implemented for the scenario earthquake simulations the largest uncertainty of a potential earthquake in the jf zone is the hypocenter four cases are used to nucleate the earthquake at different locations using these dynamic rupture sources for the jf we further simulate and analyze both the seismic wave generated by the scenario earthquake and the strong ground motion it is found that the low velocity media of the taiyuan basin redistribute the ground motion well the effects of the regional stress fields on the dynamic rupture and hazard distribution are investigated and discussed further moreover a scenario earthquake which can cause great damage to the city of taiyuan is modeled and analyzed

constraint of fault parameters inferred from nonplanar fault modeling 1 we study the distribution of initial stress and frictional parameters for the 28 june 1992 landers california earthquake through dynamic rupture simulation along a nonplanar fault system we find that observational evidence of large slip distribution near the ground surface requires large nonzero cohesive forces in the depth dependent friction law this is the only way that stress can accumulate and be released at shallow depths we then study the variation of frictional parameters along the strike of the fault for this purpose we mapped into our segmented fault model the initial stress heterogeneity inverted by peyrat et al 2001 using a planar fault model simulations with this initial stress field improved the overall fit of the rupture process to that inferred from kinematic inversions and also improved the fit to the ground motion observed in southern california in order to obtain this fit we had to introduce an additional variations of frictional parameters along the fault the most important is a weak kickapoo fault and a strong johnson valley fault

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

fissure formation and subsurface subsidence in a coalbed fire abstract coalbed fires are uncontrolled subsurface fires that occur around the world these fires are believed to be significant contributors to annual co 2 emissions although many of these fires have been burning for decades researchers have only recently begun to investigate physical mechanisms that control fire behavior one aspect of fire behavior that is poorly characterized is the relationship between subsurface combustion and surface fissures at the surface above many fires long wide fissures are observed at a coalbed fire near durango colorado these fissures form systematic orthogonal patterns that align with regional joints in the upper cretaceous fruitland formation understanding the mechanisms that form these fissures is important as the fissures are believed to play vital roles in sustaining the combustion in the subsurface in some of the coalbed fire simulation models available today these fissures are treated as fixed boundary conditions we argue using data collected field observations and simulation result that there exists a relationship between the location and magnitude of subsidence caused by the fire and the opening of fissures the results presented suggest that fissures are believed to open when subsurface subsidence gives rise to tensile stresses around pre existing joints

clustering of offsets on the haiyuan fault and their relationship to paleoearthquakes we used airborne light detection and ranging lidar data to reevaluate the single event offsets of the 1920 haiyuan ms 8 5 earthquake and the cumulative offsets along the western and middle segments of the coseismic surface rupture zone our lidar data indicate that the offset observations along both the western and middle segments fall into groups the group with the minimum slip amount is associated with the 1920 haiyuan ms 8 5 earthquake which ruptured both the western and middle segments our research highlights two new interpretations first the previously reported maximum displacement of the 1920 earthquake was likely due to at least two earthquakes second our results reveal that the cumulative offset probability density copd peaks of the same offset amounts on the western and middle segments do not correspond to one another one to one we suggest that any discussion of the rupture pattern of a certain fault based on the offset data should also consider fault segmentation and paleoseismological data therefore the copd peaks should be computed and analyzed on fault subsections and not entire fault zones to study the number of paleoearthquakes and their rupture patterns

crater relaxation on ganymede implications for ice rheology controversy has existed over whether or not viscous relaxation is an important process on the icy satellites previous models involved large extrapolations of newtonian flow laws for ice whereas ice is known to exhibit non newtonian behavior recently the flow law parameters for ice at the appropriate temperatures and stresses have been measured numerical modelling of the viscous relaxation of basins on ganymede using these parameters has given implausibly short relaxation times however this model treated ice as a purely viscous substance so that no elastic lithosphere could develop near the surface here we treat ice as a maxwell visco elastic material and numerically model the relaxation of basins on ganymede we find that realistic young s moduli lead to little relaxation occurring in basins even 4 0 ga after their formation further we demonstrate that within broad limits the near surface temperature gradient has little effect on this result finally through examination of the distribution of maxwell times in the vicinity of the crater we show that most viscous relaxation occurs early in the basin s history when stresses are high and thus maxwell time is short as stresses are relieved the maxwell time becomes long and relaxation essentially ceases

dynamic modeling of the 1992 landers earthquake we have used observed band pass filtered accelerograms and a previously determined slip distribution to invert for the dynamic rupture propagation of the 1992 landers earthquake in our simulations dynamic rupture grows under the simultaneous control of initial stress and rupture resistance by friction which we modeled using a simple slip weakening law we used a simplified landers fault model where the fault segments were combined into a single vertical planar fault by trial and error we modified an initial stress field inferred from the kinematic slip distribution proposed by wald and heaton 1994 until dynamic rupture generated a rupture history and final slip distribution that approximately matched those determined by the kinematic inversion we found that rupture propagation was extremely sensitive to small changes in the distribution of prestress and that a delicate balance with energy release rate controls the average rupture speed for the inversion we generated synthetic 0 5 hz ground displacements using an efficient green s function propagator method axitra this method enables us to propagate the radiation generated by the dynamic rupture to distances greater than those feasible using the finite difference method the dynamic model built by trial and error inversion provides a very satisfactory fit between synthetics and strong motion data we validated this model using records from stations used in the slip inversion as well as some which were not included we also inverted for a complementary model that fits the data just as well but in which the initial stress was perfectly uniform while rupture resistance was heterogeneous this demonstrates that inversion of ground motion is nonunique

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

dynamic rupture simulations of the 1920 ms 8 5 haiyuan earthquake in chinadynamic rupture simulations of the 1920 ms 8 5 haiyuan earthquake in china

estimation of site effects in beijing city for the realistic modeling of the seismic ground motion in lateral heterogeneous anelastic media the database of 3 d geophysical structures for beijing city has been built up to model the seismic ground motion in the city caused by the 1976 tangshan and the 1998 zhangbei earthquakes the hybrid method which combines the modal summation and the finite difference algorithms is used in the simulation the modeling of the seismic ground motion for both the tangshan and the zhangbei earthquakes shows that the thick quaternary sedimentary cover amplifies the peak values and increases the duration of the seismic ground motion in the northwestern part of the city therefore the thickness of the quaternary sediments in beijing city is the key factor controling the local ground effects four zones are defined on the base of the different thickness of the quaternary sediments the response spectra for each zone are computed indicating that peak spectral values as high as 0 1 g are compatible with past seismicity and can be well exceeded if an event similar to the 1697 sanhe pinggu occurs

how much does slip on a reactivated fault plane constrain the stress tensor given a fault plane and its slip vector the stress tensor which caused the displacement is sought two constraints are considered first a geometrical constraint that the shear stress applied to the fault plane is parallel to the slip wallace 1951 bott 1959 second a frictional constraint that the shear to normal stress ratio equals tan 0 coulomb 1776 in a first step the stress tensors that satisfy the geometrical constraint are sought for tensors belonging to the vectorial space of solutions shear and normal stress magnitudes become a function of the orientation of the principal stresses and are mapped extending a study by mckenzie 1969 in a second step it is investigated which of these tensors also satisfy the frictional constraint within this more restricted vectorial space there is a relationship between the magnitudes 1 2 1 3 and s 1 3 1 and the orientations of the principal stresses both the range of s and the spatial distribution of are more restricted than when the geometrical constraint alone is considered as when the geometrical constraint is solely considered mckenzie 1969 the orientations of the principal stresses may lie significantly away from and up to right angle to the p b t axes however this can happen only in two cases 1 either the effective stress difference s has reached a high value which is unlikely to happen if enough preexisting fractures are available to release the stress or 2 2 becomes close to either 1 or 3 and therefore barely distinguishable from it in that case the delocalization of the orientations of the principal stresses is best described by a tendency for to exchange role with either or when the stress difference remains small and 2 reasonably away from 1 and 3 approach positions that we define as the pf b tf axes and that are obtained from the p b t axes by a rotation of angle 0 2 around b and toward the slip vector this explains why the p b t axes gives reasonable estimates of the orientations of the principal stresses scheidegger 1964 despite objections mckenzie 1969 however whenever the fault plane can be distinguished from the auxiliary plane pf b tf should give a better estimate raleigh et al 1972 in an area where many fault planes are available and a uniform tensor is assumed the scatter in the plane orientations contains information about both the relative position of 2 represented by and the relative stress difference s the higher s or the closer to either 0 or 1 the more scatter this information could then be extracted by inverse methods because a friction law would constrain these inverse method more tightly it may show the necessity of nonuniform tensor to explain scattered fault plane

inferring stress from faulting from early concepts to inverse methods abstract we review the evolution of concepts on and methods of estimating the state of stress from fault movements theories of failure in isotropic materials suggested a simple geometrical construction of optimal principal stress directions from a fault plane and its associated slip these optimal directions align shear stress and slip directions and maximize the difference between shear stress and frictional resistance on the fault plane optimal stress directions for calcite twinning are obtained by a similar construction with the difference that they maximize shear stress force representation of seismic sources independently introduced pressure p and tension t axes at positions that also maximize shear stress on both nodal planes frictional slip theory and the constraint that slip and shear stress directions be parallel allowed to address reactivation of pre existing faults this suggested that stress could also be inverted from reactivated fault and slip data or earthquake focal mechanisms early methods relied on geometrical constructions as a substitute for calculations whereas later methods relied on software as these calculations became tractable with the help of computers similar methods were developed for the inversion of stress from crystal twin gliding with non optimal geometry with a different criterion that relies on a threshold of the component of shear stress along the gliding line even though these methods seek a common stress tensor compatible with fault and slip data their main use is to separate polyphase data into homogeneous subsets and help deciphering complex tectonic histories fault and slip data can also be analyzed to constrain the strain rather than the stress tensor in most cases this involves a summation and yields an average strain for the considered rock volume stress inversion thus appears better suited for differentiating heterogeneous data whereas strain analysis appears better suited for homogenizing them

sediment induced amplification and the collapse of the nimitz freeway the amplification of ground motion by low seismic velocity surface sediments is an important factor in determining the seismic hazard specific to a given site the ms 7 1 loma prieta earthquake of 17 october 1989 was the largest event in the contiguous united states in 37 years and yielded an unparalleled volume of seismic data from the main shock and aftershock sequence1 these data can be used to image the seismic source to study detailed earth structure and to study the propagation of seismic waves both through bedrock at depth and through sediment layers near the surface near the edge of san francisco bay site conditions vary considerably on scales of hundreds of metres the collapsed section of the two tiered nimitz freeway in oakland was built on san francisco bay mud whereas stiffen alluvial sediments underlie a southern section that was damaged but did not collapse here we analyse high quality digital aftershock recordings from several sites near the nimitz freeway and conclude that soil conditions and resulting ground motion amplification may have contributed significantly to the failure of the structure