evidence for normal and deep buried features of the longquan shan fault zone at the eastern margin of the tibetan plateau abstract the longquan shan fault zone lqsf locates in the sichuan basin of china parallel to the well known longmen shan fault zone different models for the lqsf indicate different understanding of the geological evolution of the tibetan plateau in this paper we provide evidences which demonstrate that the lqsf is a normal and deep buried fault zone firstly we find distinct extensional strains around the lqsf based on global positioning system gps observations we also find that the downward gps velocities across the lqsf decrease suddenly from 4 to 5 mm yr at the west to roughly zero at the east secondly we collate focal mechanism solutions to earthquakes of m 3 0 in the sichuan basin and find that 12 out of 21 earthquakes are normal earthquakes the surrounding extensional strains and the high proportion of normal earthquakes indicate that the shallow part of the lqsf is normal at present thirdly based on the migration section obtained from deep seismic reflection profiling we outline the geometric structure of the lqsf it is a deep buried fault zone that reaches the moho with two branches at the top such a fault model corresponds with the realities of the low seismic activities around the longquan shan anticline and the scattered earthquakes beneath the chengdu plain finally we propose a three stage evolutional model about the longquan shan fault system which includes the formation of anticline in late triassic the uplift of the mountain in oligence and the stage of normal characteristics of the fault zone from late miocene

spatial and temporal distribution of slip for the 1999 chi chi taiwan earthquake we investigated the rupture process of the 1999 chi chi taiwan earth quake using high quality near source strong motion records broadband teleseismic displacement waveforms and well distributed global positioning system gps data the near source strong motion displacement waveforms recorded significant static offsets of up to 8 m the teleseismic displacement records show a significant pulse with duration of about 18 to 20 sec taking into account the surface displacements observed along the chelungpu fault we considered two fault geometries a single planar fault and a two segment fault with a northeast striking section near the north ern end using the finite fault model with variable slip vectors we derived two models of the temporal and spatial slip distribution of the earthquake the gps data provided good surface displacement constraints for the slip distribution determina tion the spatial slip distribution is generally consistent with field observations the results for the simple fault model show a large asperity located in the region about 25 to 55 km north of the hypocenter with maximum slip of about 15 m when we use the two segment model the asperity further extends to the region where the fault bends toward the northeast with a maximum slip of up to 20 m a large amount of right lateral slip beneath station tcu068 is necessary to explain its observed large west movement it implies a local converging slip at the corner where the fault bends to the northeast the slip amplitude near the hypocenter is about 3 to 6 m the seismic moments determined from the various data sets are within the range of 2 to 4 10 27 dyne cm most of the slip concentrated at shallow depths less than 10 km the total rupture duration is about 28 sec and the rupture velocity is 75 to 80 of the shear wave velocity the slip vector shows a clockwise rotation during the fault rupture the static stress drop of the large asperity region is comparable with the dynamic stress drop as observed directly from the slip velocity at the station near the large slip region

seismic potential revealed by surface folding 1983 coalinga california earthquake the 2 may 1983 coalinga california earthquake magnitude 6 5 failed to rupture through surface deposits and instead elastically folded the top few kilometers of the crust the subsurface rate of fault slip and the earthquake repeat time are estimated from seismic geodetic and geologic data three larger earthquakes up to magnitude 7 5 during the past 20 years are also shown to have struck on reverse faults concealed beneath active folds

contemporary crustal deformation in east asia constrained by global positioning system measurements global positioning system gps measurements collected since the early 90 s allow us to derive geodetic velocities at 16 permanent stations in east asia and 68 campaign mode sites in north china the resulting velocity field shows the following 1 contrary to the early inferences that the shanxi rift has accommodated significant right slip motion our results suggest that the rift system at least in its northern part in north china is under ese wnw extension at a rate of 4 2 mm yr the velocity field also suggests that an ese wnw trending left lateral shear zone deforming at a rate of 2 1 mm yr may exist along the north rim of north china at the latitude of 40 n separating actively extending north china in the south from relatively stable mongolia in the north 2 central and east china move at a rate of 8 11 mm yr east southeast with respect to siberia implying that the overall east southeastward motion is the dominant mode of deformation in east china 3 the india plate moves at a rate of 6 1 mm yr slower than the nuvel 1a model prediction relative to the eurasia plate 4 significant eastward motion 20 2 mm yr with respect to siberia occurs in southeastern tibet about half of this eastward motion 11 mm yr is absorbed by structures along the eastern boundary of the tibetan plateau

surface deformation and lower crustal flow in eastern tibet field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern tibetan plateau since about 4 million years ago instead central eastern tibet has been nearly stationary relative to southeastern china southeastern tibet has rotated clockwise without major crustal shortening and the crust along portions of the eastern plateau margin has been extended modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle this model also predicts east west extension on the high plateau without convective removal of tibetan lithosphere and without eastward movement of the crust east of the plateau

interactions between thin and thick skinned tectonics at the western sichuan basin china abstract this study investigates the geometry kinematics and interaction of thin and thick skinned tectonics at the western sichuan basin adjacent to the eastern margin of the tibetan plateau a two level detachment system comprising a shallow triassic and basal precambrian detachment was identified three dimensional 3 d structural modeling was applied to demonstrate the geometry of the shallow detachment that developed in the sichuan foreland basin the shallow detachment forming material is an evaporite sequence deposited in the middle triassic which was subsequently buried beneath the foreland basin and later subsided rapidly during the flexural loading process during the late triassic in the cenozoic this set of evaporite rocks developed into an effective shallow detachment transferring geologic slip from the longmen shan range front to the sichuan basin the structure of this shallow detachment exhibits an asymmetrical characteristic with its deepest location consistent with the mesozoic foreland depression this relationship indicates that foreland subsidence in the late mesozoic is the main factor controlling the geometry of the detachment in the southern cenozoic foreland basin the development of thrust faults above the precambrian basal detachment resulted in a local deformation and uplift of the shallow detachment resulting in a lower basal slope 0 5 1 of the sedimentary basin taper and a high internal distribution in contrast the sedimentary basin taper in the north has a high basal slope that mainly translates along the shallow detachment lacking thrusting related structures this study reveals that the pre existing stratigraphic architecture of the sedimentary basin can influence the subsequent structural deformation of the foreland basin this has important implications for other foreland basins with multistage crustal shortening processes

3d geometry of range front blind ramp and its effects on structural segmentation of the southern longmen shan front eastern tibet abstract a 3d fault morphology model has been constructed from seismic profiles covering the piedmont of the southern longmen shan lms eastern margin of the tibetan plateau it reveals a spatial correlation between an 3 5 km high geometrical bump on the range front blind ramp rfbr and the gap between the 2008 m w 7 9 wenchuan and 2013 m w 6 6 lushan earthquakes sandbox modeling is then used to probe the effects of the geometrical irregularity of the rfbr on fault behaviors and the lms range front deformation sand wedges are designed to thrust over artificial blind ramps analogous to the thrusting of the lms orogenic wedge toward the sichuan basin through the rfbr the experiments reproduce the first order deformation features presented in the southern lms range front confirming that along strike geometrical variations of the rfbr have induced the segmentation of both fault motion and the range front deformation their results also suggest that the gap between the wenchuan and lushan earthquakes is located directly within the structural transition zone originating from the geometrical bump on the rfbr additionally there is a duplex structure occurring in the hanging wall of the geometrical bump which localizes significant shear strain with progressive shortening and represents a fracture zone corresponding to the observed geophysical anomaly low seismic velocity underneath the seismic gap it is likely that this fractured body protected the gap from the ruptures of the wenchuan and lushan earthquakes

three dimensional imaging of active structures using earthquake aftershocks the northridge thrust california abstract aftershocks of the 1994 northridge earthquake m 6 8 allow us to image the structure beneath the san fernando valley in northwestern los angeles in three dimensions we combine aftershocks and geological data to build an image of the three dimensional 3 d geometry of the previously unrecognized north vergent northridge blind thrust to a depth of 21 km the most striking feature of the imaged fault is mega corrugations oriented parallel to the mean aftershock slip vector with most of the 1994 slip confined to west of the largest corrugation we also image the partially overlying south vergent san fernando thrust which broke to the surface in a complex rupture in 1971 m 7 1 both thrusts produce fault related folding because of either fault propagation or fault bends however this deeper folding is masked by overlying complex deformation in the cover which is one reason why the northridge thrust was not identified until it ruptured in 1994 we use trishear fold modeling based on our 3 d fault geometry to evaluate possible folding due to slip on the northridge thrust as well as its interaction with the overlapping san fernando thrust and with shallow structures in the cover this example illustrates the importance of earthquake data to structural geology and the value of its 3 d integration with surface and near surface geological data

the 3 d structural model of an out of sequence earthquake in china implication for the reactivation of positive inversion structures along the northern tianshan fold and thrust belt

topography reveals seismic hazard the devastating earthquake in the chinese province of sichuan struck an area that was not expected to suffer seismic activity of such magnitude yet topographic analyses of the region indicate active deformation suggesting a way of refining maps of earthquake risk elsewhere

geodetic measurement of crustal motion in southwest china global positioning system measurements performed over a 2 4 yr period confirm the xianshuihe xiaojiang fault system as one of the primary active structures in southwest china stations southwest of these faults show southerly motions of 5 15 mm yr relative to the western sichuan basin and stations in a 200 km geodetic network located northwest of the basin move at only 0 5 mm yr these results are consistent with clockwise rotation of southwestern sichuan and western yunnan about the eastern tibetan syntaxis accommodated by left lateral slip of 12 4 mm yr on the xianshuihe xiaojiang fault system the results imply that if eastward extrusion of crustal material from the plateau occurs at present it is not accommodated by east west shortening along the margin of the plateau and must involve wholesale eastward motion of low lying regions to the east

present day kinematics at the india asia collision zone the collision of the indian subcontinent with asia drives the growth and evolution of the greater tibetan plateau region fault slip rates resulting from the relative motion between crustal blocks can provide a kinematic description of the distribution of presentday deformation i construct a three dimensional regional scale elastic block model of the india asia collision zone that is consistent with geodetic observations of interseismic deforma tion mapped fault system geometry historical seismicity and the mechanics of the earthquake cycle this mechanical model of the elastic upper crust yields a set of kinematically consistent fault slip rates and block motions that may serve to constrain dynamic models of continental crustal dynamics

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

focal mechanisms and aftershock locations of the songpan earthquakes of august 1976 in sichuan china the precursory swarm three mainshocks m 7 2 6 7 7 2 and aftershocks of the songpan earthquakes have been reanalyzed using both local and teleseismic data the three mainshocks of this sequence occurred on the huya fault over a 7 day period relocations of the aftershocks using local arrival times show that three fault strands were activated during this sequence each mainshock occurred on a separate strand each one south of the strand activated in the previous mainshock and the aftershock zones of each mainshock appear to abut rather than overlap fault plane solutions determined by matching teleseismic p waveforms at world wide standard seismograph network stations with synthetic seismograms are consistent with the observed aftershock zones the first and third mainshocks m 0 1 3 10 19 and 8 4 10 18 n m respectively showed almost identical senses of motion a combination of reverse and left lateral strike slip motion on parallel strands striking n15 w that were separated by a large rightstepping en echelon offset the second mainshock m 0 4 0 10 18 n m occurred in this offset on a fault at a steep angle 125 to the other two strands and showed almost pure reverse motion differences in the orientations of the slip vectors of the three mainshocks show that the first mainshock increased the normal and shear stresses on the fault segment that moved in the second mainshock and that the second mainshock decreased the normal stress on the fault segment activated by the third mainshock these changes in normal stresses may have given rise to the longer time between the first and second events 5 days as compared with the time between the second and third events 30 hours a precursory swarm that preceded the songpan sequence by 3 years occurred in a volume that surrounded the northernmost part of the planar aftershock zone the time between the start of the swarm and the mainshocks and the magnitude of the largest event in the swarm are similar to those seen for precursory swarms in soviet central asia

structural geology of a classic thrust belt earthquake the 1999 chi chi earthquake taiwan mw 7 6 abstract we document the structural context of the 1999 chi chi earthquake m w 7 6 in western taiwan which is one of the best instrumented thrust belt earthquakes the main surface break and large slip 3 10 m is on two segments of the shallow otherwise aseismic bedding parallel chelungpu sanyi thrust system which shows nearly classic ramp flat geometry with shallow detachments 1 6 km in the pliocene chinshui shale and mio pliocene kueichulin tungkeng formations however rupture is complex involving at least six faults including a previously unknown deeper thrust 8 10 km on which the rupture began we compare the coseismic displacements with a new 3d map of the chelungpu sanyi system the displacements are spatially and temporally heterogeneous and well correlated with discrete geometric segments of the 3d shape of the fault system geodetic displacement vectors are statistically parallel to the nearest adjacent fault segment and are parallel to large scale oblique fault corrugations the displacement magnitudes are heterogeneous at several scales which requires in the long term other non chi chi events or significant aseismic deformation the chelungpu thrust has a total displacement of 14 km but the area of largest chi chi slip 10 m is on a newly propagated north chelungpu chinshui detachment 0 3 km total slip which shows abnormally smooth rupture dynamics

structural model of the central longmen shan thrusts using seismic reflection profiles implications for the sediments and deformations since the mesozoic abstract the structural setting and deformation history are very important aspects of understanding the frequent earthquakes and assessing the hazards in this paper we interpret two new seismic profiles that were collected after the wenchuan mw7 9 earthquakes occurred on may 2008 our interpretation has integrated four wells three seismic profiles and the surface geology to reveal structural characteristics of the central longmen shan thrust the drilled wells reveal that there are two detachments within the upper triassic and the lower triassic at the longmen shan thrusts the shallow detachment fault transferred its slip to the basin and made another deformation inner the sichuan basin between the shallow detachments many faults developed and the major structures at the thrust front have formed as structural wedges both the drilled wells and seismic interpretation show the upper triassic repeated in the depth the shortening at the central longmen shan thrust is approximately 30 37 according to geological survey and the seismic interpretation the foreland basin was developed during the late triassic and the angular unconformity between the lower jurassic and the upper triassic at the longmen shan front several different tectonic events can be identified since the mesozoic which indicated that the longmen shan has a complex evolution history in our model the major beichuan fault f2 and the pengguan fault f3 at the central longmen shan dip steeply near the surface but are more gentle dipping at depth both of the shallow thrusting and the basement shortening made contribution to the rapid uplift of the longmen shan during the cenozoic the co seismic ruptured fault is like a branchy fault that developed on the major fault system the wenchuan mw7 9 earthquake and the lushan mw6 7 earthquake may be related to the reaction of the basement structures

upper crustal folding of the 2013 lushan earthquake area in southern longmen shan china insights from late quaternary fluvial terraces abstract a thrust earthquake of mw6 6 occurred on april 20 2013 near lushan county in the southern longmen shan at the east margin of tibetan plateau this earthquake did not produce a surface rupture zone and the late quaternary activities of the outcropped faults in the earthquake area were not obvious which increased the difficulty of studying the seismogenic structure this article took as the research target the middle reach of the qingyijiang river which traverses the earthquake area by surveying correlating the fluvial terraces studied quantitatively the late quaternary tectonic deformation and further discussed the seismotectonics the longitudinal profile of river terraces along the middle reach of the qingyijiang river reveals that the principal deformation style in the late quaternary was anticline type folding the folding is a typical fault bend fold involving the basement which is controlled by the newest flat ramp flat structure possibly formed in the pliocene or the early pleistocene across the fold the average shortening rate in the late quaternary is 0 6 1 3 mm yr about one third of the crustal shortening rate by gps data across the longmen shan fold and thrust belt and its foreland the foreland thin skinned structure developed in the cretaceous to paleogene strata in the earthquake area was passively involved into the fault bend folding in the late quaternary which commend the thrust ramp developing in a piggyback style the newest ramp appears to have controlled the rupture and the surface deformation of the 2013 lushan earthquake in the process of thrust sheet sliding toward foreland along the flat ramp flat detachment the ramp acts as a locking structure where earthquake ruptures the coseismic surface deformation seems to be passive folding of the thrust sheet climbing the ramp

an elusive blind thrust fault beneath metropolitan los angeles seismic reflection profiles petroleum wells and relocated earthquakes reveal the presence of an active blind thrust fault beneath metropolitan los angeles a segment of this fault likely caused the 1987 whittier narrows magnitude 6 0 earthquake mapped sizes of other fault segments suggest that the system is capable of much larger magnitude 6 5 to 7 and more destructive earthquakes

distribution of active rock uplift along the eastern margin of the tibetan plateau inferences from bedrock channel longitudinal profiles 1 current models of long term river incision into bedrock suggest that the local rate of differential rock uplift should exert a primary control on the gradient of channel longitudinal profiles however discrimination of this effect from the influence of variations in substrate erodibility sediment flux precipitation and transient changes in profile shape has proved difficult in practice here we investigate the controls on the spatial distribution of bedrock channel gradients adjacent to the sichuan basin in an effort to assess the degree and nature of active deformation along this margin of the tibetan plateau analysis of river longitudinal profiles utilizing a channel steepness index a measure of profile gradient normalized for drainage area reveals a zone of anomalously steep channels adjacent to the topographic front of the plateau margin channel profiles are systematically less steep in their headwater reaches on the plateau and in their lower reaches east of the plateau margin comparison of steepness indices to mapped lithologic variations reveals that lithology has only a limited influence on channel gradient in this field area we observe no systematic relationship between steepness indices and upstream drainage area channels of all size are steeper near the plateau margin we argue that these systematic changes are not readily explained as a consequence of increased sediment flux or of orographic precipitation we are led to conclude that steep channel profiles along the topographic front of the plateau reflect active differential rock uplift between this region and the foreland

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

differential exhumation in response to episodic thrusting along the eastern margin of the tibetan plateau abstract thermochronological data from the songpan ganze fold belt and longmen mountains thrust nappe belt on the eastern margin of the tibetan plateau in central china reveal several phases of differential cooling across major listric thrust faults since early cretaceous times differential cooling indicated by distinct breaks in age data across discrete compressional structures was superimposed upon a regional cooling pattern following the late triassic indosinian orogeny 40ar 39ar data from muscovite from the central and southern longmen mountains thrust nappe belt suggest a phase of differential cooling across the wenchuan maouwen shear zone during the early cretaceous the zircon fission track data also indicate differential cooling across a zone of brittle re activation on the eastern margin of the wenchuan maouwen shear zone during the mid tertiary between 38 and 10 ma apatite fission track data from the central and southern longmen mountains thrust nappe belt reveal differential cooling across the yingxiu beichuan and erwangmiao faults during the miocene forward modelling of apatite fission track data from the northern longmen mountains thrust nappe belt suggests relatively slow regional cooling through the mesozoic and early tertiary followed by accelerated cooling during the miocene beginning at ca 20 ma to present day regional cooling is attributed to erosion during exhumation of the evolving longmen mountains thrust nappe belt lmtnb following the indosinian orogeny differential cooling across the wenchuan maouwen shear zone and the yingxiu beichuan and erwangmiao faults is attributed to exhumation of the hanging walls of active listric thrust faults thermochronological data from the longmen mountains thrust nappe belt reveal a greater amount of differential exhumation across thrust faults from north to south this observation is in accord with the prevalence of proterozoic and sinian basement in the hanging walls of thrust faults in the central and southern longmen mountains the two most recent phases of reactivation occurred following the initial collision of india with eurasia suggesting that lateral extrusion of crustal material in response to this collision was focused along discrete structures in the lmtnb

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

crustal structure of the northeastern tibetan plateau from the southern tarim basin to the sichuan basin china abstract we present a new crustal cross section of the northeastern tibetan plateau based on active source seismic data recorded along a 1600 km long profile crossing the southern tarim basin the western flank of the south qilian shan the northeastern margin of qaidam basin east kunlun shan songpan ganzi terrane and sichuan basin the crustal p and s wave velocity structure and poisson s ratio outline the seismic characteristics of the crust and provide constraints on the crustal composition the derived crustal cross section shows several significant features 1 the crustal thickness varies considerably along this profile from 48 km to 70 km 2 north of the kunlun fault variations in total crustal thickness are mainly caused by variations in lower crustal thickness whereas south of the kunlun fault they are caused by thickness variations throughout the crust 3 north of the kunlun fault we detect a mid crustal low velocity zone that is not apparent south of the fault 4 the kunlun fault seems to act as a compositional boundary for the lower crust with a poisson s ratio of 0 29 north of the fault kunlun qaidam terrane and 0 26 south of the fault songpan ganzi terrane measured poisson s ratio and p wave velocity values suggest that the lower crust throughout the tibetan plateau south qilian shan margins of the qaidam basin east kunlun shan songpan ganzi terrane is of intermediate composition thus the ne tibetan plateau along our profile is missing a mafic lower crustal layer

active thrusting of the longquan fault in the central sichuan basin china and the seismotectonic behavior in the longmen shan fold and thrust belt present day convergence within the longmen shan fold and thrust belt lsftb was released by the 2008 mw 7 9 wenchuan earthquake which ruptured multiple thrust ramps beneath the range front structures however it is still unclear whether fault slip propagated eastward into the foreland closer to densely populated areas around chengdu in this study we provide constraints on the 3 d subsurface structure fault activity and seismic hazards of the longquan fault located in the central sichuan basin 100 km east of the range front structures of the lsftb we develop a seismotectonic model and assess the activity of the longquan fault by a combination of methods including interpretation of seismic reflection profiles analysis of satellite images field mapping trench logging and radiocarbon dating our survey reveals that at least two surface rupturing events occurred on the longquan fault in the holocene our 3 d structural model and evidence for late holocene faulting events on the longquan fault reveals that upper crustal shortening in the sichuan basin is accommodated by a frontal thrust system that is linked to the recently active range front blind structures by a shallow detachment we suggest that dynamic weakening following fault activity at the longmen shan range front might unlock the up dip portion of this shallow detachment sending slip eastward into the foreland and to the surface along the longquan thrust ramps our results have important implications for seismic hazards assessment of active frontal thrusts linked by upper crustal detachments in active fold and thrust belts around the world

exploring for hydrocarbons under thrust belts a challenging new frontier in the carpathians and elsewhere new significant reserves of hydrocarbons may occur in subthrust autochthonous and parautochthonous series buried below the frontal zones of thin skinned thrust belts the subthrust plays have been tested in several orogenic belts of the world the carpathians being one of the best examples the arcuate thin skinned carpathian orogenic belt which evolved during the mesozoic and cenozoic is thrust tens of kilometers over its neogene foredeeps and the underlying european plate various structural and stratigraphic settings and potential hydrocarbon plays have been recognized within the buried margins of the european plate including a late paleozoic hercynian compressional system mesozoic rifted margins of the tethys and a cenozoic synorogenic foreland type fault system possibly deeper parautochthonous structures documented on examples from the southern apennines may also be present below the thin skinned frontal zone of the carpathian thrust belt in addition to these structural settings large paleogene valleys submarine canyons have been found within the margins f the european plate these structural and morphologic features if combined with source rocks reservoirs and proper burial history represent potential hydrocarbon plays generation of hydrocarbons from sources within the subthrust plate was greatly enhanced by emplacement of the wedge shaped thrust belt which may also provide a regional seal therefore the combination of the long and complex geological history of the european plate with the impact of the alpine thrusting and foreland deformation created unique conditions for generation entrapment and preservation of hydrocarbons in subthrust settings

imaging the crustal structure beneath the eastern tibetan plateau and implications for the uplift of the longmen shan range abstract competing models have been proposed to account for the unusual uplift of the longmen shan fault zone in the eastern tibetan plateau and resulting hazards however due to the terrain and thick sedimentary cover the crustal structure of the eastern tibetan plateau remains uncertain therefore testing these models has been difficult in 2011 a 310 km long se trending sinoprobe 02 deep seismic reflection profile was recorded in easternmost tibet in order to study its regional crustal structure the resulting image revealed the detailed crustal structure of eastern tibet which when combined with geological gps global positioning system and geochemical evidence strongly suggests that yangtze sub continent crust extends beneath the region the seismic profile also images the tremendously thick triassic sedimentary cover in the songpan ganzi terrane sgt these triassic sediments vary considerably in thickness across several crustal blocks in addition both the longriba fault zone of the northeastern sgt and the longmen shan fault zone show strong intracrustal reflections that terminate at a depth coinciding largely with the crust mantle boundary moho accordingly we propose a new tectonic model based on an integrated analysis of this seismic reflection profile and previous gps measurements in this model crustal scale deformation is suggested to have participated in the oblique extrusion and uplift of the easternmost edge of the tibetan plateau along the longmen shan in a broader context the lithospheric configuration imaged by the seismic reflection profile will advance our understanding of the tectonic response of the eastern tibetan plateau to the ongoing india eurasia collision and has new implications for the estimating seismic risk in the region

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

active detachment of taiwan illuminated by small earthquakes and its control of first order topography we use 110 000 small earthquakes to locate and map active faults in three dimensions within the taiwan arc continent collision the structure is dominated by a nearly horizontal band of small earthquakes at 10 km depth that is interpreted to seismically illuminate the main detachment zone of the mountain belt with other illuminated fault zones abutting the detachment zone the zone steepens below eastern taiwan to 30 90 and reaches depths of 30 60 km the three dimensional shape of the detachment zone in relation to topography allows a new test of critical taper wedge mechanics and suggests that the reversal of topographic slope across taiwan is controlled by the shape of the detachment

co seismic thrusting rupture and slip distribution produced by the 2008 mw 7 9 wenchuan earthquake china field investigations reveal that the mw 7 9 wenchuan china earthquake of 12 may 2008 produced a 285 km long surface rupture zone with dominantly thrusting slip accompanied by a right lateral component along the central northern segments of the zone and left lateral component along the southern segment along the longmen shan thrust belt eastern margin of the tibetan plateau the co seismic ruptures mainly occurred along the pre existing yingxiu beichuan guanxian anxian and qingchuan faults which are the main faults of the longmen shan thrust belt the displacements measured in the field are approximately 0 5 6 5 m in the vertical typically 1 3 m accompanied by an average left lateral component of 2 m along the 50 km long southernmost segment of the rupture zone and an average right lateral component of 1 m along the 150 km long central northern segments the maximum thrust slip amount is estimated to be 10 m accompanied by 9 m of shortening across the rupture zone this finding is consistent with estimates based on seismic data the rupture length and maximum vertical displacement are the largest among all intracontinental thrust type earthquakes reported to date our findings demonstrate that i the wenchuan earthquake occurred upon pre existing active faults of the longmen shan thrust belt thereby controlling the spatial distribution of co seismic surface rupture and displacement and the rupture processes of the earthquake ii the long rupture length and large thrusting slip resulted from compressive stress associated with eastward extrusion of the tibet plateau as it accommodates the ongoing penetration of the indian plate into the eurasian plate and iii present day shortening strain upon the eastern margin of the tibetan plateau is mostly released by seismic slip along thrust faults within the longmen shan thrust belt

coseismic reverse and oblique slip surface faulting generated by the 2008 mw 7 9 wenchuan earthquake china the mw 7 9 wenchuan china earthquake ruptured two large thrust faults along the long menshan thrust belt at the eastern margin of the tibetan plateau this earthquake generated a 240 km long surface rupture zone along the beichuan fault and an additional 72 km long surface rupture zone along the pengguan fault maximum vertical and horizontal offsets of 6 5 m and 4 9 m respectively were measured along the beichuan fault a maximum vertical offset of 3 5 m was measured along the pengguan fault coseismic surface ruptures integrated with aftershocks and industry seismic profiles show that two imbricate structures have ruptured simultaneously resulting in the largest continental thrust event ever documented large oblique thrusting observed during this earthquake indicates that crustal shortening is an important process responsible for the high topography in the region as everywhere along the edge of tibetan plateau

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

longmen shan fold thrust belt and its relation to the western sichuan basin in central china new insights from hydrocarbon exploration the longmen shan fold thrust belt is one of the key regions of demonstrable mesozoic cenozoic tectonic evolution in china and the sichuan basin was the first natural gas producing area in china in this article the structural features of the longmen shan belt are presented using both seismic profiles and field data the complex structures of the northeast trending longmen shan fold thrust belt and its foreland in the western sichuan basin are formed by southeast directed thrusting several eastward verging rootless thrust sheets and imbricates of cambrian triassic rocks have been recognized in the northern longmen shan belt evidence suggests that the northern longmen shan belt experienced at least two major periods of deformation in the late triassic and cenozoic however the southern longmen shan belt is represented by the basement involved thrust structures and klippen and its major periods of deformation were in the latest cretaceous early cenozoic sedimentary features in the western sichuan basin reflect a two phase flexural loading history and illustrate that the late triassic foreland basin extends along the foredeep of the entire length of the longmen shan belt but the uppermost cretaceous paleogene rejuvenated foreland basin is restricted in the southern part of the western sichuan basin structural geometries suggest that prospective traps are mainly developed in the frontal zone of the longmen shan fold thrust belt and in the southern part of the western sichuan basin one of the major contributions of this article is finding preexisting paleozoic rift basins under the cenozoic thin skinned thrust belts which represent a new potential hydrocarbon play

high angle fault responsible for the surface ruptures along the northern segment of the wenchuan earthquake fault zone evidence from the latest seismic reflection profiles abstract the inverse right lateral yingxiu beichuan fault ruptured during the wenchuan earthquake for 270 km we investigated the northeastern segment of that fault by analysing 3 newly acquired and 3 older seismic lines that cross the fault we combine this analysis with that of the surface ruptures and of the regional geology in order to discuss the geometry the style and the amount of motion of the fault we conclude that the yingxiu beichuan fault is very steep 70 at the surface and has still a dip 45 at 6 km depth the fault offsets all previous structures and particularly the tangwangzhai nappes from which a vertical offset of 3 to 6 km is evaluated the right lateral component of motion along the yingxiu beichuan fault appears to be larger at the surface than at depth and increases only slightly towards the ne we suggest that the yingxiu beichuan fault is continuous at depth between its northern and southern segments

the co seismic slip distribution of the landers earthquake we derived a model for the co seismic slip distribution on the faults which ruptured during the landers earthquake sequence of 28 june 1992 the model is based on the inversion of surface geodetic measurements primarily vector displacements measured using the global positioning system gps the inversion procedure assumes that the slip distribution is to some extent smooth and purely right lateral strike slip for a given fault geometry a family of so lutions of varying smoothness can be generated we choose the optimal model from this family based on cross validation which measures the predictive power of the data and the trade off of misfit and roughness solutions which give roughly equal weight to misfit and smoothness are preferred and have certain features in common 1 there are two main patches of slip on the johnson valley fault and on the homestead valley emerson and camp rock faults 2 virtually all slip is in the upper 10 to 12 km and 3 the model reproduces the general features of the geologically measured sur face displacements without prior constraints on the surface slip in all models regardless of smoothing very little slip is required on the fault that represents the big bear event and the total moment of the landers event is 9 1019 n m the nearly simultaneous rupture of multiple distinct faults suggests that much of the crust in this region must have been close to failure prior to the earthquake

lack of continuity of the san andreas fault in southern california three dimensional fault models and earthquake scenarios 1 the 1200 km long san andreas fault loses its apparent continuity in southern california near san gorgonio pass allen 1957 which raises significant questions given the dominant role of this fault in active california tectonics what is the fundamental three dimensional 3 d geometry and kinematic behavior of the san andreas fault system in this complex region is a throughgoing if complex san andreas rupture from the mojave desert to the coachella valley possible we have explored the issue of 3 d continuity by mapping over 60 faults in this region to depths of 15 20 km from hypocenter locations and focal mechanisms we were able to constrain the 3 d geometry of the san andreas fault zone saf near san gorgonio pass from the 3 d geometry of the fault network surrounding it the most likely configuration is for the san andreas fault to merge into the shallow dipping san gorgonio pass thrust northwest of indio we concluded that there is no direct continuity at present but rather a network of faults and the only kind of rupture possible for the saf in this region is a complex rupture involving both strike slip and reverse faulting gps measurements also suggest that despite the fact that large motions must have occurred in the past based on offset geologic markers only minor motion is occurring today in this area applying our findings about the fault geometry we explored several simple earthquake scenarios to determine the most favorable conditions for a throughgoing rupture of the san andreas fault system from the mojave desert to the coachella valley

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

observation of coseismic seafloor crustal deformation due to m7 class offshore earthquakes 1 we have developed an observation system for seafloor crustal deformation measurement combining the two following techniques the precise acoustic ranging and kinematic gps global positioning system positioning on july 14 2003 we installed the units for this observation system at the seafloor of the kumano basin japan 33 58 n 136 60 e we performed repeated observation six times on 1 july 15 16 and 21 2004 2 november 9 10 2004 3 may 18 and 20 2005 4 july 19 20 2005 5 august 18 19 2005 and 6 august 29 30 2005 the present observation system can stably determine the seafloor position with an rms repeatability of 3 cm in both horizontal components two m7 class offshore intraplate earthquakes occurred only 60 km from the kumano basin site on september 5 2004 we observed the coseismic horizontal displacement of 18 cm at the kumano basin site using the presently developed seafloor observation system our observation system can provide seafloor crustal deformation associated with crustal activities in offshore areas

the combined inversion of seismic and geodetic data for the source process of the 16 october 1999 mw 7 1 hector mine california earthquake we investigate the source process of the m w 7 1 hector mine earthquake by inverting broadband regional and local seismic displacement waveforms com bined with global positioning system gps and synthetic aperture radar interfer ometry insar geodetic measurements we find that the three data sets individually produce remarkably similar slip distributions over a multisegment fault a simulta neous inversion of the three data sets is presented and the sensitivity of the combined inversion to the weighting of the three independent data sets is examined the results indicate that the overall length of the fault that slipped is 42 km with a peak slip of 5 50 m and total scalar seismic moment of 6 8 10 19 n m the majority of slip is located on the western branch of the lavic lake fault to the northwest of the hypo center although the overall rupture is bilateral with appreciable slip on the bullion fault to the southeast some slip is located on an eastern branch of the lavic lake fault an apparent bifurcation which is also evident from aftershock locations the average slip and stress drops are 2 70 1 62 1 60 m and 78 36 and 55 bars for the western lavic lake the eastern lavic lake and bullion faults respectively the results also indicate that the overall rupture process is relatively slow which is char acterized by a several second delay before the onset of significant slip a 1 8 km sec rupture velocity of the primary asperity and long spatially variable dislocation rise times

the role of crustal strength variations in shaping orogenic plateaus with application to tibet 1 the tibetan plateau is the type example of a large orogenic plateau formed as a result of continent continent collision the morphology of the plateau and its margins suggests that preexisting variations in crustal strength have influenced the growth of the plateau we have developed a three dimensional numerical model of deformation in a viscous crust in order to investigate the effects of lateral heterogeneities on plateau growth the model includes a two layer crust and allows for lateral variation of viscosity in both the upper and lower layers model results indicate that crustal strength variations have a dramatic effect on the morphology and dynamics of a developing plateau a region of strong crust is characterized by a very steep plateau margin that propagates extremely slowly does not accommodate significant shortening strain and is subparallel to local upper and lower crustal velocities a weak crustal region develops a gently sloping margin uplift propagates rapidly across the weak zone and crustal material within the plateau is diverted toward the low strength region with a relatively simple distribution of strength variations corresponding to strong tarim and sichuan basin crust and a weak southeastern corner our model produces a plateau with many similarities to the tibetan plateau including the overall morphology rotation around the eastern syntaxis and e w extension analysis of model results suggests that e w extension of the central plateau may be related to the rapid eastward flow of crustal material into a weak zone in the se corner without significant change in plateau elevation

surface ruptures on the transverse xiaoyudong fault a significant segment boundary breached during the 2008 wenchuan earthquake china abstract the 220 km long rupture of the 2008 mw 7 9 wenchuan earthquake breached several km scale geometric discontinuities along strike including the previously un mapped nw trending xiaoyudong fault connecting between the two major ne trending rupture planes on the beichuan and pengguan faults in this paper we present high resolution mapping of the 8 km long surface breaks and sinistral oblique thrusting coseismic slip on the xiaoyudong fault scarp height is the largest at the nw end reaching 3 5 m and decreases southward in steps to less than 0 2 m with an average slip gradient of 6 10 3 at a few tens of meters length scale but up to 50 10 3 locally left lateral offsets co vary with the vertical component the largest sinistral slip vector we observed is 2 2 m geological and geophysical evidence suggests that the xiaoyudong fault is likely a 30 sw dipping lateral ramp that soles into the pengguan fault and at its northwestern end intersects with the beichuan fault where the latter has a step in the fault plane kinematically the xiaoyudong fault functions as a tear and conjugate fault and coincides with significant coseismic slip rake rotations on both the beichuan and pengguan faults similar correlation of fault bends with sharp changes in faulting style occurs at other steps along the wenchuan rupture the xiaoyudong fault may have played a positive role in linking coseismic slip partitioning between parallel reverse fault planes facilitating the growth of a longer and more destructive rupture this highlights the role of tear faults in bridging ruptures between segments such that reverse type ruptures can breach steps wider than anticipated from strike slip fault examples transfer faults are common and perhaps poorly documented features in reverse fault systems and their roles in ruptures may increase the maximum potential earthquake magnitude for fold and thrust belts

structural interpretation of the coseismic faults of the wenchuan earthquake three dimensional modeling of the longmen shan fold and thrust belt 1 the 2008 mw 7 9 wenchuan earthquake is a result of ongoing india tibet collision and reflects the growth of the longmen shan fold and thrust belt in this paper we construct a 3 d structural model of the geometry of the coseismic faults and related structures of the wenchuan earthquake by integrating geological investigations relocated aftershocks and seismic reflection profiles in the 3 d structural model the differences between the southern and northern segments of the rupture are highlighted the structural transition zone between the two segments contains a major geometric segment boundary reflecting differences in the structural configuration of the thrust ramp and the tectonic evolution of the fault system which appears to have localized significant damage from anxian to beichuan within the northern segment we identify a transverse structure across which the beichuan fault plunges under the tangwangzhai syncline this boundary corresponds to a marked change in the nature of the surface rupture and is illuminated by a microearthquake sequence perpendicular to the longmen shan thrust belt in the southern segment our investigations confirm that uplift due to active faulting and folding is largely responsible for the areas of steepest topography on the basis of this association the southwestern segment of the longmen shan south of the wenchuan earthquake is likely active and presents a significant earthquake hazard despite the lack of historical earthquakes in this region this study illustrates the importance of building 3 d models to study active faulting and folding as well as to assess earthquake hazard

mechanics of low relief detachment folding in the bajiaochang field sichuan basin china using three dimensional 3 d seismic reflection data we apply new methods of two dimensional 2 d and 3 d structural restoration based on mechanical constraints to gain insights into the development of the bajiaochang anticline sichuan basin china this structure forms the trap for the bajiaochang field which is reported to contain substantial gas reserves within thick upper triassic delta front and lakeshore facies siliciclastics the basal detachment lies in a middle triassic evaporite unit above which layers are folded and faulted to various intensities based on their mechanical strengths the new restoration methods enable us to test a variety of fault displacement directions and to resolve that the bajiaochang structure grew primarily by dip slip and contractional folding moreover we quantify the styles and amounts of shortening within various tectonic levels of the structure large amounts of shortening and ductile thickening at the basal detachment level are consistent with general detachment fold models however we demonstrate that slip on the basal detachment is much larger than would be predicted by these models implying that substantial slip on the basal detachment extends beyond the structure into the foreland moreover structural thickening in the core of the fold is localized by a series of small ramps in the basal detachment that produce structural imbrication this implies that the bajiaochang detachment fold grew by a mechanism akin to duplexes which has important implications for the manner in which shortening and strain are partitioned within different mechanical layers of the fold

time dependent distributed afterslip on and deep below the izmit earthquake rupture surface deformation transients measured with the global positioning system during the 87 days between the 17 august 1999 izmit earthquake and the 12 november 1999 duzce earthquake indicate rapidly decaying aseismic fault slip on and well below the coseismic rupture elastic model inversions for time dependent distributed fault slip using a network inversion filter approach show that afterslip was highest between and below the regions of maximum coseismic slip and propa gated downward to or even below the base of the crust maximum afterslip rates decayed from greater than 2 m yr immediately after the i zmit earthquake to about 1 2 m yr just prior to the duzce earthquake maximum afterslip occurred below the eastern karadere rupture segment and near the i zmit hypocenter afterslip in the upper 16 km decayed more rapidly than that below the seismogenic zone these observations are consistent with a phase of rapid aseismic fault slip concentrated near the base of the seismogenic zone continued loading from the rapid deep afterslip along the eastern rupture zone is a plausible mechanism that helped trigger the nearby mw 7 2 12 november duzce earthquake

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

community fault model cfm for southern california we present a new three dimensional model of the major fault systems in southern california the model describes the san andreas fault and associated strike slip fault systems in the eastern california shear zone and peninsular ranges as well as active blind thrust and reverse faults in the los angeles basin and transverse ranges the model consists of triangulated surface representations t surfs of more than 140 active faults that are defined based on surfaces traces seismicity seismic reflection profiles wells and geologic cross sections and models the majority of earthquakes and more than 95 of the regional seismic moment release occur along faults represented in the model this suggests that the model describes a comprehen sive set of major earthquake sources in the region the model serves the southern california earthquake center scec as a unified resource for physics based fault systems modeling strong ground motion prediction and probabilistic seismic hazards assessment

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

quaternary activity of the range front thrust system in the longmen shan piedmont china revealed by seismic imaging and growth strata reliable estimates of quaternary or cenozoic upper crustal shortening in the longmen shan fold and thrust belt are rare in this paper we report on our use of high resolution 2 d and 3 d seismic reflection profiles at various scales together with borehole data to investigate the structural geometry of the longmen shan piedmont the results reveal a thrust system beneath the longmen shan termed the range front thrust system which consists of the range front blind thrust and its upward splay faults moreover on these faults we identified growth strata that provide an excellent opportunity for assessing the activity of this thrust system analyses of the growth strata reveal early to late pleistocene activity on the range front blind thrust with minimum dip slip and horizontal shortening rates of 1 1 0 2 mm yr and 1 mm yr accordingly the maximum accumulated slip on the range front blind thrust is calculated to be 7 5 0 3 km in the longmen shan using the new horizontal shortening rate and other published data we also estimated that the long term shortening rate across the longmen shan fold and thrust belt is 1 3 mm yr which is comparable to the short term gps rate the similarity of these rates suggests that the longmen shan attained a steady state condition over the past 2 myr an additional highlight of our results is that we show quaternary activity around the tibetan plateau to have been nearly synchronous in different regions including in the longmen shan the himalayas the western kunlun shan and the northern qilian shan

numerical modeling of eastern tibetan type margin influences of surface processes lithospheric structure and crustal rheology the eastern tibetan margin is characterized by a steep topographic gradient and remarkably lateral variations in crustal lithospheric structure and thermal state gps measurements show that the surface convergence rate in this area is strikingly low how can such a mountain range grow without significant upper crustal shortening in order to investigate the formation mechanism of the eastern tibetan type margins we conducted 2d numerical simulations based on finite difference and marker in cell techniques the numerical models were constrained with geological and geophysical observations in the eastern tibetan margin several major parameters responsible for topography building such as the convergence rate the erosion sediment rate and the presence of partially molten crust were systematically examined the results indicate that the presence of partially molten material in the middle lower crust can make a positive contribution to the formation of steep topography but it is not a necessary factor a steep topographic gradient may be a characteristic feature when a thin lithosphere with thick crust converges with a thick lithosphere with thin crust in the context of a high erosion rate the longmen shan range still gains and maintains its steep high topography to the present this could be explained by exerting a large push force on tibet side our numerical experiments suggest that topographic characteristic across the eastern tibetan type margins is mainly derived from isostatic equilibration forces and intensive convergence between two continental lithospheres with totally different rheological properties

structural geometry of the source region for the 2013 mw 6 6 lushan earthquake implication for earthquake hazard assessment along the longmen shan abstract the 2013 mw 6 6 lushan earthquake occurred in the longmen shan fold and thrust belt sichuan province china near the five year anniversary of the devastating 2008 mw 7 8 wenchuan earthquake to define the fault that generated the 2013 earthquake and its relationship with the beichuan fault which ruptured in the wenchuan earthquake we construct several cross sections and a 3d structural model the sections and models reveal that the main shock of the lushan earthquake occurred on a portion of the range front blind thrust rfbt and that the structural geometry of this fault varies along strike the lushan main shock occurred at a location along the strike of the fault where the geologic shortening and total fault slip are greatest a lateral ramp of the rfbt appears to coincide with the northern limit of aftershocks from the lushan earthquake leading to a 75 km seismic gap between the wenchuan earthquake and the 2013 earthquake sequence although both the wenchuan and lushan earthquakes occurred within the longmen shan fold and thrust belt different faults generated the two events based on this structural characterization and analysis of the aftershocks of the wenchuan and lushan earthquakes we suggest that the lushan earthquake may have been triggered by the 2008 rupture but is best considered as an independent event rather than an aftershock of the wenchuan earthquake the rfbt that generated the lushan earthquake is linked to a detachment that extends into the sichuan basin along the triassic evaporite layer the coulomb stress change simulation suggests that other faults linked to this detachment may have been loaded by the 2008 and 2013 earthquake posing the risk of future earthquakes along the longmen shan and in the densely populated sichuan basin

tectonics of the qinling belt build up and evolution of eastern asia the structure and history of the qinling range which separates the north and south china cratons are a key to the tectonic evolution of eastern asia the mountain range is composed of a northern palaeozoic belt and a southern mesozoic belt the palaeozoic orogeny probably involved the closure of an oceanic basin along a north dipping subduction zone followed by south vergent obduction of ophiolites and intracontinental thrusting during the devonian the mesozoic belt appears to be the product of purely intracontinental shallow crustal deformation over a large decollement with at least 100 km of horizontal transport since the devonian both belts have been sliced by huge east west sinistral strike slip faults

an unpredictably violent fault chinese researchers placed a dense array of seismometers around a dangerous looking seam in the rocks of sichuan only to be blindsided by the true killer

emplacement of the longmen shan thrust nappe belt along the eastern margin of the tibetan plateau abstract the topographic descent from the eastern margin of the tibetan plateau to the sichuan basin passes through the longmen shan thrust nappe belt which is sub divided by six nw dipping major listric thrusts with accompanying duplexes and imbricate fans into five large scale nappes each nappe has its own stratigraphic and deformational features in the inner longmen shan longmen mountains allochthonous nappe units have incorporated both mesoproterozoic basement and sinian neoproterozoic to triassic cover sequences as thick skinned horses whereas in the frontal longmen shan sinian cretaceous cover sediments have been stripped from the basement as thin skinned fold and thrust sheets including the extensively distributed klippen structures pre thrusting extension during devonian to middle late triassic times resulted in syn depositional normal faults structural inversion of these faults initiated the peng xian guan xian basement complex jiuding shan and tangwangzhai nappes during the early episode of the indosinian orogeny norian to rhaetian this was followed by episodic thrusting during latest triassic to early cretaceous times to develop the guan xian an xian and southeastern marginal nappes that have incorporated sediments from the neighbouring foreland basin into the frontal part of the thrust nappe belt during a late miocene reactivation of the pre existing thrusts differential thrusting occurred across the thrust nappe belt

petroleum exploration and production in fold and thrust belts ideas from a hedberg research symposium this paper reviews ideas presented at the february 1997 hedberg research symposium on petroleum exploration and production in fold and thrust belts held in veracruz mexico exploration in fold thrust belts has been expanding rapidly due to recent discoveries improved demand for gas and improved access to promising areas at the same time the methods for exploring in fold thrust belts and in developing fields have evolved significantly this was the first aapg conference to focus on exploration and production within this structural domain this conference brought together geologists and geophysicists from around the world who are actively working in fold thrust belts to share their experiences and to address a broad range of exploration and production concerns symposium topics included hydrocarbon generation migration entrapment and preservation exploration methods and strategies field development and data acquisition numerous case studies were presented illustrating these topics although exploration and production in fold thrust belts must address many of the same issues as in other structural plays there are additional challenges fold and thrust belts for example are characterized by complex trap geometry a complex burial and thermal history a narrow time line between the onset of petroleum generation migration and trap development and a complex history of fill and spill other challenges can include difficult terrain poor seismic quality high cost of field operations environmental constraints and drilling problems related to active tectonic stress regimes success in this setting requires efficient application of all available tools to mitigate risk and costs but given the complex geology and relatively poor imageability explorationists must be willing to persist in the face of initial failures the conference offered many illustrations of successful exploration and development programs to encourage geologists and geophysicists working in this setting

assessing soil redistribution in a complex karst catchment using fallout 137cs and gis abstract caesium 137 derived from nuclear testing in the past century has been widely used as a sediment tracer of soil redistribution providing information on medium term 40 50 years erosion rates to date most studies have focused on individual fields of limited extent but estimated rates and patterns of soil redistribution require upscaling to catchment level an attempt to assess soil redistribution processes with strong geomorphic control on complex terrain such as an internally drained karst catchment is presented in this work a comprehensive geomorphological survey of the estanya lake catchment spanish pyrenees enabled the main geomorphic elements to be identified with a grid resolution of 5 5 m which was the basis for the terrain analyses a detailed dem was constructed and improved after field identification of the drainage system and point measures on gentle slopes with total topographic station a 100 100 m sampling grid was established to derive point data of 137 cs inventories across the catchment geostatistical interpolation of point samples of 137 cs inventories in soil was carried out to identify and assess the areas of sediment gain and loss by comparing with 137 cs reference inventories profile activity models were used to calibrate 137 cs data and to derive estimates of soil redistribution gis was used to provide spatially distributed erosion and deposition rates in the landscape for the whole catchment the median values of soil erosion and deposition of 4 7 and 3 1 mg ha 1 year 1 respectively showed a large variability and reveal coupling between erosional and depositional forms in the catchment the highest erosion and deposition rates were found in cultivated fields at the southern sector of the catchment the spatial analysis of the results supports the importance of taking into account geomorphological features in karst catchments as relevant controlling factors in soil redistribution processes

determination of constitutive relations of fault slip based on seismic wave analysis constitutive laws define the boundary conditions on fault plane and govern many aspects of earthquake failure although several constitutive laws have been formulated based on laboratory rock experiments and applied to theoretical studies in various fields no actual relation during a natural earthquake has been determined the 1995 kobe earthquake is suitable for detailed kinematic analysis and this enables the first evaluation of constitutive relations for a natural earthquake in this study we determine spatiotemporal slip distribution on an assumed fault plane of the 1995 kobe earthquake by waveform inversion and then solve elastodynamic equations using a finite difference method to determine the stress distribution and constitutive relations on the fault plane an inversion method based on bayes theorem is employed to obtain a spatiotemporal slip distribution and enables us to ensure the objective uniqueness of the solution with numerous parameters and smoothing constraints this slip distribution is then used as part of the boundary condition in the finite difference calculation the time histories of slip and shear stress obtained then provide a constitutive relation at each point on the fault plane they show slip weakening relations almost everywhere on the fault plane while slip rate dependency is not clear the slip weakening behavior has a clear depth dependency indicating that the slip weakening rate d du is smaller in the shallow crust than that in the deep crust this may be associated with the paucity of shallow seismicity observed in the source region of this earthquake as reported for many mature fault systems

structural control of rupturing of the mw7 9 2008 wenchuan earthquake china abstract analyses of global seismic waveform data for the 2008 devastating wenchuan earthquake have indicated where the rupture started and how it expanded here we reveal that the rupture process of this earthquake was strongly controlled by structural heterogeneities of the upper crust we made a tomographic inversion of 200 000 local travel time data according to which the rupture was confined in a presumably brittle layer of high p and s wave velocity anomalies within the upper 15 km depths the rupture propagated northeastward through the southwest sw segment of the fault and then jumped to the northeast ne segment with little slip at the intervening presumably ductile zone characterized by low p and s velocities with high poisson s ratio the rupture initiated near the southwestern end of the sw segment within a body of high poisson s ratio which extends down into the lower crust suggesting upward migration of deep seated aqueous fluid to trigger the earthquake by reducing the mechanical strength of the brittle layer

field evidence of rupture of the qingchuan fault during the 2008 mw7 9 wenchuan earthquake northeastern segment of the longmen shan thrust belt china abstract although many studies of the 2008 mw 7 9 wenchuan earthquake have described the ground deformation features rupture mechanism and structural features of the seismogenic fault zone associated with this event debate remains concerning the total length of the co seismic surface rupture zone and whether the earthquake ruptured the qingchuan fault in the northeastern segment of the longmen shan thrust belt lstb china in this paper we present new field evidence that the qingchuan fault was ruptured by the 2008 wenchuan earthquake and that the total length of the co seismic surface rupture zone is up to 285 300 km field investigations reveal that the earthquake produced a 60 km long surface rupture zone along the pre existing qingchuan fault with the offset being mainly right lateral strike slip and a distinct component of vertical slip co seismic surface ruptures are characterized by faults and extensional cracks field measurements indicate co seismic right lateral strike slip displacements along the qingchuan fault of 0 3 0 6 m and vertical offsets of 0 2 0 5 m which differs to the displacements observed along the central and southwestern segments of the wenchuan surface rupture zone in the displacement amount and sense the change in slip sense from thrust dominated slip in the central and southwestern segments of the lstb to right lateral strike slip dominated displacement along the qingchuan fault northeastern segment of the lstb reflects a change in the orientation of compressive stress along the lstb associated with eastward extrusion of the tibetan plateau as it accommodates the ongoing penetration of the indian plate into the eurasian plate

mesozoic crustal thickening of the longmenshan belt ne tibet china by imbrication of basement slices insights from structural analysis petrofabric and magnetic fabric studies and gravity modeling this work first presents field structural analysis anisotropy of magnetic susceptibility ams measurements and kinematic and microstructural studies on the neoproterozoic pengguan complex located in the middle segment of the longmenshan thrust belt lmtb ne tibet these investigations indicate that the pengguan complex is a heterogeneous unit with a ductilely deformed nw domain and an undeformed se domain rather than a single homogeneous body as previously thought the nw part of the pengguan complex is constrained by top to the nw shearing along its nw boundary and top to these shearing along its se boundary where it imbricates and overrides the se domain two orogen perpendicular gravity models not only support the imbricated shape of the pengguan complex but also reveal an imbrication of high density material hidden below the paleozoic rocks on the west of the lmtb regionally this suggests a basement slice imbricated structure that developed along the margin of the yangtze block as shown by the regional gravity anomaly map together with the published nearby seismic profile and the distribution of orogen parallel neoproterozoic complexes integrating the previously published ages of the nw normal faulting and of the se directed thrusting the locally fast exhumation rate and the lithological characteristics of the sediments in the lmtb front we interpret the basement slice imbricated structure as the result of southeastward thrusting of the basement slices during the late jurassic early cretaceous this architecture makes a significant contribution to the crustal thickening of the lmtb during the mesozoic and therefore the cenozoic thickening of the longmenshan belt might be less important than often suggested

active faulting and growth folding in the eastern santa barbara channel california we develop new methods to identify blind thrust fault systems determine fault slip rates and estimate potential earthquake magnitudes and recurrence intervals in active fold and thrust belts these methods are applied to compressive folds along the offshore oak ridge and blue bottle trends which overlie active blind thrust faults in the eastern santa barbara channel these folds and their causative faults are interpreted using fault bend fold theory and are represented in balanced models and cross sections that integrate surface and subsurface data the structures are mapped using a new technique of axial surface mapping in seismic reflection grids which defines three dimensional structural geometries and shows changes in slip and subsurface fault geometry along strike analysis of syntectonic growth sediments yields pliocene and quaternary fault slip rates of 1 3 mm yr on a deep thrust 16 km and 1 3 mm yr on shallower faults 2 5 km the combined 2 6 mm yr slip rate represents only part of the 6 mm yr of shortening measured by geodesy across the channel and estimated from relative pacific north american plate motions across the transverse ranges additional shortening is probably accommodated on other active thrusts in the western transverse ranges and in the northern channel along the santa barbara coast deformed seafloor sediments and a swarm of axial surface seismicity along the fold trends indicate that the underlying thrusts are active and may pose significant earthquake hazards to coastal southern california unsegmented fault surfaces are used through empirical relationships between fault surface area and rupture magnitude to estimate the sizes of potential earthquakes this analysis suggests that a ramp in the channel islands fault beneath the offshore oak ridge trend is capable of rupturing in a m s 7 2 earthquake earthquakes of this magnitude may release 2 m of slip which when combined with the estimated slip rate 1 3 mm yr yields an earthquake recurrence interval of 1500 yr for this channel islands fault ramp

exhumation history and faulting activity of the southern segment of the longmen shan eastern tibet abstract the longmen shan lms which constitutes the eastern border of the tibetan plateau is about 400 km in length and characterized by a steep topographic transition from the sichuan basin to the plateau the 2008 mw7 9 wenchuan earthquake and 2013 mw6 6 lushan earthquake were associated with the central to northern segments and southern segment of the lms fault belt respectively in this paper zircon and apatite fission track zft and aft respectively dating in combination with previously published low temperature thermochronology studies are used to constrain both the exhumation history and fault activity along the lms with a special focus on the southern segment in the southern segment of the lms the zft ages in the hanging wall of the wulong yanjing fault 10 14 ma increasing to ca 30 ma to the northwest of the faults and to 100 200 ma in the plateau region the aft ages are 3 5 ma at the mountain front and increase to 8 26 ma in the plateau we show that these age distributions are controlled by fault geometry two stages of rapid exhumation were identified using apatite fission track length modeling and the age distributions in the southern segment of the lms the first stage is from ca 30 ma and the second stage is from 3 5 ma to present in contrast with the middle segment of the lms the cenozoic exhumation rate is higher in the southern segment of the lms which may be due to the influence of the collision between the india and eurasia plates and or different faulting mechanisms in the different segments

comparison of l1 and l2 norms in a teleseismic waveform inversion for the slip history of the loma prieta california earthquake abstract broadband digital teleseismic body waves p and sh are inverted to obtain the history of slip for the 17 october 1989 loma prieta earthquake comparison of finite fault waveform inversion results using an l 1 norm and an l 2 norm reveal some basic uncertainties in the rupture history that are not usually appreciated in earthquake source studies however the more robust features of the source can be identified that are less dependent on the choice of minimization norm from a consideration of first motion data and forward modeling of body waves the strike and dip of our model fault plane are set at 126 and 67 respectively the waveform inversion results indicate that the majority of the moment release occurs over a fault length of 35 to 40 km and a depth range of 2 to 18 km the hypocenter 18 km depth experienced a relatively small amount of slip the rupture propagated upward and bilaterally with a peak slip of about 3 m occurring at a depth of 10 km the average velocity of the rupture propagation is 2 5 km sec the details of the slip distribution depend on the minimization norm but two main sources can be identified with the larger source above and to the southeast of the hypocenter the rake vector varies considerably over the fault the southern source is mostly strike slip while the northern source is approximately equally partitioned between dip slip and strike slip there is also a trend for more strike slip motion at shallower depths the majority of the moment release occurs in the first 7 5 sec with an integrated moment of 2 6 10 26 dyne cm including smaller peripheral sources that are less well resolved raises the moment estimate to 3 0 10 26 dyne cm

a structural interpretation of the aftershock cloud of the 1992 mw 7 3 landers earthquake we analyze the spatial relationship of relocated aftershocks to the principal rupture planes of the m w 7 3 1992 landers mainshock from a structural point of view we find that the aftershocks constitute primarily a several kilometer wide damage zone centered on the mainshock rupture planes the intensity of damage decreases away from the principal faults less than half of the aftershocks occurred within 1 km of the mainshock planes and perhaps only 5 of the aftershocks are candidates for rerupture of the mainshock faults moreover it seems that aftershocks along the landers rupture have b values that correlate well with the complexity of the mainshock rupture low b values occur along segments that are simple whereas higher b values correlate with sections that are more complex thus structural complexity appears to correlate with a greater relative abundance of small earthquakes these observations imply that aftershock populations reflect fault populations in the medium surrounding the principal faults rather than the behavior of the mainshock planes themselves online material arcview information about the surface rupture of the landers mainshock