change from late tertiary compression to quaternary extension in southern tibet during the india asia collision field studies in southern tibet show that subsequent to folding resulting from the india asia collision 50 40 ma reverse faults and backthrusts formed as a result of nne ssw and nnw sse trending compressions they affect conglomerates of oligocene miocene age and are probably contemporaneous with shearing on the himalayan main central thrust and folding of paleogene basins along the northern border of southern tibet 25 16 ma rift systems postdate compressional structures they were active during the pleistocene and probably during the pliocene 5 2 ma change from a compressional to an extensional regime in tibet probably occurred during the late miocene 10 5 ma this change is tentatively correlated with uplift inferred by chinese workers from paleogene to present day variations of the tibetan vegetation recent and active faulting in the high plateau results from a wnw ese striking extension this is in agreement with tibetan focal mechanisms the himalayan lowlands are subjected to a nne ssw trending compression as demonstrated by superficial deformations and seismicity therefore the horizontal maximum compressive stress trajectory is roughly parallel to india asia convergence hmax being 1 in the lowlands and 2 in the high plateau this change results from the increase of the vertical principal stress value due to the weight of the elevated mass zz is 3 in the lowlands and 1 in the high plateau thus the third principal stress axis is 2 in the lowlands and 3 in the high plateau allowing extension to occur in the wnw ese direction extensional tectonics are significantly different in southern and northern tibet southern tibet being constrained between the himalayan syntaxes the e w extensional principal deviatoric stress value 3 is of rather small magnitude and the n s trending 2 value is extensional as demonstrated by analysis of recent faults normal components prevail along all the azimuths in the field this favors formation of rift systems of large axial extension on the contrary north of the himalayan syntaxes northern tibet flows easily eastward the e w extensional principal deviatoric stress value 3 is of higher magnitude and the n s stress 2 is compressional as shown by inversion of focal mechanism data this favors strike slip components on faults which deviate from the n s direction as expressed in the field by shorter n s trending graben linked with normal strike slip faults these faults permit some n s shortening in northern tibet without thickening in response to india asia collision in high plateaus which are subjected to lateral compression such as the andean altiplano and tibet the extensional direction is basically controlled by the convergence direction being roughly orthogonal to the latter

seismic structure of the longmenshan area in sw china inferred from receiver function analysis implications for future large earthquakes abstract following the 2008 mw 7 9 wenchuan and 2013 ms 7 0 lushan earthquakes the longmenshan thrust fault belt and the songpan ganzi terrane have been the focus of several investigations here we use the h k stacking technique and neighborhood algorithm to investigate the seismic structure of this area based on the presence of felsic lower crust and the mesozoic crustal architecture of the songpan ganzi and longmenshan area we exclude the model on the eastward flow of the middle and lower crust assigned as the cause for the crustal thickening in previous studies in contrast the e w trending cumulative compression induced by the continued northward motion of the indian plate and india asian collision are identified as the dominant factors leading to the crustal thickening in the longmenshan thrust fault region as well as the songpan ganzi terrane particularly the 2008 mw 7 9 wenchuan and 2013 ms 7 0 lushan earthquakes likely indicate the cumulative offsets and the e w continuing compression

the eastern tibetan plateau geothermal belt western china geology geophysics genesis and hydrothermal system abstract the eastern tibetan plateau geothermal belt etgb which is located in 98 102 e 28 32 n belongs to the eastern part of the mediterranean himalayan geothermal belt recently about 248 natural hot springs have been found in the etgb 60 of these springs have temperatures of 40 c and 11 springs have temperature above the local water boiling point using the helium isotopic data gravity magnetic and seismic data we analyzed the thermal structure and the relationship between hydrothermal activity and geothermal dynamics of the etgb results show that 1 the 248 springs can be divided into three geothermal fields kangding luhuo geothermal field kgf litang ganzi geothermal field lgf and batang xiangcheng geothermal field bgf the bgf and lgf have hot crust and warm mantle and are characterized by the higher heat flux 66 26 mw m2 and higher ratios of crust derived heat flux to total flux 47 46 60 62 the kgf has cool crust and hot mantle and is characterized by the higher heat flux and lower qc qm 2 there is a relatively 4 6 m higher gravimetric geoid anomaly dome which is corresponding with the etgb and in hydrothermal activity areas of the bgf and lgf there is a northwest southeast trending tensile stress area and the upper middle crust uplift area 3 an abnormal layer exists in the middle lower crust at a depth of 13 30 km beneath the etgb and this layer is 8 10 km thick and is characterized by lower velocity vp 2 5 high conductivity 10 m and high temperature 850 1000 c finally based on the heat source and geological and geophysical background we propose kangding type and batang type hydrothermal system models in the etgb

origin and tectonic significance of the huangling massif within the yangtze craton south china as the oldest exposed basement and the typical sedimentary cover of the yangtze craton the huangling massif is a suitable place to decipher the tectonics of south china block structural analysis shows that the huangling massif has an elliptic domal shape with n s striking long axis an asymmetric antiform with a steep western flank and a gentle eastern flank there three litho tectonic units are recognized from inner to outer parts 1 archean paleoproterozoic metamorphic rocks intruded by neoproterozoic granitoids 2 neoproterozoic to jurassic sedimentary envelope around the dome core 3 cretaceous terrigeneous alluvial fluvial deposits unconformably overlying the dome flanks coeval with the uplifting of the massif the pre cretaceous strata on the western and eastern flanks of the huangling massif were involved in a series of folds with nearly n s axes and layer parallel slip structures with top to the w and top to the e motion respectively the subsequent brittle normal faulting controlled the deposition of the graben or half graben basins on both flanks cooling history reveals that the huangling massif underwent uplifting between 160 ma and 110 ma with an average cooling rate of 2 3 c ma moreover the huangling area was not significantly affected by the early paleozoic and triassic orogenies of south china comparable with the contemporaneous extensional structures such as metamorphic core complexs syntectonic plutons bounded by ductile normal faults and rift related basins in eastern china it is proposed that the huangling massif might be an extensional structure controlled by a weak crustal extension in this case it will represent the western front of the late mesozoic lithospheric thinning in entire eastern china however the compressional model cannot be ruled out

surface deformation related to the 2008 wenchuan earthquake and mountain building of the longmen shan eastern tibetan plateau abstract the 12 may 2008 ms 8 0 wenchuan earthquake china was one of largest continental thrusting events worldwide based on interpretations of post earthquake high resolution remote sensing images and field surveys we investigated the geometry geomorphology and kinematics of co seismic surface ruptures as well as seismic and geologic hazards along the longmen shan fold and thrust belt our results indicate that the wenchuan earthquake occurred along the ne sw trending yingxiu beichuan and guanxian anxian faults in the longmen shan fold and thrust belt the main surface rupture zones along the yingxiu beichuan and guanxian anxian fault zones are approximately 235 and 72 km in length respectively these sub parallel ruptures may merge at depth the yingxiu donghekou surface rupture zone can be divided into four segments separated by discontinuities that appear as step overs or bends in map view surface deformation is characterized by oblique reverse faulting with a maximum vertical displacement of approximately 10 m in areas around beichuan county earthquake related disasters e g landslides are linearly distributed along the surface rupture zones and associated river valleys the wenchuan earthquake provides new insights into the nature of mountain building within the longmen shan eastern tibetan plateau the total crustal shortening accommodated by this great earthquake was as much as 8 5 m with a maximum vertical uplift of approximately 10 m the present results suggest that ongoing mountain building of the longmen shan is driven mainly by crustal shortening and uplift related to repeated large seismic events such as the 2008 wenchuan earthquake furthermore rapid erosion within the longmen shan fold and thrust belt occurs along deep valleys and rupture zones following the occurrence of large scale landslides triggered by earthquakes consequently we suggest that crustal shortening related to repeated great seismic events together with isostatic rebound induced by rapid erosion related unloading is a key component of the geodynamics that drive ongoing mountain building on the eastern tibetan plateau

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

active tectonics of the ganzi yushu fault in the southeastern tibetan plateau the ongoing convergence between india and eurasia apparently is accommodated not merely by crustal shortening in tibet instead also by motions along strike slip faults which are usually boundaries between tectonic blocks especially in the tibetan plateau quantification of this strike slip faulting is fundamental for understanding the collision between india and eurasia here we use a variety of geomorphic observations to place constraints on the late quaternary kinematics and slip rates of the ganzi yushu fault one of the significant strike slip faults in eastern tibet the ganzi yushu fault is an active dominantly left lateral strike slip structure that can be traced continuously for up to 500 km along the northern boundary of the clockwise rotating southeastern block of the tibetan plateau we analyse geomorphic evidence for deformation and calculate the late quaternary slip rates at four sites along the eastern portion of the fault trace the latest quaternary apparent throw rates are variable along strike but are typically 1 mm a rates of strike slip displacement are likely to be an order of magnitude higher 8 11 mm a trenching at two locations suggests that the active fault behaviour is dominated by strike slip faulting and reveals several earthquake events with refined information of timing the 2010 mw 6 9 yushu earthquake which occurred on the northwestern segment of the ganzi yushu fault zone provides additional evidence for fault activity these observations agree with gps derived estimates and show that late quaternary slip rates on the ganzi yushu fault are comparable to those on other major active strike slip faults in the eastern tibetan plateau

deep structure and seismogenesis of the north south seismic zone in southwest china 1 to understand the deep structure and seismogenesis in the north south seismic zone nssz in southwest china we collected a large number of p and s wave arrival time data from both local earthquakes and teleseismic events to invert simultaneously for the three dimensional p and s wave velocity vp vs structures in the crust and upper mantle the obtained vp and vs models are generally coherent with each other from the crust to the mantle transition zone the nssz is characterized by strong structural heterogeneities from the mountainous areas of southeastern tibet to the yangtze platform low vp and low vs anomalies are generally imaged in the upper crust under the sichuan basin showing good agreement with the surface geological features that the foreland basin contains primarily mesozoic and paleozoic sedimentary rocks with a thickness of several kilometers the deep part of the yangtze platform is characterized by a cratonic lithospheric body dipping southwestward down to 400 km depth beneath the southeastern margin of the tibetan plateau in sharp contrast to low velocity anomalies in the upper mantle beneath the songpan ganzi fold system and the northwest qiangtang block at depths of the lower crust and uppermost mantle a layer with low vp and low vs 1 2 is revealed under a region west of the yangtze platform which may reflect the ductile flow in the lower crust our results indicate that the seismotectonics in the nssz is affected significantly by the ductile flow in the lower crust and strong heterogeneities in the upper mantle under southwest china in addition to the dominant role of the india asia collision

architecture of basin mountain systems and their influences on gas distribution a case study from the sichuan basin south china abstract the basin mountain systems in the sichuan basin exert major control on today s oil gas distribution chiefly through their controlling influence on petroleum reservoirs preservation the thickness of deposited terrestrial formations and degree of uplift and denudation the composite basin mountain system in the sichuan basin and its peripheral mountains can be classified as two types margin plate systems and interior plate systems the margin plate basin mountain systems include the sichuan basin and its surrounding longmen mountains micang mountains and daba mountains which are not only the western and northern marginal area of the sichuan basin but also represent the western margin of the yangtze plate south china block the margin plate basin mountain systems with binary units of large scale thrust belts and foreland basins have different deep lithospheric structures abrupt boundaries and great contrast in today s geomorphology between the basin and the mountains on the contrary the interior plate basin mountain systems comprised by the sichuan basin and its adjacent interior plate qiyue mountains dalou mountains and daliang mountains represent the eastern and southern marginal area of the sichuan basin located within the yangtze plate they have similar lithospheric structure and gradual boundaries between the basin and the adjacent mountains lacking foreland basins today s medium large scale natural gas accumulations in the sichuan basin are mainly distributed in the areas influenced by the margin plate basin mountain systems and are located especially in the foreland basins

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

deformation partitioning and foliation reactivation during transpressional orogenesis an example from the central longmen shan china progressive localization of strain within the songpan garze fold belt at the eastern margin of the tibetan plateau has resulted in the formation of the wenchuan maowen shear zone and preservation of excellent overprinting relationships between three major phases of ductile and semi ductile deformation these relationships show that deformation in the eastern songpan garze fold belt evolved from crustal thickening during sw directed compression d1 to localized sinistral transcurrent shear d2 and finally to increasingly localized high temperature d3p and retrograde d3r reverse shear in response to se directed compression both d2 and d3 deformations were co planar and reactivation of the s2 foliation led to the formation of a composite s2 3 fabric however inclusion trails in garnet porphyroblasts preserve evidence of a transition between these strike slip and reverse shear end members indicating that d2 and d3 were part of an episode of progressive transpressional shear metamorphic grade increases from chlorite to kyanite zone within the wenchuan maowen shear zone reaching syn d3p peak conditions of 600 c and 10 kbar the d3p and d3r reverse shears were responsible for tectonic exhumation of the shear zone and resulted in the formation of retrograde d3r high strain zones along the margins of the xuelongbao granite and adjacent to the wenchuan maowen fault

active faulting and block movement associated with large earthquakes in the min shan and longmen mountains northeastern tibetan plateau the min shan and central and southern parts of the longmen mountains form the middle segment of the north trending earthquake zone at the eastern edge of the tibetan plateau the min shan mountains are a cenozoic to quaternary uplift zone that has undergone south directed block movements to produce the 1933 diexi earthquake m 7 5 on the min jiang fault and the 1976 songpan earthquake swarm m 7 2 6 7 7 2 on the huya fault the min jiang fault on the western boundary of the uplift zone is dominated by reverse movement with a right lateral component the huya fault on the eastern margin of the min shan uplift zone is also dominated by reverse movement but is associated with a left lateral component

total exhumation across the beichuan fault in the longmen shan eastern tibetan plateau china constraints from petrology and thermobarometry the deep structure and deformation mechanisms of the longmen shan thrust belt sichuan china at the eastern border of the tibetan plateau were largely debated after the devastating mw 7 9 wenchuan earthquake 2008 recent geophysical studies and field investigations have been focused on the active motion of the major beichuan fault which ruptured during the earthquake however the total exhumation across the fault still remains unclear in the hanging wall of the beichuan fault the south china block is exhumed in the pengguan massif close to the beichuan fault the rocks of the pengguan massif underwent greenschist facies metamorphism associated with brittle ductile deformation no metamorphism is observed in the footwall of the fault in this study we characterize and date the metamorphic history recorded in the hanging wall of the beichuan fault in order to constrain the depth and timing of exhumation of the rocks of the pengguan massif along the fault a high resolution petrological approach involving chemical analyses and x ray maps was used to analyze the micrometric metamorphic minerals the p t conditions of the greenschist facies metamorphic event were estimated by an inverse multi equilibrium thermodynamic approach the results 280 30 c and 7 1 kbar suggest that the rocks of the pengguan massif were exhumed from ca 20 km depth our results underline the importance of the thrusting component in the long term behavior of the beichuan fault and provide a minimal depth at which the fault is rooted in situ laser ablation 40ar 39ar dating of metamorphic white mica revealed that the greenschist overprint occurred at 135 140 ma the pengguan massif was therefore partially thrusted along the beichuan fault during the lower cretaceous long before the eocene miocene exhumation phase which is well constrained by low temperature thermochronology our results provide the first independent depth information for the exhumation history of the pengguan massif and reveal a previously undocumented lower cretaceous tectonic event that marks the onset of the thick skinned deformation in the external domain of the longmen shan east of the wenchuan fault

characteristics and remediation of a landslide complex triggered by the 2008 wenchuan china earthquake case from yingxiu near the earthquake epicenter during the 2008 wenchuan earthquake the river valley from yingxiu to wenchuan experienced numerous landslides and became a prominent area of landslide complexes the present large landslide complex near the earthquake epicenter consisted of laohuzui slide 1 laohuzui slide 2 and douyaping slide the scale geology morphology sliding process and failure mechanism of the landslide complex are analyzed by means of field investigation aerial photograph and stereographic projection technique characteristics of these three slides including seismic response of slope landslide debris damage and potential failure are discussed the convex slope and the upslope of fractured granitic rock at high altitude are highly prone to landsliding under earthquake the high source altitude and long travel path determine grain sizes and the deposit angle of the slide debris the landslide complex completely buries the g213 roadway and dams up the minjiang river in these sections after the earthquake rainfall aftershocks and river erosion may retrigger new failures such as retrogressive slide of weathered fractured rock colluvial landslide debris flow embankment failure and rockfall the following are presented as suggested remedial measures to protect the roadway and stabilize the slope the removing and trenching protective concrete rock blocks against erosion retaining structure rockfall stopping wall rockfall restraining net rock bolt and the planting of vegetation

extension across the laptev sea continental rifts constrained by gravity modeling the laptev shelf is the area where the gakkel ridge an active oceanic spreading axis approaches a continental edge causing a specific structural style dominated by extensive rift structures from the latest cretaceous to the pliocene extension exerted on the laptev shelf created there several deep subsided rifts and high standing basement blocks to understand syn rift basin geometries and sediment supply relationships across the laptev shelf accurate extension estimates are essential therefore we used 2 d gravity modeling and 3 d gravity inversion to constrain the amount of crustal stretching across the north america eurasia plate boundary in the laptev shelf the latest cretaceous cenozoic extension in that area is partitioned among two rift zones the laptev rift system and the new siberian rift these rifts were both overprinted on the eurasian margin that had been stretched by 190 250 km before the late cretaceous while the laptev rift system connected to the gakkel ridge reveals increasing extension toward the shelf edge 190 380 km the new siberian rift is characterized by approximately uniform stretching along strike 110 125 km the architecture of the laptev rift system shows that the finite extension of about 500 km is sufficient to entirely eliminate crystalline continental crust in the most stretched rift segment continental mantle is exhumed at the base of the late mesozoic basement the example of the laptev rift system shows that extension driven by divergent plate movement is a sufficient cause to produce almost complete continental breakup without an increased heat input from the asthenospheric mantle

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

post earthquake changes and prediction of debris flow scales in subao river valley beichuan county sichuan province china subao river lies along the beichuan yingxiu fault in beichuan county which has been heavily impacted by the wenchuan earthquake on 12 may 2008 and has become sources of many geo hazards on 24 september 2008 a rainstorm triggered a large debris flow in the catchment causing several deaths and significant damages a case study on changes of the debris flow was conducted in the river the peak discharges were calculated in the guanmenzi huangnidi and daanshan gullies results indicated that the peak discharges corresponded to various return periods in different gullies 200 years in daanshan 100 years in huangnidi and 50 years in guanmenzi however the triggering precipitation in these three gullies was only of a 20 year return period the debris flows had undergone significant changes analysis indicated that the changes should be ascribed to the flow characteristics initiation conditions and the channel blockage impacted by the rapid accumulation of loose material channel blockage was the principal factor increasing the scale of the debris flow the values on the blocking coefficient were presented based on density height and other characteristics of dams finally all of the peak debris flow discharges of the subao river valley for a 20 year return period were calculated using the recommended blocking coefficient values

erratum to surficial slip and rupture geometry on the beichuan fault near hongkou during the mw 7 9 wenchuan earthquake china worldwide occurrence and documentation of reverse type ruptures are sparse near hongkou the wenchuan rupture passes through the broad baisha river valley and provides excellent opportunities to trace the surface faulting in fine details for 13 km distance one of the longest continuous sections along the entire rupture in this paper we present the results of our mapping of the surface rupture in this reach based on the discontinuities in slip and geometry the rupture was divided into four sections for convenience from west to east the shenxi gou the miaoba the gaoyuan and the bajiao miao sections respectively the vertical offset is large in the shenxi gou and the bajiao miao sections locally reaching 5 6 m in maxima and generally low in the miaoba section 1 2 m or less in most places the slip gradient for vertical offset is generally 10 3 locally up to 10 1 similar to that in well documented strike slip ruptures near gaoyuan village the surface rupture con sists of two subparallel branches with the northern one exhibiting right lateral slip with minor southeast side up thrusting while the southern one is almost pure south east side up thrusting this pattern mimics the incomplete slip partitioning of oblique thrusting on parallel faults but at a local scale in addition the sense of vertical throw on these two strands is opposite to the general northwest side up thrusting of the wenchuan rupture we propose that it is likely due to the inheritance at shallow depth from the southeast dipping geological faults and that old fault zone structures can have a strong effect on the dynamic rupture by guiding the rupture propagation onto paths of preexisting though locally unfavorable dipping fault planes we also discuss the cross cutting slickenside striations observed near bajiao miao which indicated temporal rake rotation during dynamic rupture and their geological and seismological implications

seismotectonics of the 2013 lushan mw 6 7 earthquake inversion tectonics in the eastern margin of the tibetan plateau on 20 april 2013 an unexpected mw 6 7 earthquake occurred in lushan county at the southern longmen shan the eastern margin of the tibetan plateau a high resolution seismic reflection profile was combined with near surface geological data earthquake relocation and geodetic measurements and a recent deep artificial seismic reflection profile to identify the active fault and seismotectonics of this earthquake three dimensional imaging of the aftershocks was used to identify two planar faults that together form a y shape f1 and f2 seismic interpretations suggest that fault f1 did not break through the overlying mesozoic and cenozoic rocks and is a typical blind fault geodetic measurements suggest that the coseismic deformation is consistent with the geometry and kinematics of shear fault bend folding deep seismic data indicate the syndepositional nature of fault f1 a preexisting normal fault older than the triassic which underwent positive inversion tectonics during the late cenozoic a thrust fault f3 converges with f1 at a depth of approximately 12 km with an accumulated slip 3 6 km this 2013 lushan earthquake triggered by blind faults is a hidden earthquake blind and reactivated faults increase the potential risk and uncertainty related to earthquakes in the eastern margin of the tibetan plateau

the mesozoic along strike tectonometamorphic segmentation of longmen shan eastern tibetan plateau the longmen shan belt eastern border of the tibetan plateau constitutes a tectonically active region as demonstrated by the occurrence of the unexpected 2008 mw 7 9 wenchuan and 2013 mw 6 6 lushan earthquakes in the central and southern parts of the belt respectively these events revealed the necessity of a better understanding of the long term geological evolution of the belt and its effect on the present dynamics and crustal structure new structural and thermobarometric data offer a comprehensive dataset of the paleo temperatures across the belt and p t estimates for low grade metamorphic domains in the central longmen shan two metamorphic jumps of 150 200 c 5 6 kbar and 50 c 3 5 kbar acquired during the early mesozoic are observed across the wenchuan and beichuan faults respectively attesting to their thrusting movement and unrevealing a major decollement between the allochtonous songpan garze metasedimentary cover at t 500 c and the autochtonous units and the basement t 400 c in the southern longmen shan the only greenschist facies metamorphism is observed both in the basement 360 30 c 6 2 kbar and in the metasedimentary cover 350 30 c 3 1 kbar peak conditions were reached at c 80 60 ma in the basement and c 55 33 ma in the cover c 50 ma after the greenschist facies metamorphic overprint observed in the central longmen shan c 150 120 ma this along strike metamorphic segmentation coincides well with the present fault segmentation and reveals that the central and southern longmen shan experienced different tectono metamorphic histories since the mesozoic

restoration of cenozoic deformation in asia and the size of greater india a long standing problem in the geological evolution of the india asia collision zone is how and where convergence between india and asia was accommodated since collision proposed collision ages vary from 65 to 35 ma although most data sets are consistent with collision being underway by 50 ma plate reconstructions show that since 50 ma 2400 3200 km west to east of india asia convergence occurred much more than the 450 900 km of documented himalayan shortening current models therefore suggest that most post 50 ma convergence was accommodated north of the indus yarlung suture zone we review kinematic data and construct an updated restoration of cenozoic asian deformation to test this assumption we show that geologic studies have documented 600 750 km of n s cenozoic shortening across and north of the tibetan plateau the pamir hindu kush region accommodated 1050 km of n s convergence geological evidence from tibet is inconsistent with models that propose 750 1250 km of eastward extrusion of indochina approximately 250 km of indochinese extrusion from 30 to 20 ma of indochina suggested by se asia reconstructions can be reconciled by dextral transpression in eastern tibet we use our reconstruction to calculate the required size of greater india as a function of collision age even with a 35 ma collision age the size of greater india is 2 3 times larger than himalayan shortening for a 50 ma collision the size of greater india from west to east is 1350 2600 km consistent with robust paleomagnetic data from upper cretaceous paleocene tethyan himalayan strata these estimates for the size of greater india far exceed documented shortening in the himalaya we conclude that most of greater india was consumed by subduction or underthrusting without leaving a geological record that has been recognized at the surface

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

time constraints on the emplacement of klippen in the longmen shan thrust belt and tectonic implications abstract a belt of klippen and nappes was emplaced in the longmen shan thrust belt mostly lying between the yingxiu beichuan and the pengguan fault zones timing of the allochthon emplacement is hotly debated but quantitative age constraints are rarely documented this study presents the first isotopic dating of authigenic illite isolated from a 30 m wide fault gouge zone developed in reverse faults in the leading edge of the largest baishi goujia klippe a representative of the klippen and nappe belt in the longmen shan thrust belt the results show that the authigenic illite formed 180 215 ma ago combined with apatite and zircon fission track dating of the hanging wall of the yingxiu beichuan fault zone the emplacement of the baishi goujia klippe is constrained at 171 180 ma in the middle jurassic the thickness of a successive strata unit of the baishi goujia klippe measures 3 km and of the tangwangzhai nappe is over 5 km this implies that the elevation of the longmen shan was at least of 3 5 km a s l during the indosinian orogeny

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