footprints of mesoscale eddy passages in the strait of otranto adriatic sea 1 the footprints of mesoscale eddies propagating through the strait of otranto are documented from current meter records and their formation mechanism is hypothesized bottom mounted acoustic doppler current profilers data collected during 5 months november 2006 through april 2007 at a transect in the core of the outflowing adriatic dense water reveal energetic events that manifest as vertically uniform current vector rotations on a time scale of about 10 days at the two moorings close to the center of the strait coherent current vector rotations were in opposite senses simulation of the passage of an idealized cyclonic or anticyclonic rigid circular eddy confirms that these opposed rotations could be associated with passages of eddies in the southward direction characteristic parameters of the eddies were estimated the duration was several days the peak azimuthal velocity was around 10 20 cm s and advection velocity below 15 cm s was predominantly in the southwestward direction cyclones were bigger diameter 30 36 km than anticyclones 14 24 km and they traveled at greater depths the eddy passage left a prominent signal in the thermohaline and turbidity properties this latter is probably due to sediment resuspension by strong currents and to the advection of the suspended particles through an upstream located canyon the eddy formation is explained in terms of stretching of the high potential vorticity water column outflowing the strait of otranto a mechanism similar to that observed in the denmark strait overflow another possible explanation is the baroclinic instability of the overflow layer which results in the eddy formation

spatial distribution of landslides triggered by the 2008 ms 8 0 wenchuan earthquake china abstract the ms 8 0 wenchuan earthquake of may 12 2008 is one of the most disastrous earthquakes in china the earthquake triggered tens of thousands of landslides over a broad area including shallow disrupted landslides rock falls deep seated landslides and rock avalanches some of which buried large sections of some towns and dammed the rivers the purpose of this study is to investigate correlations between the occurrence of landslides with geologic and geomorphologic conditions and seismic parameters over 56 000 earthquake triggered landslides with a total area of 811 km 2 are interpreted using aerial photographs and remote sensing images taken following the earthquake the spatial distribution of these landslides is analyzed statistically using both landslide point density lpd defined as the number of landslides per square kilometer and landslide area density lad the percentage of the area affected by landslides to determine how the occurrence of landslides correlates with distance from the epicenter distance from the major surface rupture seismic intensity and peak ground acceleration pga slope angle slope aspect elevation and lithology it is found that both lad and lpd have strong positive correlations with slope steepness distance from the major surface rupture and seismic intensity and that pre sinian schist and cambrian sandstone and siltstone intercalated with slate have the most concentrated landslide activities followed by the permian limestone intercalated with shale and devonian limestone statistical analyses also indicate that the major surface rupture has influence on the spatial distribution of landslides because lad and lpd are relatively higher on the hanging wall than on the footwall however the correlation between the occurrence of landslides with distance from the epicenter of the earthquake is complicated rather than a relatively simple negative correlation as found from other reported cases of earthquakes this is possibly due to complicated rupture processes of the earthquake

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

pseudostatic analysis of tsao ling rockslide caused by chi chi earthquake during the 1999 chi chi earthquake extensive slope failures were triggered by the earthquake in central taiwan among those a large scale dip slope slide in tsao ling occurred which involved the mass movement of 120 million cubic meters four catastrophic dip slope rockslide events in history in tsao ling are reported furthermore the stability analysis of the tsao ling landslide caused by the chi chi earthquake was conducted for the original and remaining slope results of pseudostatic analysis indicated that a reduction factor of 2 3 for both vertical and horizontal peak ground acceleration with 30 of material strength degradation were likely the case for inducing the tsao ling landslide and the effects of vertical acceleration were significant accordingly it was concluded that ground motion and degradation of material strength were the major factors for the inducement of the tsao ling landslide by the chi chi earthquake

evidence for mechanically coupled lithosphere in central asia and resulting implications the recent dramatic increase in seismic anisotropy and surface global positioning system gps data for central asia permits a comprehensive examination of the mantle s role in mountain building a joint analysis of 178 shear wave splitting and 2000 gps observations using a new technique reveals that the crust and lithospheric mantle deform coherently arguing for crust mantle mechanical coupling during deformation the observed spatial variations in anisotropy refl ect the large scale pattern of lithospheric deformation as well as a change in deformational style from simple shear on the tibetan plateau transitioning to pure shear in surrounding regions

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

carbonate deposition pyramid lake subbasin nevada 1 sequence of formation and elevational distribution of carbonate deposits tufas abstract during the late quarternary the elevation of terrace cutting and carbonate deposition in the pyramid lake subbasin were controlled by constancy of lake level imposed by spill to adjoining subbasins sill elevations are 1177 1183 m mud lake slough sill 1207 m emerson pass sill and 1265 m darwin pass sill carbonate deposition was favored by 1 hydrologic closure 2 proximity to a source of calcium 3 elevated water temperature and 4 a solid substrate the thickness and aspect of tufa are a function oflake level dynamics relatively thin sheets and pendant sheets were deposited during a rising or falling lake the upper parts of thick reef form tufas have a horizontal aspect and were deposited in a lake which was stabilized by spill to the carson desert subbasin the lower parts of the reef form tufas are thinner and their outer surface has a vertical aspect indicating that the lower part formed in a receding lake the thickest and most complete sequences of tufa are mounds that border the pyramid lake shore the tops of the tallest mounds reach the elevation of the darwin pass sill and many mounds have been eroded to the elevations of the mud lake slough sill of the emerson pass sill the sequence of tufa formation from oldest to youngest displayed in these mounds is 1 a beachrock containing carbonate cemented volcanic cobbles 2 broken and eroded old spheroids that contain thinolitic tufa and an outer rind of dense laminated tufa 3 large cylindrical tubular tufas capped by 4 coatings of old dense tufas and 5 several generations of old branching tufa commonly associated with thin platy tufas and coatings of thinolitic tufa 6 young spheroids that contain poorly oriented young thinolitic tufa in the center and several generations of radially oriented young thinolitic tufas near the outer edge 7 a transitional thinolite to branching tufa 8 two or more layers of young branching tufa 9 a 0 5 cm thick layer of fine grained dolomite 10 a 2 cm thick layer of young dense laminated tufa 11 a 0 1 cm thick layer of encrusting tufa that was covered by a beach deposit and 12 a 1 0 cm thick layer of porous encrusting tufa that coated the beach deposit and the sides of tufa mounds the elevational ranges of the principal varieties of tufa are not related to terrace or spill elevations it seems likely that the distribution of tufa varieties is related to variation in the thermal structure or chemistry of lake lahontan it is hypothesized that the thinolitic tufa ikaite formed in the near freezing hypolimnion and the braching tufa calcite formed in the seasonally warmer epiliminion of the lake

tectonics and denudation adjacent to the xianshuihe fault eastern tibetan plateau constraints from fission track thermochronology the xianshuihe xiaojiang fault system extending from eastern tibet to central yunnan china is a major left shear structural boundary accommodating the clockwise rotation of crustal rocks between the eastern himalayan syntaxis and the south china block zircon and apatite fission track ft data are reported for 111 samples of basement collected from both sides of the northern part of this fault and spanning 300 km across the eastern margin of the tibetan plateau where its mean elevation drops from 3500 to 1500 m above sea level the zircon ft ages define two fossil partial annealing zones at different elevations one fossilised at circa 130 ma and the other at circa 21 ma as a result of cooling probably via regional denudation the apatite ft ages are mostly less than 25 ma but a few granitoids higher up on the plateau retain late cretaceous apparent ages within the apatite ft data with neogene ages there may be several partial annealing zones with mixture modeling identifying age components suggestive of discrete cooling phases at circa 22 7 and 2 ma the first order pattern of the minimum amount of neogene denudation for a section across the plateau margin immediately northeast of xianshuihe fault suggests that a relatively uniform 4 6 km has been eroded from the inner part of the plateau margin increasing to 7 10 km at kangding where the oldest rocks precambrian are exposed and then decreasing markedly into sichuan basin these new ft data combined with published ft data suggest that the present extent of the tibetan plateau was defined during the early miocene

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

structural heterogeneity of the longmenshan fault zone and the mechanism of the 2008 wenchuan earthquake ms 8 0 we determined detailed 3 d images of p and s wave velocity vp vs and poisson s ratio in and around the longmenshan lms fault zone by using a large number of p and s wave arrival times from the aftershocks of the 2008 wenchuan earthquake ms 8 0 and other local events our results show that the structure of the lms fault zone north of the wenchuan main shock is very different from that south of the main shock the southern section of the lms fault zone contains a broad zone with low vp low vs and high anomalies while the northern segment exhibits more scattered heterogeneities corresponding to most of the aftershocks which occurred there a prominent low vp low vs and high anomaly exists directly beneath the wenchuan main shock hypocenter suggesting that in addition to compositional variations fluid filled fractured rock matrices may exist in the lms fault zone which may have influenced the generation of the large wenchuan earthquake our tomographic results provide sound seismic evidence for the hypothesis that an upward intrusion of lower crustal flow occurred along the lms fault zone in addition most small earthquakes before the 2008 wenchuan main shock occurred around the guanxian jiangyou fault while the wenchuan aftershocks were mainly concentrated on the yingxiu beichuan fault suggesting that the rupture process of the wenchuan earthquake may belong to an out of sequence thrusting event a suggestion which is in good agreement with the results from geological surveys and also quite similar to the rupture processes of the 1999 chi chi earthquake m 7 5 and the 2005 kashmir earthquake m 7 6 a few aftershocks occurred close to the blind guangyuan dayi fault in the sichuan basin suggesting that this blind fault was also ruptured by the wenchuan earthquake consistent with geological surveys

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

brittle modification of triassic architecture in eastern tibet implications for the construction of the cenozoic plateau abstract in the songpan ganzi fold belt east tibetan plateau post triassic deformation is localised within northwest trending sinistral and southwest trending dextral brittle fault zones between these zones large tracts of the fold belt preserving late triassic indosinian architecture have been transported effectively intact this transport was almost exclusively strike slip and did not accommodate significant differential exhumation or uplift right dihedra paleostress reconstructions from fault plane kinematic data indicate a rotation of the principal compressive stress from ne sw trending in the north to a dominant e w trend throughout the eastern songpan ganzi fold belt exceptions occur adjacent to competent proterozoic basement complexes and other rigid bodies these stress solutions are consistent with a compressive stress regime that radiates about the eastern himalayan syntaxis a secondary n s compressive paleostress identified in southern regions may record late southwards transportation of the songpan ganzi fold belt relative to the eastern himalayan syntaxis the lack of pervasive cenozoic recent upper crustal shortening in this region suggests that thickening of the east tibetan crust was predominantly accommodated by viscous deformation at depth we envisage decoupling of the lower and upper crust and partitioning of an e w compressive stress between 1 a laterally mobile thin skinned veneer and 2 a homogeneously thickened tectonic basement

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

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

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

erosion driven uplift of the modern central alps abstract we present a compilation of data of modern tectono geomorphic processes in the central european alps which suggest that observed rock uplift is a response to climate driven denudation this interpretation is predominantly based on the recent quantification of basin averaged late holocene denudation rates that are so similar to the pattern and rates of rock uplift rates as determined by geodetic leveling furthermore a gps data based synthesis of adriatic microplate kinematics suggests that the central alps are currently not in a state of active convergence finally we illustrate that the central alps have acted as a closed system for holocene redistribution of sediment in which the peri alpine lakes have operated as a sink for the erosional products of the inner central alps while various hypotheses have been put forward to explain central alpine rock uplift e g lithospheric forcing by convergence mantle processes or ice melting we show with an elastic model of lithospheric deformation that the correlation between erosion and rock uplift rates reflects a positive feedback between denudation and the associated isostatic response to unloading thus erosion does not passively respond to advection of crustal material as might be the case in actively converging orogens rather we suggest that the geomorphic response of the alpine topography to glacial and fluvial erosion and the resulting disequilibrium for modern channelized and associated hillslope processes explains much of the pattern of modern denudation and hence rock uplift therefore in a non convergent orogen such as the central european alps the observed vertical rock uplift is primarily a consequence of passive unloading due to erosion

landslides triggered by the 8 october 2005 kashmir earthquake abstract the 8 october 2005 kashmir earthquake triggered several thousand landslides these were mainly rock falls and debris falls although translational rock and debris slides also occurred in addition a sturzstrom debris avalanche comprising 80 million m3 buried four villages and blocked streams to create two lakes although landsliding occurred throughout the region covering an area of 7500 km2 the failures were highly concentrated associated with six geomorphic geologic anthropogenic settings including natural failures in 1 highly fractured carbonate rocks comprising the lowest beds in the hanging wall of the likely earthquake fault 2 tertiary siliciclastic rocks along antecedent drainages that traverse the hazara kashmir syntaxis 3 steep 50 slopes comprising precambrian and lower paleozoic rocks 4 very steep 50 lower slopes of fluvially undercut quaternary valley fills and 5 ridges and spur crests the sixth setting was associated with road construction extensive fissuring in many of the valley slopes together with the freshly mobilized landslide debris constitutes a potential hazard in the coming snowmelt and monsoon seasons this study supports the view that earthquake triggered landslides are highly concentrated in specific zones associated with the lithology structure geomorphology topography and human presence

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

neotectonics of the min shan china implications for mechanisms driving quaternary deformation along the eastern margin of the tibetan plateau the min shan region located along the eastern margin of the tibetan plateau north of the sichuan basin provides an important natural laboratory in which to study the rates and patterns of deformation and their relationship to mountain building at the margin of the plateau the topographic margin of the plateau is coincident with a north trending mountain range the min shan that stands nearly 2 km above the mean elevation of the plateau 3500 m in this region we exploit the preservation of a series of variably deformed quaternary sediments along the western flank of the range to investigate the pleistocene holocene deformation field within the min shan region mapping and field observations of remnant alluvial fans of late pleistocene age indicate that deformation within the min shan involved substantial 10 rapid down to the northwest tilting the geometry of the deposits and the partial preservation of an erosion surface beneath the basin suggest that much of the modern relief of the min shan relative to the tibetan plateau is a consequence of this late pleistocene tilting rates of tilting inferred from luminescence dating of interbedded loess have been remarkably rapid 10 8 rad yr similarly rapid rates of holocene differential rock uplift are inferred from tilted lacustrine sediments in the southwestern part of the range the range is bounded on the west by the min jiang fault zone an east vergent reverse fault however holocene alluvial terraces in headwaters of the min river are preserved across the fault in several places indicating that displacement rates on the min jiang fault are 1 mm yr active faulting only occurs along the eastern foot of the range huya fault for a short distance 60 km despite 3 km of relief on the eastern range front the relationship between these structures and the tilting observed in the min jiang basin is enigmatic the faults do not appear to exert a strong control on the rates and pattern of deformation within the basin a simple flexural model demonstrates that rates of tilting on the western flank of the min shan are too high to be simply attributed to an isostatic response to surficial loading and unloading of the lithosphere present day horizontal shortening across the min shan is geodetically determined to be less than 2 3 mm yr suggesting that only a small part of the observed tilting can be attributed to horizontal shortening thus tilting and concomitant differential rock uplift in the min shan appear to require an additional driving component we suggest that quaternary deformation along the western min shan may reflect the surface response to thickening of a weak lower crust at the margin of the tibetan plateau

mesozoic sedimentary evolution of the northwest sichuan basin implication for continued clockwise rotation of the south china block we present new sedimentary data integrated into a regional mesozoic stratigraphic framework to provide a detailed picture of spatio temporal variations in deposition and depocenter migration of the northwest sichuan basin the mesozoic sedimentary evolution is utilized to interpret basin subsidence history and to unravel coeval basin margin tectonics the northwest sichuan basin together with the songpan ganzi terrane behaved as a passive margin south of the qinling paleo tethys from late paleozoic to early middle triassic times and then evolved into a peripheral foreland basin in response to collision of the north and south china blocks since the late middle triassic coeval with strong north south contraction of the songpan ganzi terrane in the late triassic sinistral transpressional deformation of the longmen shan belt led to flexural subsidence of the adjacent western sichuan basin renewed basin margin fold thrust activity triggered recurrence of flexural subsidence of the northwest sichuan basin since the middle jurassic with the depocenter eventually shifting to the northwestern corner of the basin in the early cretaceous sedimentary evolution of the northwest sichuan basin and the basin margin deformation imply that the south china block had been rotating clockwise relative to the north china block throughout the mesozoic with an interim period of early jurassic tectonic quiescence a model is advanced that invokes clockwise rotation of the south china block as a driver for tectonic evolution of both the basin and adjoining structural belts and provides an explanation for several salient features that are otherwise puzzling

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

cenozoic and mesozoic metamorphism in the longmenshan orogen implications for geodynamic models of eastern tibet new zircon u pb and mica 40ar 39ar dating combined with structural studies in the longmenshan orogen confirm that most of the upper crustal deformation in the eastern margin of tibet is mesozoic however at lower structural levels apatite u pb and monazite electron microprobe dating reveals a previously unknown domain of cenozoic ca 65 ma barrovian type metamorphism and deformation this discovery shows that the crust in the eastern margin of tibet was already a substantial thickness around the time of the india asia collision associated deformation has a n s oriented stretching lineation implying that deformation was not driven by topographic gradients in the tibetan plateau the observed moderate amounts of distributed postmetamorphic e w shortening can probably explain the present thickness of the continental crust in the area these results do not support models of crustal thickening caused by solid state lateral flow of midcrustal metamorphic rocks

surface wave array tomography in se tibet from ambient seismic noise and two station analysis i phase velocity maps summary empirical green s functions egfs between pairs of seismographs can be estimated from the time derivative of the long time cross correlation of ambient seismic noise these egfs reveal velocity dispersion at relatively short periods which can be used to resolve structures in the crust and uppermost mantle better than with traditional surface wave tomography we combine rayleigh wave dispersion estimates from egfs and from traditional two station ts analysis into a new approach to surface wave array tomography with data from dense receiver arrays we illustrate the methodology with continuous broad band recordings from a temporary seismographic network on the southeastern part of the tibetan plateau in sichuan and yunnan provinces sw china the egfs are robust under temporal changes in regional seismicity and the use of either ambient noise approximated by records without signal from events with magnitude mb 5 or 4 or surface wave coda produces similar results the egfs do not strongly depend on the presence of large earthquakes but they are not reciprocal for stations aligned in the n s direction this directionality reflects the paucity of seismicity to the north of the array using a far field representation of the surface wave green s function and an image transformation technique we infer from the egfs the rayleigh wave phase velocity dispersion in the period band from 10 30 s a classical ts approach is used to determine rayleigh wave phase velocity dispersion between 20 120 s together they constrain phase velocity variations for t 10 120 s which can be used to study the structure from the crust to the upper mantle beneath se tibet short and intermediate period 10 80 s phase velocities are prominently low suggesting that the crust and upper mantle beneath se tibet is characterized by slow shear wave propagation

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

the growth of geological structures by repeated earthquakes 2 field examples of continental dip slip faults a strong test of our understanding of the earthquake cycle is the ability to reproduce extant fault bounded geological structures such as basins and ranges which are built by repeated cycles of deformation along strike slip faults the coseismic and interseismic deformation can be nearly equal in magnitude and opposite in sign resulting in little permanent deformation except for the fault offset for dip slip faults portions of the crust are lifted and dropped and so buoyancy forces are exerted the seismic and interseismic deformations do not balance and structures grow and become subject to erosion and deposition we consider three examples for which the structure and fault geometry are well known the white wolf reverse fault in california site of the 1952 kern county m 7 3 earthquake the lost river normal fault in idaho site of the 1983 borah peak m 7 0 earthquake and the cricket mountain normal fault in utah site of quaternary slip events basin stratigraphy and seismic reflection records are used to profile the structure and coseismic deformation measured by leveling surveys is used to estimate the fault geometry to reproduce these structures we add the deformation associated with the earthquake cycle the coseismic slip and postseismic relaxation to the flexure caused by the observed sediment load treating the crust as a thin elastic plate overlying a fluid substrate the cumulative deformation is principally dependent on the elastic plate thickness modestly sensitive to the sediment substrate density difference and insensitive to the fluid viscosity for the 4 to 8 ma structures we deduce a longterm flexural rigidity of 2 15 1019 nm this is equivalent to an elastic plate thickness of 2 4 km for a young s modulus of 2 5 1010 nm 2 this value is found where independent estimates of the elastic thickness from the coherence between surface topography and gravity yield values of about 4 km but where coseismic fault slip extends to a depth of 10 15 km thus much of the seismogenic crust must weaken substantially during the life of active faults causing the fault bounded basins to narrow over time

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

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

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

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

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

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

the growth of geological structures by repeated earthquakes 1 conceptual framework in many places earthquakes with similar characteristics have been shown to recur if this is common then relatively small deformations associated with individual earthquake cycles should accumulate over time to create geological structures following this paradigm we show that existing models developed to describe leveling line changes associated with the seismic cycle can be adapted to explain geological features associated with a fault in these models an elastic layer containing the fault overlies a viscous half space with a different density fault motion associated with an earthquake results in immediate deformation followed by a long period of readjustment as stresses relax in the viscous layer and isostatic equilibrium is restored deformation is also caused as a result of the loading and unloading due to sediment deposition and erosion in this paper the parameters that control the growth of dip slip structures are identified we find that the flexural rigidity of the crust or the apparent elastic thickness provides the main control of the width of a structure the loading due to erosion and deposition of sediment determines the ratio of uplift to subsidence between the two sides of the fault the flexure due to sediment load is much more important in this respect than whether the fault is normal or reverse in character we find that in general real structures are associated with apparent elastic thicknesses of 4 km or less and thus with very low flexural rigidities

quaternary erosion induced isostatic rebound in the western alps the high elevation and deep incision of the alps have traditionally been used as an argument for recent tectonic activity that has elevated the belt and increased erosion rates normal faulting and horizontal extension however dominate current tectonic activity and isostatic compensation of thinning crust should lead not to increased but to decreased mean elevations here we test the idea that enhanced quaternary erosion of the alps and isostatic compensation of the mass removed can account for the distribution of present day geodetically measured rates of vertical movement in the western alps using geophysical relief and kuhlemann s estimated average erosion rate for the alps we quantify the spatial distribution of erosion and the volume of eroded rock respectively from these we obtain a map of rock eroded within a given time span the calculated isostatic response of the alpine lithosphere to erosional unloading for a variety of values of the flexural rigidity of the alpine lithosphere reaches a maximum of 500 m since 1 ma in the inner swiss alps and vertical movement extends across the entire belt including peri alpine basins assuming a steady erosion rate since 1 ma this rebound accounts for half of the measured vertical motion of 1 1 mm yr in the southern valais thus a significant fraction 50 of the present day vertical movement results from the isostatic response to enhanced erosion during plio quaternary time

mountain erosion over 10 yr 10 k y and 10 m y time scales we used cosmogenic 10 be to measure erosion rates over 10 k y time scales at 32 idaho mountain catchments ranging from small experimental watersheds 0 2 km 2 t o large river basins 35 000 km 2 these long term sediment yields are on average 17 times higher than stream sediment fluxes measured over 10 84 yr but are consistent with 10 m y erosion rates measured by apatite fission tracks our results imply that conventional sediment yield measurements even those made over decades can greatly underestimate long term average rates of sediment delivery and thus overestimate the life spans of engineered reservoirs our observations also suggest that sediment delivery from mountainous terrain is extremely episodic sporadically subjecting mountain stream ecosystems to extensive disturbance

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

late cenozoic denudation by large magnitude landslides in the eastern edge of tibetan plateau abstract eastern edge of the tibetan plateau is marked by the longmen shan which experienced pronounced denudation in late cenozoic and was previously attributed to river erosion our recent work however demonstrated that the landsliding must have played an important integral role in the surface processes various scale landslides are present in the peripheral zone of the southern longmen shan which were interpreted as overthrust related klippen in previous works we revisited these exotic blocks and demonstrated that they were actually gravity driven landslides in origin the landslides are composed mostly of thick bedded marine limestone and sandstone of paleozoic early triassic ages and were detached along some weak zones like lower silurian phyllite and unconformities three types of landslides can be categorized distributed stacked and coherent and their differential occurrence is considered to bear upon both uplift rates of the longmen shan and foreland topography outward flow of lower crustal materials from the tibetan plateau interior provides a feasible mechanism for initiating the uplift of its eastern flank in cenozoic positive feedbacks are believed to have existed between extrusion of lower crustal channel flow and surface denudation processes rapid denudation by large magnitude landslides in conjunction with coeval river erosion in the southern longmen shan might have led to predominant sub vertical extrusion of lower crustal flow channel as evidenced by nearly symmetric exhumation of the pengguan massif the northern longmen shan was comparatively less denuded with few basement rocks cropping out and landslides are absent in its front as well differential denudation between the southern and northern longmen shan might have in large part resulted from the lower crustal flow that presumably moved to the southeast and had less impact on the northern longmen shan

erosion as a driving mechanism of intracontinental mountain growth in nature mountains can grow and remain as localized tectonic features over long periods of time 10 m y by contrast according to current knowledge of lithospheric rheology and neglecting surface processes any intracontinental range with a width that exceeds that which can be supported by the strength of the lithosphere should collapse within a few tens of millions of years for example assuming a quartz dominated crustal rheology the relief of a range initially 3 km high and 300 400 km wide is reduced by half in about 15 m y as a result of lateral spreading of its crustal root we suggest that surface processes might actually prevent such a subsurface collapse removal of material from topographic heights and deposition in the foreland oppose spreading of the crustal root and could eventually drive a net influx of material toward the orogeny we performed a set of numerical experiments in order to validate this hypothesis a section of a lithosphere with a brittle elasto ductile rheology initially loaded by a mountain range is submitted to horizontal shortening and to surface processes if erosion is intense material is removed more rapidly than it can be supplied by crustal thickening below the range and the topography is rapidly smoothed for example a feature 3 km high and 300 400 km wide is halved in height in about 15 m y for an erosion coefficient k 10 3 m 2 yr the erosion rate is of the order of a few 0 1 mm yr this regime might be called erosional collapse if erosion is not active enough the crustal root spreads out laterally and subsurface collapse occurs in the third intermediate regime removal of the material by erosion is dynamically compensated by isostatic rebound and inward flow in the lower crust so that the range can grow in this mountain growth regime the range evolves toward a characteristic graded shape that primarily depends on the erosion law the erosion rate may be high e g 0 5 0 9 mm yr close to the rate of tectonic uplift e g 0 7 1 1 mm yr and few times higher than the rate of topographic uplift 0 15 0 2 mm yr these experiments show that surface processes can favor localized crustal shortening and participate in the development of an intracontinental mountain surface processes must therefore be taken into account in the interpretation and modeling of long term deformation of continental lithosphere conversely the mechanical response of the lithosphere must be accounted for when large scale topographic features are interpreted and modeled in terms of geomorphologic processes

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

coseismic deformation from the 2008 wenchuan china earthquake derived from alos palsar images abstract we analyzed alos palsar images along eight paths acquired before and after the mainshock of an earthquake in wenchuan in the sichuan province of china may 12 2008 we found entire coseismic deformation features and detected many fringes in an approximately 100 km wide region surrounding the longmen shan fault zone we found 6 7 broad elliptic fringes north of the epicenter which indicated around 70 80 cm increase in range distance between the ground and satellite this pattern corresponded to subsidence or eastward shift of ground which is often seen above the lower margin of a low angled thrust we also counted 8 9 fringes i e 90 100 cm range decrease between the fault zone and chengdu chengdu is located roughly 50 km away from the pengguan fault which is the southernmost trace of the longmen shan fault zone as this area is located on the footwall side the pattern suggested a westward shift of the earth s surface however we could not obtain high correlations due to large displacements in the about 240 km long belt along the surface faults several concentric fringes were found along the beichuan fault which is the central trace of the longmen shan fault zone this implied that the rupture process of this earthquake was complicated we also performed pixel matching to estimate offsets in the region of low correlation positive and negative range offsets larger than 2 m were found on the north and south sides of the beichuan fault respectively we observed a belt of negative range and azimuth offsets between the beichuan and pengguan faults we calculated an interferogram using a multi segment fault model with uniform slip along the beichuan and pengguan faults and estimated the slip distribution based on previous seismological studies we assumed that the southwestern part dipped toward the northwest by 33 degrees whereas the central and northeastern parts had a much steeper dip angle we found two regions of slips larger than 4 m in the southwest and central parts of the beichuan fault the pengguan segments may have much smaller slips around 1 m the southwestern segments of the beichuan fault and the entire pengguan fault had dominant thrust components whereas dextral slip prevailed in the central and northeastern segments of the beichuan fault the estimated geodetic moment was 5 87 1020nm mw 7 78

rupture imaging of the mw 7 9 12 may 2008 wenchuan earthquake from back projection of teleseismic p waves 1 the mw 7 9 wenchuan earthquake of 12 may 2008 was the most destructive chinese earthquake since the 1976 tangshan event tens of thousands of people were killed hundreds of thousands were injured and millions were left homeless here we infer the detailed rupture process of the wenchuan earthquake by back projecting teleseismic p energy from several arrays of seismometers this technique has only recently become feasible and is potentially faster than traditional finite fault inversion of teleseismic body waves therefore it may reduce the notification time to emergency response agencies using the iris dmc we collected 255 vertical component broadband p waves at 30 95 from the epicenter we found that at periods of 5 s and greater nearly all of these p waves were coherent enough to be used in a global array we applied a simple down sampling heuristic to define a global subarray of 70 stations that reduced the asymmetry and sidelobes of the array response function arf we also considered three regional subarrays of seismometers in alaska australia and europe that had apertures less than 30 and p waves that were coherent to periods as short as 1 s individual arfs for these subarrays were skewed toward the subarrays however the linear sum of the regional subarray beams at 1 s produced a symmetric arf similar to that of the groomed global subarray at 5 s for both configurations we obtained the same rupture direction rupture length and rupture time we found that the wenchuan earthquake had three distinct pulses of high beam power at 0 23 and 57 s after the origin time with the pulse at 23 s being highest and that it ruptured unilaterally to the northeast for about 300 km and 110 s with an average speed of 2 8 km s it is possible that similar results can be determined for future large dip slip earthquakes within 20 30 min of the origin time using relatively sparse global networks of seismometers such as those the usgs uses to locate earthquakes in near real time

paleoseismic evidence and repeat time of large earthquakes at three sites along the longmenshan fault zone abstract in historical records no earthquake of magnitude comparable with that of the wenchuan mw 7 9 earthquake has ever been reported in chengdu and longmenshan regions it is important therefore to assess if there is any evidence of prior large earthquakes in the recent geological record in order to explore this problem 3 trenches were excavated separately at 3 sites along the surface rupture zones in the middle segment of the beichuan yingxiu fault and jiangyou guanxian fault of the longmenshan fault zone and the offsets of geomorphic surfaces were measured in the trenches the basic facts of recurrence of large earthquake on the seismogenic fault of the wenchuan earthquake are demonstrated in this paper on the basis of the accumulated deformation amounts of old and young geomorphic surfaces as well as the paleoearthquake events revealed in the trenches the document that at leigu along the beichuan yingxiu fault at bailu along the jiangyou guanxian fault and xiaoyudong on a nw trending fault the height of fault scarp on the second terrace has a multiple relationship to that on the first terrace after the wenchuan earthquake of 12 may the elevation difference of the marker horizon the yellow sandy clay bed of the second terrace revealed in the trenches on both sides of the fault is nearly twice or three times larger in bailu of that produced by the wenchuan earthquake these observations suggest the occurrences of paleoearthquake events with surface deformation comparable to that produced by the wenchuan mw 7 9 earthquake according to the dating data and the fact that there is no such slip of comparable paleoearthquakes in the 2300 year long historic literature in longmenshan region we suggest that the penultimate event occurred between 2300 a bp and 3300 a bp

the role of landslides in mountain range evolution abstract we review the role of landslides in current concepts of the topographic development of mountain ranges we find that many studies in this field address basin or orogen scale competition between rock uplift and fluvial bedrock erosion hillslopes in general and bedrock landslides in particular are often assumed to respond rapidly to incision and development of the fluvial drainage network this leads to a one sided view of the geomorphic coupling between hillslopes and rivers that emphasizes the fluvial control of hillslopes but ignores the alternative view that landslides can affect the fluvial network there is growing evidence that landslides are a dominant source of sediment in mountain belts and that they exert a direct geomorphic control on fluvial processes landslides can influence the river network in a variety of ways from determining basin area and drainage divide positions to setting streamwise variations in sediment load and calibre the geomorphic legacy of large landslides on hillslope and channel morphologies may persist for up to 104 yr adding considerable variability to fluvial erosion and sedimentation patterns over these timescales we identify a number of questions for future research and conclude that a better understanding and quantification of the geomorphic feedbacks between landslides and river channels builds an important link between short term 105 yr landscape evolution models

the morphology of strike slip faults examples from the san andreas fault california fault zones are seldom straight nor are fractures within them continuous permanent strain fields are imprinted near a fault of complex geometry as a result of continued slip these strain fields may be manifest as vertical deformation near the fault strain fields that increase area result in subsidence and strain fields that reduce area result in uplift although these effects are modified by erosion and deposition the general features of fault zone morphology are a consequence of the geometry and slip distribution along strike graphical views of strain fields associated with simple vertical strike slip faults are derived using boundary element methods if the fault is straight and parallel to the applied shear strain the hills and valleys resulting from finite fault rupture are separated by the fault trace this is rarely observed in nature instead strike slip faults cut through hills and valleys apparently of their own making we show this to be a consequence of segments of the fault being nonparallel to each other and to the overall applied shear strain coseismic strains are large but transient since they are substantially annulled by rupture on contiguous fault segments we test our theory with examples from parts of the san andreas fault system in california the morphologies of the parkfield region and the southern san andreas fault in the coachella valley are shown to be consistent with plausible distributions of slip on mapped surface faults the location of the salton sea appears to be a consequence of a reduction of slip on the san andreas fault toward the brawley seismic zone

late cenozoic evolution of the central longmen shan eastern tibet insight from u th he thermochronometry 1 this article presents u th he thermochronological data from the longmen shan belt eastern tibet located between the songpan garze terrane and the yangtze craton this mountain range is one of the steepest margins of the tibetan plateau and an important area for the comprehension of the mechanisms that control the dynamics of such plateau borders in terms of spatial distribution of deformation or timing of topographic building we describe several age elevation transects and perform forward modeling of our data to derive quantitative information on the exhumation of the range a major phase of exhumation started at 8 11 ma with an average rate of 0 65 mm a a1 comparison of zircon and apatite ages indicates that the eastern part of the range may have experienced a significant decrease in exhumation since 2 3 ma we use the distribution of finite exhumation across the major faults of the area to quantify their dip slip throw rate over the last 10 ma the beichuan fault which was activated during the 2008 sichuan earthquake is the major active structure of the longmen shan since the late miocene with an average thrusting slip rate between 0 4 and 1 mm a a1 conversely over the same time period only minor dip slip activity occurred on the wenchuan fault zone this distribution in space and time of exhumation and deformation is discussed and compared to the different proposed models for the geodynamical evolution of the eastern tibetan margin it also provides an important long term perspective to put in context the destructive 2008 sichuan earthquake that struck the central longmen shan

landscape dissection isostatic uplift and the morphologic development of orogens we examine the morphologic factors that determine the isostatic response to landscape dissection in orogenic terrains in order to quantify the relative contributions of active tectonic uplift and passive isostatic uplift in generating mountain topography we demonstrate that although peaks many times the elevation of an assumed initial plateau can theoretically be generated only moderate amounts of peak uplift can be explained by isostatic rebound in real terrains analysis of topographic data from the european alps and other orogens indicates that isostatic uplift in response to dissection can account for about one fourth of the elevation of the highest peaks if local isostatic compensation is assumed and less if the lithosphere has significant flexural rigidity we conclude that although isostatic uplift can be significant in orogens high peaks are predominantly a consequence of tectonic processes in convergent settings

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