channel flow and fault segmentation with implications for the generation of earthquakes in the longmenshan fault zone eastern tibetan plateau abstract the ms 8 0 wenchuan earthquake occurred in the longmenshan fault zone lfz of the eastern margin of the tibetan plateau tp the tectonic activities in this region have been a focus of extensive studies in the past two decades two different models involving oblique stepwise rise and channel flow respectively are proposed and can be used to explain the generation of earthquakes the oblique stepwise rise model emphasizes more about the fault of the upper crust whereas the channel flow model concerns more about the different crustal rheological structures currently because of the confirmation of geophysical data on the rheological structure of the tp more researchers agree with the channel flow model to investigate the generation of earthquakes in the lfz this study establishes a three dimensional viscoelastic model based on the heterogeneity of the lithospheric structure and the segmentation of faults using ansys finite element software to simulate the evolution of stress and strain the calculated results are consistent with focal mechanism solutions fault striations and topography the best fit stress field suggests that stress localization in the longmenshan range is mainly controlled by the channel flow and fault segmentation the differing viscosities and relative movement between the channel flow and the sichuan basin induce a concentration of stress in the lfz the stress was most concentrated in segment ii closest to the leading edge of the channel flow and wherein the wenchuan earthquake occurred additionally the higher locking degree of segment ii found before the wenchuan earthquake induced higher stress levels at shallow depths corresponding to higher seismic activity in segment ii thus the combined action of the channel flow and fault segmentation controls the distribution of stress and causes the generation of earthquakes in the lfz

bright prospects for radar detection of europa s ocean abstract the surface of europa has been hypothesized to include an ice regolith layer from hundreds of meters to kilometers in thickness however contrary to previous claims it does not present a significant obstacle to searching for europa s ocean with radar sounding this note corrects prior volume scattering loss analyses and expands them to includes observational and thermo mechanical constraints on pore size and regolith depth this provides a more physically realistic range of potential ice regolith volume scattering losses for radar sounding observations of europa s ice shell in the hf and vhf frequency bands we conclude that for the range of physical processes and material properties observed or hypothesized for europa volume scattering losses are not likely to pose a major obstacle to radar penetration

in situ demonstration of a passive radio sounding approach using the sun for echo detection ice sheet contributions to sea level rise present one of the greatest challenges that our society will face in the next century however models predicting sea level rise due to ice melt lack critical information regarding processes at the base of ice sheets although radio echo sounders are powerful tools that are currently used to constrain subglacial conditions existing ice penetrating radar systems are too resource intensive in terms of cost power and logistics for multiyear deployment at a large scale to address this we present passive radio sounding as a low resource approach for observing ice sheets across a range of spatial and temporal scales while passive radar has been used for target tracking and military purposes it has never been used for the sounding of ice sheets some recent work has proposed using passive radio sounding of europa s icy shell using jupiter s decametric radiation we expand on this idea by evaluating and discussing challenges and opportunities for developing a passive radio sounder using the sun as an illuminator of opportunity for echo detection here our prototype instrument sits on the side of a cliff and measures the sun s direct and reflected path off the ocean surface we then use an autocorrelation based method to extract the amplitude and delay of the reflection this serves as the first in situ demonstration of an autocorrelation based passive sounder using a compact astronomical white noise signal

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

two phase growth of high topography in eastern tibet during the cenozoic high topography in eastern tibet is thought to have formed in response to weak lower crust flowing towards the plateau margin thermochronologic analyses of rocks exposed at the eastern plateau margin record periods of mountain growth early in the indo asian collision implying that crustal flow alone could not have created the high topography

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

thermal effects of linked lithospheric and upper crustal scale processes insights from numerical modeling of the cenozoic central catalan coastal ranges ne spain processes influencing the thermal state of the continental crust such as heat upwelling related to rifting and isotherm reorganization due to mass redistribution by erosion deposition and fault tectonic transport operate at different scales and their effects overlap in this paper we use lithospheric as well as crustal scale numerical modeling tools in order to quantify the contributions of these various factors to the geothermal field establishing their relative relevance we apply the models to address the thermal evolution of the catalan coastal ranges ne spain during the cenozoic a period that is characterized by a change in tectonic style from pyrenean compression to extension related to the western mediterranean rifting results of the lithospheric scale thermal model for extensional basins show an increase in the geothermal surface gradient of about 11 c km in the catalan coastal ranges during the neogene related to extensional thinning of the lithosphere in the valencia trough western mediterranean predictions of the upper crustal scale thermal model incorporating fault motions and surface mass redistribution erosion and sedimentation point to little changes in the isotherms due to fault block movements in the paleogene and neogene in contrast erosion appears to have a significant effect on the then nal history of basement rocks sited in the shallowest crust comparison of the integrated lithospheric and upper crustal scale modeling results with apatite fission track and apatite u th he thermochronology data reveals larger amounts of neogene to present cooling than predicted by the models on the basis of this unresolvable mismatch we suggest that similar to present forced fluid convection along fault planes played an important role in the evolution of the geothermal field during the neogene stage of rifting copyright 2007 by the american geophysical union

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

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

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

active tectonics of the beichuan and pengguan faults at the eastern margin of the tibetan plateau the steep high relief eastern margin of the tibetan plateau has undergone rapid cenozoic cooling and denudation yet shows little evidence for large magnitude shortening or accommodation generation in the foreland basin we address this paradox by using a variety of geomorphic observations to place constraints on the kinematics and slip rates of several large faults that parallel the plateau margin the beichuan and pengguan faults are active dominantly dextral slip structures that can be traced continuously for up to 200 km along the plateau margin both faults offset fluvial fill terraces that yield inheritance corrected cosmogenic 10be exposure ages of 15 kyr indicating latest pleistocene activity the pengguan fault appears to have been active in the holocene at two sites along strike latest quaternary apparent throw rates on both faults are variable along strike but are typically 1 mm yr 1 rates of strike slip displacement are likely to be several times higher probably 1 10 mm yr 1 but remain poorly constrained late quaternary folding and dextral strike slip has also occurred along the western margin of the sichuan basin particularly associated with the present day mountain front these observations support models for the formation and maintenance of the eastern plateau margin that do not involve major upper crustal shortening they also suggest that activity on the margin parallel faults in eastern tibet may represent a significant seismic hazard to the densely populated sichuan basin

upper oligocene lower miocene gangrinboche conglomerate in the xigaze area southern tibet implications for himalayan uplift and paleo yarlung zangbo initiation abstract the gangrinboche conglomerate exposed along the yarlung zangbo suture zone records a crucial stage of the himalayan orogeny the type section of these strata in the xigaze area southern tibet including the qiuwu and dazhuka formations was studied by integrated stratigraphic sedimentologic petrographic and geochemical techniques palynological data and detrital zircon u pb ages indicate that the qiuwu formation was deposited during the latest oligocene to the earliest miocene most probably 23 ma while the overlying dazhuka formation was deposited during 23 18 ma the qiuwu formation was deposited in a deltaic setting and detritus was entirely derived from the gangdese magmatic arc in the north the dazhuka formation in contrast was deposited in mainly braided river environments and contains clasts derived from both the gangdese arc in the north and the himalayan orogen in the south clasts derived from the south first occur at the base of the dazhuka formation and increase in abunda

effect of spatial trends on interpolation of river bathymetry continuous surface of river bathymetry bed topography is typically produced by spatial interpolation of discrete point or cross section data several interpolation methods that do not account for spatial trend in river bathymetry produce inaccurate surfaces thus requiring complex interpolation methods such as anisotropic kriging although isotropic methods are unsuitable for interpolating river bathymetry issues that limit their use remain unaddressed this paper addresses the issue of effect of spatial trend in river bathymetry on isotropic interpolation methods it is hypothesized that if the trend is removed from the data before interpolation the results from isotropic methods should be comparable with anisotropic methods data from six river reaches in the united states are used to i interpolate bathymetry data using seven spatial interpolation methods ii separate trend from bathymetry iii interpolate residuals bathymetry minus trend by using all seven interpolation methods to get residual surfaces iv add the trend back to residual surfaces and v compare resulting surfaces from iv with surfaces created in i quantitative and qualitative comparison of results through root mean square error rmse semi variograms and cross section profiles show that significant improvement as much as 60 in rmse can be accomplished in spatial interpolation of river bathymetry by separating trend from the data although this paper provides a new simple way for interpolating river bathymetry by using otherwise deemed inappropriate isotropic methods the choice of trend function and spatial arrangement of discrete bathymetry data play a vital role in successful implementation of the proposed approach

along strike variation of the frontal zone structural geometry of the central longmen shan thrust belt revealed by seismic reflection profiles abstract the 2008 ms 8 0 wenchuan earthquake of china ruptured two large faults along the beichuan yingxiu thrust belt and the pengguan thrust belt at the longmen shan orogenic belt eastern margin of the tibetan plateau our study focused on the structural geometry at the pengguan thrust belt located at the frontal zone of the central longmen shan in this paper in order to identify the co seismic fault at the pengguan thrust belt many 2 d 3 d seismic reflection profiles have been interpreted by integrating with the geological maps drilling data dem data and the surface ruptures the results show that there were three major faults and other branch faults at the pengguan thrust belt the major faults have formed as imbricates and associated minor duplexes within the shallow strata the pengguan fault has a steep dip at the shallow surface and a gentle dip at depth both the beichuan yingxiu fault and the pengguan fault were developed on the shallow detachment in the central segment of longmen shan the third no pengguan fault is coincident with the co seismic surface ruptures it was a pre existing fault and re activated during the wenchuan earthquake three dimensional geometries show that the no fault is heterogeneous and it has controlled the slip of co seismic ruptures based on the regional geology the 3 d fault geometry and the surface ruptures the frontal zone of the central longmen shan has been divided into the bailu segment and the hanwang segment our studies suggest that the pengguan fault has been active since the cenozoic the frontal zone of the central longmen shan thrust belt has potential for future earthquakes

transformation of coseismic faults in the northern longmenshan tectonic belt eastern tibetan plateau implications for potential earthquakes and seismic risks abstract increasingly frequent earthquakes in the longmenshan lms tectonic belt are linked to the ongoing eastward growth of the tibetan plateau during the late cenozoic following the devastating 2008 ms 8 0 wenchuan earthquake in the central lms and the 2013 ms 7 0 lushan earthquake in the southern segment an unexpected ms 5 4 qingchuan earthquake occurred on september 30 2017 in the northern lms we synthesize focal mechanism solutions relocated aftershocks regional geology and seismic reflection profiles in order to determine the pre existing faults and active fault system in the northern lms thus to better assess potential seismic hazards at a seismically resolvable scale we identify a large structural wedge at the basement that is cross cut by numerous multiphase and multi behavior active faults our seismotectonic model indicates that the seismogenic fault responsible for the 2017 ms 5 4 qingchuan earthquake is a pre existing thrust fault with a dip of 34 in the frontal thrust ramp reactivation of this fault then triggered the activity of the co seismic strike slip fault that was formed in the 2008 wenchuan event the seismic interpretation focal mechanism solutions and aftershock distribution indicate that two sub segment faults with different geometries are distinguished along the northern lms accordingly a transformation of the coseismic fault with different geometry and kinematics is formed with the constraints that the mainshock and aftershocks occurred on two different faults we propose that both the frontal ramp thrust fault and the recently formed strike slip fault are tectonically active this study highlights the importance of the influence of the pre existing fault system on the evolution of the northern lms during the late cenozoic the rapid uplift of the eastern tibetan plateau and the complex fault system indicate the potential for seismic risks in the northern lms

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

characteristics of the fault related rocks fault zones and the principal slip zone in the wenchuan earthquake fault scientific drilling project hole 1 wfsd 1 abstract scientific drilling in active faults after a large earthquake is ideal to study earthquake mechanisms the wenchuan earthquake fault scientific drilling project wfsd is an extremely rapid response to the 2008 ms 8 0 wenchuan earthquake which happened along the longmenshan fault eastern margin of the tibetan plateau in order to better understand the fault mechanism and the physical and chemical characteristics of the rocks the wfsd project will eventually drill 5 boreholes along the two main faults this paper focuses on the first hole wfsd 1 which started just 178 days after the earthquake down to a final depth of 1201 15 m petrological and structural analyses of the cores allowed the identification of fault related rocks in the yingxiu beichuan fault fault gouge cataclasite and fault breccia and the principle slip zone psz location of the wenchuan earthquake was determined we found 12 fault zones in the entire core profile with at least 10 including the yingxiu beichuan fault zone with a multiple cores structure and minimum width of 100 m the co seismic slip plane of the wenchuan earthquake at depth corresponding to the yingxiu beichuan fault zone at the outcrop as well as its psz was expected to be located at the bottom of the fault zone at 759 m depth instead it was found at 590 m depth with 1 cm wide fresh fault gouge as determined by logging data such as temperature natural gamma ray p wave velocity and resistivity combined with the fresh appearance magnetic susceptibility and microstructure of the gouge the wenchuan earthquake slip plane has a dip angle of 65 showing the high angle thrust feature the distribution of fault gouge with several meters thick the location of the wenchuan earthquake s psz and the thickness of fresh gouge all imply a correlation between the width of the fault zone and the number of seismic events

using two dimensional hydrodynamic models at scales of ecological importance modeling of flow features that are important in assessing stream habitat conditions has been a long standing interest of stream biologists recently they have begun examining the usefulness of two dimensional 2 d hydrodynamic models in attaining this objective current modeling practices consider relatively long channel sections with their bathymetry represented in terms of large macro scale topographic features meso scale topographic features such as boulders root wads and other obstructions are typically not considered in the modeling process instead the overall effects of these flow obstructions are captured through increased values in the channel roughness parameters such an approach to 2 d modeling allows one to accurately predict average depth and velocity values however it is not capable of providing any information about the flow patterns in the vicinity of these obstructions biologists though have known that such meso scale features and the complex velocity patterns generated by their presence play an important role in the ecology of streams and thus cannot be ignored it is therefore evident that there is a need to develop better tools capable of modeling flow characteristics at scales of ecological importance the purpose of this study is to expand the utility of 2 d hydraulic models to capture these flow features that are critical for characterizing stream habitat conditions there exists a paucity of research addressing what types of topographic features should be included in 2 d model studies and to what extent a boulder or series of exposed boulders can influence predicted flow conditions and traditional useable habitat computations moreover little research has been performed to evaluate the impact mesh refinement has on model results in natural streams numerical simulations based on a natural river channel containing several large boulders indicate that explicitly modeling local obstructions boulders can significantly impact predicted flow parameters the presence of these obstructions create velocity gradients velocity shelters transverse flows and other ecologically important flow features that are not reproduced when their geometry is not incorporated into the hydraulic model sensitivity analyses show that reducing element sizes in the vicinity of obstructions and banks is crucial in modeling the spatial flow patterns created by meso scale topographic features this information combined with similar data obtained in future studies can provide guidelines for the placement of fishrocks and other structures often used in stream restoration projects as well as determining what types of mesoscale topographic features might need to be incorporated into habitat suitability studies such information may also ultimately allow new spatial habitat metrics to be developed q 2000 elsevier science b v all rights reserved

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

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

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

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

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

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

a passive probe for subsurface oceans and liquid water in jupiter s icy moons abstract we describe an interferometric reflectometer method for passive detection of subsurface oceans and liquid water in jovian icy moons using jupiter s decametric radio emission dam the dam flux density exceeds 3000 times the galactic background in the neighborhood of the jovian icy moons providing a signal that could be used for passive radio sounding an instrument located between the icy moon and jupiter could sample the dam emission along with its echoes reflected in the ice layer of the target moon cross correlating the direct emission with the echoes would provide a measurement of the ice shell thickness along with its dielectric properties the interferometric reflectometer provides a simple solution to sub jovian radio sounding of ice shells that is complementary to ice penetrating radar measurements better suited to measurements in the anti jovian hemisphere that shadows jupiter s strong decametric emission the passive nature of this technique also serves as risk reduction in case of radar transmitter failure the interferometric reflectometer could operate with electrically short antennas thus extending ice depth measurements to lower frequencies and potentially providing a deeper view into the ice shells of jovian moons

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

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

radar attenuation in europa s ice shell obstacles and opportunities for constraining the shell thickness and its thermal structure young surface and possible recent endogenic activity make europa one of the most exciting solar system bodies and a primary target for spacecraft exploration future europa missions are expected to carry ice penetrating radar instruments designed to investigate its subsurface thermophysical structure several authors have addressed the radar sounders performance at icy moons often ignoring the complex structure of a realistic ice shell here we explore the variation in two way radar attenuation for a variety of potential thermal structures of europa s shell determined by reference viscosity activation energy tidal heating surface temperature and shell thickness as well as for low and high loss temperature dependent attenuation model we found that i for all investigated ice shell thicknesses 5 30 km the radar sounder will penetrate between 15 and 100 of the total thickness ii the maximum penetration depth varies laterally with deepest penetration possible through cold downwellings iii direct ocean detection might be possible for shells of up to 15 km thick if the signal travels through cold downwelling ice or the shell is conductive iv even if the ice ocean interface is not directly detected penetration through most of the shell could constrain the deep shell structure through returns from deep non ocean interfaces or the loss of signal itself and v for all plausible ice shells the two way attenuation to the eutectic point is 30 db which shows a robust potential for longitudinal investigation of the ice shell s shallow thermophysical structure

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

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

filtering the signature of submerged large woody debris from bathymetry data modeling water velocities and depth for riverine aquatic habitat analysis requires fine scale surveys of river bathymetry the presence of submerged large woody debris lwd distorts the results of acoustic bathymetry surveys and subsequent modeling if the lwd data is not separated from the background river bathymetry submerged lwd typically appears in digital acoustic data for a low gradient sand bed river as impulse spikes of a few data points with a substantially shallower depth than the surrounding data this paper examines the performance of linear and nonlinear filtering algorithms for removing impulse spikes from a digital bathymetry signal a synthesized data set is used for control tests that quantify the error associated with each method the more successful nonlinear filtering techniques median and erosion filters are used to filter single beam echosounder data from the sulphur river in northeastern texas usa median filtering proved to be the best technique for removing lwd impulse spikes while leaving the background bathymetry relatively unchanged efficient automation of spike removal from a data set requires a method for selecting the filter characteristics without recourse to engineering judgment or prior experience a method of a priori selecting the minimum filter order based upon the physical scales of the lwd and the statistics of the data separation in the survey is proposed based on scaling analysis and validated with the study results

on the evolution of seismogenic faults in the longmen shan eastern tibet abstract a fundamental debate exists regarding the geometry and depth extent of seismogenic faults in eastern tibet along the longmen shan geologic and seismic reflection data reveal a belt of low to moderate angle thrust faults some of which may have been activated in devastating earthquakes in 2008 mw 7 9 wenchuan and 2013 mw 6 6 lushan however geologic and geodetic constraints on these ruptures suggest rupture along relatively high angle listric reverse faults here we use a combination of focal mechanisms determined from 276 aftershocks ms 4 0 with well determined waveforms and aftershock distributions from the 2008 event to determine subsurface fault geometry our results imply that seismogenic slip occurred along relatively high angle structures that cross cut low angle imbricate faults imaged in reflection seismic data thus we suggest that current geometric models of seismogenic faults may not fully represent the distribution of subsurface seismic hazard along the heavily populated sichuan basin

a coherent method for simulating active and passive radar sounding of the jovian icy moons the possibility to apply passive radar sounding techniques to the jovian icy moons making use of jupiter s strong decametric emissions dams has recently garnered large research interest in this article we propose a radar sounding simulation approach being able to simulate and compare passive and active acquisitions for a given scenario the proposed simulator is based on the stratton chu integral used with the linear phase approximation on triangular facets the external field is modeled with plane waves the direction polarization and amplitude of which can be freely chosen the time domain dependence can be either synthetically generated e g gaussian white noise or taken from experimental measurements e g waveforms recorded by a radio telescope observing jupiter for passive sounding both autocorrelation and cross correlation processing are considered validation tests were conducted on a series of ideal digital elevation models dems such as flat surfaces and subsurfaces or gaussian rough surfaces and a good agreement with the existing literature was obtained to illustrate the capabilities of the proposed simulator we conducted additional more realistic experiments of radar sounding simulations where we use both white noise and jovian waveforms recorded by the lwa1 radio telescope

three dimensional surface displacement of the 2008 may 12 sichuan earthquake china derived from synthetic aperture radar evidence for rupture on a blind thrust summary the sichuan earthquake mw 7 9 struck the longmen shan lms range front china on 2008 may 12 affecting an area of moderate historical seismicity where little active shortening has been previously reported recent studies based on space geodesy have succeeded in retrieving the far field surface displacements caused by the earthquake but the near field 25 km from the faults coseismic surface displacement is still poorly constrained thus shallow fault geometry and shallow coseismic slip are still poorly resolved here for the first time for this earthquake we combine c and l band synthetic aperture radar offsets data from ascending and descending tracks to invert for the 3 d surface displacement in the near coseismic field of the sichuan earthquake our data coupled with a simple elastic dislocation model provide new results strongly suggesting the presence of a blind thrust striking along the range front and being active at depth during the earthquake the presence of a rupture on a blind thrust brings new evidence for an out of sequence thrusting event and new elements for interpreting the tectonic strain partitioning in the lms which has important implications both for seismic hazard assessment and long term evolution of the mountain belt

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

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

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

late quaternary paleoseismic behavior and rupture segmentation of the yingxiu beichuan fault along the longmen shan fault zone china late quaternary rupture behavior of large earthquakes along the yingxiu beichuan fault and the longmen shan fault zone has been the focus of geoscientists since the 2008 wenchuan earthquake however most studies have concentrated on the southern segment of the fault from yingxiu to beichuan here we opened trenches and used borehole drilling in guixi and pingxi along the northern segment north of beichuan with the following paleoseismic results 1 trenches at pingxi and guixi reveal that at least one paleoseismic event occurred prior to the 2008 wenchuan earthquake with ages of 770 955 a d and 665 1030 a d determined at the two locations respectively this event is possibly associated with a historical earthquake documented from 16 november to 15 december of 942 a d furthermore the trench and boreholes at guixi may reveal another paleoseismic event occurred at 8240 7785 b c 2 the northern segment north of beichuan of the seismogenic structure of the 2008 wenchuan earthquake ruptured independently from the southern segment specifically the southern segment records three events within the past 6000 years whereas the northern segment shows a different rupture behavior we suggest that the yingxiu beichuan fault can be divided into at least two rupture segments

amounts and styles of coseismic deformation along the northern segment of surface rupture of the 2008 wenchuan mw 7 9 earthquake china abstract the may 12 2008 mw 7 9 wenchuan earthquake occurred along the longmen shan fault zone a thrust fault zone on the eastern margin of tibet plateau and ruptured the ground surface for more than 200 km a field investigation suggests that the earthquake also ruptured the northern segment from beichuan to qingchuan along which active evidence had been less identified before 75 95 km long this rupture commonly presents a relatively simple 1 to 6 m high scarp with folding and tension cracks along the crest and with minor deformation on both the hanging wall and the footwall the maximum measured vertical and dextral displacements along this segment are 9 0 m and 3 0 m respectively the amounts of the vertical coseismic displacements decrease from southwest to northeast but the amounts of the dextral displacements increase toward the northeastern end of the rupture the surface rupture apparently terminates as mainly strike slip faulting at the northeastern end the observable rupture zone is about 75 km long between beichuan and shuiguan showing mainly thrust slip with a component of dextral strike slip dipping nw at an angle of 54 84 the surface deformation along this segment is classified into five characteristic styles that range from pure thrusting a mixture of thrust and dextral slip to pure dextral slip the amount of shortening is estimated to be minor 0 2 1 0 m

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

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

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