a bound on the rheology of continental lithosphere using very long baseline interferometry the velocity of south china with respect to eurasia very long baseline interferometric vlbi measurements using the antenna near shanghai china between 1987 and 1994 show that this site moves at 8 0 5 mm yr 1 in the direction n116 5 e 4 1 with respect to vlbi sites in europe on the eurasia plate independent measurements of the site at shanghai with respect to sites on nearly all major plates eurasia north america pacific australia and africa determine this velocity south china translates east southeast relative to eurasia more slowly than 20 of india s roughly 50 mm yr convergence rate with eurasia and hence accommodates only a small fraction of india s penetration into eurasia apparently crustal thickening absorbs most of india s convergence the relatively low speed of south china supports treatments of continental lithosphere as a thin viscous sheet whose strength is governed primarily by power law creep in the upper mantle and not by friction in the crust

calculating velocity fields across plate boundaries from observed shear rates summary a general horizontal velocity field can be expressed uniquely in terms of the velocities at points along a line and an integral function of the 2 d shear rate consequently the relative motion across a plate boundary can be calculated from observed shear rates by taking the velocities along a line within one of the plates to be zero

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

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

kinematics of active deformation in the sulaiman lobe and range pakistan the western margin of the indian plate is highly oblique to the direction of convergence between india and asia and represents an excellent example of large scale oblique continent continent collision determining the strain field in western pakistan and how it relates to the plate motion and plate margin geometry affords an exceptional opportunity for understanding oblique margin processes in general through the inversion of regional and teleseismic body waves we have determined the source parameters of 10 moderate sized earthquakes that occurred between 1964 and 1985 in and around the sulaiman range pakistan the earthquakes are dominantly thrust events with slip vectors that are approximately perpendicular to the lobate sulaiman mountain front slip vector orientations rotate 60 70 from a n s to a wnw ese direction of compression consistent with the geometries of the complex festoon shaped mountain belts of this margin we have estimated the spatial variation of the horizontal strain rate and velocity fields within sulaiman using vertically averaged models that accommodate plate motion constraints within a deforming layer the most important factors determining the style of strain rotation in the sulaiman lobe and range are the presence of pure strike slip motion along the chaman fault and the relatively rigid and undeformed katawaz basin that is therefore allowed to translate obliquely relative to india this same conclusion is obtained using either a three dimensional frictional analogue model with significant basal tractions or a thin sheet viscous numerical model without basal tractions thrusting in a predominantly nw se direction in the sulaiman range accommodates 5 14 mm yr of n s motion between india eurasia and 3 6 mm yr of e w shortening seismic moment release this century within the india eurasia plate boundary zone west of the western himalayan syntaxis constitutes roughly 40 of the expected total seismic moment release for this time period particularly significant moment rate deficits exist within the sulaiman range and along the chaman fault

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

block modeling with connected fault network geometries and a linear elastic coupling estimator in spherical coordinates geodetic observations of interseismic deformation provide constraints on the partitioning of fault slip across plate boundary zones the spatial distribution of both elastic and inelastic strain accumulation and the nature of the fault system evolution here we describe linear block theory which decomposes surface velocity fields into four components 1 plate rotations 2 elastic deformation from faults with kinematically consistent slip rates 3 elastic deformation from faults with spatially variable coupling and 4 homogeneous intrablock strain elastic deformation rates are computed for each fault segment in a homogeneous elastic half space using multiple optimal planar cartesian coordinate systems to minimize areal distortion and triangular dislocation elements to accurately represent complex fault system geometry block motions fault slip rates elastic coupling and internal block strain rates are determined simultaneously using a linear estimator with constraints from both geodetically determined velocity fields and geologic fault slip rate estimates we also introduce algorithms for efficiently implementing alternative fault network geometries to quantify parameter sensitivity to nonlinear perturbations in model geometry

magnitude of late quaternary left lateral displacements along the north edge of tibet images taken by the earth observation satellite spot of the quaternary morphology at 18 sites on the 2000 kilometer long altyn tagh fault at the north edge of tibet demonstrate that it is outstandingly active long term left lateral strike slip offsets of stream channels alluvial terrace edges and glacial moraines along the fault cluster between 100 and 400 meters the high elevation of the sites mostly above 4000 meters in the periglacial zone suggests that most offsets resulted from slip on the fault since the beginning of the holocene these data imply that slip rates are 2 to 3 centimeters per year along much of the fault length and support the hypothesis that the continuing penetration of india into asia forces tibet rapidly toward the east

the neotectonics of the tibetan plateau part of the continuing northward convergence between india and eurasia is probably taken up by strike slip displacement with tibet as a whole moving eastward away from the collision zone and undergoing east west extension molnar and tapponnier 1975 ni and york 1978 on the basis of our interpretation of landsat images we propose that strike slip faulting occurs throughout the tibetan plateau such that its north south cross section is being shortened with little contemporary folding or thrusting

a model for tectonic rotations about a vertical axis abstract the rotation of a rigid ellipsoidal inclusion within a highly viscous fluid orientated so that two of the principal axes remain horizontal is used as a model for the rotation of crustal inclusions in wide zones of continental deformation this model is also applicable to other geological problems involving the rotation of inclusions in a matrix the pattern of behaviour in such a model is shown to be complex in general the rotation rate of the inclusion is a function of all components of the velocity field of the deforming medium and the horizontal aspect ratio of the inclusion however for a given velocity field this aspect ratio must exceed a critical value before the inclusion can rotate continuously inclusions with lower aspect ratios will rotate for a certain range of orientations in an opposite direction to the sense of shear in the deforming zone the possibility of the inclusion changing shape during rotation adds to the complexity of behaviour

source parameters for 11 earthquakes in the tien shan central asia determined by p and sh waveform inversion the tien shan mountain belt of central asia was formed in late paleozoic time and reactivated in tertiary time following the collision of india with eurasia more than 1500 km to the south to study the style and distribution of faulting occurring today in the tien shan we digitized long period world wide standard seismograph network p and sh waveforms of 11 of the largest tien shan earthquakes between 1965 and 1982 and then used a least squares inversion routine to constrain their fault plane solutions and depths four of the earthquakes occurred near the southern edge of the tien shan and two occurred in the intermontane fergana basin these earthquakes occurred at depths of 10 20 km and are associated with thrust faulting on east west to southwest northeast striking fault planes that dip moderately 35 55 the other five earthquakes in the northern tien shan were mostly deeper 15 44 km and the fault plane solutions of four of them are similar to the events farther south the exception an event on june 2 1973 probably occurred on a gently northward dipping east west striking fault plane all events occur within the basement at depths of 10 km or greater waveforms for earthquakes near the edges of the dzungarian fergana and kucha basins are fit best using velocity structures with thick sediment layers implying that sediments from these basins have been and are being underthrust beneath the neighboring mountains we examined only the relatively small mb 5 5 6 2 events after 1965 and did not study any of the largest events ms 8 that occurred in the tien shan earlier in this century still we can conclude that north south shortening is presently occurring in the tien shan with the formation of basement uplifts flanked by moderately dipping thrust faults the present day tectonics of the tien shan seem to be analogous to those of the rocky mountains in colorado wyoming and utah during the laramide orogeny in late cretaceous and early tertiary time

late quaternary slip rates across the central tien shan kyrgyzstan central asia 1 slip rates across active faults and folds show that late quaternary faulting is distributed across the central tien shan not concentrated at its margins nearly every intermontane basin contains neogene and quaternary syntectonic strata deformed by holocene north south shortening on thrust or reverse faults in a region that spans two thirds of the north south width of the central tien shan slip rates on eight faults in five basins range from 0 1 to 3 mm yr fault slip rates are derived from faulted and folded river terraces and from trenches radiocarbon optically stimulated luminescence and thermoluminescence ages limit ages of terraces and aid in their regional correlation monte carlo simulations that sample from normally distributed and discrete probability distributions for each variable in the slip rate calculations generate most likely slip rate values and 95 confidence limits faults in basins appear to merge at relatively shallow depths with crustal scale ramps that underlie mountain ranges composed of pre cenozoic rocks the sum and overall pattern of late quaternary rates of shortening are similar to current rates of north south shortening measured using global positioning system geodesy this similarity suggests that deformation is concentrated along major fault zones near range basin margins such faults separated by rigid blocks accommodate most of the shortening in the upper crust index terms 8107 tectonophysics continental neotectonics 9320 information related to geographic region asia 8010 structural geology fractures and faults

focal depths and fault plane solutions of earthquakes and active tectonics of the himalaya synthetic seismograms were compared with long period body waves for nine earthquakes with epicenters in the himalayan arc to determine depths of foci and to improve fault plane solutions focal depths are shallow 10 20 km inferred slip vectors are locally perpendicular to the mountain range they plunge very gently about 10 deg in the eastern sections of the range and more steeply about 25 deg in western sections assuming india to be a rigid plate the radially oriented slip vectors imply that southern tibet extends at about half the rate of underthrusting in the himalaya and therefore probably at about 5 10 mm yr the shallow depths and gentle dips of the fault planes at least for the events in the eastern half of the range are consistent with coherent underthrusting of the indian plate beneath at least the lesser himalaya the steeper dips of fault planes in the western part of the arc might reflect deformation of the overriding thrust plate or simply a steepening of the main underthrusting zone beneath the greater himalaya

fault plane solutions of earthquakes and active tectonics of the tibetan plateau and its margins summary fault plane solutions of earthquakes within and on the margins of the tibetan plateau show diverse styles of faulting and deformation with thrust faulting and crustal shortening normal to the margins of the plateau and with normal and strike slip faulting resulting in roughly east west crustal extension within the plateau the direction of overthrusting of the himalaya onto the indian shield is radially outward varying from southwest in the western himalaya to south southeast in the east assuming that the indian shield behaves rigidly this requires a west northwest divergence of western tibet from southeastern tibet at a rate of 18 9 mm yr 1 comparable with the rate of convergence at the himalaya fault plane solutions of earthquakes in the southern portion of the tibet plateau consistently show large components of normal faulting on roughly north striking planes and corroborate such extension within the high plateau where elevations exceed 5000 m normal and strike slip faulting occur so that an overall east southeast west northwest extension of the region at about 10 mm yr 1 is partitioned into roughly equal parts of crustal thinning and north northeast south southwest crustal shortening about 5 mm yr 1 in general strike slip faulting characterizes solutions for earthquakes within eastern tibet where mean elevations drop below 4500 5000 m but the orientations of the strike slip faults vary across the region in central tibet left lateral slip occurs on planes trending roughly northeast but for earthquakes farther east the orientations of that plane become progressively east west and then southeast this variation in orientation implies a rotation of material along curved left lateral shear zones thus the eastward extrusion of tibet appears to be facilitated not only by rapid left lateral shear but also by large clockwise rotations of the material in eastern tibet the rate of eastward extrusion of material in eastern tibet relative to the tarim basin to its north is roughly 30 40 mm yr 1 fault plane solutions of earthquakes in the northern and eastern margins of tibet show large components of thrust faulting with the p axes oriented radially outward from the plateau and approximately perpendicular to the regional topographic contours of the plateau the orientation of this crustal shortening is northeast southwest on the northeastern margin east west on the eastern margin and northwest southeast in the longmenshan on the southeastern margin thus at least some of the extrusion of eastern tibet out of india s northward path into asia is absorbed by crustal shortening on the margins of the plateau the variation from normal faulting in the high tibetan plateau where elevations exceed 5000 m to dominantly strike slip faulting farther east where elevations are lower and then to thrust faulting on the margins of the plateau where elevations drop below 3000 m surely results at least in part from a decrease in the value of the vertical stress the magnitude of the east west compressive stress need not vary across the plateau

structural petrological and thermal evolution of a tertiary ductile strike slip shear zone diancang shan yunnan the diancang shan a horst massif within the red river fault zone in yunnan people s republic of china preserves a structural petrological and thermal record of two distinct phases of tectonic activity a left lateral ductile shear that terminated between 20 and 17 ma and a ductile to brittle phase of normal faulting which began at 4 7 ma and remains active mylonitic rocks in the core of the range display an early steep high temperature ht schistosity and a horizontal stretching lineation that are both parallel to the trend of the belt kinematic indicators indicate that shear was left lateral the complex shape of the ht schistosity at the southern termination of the massif likely results from a large scale oblique left lateral c shear plane that dismembered the shear zone and separated the ailao shan and the diancang shan as left lateral deformation terminated thermochronological and thermobarometric results suggest that the gneisses were partially unroofed during this event along the eastern edge of the diancang shan the ht fabrics were overprinted by low temperature structures during activation of east dipping normal faults cooling associated with this normal right lateral faulting along the diancang shan and perhaps activation of the right lateral normal movement on the range front fault farther south along the ailao shan began at 4 7 0 1 ma these results tend to support the view that extrusion of indochina occurred along the left lateral red river shear zone between 35 and 19 17 ma initiation of right lateral normal slip during the late miocene may relate to eastward extensional collapse of the thickened tibetan crust or more probably to initiation of the second phase of extrusion

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

evidence of nonlinear elasticity of the crust from the mw7 6 manyi tibet earthquake satellite synthetic aperture radar sar interferometry shows that the magnitude 7 6 manyi earthquake of 8 november 1997 produced a 170 kilometer long surface break with up to 7 meters of left lateral slip reactivating a n76 e quaternary fault in western tibet the radar interferometric map reveals asymmetric along strike displacement profiles between the two sides of the surface rupture a pattern that cannot be explained with linear elastic theory this observation suggests that the elastic moduli of the crust in tension and in compression are different because of the presence of cracks in the crust at shallow depth a model indicates that a ratio of 2 between compressive and tensile elastic moduli can account for the observed asymmetry a ratio that is consistent with laboratory and borehole measurements

velocity field in asia inferred from quaternary fault slip rates and global positioning system observations we perform a joint inversion of quaternary strain rates and 238 global positioning system gps velocities in asia for a self consistent velocity field the reference frames for all geodetic velocity observations are determined in our inversion procedure india in moves relative to eurasia eu about a pole of rotation at 29 78 n 7 51 e 0 353 myr 1 which yields a velocity along the himalaya within india that is 73 76 of the magnitude of the in eu nuvel 1a velocity and a vector azimuth that is 8 10 clockwise of nuvel 1a in eu vector azimuth relative to eurasia south china moves at 9 11 mm yr in the direction 110 120 with a pole position 64 84 n 156 74 e 0 12 myr 1 amurian block motion has a pole position in a similar location but at a slower rate 64 61 n 158 23 e 0 077 myr 1 and most of the amurian eurasia motion is accommodated by extension across lake baikal tarim basin moves relative to eurasia about a pole of rotation at 39 24 n 98 2 e 0 539 myr 1 and 16 18 mm yr of shortening is accommodated across the west central tien shan there is distributed e w extension throughout both southern and north central tibet within southern tibet between the longitudes of 77 e to 92 e the deformation field accommodates 16 19 mm yr of e w extension we compare predicted seismic moment rates with those observed in this century in asia total observed seismic moment rates within the entire area of central and east asia 2 2 107 km2 in this century are 2 26 0 7 1020 n m yr 1 as compared with a predicted total rate of 2 03 0 066 1020 n m yr 1 comparisons between observed and predicted moment rates within 42 subregions reflect the generally unstable process of inferring long term seismic moment rates from a catalog of limited duration 94 years an observation period of 10 000 years would be required to reduce uncertainties in observed seismic moment rate to the same size as the uncertainties in model tectonic moment rates inferred from the joint inversion of gps and quaternary rates of strain we show that in general a better correlation with model tectonic moment rate is inferred from the seismicity catalog by considering the numbers of earthquakes above a cutoff magnitude mb 5 0 for the period january 1 1965 to january 1 1999

intraplate deformation in the japanese islands a kinematic study of intraplate deformation at a convergent plate margin relative motions within the deforming japanese islands with respect to the sea of japan are determined using earthquake records over the last 414 years slip rates on quaternary faults and angular change rates obtained from triangulation in the last century we use a least squares inversion method to match the strain rates on the surface of the earth with continuous spline functions to recover the velocity gradient tensors the directions of the principal strain axes obtained from seismic geological and geodetic data are in general agreement with each other with the maximum shortening axis oriented in a wnw direction principal strain rate magnitudes obtained from the geodetic data are about 3 5 times larger than the principal strain rates obtained from the seismic and geological data intraplate deformation in southwestern japan determined from the seismic data accommodates a velocity of5 5 2 l mm yr in a direction parallel to the nankai trough which is about 25 of the plate motion velocity component parallel to the nankai trough between the philippine sea and eurasian plates in northern honshu the velocity vectors from the seismic data are nearly parallel to the plate motion vector at the japan trench and the intraplate deformation accommodates about 6 of the total pacific eurasian or north american plate motion velocity the velocity vector at kashima northern honshu calculated from the geodetic data is about 9 12 mm yr in a direction of n55 w n76 w which is about half of the very long baseline interferometry velocity calculated in the eurasian reference frame suggesting that the sea of japan may not be rigidly attached to the assumed rigid eurasian plate

on the consistency of earthquake moment rates geological fault data and space geodetic strain the united states new and dense space geodetic data can now map strain rates over continental wide areas with a useful degree of precision stable strain indicators open the door for space geodesy to join with geology and seismology in formulating improved estimates of global earthquake recurrence in this paper 174 gps vlbi velocities map united states strain rates of 30 0 10 8 yr 1 with regional uncertainties of 5 to 50 per cent kostrov s formula translates these strain values into regional geodetic moment rates two other moment rates m seismic and m geologic extracted from historical earthquake and geological fault catalogues contrast the geodetic rate because m geologic m seismic and m geodetic derive from different views of the earthquake engine each illuminates different features in california the ratio of m geodetic to m geologic is 1 20 the near unit ratio points to the completeness of the region s geological fault data and to the reliability of geodetic measurements there in the basin and range northwest and central united states both m geodetic and m seismic greatly exceed m geologic of possible causes high incidences of understated and unrecognized faults probably drive the inconsistency the ratio of m seismic to m geodetic is everywhere less than one the ratio runs systematically from 70 80 per cent in the fastest straining regions to 2 per cent in the slowest although aseismic deformation may contribute to this shortfall i argue that the existing seismic catalogues fail to reflect the long term situation impelled by the systematic variation of seismic to geodetic moment rates and by the uniform strain drop observed in all earthquakes regardless of magnitude i propose that the completeness of any seismic catalogue hinges on the product of observation duration and regional strain rate slowly straining regions require a proportionally longer period of observation characterized by this product gamma distributions model statistical properties of catalogue completeness as proxied by the ratio of observed seismic moment to geodetic moment i find that adequate levels of completeness should exist in median catalogues of 200 to 300 year duration in regions straining 10 7 yr 1 comparable to southern california similar levels of completeness will take more than 20 000 years of earthquake data in regions straining 10 9 yr 1 comparable to the southeastern united states predictions from this completeness statistic closely mimic the observed m seismic to m godetic ratios and allow quantitative responses to previously unanswerable questions such as what is the likelihood that the seismic moment extracted from an earthquake catalogue of x years falls within y per cent of the true long term rate the combination of historical seismicity fault geology and space geodesy offers a powerful tripartite attack on earthquake hazard few obstacles block similar analyses in any region of the world

geodetic evidence for a low slip rate in the altyn tagh fault system the collision between india and asia has been simulated with a variety of computational models that describe or predict the motions of the main faults of east asia geological slip rate estimates of 20 30 mm yr 1 suggest that the largest of these faults the 2 000 km long altyn tagh fault system on the northern edge of the tibetan plateau absorbs as much of the indo asian convergence signal as do the himalayas partly by oblique slip and partly by contraction and mountain growth however the predictions of dynamic models for asian deformation and the lower bounds of some geological slip rates estimates 3 9 mm yr 1 refs 7 8 suggest that the altyn tagh system is less active here we report geodetic data from 89 91 degrees e that indicate left lateral shear of 9 5 mm yr 1 and contraction of 3 1 mm yr 1 across the altyn tagh system this result combined with our finding that at 90 degrees e tibet contracts north south at 9 1 mm yr 1 supports the predictions of dynamic models of asian deformation

multiple mineralization events of the paleozoic tuwu porphyry copper deposit eastern tianshan evidence from geology fluid inclusions sulfur isotopes and geochronology the tuwu porphyry cu deposit located in eastern tianshan nw china is hosted by a plagiogranite porphyry and carboniferous qi eshan group volcanic rocks based on crosscutting relationships and mineral assemblages hydrothermal alteration and mineralization processes at tuwu can be divided into four stages early propylitic alteration stage i porphyry mineralization stage ii overprinting mineralization stage iii and post mineralization stage iv the porphyry mineralization stage stage ii contributed to the majority of the cu mo resource with cu mineralization occurring mainly as quartz chalcopyrite veins stage iii also produced minor cu mineralization characterized by chalcopyrite anhydrite chlorite calcite assemblages fluid inclusion fi study reveals that stage ii is characterized by a high temperature high salinity highly oxidized and k rich h2o nacl cacl2 fluid fluid boiling and mixing likely occurred during the porphyry mineralization stage leading to the precipitation of chalcopyrite and pyrite alteration and mineralization in stage iii were derived from a s rich h2o nacl cacl fluid with fluid boiling leading to the precipitation of chalcopyrite the 34s values of chalcopyrite from stages ii and iii are 0 8 0 6 and 1 1 1 3 respectively suggesting magmatic sources for the ore forming components of both stages 40ar 39ar dating indicates that stage ii likely occurred at 328 1 1 4 ma around the age emplacement of the causative plagiogranite porphyry ca 337 7 330 3 ma we suggest the overprinting mineralization event occurred at ca 323 ma spatially and genetically related to the emplacement of the quartz albite porphyry at 323 6 2 5 ma

the amurian plate motion and current plate kinematics in eastern asia we use global positioning system gps velocity data to model eastern asian plate kinematics out of 15 stations in korea russia china and japan studied here three sites considered to be on the stable interior of the hypothetical amurian plate showed eastward velocities as fast as 9 10 mm yr with respect to the eurasian plate they were stationary relative to each other to within 1 mm yr and these velocity vectors together with those of a few additional sites were used to accurately determine the instantaneous angular velocity euler vector of the amurian plate the predicted movement between the amurian and the north american plates is consistent with slip vectors along the eastern margin of the japan sea and sakhalin which reduces the necessity to postulate the existence of the okhotsk plate the euler vector of the amurian plate predicts left lateral movement along its boundary with the south china block consistent with neotectonic estimates of the displacement at the qinling fault possibly the southern boundary of the amurian plate the amurian plate offers a platform for models of interseismic strain buildup in southwest japan by the philippine sea plate subduction at the nankai trough slip vectors along the baikal rift the boundary between the amurian and the eurasian plates are largely inconsistent with the gps based euler vector suggesting an intrinsic difficulty in using earthquake slip vectors in continental rift zones for such studies

centroid moment tensor solutions for july september 1995 abstract centroid moment tensor solutions are presented for 230 earthquakes that occurred during the third quarter of 1995 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward 1992 acoustical imaging plenum press pp 785 797 a new model of anelastic attenuation of durek and ekstrom 1994 eos trans am geophys union spring meet suppl 75 83 is used to predict the decay of the waveforms

active deformation of asia from kinematics to dynamics using estimated strain rates across the actively deforming region of asia to infer variations in viscous stress it is shown that gradients of stress point uphill toward the center of tibet where gravitational potential energy per unit surface area reaches a maximum thus the dynamics of the deformation seem to obey the equation of creeping flow which expresses a balance between gradients in stress and the gravitational body force this balance in the region of the tibetan plateau yields an estimate of 10 22 pascal second for the average viscosity of the tibetan lithosphere which is only about 10 to 100 times greater than the viscosity of the convecting upper mantle

seismotectonics of the himalayan collision zone geometry of the underthrusting indian plate beneath the himalaya fault plane solutions and well determined focal depths of medium sized earthquakes topography and landsat imagery in conjunction with seismicity maps cross sections and available geological information are used to investigate the present tectonics of the himalayan continental collision zone most of the accurately located epicenters of events along the himalayan arc 78 e 95 e that occurred between 1961 and 1981 are concentrated in a narrow zone about 50 km wide lying between the northerly dipping main boundary mbt and main central mct thrusts most of these events are located just south of the mct though the epicenters of the events are in general well located their depths as determined by teleseismic travel time data are very unreliable events with accurately determined depths obtained from identification of surface reflected phases define a simple planar zone from about 10 km and 20 km depth with an apparent dip of about 15 this result is all the more remarkable considering that the events used were located along about an 1800 km length of the himalyan arc except for one all available focal mechanisms of events within this zone indicate shallow 30 north dipping thrusts this shallow north dipping zone apparently defines a part of the detachment that separates the underthrusting indian plate from the lesser himalayan crustal block the spatial extent and the geometry of this interplate thrust zone strongly indicate that the mbt and nearby subsidiary surface and blind thrusts rather than the mct are currently the most active structures of the himalayan arc we suggest that the great himalayan earthquakes m 8 occur along the same detachment surface as defined by the thrust type medium sized events events located to the south of the mbt and beneath the ganges foredeep show normal faulting with t axes perpendicular to the himalayan trend the above results suggest that the indian continental plate is underthrusting the himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones the november 19 1980 earthquake that occurred near the mct near 88 5 e shows a predominantly strike slip focal mechanism one of the nodal planes of this mechanism is transverse to the himalayan structural grain and moreover this plane has a trend similar to that of the recently mapped yadong gulu rift in the tethyan himalaya and in southern tibet just northeast of the earthquake we interpret this predominantly left lateral strike slip mechanism to indicate a possible genetic relationship between transverse structural features in the underthrusting indian plate the kishangang basement fault and the upper himalayan blocks and tibet

active faulting in and along the qinling range china inferred from spot imagery analysis and extrusion tectonics of south china abstract since the beginning of the india asia collision about 2500 km of convergence has been accommodated by crustal thickening in and around the tibetan plateau and by extrusion of tibetan blocks and of the south china block the relative amounts of convergence accommodated by the two mechanisms are however still largely a matter of debate the main purpose of the present study is to determine the rate of left lateral movement between south china and north china during the late cenozoic this movement is accommodated by offsets along the more than 1000 km long e w trending qinling fault system which separates the south china block from the north china block and terminates to the east in the right lateral ndashs trending tanlu fault zone physiographic features typical of active faulting such as triangular facets along scarps and drainage deviations have been observed on spot images throughout the qinling fault system recent active faulting involves both left lateral strike slip and normal dip slip which are partitioned laterally east of the weihe graben two major faults the luonan and danfeng faults of the qinling fault system slip left laterally a cumulative slip rate of about 7 2 2 2 mm yr between the qinling shan south china and the hua shan north china has been estimated using quaternary morphological offsets in contrast the qinling frontal fault which bounds the cenozoic weihe graben to the south exhibits abundant evidence of normal faulting that accommodated large post early eocene vertical displacement in the graben crustal extension estimated from published seismic profiles and boreholes across the weihe graben contributes to a late cenozoic rate of left lateral movement of 2 0 5 mm yr in a n140 e direction between the hua shan and the ordos block combining these yields a rate of left lateral movement of 8 5 2 5 mm yr in a n100 e direction between south china and the ordos block is achieved additionally the ordos block rotates counterclockwise relative to gobi mongolia resulting in nw se crustal extension along the yinchuandashhetao grabens this is estimated from published seismic sections and adds a component of left lateral movement of 4 1 mm yr in a n125 e direction between south china and gobi mongolia the total rate of left lateral movement of south china with respect to gobi mongolia is 12 4 mm yr in a n110 e direction the eastward decrease of the left lateral strike slip on the active qinling fault system may be explained by the partitioning of left lateral movement on the faults bounding the dabie shan to the south and north and by a book shelf mechanism of counterclockwise rotating blocks separated by active ne sw right lateral faults in the dabie shan

finite element modelling of crustal deformation in the baikal rift zone new insights into the active passive rifting debate abstract the origin of the forces responsible for crustal extension in the baikal rift zone siberia is the object of a debate between passive rifting models where crustal extension is primarily caused by horizontal forces related to the kinematics of asia india eurasia collision and active rifting models where crustal extension is primarily caused by a diapiric mantle upwelling in this work we used a two dimensional visco elastic finite element model in order to determine whether horizontal forces alone can account for the present day deformation in the baikal rift zone we tested a number of kinematic boundary conditions and compared predictions of various models against the observed stress and strain field deduced from seismotectonic data earthquake focal mechanisms and microtectonic analyses by adjusting the kinematic boundary conditions and using a three plate model with a differential displacement between the mongolian and amurian plates we found a best fit model that correctly accounts for the observed strain and stress field over the entire baikal rift zone the fact that our model does not take into account vertical forces but still explains most of the observed deformation suggests that the present day opening of the baikal rift is essentially controlled by horizontal forces related to the regional kinematics these forces could have their origin in the india eurasia collision zone further south this result does not imply that the asthenosphere played no role in the rifting process in particular before the fast rifting stage of the baikal rift evolution 3 4 ma but might suggest a recent plio quaternary triggering effect of the india asia collision on the deformation in the baikal rift

quaternary extension in southern tibet field observations and tectonic implications we summarize evidence for quaternary and active faulting collected in the field during three sino french expeditions to southeastern tibet 1980 1982 detailed mapping of quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the himalayas in the last 2 0 5 m y the maximum horizontal principal stress in south tibet appears to be only the intermediate principal stress 2 1 being vertical south of the chord joining the eastern and western syntaxes of the himalayan arc extensional strains are principally localized within seven regularly spaced rift zones three of which have been studied in some detail the extension direction is determined to be n96 e 7 mainly from statistical averaging of strikes of newly formed normal faults throw rates on normal faults are evaluated for different time spans 2 0 5 m y 60 40 kyr and 10 2 kyr b p using structural and topographic reliefs as well as synglacial and postglacial vertical offsets the rate of quaternary extension is about 1 m y 1 along an 1100 km long ese traverse across south tibet this corresponds to a spreading rate of 1 0 6 cm yr this rate and the divergent horizontal projections of slip vectors of earthquakes along the himalayan front constrain the rate at which rigid india underthrusts southern tibet to be 2 1 cm yr although most of the normal faults appear to be independent of and nearly orthogonal to the e w mesozoic tertiary tectonic fabric the yadong gulu rift appears to be guided for over 130 km by the older oblique ne sw nyainqentanglha range and fault zones along it this reactivated zone is the most prominent left lateral strike slip fault system in se tibet excepting this zone and the vicinity of the se extremity of the karakorum fault quaternary strike slip faulting is rare in south tibet i e south of the chord between the syntaxes of the himalayan arc north of the chord the tectonic style is different there minor conjugate strike slip faulting is widespread and appears to control quaternary normal faulting which is more diffuse and subdued than in south tibet along the chord the presence of a major zone of active right lateral en echelon strike slip faults karakorum jiali fault zone probably reflects the greater facility of eastward extrusion in north central tibet in response to the northward push of india the eastern himalayan syntaxis may be an obstacle to such extrusion movements south of the chord

the kinematics of northern south island new zealand determined from geologic strain rates relative motions within the distributed plate boundary zone of northern south island new zealand are determined through an inversion of geologic strain rate estimates the quaternary fault slip rate estimates define the shear strain rates and rock uplift rates provide information on the horizontal divergence rates an erosion rate to rock uplift rate ratio along with a crustal compensation factor is estimated in order to convert rock uplift rates to horizontal divergence rates because of the uncertainty in erosion rates horizontal divergence rates are given a large standard error of the three horizontal strain rate components obtained from these data completely define the horizontal velocity gradient tensor strain rate distributions are matched with spline polynomial functions which can be constrained to behave rigidly within specified regions such as the pacific or australian plates inversion of the strain rate distribution assuming uniform erosion rates across the northern south island yields a velocity field that has small differences in both magnitude 10 larger and direction with the nuvel 1a plate motion model between pacific and australian plates a revised strain rate data set obtained from a variable erosion model in which erosion rates are a linear function of the log of the average annual rainfall magnitudes yields a velocity field with expected directions that are indistinguishable from the nuvel 1a plate motion model between pacific and australian plates but velocity magnitudes are still 10 15 higher than the plate motion model therefore the average values of slip rate on strike slip faults in marlborough required by the nuvel 1a plate motion model are typically close to the low end of the published range of slip values for those structures the major strike slip structures within the marlborough region are accommodating 80 100 of the total plate motion between australia and pacific plates on northern south island as much as 20 of the relative motion could be accommodated by shear generated by folding or thrust faulting with a single orientation between the major structures the magnitude of plate motion contributed by the major faults indicates that the distributed geodetic shear strains measured across northern south island and discussed by bibby 1981 and walcott 1984 are not a form of irrecoverable strain but rather a feature of the strain field that will eventually be released primarily as concentrated slip on the strike slip structures within the region strain modeling indicates that the earthquake moment release over the last 150 years within the northwest nelson province which is west of the marlborough region is at least half an order of magnitude higher than the long term rate of moment release overall the northwest nelson region is playing only a minor role in taking up the long term plate motion

velocity fields in deforming asia from the inversion of earthquake released strains average strain rates in sectors of deforming asia are matched by a fifth order polynomial function and that function integrated to obtain the relative velocities and rotations occurring within east tibet western sichuan yunnan and south china the method was applied to strain rates obtained from moment tensor summation of both modern and historic earthquakes but can be applied as well to strains obtained from quaternary slip rates on major faults if south china has negligible motion relative to siberia then the velocity results indicate that nearly all of the expected motion between india and the south china portion of eurasia has in the last 85 years been accommodated by distributed intraplate deformation in east burma yunnan western sichuan and east tibet calculations indicate that these regions constitute a zone of distributed right lateral shear that accommodates an overall north south sense of relative motion between east tibet and south china and india and south china line elements parallel to both right lateral and left lateral faults in east burma and western yunnan are rotating clockwise relative to south china with the line elements parallel to left lateral faults rotating most rapidly 2 0 0 5 m y in eastern tibet and the gansu ningxia nw se trending left lateral faults give rotation clockwise relative to south china 1 2 5 m y in central tibet and western sichuan right lateral faults give slight counterclockwise rotation rates relative to south china 0 5 0 75 m y instantaneous rotation rates within the deforming region extrapolated over a 20 40 m y time period are in rough agreement with the paleomagnetic rotations measured in cretaceous aged rocks

observing plate motions in s e asia geodetic results of the geodyssea project this paper presents the final geodetic results of the geodyssea project the gps data from a 42 station network observed during two field campaigns 1994 1996 were analyzed by four groups using different software packages and analysis strategies the precision of both campaign coordinate solutions was found to be 4 7 mm for the horizontal and 1 cm for the vertical component the campaign solutions were merged into one unique solution which was accurately mapped into the itrf 96 reference frame the global accuracy of this solution with respect to itrf 96 is 1 cm while the resolution of the relative horizontal velocities is estimated to be at the level of 2 3 mm yr this solution was used as the basis for all scientific interpretations which are published in separate papers the velocity estimates of a part of the network provided the first direct measurement of a relative motion of the sundaland block with respect to eurasian plate

azimuthal anisotropy of lg attenuation in eastern tibetan plateau 1 the q of seismic phase lg is measured to approach the crustal q which can be used to infer crustal rheology a reverse two station event method is used to measure the interstationqlg which theoretically eliminates effects from the source and site response strong azimuthal anisotropy of 1 qlg in northern tibet is observed which approximately correlates with the seismic velocity anisotropy observed using both surface waves and teleseismic s waves both the intrinsic and scattering attenuation contribute the isotropic q whereas the anisotropic q may be associated with the fractures and faults in the crust strong 1 qlgis observed in the northwestern songpan ganzi fold belt where the high qdirections correspond with the orientations of major strike slip faults intrinsic and scatteringq values are estimated for different tectonic terranes in eastern tibetan plateau the intrinsic qvalues are approximately 500 in the northern tibetan plateau which suggests a hot 700 c crust consistent with low seismic velocity measurements our result suggests that the crust of northwestern songpan ganzi fold belt may be hotter than that of the qiangtang terrane which may be related to the strain heating along the major strike slip fault zones that dominate the northernmost tibet

a thin viscous sheet model for continental deformation summary for the purposes of describing its large scale and long term deformation the continental lithosphere is regarded as a continuum obeying a newtonian or a power law rheology the flow of a thin sheet of power law material overlying an inviscid substrate is studied under the assumption that vertical gradients of the horizontal velocity are negligible a numerical model is used to investigate the deformation of such a sheet under conditions approximating those of continent continent collision the material flows in response to forces applied to its boundaries for example the indenting of one continent by another and to forces in its interior arising from gradients in crustal thickness the horizontal divergence of the flow produces changes in the crustal thickness and hence a time dependent form to the flow itself for a given set of boundary conditions the flow depends on the stress exponent in the power law rheology n and on the argand number which is a measure of the ratio between the stress arising from crustal thickness contrasts and the stress required to deform the material at the ambient strain rates when the effective viscosity of the medium is very high ar o crustal thickness variations do not influence the flow if the material is newtonian n l the deformation associated with an influx of material approximating an indenter is of much greater lateral dimension than the width of the indenter whereas when material has a power law rheology n 3 5 are used the deformation is confined to a region of lateral extent comparable to that of the indenter as ar increases the forces arising from crustal thickness contrasts exert more influence on the flow and the maximum crustal thickness that can be sustained by a given influx of material is related by a simple expression to the effective viscosity of the medium at the ambient strain rates in the limit of a very weak medium ar 10 the lithosphere is unable to sustain appreciable crustal elevation contrasts the results of these numerical experiments show that systems in which the effective viscosities are such that the maximum deviatoric stresses are between 1 kbar

tests of the rigid plate hypothesis and bounds on intraplate deformation using geodetic data from very long baseline interferometry the geodetic results of ma et al 1994 from very long baseline interferometry are used to assess rates of intraplate deformation we analyze the resulting set of velocities of 18 plate interior sites nine on the north american plate four western european sites on the eurasian plate three on the pacific plate and two on the australian plate we formulate three alternative error budgets based partly on the work of ryan et al 1993a an optimistic error budget a conservative error budget and an upper bound error budget all three budgets assume the existence of a previously unmodeled error that is inversely proportional to the time span of observations at a site use of the conservative error budget indicates no significant motion between sites on any one of the four plates use of the upper bound error budget designed to be precisely large enough to be consistent with rigid plates places a usefully small upper bound on how fast any site might be moving relative to the rest of its plate speeds faster than 2 mm yr are excluded at the 95 confidence level for seven of the 18 plate interior sites adjustments of the site velocities for motion due to postglacial rebound as predicted from the model of tushingham and peltier 1991 give an insignificant improvement to the fit of the horizontal velocities to the rigid plate model the velocities of six sites near the western margin of the interior of the north american plate were also analyzed use of the conservative error budget indicates that a site near fairbanks alaska has an upper bound of 3 mm yr on its speed a site in nome alaska has an upper bound on its speed of 8 mm yr and a site in penticton british columbia has an upper bound on its speed of 4 mm yr of three sites on the colorado plateau two move marginally significantly and one moves insignificantly relative to stable north america upper limits on their speeds relative to stable north america range from 4 to 5 mm yr we conclude that the data do not yet demonstrate significant velocities between sites in the stable interior of any one plate but do provide useful and small upper bounds of 2 mm yr or less on the speeds of the best observed intraplate sites six sites near the western margin of the north american interior have upper bound speeds of 3 to 8 mm yr

role of oblique convergence in the active deformation of the himalayas and southern tibet plateau noting similarities with subduction along curved oceanic trenches and using a simple block model we show that radial vergence evident in earthquake slip vectors along the himalayan deformation front east west extension on north trending normal faults in the himalayas and southern tibet and right lateral strike slip on the karakorum jiali fault zone can all result from basal shear caused by the indian plate sliding obliquely beneath tibet along a gently dipping arcuate plate boundary within the framework of this mechanism the normal faults in the himalayas and southern tibet are not proxies for the uplift history of tibet the distribution and style of the faults in the himalayas and southern tibet suggest that the basal drag from the underthrusting indian lithosphere extends northward beneath most of southern tibet

extension in the graben systems around the ordos china and its contribution to the extrusion tectonics of south china with respect to gobi mongolia the graben basins around the ordos block are major tectonic features of late cenozoic extension in north china this paper gives a synthetic view of the basic characteristics of the graben basins and of the kinematics of the graben bounding faults this view is based on the available geological data spot imagery analysis field observations and focal mechanisms of earthquakes from this region these graben basins have been grouped into two major systems the yinchuan hetao graben system along the northern and northwestern margins of the ordos and the weihe shanxi graben system along the southern and eastern margins of the ordos crustal deformation along these graben systems involves normal slip on ne sw striking graben bounding faults normal right lateral and normal left lateral slip on nne ssw and wnw ese striking faults respectively this fault pattern is consistent with nw se trending extension the amount and rate of deformation resulting from this extension have been estimated from geological data using a cross sectional area balance and the extensional factor method deduced from the tilt of faulted blocks the results of these estimates show that the uppermost pliocene quaternary extension rate in a nw se direction is in the order of 1 6 mm yr 1 across the weihe graben 0 5 mm yr 1 across the central shanxi graben on the southeastern margin of the ordos block and 3 1 mm yr 1 across the linhe graben on the northwestern margin of the ordos block the extension across these graben systems is accompanied with counterclockwise rotation of continental blocks in north china ordos taihang shan north china plain a kinematic model is proposed in which the late cenozoic extension and block rotation in north china are interpreted as the effect of the eastward termination of the left lateral slip haiyuan fault and kunlun taibai fault system the ordos block rotates counterclockwise as a result of the push of tibet through the left lateral strike slip haiyuan fault and the liupan shan thrust and fold belt the extension along the weihe shanxi graben system may represent the effect of the left lateral slip on the kunlun taibai qinling fault system the rough estimates of the extensional deformation around the ordos block indicate that this contributes to about 5 2 mm yr 1 of left lateral movement in a n125 e direction between south china and gobi mongolia this motion adds to the left lateral slip on the qinling fault zone about 7 2 mm yr 1 in a n90 e direction between the qinling shan and the hua shan north china thus the eastward motion of south china with respect to gobi mongolia is partitioned between normal faulting around the ordos and strike slip faulting in the qinling shan it is estimated to be in the order of 12 4 mm yr 1 in a n105 e direction during the quaternary

hairpin river loops and slip sense inversion on southeast asian strike slip faults in the golden triangle region of southeast asia northern thailand laos and burma southern yunnan the mekong salween and neighboring rivers show hairpin geometries where they cross active strike slip faults restoration of young left lateral offsets of these rivers leaves residual right lateral bends of many kilometers we interpret these hairpins as evidence of late cenozoic slip sense inversion on these faults about 5 to 20 ma near the red river fault stress field and slip sense inversion occurred ca 5 ma this implies that the present course of these large rivers has existed for at least several million years pliocene quaternary slip rates possibly on the order of 1 mm yr are inferred on each of the strike slip faults of the golden triangle

gps observation of crustal deformation in the taiwan luzon region fifteen gps stations in the batan luzon area were surveyed three times during 1996 to 1998 in order to study crustal deformation in the taiwan luzon region the data from these annual surveys are processed together with data from 20 permanent stations in the taiwan area and igs stations in the asia pacific region we found that the chinese continental margin is moving in directions of 102 112 with rates of 11 12 mm yr relative to stable eurasia there is a significant southward increase in crustal motion with respect to eurasia along the n s trend of the luzon arc in the coastal range of taiwan the velocity is 53 mm yr in the direction 313 further south at two volcanic islands lanhsu and batan the velocities increase to 68 mm yr in the direction 306 and 81 mm yr in the direction 299 respectively in northern luzon the velocity reaches 86 mm yr in the direction 301 remarkable fault slips of 17 31 mm yr across the philippine fault system are detected

earthquake strain rates and instantaneous relative motions within central and eastern asia summary we use the spatial distribution of moment tensors of earthquakes in this century to estimate the velocity field in asia within a eurasian reference frame in a least squares inversion strain rates on the surface of the earth are matched with continuous spline functions in order to recover the velocity gradient tensor associated with the seismic moment release in asia earthquakes account for 40 60 per cent of the expected motion of india relative to eurasia with the missing component of strain rate equivalent to about 20 mm yr 1 of n s shortening between siberia and india in this solution south china rotates counterclockwise and moves eastwards relative to siberia using rigid plate constraints we next investigate the characteristics of the complete horizontal strain field in asia that accommodates plate motions our strain rate solutions are analogous to the response of a newtonian thin viscous sheet in which the rate of work done by the straining medium in accommodating the velocity boundary conditions is a minimum in these solutions the euler pole for india relative to eurasia is constrained nuvel 1a demets et al 1994 but in the process of fitting the vlbi velocity at shanghai china ward 1994 heki et al 1995 the euler pole for south china is determined in the inversion a solution that both fits the velocity at shanghai china and yields a strain rate field consistent with the earthquake mechanisms is one where the south china block has a motion relative to siberia described by the pole at 51 n 131 e 0 3 deg myr 1 comparison of the complete strain field that accommodates plate motion with the seismic strains indicates that earthquake moment release rates in this century within mongolia are about a factor of 4 larger than the long term rate within gansu ningxia the earthquake moment rates have been about a factor of 2 higher than the long term rate the strike slip faulting within mongolia gansu ningxia western sichuan and yunnan is possibly a direct result of velocity boundary conditions imposed on the south china block by forces unrelated to continental collision of india and eurasia such as forces associated with subduction along the margins of south eastern asia verification of this requires a better understanding of the role of pre existing zones of weakness within the asian continental lithosphere

gps determined eastward sundaland motion with respect to eurasia confirmed by earthquakes slip vectors at sunda and philippine trenches abstract gps measurements acquired over southeast asia in 1994 and 1996 in the framework of the geodyssea program revealed that a large piece of continental lithosphere comprising the indochina peninsula sunda shelf and part of indonesia behaves as a rigid sundaland platelet a direct adjustment of velocity vectors obtained in a eurasian frame of reference shows that sundaland block is rotating clockwise with respect to eurasia around a pole of rotation located south of australia we present here an additional check of sundaland motion that uses earthquakes slip vectors at sunda and philippine trenches seven sites of the geodyssea network are close to the trenches and not separated from them by large active faults two at sumatra trench three at java trench and two at the philippine trench the difference between the vector at the station and the adjacent subducting plate vector defines the relative subduction motion and should thus be aligned with the subduction earthquake slip vectors we first derive a frame free solution that minimizes the upper plate or sundaland motion when corrected for australia eurasia and philippines eurasia nuvel1 a motion the misfit between gps and slip vectors azimuths is significant at 95 confidence indicating that the upper plate does not belong to eurasia we then examine the range of solutions compatible with the slip vectors azimuths and conclude that the minimum velocity of sundaland is a uniform 7 10 mm a eastward velocity however introducing the additional constraint of the fit of the geodyssea sites with the australian igs reference ones or tie with the ntus singapore station leads to a much narrower range of solutions we conclude that sundaland has an eastward velocity of about 10 mm a on its southern boundary increasing to 16 18 mm a on its northern boundary

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

potential controls of alluvial bench deposition and erosion in southern piedmont streams alabama usa abstract benches are bank attached channel deposits occurring at an elevation between the channel bed and top of banks their occurrence in a variety of geologic and hydrologic settings has led to confusion about the mechanisms driving their formation which in turn contributes to difficulty identifying the active floodplain bankfull stage and the determination of environmental flows in some rivers hydrodynamic modeling software river 2d in combination with sediment particle size analysis and total station topographic surveys was used to simulate flow conditions needed to erode and deposit the d84 d50 and d15 particle sizes of concave and lateral benches in two rivers talladega and hillabee creeks in alabama results suggest that bench erosion requires flows at least 150 larger than benchfull stage at the talladega site while the hillabee site experienced erosion at all discharges meeting and exceeding benchfull flow stage likely owing to its overall smaller sediment particle sizes at both sites the presence of vegetation increased the bench area subjected to deposition but somewhat counterintuitively also helped influence the location of erosion by limiting flow vectors in contrast with previous research findings the occurrence of reverse flow was neither sustained nor widespread at either site these findings provide new insight into alluvial benches suggest that the study benches are relatively stable features under the prevailing hydrologic regime and that in some temperate climate settings such as the southern piedmont localized hydraulic controls on bench formation can be superseded in importance by hydrologic flow regime even in the case of concave benches and where flow regulation is not a factor

active tectonics of the pamirs and karakorum the source parameters of moderate to large sized earthquakes and the spatial distribution of earthquake hypocenters are used to investigate the active tectonics and three dimensional configuration of the subducted lithosphere in the pamir karakorum intracontinental convergence zone the continental collision has resulted in intense deformation in the upper crust the deformation is distributed over a broad area and is absorbed by thrust and strike slip faulting along the northern margin of the pamirs where the deformation due to continental collision is most intense the northern pamir thrust and several major fault zones mark the present boundary most of the earthquakes that occurred in these fault zones are shallow crustal events with focal mechanism solutions correlated with the tectonic features of the region along the pamir front thrust faulting dominates while on the western and eastern edges of the pamirs the style of deformation is characterized by oblique thrusting with a component of strike slip motion thrust type events beneath the tadjik depression indicate that both the sedimentary rocks and the basement are involved in shortening right lateral strike slip motion is observed on the eastern edge of the pamirs where they border the tarim basin and in the talas fergana kun lun fault zone a southward dipping seismic zone beneath the pamirs and karakorum indicates that the asian lithosphere has been subducted along the pamir front to a depth of at least 200 km this interpretation is consistent with published geological and geophysical data focal mechanism solutions of some intermediate depth events beneath the pamirs show strike slip faulting with approximately n s horizontally oriented p axes indicating that nearly horizontal compression at the intermediate depth is the predominant mode of deformation a 90 km deep event beneath the karakorum is interpreted as occurring in the subducted asian lithosphere the fact that the p axis of this event is oriented parallel to the descending plate suggests downdip compression within the asian lithosphere the overall tectonics of the region is interpreted as a consequence of the underthrusting asian lithosphere being impinged upon by the shallow northward underthrusting indian lithosphere

velocity gradients in the northern indian ocean inferred from earthquake moment tensors and relative plate velocities the region in the northern indian ocean between the central indian ridge the sumatra trench and 15 s to 9 n exhibits high seismicity along with basement and sediment deformation this area represents a diffuse plate boundary between the distinct and separate portions of the indian and australian plates we invert the spatial distribution of horizontal strain rates in this diffuse plate boundary zone to obtain the horizontal velocity field associated with the moment release from 61 earthquakes that have occurred over the past 80 years in the inversion the three dimensional rotation vector function w is determined at all corner points i e knot points of a grid such that the predicted strain rate values match the observed strain rates within the grid areas in a least squares sense the rotation vector of australia relative to india defined by the earthquake data alone is 10 1 s 9 1 81 5 e 5 4 0 1 0 06 m y 1 sigma error which is slightly different in location from the expected vector estimated using seafloor magnetic anomalies and transform fault trends 3 2 s 75 1 e 0 288 m y demets et al 1994a b by minimizing the rate of work within a continuous viscous medium that accommodates australia s motion relative to india demets et al 1994a we determine the complete horizontal velocity gradient tensor within the zone of diffuse deformation the viscosity tensor within all of the deforming areas can be specified when all the regions are free to strain in any direction and have the same viscosity uniform isotropic viscosity the predicted strain pattern is either pure extension or pure compression which is in contrast to the style of earthquake deformation east of chagos where both thrust and strike slip mechanisms are observed however when the isotropic viscosity of regions within the wharton basin is increased relative to the isotropic viscosity levels of areas along the ninetyeast ridge the plate motion is accommodated by combined thrust and strike slip styles of strain along the ninetyeast ridge and within the eastern central indian basin this predicted strain that accommodates plate motion is in agreement both in direction and style with the earthquake related strains in these regions although most of the observed style and direction of strain can be explained by lithospheric strength differences between the wharton basin and ninetyeast ridge areas alone the presence of strike slip faulting within the wharton basin requires a preexisting fabric that favors strike slip faulting there as a strain mechanism that accommodates in part the motion of australia relative to india to first order the direction of principal strain rates the style of strain and the spatial distribution of strain rates from the earthquakes are in accord with the accommodation of the expected plate motion whereas across the plate boundary zone the rates from 80 years of seismicity average out to at most 60 of the total strain rate

the horizontal velocity field in the deforming aegean sea region determined from the moment tensors of earthquakes we use the spatial distribution of seismic moment tensors of earthquakes in the aegean region over the time interval 1909 1983 to recover a continuous horizontal velocity field that describes the overall deformation of the lithosphere at large length scales the calculated velocity field is dominated by two effects 1 an e w right lateral shear of the eastern aegean related to motion on the north anatolian fault becoming distributed as it enters the aegean and 2 a n s extension probably related to the sinking of the slab in the hellenic trench the southern part of the central aegean is found to be moving in a sw direction relative to europe at a rate of about 30 mm yr probably a lower bound with an error of around 10 mm yr and rotating clockwise in the seismogenic upper crust this velocity field is accommodated by right lateral strike slip faults in the eastern aegean and by normal faults that rotate clockwise in central greece a comparison of paleomagnetic declination data with the expected rotation of rigid elongate inclusions in the velocity field shows in most places an agreement in sense and approximate agreement in rate of rotation expected rotation rates of line elements are sometimes too low probably because our derived velocity field is smoothed and unable to match locally high strain rates there is only one part of the region where line elements are predicted to rotate in either clockwise or counterclockwise directions depending on their orientation this is in western turkey which coincident ally is the only place where paleomagnetic rotations in both directions have been observed this coincidence in particular suggests to us that the analogy of rigid elongate inclusions in the velocity field responding to forces on their bases may be useful in predicting the senses and approximate rates of rotation of crustal blocks in deforming continental regions the velocity field we obtain preserves the strike directions of the major faults as directions of zero length change in spite of considerable smoothing we use this observation to speculate that the interaction between the upper crust and the rest of the lithosphere beneath it may involve an interplay of effects on one hand the variation of strength with direction in the crust may control the strike directions of faults that form or become reactivated and may also limit the velocity fields that are allowable on the other hand the fault bounded blocks may rotate in the velocity field in response to forces on their bases which would require the velocity field to change with time if the directions of zero length change are fixed to the blocks

focal depths and fault plane solutions of earthquakes under the tibetan plateau we compare synthetic and recorded p wave forms to place constraints on the focal depths and fault plane solutions of 16 crustal earthquakes beneath the highest parts 4000 m of the tibetan plateau fault plane solutions for all 16 events show combinations of normal and strike slip faulting with t axes oriented approximately east west none of these solutions show thrust faulting thus the data corroborate previous inferences that the active tectonics are dominated by east west extension focal depths for all 16 events are less than 15 km and appear to be between 5 and 10 km this style of deformation and these depths of faulting are similar to those in the basin and range province of the western united states two intermediate depth events below the crust of southern tibet also show primarily normal faulting with east west t axes the solution for one discussed by chen et al 1981 is unambiguous the solution for the other the event of august 1 1973 27 59 n 89 17 e 85 10 km mb 4 9 is less certain both apparently occurred in the mantle beneath a thick aseismic lower crust and their occurrence suggests that brittle deformation occurs there in response to a stress field similar to that operating at shallow depths beneath tibet

joint inversion of observed gravity and gps baseline changes for the detection of the active fault segment at the red river fault zone summary methods for the determination of active fault segments by inversion of temporal gravity and gps global positioning system baseline changes are presented in this paper a numerical test is performed for estimating four types of fault movement models from simulated gravity changes with random noise results of the numerical test show clearly the possibility of detecting fault movement from observed gravity changes based on this work active segments of the red river fault zone rrfz are investigated by inversion of observed gravity changes from 1985 november to 1988 november and gps baseline changes from 1988 august to 1991 october both separately and jointly the results from the joint inversion indicate an active segment of the red river fault characterized by right lateral strike slip 1 0 0 2 m with a length of 232 3 km a width of 6 3 km a dip angle of 100 5 80 5 ne a depth of 10 1 km and a strike direction of 169 2 se these characteristics of the detected active segment at the rrfz agree with those of geological investigations and seismic activity in the area estimated horizontal displacements at the rrfz indicate that drastic movements are concentrated on the northern segment whereas the southern segment of the fault is relatively stable the estimated fault slip rate along strike at the red river fault is 8 11 mm yr 1 larger than the geological estimate of 6 mm yr 1 which implies that the rrfz is presently active the results obtained in this research support previous interpretations that the fault movements at the rrfz are mainly a result of the collision of the indian and the eurasian plates

rupture complexity of the 1970 tonghai and 1973 luhuo earthquakes china from p wave inversion and relationship to surface faulting the source processes of the 4 january 1970 tonghai earthquake m s 7 5 and the 6 february 1973 luhuo earthquake m s 7 5 in southwestern china were investigated using an inversion technique on the very complex body waves the two earthquakes were associated with 48 and 90 km of surficial strike slip rupture respectively and the distribution of displacement with distance along the fault was well documented by field studies of both events the source process for both earthquakes comprised three to four subevents with different moments and rupture durations these calculated parameters agree well with the field observations and aftershock distributions particularly in the total rupture length and in the amount and asymmetry of fault displacements relative to the locations of the main epicenters

the active tectonics of the eastern himalayan syntaxis and surrounding regions source parameters of 53 moderate sized earthquakes obtained from the joint inversion of regional and teleseismic distance long period body waves provide the data set for an analysis of the style of deformation and kinematics in the region of the eastern himalayan syntaxis focal mechanisms of eastern himalayan events show oblique thrust consistent with the n ne directed movement of the indian plate as it underthrusts a boundary that strikes at an oblique angle to the direction of convergence earthquakes near the sagaing fault show strike slip mechanisms with right lateral slip earthquakes on its northern splays however indicate predominant thrusting evidence that the dextral motion on the sagaing fault which accommodates a portion of the lateral motion between india and southeast asia terminates in a zone of thrust faulting at the eastern himalayan syntaxis remaining motion between india and southeast asia is accommodated in a zone of distributed shear in east burma and yunnan manifested by strike slip and oblique normal faulting east west extension crustal thinning and clockwise rotation of crustal blocks we determined strain rates throughout the region with a moment tensor summation using 25 years modern and 85 years modern and historic of earthquake data we matched the observed strains with a fifth order polynomial function and from this we determined both the velocity field and rotations with respect to a specified region velocities calculated relative to south china stationary show that the entire area extending from 20 n 36 n within deforming asia yunnan western sichuan and east tibet constitutes a distributed dextral shear zone with clockwise rotations up to 1 7 m y maximum in the region of the eastern syntaxis proper integrated strains across this zone relative to south china stationary show 38 mm yr 12mm yr of north directed motion at the himalaya remaining plate motion relative to south china fixed must be taken up by the underthrusting of india beneath the lesser himalaya strike slip motion on the sagaing fault and intraplate ne directed shortening within ne india as well as ne directed shortening within the eastern syntaxis proper 10 mm yr 2 mm yr of relative right lateral motion between india and southeast asia is absorbed in the region between the sagaing and red river faults 94 e 100 e it is the clockwise vorticity relative to south china associated with the deformation in yunnan east tibet and western sichuan that provides the relative north directed motion of 38 12 mm yr at the himalaya not all of the deformation is accommodated in right lateral shear between india and south china and between east tibet and south china velocity gradients exist that are parallel to the trend of the shear zone relative to a point within western sichuan 32 n 100 e the velocity field shows that the yunnan crust is moving s se at rates of 8 10 mm yr relative to south china there is no eastward expulsion of crustal material beyond the eastern margin of the tibetan plateau

present day kinematics of asia derived from geologic fault rates active fault geometry available quaternary rates on major faults and the far field plate motion are used to determine crustal kinematics in the collision zone between india and asia using a finite element formalism to construct a spherical shell model of the asian continent with embedded faults we seek a velocity solution approaching the motion of rigid blocks by minimizing the elastic strain energy in the fault bounded blocks by doing so we test the assumption that long term deformation within continents is mostly localized into major faults in the solution fault motion accounts for more than 80 of the deformation allowing us to describe our velocity model in terms of quasi rigid block rotations on the sphere south china is rotating clockwise about a pole located southwest of borneo implying an e ese velocity vector of 11 mm yr for a point at shanghai in agreement with the velocity vector determined by very long baseline interferometry heki et al 1995 the eastward movement of south china is accommodated by oblique extension along the red river fault at a rate of 10 5 mm yr in the south and by the combination of left lateral strike slip motion on the qinling dabie shan fault and the counterclockwise rotation of the ordos and adjacent blocks in the north the tarim rotates clockwise with respect to dzungaria about a pole located at 44 n 92 e consistent with increasing crustal shortening toward the west throughout the tien shan assuming incompressibility a crustal volume budget over a domain encompassing the tertiary mountain ranges in asia shows that over the last 10 000 years 73 4 of the north south shortening between india and asia has been absorbed by thickening of the lithosphere and 27 has been accommodated by lateral extrusion of continental blocks the present day predominance of thickening in asia results from the relatively slow eastward motion of south china controlled by strike slip faulting in the qinling shan and oblique extension in northeastern china

late cenozoic right lateral strike slip faulting in southern tibet field observations collected during the sino french himalaya tibet cooperation project 1980 1982 show that right lateral faulting between southern and northern tibet roughly along the chord joining the eastern and western syntaxes of the himalayan arc is a major component of the active tectonics north of the himalayas just north of the well developed rifts of southern tibet we studied three right lateral 100 200 km long strike slip faults forming an en echelon array along that chord evidence for earthquake surface breaks was found on each of these faults for the m 8 beng co or damxung strike slip earthquake of november 18 1951 rupture parameters could be constrained to be 8 2 m and l 90 km offset glacial and postglacial morphological markers 105 years and 104 years b p imply displacement rates of the order of 1 2 cm yr on the three faults the en echelon fault zone appears to extend westward 2000 km across the plateau to the karakorum fault and is thus referred to as the karakorum jiali fault zone kjfz fast rates of slip on it and on faults along the northern rim of tibet appear to contrast with the slower rates of deformations in the interior of the plateau our estimates of slip rates on the strike slip and normal faults of southeastern tibet suggest that eastward extrusion of north tibet between the right lateral kjfz and the left lateral altyn tagh and kun lun faults absorbs at least 30 of the present convergence between india and asia we propose an instantaneous velocity model of the active tectonics of asia compatible with such faulting rates and geometries evidence for tertiary right lateral strike slip movements in southern tibet and around the eastern syntaxis of the himalayas is also found in the structural record offsets of various large scale geological features imply that these movements have been large

no net rotation model of current plate velocities incorporating plate motion model nuvel 1 we present nnr nuvel1 a model of plate velocities relative to the unique reference frame defined by requiring no net rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model nuvel 1 demets et al 1990 differences between nnr nuvel1 and no net rotation plate motion model am0 2 minster and jordan 1978 are as large as 15 mm yr in nnr nuvel1 the pacific plate rotates in a right handed sense relative to the no net rotation reference frame at 0 67 m y about 63 s 107 e this rotation nearly parallels but is 32 slower than the pacific hotspot euler vector of hs2 nuvel1 which is a global model of plate hotspot velocities constrained to consistency with nuvel 1 gripp and gordon 1990 at hawaii the pacific plate moves relative to the no net rotation reference frame at 70 mm yr which is 25 mm yr slower than the pacific plate moves relative to the hotspots differences between nnr nuvel1 and hs2 nuvel1 are described completely by a right handed rotation of 0 33 m y about 49 s 65 e the 99 confidence ellipsoids for plate hotspot motion in model hs2 nuvel1 exclude the corresponding euler vectors from model nnr nuvell thus the no net rotation reference frame differs significantly from the hotspot reference frame if the difference between reference frames is caused by motion of the hotspots relative to a mean mantle reference frame then hotspots beneath the pacific plate move with coherent motion towards the east southeast alternatively the difference between reference frames may show that the uniform drag no net torque reference frame which is kinematically equivalent to the no net rotation reference frame is based on a dynamically incorrect premise possible exceptions to the assumption of uniform drag include a net torque on the lithosphere due to attached subducting slabs and greater resistance to plate motion beneath continents than beneath oceans

seismogenic strike slip faulting and the development of the north china basin the actively subsiding north china sedimentary basin is associated with an unusually high level of seismic activity this oil and gas producing basin has been the site of nine large m 7 destructive earthquakes since 1600 a d an analysis of faulting during the tangshan earthquake sequence which includes some of the largest shocks that have occurred in this basin during the past 400 years showed that the dominant pattern of deformation during this sequence was associated with displacement on right stepping right lateral strike slip faults a large amount of subsidence 1 0 1 5 m occurred in pull apart regions between steps of the north northeast nne trending strike slip faults the directivity of the p wave radiation pattern and the distribution of aftershocks of the bohai gulf earthquake of july 18 1969 also indicate strike slip faulting on planes of similar nne trend together with the four largest shocks of the hsingtai sequence in 1966 earthquakes with right lateral slip on nne trending faults account for about two thirds of the seismic moment released in this region for the past 100 years the average regional strain due to seismic slip has a dominant component of dextral simple shear on nne striking planes that is approximately twice as large as north south extension or east west shortening based on a combination of published field and borehole data the dominance of horizontal dextral simple shear over subsidence seems to have begun no later than the mid pliocene and the total amount of extension over the entire basin is only about 20 30 this pattern of deformation the spatially variable heat flow values the scattered locations of rapid deposition of quaternary sediments and the fluctuating rate of sedimentation in space and time during the neogene in this basin are difficult to explain by pure extension and thermal subsidence we propose that these observations and the shape of the whole north china basin that of a lazy z are a consequence of pulling apart associated with right lateral movement on the nne trending strike slip fault systems and that the basin as a whole has formed and evolved as a composite pull apart basin due to right lateral slip on numerous right stepping faults since the eocene

moment tensor estimation using regional seismograms from a tibetan plateau portable network deployment the authors present the results of moment tensor inversions using regional seismograms recorded during the 1991 1992 passcal passive seismic experiment on the tibetan plateau using data recorded over a one year period they estimate the source mechanisms for 38 earthquakes within and near the tibetan plateau with moment magnitudes m sub w ranging from 3 8 to 5 0 with only one exception all the events within the plateau but away from the plateau boundary indicate either strike slip or extensional faulting a result consistent with previous studies three fourths of all the events occurred at depths less than 10 km and all but two at depths less than 15 km several events located near the southeastern section of the plateau exhibit an unusual m sub b m sub w difference of approximately one magnitude unit 19 refs 3 figs

internal crustal deformation in the northern part of shan thai block new evidence from paleomagnetic results of cretaceous and paleogene redbeds in order to describe the internal deformation of the northeast part of the shan thai block resulting from the penetration of the indian plate into asia a paleomagnetic study was carried out on the cretaceous and paleogene strata in the southern part of the simao terrane high temperature magnetic components with unblocking temperatures around 680 degrees c were isolated and positive fold test shows its primary nature of magnetization the tilt corrected site mean directions of the lower cretaceous and upper cretaceous from the menglun area are d s 46 2 degrees i s 45 9 degrees k 11 0 alpha 95 10 6 degrees and d s 33 2 degrees i s 30 9 degrees k 68 4 alpha 95 8 2 degrees respectively the site mean directions of the upper cretaceous and lower paleogene for the mengban area are d s 50 5 degrees i s 31 0 degrees k 207 6 alpha 95 6 4 degrees and d s 43 5 degrees i s 23 0 degrees k 26 1 alpha 95 13 4 degrees respectively the results of the lower cretaceous and upper paleogene from the mengla area are d s 46 9 degrees i s 42 2 degrees k 27 3 alpha 95 7 7 degrees and d s 41 8 degrees i s 23 8 degrees k 38 9 degrees alpha 95 5 8 degrees respectively in comparison with previous paleomagnetic data of the simao terrane the rotational deformation can be divided into four stages the cretaceous and paleocene sediments of the simao terrane experienced intensive folding before the early oligocene during the early oligocene to early miocene the shan thai and indochina blocks experienced southeastward extrusion with similar to 20 degrees clockwise rotation relative to the south china block during the middle to late miocene the shan thai blocks experienced more 15 degrees clockwise rotation since the late miocene the activity of strike slip faults surrounding the simao terrane enhanced the internal differential rotations of the terrane these deformation processes finally resulted in a complex internal deformation of the simao terrane c 2013 elsevier b v all rights reserved

active faulting and tectonics of burma and surrounding regions this study of the active tectonics of burma and surrounding regions is based mostly on an interpretation of landsat imagery and on fault plane solutions for shallow and intermediate earthquakes fold axes in the indoburman ranges and an east dipping inclined zone of intermediate depth earthquakes suggest that a slab of oceanic lithosphere was recently subducted to the east under the indoburman ranges fault plane solutions of shallow earthquakes however do not show underthrusting at the present time instead p axes are oriented roughly north south parallel not perpendicular to the fold axes in the ranges p axes for fault plane solutions of intermediate shocks also trend north south parallel to the strike of the subducted slab and may indicate that the hanging slab is being dragged north by india through the surrounding asthenosphere the sagaing fault probably accommodates most of the right lateral slip of india past indochina but india s northward movement also causes internal deformation within burma thailand and yunnan differences between the tectonic fabric seen on the landsat images and the tectonic regime compatible with the fault plane solutions throughout the region imply major changes in the directions of relative motion in the orientations of strain and in the style of deformation in the late cenozoic presumably these changes reflect the transition from subduction to collision and strike slip motion as india penetrated into eurasia past burma large parts of burma and thailand may have rotated several tens of degrees clockwise in this process

global positioning system measurements of indian plate motion and convergence across the lesser himalaya we use global positioning system gps measurements acquired from 1991 to 1995 to constrain the motion of sites in bangalore in southern india and kathmandu nepal relative to a global gps network these measurements permit estimates of the northward motion of the indian plate and convergence between the southern himalaya and the indian subcontinent the velocities of bangalore and kathmandu in the itrf92 reference frame agrees with that predicted by the nnr nuvel1a plate motion model for indian plate motion and differ from that predicted for the australian plate confirming the independent motion of the indian and australian plate fragments no significant motion was detected between bangalore and kathmandu during the three years from 1991 1994 even though kathmandu is located in the hanging wall of the active himalayan thrust system the himalayan thrust system is thought to accommodate 18 7 mm yr of convergence and has been the source of several historic m 8 earthquakes the absence of motion of kathmandu relative to the indian plate can be explained if the thrust system is presently locked south of the greater himalaya our preferred model has no steady slip on the detachment south of the greater himalaya and steady slip at a rate greater than 6 mm yr 1 3 of the long term convergence rate can be ruled out at 95 confidence level

crustal thickening versus lateral expulsion in the indian asian continental collision since the beginning of the continental collision between india and asia there has been about 2500 km of convergence and the northward movement of india has been accommodated by major internal deformation of the asian lithosphere the crustal thickening in and around the tibetan plateau is clearly a direct consequence of this collision but there is considerable debate as to whether a large fraction of the indentation has been accommodated by eastward motion of the lithospheric blocks of southeastern asia and southern china numerical experiments described here test this hypothesis for a range of indentation geometries and rheological models of the lithosphere we employ a thin viscous sheet model of the lithosphere with a depth averaged nonlinear viscous rheology described by a stress strain rate exponent n and including gravitational buoyancy forces scaled by the dimensionless argand number ar the eastern boundary for the collision region is described as a lithostatic boundary the precollision normal stress is determined by static balance and that constant stress is applied throughout the collision the experiments show that during collision the eastern boundary is smoothly displaced to the east at a rate about 1 4 of the indentation rate with only minor variation due to geometry or rheology crustal thickening rates in the region of the plateau are reduced by between 10 and 25 of the corresponding rates determined for similar experiments with a rigid eastern boundary to generalize from the results of these experiments the total north south shortening strain produced by the collision is partitioned between crustal thickening and eastward displacement in the ratio of at least 3 1 and more probably 4 1

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

crustal deformation in the baikal rift from gps measurements three years and four campaigns of global positioning system gps measurements 1994 1997 in the baikal rift zone largest active continental rift system in eurasia show crustal extension at a rate of 4 5 1 2 mm yr in a wnw ese direction a comparison with moment release of large historical earthquakes suggests that elastic strain is currently accumulating in the baikal rift zone along active faults that currently have the potential for a m 7 5 earthquake the gps derived extension rate in the baikal rift zone is at least two times greater than the prediction of most deformation models of asia this result could reflect the dynamic contribution of the pacific eurasia subduction to intracontinental deformation in asia in addition to the effect of the india eurasia collision

the field of crustal velocity in asia calculated from quaternary rates of slip on faults rates of quaternary faulting when treated as measures of strain rates within regions several times larger than the depths of brittle faulting yield a velocity field for asia that matches the average relative velocity between the indian and eurasian plates over the past 2 myr nuvel 1a and the velocity of shanghai with respect to eurasia measured with very long baseline interferometry vlbi by using rates of slip on discrete surfaces faults to define average strain rates we explicitly assume that the large scale deformation can be treated as that of a continuum depending on the jcales over which strain rates are averaged 87 to 93 per cent of the assumed strain ites are fit within assigned 1 sigma uncertainties and 97 to 99 per cent are fit within 2 sigma the internal consistency of these data and the agreement with independent rates nuvel 1a and vlbi test the validity of treating large scale deformation of continents as that of a continuum in the calculated velocity field a large fraction 85 per cent of india s convergence with eurasia is absorbed by crustal or lithospheric thickening among consistently misfit assumed strain rates are those dominated by high rates of strike slip faulting strain associated with 20 30 mm a 1 of slip on the altyn tagh karakax and karakorum faults is inconsistent with the distributions of strain in surrounding regions we conclude that these rates all of which are based on correlations of ages of offset landforms with changes in global climate and not on radiometric dating have been systematically overestimated lateral transport out of india s northward path is relatively minor south china is calculated to move east southeast at less than 10 mm a 1

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

horizontal and vertical crustal movements from three dimensional very long baseline interferometry kinematic reference frame implication for the reversal timescale revision three dimensional kinematic reference frame of geodetic very long baseline interferometry vlbi stations tied to a geologic plate motion model was established using the glb907 solution by first selecting globally distributed stable plate interior stations and then applying a small translation and a rotation for the entire network in a three dimensional space so that the differences in the horizontal velocities between the vlbi observations and the model predictions are minimized since the vlbi network is global we only assume that the horizontal movements of technically stable stations obey a plate motion model we need not introduce any unwarranted constraints to the vertical velocities of specific stations to realize the frame a suggestive correlation was found between the estimated vertical velocities of north american stations and those predicted by a postglacial rebound model the revision of the magnetic polarity timescale mpts causes a uniform increase or decrease of the predicted velocities which could be detected as the small difference between the measured and the predicted relative plate velocities direct estimation of the correction suggests that the vlbi data fit best to the model when the nuvel1 model is corrected by 3 4 1 2 which differs significantly from the 4 5 deduced from the astronomical mpts calibration this was further confirmed by estimating the rotation rates for individual plate pairs

universality of the seismic moment frequency relation we analyze the seismic moment frequency relation in various depth ranges and for different seismic regions using flinn engdahl s regionalization of global seismicity three earthquake lists of centroid moment tensor data have been used the harvard catalog the usgs catalog and the huang et al 1997 catalog of deep earthquakes the results confirm the universality of the values and the maximum moment for shallow earthquakes in continental regions as well as at and near continental boundaries moreover we show that although fluctuations in earthquake size distribution increase with depth the values for earthquakes in the depth range of 0 500 km exhibit no statistically significant regional variations the regional variations are significant only for deep events near the 660 km boundary for declustered shallow earthquake catalogs and deeper events we show that the worldwide values have the same value of 0 60 0 02 this finding suggests that the value is a universal constant we investigate the statistical correlations between the numbers of seismic events in different depth ranges and the correlation of the tectonic deformation rate and seismic activity the number of earthquakes above a certain threshold level per year the high level of these correlations suggests that seismic activity indicates tectonic deformation rate in subduction zones combined with the universality of the value this finding implies little if any variation in maximum earthquake seismic moment among various subduction zones if we assume that earthquakes of maximum size are similar in different depth ranges and the seismic efficiency coefficient is close to 100 for shallow seismicity then we can estimate for deeper earthquakes for intermediate earthquakes 5 and 1 for deep events these results may lead to new theoretical understanding of the earthquake process and better estimates of seismic hazard

contemporary kinematics of the western united states determined from earthquake moment tensors very long baseline interferometry and gps observations using moment tensors from earthquakes between 1850 and 1995 we determine the horizontal velocity gradient tensor field associated with the seismic deformation in the western u s plate boundary zone the velocity vectors obtained from the integration of the seismic strain rates across the entire plate boundary lie within 5 of the nuvel ia pacific north american plate motion direction the magnitude of the earthquake related velocity is 62 of the nuvel 1a total pacific north american plate motion if earthquake occurrence is a random poisson like process then the large formal errors associated with the model velocity estimates are an indication that the 144 year interval is too short to define the long term seismic moment release rate to within an uncertainty less than the deficit between the observed seismic moment release rate and the total long term moment release rate associated with both the seismic and aseismic deformation to spatially resolve the deficit of the earthquake moment release in the last 144 years we have also estimated the total long term horizontal velocity gradient tensor field using seismic strain rate tensors and recent geodetic velocities both with and without the nuvel 1a pacific north american rigid plate motion constraint we find a systematic difference between the southern california earthquake center scec geodetic velocity map and nuvel 1a north american reference frames with a pole at 38 8 n 124 2 w 0 33 m y 1 this difference is significant at the 99 confidence level and indicates that 4 7 mm yr of ne sw convergence is absorbed in offshore areas of southern california if both the scec velocity map and nuvel 1a correctly describe the relative motion between the pacific and north america plates deficit strain rates calculated from comparison of observed seismic strain rates over the last 144 years with long term model strain rate tensors are largest in areas east of san francisco bay in the transverse ranges and along the southern san andreas fault and san jacinto fault the deficit in each 100 by 50 km grid area within these regions is equivalent to an accumulation of strain in the last 144 years that would be released by an mw 7 earthquake elsewhere the accumulated strain in the last 144 years is small except in northern mojave desert along the garlock fault and in the region southwest of the southern san andreas san jacinto fault zone within each 100 by 50 km grid area in these regions the accumulated strain is equivalent to that released by an mw 6 5 7 0 earthquake

active deformation in eastern indonesia and the philippines from gps and seismicity data in this study we combine global positioning system gps velocities with information on the style of regional seismicity to obtain a self consistent model velocity and strain rate field for the entire eastern indonesia and philippines region in the process of interpolating 93 previously published gps velocities the style and direction of the seismic strain rate field inferred from earthquakes with m0 1 1020 n m from the harvard centroid moment tensor catalog are used as constraints on the style and direction of model strain rates within the plate boundary zones the style and direction of the seismic strain rate field are found to be self similar for earthquakes up to m0 1 1020 n m equivalent to mw 7 3 our inversion result shows the following the java trench which lacks any significant historic seismicity delineates the australian plate au sunda block sunda plate boundary west of the island of sumba east of sumba convergence is distributed over the back arc and banda sea and there is no subduction at the timor trough suggesting that the northern boundary of the au plate runs north of this part of the banda arc through the banda sea in new guinea most motion is taken up as strike slip deformation in the northern part of the island delineating the pacific plate pa au boundary however some trench normal convergence is occurring at the new guinea trench evidence that the strain is partitioned in order to accommodate oblique pa au motion pa au motion is consistent with nuvel 1a direction but 8 mm yr 1 slower than the nuvel 1a estimate for pa au motion the sulawesi trench and molucca sea delineate zones of high strain rates consistent with high levels of active seismicity the sulawesi trench may take up some of the au sunda motion philippine sea plate motion is in a direction slightly northward of the nuvel ia estimate and is partitioned in some strike slip strain rates along the philippine fault and relatively larger trench normal convergence along the philippine trench and on the philippine mainland in the southern philippines and along the manila trench in the northern philippine islands the high level of strain rate along the manila trench is not released by any significant historic seismic activity for the entire eastern indonesia philippines region seismicity since 1963 has taken up 40 of the total moment rate inferred from our model

continental tectonics in the aftermath of plate tectonics the success of plate tectonics required an acceptance of continental drift and thus a reinterpretation of the large scale geological history of most of the earth but the basic tenet of plate tectonics rigid body movements of large plates of lithosphere fails to apply to continental interiors where buoyant continental crust can detach from the underlying mantle to form mountain ranges and broad zones of diffuse tectonic activity

relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates the tien shan a high seismically active intracontinental mountain belt 1 000 2 000 km north of the himalaya has grown as a result of india s collision with asia1 the crustal shortening 200 50 km refs 2 3 and thickening that gave rise to the tien shan accommodates only a small fraction of india s total penetration into asia 2 000 3 000km and the temporal relationship of deformation in this belt to the india asia collision remains unclear here we report geodetic measurements of the tien shan using the global positioning system gps that indicate that the current crustal shortening rate is nearly half of india s convergence rate with eurasia in this area4 we infer a total shortening rate for the tien shan of 20 mm yr 1 which is approximately twice that inferred previously from the extrapolation of slip rates in the holocene3 and earthquake induced displacements during this century5 suggesting that the rate of mountain building in this region has accelerated several fold since the onset of collision 50 55 myr ago6 7 if as we argue the current shortening rate can be extrapolated to geological timescales then our results suggest that most of the tien shan has been constructed during the past 10 myr perhaps in response to an increased horizontal force following an abrupt rise of the tibetan plateau8 9

statistical significance of the seismic coupling coefficient abstract variations in the seismic coupling coefficient the ratio of the observed to expected seismic moment release rates at subduction zones are commonly used to make inferences about the physics of subduction taking into account the power law form of the earthquake frequency moment relation it is shown that the observed distribution of at the world9s subduction zones based on the twentieth century9s earthquakes can be matched by a single value of 0 3 if as is likely the case the 90 yr observation time is less than or comparable to the repeat time of the largest possible earthquake it is shown that because our reliable earthquake record is short global variations in based on seismicity alone are poorly resolved and cannot be used to distinguish among subduction models

seismic risk on the northern xiaojiang fault implied by the latest and nearest gps observations on the basis of the continuous and dense gps observations covering the northern segment of the xiaojiang fault zone n xjfz from march 2012 to march 2016 we present the velocity field spatiotemporal deformation slip rate and locking depth of the n xjfz the results provide strong support for achieving a better understanding of the deformation behavior of this fault the heterogeneity of the gps velocity field and relatively nonuniform distribution of seismicity suggest that the observational area is fragmented shear strain has been accumulating with an almost constant azimuth which is consistent with the trends of the mapped major faults the 2014 ms 6 5 ludian earthquake produced a sudden change in the dilatational strain which was almost constant prior to the event and an increase in the shear strain rate the near field deformation of the n xjfz estimated with the near field data was larger than expected revealing that the n xjfz is becoming more locked these results imply that the seismic risk in the study area is currently rising and that similar to the 2014 ms 6 5 ludian earthquake future earthquakes will possibly occur away from mapped faults

seismic strain rates in regions of distributed continental deformation we compare the rates and configurations of seismic deformation determined from moment tensor mechanisms of earthquakes in five continental regions with the rates and configurations expected if the seismicity reflected the relative plate motions in the regions the five regions the aegean iran california western new guinea and central asia are characterized by high levels of seismicity distributed over hundreds to thousands of kilometers from the accepted plate boundaries the earthquake mechanisms are compiled primarily from the catalog of centroid moment tensor solutions which is nearly complete over the interval 1977 1987 for earthquakes greater than ms 5 the thickness of the seismogenic layer in each region is constrained by the results of modeling broadband body wave phases and of previous earthquake studies in the aegean california and western new guinea the observed configurations of deformation agree with a simple model of distributed accommodation of relative plate motion in iran and central asia the moment tensors indicate that there is appreciable strain parallel to the strikes of the belts we augment our 10 year estimates of seismic deformation with the available historical moment and magnitude estimates for the five regions and find that moderate and large earthquakes account for between 25 and 70 of the deformation of the seismogenic layer

the akato tagh bend along the altyn tagh fault northwest tibet 2 active deformation and the importance of transpression and strain hardening within the altyn tagh system we investigated active deformation within the akato tagh restraining double bend to determine the age of the active altyn tagh fault relative to the altyn tagh system and thereby evaluate the extent to which this system evolved by net strain hardening or softening active structures were mapped based on their geomorphology and disruption of quaternary deposits surfaces the style of active faulting is strongly correlated with fault strike 065 070 striking segments show pure left slip whereas faults with more northward or eastward strikes are transtensional or transpressional respectively our mapping further suggests that the 065 to 070 striking western and eastern segments of the akato tagh bend are characterized by pure strike slip motion with partitioned transpression along the 090 striking central segment of the double bend it remains unclear how this active bend perpendicular shortening is absorbed in conjunction with previous work the present study fails to support the commonly held idea that tarim tibet motion is strongly oblique to the altyn tagh system estimates for the age of the akato tagh bend derived in a companion study suggest the bend is only a few million years old the current principal trace is probably similarly young because formation of the bend by recent deformation of an old trace should result in transpression along the western and eastern segments contrary to the pure left slip shown here the altyn tagh system comprises multiple fault strands in a zone 100 km wide across strike because the main trace appears to be much younger than the system in which it is embedded we speculate that this system evolved by the sequential formation and death of short lived fault strands in particular we suggest that geometrically complex strike slip fault systems such as the altyn tagh may form via system strain hardening where this net response reflects a dynamic competition between hardening and softening processes that are active simultaneously within the fault zone hardening mechanisms may include growth of restraining bend topography or material hardening of phyllosilicate rich gouge whereas softening processes might include r p shear linkage or reduction in bend angle by vertical axis rotation our analysis suggests that net strain hardening of a fault system can produce continental deformation that is spatially localized over the 1 5 m y during which an individual strand is active but distributed over the 10 100 m y corresponding to the life span of the whole fault system and the collision zone in which it is contained thus time scale is critically important in determining whether or not continental deformation is spatially distributed or localized