horizontal surface velocity and strain patterns near thrust and normal faults during the earthquake cycle the importance of viscoelastic relaxation in the lower crust and implications for interpreting geodetic data in recent years more and more space geodetic data on the surface deformation associated with earthquakes on intracontinental normal and thrust faults have become available however numerical models investigating the coseismic and postseismic deformation near such faults in a general way i e not focused on a particular earthquake are still sparse here we use three dimensional finite element models that account for gravity far field regional extension shortening and postseismic relaxation in a viscoelastic lower crust to quantify the surface deformation caused by an mw 7 earthquake on a dip slip fault the coseismic deformation is characterized by horizontal shortening in the footwall of the normal fault and extension in the hanging wall of the thrust fault consistent with elastic dislocation models geological field observations and gps data from earthquakes in italy and taiwan during the postseismic phase domains of extensional and contractional strain exist next to each other near both fault types the spatiotemporal evolution of these domains as well as the postseismic velocities and strain rates strongly depend on the viscosity of the lower crust for viscosities of 1018 1020 pa s the signal from postseismic relaxation is detectible for 20 50 years after the earthquake if gps data containing a postseismic relaxation signal are used to derive regional rates the stations may show rates that are too high or too low or even an apparently wrong tectonic regime by quantifying the postseismic deformation through space and time our models help to interpret gps data and to identify the most suitable locations for gps stations

earthquake cycle deformation in the tibetan plateau with a weak mid crustal layer 1 geodetic observations of interseismic deformation across the tibetan plateau contain information about both tectonic and earthquake cycle processes time variations in surface velocities between large earthquakes are sensitive to the rheological structure of the subseismogenic crust and in particular the viscosity of the middle and lower crust here we develop a semianalytic solution for time dependent interseismic velocities resulting from viscoelastic stress relaxation in a localized midcrustal layer in response to forcing by a sequence of periodic earthquakes earthquake cycle models with a weak midcrustal layer exhibit substantially more near fault preseismic strain localization than do classic two layer models at short 50 mm yr postseismic velocities in the years following the coseismic ruptures we suggest that earthquake cycle models with a localized midcrustal layer can simultaneously explain both preseismic and postseismic geodetic observations with a single maxwell viscosity while the classic two layer model requires a rheology with multiple relaxation time scales

edge driven mechanical microplate models of strike slip faulting in the tibetan plateau 1 the india asia collision zone accommodates the relative motion between india and eurasia through both shortening and pervasive strike slip faulting to gain a mechanical understanding of how fault slip rates are driven across the tibetan plateau we develop a two dimensional linear elastic two stage deformable microplate model for the upper crust based on the behavior of an idealized earthquake cycle we use this approach to develop a suite of simple india asia collision zone models differing only in boundary conditions to determine which combination of edge forces and displacements are consistent with both the slip rate measurements along major tibetan faults as well as the geodetically observed extrusion of crustal material toward southeast asia model predictions for the altyn tagh 1 14 mm yr kunlun 3 10 mm yr karakorum 5 12 mm yr and haiyuan 3 5 mm yr faults are in agreement with geologically and geodetically inferred slip rates further models that accurately reproduce observed slip rate gradients along the altyn tagh and kunlun faults feature two critical boundary conditions 1 oblique compressive displacement along the himalayan range front west of the shillong plateau and 2 forcing in southeast asia additionally the ratio of internal block potency rate to the total potency rate for each microplate ranges from 28 to 79 suggesting a hybrid view of deformation in tibet as simultaneously localized on major faults and distributed at length scales 500 km

earthquakes beneath the himalayas and tibet evidence for strong lithospheric mantle eleven intracontinental earthquakes with magnitudes ranging from 4 9 to 6 occurred in the mantle beneath the western himalayan syntaxis the western kunlun mountains and southern tibet near xigaze between 1963 and 1999 high resolution seismic waveforms show that some focal depths exceeded 100 kilometers indicating that these earthquakes occurred in the mantle portion of the lithosphere even though the crust has been thickened there the occurrence of earthquakes in the mantle beneath continental regions where the subduction of oceanic lithosphere ceased tens of millions years ago indicates that the mantle lithosphere is sufficiently strong to accumulate elastic strain

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

viscoelastic coupling model for the earthquake cycle driven from below in a linear system the earthquake cycle can be represented as the sum of a solution which reproduces the earthquake cycle itself viscoelastic coupling model and a solution that provides the driving force we consider two cases one in which the earthquake cycle is driven by stresses transmitted along the schizosphere and a second in which the cycle is driven from below by stresses transmitted along the upper mantle i e the schizosphere and upper mantle respectively act as stress guides in the lithosphere in both cases the driving stress is attributed to steady motion of the stress guide and the upper crust is assumed to be elastic the surface deformation that accumulates during the interseismic interval depends solely upon the earthquake cycle solution viscoelastic coupling model not upon the driving source solution thus geodetic observations of interseismic deformation are insensitive to the source of the driving forces in a linear system in particular the suggestion of bourne et al 1998 that the deformation that accumulates across a transform fault system in the interseismic interval is a replica of the deformation that accumulates in the upper mantle during the same interval does not appear to be correct for linear systems

deformation processes adjacent to active faults examples from eastern california 1 major seismogenic faults are embedded within narrow zones of inelastic off fault deformation ofd where both distributed displacement and modification of rock properties occur active distributed displacement may affect slip rate estimates seismic energy radiation and geodynamic models this study addresses the role of ofd in the displacement history and mechanical behavior of seismogenic faults by multisite study of deformed geologic features adjacent to 30 60 km long active strike slip faults of 10 km of dextral displacement in the mojave desert eastern california we find that distributed displacement accommodates 0 to 25 of the total displacement over zones of one to two kilometers width displacement occurs mostly within 100 200 m of faults and decreases nonlinearly away from the main fault we show evidence for distributed displacement through simple shear in the form of parallel secondary faults and progressive deformation of linear markers adjacent to the calico fault we also find evidence for shear via rotation and progressive fragmentation adjacent to the harper lake fault analysis of block dimensions show that blocks tend to decrease in size toward faults and that cumulative length of secondary faults is longer than the main fault by at least a factor of 10 based on crosscutting relationships and the relationship of ofd to geophysically imaged compliant zones around active faults we argue that distributed displacement is an active process and suggest that zones of diminished rigidity near faults may be at least in part driven by secondary faulting during the rupture propagation along the main fault

uniform postglacial slip rate along the central 600 km of the kunlun fault tibet from 26al 10be and 14c dating of riser offsets and climatic origin of the regional morphology late pleistocene holocene sinistral slip rates on several segments of the kunlun fault in northeastern tibet have been determined these determinations are based on the measured displacement of alluvial surfaces whose surface ages were determined by cosmogenic 2 6 al and 1 0 be dating of quartz pebbles and by 1 4 c dating of charcoal in the west at three sites along the xidatan dongdatan segment of the fault near 94 e terrace riser offsets ranging from 24 to 110 m with cosmogenic ages ranging from 1800 to 8200 yr yield a mean left lateral slip rate of 11 7 1 5 mm yr 1 field observations indicate minimum offsets of 9 12 m this offset when combined with the long term slip rate indicates that great earthquakes m 8 rupture this segment of the fault with a recurrence interval of 800 1000 yr at two sites along the dongxi anyemaqin segment of the fault near 99 e terrace riser offsets ranging from 57 to 400 m with 1 4 c ages ranging from 5400 to 37 000 yr bp yield a minimum slip rate of 10 mm yr 1 at one site the 1937 january 7 m 7 5 and the penultimate earthquakes produced 4 m of left slip and 0 4 m of reverse slip the maximum recurrence interval of earthquakes with such characteristic slip is thus 400 yr farther east near 100 5 e along the maqen segment of the fault the 180 m offset of a lateral moraine emplaced between the last glacial maximum 20 ka and 11 100 yr bp yields a mean slip rate of 12 5 2 5 mm yr 1 the slip rates are constant within uncertainty throughout the 600 km of the kunlun fault that we studied the average slip rate is 11 5 2 0 mm yr 1 extrapolating this rate to the reminder of the fault we conclude that most 80 per cent of the 300 morphological offsets measured in the field or on spot satellite images post date the last glacial maximum most of the terraces we studied were deposited during the humid period of the early holocene optimum 9 5 ka the formation of younger terraces reflects late holocene climate change

fluvial terrace riser degradation and determination of slip rates on strike slip faults an example from the kunlun fault china 1 the use of displaced fluvial terrace risers to determine slip rates along strike slip faults depends on knowing when risers become passive markers typically chronologic constraints from terrace deposits only place bounds on this age consequent slip rates may be highly uncertain along the kunlun fault in northeastern tibet we demonstrate that consideration of riser degradation can augment terrace chronology and improve the precision of slip rate estimates multiple offset risers and 14c age determinations from terrace treads yield a narrow range of slip rates of 4 5 0 5 m kyr at one site but permit a wide range of allowable rates 3 10 m kyr in an adjacent drainage using a locally calibrated sediment transport rate of 3 2 5 4 m2 ka we show that riser morphology at this latter site is consistent with degradation since abandonment of the upper terrace tread our analysis indicates that slip rates at this site are 5 2 m kyr

channel flow extrusion model to constrain dynamic viscosity and prandtl number of the higher himalayan shear zone constraining magnitudes of mechanical and thermo mechanical parameters of rocks and shear zones are the important goals in structural geology and tectonics talbot in j struct geol 21 949 957 1999 such parameters aid dynamic scaling of analogue tectonic models ramberg in gravity deformation and the earth s crust in theory experiments and geological applications 2nd edn academic press london 1981 which are useful to unravel tectonics in further details schultz ela and walsh in j struct geol 24 247 275 2002 the channel flow extrusion of the higher himalayan shear zone hhsz higher himalaya can be explained by a top to s sw simple shear i e the d2 deformation in combination with a pressure gradient induced flow against gravity presuming its newtonian incompressible rheology with parallel inclined boundaries the viscosity of this shear zone along a part of the himalayan chain through india nepal and bhutan is estimated to vary widely between 1016 and 1023 pa s and its prandtl number pr within 1021 1028 the estimates utilized ranges of known thickness 6 58 km of the hhsz that of its top subzone of ductile shear of normal shear sense stdsu 0 35 9 4 km total rate of slip of its two boundaries 0 7 131 mm year 1 pressure gradient 0 02 6 kb km 1 density 2 2 3 1 g cm 3 and thermal diffusivity 0 5 10 6 2 1 10 6 m s 2 along the orogenic trend considering most of the parameters specifically for the sutlej section india the calculated viscosity and the prandtl number pr of the hhsz are deduced to be 1017 1023 pa s and pr 1022 1028 the upper limits of the estimated viscosity ranges are broadly in conformity with a strong tibetan mid crust from where a part of the hhsz rocks extruded on the other hand their complete ranges match with those for its constituent main rock types and partly with those for the superstructure and the infrastructure the estimated mechanical and thermo mechanical parameters of the hhsz will help to build dynamically scaled analogue models for the himalayan deformation of the d2 phase

a dimensional analysis to quantify the thermal budget around lithospheric scale shear zones the thermal evolution around shear zones is controlled by three major thermal processes diffusion advection and shear heating we present a dimensional analysis to quantify to first order the relative contributions of these three processes to the thermal evolution around lithospheric scale shear zones we consider 11 parameters that control the kinematics the three dimensional 3 d geometry the initial thermal structure and the average strength of the shear zone three dimensionless parameters are presented to quantify the relative contributions of the three thermal processes we validate the dimensional analysis with 2 d thermo kinematic numerical models the applicability of the dimensional analysis to any kind of shear zone i e thrust normal slip and strike slip shear zones makes it a useful tool that is complementary to previous numerical and analytical studies finally thrust type shear zones are used to illustrate how the three thermal processes control the thermal evolution

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

a bound on the viscosity of the tibetan crust from the horizontality of palaeolake shorelines abstract palaeoshorelines around four large lakes in central tibet record a latest pleistocene to holocene high stand during which the lakes were filled 150 200 m more deeply than they are at present gps measurements of shoreline elevations around zhari namtso show that they are horizontal to within 2 m at the 2 level measurements of height made by combining shuttle radar topographic mission elevations with google earth imagery of shorelines around zhari namtso tangra yumtso taro tso and ngangla ringtso show that all the palaeoshorelines are horizontal within measurement uncertainty support of the lake loads by elastic stresses can explain the horizontality of the shorelines only if the equivalent elastic thickness of the crust exceeds 15 25 km the observations are more plausibly explained by support of the lake loads through viscous stresses in the middle to lower crust this support requires that the viscosity of the middle to lower crust is at least 10 19 10 20 pa s these values are consistent with estimates from studies of post seismic relaxation after large earthquakes of the region and are higher by two orders of magnitude than would permit significant lateral flux of material through a channel in the middle to lower crust

lower crust s wave velocity beneath western yunnan province from waveform inversion of dense seismic observations we use teleseismic body waveforms to explore s wave layered velocity structures beneath 30 portable digital seismic stations deployed around western yunnan province results show that the moho depth in this region is 40 km and decreases in general from north to south consistent with previous geophysical studies associated with this lateral variation of the moho depth the lower crust above the moho discontinuity has a 15 25 km thick zone with an s wave velocity lower than that of the upper crust this lower velocity zone might be interpreted as a lower crust weak channel which may mechanically partially decouple the upper crust deformation from the underlying mantle thus the inverted s wave velocity structure could provide new evidence for the lateral flow of lower crust in the build up of the south eastern tibetan plateau

a review on active tectonics and deep crustal processes of the western sichuan region eastern margin of the tibetan plateau abstract one of remarkable geological and geomorphological features in continental china is the presence of a north south trending tectonic zone which separates the seismically active tibetan plateau to the west from the tectonically stable south china and ordos blocks to the east the zone also owns a name of north south seismic belt as a large number of great historical earthquakes occur on it the most recent one the 2008 wenchuan earthquake attests its recent tectonic activity in this review i take the western sichuan region as an example to probe the structural styles and kinematic pattern as well as deep geological process associated with tectonic deformation of the north south trending zone through integrated studies on active faults gps crustal deformation and geophysical structure we show that deformation in the western sichuan is governed by interactions among three crustal blocks songpan chuandian and south china of distinctive rheological properties under the tectonic framework that eastward growth of the soft eastern tibet is blocked by the hard lithosphere of the south china block the left lateral xianshuihe fault continues to the north south trending fault system without crustal shortening to form a bounding fault to limit the northern extend of the magnificent clockwise rotation of crustal material around the eastern himalaya syntax upper crust of the three blocks is dominated by brittle deformation whereas the ductile flow of lower crust would drag the brittle upper crustal blocks to move with respect to each other the relative motions among the brittle upper crustal blocks cause strain accumulations among their bounding faults to generate large earthquakes deformation of the western sichuan region can thus be described in terms of combined model of rigid block movement and continuous deformation we suggest this combined model can be applied to entire continental china

crustal rheology of southern tibet constrained from lake induced viscoelastic deformation we probe the rheology of the tibetan lithosphere using the rebound that accompanied climate driven lake level variations at the modern decadal time scale we used deformation around siling tso measured from insar at the millennial time scale we use holocenepaleoshorelines around siling tso and zhari nam tso we use chronological constraints from the literature and digital elevation models to constrain their ages and geometry we observe a small post highstand subsidence of the area near the center of mass of the paleolake load and a low amplitude short wavelength outer bulge in the context of a model consisting of an elastic lid over a viscous channel with a rigid base these observations preclude the existence of a thick low viscosity channel and require a thin elastic lid based on monte carlo inversion we constrain the range of possible equivalent elastic thickness of the lid 20 km and a 20 km thick channel with lower crustal viscosity 10 20 pa s in both cases the interferences in space of the deformation signals induced by the lakes geometry and in time through the viscoelastic response to the lake level variations results in limited distortion of the paleo shorelines while the elastic lid in the upper crust needs in any case to be thin 20 km inferred in some previous studies of holocene paleoshorelines in the longer term the effective elastic thickness of the lithosphere must drop asymptotically to the value of the elastic lid in the upper crust 10 km this explains the low effective elastic thickness derived from gravity studies

postorogenic rigid behavior of the eastern songpan ganze terrane insights from low temperature thermochronology and implications for intracontinental deformation in central asia 1 the songpan ganze terrane sgt formed by early mesozoic closure of the paleo tethys ocean occupies a large area of the central eastern tibetan plateau late mesozoic and cenozoic strike slip deformation has been identified in the surrounding terranes and faults e g western qinling altyn tagh and kunlun faults however the coeval evolution of the sgt has not been well explored we report apatite fission track and apatite and zircon u th he data from a 7 km deep borehole and outcrop samples covering an area of 150 150 km in the eastern sgt thermal history modeling suggests a distinct phase of late jurassic early cretaceous 150 100 ma cooling followed by a prolonged stage of slow cooling for all samples despite of their differences in depositional age mid late triassic time and locality within a large area the ubiquitous late jurassic early cretaceous cooling implies little differential deformation in the eastern sgt and is best explained by regional rock uplift resulting from the transpressional strain field created by the contemporaneous lhasa qiangtang collision to the south projecting the contemporaneous deformation surrounding the sgt onto an early cretaceous paleogeographic terrane reconstruction results in a new tectonic model the model relates the lhasa qiangtang collision to tens to hundreds of kilometers of shearing along the altyn tagh and kunlun faults which transferred strain into central asia e g qinling dabie orogen results of this study suggest a rigid behavior for the eastern sgt and highlight the important role of crustal strength discontinuities in accommodating and transferring crustal deformation

paleoseismology and global positioning system earthquake cycle effects and geodetic versus geologic fault slip rates in the eastern california shear zone published slip rates for the owens valley fault zone in eastern california based on geodetic data and elastic half space models 5 7 mm yr are faster than longer term geologic rates 2 3 mm yr we use global positioning system data spanning the central owens valley a more realistic rheological model with an elastic upper crust over a viscoelastic lower crust and upper mantle and paleoseismic data from adjacent faults to show that this difference could reflect earthquake cycle effects we estimate a long term rate 2 1 0 7 mm yr and earthquake recurrence interval 2750 350 1000 yr from the geodetic data both in agreement with independent geologic estimates

quaternary and active faulting observed on the 1985 academia sinica royal society geotraverse of tibet active and recent faulting along the main north south road in tibet is dominated by normal faulting occurring on northerly trending planes and by strike slip faulting both of which reflect an east west extension of the plateau normal faulting is prevalent in the southern half of the plateau but we saw no evidence for any major graben in the northern half strike slip faulting on roughly easterly trending structures is m ore prevalent in the northern half but conjugate faulting with right lateral slip on northwesterly trending planes and left lateral slip on northeasterly trending planes is common in the southern half in two areas we also observed components of thrust faulting apparently in association with young strikeslip faulting our most important results are bounds on the rates of slip on the two main strands of the kunlun strike slip fault system which trends east w est through the kunlun range ground moraine containing boulders of pyroxenite is separated by 30 km from the nearest outcrop of such rock implying that amount of displacement in the last 1 5 to 3 m a therefore the average rate of slip during the quaternary period has been between 10 and 20 mm a with a likely value of 13 mm a abundant fresh tension cracks and mole tracks imply continued slip on the main strand the xidatan tuosuohu maqu fault and the likely occurrence of a major earthquake in the last few hundred years consistent offsets of gullies and dry stream channels of about 10 m may reflect slip of that amount during such an earthquake and possible multiple offsets at one site suggest that slip may occur by large displacements of 10 m during infrequent great earthquakes along the other strand the kunlun pass fault offsets of roughly 50 to 150 m of apparently post glacial valleys and of one glacier and its terminal moraine suggest a holocene rate of slip between 5 and 20 mm a and most likely about 10 mm a on this fault these rapid rates of displacement imply that tibet is being extruded rapidly eastward at a rate com parable to the rate at which india is penetrating into eurasia and therefore that at present a substantial fraction of this penetration is being absorbed by the eastward extrusion of tibet

crustal strength in central tibet determined from holocene shoreline deflection around siling co abstract controversial end member models for the growth and evolution of the tibetan plateau demand quantitative constraints of the lithospheric rheology direct determinations of bulk crustal rheology however remain relatively sparse here we use the flexural rebound of lacustrine shorelines developed during the lingtong highstand around siling co in central tibet to place bounds on the effective elastic thickness t e and viscosity of tibetan crust shoreline features associated with the lingtong highstand complex 60 m above present lake level are deflected from horizontal by 2 4 m over wavelengths of 200 km optically stimulated luminescence dating of aggradational shoreline deposits indicates that these lake levels were reached at 6 4 ka assuming that surface loads were entirely supported by an elastic layer overlying an inviscid fluid the range and spatial distribution of variations in shoreline elevation are consistent with deflections predicted by a uniform elastic plate with thickness t e of 20 30 km if viscoelastic relaxation in response to lake withdrawal is complete our data suggest an average viscosity 10 19 pa s these results imply that the apparent viscosity of the lower crust inferred over millennial timescales is comparable with that estimated from post seismic relaxation over decadal timescale

evolution of the west siberian basin the west siberian basin is one of the largest intracratonic basins of the world and an important hydrocarbon province of russia perhaps the most important geologic event in siberia was the emplacement of basalts around 250 ma i e permo triassic boundary covering an area of about 5 10 6 km 2 this volcanism may be responsible for a mass extinction that occurred around permian triassic time the prebasaltic rifting event was limited to the north northeastern sector of the basin initial basin wide subsidence took place in the jurassic as a result of which the western part of siberia became the west siberian basin bounded by uplifts to the east and to the west one of the surprising aspects of the west siberian basin is the abundance of subvertical faults believed to be result of strike slip movement while intraplate inversions and fault reactivation structures have been observed in many cratons subvertical faults observed in the west siberian basin are unique because of their geometries and abundance the differentiation between the effects of tectonics and eustasy in cratonic basins is simple the global eustatic signal is basin wide with regional and local tectonics playing an overprinting role thus the middle jurassic turonian first second and third order cycles in the west siberian basin were primarily driven by eustasy the middle jurassic turonian series can be subdivided into two second order and 16 third order transgressive regressive cycles within dataset extent fourth order cycles appear to be controlled by delta shifting although extensively studied a number of fundamental questions regarding the origin and evolution of the west siberian basin remain unresolved or poorly documented in the literature

slip rates of the altyn tagh kunlun and karakorum faults tibet from 3d mechanical modeling we use 3 d mechanical modeling representing faults as planar surfaces with frictional properties that obey coulomb failure process to explore the long term slip rates of the altyn tagh fault and kunlun faults in the north tibetan plateau crustal theology is simplified as an elastoplastic upper crust and a viscoelastic lower crust far field gps velocities and late quaternary fault slip rates are used to constrain the model results rheological tests show that effective fault friction lower than 0 1 0 08 leads to high slip rates that fit with geologically and geodetically determined slip rates of the kunlun fault 10 11 7 1 5 mm yr meanwhile the modeled altyn tagh fault reaches slip rates similar to 13 7 mm yr to similar to 7 8 mm yr in its central portion between ranges of the geological slip rates associated with high slip rates our model predicts that central tibet similar to 84 degrees e 95 degrees e from the altyn tagh fault to the north of the himalayan arc accommodates north south shortening and east west extension rates of similar to 10 12 mm yr and similar to 8 10 mm yr respectively we also question the widely accepted idea that interseismic strain is driven at the base of the seismogenic zone by a screw dislocation if this assumption fails the presented model implies that interseismic strain around large strike slip faults could be distributed in a much broader way if the lithosphere deforms as a thin elastic plate rather than an elastic half space with an embedded dislocation if this distributed deformation is ignored and the instantaneous surface deformation field modeled as that resulting from slip on a dislocation below a specified depth embedded in an elastic half space the estimated slip rate will inevitably be lower than the true long term slip rate this appears to explain why geodetic slip rates proposed for the altyn tagh fault 510 mm yr are lower than some of the geological slip rates c 2008 elsevier b v all rights reserved

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

comment on crustal strength in central tibet determined from holocene shoreline deflection around siling co by xuhua shi eric kirby kevin p furlong kai meng ruth robinson and erchie wang abstract shi et al 2015 analysed the distributions of elevation of palaeoshorelines around siling tso central tibet assuming a model in which surface loads are entirely supported by an elastic lid overlying an inviscid fluid they concluded that the thickness of the elastic lid is 20 30 km and that for the assumption of an inviscid substrate in this model to be valid the viscosity of the crust below the elastic lid must be less than 1 2 10 19 pa s here we relax the assumption of an inviscid lower crust and show that the distribution of shoreline elevations may be explained either by a thick elastic lid or by high viscosity in the lower crust in the limit of an inviscid lower crust the thickness of the elastic lid must be greater than 25 to 39 km if the elastic lid is thinner than this then the viscosity of the crust beneath must be at least 5 10 19 to 2 10 20 pa s depending on the time interval over which the lake was loaded

active faulting mountain growth and erosion at the margins of the tibetan plateau constrained by in situ produced cosmogenic nuclides abstract the india asia collision zone is a key area for understanding continental plateau formation and mountain building two fundamental questions in this context are how the northeastward motion of india is partitioned between strike slip and thrust faults and how mountain building is counteracted by erosion cosmogenic nuclides allow us to address these questions because they provide age constraints on tectonically offset landforms and constraints on erosion rates after considerable debate on whether or not major strike slip faults move at high rates of up to 20 30 mm yr and absorb most of the continental deformation it now appears that the three largest faults altyn tagh haiyuan kunlun have millennial slip rates of no more than 8 13 mm yr consistent with rates of elastic strain accumulation determined by geodetic methods furthermore a significant portion of the lateral slip on these faults is transferred to thrust faults within the collision zone both observations indicate that the eastward tectonic escape of material along these faults is less important than often assumed with respect to mountain building and erosion cosmogenic nuclide studies show that thrust faults at the northeastern and eastern margins of tibet qilian shan longmen shan have vertical slip rates of 0 3 to 2 mm yr while catchment wide erosion rates vary from 0 02 to 1 0 mm yr with high relief areas eroding significantly faster than the plateau interior and growing mountains in the foreland the deeply incised regions have apparently reached an erosional steady state in which rock uplift is balanced by erosion river terraces at active mountain fronts document repeated changes between sediment deposition and fluvial incision during the quaternary incision and terrace formation occurred predominantly at glacial interglacial transitions but also during interglacial periods hence flights of terraces at the fault bounded mountain fronts record the interplay between sustained rock uplift and a temporally variable climate

three dimensional finite element modeling of stress evolution around the xiaojiang fault system in the southeastern tibetan plateau during the past 500 years abstract the left lateral strike slip xiaojiang fault system is a main boundary between the southeastern tibetan plateau and the south china block and accumulates several large m 7 earthquakes in the past 500 years and a dozen of moderate 5 7 earthquake ruptures occurred in the past 500 years are simulated with split node technique in seismogenic upper crust we investigate the coulomb failure stress changes mainly on vertical planes parallel to the different strands of the xiaojiang fault system and at the epicenters of large m 7 earthquakes in the past 500 years and of moderate 5 7 earthquakes that occurred in the past 500 years both from their coseismic and postseismic effects among which the postseismic effect results in the stressing rate being obviously accelerated near epicenters of the large m 7 earthquakes after their occurrence thus the percentage of positive coulomb failure stress changes of 0 01 mpa at the epicenters increases from 37 to 50 for the large m 7 earthquakes and from 43 to 64 for the moderate 5

present day shortening in southern haiti from gps measurements and implications for seismic hazard abstract the 3 m inhabitant capital region of haiti severely affected by the devastating january 12 2010 m7 0 earthquake continues to expand at a fast rate accurate characterization of regional earthquake sources is key to inform urban development and construction practices through improved regional seismic hazard estimates here we use a recently updated global positioning system gps data set to show that seismogenic strain accumulation in southern haiti involves an overlooked component of shortening on a south dipping reverse fault along the southern edge of the cul de sac basin in addition to the well known component of left lateral strike slip motion this tectonic model implies that ground shaking may be twice that expected if the major fault was purely strike slip as assumed in the current seismic hazard map for the region

crustal channel flows 1 numerical models with applications to the tectonics of the himalayan tibetan orogen 1 plane strain thermal mechanical numerical models are used to examine the development of midcrustal channel flows in large hot orogens in the models radioactive self heating reduces the viscosity of tectonically thickened crust and increases its susceptibility to large scale horizontal flow channels can be exhumed and exposed by denudation focused on the high relief transition between plateau and foreland we interpret the himalaya to have evolved in this manner channel flows are poorly developed if the channel has a ductile rheology based on wet quartz flow laws and well developed if there is an additional reduction in viscosity to 1019 pa s this reduction occurs from 700 c to 750 c in the models and is attributed to a small percentage of in situ partial melt melt weakening model ht1 provides an internally consistent explanation for the tectonic evolution of many features of the himalayan tibetan orogenic system erosional exhumation exposes the migmatitic channel equivalent to the greater himalayan sequence ghs between coeval normal and thrust sense ductile shear zones corresponding to the south tibetan detachment and the main central thrust systems outward flow of unstable upper crust rotates these shears to low dip angles in the model both the ghs and the lesser himalayan sequence are derived from indian crust with the latter from much farther south similar models exhibit a range of tectonic styles including the formation of domes resembling north himalayan gneiss domes model results are relatively insensitive to channel heterogeneities and to variations in the behavior of the mantle lithosphere beneath the model plateau

viscoelastic earthquake cycle models with deep stress driven creep along the san andreas fault system 1 we develop a two dimensional boundary element earthquake cycle model including deep interseismic creep on vertical strike slip faults in an elastic lithosphere coupled to a viscoelastic asthenosphere uniform slip on the upper part of the fault is prescribed periodically to represent great strike slip earthquakes below the coseismic rupture the fault creeps in response to lithospheric shear stresses within a narrow linear viscous fault zone the model is applied to the gps contemporary velocity field across the carrizo plain and northern san francisco bay segments of the san andreas fault as well as triangulation measurements of postseismic strain following the 1906 san francisco earthquake previous analysis of these data using conventional viscoelastic coupling models without stress driven creep segall 2002 shows that it is necessary to invoke different lithosphere asthenosphere rheology in northern and southern california in order to explain the data we show that with deep stress driven interseismic creep on the san andreas fault the data can be explained with the same rheology for northern and southern california we estimate elastic thickness in the range 44 100 km 95 confidence level fault zone viscosity per unit width of 0 5 8 2 1017 pa s m and asthenosphere relaxation time of 24 622 years 0 1 2 9 1020 pa s for northern and southern california we estimate a slip rate of 21 27 mm yr and recurrence time of 188 315 years for the northern san francisco bay san andreas fault and slip rate of 32 42 mm yr with recurrence time of 247 536 years for the carrizo plain

rupture models and viscoelastic stress changes of three mw 6 3 earthquakes along the southern front of the qilian mountains northeastern tibetan plateau abstract around the southern front of the qilian mountains three mw 6 3 strong earthquakes have occurred since 2003 the distances between the epicenters of these events range from 18 to 46 km by collecting available datasets including broadband waveforms coseismic surface geodetic measurements and active fault mapping results we invert rupture models for these strong earthquakes with a finite fault model approach in elastic half space constrained by these detailed rupture models we then build a three dimensional finite element model to calculate coulomb stress change due to the coseismic displacement and postseismic viscoelastic relaxation combined with an effective friction coefficient of 0 2 0 8 and variable rheological characteristics numerical results show that following the 2003 event the coulomb stress change along the 2008 rupture segment was positive with magnitudes between 1 8 103 pa and 2 2 103 pa among the stresses the postseismic viscoelastic relaxation contributed 10 7 23 3 just prior to the occurrence of the 2009 earthquake the total changes of the coulomb stress around its hypocenter reached 2 71 104 3 72 104 pa to which the 2003 event and the 2008 event contributed approximately 7 102 1 5 103 pa 2 58 4 03 and 2 64 104 3 57 104 pa 95 97 97 42 respectively we believe that other postseismic behaviors including afterslip and poroelastic rebound could also yield extra changes in the coulomb stress which probably further enhance the triggering effect among the sequential earthquakes the numerical results also show that the increased stress around the hypocenters of latter two events was mainly determined by the positive shear stress after the three strong earthquakes the coulomb stress on some active faults increased and is still increasing suggesting that great attention should be paid to the potential earthquake hazards in this region

strain accumulation across the gazikoy saros segment of the north anatolian fault inferred from persistent scatterer interferometry and gps measurements abstract we use a combination of persistent scatterer interferometry psi and gps observations to study interseismic crustal deformation on the gazikoy saros segment ganos fault of the north anatolian fault naf zone northwestern turkey the data include 44 c band radar images collected by the ers1 and ers2 satellites in descending orbits between 1992 and 2003 over the study area and campaign gps horizontal velocities from 7 stations the resultant secular velocity field is inverted using a nonlinear minimization algorithm to estimate parameters of two interseismic deformation models aseismic deep slip in a purely elastic earth model elastic half space rheology and viscoelastic flow in an elastic viscoelastic earth model viscoelastic coupling rheology the following conclusions are drawn 1 the fault locking depth is estimated in the range of 8 17 km 95 confidence interval regardless of the rheological model 2 the elastic half space model implies an upper bound of 20 27 mm yr for the slip rate on the ganos fault 3 models incorporating viscoelastic rheology and seismic cycle effects suggest a lower slip rate of 18 24 mm yr which agrees more closely with geological estimates however these values are slightly sensitive to the assumed earthquake recurrence interval 4 a bootstrap analysis of deformation data yields average crust upper mantle viscosities of 1 3 10 19 3 6 10 20 pa s for the ganos area

southern san andreas san jacinto fault system slip rates estimated from earthquake cycle models constrained by gps and interferometric synthetic aperture radar observations we use ground geodetic and interferometric synthetic aperture radar satellite observations across the southern san andreas saf san jacinto sjf fault systems to constrain their slip rates and the viscosity structure of the lower crust and upper mantle on the basis of periodic earthquake cycle maxwell viscoelastic finite element models key questions for this system are the saf and sjf slip rates the slip partitioning between the two main branches of the sjf and the dip of the saf the best fitting models generally have a high viscosity lower crust 10 21 pa s overlying a lower viscosity upper mantle 10 19 pa s we find considerable trade offs between the relative time into the current earthquake cycle of the san jacinto fault and the upper mantle viscosity with reasonable assumptions for the relative time in the earthquake cycle the partition of slip is fairly robust at around 24 26 mm a for the san jacinto fault system and 16 18 mm a for the san andreas fault models for two subprofiles across the saf sjf systems suggest that slip may transfer from the western coyote creek branch to the eastern clark superstition hills branch of the sjf from nw to se across the entire system our best fitting model gives slip rates of 2 3 12 9 12 9 and 17 3 mm a for the elsinore coyote creek clark and san andreas faults respectively where the large uncertainties in the slip rates for the sjf branches reflect the large uncertainty in the slip rate partitioning within the sjf system

interseismic strain accumulation spin up cycle invariance and irregular rupture sequences using models of infinite length strike slip faults in an elastic layer above linear viscoelastic regions we investigate interseismic deformation in the models we investigate interseismic strain accumulation on mature faults is the result of the cumulative effects of all previous ruptures and is independent of the fault loading conditions the time for a fault to spin up to a mature state depends on the rheologies and the fault loading conditions after the model has spun up the temporal variation of shear stresses is determined by the fault slip rate and model rheologies the change in stress during spin up depends on the slip rate rheologies and fault loading conditions but is independent of the magnitude of the initial stress over enough cycles such that the cumulative deformation is block like the average mature interseismic velocities are equal to the interseismic velocities of an elastic model with the same geometry and distribution of shear moduli in a model that has spun up with the fault rupturing periodically the cumulative deformation is block like at the end of each seismic cycle and the interseismic deformation is cycle invariant i e the same in all cycles when the fault ruptures nonperiodically the fault spins up to a mature state that is the same as if the fault had ruptured periodically with the mean slip rate when the fault slip rate within each cycle varies the interseismic deformation evolves toward the cycle invariant deformation determined by the most recent fault slip rate around a fault whose slip rate has been faster slower than average interseismic velocities are larger smaller than the cycle invariant velocities and increase decrease from cycle to cycle

finite strain calculations of continental deformation 2 comparison with the india asia collision zone numerical experiments on a thin viscous sheet model for deformation of continental lithosphere subjected to an indenting boundary condition yield distributions of crustal thickness of stress and strain rate and of latitudinal displacements that may be compared with observations in the india asia collision zone a simple indenting boundary condition applied to initially laterally homogeneous sheets obeying a power law rheology produces results that are in broad agreement with the observations provided that the power law exponent is three or greater and the sheet can support vertically integrated stress differences of 2 1013 5 1012 n m 1 in regions in front of the indenter under these conditions the calculated deformation shows accommodation of convergence primarily by crustal thickening to produce a plateau in front of the indenter palaeomagnetic data from india and tibet and the observed distribution of topography suggest that much of the post eocene convergence of india with asia has been taken up by deformation within asia that involved crustal thickening the principal difference between calculation and observation is the absence from the calculated strain rate fields of east west extension of the plateau in front of the indenting boundary the calculations show that once such a plateau is formed the buoyancy force associated with the crustal thickness contrast inhibits further thickening and the plateau strains at less than half the rate of its immediate surroundings seismically determined regional strain rates exhibit a similar distribution with the tibetan plateau straining at about one quarter the rate of the tien shan and ningxia gansu regions calculated principal compressive stress orientations and regional strain rates agree with the seismically determined quantities in the mongolia baikal tien shan tibet and ningxia gansu regions of asia to within the uncertainty of the latter the vertically integrated stresses that are calculated for the viscous sheet are comparable with those that can be supported by a theologically stratified continental lithosphere obeying laboratory determined flow laws we suggest that the thin viscous sheet model described in this paper and its companion gives a simple and physically plausible description of the observed deformation in central asia in this description the predominant mechanism of accommodation of continental convergence is diffuse crustal thickening with shear on vertical planes playing a subsidiary role once large crustal thickness contrasts have been established

postseismic motion after the 2001 mw 7 8 kokoxili earthquake in tibet observed by insar time series 1 on november 14th 2001 a mw 7 8 earthquake occurred in the kokoxili region of northern tibet the earthquake ruptured more than 400 km along the western part of the kunlun fault with a maximum of 8 m left lateral slip in this paper we use a multitemporal interferometric sar insar time series technique to map the postseismic motion following the large kokoxili event sar data from envisat descending orbits along five adjacent tracks covering almost the entire ruptured fault length are used to calculate the displacement time series for a period between 2 and 6 years after the earthquake a peak to trough signal of 8 cm in the radar line of sight is observed during the period between 2003 and 2008 two different mechanisms are employed to explain the observed surface displacements namely afterslip and viscoelastic relaxation the observations inverted for afterslip on and below the coseismic rupture plane shows that the maximum slip in the afterslip model is 0 6 m the position of the maximum postseismic slip is located in the middle of two relatively high coseismic slip patches which suggests that afterslip is a plausible mechanism models of viscoelastic stress relaxation in a maxwell half space give a best fitting viscosity for the mid to lower crust of 2 5 1019 pa s and the principal postseismic relaxation process is due to viscous flow in the lower crust to upper mantle however the insar observations are incapable of distinguishing between localized afterslip and distributed viscoelastic relaxation deformation and the lowest misfits are produced by mixed models of viscoelastic relaxation in the mantle below 70 km and afterslip in the crust modeling of viscoelastic relaxation in a maxwell half space and also a mixed mechanism model enables us to place an effective viscosity of 2 1019 pa s on the lower crust to mantle of northern tibet

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

finite strain calculations of continental deformation 1 method and general results for convergent zones a finite element method is used to calculate stresses and strain rates in a thin viscous sheet representing the continental lithosphere that is bordered in one part by an indenting boundary we calculate solutions for velocity fields crustal thickness distributions strain rates rotation time integrated vorticity and finite strain ellipsoids to show the dependence of these quantities on the controlling parameters the stress strain exponent n and the strength of the sheet relative to the gravitational forces which may be expressed as a dimensionless number the argand number ar for n 3 and ar between 1 and 10 a plateau of thickened crust is formed in front of the indenter the strain histories of individual elements within the viscous sheet may be quite complex and the finite strain at the end of deformation may bear no obvious relation to the principal stress orientations during the deformation the strain rate fields are interpreted in terms of the style of faulting that would be expected in the brittle upper crust if it were coupled to the ductile but stronger upper mantle in general the length scale of deformation increases with ar and time since the start of the collision and decreases with n for ar 3 the increase in length scale is accompanied by a change in the style of deformation from predominantly crustal thickening with thrust faulting in the brittle layer to predominantly transcurrent deformation strike slip faulting in the brittle layer

relationship of geodetic velocities to velocities in the mantle 1 we examine the relationship of the velocities at the surface i e geodetic velocities to the velocities in the upper most mantle throughout a seismic cycle we model the rheology of the lower crust and mantle as linear viscoelastic and vary the relative viscosities between the lower crust and mantle as well as the distribution of viscosities and secular velocities in the mantle we find that the geodetic velocities are related to the transient velocities at depth the strength of the relationship decreases as the contrast between the lower crust and mantle viscosity increases in these models we find that the geodetic velocities are not related to the secular velocities at depth

cenozoic shortening budget for the northeastern edge of the tibetan plateau is lower crustal flow necessary 1 two of the most popular mechanisms for thickening the crust beneath the tibetan plateau are 1 pure shear with faulting and folding in the upper crust and horizontal shortening below and 2 flow of lower or middle crust without significant shortening of the upper crust to help discriminate between the relative contributions of these two mechanisms well constrained estimates of upper crustal shortening are needed here we document the cenozoic shortening budget across the northeastern tibetan plateau margin with several balanced cross sections that exploit thermochronological and magnetostratigraphic constraints these sections indicate 11 2 1 east west shortening since middle miocene time and 9 2 3 nne ssw shortening between middle eocene and middle miocene times with little subsequent shortening of this orientation shortening rates accelerate fivefold after middle miocene time given the present day crustal thickness of 56 4 km in northeastern tibet crustal restorations that remove cenozoic shortening suggest that the northeastern tibetan crust was 45 5 km thick prior to the india asia continental collision this precollision thickness estimate is equivalent to average continental crustal thicknesses both adjacent to the tibetan plateau 44 4 km and globally 41 6 km and suggests that pure shear alone may account for cenozoic crustal thickening in northeastern tibet in contrast to eastern tibet where in the absence of significant shortening structures crustal flow has been invoked to explain the addition of crustal material since middle miocene time our results may obviate lower crustal flow as a necessary crustal thickening agent in northeastern tibet

large scale crustal deformation of the tibetan plateau the topography velocity and strain fields calculated from a three dimensional newtonian viscous model for large scale crustal deformation are generally in good agreement with results from geological geodetic and earthquake studies in and around the tibetan plateau provided that the model rheology incorporates a weak zone within the deep crust beneath the plateau equivalent to a viscosity of 1012 pa s within a 250 m thick channel or 1018 pa s within a 15 km thick channel model studies and observations show a plateau at 5 km elevation with steep topographic gradients across the southern and northern plateau margins and more gentle gradients across the southeastern and northeastern margins rapid shortening strain is concentrated along the lower portions of the northern and southern plateau margins at rates 20 mm yr model results show north south shortening 10 mm yr in reasonable agreement with gps data 5 8 mm yr of north south shortening across the northern two thirds of the plateau and east west stretching 10 15 mm yr across the eastern half of the high plateau in reasonable agreement with seismic geologic and gps data upper crustal material moves eastward from the plateau proper into a lobe of elevated topography that extends to the south and east clockwise rotation of material around the east himalayan syntaxis at rates up to 10 mm yr occurs partly as a result of dextral shear between indian and asian mantle at depth and partly as a result of gravitational spreading from the high plateau to the south and east there is little difference in model surface deformation for assumptions of moderately weak or extremely weak lower crust except in southern and northern tibet where margin perpendicular extension occurs only for the case of an extremely weak lower crust our results suggest that the tibetan plateau is likely to have gone through a two stage development the first stage produced a long narrow high orogen whose height may have been comparable to the modern plateau the second stage produced a plateau that grew progressively to the north and east east west stretching eastward plateau growth and dextral rotation around the east himalayan syntaxis probably did not begin until well into the second stage of plateau growth perhaps becoming significant after 20 m y of convergence

co seismic strike slip and rupture length produced by the 2001 ms 8 1 central kunlun earthquake field investigations show that the surface wave magnitude ms 8 1 central kunlun earthquake tibetan plateau of 14 november 2001 produced a nearly 400 kilometer long surface rupture zone with as much as 16 3 meters of left lateral strike slip along the active kunlun fault in northern tibet the rupture length and maximum displacement are the largest among the co seismic surface rupture zones reported on so far the strike slip motion and the large rupture length generated by the earthquake indicate that the kunlun fault partitions its deformation into an eastward extrusion of tibet to accommodate the continuing penetration of the indian plate into the eurasian plate

earthquake cycle deformation and fault slip rates in northern tibet fault slip rate estimates along the altyn tagh and kunlun strike slip faults in northern tibet vary considerably between short term geodetic and long term geologic studies here we reanalyze and model all global positioning system gps data from northern tibet to determine if these differences might be explained by previously unmodeled transient processes associated with the earthquake cycle which can bias slip rate estimates from geodetic data we find that these effects cannot reconcile the geodetic data with the lowest bounds on the geologic slip rates along these faults even in the presence of low 1018 pa s viscosities within the mid crust or crust and mantle lithosphere surface velocities derived from gps measurements are best reproduced with models with a high viscosity 1018 pa s middle to lower crust and mantle lithosphere

eastward glacier like flow of the tibetan crust constrained from power law rheology abstract we propose that topography can be used as a proxy for the eastward lateral glacier like flow of the tibetan crust in the himalayan tibetan orogenic system geodetic observations across the tibetan plateau indicate 22 mm yr of crustal motion with respect to stable eurasia by considering newtonian channel flow model further correlation between regional strain rate e and topographic elevation h is found to be statistically robust with stress exponent n of 3 03 0 1 therefore we suggest that the tibetan crust follows well defined power law relation that is consistent with the nonlinear deformation associated with dislocation creep moreover the predicted viscosity range of the tibetan crust is consistent with the channel flow model proposed by previous investigators using different approaches in different time scales

slip rate gradients along the eastern kunlun fault 1 whether strike slip fault systems in eurasia accomplish eastward extrusion of tibetan crust and lithosphere depends largely on the kinematics of deformation at the fault tip here we present new slip rate determinations using millennial scale geomorphic markers from sites along the easternmost segment of the kunlun fault in north central tibet this fault system represents one of the major strike slip faults within the indo asian collision zone has been argued to exhibit uniform slip rates along much of its length and plays a central role in models for eastward extrusion of tibetan lithosphere displaced fluvial terrace risers along tributaries of the yellow river coupled with 14c ages of terrace material provide constraints on slip rates over late pleistocene to holocene time results indicate that slip rates decrease systematically along the eastern 150 km of the fault from 10 to 2 mm yr these data challenge the view that slip along the kunlun fault remains uniform along the entire length of the fault and instead reveal gradients in displacement similar to those expected at fault tips moreover slip along the fault appears to terminate within the thickened crust of the plateau and therefore any extrusion of tibetan lithosphere accomplished by slip along the kunlun fault must be absorbed by internal deformation of the plateau surrounding the fault tip

a comparison of geodetic and geologic rates prior to large strike slip earthquakes a diversity of earthquake cycle behaviors comparison of preevent geodetic and geologic rates in three large magnitude mw 7 6 7 9 strike slip earthquakes reveals a wide range of behaviors specifically geodetic rates of 26 28 mm yr for the north anatolian fault along the 1999 mw 7 6 izmit rupture are 40 faster than holocene geologic rates in contrast geodetic rates of 6 8 mm yr along the denali fault prior to the 2002 mw 7 9 denali earthquake are only approximately half as fast as the latest pleistocene holocene geologic rate of 12 mm yr in the third example where a sufficiently long pre earthquake geodetic time series exists the geodetic and geologic rates along the 2001 mw 7 8 kokoxili rupture on the kunlun fault are approximately equal at 11 mm yr these results are not readily explicable with extant earthquake cycle modeling suggesting that they may instead be due to some combination of regional kinematic fault interactions temporal variations in the strength of lithospheric scale shear zones and or variations in local relative plate motion rate whatever the exact causes of these variable behaviors these observations indicate that either the ratio of geodetic to geologic rates before an earthquake may not be diagnostic of the time to the next earthquake as predicted by many rheologically based geodynamic models of earthquake cycle behavior or different behaviors characterize different fault systems in a manner that is not yet understood or predictable

paleoseismic event dating and the conditional probability of large earthquakes on the southern san andreas fault california we introduce a quantitative approach to paleoearthquake dating and apply it to paleoseismic data from the wrightwood and pallett creek sites on the southern san andreas fault we illustrate how stratigraphic ordering sedimentolog ical and historical data can be used quantitatively in the process of estimating earth quake ages calibrated radiocarbon age distributions are used directly from layer dating through recurrence intervals and recurrence probability estimation the method does not eliminate subjective judgements in event dating but it does provide a means of systematically and objectively approaching the dating process date dis tributions for the most recent 14 events at wrightwood are based on sample and contextual evidence in fumal et al 2002 and site context and slip history in weldon et al 2002 pallett creek event and dating descriptions are from published sources for the five most recent events at wrightwood our results are consistent with pre viously published estimates with generally comparable or narrower uncertainties for pallett creek our earthquake date estimates generally overlap with previous results but typically have broader uncertainties some event date estimates are very sensitive to details of data interpretation the historical earthquake in 1857 ruptured the ground at both sites but is not constrained by radiocarbon data radiocarbon ages peat accumulation rates and historical constraints at pallett creek for event x yield a date estimate in the earliest 1800s and preclude a date in the late 1600s this event is almost certainly the historical 1812 earthquake as previously concluded by sieh et al 1989 this earthquake also produced ground deformation at wrightwood all events at pallett creek except for event t about a d 1360 and possibly event i about a d 960 have corresponding events at wrightwood with some overlap in age ranges event t falls during a period of low sedimentation at wrightwood when conditions were not favorable for recording earthquake evidence previously pro posed correlations of pallett creek x with wrightwood w3 in the 1690s and pallett creek event v with w5 around 1480 fumal et al 1993 appear unlikely after our dating reevaluation apparent internal inconsistencies among event layer and dating relationships around events r and v identify them as candidates for further inves tigation at the site conditional probabilities of earthquake recurrence were estimated using poisson lognormal and empirical models the presence of 12 or 13 events at wrightwood during the same interval that 10 events are reported at pallett creek is reflected in mean recurrence intervals of 105 and 135 years respectively average poisson model 30 year conditional probabilities are about 20 at pallett creek and 25 at wrightwood the lognormal model conditional probabilities are somewhat higher about 25 for pallett creek and 34 for wrightwood lognormal variance rln estimates of 0 76 and 0 70 respectively imply only weak time predictability conditional probabilities of 29 and 46 respectively were estimated for an em pirical distribution derived from the data alone conditional probability uncertainties are dominated by the brevity of the event series dating uncertainty contributes only secondarily wrightwood and pallett creek event chronologies both suggest varia tions in recurrence interval with time hinting that some form of recurrence rate modulation may be at work but formal testing shows that neither series is more ordered than might be produced by a poisson process

inferring fault characteristics using fold geometry constrained by airborne laser swath mapping at raplee ridge utah 1 we used airborne laser swath mapping alsm data to define the geometry of strata in raplee ridge in southeastern utah that were likely deformed by slip on an underlying fault the fold geometry was used to infer the fault geometry and loading responsible for the folding using the boundary element model poly3d monte carlo markov chain mcmc methods created probability density functions pdfs that reveal the most likely fault geometry and loading conditions and their uncertainties despite the restrictive assumptions of poly3d in which body deformations occur from slip on displacement discontinuities in a homogeneous linear elastic half space the strata deflections are matched remarkably well and the resulting inferences of fault geometry and stress field appear reasonable we propose that similar methods may be used with models that include more complicated rheologies and heterogeneous and anisotropic material properties to estimate fault geometries and loading conditions where only deflection of strata record these parameters

partitioning of localized and diffuse deformation in the tibetan plateau from joint inversions of geologic and geodetic observations abstract the spatial complexity of continental deformation in the greater tibetan plateau region can be defined as the extent to which relative motion of the indian and asian plates is partitioned between localized slip on major faults and distributed deformation potency rates provide a quantitative metric for determining the magnitudes of diffuse and on fault crustal deformation which are proportional to strain rates within crustal micro plates and fault slip rates respectively we simultaneously estimate micro plate rotation rates interseismic elastic strain accumulation fault slip rates on major structures and strain rates within 24 tectonic micro plates inferred from active fault maps in the greater tibetan plateau region using quasi static block models constrained by interseismic surface velocities at 731 gps sites and 9 holocene late quaternary geologic fault slip rates the joint geodetic geologic inversion indicates that geologic slip rates are kinematically consistent with differential micro plate motions estimated left lateral slip rates on the altyn tagh west central kunlun and xianshuihe faults are relatively homogeneous along strike 11 5 10 5 and 11 mm yr respectively while segmentation of the eastern kunlun fault by the intersecting elashan and riyueshan faults results in a decreased slip rate consistent with geologic observations the fraction of total potency rate associated with intrablock strain uncorrected for observational noise ranges from 0 27 in the himalayan range block to 0 91 in the aksai chin block monte carlo simulations are used to quantify the likelihood that internal deformation is statistically distinguishable from the uncertainties in geodetic velocities these simulations indicate that internal block deformation is statistically significant only within the himalayan range front where internal deformation accounts for id 0 11 of block potency rate budget west central plateau id 0 68 ganzi yushu xianshuihe 0 58 burma 0 09 jiali 0 38 and aksai chin 0 68 blocks in the other 18 tectonic micro plates within the plateau region estimated internal block potency is not currently distinguishable from the expected contribution of observational noise to residual velocities of the total potency budget within the tibetan plateau 85 is taken up by slip on major faults with the remaining 15 accommodated by internal processes at sub block scale distinguishable from observational noise the localization of the majority of plate boundary activity is also supported by the spatial distribution of modern and historical crustal earthquakes sixty seven percent of the total moment released by earthquakes in the cmt catalog and 90 of historical moment since 1900 have been released within 25 km of the major faults included in the block model representing only 12 of the characteristic half block length scale of 215 km the localization of deformation inferred from geologic geodetic and seismic observations suggests that forces applied to tectonic micro plates drive fault system activity at the india asia collision zone over decadal to quaternary time scales

lower crustal heterogeneity beneath the northern tibetan plateau constrained by gps measurements following the 2001 mw7 8 kokoxili earthquake

bayesian inference of plastosphere viscosities near the kunlun fault northern tibet 1 flow of the mid crust in the tibetan plateau may strongly influence the patterns of deformation and topography within this area this flow requires the lower crust to have low viscosity and so quantifying this viscosity may be used to test the idea of channel flow an application of bayesian methods to geologic and geodetic data from north central tibet yields lower crustal viscosities assumed newtonian of 1 1019 pa s and 2 1021 pa s 95 bounds the lower bound is larger than the value of 1016 1018 pa s required by models of flow of the lower crust of tibet unless the entire lower crust participates in channel flow

deducing paleoearthquake timing and recurrence from paleoseismic data part i evaluation of new bayesian markov chain monte carlo simulation methods applied to excavations with continuous peat growth determining the timing of paleoearthquakes is a central goal of paleoseismology and serves as an important input to seismic hazard evaluations herein we develop a bayesian statistical method for refining the ages of strata and earthquakes and calculating the recurrence of earthquakes based on data from paleoseismic excavations our work extends previous paleoseismic bayesian modeling by simultaneously calculating the joint posterior probability density of recurrence intervals earthquake ages and layer ages to estimate this joint posterior density we employed the metropolis hastings markov chain monte carlo mcmc sampling method we used the wrightwood paleoseismic excavation site as a test bed for our method by comparing the results derived from our simulation to those of previous studies we found that for stratigraphic order constraints our results agreed well with previously used methods however when peat growth was used to constrain the minimum time that separates layers from one another a systematic aging of strata in the lower portion of the stratigraphic column resulted inspection of our results indicated that rather than representing a minimum time that separates layers peat growth instead determined the strata s ages exactly when a constant peat growth rate was prescribed using this information we developed a new method of improving layer age earthquake age and recurrence interval estimates at sites where peat bearing layers are present this method generally produces layer age estimates with less variance than previous methods and requires that both proximal stratigraphic constraints and trench wide constraints be obeyed the benchmarking of the mcmc simulation results shows that simulation provides an effective and efficient way of improving estimates of layer ages earthquake ages and recurrence intervals

inference of multiple earthquake cycle relaxation timescales from irregular geodetic sampling of interseismic deformation abstract characterizing surface deformation throughout a full earthquake cycle is a challenge due to the lack of high resolution geodetic observations of duration comparable to that of characteristic earthquake recurrence intervals 250 10 000 years here we approach this problem by comparing long term geologic slip rates with geodetically derived fault slip rates by sampling only a short fraction 0 001 0 1 of a complete earthquake cycle along 15 continental strike slip faults geodetic observations provide snapshots of surface deformation from different times through the earthquake cycle the timing of the last earthquake on many of these faults is poorly known and may vary greatly from fault to fault assuming that the underlying mechanics of the seismic cycle are similar for all faults geodetic observations from different faults may be interpreted as samples over a significantly larger fraction of the earthquake cycle than could be obtained from the geodetic record along any one fault alone as an ensemble we find that geologically and geodetically inferred slip rates agree well with a linear relation of 0 94 0 09 to simultaneously explain both the ensemble agreement between geologic and geodetic slip rate estimates with observations of rapid postseismic deformation we consider the predictions from simple two layer earthquake cycle models with both maxwell and burgers viscoelastic rheologies we find that a two layer burgers model with two relaxation timescales is consistent with observations of deformation throughout the earthquake cycle whereas the widely used two layer maxwell model with a single relaxation timescale is not suggesting that the earthquake cycle is effectively characterized by a largely stress recoverable rapid postseismic stage and a much more slowly varying interseismic stage

how does crustal shortening contribute to the uplift of the eastern margin of the tibetan plateau the eastern margin of the tibetan plateau the longmen shan has triggered a vigorous debate to explain the uplift and maintaining of its steep and high topography several mechanical and kinematic models have been previously developed in order to investigate the tectonic and erosional control on the formation mechanism of the longmen shan but the contribution of crustal shortening has never been taken into account due to the lack of significant surface convergence rate about 3 mm a across the longmen shan range we investigate this question through 2d finite element modelling assuming visco elasticity rheology the numerical results are constrained with geological and geophysical observations across the longmen shan range we find that even low rate of crustal shortening contributes significantly to the uplift of the longmen shan this contribution has been greatly underestimated in previous studies the viscosity contrast between the tibetan plateau lower crust and the yangtze crust crucially controls the uplift of the longmen shan due to crustal shortening the ductile tibetan lower crust thickens to accommodate most of crust shortening as the eastward movement of the tibetan plateau is obstructed by the mechanical strong and stable yangtze craton the uplift rate contrast between the tibetan plateau and the sichuan causes a steep uplift rate gradient to produce and maintain the longmen shan steep and high topography in the time scale of several million years our results support a possible explanation for the paradox of the high topography and low convergence rate at the longmen shan range

inescapable slow slip on the altyn tagh fault 1 gps surveys conducted in 1994 1998 and 2002 on the central portion of the altyn tagh fault confirm left lateral slip rates of 9 4 mm yr significantly slower than geological estimates of slip rate for the past several thousand years the measurements were obtained on a 300 km long profile between 88 and 91 e within one fault dimension of the mw 7 6 and mw 7 8 kunlun earthquakes of 1997 and 2001 the inferred elastic displacements from these events are incorporated into the interpreted 1994 2002 velocity field the recent serendipitous occurrence of these two large earthquakes on a sub parallel fault system suggests that slip on the kunlun fault may have recently accelerated thereby reducing the slip rate on the altyn tagh fault however geodetic data from northern tibet prior to the 2001 earthquake indicate present day rates similar to long term rates this suggests that systematic errors may be present in published geologic slip rate estimates for the altyn tagh fault

precambrian fossil vermiforma is a tectograph vermiforma antiqua cloud 1976 1 once celebrated as the earliest animal fossil of the united states is actually a tectonic artifact the main argument is that the congruence and equal orientation of multiple patterns on the same bedding plane are incompatible with swaying worm bodies or worm burrows as shown by analog and numerical simulations these structures can be explained as tracks of particles that broke out from the base of an overlying turbidite and became rolled between beds during bed to bed shearing 1 ref 5

crustal rheological strength heterogeneities control the formation of continental plateau margins the margins bordering the tibetan plateau show two end member morphologies in topographic gradient steep margins and low gradient margins to investigate the formation mechanism of convergent intracontinental plateau margins we conduct 2d numerical experiments to simulate crustal deformation process across plateau margins our numerical experiments demonstrate that heterogeneities in crustal rheological strength control significantly the formation of plateau margins when subjected to crustal convergence a very steep margin is the result of crustal convergence between plateau with weak lower crust and foreland basin with strong lower crust by contrast a low gradient margin could result from crustal convergence between plateau and foreland with less strength contrast this finding suggests that the diversity in topographic gradient along the tibetan plateau borders reflects heterogeneities in crustal rheological strength across the plateau margins steep gradient at the margins indicate large crustal rheological strength contrasts between the weak ductile lower crust of the tibetan plateau and its strong surrounding foreland basins like the sichuan basin the tarim basin and the qaidam basin beneath these steep margins the horizontal flow of the tibetan ductile lower crust is inhibited and forced to extrude to support escarpments low gradient at the margins indicate less crustal strength variations between the plateau and outer forelands like at the northeastern and southeastern margins where they might be outlets for the weak ductile tibetan lower crust to flow away from the plateau

effect of ice sheet growth and melting on the slip evolution of thrust faults abstract field investigations suggest that postglacial unloading and rebound led to the formation or re activation of reverse faults even in continental shields like scandinavia here we use finite element models including a thrust fault embedded in a rheologically layered lithosphere to investigate its slip evolution during glacial loading and subsequent postglacial unloading the model results show that the rate of thrusting decreases during the presence of an ice sheet and strongly increases during deglaciation the magnitude of the slip acceleration is primarily controlled by the thickness of the ice sheet the viscosity of the lithospheric layers and the long term shortening rate in contrast the width of the ice sheet the rate of deglaciation or the fault dip have an only minor influence on the slip evolution in all experiments the slip rate variations are caused by changes in the differential stress the modelled deglaciation induced slip acceleration agrees well with the occurrence of large earthquakes soon after the melting of the fennoscandian ice sheet which led to the formation of spectacular fault scarps in particular in the lapland fault province furthermore our model results support the idea that the low level of seismicity in currently glaciated regions like greenland and antarctica is caused by the presence of the ice sheets based on our models we expect that the decay of the greenland and antarctica ice sheets in the course of global warming will ultimately lead to an increase in earthquake frequency in these regions