shallow creep on the haiyuan fault gansu china revealed by sar interferometry interferometric synthetic aperture radar data are used to map the interseismic velocity field along the haiyuan fault system hfs at the north eastern boundary of the tibetan plateau two m 8 earthquakes ruptured the hfs in 1920 and 1927 but its 260 km long central section known as the tianzhu seismic gap remains unbroken since 1000 years the envisat sar data spanning the 2003 2009 period cover about 200 300 km2 along three descending and two ascending tracks interferograms are processed using an adapted version of roi pac the signal due to stratified atmospheric phase delay is empirically corrected together with orbital residuals mean line of sight velocity maps are computed using a constrained time series analysis after selection of interferograms with low atmospheric noise these maps show a dominant left lateral motion across the hfs and reveal a narrow 35 km long zone of high velocity gradient across the fault in between the tianzhu gap and the 1920 rupture we model the observed velocity field using a discretized fault creeping at shallow depth and a least squares inversion the inferred shallow slip rate distribution reveals aseismic slip in between two fully locked segments the average creep rate is 5 mm yr 1 comparable in magnitude with the estimated loading rate at depth suggesting no strain accumulation on this segment the modeled creep rate locally exceeds the long term rate reaching 8 mm yr 1 suggesting transient creep episodes the present study emphasizes the need for continuous monitoring of the surface velocity in the vicinity of major seismic gaps in terms of seismic hazard assessment

viscosity structure of the crust and upper mantle in western nevada from isostatic rebound patterns of the late pleistocene lake lahontan high shoreline received 13 july 2005 revised 26 october 2006 accepted 31 january 2007 published 8 june 2007 1 large lakes can both produce and record significant crustal deformation we present an analysis of the isostatic rebound pattern recorded in the shorelines of paleolake lahontan in western nevada using a layered maxwell viscoelastic model the inferred viscosity structure depends on loading history we use three variants of a well documented lake surface elevation model as input and recover corresponding estimates of viscosity and density structure a simple two layer model with an elastic plate over an inviscid half space fits the observed elevation pattern quite well with a residual variance of 32 of the data variance using multilayered finite viscosity models the residual variance is reduced to 20 of the data variance which is very near to the noise level in the higher resolution models the viscosity is below 10 18 pa s over the depth range from 80 to 160 km the minimum viscosity is very similar to the value that has been seen in the eastern great basin from similar analyses of lake bonneville shorelines but the lowviscosity zone is thinner beneath bonneville making small adjustments to a seismically derived density structure allows an improved fit to the shoreline observations additionally we find that small variations in proposed loading models can result in presumably spurious density inversions and suggest that this modeling approach provides a test for loading histories

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

seasonal cross shelf distribution of major zooplankton taxa on the northern gulf of alaska shelf relative to water mass properties species depth preferences and vertical migration behavior the cross shelf distribution of major zooplankton species was examined on the northern gulf of alaska goa shelf during the production season for four years between october 1997 and october 2001 the zooplankton community on the northern goa shelf consisted of oceanic and neritic species of the north pacific subarctic species complex cross shelf distribution of the major zooplankton species was influenced by their depth preferences vertical migration behavior salinity temperature preferences and by cross shelf water mass distribution and movement the neritic community dominated by pseudocalanus spp metridia pacifica and calanus marshallae had highest abundances on the inner shelf in the alaska coastal current and in the adjacent fjords in late spring and early summer the oceanic community which contained primarily neocalanus cristatus and eucalanus bungii was observed in the alaskan stream and adjacent waters near the shelf break a mid shelf transition zone contained a mixture of oceanic and neritic species prince william sound pws contained a unique species complex of large mesopelagic copepods amphipods and shrimp neocalanus flemingeri and oithona similis were abundant in all four regions during spring and early summer the transition zone commonly crossed much of the shelf between the shelf break and the acc but satellite images and ctd data indicate that occasionally a narrow shelf break front can form in which case distinct zooplankton species groups are observed on either side of the front satellite data also revealed numerous large and small eddies which probably contribute to cross shelf mixing in the transition zone

indepth iii seismic data from surface observations to deep crustal processes in tibet 1 during the summer of 1998 active source seismic data were collected along a transect running 400 km nnw sse across the central tibetan plateau as the third phase of project indepth international deep profiling of tibet and the himalaya the transect extends northward from the central lhasa block across the jurassic bangong nujiang suture bns at 89 5 e to the central qiangtang block a seismic velocity model for the transect to 25 km depth produced by inversion of p wave first arrivals on 3000 traces shows 1 a 50 km wide region of low velocity at least 5 less than surrounding velocities extending to the base of the model at the bns 2 sedimentary cover for the southern qiangtang block that is 3 5 km thick 3 a distinct interface between sedimentary cover and qiangtang basement or underplated jurassic melange in the central qiangtang block and 4 evidence that the bangoin granite extends to a depth of at least 15 km the bns has little geophysical signature and appears unrelated to the 5 km northward shallowing of the moho which is associated with the bns in central tibet geophysical data along the main indepth iii transect show little evidence for widespread crustal fluids in contrast to the seismic bright spots found in southern tibet and to magnetotelluric evidence of fluid accumulations in eastern tibet a comparison between the global average and tibetan velocity depth functions offers constraints for models of plateau uplift and crustal thickening taken together with the weak geophysical signature of the bns these velocity depth functions suggest that convergence has been accommodated largely through pure shear thickening accompanied by removal of lower crustal material by lateral escape likely via ductile flow although we cannot resolve the details we believe lateral lower crustal flow has overprinted or destroyed evidence in the deep crust for the earlier assembly of tibet as a series of accreted terranes

the crustal viscosity gradient measured from post seismic deformation a case study of the 1997 manyi tibet earthquake abstract we here analyse an insar dataset which constrains the temporal and spatial distribution of post seismic ground displacement following the 1997 manyi tibet earthquake to estimate the depth variation of creep viscosity within the crust we use a method which depends on the detection and measurement of a systematic variation in post seismic relaxation rate with distance from the fault at a given distance the displacement rates may be compared with the prediction of a uniform viscosity model with apparent viscosity u the rate at which u decreases with distance from the fault is directly diagnostic of the parameter that controls the vertical gradient of viscosity in a stratified crust our best fit viscosity profile for manyi exponentially decreases from 1 2 10 21 pa s at the top of the visco elastic layer at 10 km to 1 6 10 18 pa s at the moho at 60 km the predicted temporal and spatial variations of post seismic displacements generally fit the observed post day 165 displacements within error if we assume that displacements pre day 165 are attributed to after slip on the fault within error the crustal viscosity at 10 km depth may range between 6 1 10 20 pa s and 1 4 10 22 pa s estimates of the maxwell time constant consistent with an inter seismic period of 500 1000 yr imply an effective elastic layer thickness of 20 km for best fit and upper bound viscosity solutions we also show that the estimated viscosity profile is broadly consistent with laboratory measurements of creep for crustal materials like quartzite and granite by deducing from our viscosity profile the ratio q n of activation energy to stress exponent at 45 81 kj mole thus providing a new link between laboratory scale measurements of creep deformation and viscosity measured from post seismic relaxation

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

tandem afterslip on connected fault planes following the 2008 nima gaize tibet earthquake 1 on 9 january 2008 a m 6 4 normal faulting earthquake occurred in central tibet near the border of nima and gaize counties and just north of the bangong nujiang suture zone a week later a m 5 9 aftershock occurred a few kilometers to the northwest of the main shock here we consider interferometric synthetic aperture radar insar data from the japanese alos and european envisat satellites covering both the coseismic phase and 9 months of postseismic deformation the coseismic interferograms clearly show surface deformation resulting from both main shock and aftershock ruptures and data inversions using elastic dislocation models suggest that two northwest dipping faults form a synthetic system with the more steeply dipping aftershock plane meeting the main shock plane at depth postseismic interferograms show first order similarities with their coseismic counterparts indicating that afterslip occurred on both main shock and aftershock rupture surfaces during the months following the earthquakes the afterslip occurred at comparable depths to the coseismic slip but the amount of slip was about an order of magnitude smaller a slip template method is used to obtain moment release estimates at different postseismic time intervals and hence document the time dependence of the postseismic transient the exponential decay time of the afterslip is 34 days and the moment release due to the afterslip was about 10 of the coseismic moment models of viscoelastic stress relaxation in a maxwell half space place a strong lower bound on midcrust to lower crustal viscosity of 3 1017 pa s postseismic data covering a longer time span have the potential to improve this constraint

crustal structure of central tibet as derived from project indepth wide angle seismic data summary in the summer of 1998 project indepth recorded a 400 km long nnw sse wide angle seismic profile in central tibet from the lhasa terrane across the banggong nujiang suture bns at about 89 5 e and into the qiangtang terrane analysis of the p wave data reveals that 1 the crustal thickness is 65 5 km beneath the line 2 there is no 20 km step in the moho in the vicinity of the bns as has been suggested to exist along strike to the east based on prior fan profiling 3 a thick high velocity lower crustal layer is evident along the length of the profile 20 35 km thick 6 5 7 3 km s 1 and 4 in contrast to the southern lhasa terrane there is no obvious evidence of a mid crustal low velocity layer in the p wave data although the data do not negate the possibility of such a layer of modest proportions combining the results from the indepth iii wide angle profile with other seismic results allows a cross section of moho depths to be constructed across tibet this cross section shows that crustal thickness tends to decrease from south to north with values of 70 80 km south of the middle of the lhasa terrane 60 70 km in the northern part of the lhasa terrane and the qiangtang terrane and less than 60 km in the qaidam basin the overall northward thinning of the crust evident in the combined seismic observations coupled with the essentially uniform surface elevation of the plateau south of the qaidam basin is supportive of the inference that northern tibet until the qaidam basin is underlain by somewhat thinner crust which is isostatically supported by relatively low density hot upper mantle with respect to southern tibet

cold halocline in the northern california current an invasion of subarctic water 1 subsurface upper ocean waters off oregon and vancouver island were about 1 c cooler in july 2002 than in july 2001 the anomalously cool layer coincides with the permanent halocline which has salinities of 32 2 to 33 8 suggesting an invasion of nutrient rich subarctic waters the anomalously cool layer lies at 30 150 m the cool anomaly is likely caused by stronger southward flow in the california current and weaker northward flow in the alaska and davidson currents during spring 2002 other factors may include reduced coastal downwelling in late winter and early spring 2002 enhanced eastward flow in the subarctic current and enhanced winter mixing offshore

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

interpretation of interseismic deformations and the seismic cycle associated with large subduction earthquakes abstract the deformations of the overriding and subducting plates during the seismic cycle associated with large subduction earthquakes are modelled using 2d and 3d finite element techniques a particular emphasis is put on the interseismic velocities and on the impact of the rheology of the asthenosphere the distance over which the seismic cycle perturbs significantly the velocities depends upon the ratio of the viscosity in the asthenosphere to the period of the seismic cycle and can reach several thousand km for rheological parameters deduced from the first years of deformation after the aceh earthquake for a same early postseismic velocity a burger rheology of the asthenosphere implies a smaller duration of the postseismic phase and thus smaller interseismic velocities than a maxwell rheology a low viscosity wedge lvw modifies very significantly the predicted horizontal and vertical motions in the near and middle fields in particular with a lvw the peak in vertical velocity at the end of the cycle is predicted to be no longer above the deep end of the locked section of the fault but further away above the continentward limit of the lvw the lateral viscosity variations linked to the presence at depth of the subducting slab affect substantially the results the north south interseismic compression predicted by this preliminary 2d model over more than 1500 km within the sunda block is in good agreement with the pre 2004 velocities with respect to south china inferred from gps observations in thailand malaysia and indonesia in japan before the tohoku earthquake the eastern part of northern honshu was subsiding while the western part was uplifting this transition from subsidence to uplift so far away from the trench is well fitted by the predictions from our models involving a lvw most of the results obtained here in a 2d geometry are shown to provide a good estimate of the displacements for fault segments of finite lateral extent with a 3d spherical geometry as long as the displacements during the seismic cycle are normalised by the coseismic displacement

evidence for mechanical coupling and strong indian lower crust beneath southern tibet how surface deformation within mountain ranges relates to tectonic processes at depth is not well understood the upper crust of the tibetan plateau is generally thought to be poorly coupled to the underthrusting indian crust because of an intervening low viscosity channel here however we show that the contrast in tectonic regime between primarily strike slip faulting in northern tibet and dominantly normal faulting in southern tibet requires mechanical coupling between the upper crust of southern tibet and the underthrusting indian crust such coupling is inconsistent with the presence of active channel flow beneath southern tibet and suggests that the indian crust retains its strength as it underthrusts the plateau these results shed new light on the debates regarding the mechanical properties of the continental lithosphere and the deformation of tibet

seismicity of central tibet from project indepth iii seismic recordings as part of project international deep profiling of tibet and the himalaya iii a 400 km long densely spaced array of 57 broadband and short period seismic stations was deployed in central tibet from august 1998 through may 1999 although originally designed to image the lithosphere with teleseismic events the array also recorded numerous local and regional seismic events more than 900 local and regional events were detected on at least 10 stations during the 1 year deployment and we were able to locate 267 local earthquakes a substantial number of the events were found to cluster in or near large grabens and along known strike slip faults while other events show no obvious correlation with known structures in addition to spatial clustering at least one of the large clusters also exhibits temporal clustering that may be associated with magmatic or geothermal activity in the upper crust the average v p and v s are estimated to be 5 85 and 3 35 km sec for the upper crust and 7 0 and 3 9 km sec for the lower crust respectively the 50 focal mechanisms computed from this set of events are consistent with north south shortening and east west extension there are no clear indications of significant local perturbations in the regional stress field induced by the collision between india and eurasia the majority of the focal mechanisms indicate normal and strike slip faulting at least six of the newly computed focal mechanisms however indicate thrust faulting which is a phenomenon not well documented previously ninety nine percent of the local earthquakes have focal depths shallower than 25 km and the locations of the few deeper events are poorly constrained the shallow earthquake focal depths are consistent with high temperatures and proposed ductile or aseismic behavior in the middle to lower crust of central tibet figure 6 1 figure 6 a earthquake locations computed from this study shown on shaded topographic data triangles are indepth iii seismic stations circles are events and are scaled by magnitude graphic 2 a color version of this figure is available online at the ssa web site b earthquake locations shown with major geologic structures from taylor et al 2003 3 reproduced with permission m h taylor personal comm 2002 triangles are indepth iii seismic stations geologic structures are as in figure 2 4 1 pending yes 2 f1 embed inline graphic 1 gif 3 ref 46 4 f3

post seismic motion following the 1997 manyi tibet earthquake insar observations and modelling summary on november 8 1997 a mw 7 6 earthquake occurred in the manyi region of northern tibet near the western end of the kunlun fault over 7 m of left lateral slip occurred on a 200 kmlong fault here we use insar observations of post seismic surface deformation following the manyi earthquake to investigate possible causal mechanisms time series of deformation are constructed from 26 interferograms covering the entire length of the fault for nearly 4 yr after the earthquake three different modelling approaches are used to try and understand the observed variations in surface displacement first order poroelastic models predict displacement fields which do not match those observed modelling of viscoelastic stress relaxation in a half space with standard linear solid rheology beneath an elastic lid provides a reasonable fit to the observations and demonstrates that two relaxation times are needed to characterize the post seismic transient the best fitting viscosity is 4 10 18 pa s and the fully relaxed shear modulus is 32 per cent of the purely elastic value a model with a maxwell viscoelastic halfspace underlying the lid cannot explain the observations at later times larger viscosities are required than at earlier times this increase in effective viscosity with time may be consistent with stress relaxation occurring in a power law rheology the time series are also inverted for distributed afterslip on an extension of the coseismic rupture along strike correlation of coseismic and post seismic slip maxima suggests that afterslip is a plausible mechanism the maximum slip in the afterslip model is 0 72 m after 3 yr and the equivalent moment release is approximately 20 per cent of the coseismic moment this study shows that it is possible to rule out certain mechanisms as the dominant post seismic process but with the current insar data set it is difficult to distinguish between other plausible options

measurement of interseismic strain across the haiyuan fault gansu china by insar the haiyuan fault is part of a major left lateral fault system at the northeastern edge of the tibet qinghai plateau two m8 earthquakes 1920 and 1927 occurred along the fault bracketing an unbroken section of the fault identified as the tianzhu seismic gap we use interferometric synthetic aperture radar data from descending orbits of the ers satellites acquired between 1993 and 1998 along two adjacent tracks covering the gap to measure the current surface movements and better understand the present day mechanical behavior of this fault section the analysis of the radar data involves first the combined correction of orbital errors and errors associated with the phase delay through the troposphere a subset of the data is then selected based on the analysis of the residual noise spectra for each pair of data the selected interferograms are stacked and the average phase change rate is converted in fault parallel velocity assuming that the ground movement is horizontal and parallel to the fault velocity maps from both tracks show a zone of high velocity gradient across the fault a few kilometers wide consistent with left lateral slip on the haiyuan fault the average velocity field from the two tracks in their overlapping area is well fit with a single screw dislocation model in an elastic half space the derived fault slip rate at depth 4 2 8 mm yr is consistent with recent gps results the corresponding shallow apparent locking depth 0 4 2 km can be explained by a current low stress accumulation on the fault due to creep almost on the entire fault plane however unless it is transient this creep would be paradoxical with the occurrence of past large earthquakes along this fault section as revealed by paleoseismology an alternative model implying both shallow creep in the brittle upper crust and deep aseismic slip beneath the seismogenic layer separated by a locked section would be consistent with insar observations and with the potential for large earthquakes on the fault as well a two dislocation model with slip at 5 mm yr beneath 15 km and a transient creep rate of 11 mm yr between 2 and 7 km fits the insar data however the width and creep rate of the shallow creeping zone and their possible along strike variations are still poorly resolved with the present data set

implications of deformation following the 2002 denali alaska earthquake for postseismic relaxation processes and lithospheric rheology 1 during the first 2 years following the 2002 mw 7 9 denali alaska strike slip earthquake a large array of global positioning system gps receivers recorded rapid postseismic surface motions extending at least 300 km from the rupture and at rates of more than 100 mm yr in the near field here we use three dimensional 3 d viscoelastic finite element models to infer the mechanisms responsible for these postseismic observations we consider afterslip both from an inversion of gps displacements and from stress driven forward models poroelastic rebound and viscoelastic flow in the lower crust and upper mantle several conclusions can be drawn 1 no single mechanism can explain the postseismic observations 2 significant postseismic flow below a depth of 60 km is required to explain observed far field motions best explained by a weak upper mantle with a depth dependent effective viscosity that ranges from 1019 pa s at the moho 50 km depth to 3 4 1018 pa s at 100 km depth 3 shallow afterslip within the upper crust occurs adjacent to and beneath the regions of largest coseismic slip 4 there is a contribution from deformation in the middle and lower crust from either lower crustal flow or stress driven slip afterslip is preferred over broad viscoelastic flow owing to the existence of seismic velocity discontinuities across the fault at depth though our modeling does not favor either mechanism if the process is viscoelastic relaxation the viscosity is a factor of 3 greater than the inferred mantle viscosity 5 poroelastic rebound probably contributed to the observed postseismic deformation in the immediate vicinity of the denali totschunda junction these conclusions lead us to infer an alaskan mechanical lithosphere that is about 60 km thick overlying a weak asthenosphere and a denali fault that cuts through the entire lithosphere with shear accommodated by faulting in the top 20 km and time dependent aseismic shear below

estimates of sea surface height and near surface alongshore coastal currents from combinations of altimeters and tide gauges 1 present methods used to retrieve altimeter data do not provide reliable estimates of sea surface height ssh in the nearshore region resulting in a measurement gap of 25 50 km next to the coast in the present work gridded ssh fields produced by archiving validation and interpretation of satellite oceanographic data aviso in the offshore region are combined with coastal tide gauge time series of ssh to improve estimation in that gap along the west coast of the united states in the northern california current system between 40 and 45n and 123 8 and 126w to assess the increase in skill provided by this procedure the geostrophic alongshore currents calculated from the new ssh fields in the gap region are compared to three in situ nearshore current measurements resulting in correlation coefficients of 0 73 0 83 and standard deviations of the differences of 11 6 12 6 cm s substantially improved from the aviso only results when the ekman current components are estimated and added to the geostrophic currents comparisons to the 10 m deep acoustic doppler current profiler velocities are only slightly improved the ekman components make a more significant contribution when compared to hf radar surface current measurements providing correlations of 0 94 and standard deviations of the differences of 6 4 9 5 cm s these results represent a dramatic improvement in the quality of the ssh fields and estimated alongshore currents when additional realistic ssh data from the coastal region are added here we use coastal tide gauges to provide the additional ssh data but also discuss more general approaches for altimeter ssh retrievals in coastal regions where tide gauge data are not available

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

lateral variations of crustal seismic attenuation along the indepth profiles in tibet from lg q inversion 1 fourier spectra of crustal guided lg waves are collected to study seismic attenuation or q along the indepth profiles the 1 hz lg q q0 values are measured between many pairs of two stations and input to a back projection algorithm to obtain laterally varying q0 models along the indepth iii profile in central tibet the q0 model consists of low and nearly constant values of 90 these low values are consistent with abnormally high temperature as well as partial melts in the crust along the indepth ii profile in southern tibet the q0 values increase southward they are extremely low 60 over the northernmost segment but increase by a factor of 2 over a distance of 100 km between the indus yalong suture and the kangmar dome farther south and into the high himalayas q0 values are higher than 300 regional rayleigh waves observed along the northern indepth ii profile are used to infer a low velocity low q layer at midcrustal depths between 15 and 30 km in southern tibet the aqueous fluid trapped in the upper crust and a midcrust partial melting zone associated with the underthrusting of the indian lithosphere are the likely causes of the high lg attenuation in southern tibet low q rather then a systematic lg conversion along a dipping moho is the main cause of the previously observed lg blockage over paths crossing the southern tibetan boundary

a reevaluation of the isostatic rebound of lake bonneville recent data pertaining to the uplift of the provo and bonneville shorelines of the late pleistocene lake bonneville are evaluated in a reanalysis using a rigorous model of deformation of a plane earth comprising an elastic layer overlying a viscoelastic channel the new observations constrain the wavelength and amplitude of the uplift of two shorelines formed at two different epochs and they partly resolve the ambiguities in the plausible mechanical parameters found in previous solutions the results indicate that the effective thickness of the elastic lithosphere is 28 to 30 km equal to the seismically determined crustal thickness in the region the estimate of the upper mantle viscosity in the region varies from 1 5 3 4 lo19 pa s to 2 1 5 8 l018 pa s depending on whether the upper mantle is assumed to be of uniform viscosity or the flow is confined to a narrow channel in the asthenosphere the predicted rate of present uplift at the center of the desiccated lake is 0 06 mm yr and 0 03 mm yr for the shallow channel and uniform mantle models respectively these values are beyond the first order leveling accuracies and the question of the existence of a narrow channel in the region cannot be resolved with the available observations

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

glacial isostatic adjustment and earth rotation refined constraints on the viscosity of the deepest mantle we explore the extent to which two properties of earth s present day rotational state may be applied to constrain the viscosity of the lower regions of the lower mantle the analysis builds upon recent advances in understanding the radial resolving power of the relative sea level data of postglacial rebound which have demonstrated anew that no significant increase of viscosity across the 660 km seismic discontinuity appears to be allowed by these data such observations do not constrain the viscosity of the mantle below about 1400 km depth however and here we estimate the average viscosity in this deepest region by invoking observations of the present day rate and direction of polar wander and the present day magnitude of the nontidal acceleration of the rate of planetary rotation since the rotational response to the glaciation cycle depends only upon the degree 2 spherical harmonic components of the induced deformation this response is expected to provide the most specific sampling possible of deep mantle properties our analysis is based upon the use of glacial excitation functions calculated from complete gravitationally self consistent solutions of the sea level equation for the most recent refinement of the history of ice sheet thickness variations across the last glacial interglacial transition namely the ice 4g model this analysis shows that when earth rotation observations are combined with relative sea level constraints the viscosity of the deepest mantle is required to be 1 order of magnitude higher than the viscosity of the upper part of the lower mantle such significant elevation of viscosity in the lowermost region of the lower mantle is also in accord with recent inferences based upon analysis of the nonhydrostatic geoid the analyses presented herein therefore suffice to effect a reconciliation between the requirements of these distinct geophysical observations

viscosity of the asthenosphere from glacial isostatic adjustment and subduction dynamics at the northern cascadia subduction zone british columbia canada 1 late glacial sea level curves located in the cascadia subduction zone csz fore arc in southwestern british columbia show that glacial isostatic adjustment gia was rapid when the cordilleran ice sheet collapsed in the late pleistocene gia modeling with a linear maxwell rheology indicates that the observations can be equally well fit across a wide range of asthenospheric thicknesses provided that the asthenospheric viscosity is varied from 3 1018 pa s for a thin 140 km asthenosphere to 4 1019 pa s for a thick 380 km asthenosphere present day vertical crustal motion predicted by the gia models shows rates of a few tenths of a millimeter per year consistent with previous analyses the model viscosities largely pertain to the viscosity of the oceanic mantle beneath the subducting juan de fuca slab but include a contribution from the mantle wedge above the slab for comparison effective viscosities for the upper mantle due to the tectonic regime subduction were computed using the strain rates and temperatures of an independent geodynamic model of the csz with a wet olivine power law rheology the effective viscosities agree well with gia model viscosities of 1019 pa s or less corresponding to an asthenosphere of 100 or 200 km thickness the agreement suggests a significant role for power law flow in the gia response regardless of the microphysical mechanisms responsible for the gia response the viscosity values inferred from gia can be applied to studies of the megathrust earthquake cycle because both processes take place on comparable time scales

glacial isostatic adjustment and the viscosity structure underlying the vatnajokull ice cap iceland we examine the dependence of glacial isostatic adjustment gia due to changes in the vatnajokull ice cap iceland on the underlying viscosity structure iceland offers a unique case study for gia research with a thinner elastic lithosphere underlain by a low viscosity zone or asthenosphere as opposed to regions such as fennoscandia or north america described by a thicker lithosphere while not necessarily featuring an asthenosphere

rapid viscoelastic uplift in southeast alaska caused by post little ice age glacial retreat our observations show that extreme uplift in southeast alaska began about 1770 ad with relative sea level rsl change to 5 7 m and current uplift rates to 32 mm yr this region experienced widespread glacial melting following the little ice age lia with the collapse of the glacier bay icefield alone equivalent to 8 mm of global sea level rise geodynamic modelling links the uplift to post lia isostatic rebound with the extreme uplift signal and a priori knowledge of ice load changes requiring the presence of a low viscosity asthenosphere 3 710 18 pa s these crustal deformations are triggered by climate change

low slip rates and multimillennial return times for mw 7 earthquake faults in southern calabria italy the calabrian arc is the epicentral region of one third of the strongest earthquakes of italy mw 7 0 these are confined within a narrow peninsula which is the emerging portion of a slab related accretionary wedge and all occurred in the past four centuries therefore here more than anywhere in italy historical seismicity alone is not sufficient for seismic hazard assessment we carried out geological and paleoseismological studies in southern calabria that allowed characterizing the seismogenic behavior of the cittanova fault which was responsible for one of the most catastrophic earthquakes to ever occur in europe the mw 7 0 5 february 1783 event we have found out conclusive evidence for four holocene earthquakes prior to 1783 with a recurrence time longer 3 2 kyr than the other apennine faults 0 3 2 4 kyr we have also estimated a robust slip rate for the late upper pleistocene 0 6 mm yr and an extension rate 0 4 mm yr that could reflect the residual back arc opening of the tyrrhenian basin

rising of the lowest place on earth due to dead sea water level drop evidence from sar interferometry and gps 1 the dead sea water level has been dropping at an exceedingly increasing rate since 1960 and between 1993 and 2001 the interval of the insar data examined in this study it has dropped at an average rate of 0 88 m per year such a water level change could potentially give rise to a resolvable lithospheric rebound and regional uplift with spatial extent and amplitude that are controlled by the effective mechanical properties of the crust and upper mantle combined we measure that deformation for the years 1993 to 2001 using 149 short baseline interferograms made of 31 ers 1 and ers 2 synthetic aperture radar sar images and continuous gps data from the survey of israel recorded between 1997 and 2011 the uplift rate at the dead sea is small up to 4 mm year and the basin topography is almost a mirror of the displacement introducing a strong trade off between uplift and stratified atmosphere noise to overcome this complication we impose a linearity constraint on the satellite to ground line of sight los phase changes based on the steady uplift observed by a continuous gps station in the area of interest and simultaneously solve for the los change rate digital elevation model dem errors and the elevation phase correlation while the los rate and dem errors are solved for each pixel independently the elevation phase correlation is solved for each sar acquisition independently using this approach we separated the stratified atmospheric delay from the ground displacement we observed a regional uplift around the dead sea northern basin with maximum uplift close to the shorelines and diminishing to zero by the mediterranean coast we modeled the effect of water load changes using a homogeneous elastic half space and found a good agreement between modeled and observed ground displacements using elastic properties that are compatible with seismic and gravity data down to a depth of 15 km below the dead sea basin suggesting that the response of the crust to the sea level drop is controlled mainly by the elastic properties of the upper crust immediately below the dead sea basin

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

west east variation in crustal thickness in northern lhasa block central tibet from deep seismic sounding data 5 30 km depth 5 0 vp 6 4 km s a middle crust 33 45 km depth 6 5 vp 6 8 km s and a lower crust depths below 48 km 7 0 vp 7 4 km s the west to east increase in crustal thickness is accomplished by a 50 thickening of the middle and lower crust larger vertical velocity gradients separate these three layers and bound them above surficial and sedimentary rocks and below moho transition zone the most notable low velocity zone in the crust lies at the base of the upper crustal layer s wave velocity structure is less well constrained but parallels the p wave structure except that vp vs ratios may decrease from west to east in the lower crust our data suggest considerable variation in structure along strike of the tibetan plateau and show that interpretations of tibet as a purely two dimensional orogen are overly simplistic the west east increase in crustal thickness may occur across the karakorum jiali fault system and be an indicator of lateral tectonic escape of the qiangtang terrane

poroelastic rebound along the landers 1992 earthquake surface rupture maps of surface displacement following the 1992 landers california earthquake generated by interferometric processing of ers 1 synthetic aperture radar sar images reveal effects of various postseismic deformation processes along the 1992 surface rupture the large scale pattern of the postseismic displacement field includes large lobes mostly visible on the west side of the fault comparable in shape with the lobes observed in the coseismic displacement field this pattern and the steep displacement gradient observed near the emerson camp rock fault cannot be simply explained by afterslip on deep sections of the 1992 rupture models show that horizontal slip occurring on a buried dislocation in a poisson s material produces a characteristic quadripole pattern in the surface displacement field with several centimeters of vertical motion at distances of 10 20 km from the fault yet this pattern is not observed in the postseismic interferograms as previously proposed to explain local strain in the fault step overs peltzer et al 1996b we argue that poroelastic rebound caused by pore fluid flow may also occur over greater distances from the fault compensating the vertical ground shift produced by fault afterslip such a rebound is explained by the gradual change of the crustal rocks poisson s ratio value from undrained coseismic to drained postseismic conditions as pore pressure gradients produced by the earthquake dissipate using the poisson s ratio values of 0 27 and 0 31 for the drained and undrained crustal rocks respectively elastic dislocation models show that the combined contributions of afterslip on deep sections of the fault and poroelastic rebound can account for the range change observed in the sar data and the horizontal displacement measured at global positioning system gps sites along a 60 km long transect across the emerson fault savage and svarc 1997 using a detailed surface slip distribution on the homestead valley kickapoo and johnson valley faults we modeled the poroelastic rebound in the homestead valley pull apart a poisson s ratio value of 0 35 for the undrained gouge rocks in the fault zone is required to account for the observed surface uplift in the 3 5 years following the earthquake this large value implies a seismic velocity ratio vp vs of 2 1 consistent with the observed low vs values of fault zone guided waves at shallow depth li et al 1997 the sar data also reveal postseismic creep along shallow patches of the eureka peak and burnt mountain faults with a characteristic decay time of 0 8 years coseismic dilatant hardening locking process followed by post seismic pore pressure controlled fault creep provide a plausible mechanism to account for the decay time of the observed slip rate along this section of the fault

reservoir induced deformation and continental rheology in vicinity of lake mead nevada lake mead is a large reservoir in nevada formed by the construction of the 221 m high hoover dam in the black canyon of the colorado river the lake encompasses an area of 635 km2 and the total volume of the reservoir is 35 5 km3 filling started in february 1935 on the basis of a first order leveling in 1935 several levelings were carried out to measure the deformation induced by the load of the reservoir subsidence in the central parts of the lake relative to the first leveling was around 120 mm 1941 218 mm 1950 and 200 mm 1963 the subsidence pattern clearly shows relaxation of the underlying basement due to the water load of the lake which ceased after 1950 modeling of the relaxation process by means of layered viscoelastic compressible flat earth models with a detailed representation of the spatial and temporal distribution of the water load shows that the thickness of the elastic crust underneath lake mead is 30 3 km the data are also consistent with a 10 km thick elastic upper crust and a 20 km thick viscoelastic lower crust with 1020 pa s as a lower bound for its viscosity the subcrust has an average viscosity of 1018 0 2 pa s a surprisingly low value the leveling data constrain the viscosity profile down to 200 km depth

postseismic deformation in chile constraints on the asthenospheric viscosity by means of a spherical earth model with maxwell rheology an analysis of the postseismic deformation field due to the viscoelastic relaxation of the mantle and asthenosphere following the great 1960 chile earthquake is performed due to the exceptional energy release of that earthquake geomorphological evidences of postseismic deformation are available in a broad area surrounding the rupture zone the comparison of the synthetic results with the available data allows to put some constraints on the viscosity of the asthenosphere beneath the chilean region values between 8 1019 and 1020pa s are compatible with the available postseismic deformation field data

mobility of continental mantle evidence from postseismic geodetic observations following the 1992 landers earthquake the crust around the rupture zone of the 1992 landers earthquake has continued to deform in the years following the earthquake at rates 3 times greater than pre earthquake rates we use a combination of global positioning system gps and synthetic aperture radar insar data collected during a 3 year epoch following the earthquake in order to investigate postseismic mechanisms responsible for the high transient velocities in order to maximize the potential signal from viscoelastic relaxation we evaluate and model postseismic relaxation following the first few months of documented accelerated deformation the combination of gps and insar data allows us to establish viscoelastic relaxation of the lower crust and upper mantle as the dominant postseismic process and to discriminate among possible viscoelastic models the data particularly require the presence of a highly ductile uppermost mantle beneath the central mojave domain with temperature between the wet and dry basalt solidus this is consistent with independent seismic and geochemical inferences of a regionally warm uppermost mantle further consideration of seismic velocity variations in conjunction with faulting patterns within the mojave desert suggests that the primary faulting characteristics of the mojave desert namely the pervasive late cenozoic deformation within the eastern california shear zone versus the near absence of faults in the western mojave domain are controlled by the rheology of the uppermost mantle

dynamic and static moduli static and dynamic bulk moduli ks and kd are measured as continuous functions of pressure from zero to 2 3 kilobars for two sandstones a tuff limestone granite and oil shale results for the sandstones and granite are in good agreement with previously reported data with ks kd varying from about 0 5 at atmospheric pressure to close to unity at pressures 2 kilobars and above for rocks behaving elastically under static loading the ks kd ratio is inversely related to the microcrack density for the limestone time dependent deformation associated with pore collapse results in ks kd ratios approaching 0 1 at high pressure upon unloading while initially high 1 0 at high pressures ks kd becomes lower than values obtained during loading at low pressures 1 kilobar due to opening of microcracks generated during pore collapse for the oil shale in which few microcracks exist ks kd remains relatively constant with pressure at a value of about 0 7

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

large scale forcing of environmental conditions on subarctic copepods in the northern california current system in the ocean dominant physical processes often change at various spatial and temporal scales here we examined associations between large scale physical forcing indexed by the pacific decadal oscillation pdo regional ocean conditions including alongshore currents in relation to the abundance of two subarctic oceanic copepods neocalanus plumchrus and n cristatus in the offshore portions of the northern california current ncc system in spring of 1998 2008 we found significant relationships between the abundance of copepods water temperature and alongshore currents with a lag of two or four months in response to the pdo in the ncc system during the growth season in march april both subarctic copepod species displayed consistent cross shelf patterns with shoreward decreasing gradient in abundance and were negatively correlated with the pdo sea water temperature and alongshore currents our studies highlight the responses of regional ocean conditions to large scale physical forcing and illustrate the potential for neocalanus copepods as unique vectors for a new understanding of the ecological response in the offshore oceanic waters of the ncc system to climate variability

lithospheric flexure in the sichuan basin and longmen shan at the eastern edge of tibet 1 the mountain range at the steep eastern edge of the tibetan plateau the longmen shan was deformed by a mw7 9 earthquake with oblique thrust and strike slip motion in 2008 the tectonic processes and structure of the lithosphere beneath this range have been controversial gravity measurements reflect the distribution of mass within the earth including the large load of rock above the geoid in mountain ranges we investigate the response of the lithosphere to the load of the longmen shan and estimate the flexural rigidity or effective elastic thicknessteusing new gravity data acquired by recent satellites and the combined goco2s and eigen 6c datasets the free air gravity anomalies over the longmen shan show that its mass is supported by flexure of the adjacent sichuan basin lithosphere similar to the flexural support of the himalayas analysis of a stacked profile of the free air anomalies shows that the effective elastic thickness of the basin lithosphere is greater than 10 km but has a broad minimum misfit function with no upper limit on the thickness two dimensional admittance analysis shows thete of easternmost tibet is very low approximately 7 km

lower crustal relaxation beneath the tibetan plateau and qaidam basin following the 2001 kokoxili earthquake summary in 2001 november a magnitude 7 8 earthquake ruptured a 400 km long portion of the kunlun fault northeastern tibet in this study we analyse over five years of post seismic geodetic data and interpret the observed surface deformation in terms of stress relaxation in the thick tibetan lower crust we model gps time series first year and insar line of sight measurements years two to five and infer that the most likely mechanism of post seismic stress relaxation is time dependent distributed creep of viscoelastic material in the lower crust since a single relaxation time is not sufficient to model the observed deformation viscous flow is modelled by a lower crustal burgers rheology which has two material relaxation times the optimum model has a transient viscosity 9 1017 pa s steady state viscosity 1 1019 pa s and a ratio of long term to maxwell shear modulus of 2 3 this model gives a good fit to gps stations south of the kunlun fault while displacements at stations north of the fault are over predicted we attribute this asymmetry in the gps residual to lateral heterogeneity in rheological structure across the southern margin of the qaidam basin with thinner crust higher viscosities beneath the basin than beneath the tibetan plateau deep afterslip localized in a shear zone beneath the fault rupture gives a reasonable match to the observed insar data but the slip model does not fit the earlier gps data well we conclude that while some localized afterslip likely occurred during the early post seismic phase the bulk of the observed deformation signal is due to viscous flow in the lower crust to investigate regional variability in rheological structure we also analyse post seismic displacements following the 1997 manyi earthquake that occurred 250 km west of the kokoxili rupture we find that viscoelastic properties are the same as for the kokoxili area except for the transient viscosity which is 5 1017 pa s the viscosities estimated for the manyi and kokoxili areas are consistent with constraints obtained from other earthquakes in the northwest and south central parts of the tibetan plateau

glacial rebound of the british isles iii constraints on mantle viscosity summary observations of sea level change since the time of the last glacial maximum provide important constraints on the response of the earth to changes in surface loading on time scales of 103 104 years this response is conveniently described by an effective elastic lithospheric thickness and effective viscosities for one or more mantle layers considerable trade off between the parameters describing these layers can occur and different combinations can give rise to comparable predictions of sea level change in particular the trade off between lithospheric thickness and upper mantle viscosity can be important and for any reasonable value for the lithospheric thickness a corresponding mantle viscosity structure can be found that gives a plausible comparison of sealevel predictions with observations in particular thin lithosphere models will lead to low estimates for the upper mantle viscosity while thick lithosphere models lead to high viscosity values however either solution may represent only a local minimum in the model parameter space and may not correspond to the optimum solution it becomes important therefore that in the inversion of observational data a comprehensive search is conducted throughout the entire model parameter space to ensure that the solution identified does indeed correspond to the optimum solution the sea level data for the british isles lend themselves well to such an inversion because of the relatively high quality of the data the good geographic distribution of the data relative to the former ice sheet and reasonable observational constraints on the dimensions of the former ice sheet and on its retreat furthermore because of the contribution to the sea level signal from the distant ice sheets as well as from the melt water load the observational data base for the region also has some resolving power for the viscosity of the deeper mantle the parameter space explored is defined by up to five mantle layers the lithosphere of effective elastic thickness d and a series of upper mantle layers i 2 4 extending down to depths of 200 400 and 670 km respectively each of viscosity qi and a lower mantle layer of viscosity qlm extending down to the coremantle boundary the range of parameters explored is 30 d i 120 km 3 x loi9 iqi

spatial variations of flexure parameters over the tibet quinghai plateau we investigate the tibet quinghai plateau and the tarim basin in terms of spatial variations of the elastic thickness te in the frame of the thin plate flexure model the method of investigation makes use of a convolutive method which allows high spatial resolution of the flexure properties and overcomes some of the problems tied to the spectral admittance coherence methodologies we study the relation between the topographic and subsurface loads and the observed crust mantle interface cmi undulations the latter having been obtained from gravity inversion the gravity data used for the inversion are a unique set of high quality data available over the chinese part of the plateau and constitute the highest resolution grid today available in this impervious area the gravity inversion is constrained by results from the study of the propagation of seismic waves the two extensive sedimentary basins the tarim and the qaidam basins are modeled by forward gravity modeling the oscillations of the cmi obtained from the gravity inversion agree well with those expected by loading the thin plate model of spatially variably elastic thickness with the surface and subsurface loads it is found that the modeling of the sedimentary basins is essential in the flexure analysis the spatial variations of elastic thickness correlate with the extensions of the different terrains that constitute the plateau most of the tibet plateau has low te varying in the bounds 10 30 km with lower values in the qiangtang terrain where the te reaches 8 km the tarim and the qaidam basins precambrian platforms overlain by sediments are rigid and have a te of up to 110 km and 70 km respectively the flexural analysis distinctly discerns the tibet plateau with thick crust part of which is molten from the cratonic areas the tarim and qaidam basins which though of thinner crust act as undeformable rigid blocks

ground motion measurement in the lake mead area nevada by differential synthetic aperture radar interferometry time series analysis probing the lithosphere rheological structure 1 we measure ground motion around the lake mead nevada using synthetic aperture radar interferometry the lake water level has fluctuated through time since impoundment in 1935 to quantify the deformation due to water level variations over the past decade and to constrain the crust and mantle rheological parameters in the lake area we analyze 241 interferograms based on 43 ers images acquired between 1992 and 2002 all interferograms have a high coherence due to arid conditions most of them show strong atmospheric artefacts tropospheric phase delays are estimated and corrected for each interferogram by analyzing the phase elevation correlation corrections are validated using data from the era40 global atmospheric reanalysis corrected interferograms are inverted pixel by pixel to solve for the time series of ground motion in the lake area temporal smoothing is added to reduce random atmospheric artefacts the observed deformation is nonlinear in time and spreads over a 50 50 km2 area we observe a 16 mm subsidence between 1995 and 1998 due to an 11 m water level increase followed by an uplift due to the water level drop after 2000 we model the deformation taking into account the loading history of the lake since 1935 a simple elastic model with parameters constrained by seismic wave velocities does not explain the amplitude of the observed motion the two layer viscoelastic model proposed by kaufmann and amelung 2000 with a mantle viscosity of 1018 pa s adjusts well the data amplitude and its spatiotemporal shape

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

insar measurement of the deformation around siling co lake inferences on the lower crust viscosity in central tibet the siling co lake is the largest endorheic lake in central tibet altimetric measures combined with lake contours show that in 1972 1999 its water level remained stable while it increased by about 1 0 m yr in the period 2000 2006 the increased rate gradually stepped down to 0 2 m yr in 2007 2011 the ground motion associated with the water load increase is studied by interferometric synthetic aperture radar insar using 107 ers and envisat sar images during the period 1992 2011 the deformation amplitude closely follows the lake level temporal evolution except that subsidence continues in 2008 2011 while the lake level stagnated this temporal evolution suggests a non elastic relaxation process taking place at a decade timescale phase delay maps are used to constrain possible layered viscoelastic rheological models an elastic model could partly explain the observed subsidence rate if elastic moduli are about twice lower than those extracted from vp vs profiles the surface deformation pattern is also extracted by projecting the phase delay maps against the best fit model temporal behavior it shows that deep relaxation in the asthenosphere is negligible at the decade timescale and favors the existence of a ductile channel in the deep crust above a more rigid mantle overall the best fit model includes a ductile lower crust with a viscosity of 1 3 1018 pa s between 25 and 35 km and the moho at 65 km overlying a rigid mantle

precise temperature estimation in the tibetan crust from seismic detection of the α β quartz transition in the deep crust temperature which is among the key pa rameters controlling lithospheric dynamics is inferred by extrap olation from the surface using several assumptions that may fail in regions of active tectonics and fluid migration in the rare case that temperatures of 700 8c or higher are exceeded in the upper and middle continental crust composed of quartz rich felsic rocks the a b quartz transition abqt will occur generating a mea surable seismic signature and offering the possibility for precisely estimating temperature from the known abqt phase diagram here it is shown that all expected seismic features of the abqt are met by the boundary between the upper and middle crust be low the indepth iii profile in central tibet this finding implies that a temperature of 700 8c is achieved at a depth of 18 km under the southern qiangtang block which agrees with the depth to the top of a high electrical conductivity anomaly likely representing partially melted crust to the south in the northern lhasa block the abqt is at 32 km depth corresponding to a temperature of 800 8c it thus appears that this seismic boundary representing the abqt is the result of recent geologic processes rather than being a lithologic boundary

current slip rates on conjugate strike slip faults in central tibet using synthetic aperture radar interferometry this is the published version copyright 2006 american geophysical union all rights reserved

on the rapid postseismic uplift along turnagain arm alaska following the 1964 prince william sound earthquake an analysis of leveling data obtained along turnagain arm alaska in the aftermath of the 1964 prince william sound earthquake shows that the postseismic uplift rate was constant during the first year following the earthquake the maximum 1 yr peak to trough uplift was about 15 cm while the maximum uplift relative to a tide gauge site in anchorage was about 9 cm there is some evidence for a modest decrease in the uplift rate between may and october of 1965 although the evidence is weakened by the lack of an appropriate reference point the longer term temporal evolution of uplift rates as compiled from leveling gps tide gauge and vlbi observations by cohen 1996 can be modeled by an omori like or exponential transient decay curve with a time constant of several years the geodetic data taken in conjunction with seismological constraints can be explained by aseismic slip at depth along the tectonic plate interface with an initial slip rate of 35 cm yr and a slip depth of 25 37 km

dispersion of elastic moduli in a porous cracked rock theoretical predictions for squirt flow abstract crustal rocks contain variable amount of both cracks and equant pores depending on tectonic and thermal stresses but also on their geological origin crack damage and porosity change result in effects on elastic waves velocities when rocks are fluid saturated dispersion of the p and s waves should be taken into account this paper deals with frequency dispersion of elastic moduli in a fluid saturated porous and cracked rock with the assumption that squirt flow is the dominant process we develop a theoretical approach to calculate both high hf and low lf frequency bulk and shear moduli the hf moduli are derived from a new effective medium model called cpem with an isotropic distribution of pores or cracks with idealized geometry respectively spheres and ellipsoids lf moduli are obtained by taking hf dry moduli from the cpem and substituting into gassmann s equations in the case of a porosity only supported by equant pores the calculated dispersion in elastic moduli is equal to zero in the case of a crack porosity no bulk dispersion is predicted but a shear dispersion appears finally in the general case of a mixed porosity pores and cracks dispersion in bulk and in shear is predicted our results show that the maximum dispersion is predicted for a mixture of pores and spheroidal cracks with a very small aspect ratio 10 3 our theoretical predictions are compared to experimental data obtained during hydrostatic experiment performed on a basaltic rock and a good agreement is observed we also used our theoretical model to predict elastic waves velocities and vp vs ratio dispersion we show that the p waves dispersion can reach almost 20 and the vp vs dispersion a maximum value of 9 for a crack porosity of about 1 since laboratory data are ultrasonic measurements and field data are obtained at much lower frequencies these results are useful for geophysicists to interpret seismic data in terms of fluid and rock interactions

rift flank uplift in tibet evidence for a viscous lower crust analysis of high resolution digital topography across 21 plio pleistocene grabens in central and southern tibet shows that high topography occurs along the graben margins profiles across these marginal highlands fit curves describing the flexure of an elastic plate under vertical loading we interpret the features as flexural rift flank uplifts resulting from regional isostatic compensation of low density grabens the short wavelengths of the uplifts 30 40 km imply a low flexural rigidity for the plateau d 2 6 1020 n m similar to values inferred for the basin and range of western north america in addition the grabens themselves are extremely narrow compared to typical continental rifts taken together these observations suggest the existence of a low viscosity lower crust and suggest that isostatic compensation is taking place within this ductile lower crust simple channel flow calculations suggest that crustal viscosities below 1022 pa s are necessary to accommodate this compensation over reasonable timescales