crustal deformation along the altyn tagh fault system western china from gps we collected gps data from the southern tarim basin the qaidam basin and the western kunlun shan region between 1993 and 1998 to determine crustal deformation along the altyn tagh fault system at the northern margin of the tibetan plateau we conclude from these data that the altyn tagh is a left lateral strike slip fault with a current slip rate of 9 mm yr in sharp contrast with geological estimates of 20 30 mm yr this contrast poses an enigma because the gps data cover a wider region than the geologic data they might be expected to reveal somewhat more slip we also find that the tarim and qaidam basins behave as rigid blocks within the uncertainty of our measurements rotating clockwise at a rate of 11 and 4 5 nrad yr respectively with respect to the eurasia plate the rotation of the tarim basin causes convergence across the tian shan increasing progressively westward from 6 mm yr at 87 e to 18 mm yr at 77 e our data and other gps data suggest that the indo asia collision is mainly accommodated by crustal shortening along the main himalayan thrust system 53 and the tian shan contractional belt 19 eastward extrusion of the tibetan plateau along the altyn tagh and kunlun faults accommodates only 23 of the indo asia convergence

stress transfer and its implication for earthquake hazard on the kunlun fault tibet abstract the 1600 km long kunlun fault striking e w to wnw ese had long been recognized as one of the major left lateral strike slip faults bounding the tibetan plateau and ranked one of the most active faults in china continent during the past hundred years over twenty strong earthquakes occurred along and near the kunlun fault including six large earthquakes m 7 since some major highly populated and industrialized cities are close to the kunlun fault understanding of stress transfer and earthquakes migration along the kunlun fault is most important for assessing seismic hazard in this region in this study by integrating coseismic effect viscoelastic relaxation and tectonic loading we studied the evolution of the regional coulomb stress field by analyzing a sequence of strong earthquakes along the kunlun fault we studied the stress evolution over one century by analysing a sequence of five earthquakes m 7 that occurred along the kunlun fault since 1937 the model of dislocation sources embedded in a mixed elastic inelastic layered half space was used and the layered model and relevant parameters were constrained by seismic studies fault rupture locations and geometry as well as slip distribution of earthquakes were taken from field observations and seismic studies numerical results showed a good correlation between stress transfer accumulation and earthquakes occurrence all four studied earthquakes occurred after the 1937 tuosuo lake quake were encouraged by the preceding earthquakes with positive stress loading in subject to the choice of the earthquake source parameter two or three out of four events occurred in regions that experienced previous coseismic and postseismic stress changes of at least 0 01 mpa suggesting that earthquake triggering due to stress transfer has occurred along the kunlun fault the total stress change since 1937 of the kunlun fault region has lead to high levels of stress accumulated on the xidatan dongdatan segment and maqin maqu segment which have not experienced any significant large earthquake over at least several hundred or several thousand years the accumulated stress raises the potential earthquake hazard in these areas our study demonstrated the crucial importance of postseismic viscoelastic relaxation in the stress transfer and accumulation following large earthquakes

combined gas and ion chromatographic analysis of fluid inclusions applications to archean granite pegmatite and gold quartz vein fluids the first stage in the interpretation of bulk fluid inclusion analytical data involves consideration of the relative amounts and types of fluid inclusions in a sample in order to determine which inclusion type dominates the volatile and or ion bulk analytical data this then permits discussion of processes affecting fluid chemistry such as fluid mineral equilibria metasomatism and phase separation and leads to constraints on primary source region fluid composition this interpretive procedure has been applied to data obtained by combined gas and ion chromatographic analysis of well characterized samples from the archean tanco granitic pegmatite southeastern manitoba and the hollinger mcintyre and kerr addison archean au quartz vein systems northern ontario the bulk composition of an homogeneous late stage magmatic fluid in lower intermediate zone vug quartz from the tanco pegmatite is 90 6 mol h2o 3 35 mol co2 2 45 mol li 2 40 mol cl 1 01 mol na and other trace species 1 mol the li li na ratio of 0 69 0 008 for this fluid is greater than a published experimental determination of 0 45 0 02 for a comparable system probably owing to the co2 rich nature of the vug quartz fluids the halogen cl br i and alkali metal enriched nature of this fluid is consistent with the advanced degree of igneous fractionation of the pegmatite compared to estimated bulk earth values the br cl ratio of 12 9 10 3 molar is high and may be the result of igneous fractionation while the i cl ratio 140 10 6molar is low suggesting that another process governs i behaviour tanco quartz zone samples show trace gas depletion trends comparable to those obtained from samples trapping phase separated fluids in low pressure geothermal systems trends in the tanco cation anion data reflect both fluid mineral equilibria and phase separation effects li and cl show a closely correlated decrease with increasing co2ch4 ratio while na shows no change consistent with partitioning of li and cl in favour of the co2 rich phase which could have contributed to the calcite and holmquistite bearing propylitic alteration zone around the pegmatite average bulk compositions for hollinger mcintyre and kerr addison fluids are similar and consist of 80 90 mol h2 2 15 mol co2 1 3 mol cl 2 4 mol na and trace species 1 mol hollinger mcintyre volatiles show clear wall rock reaction effects while kerr addison fluids show strong phase separation trends br cl ratios of 5 5 to 10 10 3 for hollinger mcintyre and kerr addison fluids are greater than bulk earth while i cl 106 ratios are low with a range from 20 105 hollinger mcintyre and tanco samples dominated by secondary brine inclusions have br cl 103 ratios of 13 and 15 respectively showing that these secondary fluids are distinct from shield brines br cl 3 to 5 5 10 3 both of these samples have distinctive trace hydrocarbon signatures

investigation on afterslip and steady state and transient rheology based on postseismic deformation and geoid change caused by the sumatra 2004 earthquake the commonly used rheological model for the earth s mantle when considering geological time scales mantle convection is the viscoelastic maxwell model which assumes a steady state creep process however application of this model to phenomena on shorter time scales such as postglacial rebound or postseismic relaxation leads to difficulties in finding a consistent interpretation of obtained viscosities using standard maxwell viscosity of 1e19 pa s to analyze postseismic near field gps time series from the 2004 sumatra andaman earthquake requires large time dependent afterslip with a relaxation time of about 1 year we show that using linear biviscous burgers rheology for the asthenosphere together with a refined coseismic slip model we can drastically reduce the amount of apparent afterslip comparison of predicted geoid change to observations by the grace satellite mission shows that a univiscous maxwell model with afterslip is not compatible with observations since even large afterslip has a more localized effect than transient relaxation due to the main earthquake which in turn is in agreement with observations thus a combination of ground and space based geodetic observations is very useful in differentiating between rheological models an additional independent discrimination between afterslip and biviscous relaxation could be obtained by installing ocean bottom pressure gauges close to the trench

lithospheric and upper mantle structure of southern tibet from a seismological passive source experiment fifteen seismic stations were operated with about 20 km spacing in southern tibet across the zangbo suture the collision zone between india and asia between may and october 1994 as part of the international deep profiling of tibet and the himalaya project indepth ii for wide angle recording of the controlled source experiment and for passive earthquake recording in addition a dense deployment 4 km spacing of stations within the german depth profiling of tibet and the himalayas gedepth project also recorded a number of teleseismic earthquakes the third data source used in this study is the records of the permanent broadband station at lhasa teleseismic records have been obtained in sufficient quantity and quality to derive an image of the structure of the lithosphere and upper mantle from p to s converted phases important results are as follows the moho at 70 80 km and a second discontinuity at 50 60 km depth are observed over the entire profile south and north of the zangbo suture the data from the gedepth dense array enable the detection of inclined structures penetrating the crust at the zangbo suture a pronounced low velocity zone exists north of the zangbo suture at about 10 20 km depth the locations of the upper mantle discontinuities at 410 and 660 km depth are in agreement with the global reference model iasp91 kennett 1991 over a large region of the himalaya and southern tibet

alteration mineralogy fluid inclusions and stable isotope studies from chigargunta and bisanatham gold deposits south kolar greenstone belt dharwar craton india implications on genesis of gold mineralization abstract there are many neoarchaean orogenic gold hosting greenstone belts in the dharwar craton dc india among them the southern extension of the kolar greenstone belt skgb contain promising gold deposits such as chigargunta and bisanatham auriferous laminated quartz calcite veins are hosted mainly within the sheared and altered champion gneiss and amphibolite in chigargunta and bisanatham respectively the hydrothermal alteration mineral assemblages show three main alteration zones at chigargunta however only two alteration zones were identified at bisanatham the hydrothermal mineral assemblage at chigargunta and bisanatham indicate a similar mineralogy that consists of tourmaline muscovite biotite chlorite epidote sericite calcite and quartz along with sulfide and gold sulfides associated with ore are predominantly pyrrhotite pyrite arsenopyrite chalcopyrite molybdenite in both the places native gold is mainly associated with pyrrhotite in the inner and proximal zone of both the deposits fluid inclusion petrography and microthermometry from quartz calcite veins within the mineralized zone at chigargunta reveal a low to medium salinity 0 5 to 13 3 wt nacl equiv h2o nacl co2 ch4 n2 bearing fluid however at bisanatham only h2o nacl fluid with low salinity 1 56 to 6 44 wt nacl equiv was observed p t conditions of the gold mineralization at the chigargunta and bisanatham deposits range between 1 7 and 3 5 kbar pressure 285 c to 378 c temperature and 0 8 to 1 2 kbar pressure 365 c to 405 c temperature respectively alteration mineralogy ore mineral assemblages fluid compositions and p t conditions from the skgb confirm that the near neutral to slightly alkaline mineralizing fluid transported gold as au hs 2 complexes with low o2 conditions the observed drastic pressure and temperature fluctuation suggests that fault valve mechanism pressure cycling occurred at the time of gold precipitation carbon 13cco2 isotopic composition of ore fluid deduced from calcite varies from 2 4 to 3 3 average 0 3 and 2 1 to 1 4 average 0 8 for chigargunta and bisanatham respectively oxygen isotopic 18oh2o values for both the deposits vary from 7 2 to 14 6 average 9 3 and 7 3 to 8 9 average 8 3 respectively ore forming fluid could have possibly been derived from the decarbonation of marine carbonates during the metamorphic devolatilization of greenstones the slight intra deposit variation of the carbon isotopic value implies the rayleigh fractionation with progressive consumption of the co2 as a result of interaction between hydrothermal fluid and wall rock as well as immiscibility of ch4 and co2 fluid ore fluid sulfur 34sh2s isotopic composition derived from 34s values of sulfides varies from 0 42 to 2 43 and 0 25 to 2 34 for chigargunta and bisanatham respectively both the sulfur and carbon isotopic values from these deposits are comparable with other orogenic gold deposits in the dc and elsewhere in the world although carbon isotopic values possibly indicate the metamorphic fluid source the sulfur isotopes signify average crustal sulfur composition that is from crustally derived modified fluid based on the field geological mineralogical fluid and isotopic compositions the possible fluid source could be from the metamorphic devolatilization process of the thick greenstone sequence in the skgb however a magmatic source could be further tested with geochronological studies on intrusives in the area

k bentonites volcanic ash preservation and implications for early to middle devonian volcanism in the acadian orogen eastern north america lower to middle devonian marine strata in the appalachian foreland basin feature up to 80 or more thin k bentonites that represent ancient volcanic ashes the time vs space distribution of k bentonites through the lochkovian to eifelian stages representing 30 m y shows a distinct pattern of clustered multiple beds several scattered beds and thick intervals with no k bentonites four clusters of 7 to 15 individual closely spaced layers occur in the middle lochkovian bald hill k bentonites kalkberg new scotland formations late pragian or early emsian sprout brook k bentonites esopus formation and early eifelian two clusters the tioga middle coarse zone and tioga a g k bentonites onondaga formation detailed examination of these devonian k bentonites shows that in many cases they do not represent a single eruption multilayered beds fossil layers within beds authigenic minerals e g glauconite and phosphate nodules subjacent hardgrounds and an irregular distribution of beds through space and time raise questions about the depositional history and preservation potential of volcanic ash in marine environments and the degree to which the beds represent a primary record of volcanism these and other lines of evidence indicate that postdepositional physical biological and geochemical processes e g sedimentation rate event and background physical processes burrowing have modified the primary record of these water laid ash fall events these factors may lead to preservation of primary ash deposits or to their resedimentation and or partial to complete mixing with background sediments the preservation potential and resulting distribution of the devonian k bentonites can be analyzed across a spectrum of preservational magnafacies in this paper i present a model of ash preservation the model incorporates environmentally related physical biological and chemical processes active in epicontinental seas and marine foreland basins conclusions based on the model indicate that the middle lochkovian early emsian and early eifelian were times of peak volcanic activity in eastern north america related to times of increased tectonism in the acadian orogen

detection of a locked zone at depth on the parkfield california segment of the san andreas fault the parkfield california segment of the san andreas fault is transitional in character between the creeping segment of the fault to the northwest and the locked carrizo plain segment to the southeast the rate of shallow fault slip decreases from 25 30 mm yr northwest of the epicenter of the 1966 parkfield earthquake to zero at the southeastern end of the 1966 rupture zone data from a network of trilateration lines spanning the san andreas fault near parkfield and extending to the pacific coast near san luis obispo shed light on the rate of fault slip at depth since the 1966 earthquake in this study average rates of line length change and shallow fault slip were inverted to determine the slip rate at depth on the parkfield fault segment the fault is taken to be a vertical surface with unknown distribution of strike slip displacement in an elastic half space a striking result of the inversions is that all solutions providing acceptable fits to the data exhibit a locked zone essentially coincident with the rupture surface of the 1966 parkfield earthquake the data require that the locked zone extend nearly as far north as the 1966 epicenter however the vertical extent of the locked zone is not well resolved over much of the parkfield segment the fault is slipping faster at the earth s surface than it is at seismogenic depths in order to fit the trilateration measurements it is necessary to include a component of contraction normal to the trend of the san andreas the inversion results suggest a spatially uniform normal strain of 0 06 strain yr the orientation of the contraction is compatible with geologic and seismic evidence of active folding and reverse faulting in the region the magnitude of the contraction is consistent with convergence rates inferred from global plate motion models

surface displacements and source parameters of the 2003 bam iran earthquake from envisat advanced synthetic aperture radar imagery 1 the mw 6 6 26 december 2003 bam iran earthquake was one of the first earthquakes for which envisat advanced synthetic aperture radar asar data were available using interferograms and azimuth offsets from ascending and descending tracks we construct a three dimensional displacement field of the deformation due to the earthquake elastic dislocation modeling shows that the observed deformation pattern cannot be explained by slip on a single planar fault which significantly underestimates eastward and upward motions se of bam we find that the deformation pattern observed can be best explained by slip on two subparallel faults eighty five percent of moment release occurred on a previously unknown strike slip fault running into the center of bam with peak slip of over 2 m occurring at a depth of 5 km the remainder occurred as a combination of strike slip and thrusting motion on a southward extension of the previously mapped bam fault 5 km to the east

effects of crustal layering on source parameter inversion from coseismic geodetic data summary we study the effect of a superficial layer overlying a half space on the surface displacements caused by uniform slipping of a dip slip normal rectangular fault we compute static coseismic displacements using a 3 d analytical code for different characteristics of the layered medium different fault geometries and different configurations of bench marks to simulate different kinds of geodetic data gps synthetic aperture radar and levellings we perform both joint and separate inversions of the three components of synthetic displacement without constraining fault parameters apart from strike and rake and using a non linear global inversion technique under the assumption of homogeneous half space differences between synthetic displacements computed in the presence of the superficial soft layer and in a homogeneous half space do not show a simple regular behaviour even if a few features can be identified consequently also retrieved parameters of the homogeneous equivalent fault obtained by unconstrained inversion of surface displacements do not show a simple regular behaviour we point out that the presence of a superficial layer may lead to misestimating several fault parameters both using joint and separate inversions of the three components of synthetic displacement and that the effects of the presence of the superficial layer can change whether all fault parameters are left free in the inversions or not in the inversion of any kind of coseismic geodetic data fault size and slip can be largely misestimated but the product fault length fault width slip which is proportional to the seismic moment for a given rigidity modulus is often well determined within a few per cent because inversion of coseismic geodetic data assuming a layered medium is impracticable we suggest that only a case to case study involving some kind of recursive determination of fault parameters through data correction seems to give the proper approach when layering is important

probing the mechanical properties of seismically active crust with space geodesy study of the coseismic deformation due to the 1992 mw7 3 landers southern california earthquake 1 the coseismic deformation due to the 1992 m w 7 3 landers earthquake southern california is investigated using synthetic aperture radar sar and global positioning system gps measurements the ers 1 satellite data from the ascending and descending orbits are used to generate contiguous maps of three orthogonal components east north up of the coseismic surface displacement field the coseismic displacement field exhibits symmetries with respect to the rupture plane that are suggestive of a linear relationship between stress and strain in the crust interferometric synthetic aperture radar insar data show small scale deformation on nearby faults of the eastern california shear zone some of these faults in particular the calico rodman and pinto mountain faults were also subsequently strained by the 1999 m w 7 1 hector mine earthquake i test the hypothesis that the anomalous fault strain represents essentially an elastic response of kilometer scale compliant fault zones to stressing by nearby earthquakes fialko et al 2002 the coseismic stress perturbations due to the landers earthquake are computed using a slip model derived from inversions of the insar and gps data calculations are performed for both homogeneous and transversely isotropic half space models the compliant zone model that best explains the deformation on the calico and pinto mountain faults due to the hector mine earthquake successfully predicts the coseismic displacements on these faults induced by the landers earthquake deformation on the calico and pinto mountain faults implies about a factor of 2 reduction in the effective shear modulus within the similar to 2 km wide fault zones the depth extent of the low rigidity zones is poorly constrained but is likely in excess of a few kilometers the same type of structure is able to explain high gradients in the radar line of sight displacements observed on other faults adjacent to the landers rupture in particular the lenwood fault north of the soggy lake has likely experienced a few centimeters of left lateral motion across 1 km wide compliant fault zone having the rigidity reduction of more than a factor of 2 the inferred compliant fault zones are interpreted to be a result of extensive damage due to past earthquakes

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

space geodetic investigation of the coseismic and postseismic deformation due to the 2003 mw7 2 altai earthquake implications for the local lithospheric rheology 1 we use envisat advanced synthetic aperture radar data and spot optical imagery to investigate the coseismic and postseismic deformation due to the 27 september 2003 mw7 2 altai earthquake which occurred in the chuya basin near the russia china mongolia border on the basis of the synthetic aperture radar sar and spot data we determined the rupture location and developed a coseismic slip model for the altai earthquake the inferred rupture location is in a good agreement with field observations and the geodetic moment from our slip model is consistent with the seismic moment determined from the teleseismic data while the epicentral area of the altai earthquake is not optimal for radar interferometry in particular due to temporal decorrelation we were able to detect a transient signal over a time period of 3 years following the earthquake the signal is robust in that it allows us to discriminate among several commonly assumed mechanisms of postseismic relaxation we find that the postearthquake interferometric sar data do not warrant poroelastic rebound in the upper crust the observed deformation also disagrees with linear viscoelastic relaxation in the upper mantle or lower crust giving rise to a lower bound on the dynamic viscosity of the lower crust of the order of 1019 pa s the data can be explained in terms of fault slip within the seismogenic zone on the periphery of areas with high coseismic slip most of the postseismic deformation can be explained in terms of seismic moment release in aftershocks some shallow slip may have also occurred aseismically therefore the observed postseismic deformation due to the altai earthquake is qualitatively different from deformation due to other similarly sized earthquakes in particular the landers and hector mine earthquakes in the mojave desert southern california the observed variations in the deformation pattern may be indicative of different rheologic structure of the continental lithosphere in different tectonically active areas

effect of crustal layering upon dislocation modeling slip distribution at depth on a fault may be inferred from the deformation observed on the surface in inverting the surface deformation data to obtain the slip distribution the earth is generally approximated by an elastic half space slip distributions inferred from a half space model may contain artifacts including zones of reversed slip due solely to effects of layering in the real earth this effect is demonstrated for a vertical strike slip fault in an earth consisting of an elastic layer overlying an elastic half space slip on the fault is taken to be independent of the along strike coordinate i e antiplane strain is assumed for a given slip distribution in this model the slip distribution on a similar fault in an elastic half space is found that produces the identical surface deformation comparison of the two slip distributions reveals structure introduced into the half space equivalent slip profile by crustal layering the comparisons suggest that low resolution inversion schemes e g single screw dislocation models are not drastically affected by earth structure but attempts at detailed inversion are likely to produce profiles contaminated by artifacts of earth structure

atmospheric effects in interferometric synthetic aperture radar surface deformation and topographic maps interferogram images derived from repeat pass spaceborne synthetic aperture radar systems exhibit artifacts due to the time and space variations of atmospheric water vapor other tropospheric variations such as pressure and temperature also induce distortions but the effects are smaller in magnitude and more evenly distributed throughout the interferogram than the wet troposphere term spatial and temporal changes of 20 in relative humidity lead to 10 cm errors in deformation products and perhaps 100 m of error in derived topographic maps for those pass pairs with unfavorable baseline geometries in wet regions such as hawaii these are by far the dominant errors in the spaceborne imaging radar c and x band synthetic aperature radar sir c x sar interferometric products the unknown time delay from tropospheric distortion is independent of frequency and thus multiwavelength measurements such as those commonly used to correct radar altimeter and global positioning system gps ionospheric biases cannot be used to rectify the error in the topographic case the errors may be mitigated by choosing interferometric pairs with relatively long baselines as the error amplitude is inversely proportional to the perpendicular component of the interferometer baseline for the sir c x sar hawaii data we found that the best longest baseline pair produced a map supporting 100 m contouring whereas the poorest baseline choice yielded an extremely noisy topographic map even at this coarse contour interval in the case of deformation map errors the result is either independent of baseline parameters or else very nearly so here the only solution is averaging of independent interferograms so in order to create accurate deformation products in wet regions many multiple passes may be required rules for designing optimal data acquisition and processing sequences for interferometric analyses in nondesert parts of the world are 1 to use the longest radar wavelengths possible within ionospheric scintillation and faraday rotation limits 2 for topography maximize interferometer baseline within decorrelation limits and 3 for surface deformation use multiple observations and average the derived products following the above recipe yields accuracies of 10 m for digital elevation models and 1 cm for deformation maps even in very wet regions such as hawaii

the 1999 hector mine earthquake southern california vector near field displacements from ers insar two components of fault slip are uniquely determined from two line of sight los radar interferograms by assuming that the fault normal component of displacement is zero we use this approach with ascending and descending interferograms from the ers satellites to estimate surface slip along the hector mine earthquake rupture the los displacement is determined by visually counting fringes to within 1 km of the outboard ruptures these los estimates and uncertainties are then transformed into strike and dip slip estimates and uncertainties the transformation is singular for a n s oriented fault and optimal for an e w oriented fault in contrast to our previous strike slip estimates which were based only on a descending interferogram we now find good agreement with the geological measurements except at the ends of the rupture the ascending interferogram reveals significant west side down dip slip 1 0 m which reduces the strike slip estimates by 1 to 2 m especially along the northern half of the rupture a spike in the strike slip displacement of 6 m is observed in central part of the rupture this large offset is confirmed by subpixel cross correlation of features in the before and after amplitude images in addition to strike slip and dip slip we identify uplift and subsidence along the fault related to the restraining and releasing bends in the fault trace respectively our main conclusion is that at least two look directions are required for accurate estimates of surface slip even along a pure strike slip fault models and results based only on a single look direction could have major errors our new estimates of strike slip and dip slip along the rupture provide a boundary condition for dislocation modeling a simple model which has uniform slip to a depth of 12 km shows good agreement with the observed ascending and descending interferograms

time dependent land uplift and subsidence in the santa clara valley california from a large interferometric synthetic aperture radar data set 1 we invert 115 differential interferograms derived from 47 synthetic aperture radar sar scenes for a time dependent deformation signal in the santa clara valley california the time dependent deformation is calculated by performing a linear inversion that solves for the incremental range change between sar scene acquisitions a nonlinear range change signal is extracted from the ers insar data without imposing a model of the expected deformation in the santa clara valley cumulative land uplift is observed during the period from 1992 to 2000 with a maximum uplift of 41 18 mm centered north of sunnyvale uplift is also observed east of san jose seasonal uplift and subsidence dominate west of the silver creek fault near san jose with a maximum peak to trough amplitude of 35 mm the pattern of seasonal versus long term uplift provides constraints on the spatial and temporal characteristics of water bearing units within the aquifer the silver creek fault partitions the uplift behavior of the basin suggesting that it acts as a hydrologic barrier to groundwater flow while no tectonic creep is observed along the fault the development of a low permeability barrier that bisects the alluvium suggests that the fault has been active since the deposition of quaternary units

postseismic relaxation driven by brittle creep a possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks application to the chi chi earthquake taiwan we evaluate the effect of coseismic stress changes on the fault slip at midcrustal depth assuming a velocity strengthening brittle creep rheology we show that this model can help reconcile the time evolution of afterslip as measured from geodesy with aftershocks decay we propose an analytical expression for slip of the brittle creeping fault zone bcfz that applies to any dynamic or static stress perturbation including shear stress and normal stress changes the model predicts an initial logarithmic increase of slip with time postseismic slip rate decays over a characteristic time t r a that does not depend on the amplitude of the stress perturbation and it asymptotically joins the long term creep imposed by interseismic stress buildup given that the seismicity rate might be considered proportional to the sliding velocity of the bcfz the model predicts a decay rate of aftershocks that follows omori s law with a mathematical formalism identical to that of dieterich 1994 although based on a different mechanical rationale our model also differs from dieterich s model in that it requires that aftershock sequences and deep afterslip as constrained from geodetic measurements should follow the same temporal evolution we test this for the 1999 chi chi earthquake m w 7 6 and find that both sets of data are consistent with a model of afterslip due to the response of the bcfz the inferred relaxation time t r 8 5 years requires a value for a log v being the coefficient of friction in the range between 1 3 10 3 and 10 2

postseismic rebound in fault step overs caused by pore fluid flow near field strain induced by large crustal earthquakes results in changes in pore fluid pressure that dissipate with time and produce surface deformation synthetic aperture radar sar interferometry revealed several centimeters of postseismic uplift in pull apart structures and subsidence in a compressive jog along the landers california 1992 earthquake surface rupture with a relaxation time of 270 45 days such a postseismic rebound may be explained by the transition of the poisson s ratio of the deformed volumes of rock from undrained to drained conditions as pore fluid flow allows pore pressure to return to hydrostatic equilibrium

seismic images of crust and upper mantle beneath tibet evidence for eurasian plate subduction seismic data from central tibet have been combined to image the subsurface structure and understand the evolution of the collision of india and eurasia the 410 and 660 kilometer mantle discontinuities are sharply defined implying a lack of a subducting slab beneath the plateau the discontinuities appear slightly deeper beneath northern tibet implying that the average temperature of the mantle above the transition zone is about 300 c hotter in the north than in the south there is a prominent south dipping converter in the uppermost mantle beneath northern tibet that might represent the top of the eurasian mantle lithosphere underthrusting the northern margin of the plateau

source model for the mw 6 7 23 october 2002 nenana mountain earthquake alaska from insar 1 the 23 october 2002 nenana mountain earthquake mw 6 7 occurred on the denali fault alaska to the west of the mw 7 9 denali earthquake that ruptured the same fault 11 days later we used 6 interferograms constructed using radar images from the canadian radarsat 1 and european ers 2 satellites to determine the coseismic surface deformation and a source model data were acquired on ascending and descending satellite passes with incidence angles between 23 and 45 degrees and time intervals of 72 days or less modeling the event as dislocations in an elastic half space suggests that there was nearly 0 9 m of right lateral strike slip motion at depth on a near vertical fault and that the maximum slip in the top 4 km of crust was less than 0 2 m the nenana mountain earthquake increased the coulomb stress at the future hypocenter of the 3 november 2002 denali earthquake by 30 60 kpa

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 crustal property variations for models of tibetan plateau evolution shear coupled teleseismic p waves sampling the interior of the tibetan plateau provide evidence of systematic variations in crustal structure the crust thins by up to 20 km from south to north with a concomitant increase in poisson s ratio from normal values in the south to unusually high values in the north this suggests that the crust of the northern plateau is partially melted due to high temperatures these changes imply spatial and perhaps temporal variations in the way the elevation of the high plateau is created and maintained

viscoelastic flow in the lower crust after the 1992 landers california earthquake space geodesy showed that broad scale postseismic deformation occurred after the 1992 landers earthquake three dimensional modeling shows that afterslip can only explain one horizontal component of the postseismic deformation whereas viscoelastic flow can explain the horizontal and near vertical displacements the viscosity of a weak about 10 km thick layer in the lower crust beneath the rupture zone that controls the rebound is about 10 18 pascal seconds the viscoelastic behavior of the lower crust may help to explain the extensional structures observed in the basin and range province and it may be used for the analysis of earthquake hazard

3 d finite element modelling of deformation and stress associated with faulting effect of inhomogeneous crustal structures summary modelling of deformation and stress caused by earthquake faulting or fault motion based on a homogeneous elastic half space model does not include crustal rigidity layering and lateral variations geological data and seismic surveys indicate that the crust is elastically inhomogeneous and that rigidity layering and heterogeneities are likely to affect the magnitude and pattern of deformation and stress we use the finite element method fem to investigate deformation and stress generated by strike slip tensile and thrust faulting considering rigidity layering in the crust for a fault with a dimension of 25 10 km and a slip value of 0 5 m cutting through the top 10 km of the crust the deformation and stress change associated with the three modes of faulting are calculated for an island arc crustal structure represented by three models of rigidity layering the results indicate i the maximum effect in horizontal displacements due to crustal layering for the investigated models is 19 7 mm and 28 8 mm for strike slip and tensile faulting respectively for thrust faulting the effect is up to 58 3 mm this remarkable effect is due to the offset of layers by thrust faulting which dynamically changes the crustal structure both horizontally and vertically ii the maximum effect in vertical deformation due to crustal rigidity layering for strike slip and tensile faulting is 5 mm in contrast the effect for thrusting is 30 3 mm iii the effect in the shear stress change at a depth of 7 5 km for the different styles of faulting ranges from 0 02 mpa to 0 10 mpa an additional modelling analysis of subduction thrusting at the japan trench with a detailed structural model based on seismic surveys further confirms the significant distortion caused by a homogeneous model that ignores crustal structural information overall the effect of crustal rigidity layering is at least 20 per cent for surface deformation and 15 per cent for stress changes at depth in light of the present accuracy of global positioning system gps observations 2 mm and the estimate of stress change required for earthquake hazard analysis ca 0 01 mpa the results from the numerical experiments indicate that crust inhomogeneity rigidity layering and lateral variations should be included in any quantitative models of faulting

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

topography associated with crustal flow in continental collisions with application to tibet summary collision between an undeformable indenter and a viscous region generates isostatically compensated topography by solid state flow we model this process numerically using a finite element scheme the slope amplitude and symmetry of the topographic signal depend on the indenter size and the argand number of the viscous region a dimensionless ratio of gravitational body forces to viscous forces when applied to convergent continental settings these scaling rules provide estimates of the position of an indenter at depth and the mechanical properties of the viscous region especially effective viscosity in tibet forward modelling suggests that some elevated low relief topography within the northern plateau may be attributed to lower crustal flow stimulated by a crustal indenter possibly indian lithosphere the best fit model constrains the northernmost limit of this indenter to 33 7 n and the maximum effective viscosity of eurasian middle and lower crust to 1 10 20 0 3 10 20 pa s

regional trends in active diapirism revealed by mountain range scale insar time series 1 we construct an orogen wide insar time series over the zagros mountains and eastern markan subduction zone in southern iran from 19 envisat tracks spanning 2003 2010 we observe active salt diapirism of the infra cambrian hormuz salt at 20 locations and identify several diapirs that are not moving all active diapirs reach the surface within the asmari limestone or older rock units while we do not observe any active diapirism occurring within younger exposures reflecting a complex vertical accumulation of the basal salt and reactivation of diapirs by erosion diapir reactivation of this sort may be a critical factor affecting the feasibility of sequestering nuclear waste and co2 in evaporite sequences over geologic time scales the distribution of active diapirism is indifferent to increases in mean elevation suggesting a relatively uniform thickness of the zagros fold belt above the basal salt with steps in topography driven by basement thickening we do not observe aseismic uplift of anticlines because rates are likely below the detection threshold of our time series this suggests that uplift is accommodated at small rates 2 3 mm yr over numerous structures instead of focused at the deformation front

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

frictional afterslip following the 2005 nias simeulue earthquake sumatra continuously recording global positioning system stations near the 28 march 2005 rupture of the sunda megathrust moment magnitude m w 8 7 show that the earthquake triggered aseismic frictional afterslip on the subduction megathrust with a major fraction of this slip in the up dip direction from the main rupture eleven months after the main shock afterslip continues at rates several times the average interseismic rate resulting in deformation equivalent to at least a m w 8 2 earthquake in general along strike variations in frictional behavior appear to persist over multiple earthquake cycles aftershocks cluster along the boundary between the region of coseismic slip and the up dip creeping zone we observe that the cumulative number of aftershocks increases linearly with postseismic displacements this finding suggests that the temporal evolution of aftershocks is governed by afterslip

rheology of the lithosphere inferred from postseismic uplift following the 1959 hebgen lake earthquake 1 we have modeled the broad postseismic uplift measured by geodetic leveling in the epicentral area of the 1959 mw 7 3 hebgen lake montana earthquake a normal faulting event in the northern basin and range province to fit the observed uplift we calculate synthetic postseismic deformation using the relaxation response of a gravitational viscoelastic earth to the earthquake for a model with an elastic plate overlying a viscoelastic half space we find that the elastic thickness is 38 8 km which is close to the local crustal thickness the half space viscosity is estimated at 4 1018 0 5 pa s the leveling data do not require a viscous lower crust but permit a lower bound viscosity of 1020 pa s the observed broad uplift cannot be explained by physically plausible afterslip on and below the coseismic fault however local deformation across the coseismic surface rupture requires shallow afterslip reaching the surface the postseismic deformation induced by the estimated viscoelastic structure decays exponentially with a time constant of 15 years because of coupling between the elastic layer and the viscoelastic substrate this relaxation time is significantly longer than the 2 year maxwell relaxation time of the viscous half space itself our result suggests the importance of postseismic relaxation in interpreting high precision global positioning system velocities for example our model results suggest that postseismic transient velocities from both the 1959 hebgen lake and the 1983 mw 6 9 borah peak earthquakes are currently as large as 1 2 mm yr

some thoughts on the use of insar data to constrain models of surface deformation noise structure and data downsampling repeat pass interferometric synthetic aperture radar insar provides spatially dense maps of surface deformation with potentially tens of millions of data points here we estimate the actual covariance structure of noise in insar data we compare the results for several independent interferograms with a large ensemble of gps observations of tropospheric delay and discuss how the common approaches used during processing of insar data affects the inferred covariance structure motivated by computational concerns associated with numerical modeling of deformation sources we then combine the data covariance information with the inherent resolution of an assumed source model to develop an efficient algorithm for spatially variable data resampling or averaging we illustrate these technical developments with two earthquake scenarios at different ends of the earthquake magnitude spectrum for the larger events our goal is to invert for the coseismic fault slip distribution for smaller events we infer the hypocenter location and moment we compare the results of inversions using several different resampling algorithms and we assess the importance of using the full noise covariance matrix

a survey of volcanic deformation on java using alos palsar interferometric time series of the hundreds of volcanic centers throughout the indonesian archipelago few are adequately monitored for pre eruptive activity due to socioeconomic and logistical barriers with the result that volcanic hazards in the region are not well quantified the advent of satellite borne l band synthetic aperture radar provides an opportunity for detection and measurement of volcanic deformation over broad regions in heavily vegetated tropical island arcs we use data from the palsar instrument on the japanese alos satellite to conduct a comprehensive survey of volcanic deformation on the indonesian island of java over a time period of two years 2007 2008 to obtain the most complete temporally continuous record of ground deformation we use a temporally overlapping set of short time interval radar image pairs to produce a deformation time series consistent with previous results from other regions our survey suggests that volcanoes experiencing small eruptions are typically fed by magma bodies too small and or too shallow or deep to produce a recognizable insar signal however we identified a deformation event at lamongan volcano which is likely linked to a magmatic intrusion at several kilometers depth and a second one at slamet volcano at a shallower depth that may have been related to a subsequent eruption this initial test of a broad application of l band data allowed us to better define the satellite imaging criteria required for successful observation as well as developing a useful methodology for monitoring deformation over a wide region

frictional properties on the san andreas fault near parkfield california inferred from models of afterslip following the 2004 earthquake the abundance of geodetic and seismic data recording postseismic deformation following the 2004 parkfield earthquake provides an unprecedented opportunity to resolve frictional properties on the parkfield section of the san andreas fault the parkfield segment is a transition between the locked section to the southeast that last ruptured in the 1857 fort tejon earthquake and the creeping section to the northwest we develop three dimensional rate and state dependent friction models of afterslip following the 2004 earthquake to investigate the frictional behavior of the fault it is assumed that the coseismic rupture occurred on an area of the fault surrounded by aseismic creep that accelerated after the earthquake we estimate the distribution of coseismic slip afterslip and rate state frictional parameters by inverting a two step slip model in the model we 1 estimate the coseismic slip distribution from 1 hz global positioning system gps data and 2 use the corresponding coseismic shear stress change on the fault as input into a numerical afterslip model governed by rate state friction we find the rate state frictional parameter a b an indicator of frictional stability is in the range 10 4 10 3 at 50 mpa normal stress which is near the transition from potentially unstable negative a b to nominally stable positive a b friction the estimate of a b values falls within a wide range of experimental values reported for serpentinite which crops out along the san andreas fault zone the critical slip distance d c which characterizes the distance over which strength breaks down during a slip event is in the range 0 01 0 1 m consistent with seismic estimates and a fault gouge thickness of 1 10 m the afterslip model reproduces most features observed in the gps time series data including high surface velocities in the first few months after the earthquake and lower rates at later times as well as the cumulative postseismic displacement the model tends to underpredict the displacement data at later times suggesting that perhaps the modeled afterslip period ends too quickly or an unmodeled deformation process dominates the signal at later times

space time distribution of afterslip following the 2009 l aquila earthquake 1 the inversion of multitemporal dinsar and gps measurements unravels the coseismic and postseismic afterslip slip distributions associated with the 2009 mw 6 3 l aquila earthquake and provides insights into the rheological properties and long term behavior of the responsible structure the paganica fault well resolved patches of high postseismic slip 10 20 cm appear to surround the main coseismic patch maximum slip 1 m through the entire seismogenic layer above the hypocenter without any obvious depth dependent control time series of postseismic displacement are well reproduced by an exponential function with best fit decay constants in the range of 20 40 days a sudden discontinuity in the evolution of released postseismic moment at 130 days after the main shock does not correlate with independent seismological and geodetic data and is attributed to residual noise in the insar time series the data are unable to resolve migration of afterslip along the fault probably because of the time interval six days between the main shock and the first radar acquisition surface fractures observed along the paganica fault follow the steepest gradients of postseismic line of sight satellite displacements and are consistent with a sudden and delayed failure of the shallow layer in response to upward tapering of slip the occurrence of afterslip at various levels through the entire seismogenic layer argues against exclusive depth dependent variations of frictional properties on the fault supporting the hypothesis of significant horizontal frictional heterogeneities and or geometrical complexities we support the hypothesis that such heterogeneities and complexities may be at the origin of the long term variable behavior suggested by the paleoseismological studies rupture of fault patches with dimensions similar to that activated in 2009 appears to have a 500 year recurrence time interval documented by paleoseismic and historical studies in addition to that paleoseismological evidence of large 0 5 m coseismic offsets seems to require seismic events recurring every 1000 2000 years characterized by 1 multisegment linkage 2 surface ruptures larger than in 2009 and 3 complete failure of the 2009 coseismic and postseismic patches

phantom earthquakes and triggered aseismic creep vertical partitioning of strain during earthquake sequences in iran 1 we present evidence for significant aseismic fault slip at shallow depth above a pair of mainshock aftershock sequences in the zagros mountains of iran the two mw 5 9 earthquakes are each spanned by high quality geodetic imagery and have well recorded sequences of aftershocks that occurred beneath a salt decollement earlier studies of the geodetic data inferred that the mainshocks were located above the decollement requiring a 10 km spatial separation between aftershock cluster and earthquake centroid we find that the geodetic data simultaneously allow two slip sources of similar magnitude one within the basement collocated with aftershocks and one shallow source also equivalent to mw 6 responsible for the primary signal apparent in the geodetic imagery should this phenomenon be widespread in the zagros it would partially explain a previously noted discrepancy between observed seismic moment release in the zagros and current convergence rates between the arabian and eurasian plates

time dependent distributed afterslip on and deep below the izmit earthquake rupture surface deformation transients measured with the global positioning system during the 87 days between the 17 august 1999 izmit earthquake and the 12 november 1999 duzce earthquake indicate rapidly decaying aseismic fault slip on and well below the coseismic rupture elastic model inversions for time dependent distributed fault slip using a network inversion filter approach show that afterslip was highest between and below the regions of maximum coseismic slip and propa gated downward to or even below the base of the crust maximum afterslip rates decayed from greater than 2 m yr immediately after the i zmit earthquake to about 1 2 m yr just prior to the duzce earthquake maximum afterslip occurred below the eastern karadere rupture segment and near the i zmit hypocenter afterslip in the upper 16 km decayed more rapidly than that below the seismogenic zone these observations are consistent with a phase of rapid aseismic fault slip concentrated near the base of the seismogenic zone continued loading from the rapid deep afterslip along the eastern rupture zone is a plausible mechanism that helped trigger the nearby mw 7 2 12 november duzce earthquake

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

preceding coseismic and postseismic slips of the 2011 tohoku earthquake japan 1 we estimated the spatial and temporal evolution of the preceding aseismic slip from january 2003 to january 2011 the coseismic slip of the tohoku earthquake and the postseismic slip after the earthquake based on global positioning system gps data time dependent analysis indicates aseismic slip offshore of miyagi and fukushima prefectures from 2004 associated with a series of subduction earthquakes that overlap the aseismic slip area these preceding aseismic and coseismic slip areas are centered between the centers of the coseismic and afterslip areas of the tohoku earthquake offshore of miyagi prefecture while they overlap the coseismic and afterslip areas of the tohoku earthquake off fukushima prefecture the timing of moment magnitude nine mw9 class earthquakes appears to be controlled by multiple preceding slip events smaller earthquakes and their afterslip the preceding aseismic and coseismic slip decreased the coupling rate off the tohoku coast suggesting the possibility that the preceding slip represented a precursive stage of the tohoku earthquake the afterslip of the tohoku earthquake occurred in an area where the coseismic slip was not large complementing the large coseismic slip zone the afterslip along iwate miyagi extends up to 80 km in depth and is currently the sole mechanism of strain release in this depth range the source region of the anticipated miyagi oki earthquake shows small postseismic slip after the tohoku earthquake reflecting the energy release at the time of the earthquake aftershock activity is roughly governed by an afterslip process

depths and focal mechanisms of crustal earthquakes in the central andes determined from teleseismic waveform analysis and insar 1 we investigate the depths of crustal earthquakes mw 5 5 earthquakes from the global cmt catalog and previous work spanning 1944 2007 for 38 well recorded events we use teleseismic p and sh waveforms to model the strike dip rake focal depth and source time function we use insar observations of surface deformation from 9 earthquakes to compare inferred fault parameters with the waveform inversions and global catalogs to assess their accuracies while the depths from the insar and waveform analyses generally agree within error horizontal and depth errors in global catalogs are 10 to 50 km as found elsewhere as noted in previous work the majority of crustal earthquakes occur in the eastern cordillera and foreland regions of the central andes although a few normal and strike slip earthquakes occur beneath the altiplano plateau and in the forearc in southern peru and northernmost chile we propose a new interpretation of one of the basement thrusts shira mountain peru as a pop up block on the basis of our new earthquake depths we confirm that earthquakes in the flat slab areas of peru and argentina are within the sometimes aseismic lower crust lower crustal earthquakes are globally found in all types of tectonic settings only when the thermal lithosphere is more than 80 km thick and the amount of recent shortening extension is 30

the effect of elastic layering on inversions of gps data for coseismic slip and resulting stress changes strike slip earthquakes we investigate the effect of depth dependent elasticity on slip inversions and coseismic stress change estimates for large strike slip earthquakes using a series of hypothetical models and the 1999 izmit turkey earthquake as examples slip inversions are performed using both semianalytical and finite element solutions for surface displacements due to a shear dislocation in layered and uniform elastic earth models we find that incorporating realistic increases to shear modulus with depth in our inversions increases recovered centroid depth and seismic potency relative to uniform elastic half space models recovered seismic moment is up to 40 greater for models incorporating depth dependent than it is for uniform elastic half space models incorporating depth dependent also increases our estimate of the maximum slip depth for the izmit turkey earthquake to at least 20 km our estimates of coseismic stress change in the upper crust do not change significantly when we incorporate depth dependent elasticity in our inversions as long as slip at depth is tuned increased to match surface displacements coseismic differential stresses in the lower crust increase by up to a factor of 3 in the near field but further from the fault stresses from layered and uniform elastic models are approximately equal with increasing depth in the mantle the ratio of modeled differential stresses for the layered and uniform elastic models approaches the ratio of mantle values for these two models we conclude that models of postseismic viscoelastic relaxation following large strike slip earthquakes should incorporate depth dependent elasticity but that uniform elastic half space models are adequate to calculate coseismic coulomb stresses in the upper crust for most triggering studies

extension on the tibetan plateau recent normal faulting measured by insar and body wave seismology we use insar and body wave modelling to determine the faulting parameters for a series of five mw 5 9 7 1 normal faulting earthquakes that occurred during 2008 including the march 20 yutian earthquake mw 7 1 one of the largest normal faulting events to have occurred recently on the continents we also study three earlier normal faulting earthquakes that occurred in southern tibet between 1992 and 2005 coseismic deformation for each of these eight events is measured with ascending and descending interferograms from envisat ers and alos sar data elastic dislocation modelling of the line of sight insar displacements and body wave seismological modelling of p and sh waves are used to estimate fault parameters and are found to be in good agreement for all the events studied the use of insar to measure deformation allows a relatively precise determination of the fault location in addition to resolving the focal plane ambiguity only five of the eight events are associated with a clear surface topographic feature suggesting that an underestimation of the amount of extension would result from using the surface expressions of normal faulting alone the observations in all cases are consistent with slip on planar surfaces with dips in the range 40 50 that penetrates the uppermost crust to a depth of 10 15 km we find no evidence for active low angle dip less than 30 normal faulting the contribution of the normal faulting to overall extension estimated by summing seismic moments over earthquakes for the past 43 yr is 3 4 mm yr 1 or 15 20 per cent of the rates of extension measured across the plateau using gps 85 per cent of the moment release in normal faulting over the past 43 yr has occurred in regions whose surface height exceeds 5 km this observation adds weight to the suggestions that the widespread normal faulting on the plateau is the result of variations in the gravitational potential energy of the lithosphere

mechanical constraints on inversion of coseismic geodetic data for fault slip and geometry example from insar observation of the 6 october 2008 mw 6 3 dangxiong yangyi tibet earthquake 1 modern geodetic techniques such as the global positioning system gps and interferometric synthetic aperture radar insar provide high precision deformation measurements of earthquakes through elastic models and mathematical optimization methods the observations can be related to a slip distribution model the classic linear kinematic and static slip inversion problem requires specification of a smoothing norm of slip parameters and a residual norm of the data and a choice about the relative weight between the two norms inversions for unknown fault geometry are nonlinear and therefore the fault geometry is often assumed to be known for the slip inversion problem we present a new method to invert simultaneously for fault slip and fault geometry assuming a uniform stress drop over the slipping area of the fault the method uses a full bayesian inference method as an engine to estimate the posterior probability distribution of stress drop fault geometry parameters and fault slip we validate the method with a synthetic data set and apply the method to insar observations of a moderate sized normal faulting event the 6 october 2008 mw 6 3 dangxiong yangyi tibet earthquake the results show a 45 0 0 2 west dipping fault with a maximum net slip of 1 13 m and the static stress drop and rake angle are estimated as 5 43 mpa and 92 5 respectively the stress drop estimate falls within the typical range of earthquake stress drops known from previous studies

postseismic mantle relaxation in the central nevada seismic belt holocene acceleration of deformation and postseismic relaxation are two hypotheses to explain the present day deformation in the central nevada seismic belt cnsb discriminating between these two mechanisms is critical for understanding the dynamics and seismic potential of the basin and range province interferometric synthetic aperture radar detected a broad area of uplift 2 to 3 millimeters per year that can be explained by postseismic mantle relaxation after a sequence of large crustal earthquakes from 1915 to 1954 the results lead to a broad agreement between geologic and geodetic strain indicators and support a model of a rigid basin and range between the cnsb and the wasatch fault

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

transient rheology of the upper mantle beneath central alaska inferred from the crustal velocity field following the 2002 denali earthquake the m7 9 2002 denali earthquake alaska is one of the largest strike slip earthquakes ever recorded the postseismic gps velocity field around the 300 km long rupture is characterized by very rapid horizontal velocity up to 300 mm yr for the first 0 1 years and slower but still elevated horizontal velocity up to 100 mm yr for the succeeding 1 5 years i find that the spatial and temporal pattern of the displacement field may be explained by a transient mantle rheology representing the regional upper mantle as a burghers body 1 infer steady state and transient viscosities of 1 2 8 x 10 18 pa s and 2 1 0 x 10 17 pa s respectively corresponding to material relaxation times of 1 3 and 0 05 years the lower crustal viscosity is poorly constrained by the considered horizontal velocity field and the quoted mantle viscosities assume a steady state lower crust viscosity that is 7 1 systematic bias in predicted versus observed velocity vectors with respect to a fixed north america during the first 3 6 months following the earthquake is reduced when all velocity vectors are referred to a fixed site this suggests that the post denali gps time series for the first 1 63 years are shaped by a combination of a common mode noise source during the first 3 6 months plus viscoelastic relaxation controlled by a transient mantle rheology

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

source parameters of the 1 october 1995 dinar turkey earthquake from sar interferometry and seismic bodywave modelling abstract the 1 october 1995 m s 6 1 dinar earthquake ruptured a 10 km section of the nw se dinar civril fault there are discrepancies between the published source parameters from seismic data with seismic moments in disagreement by over a factor of two we use both sar interferometry and seismic bodywave modelling to determine earthquake source parameters an interferogram generated from ers 1 2 sar imagery spanning the event and separated by 5 months is used to derive source parameters by a downhill simplex inversion with multiple monte carlo restarts we model the displacements in the satellite line of sight initially using uniform slip on a rectangular dislocation in an elastic half space the resultant model fault plane agrees in strike and location with the observed surface break but systematic residuals exist in the line of sight deformation field resulting in a r m s residual of 20 mm in the interferogram the residuals are reduced if the depth distribution of slip is allowed to vary spatially in four segments along a continuous fault plane our best fitting solution with a r m s misfit of 8 mm reveals two distinct areas of slip on the fault plane strike 145 dip 49 rake 270 a main rupture slipping by 1 44 m between depths of 1 and 8 km becoming deeper to the se and matching the observed surface rupture and an along strike continuation to the nw of the same fault plane but between depths of 8 and 13 km and not associated with a surface break the total geodetic moment 4 5 0 1 10 18 nm is more than twice as large as published seismic moments based on the inversion of p waveforms alone but close to the harvard cmt moment 4 7 10 18 nm we use sh waveforms in addition to the p waves used previously to determine an alternative seismic source mechanism sh waves constrain the depth to be shallower than solutions based on p waves alone agreeing with the depths from the interferometric inversion and resulting in a larger moment 3 1 0 4 10 18 nm than the previous bodywave estimates 2 2 1 10 18 nm the cmt moment reduces in magnitude to a similar size 3 3 10 18 nm if the centroid depth and fault dip are constrained to the values determined from bodywave modelling and interferometry thus the geodetic moment is 40 bigger than the moment determined from seismology

crustal structure of northern and southern tibet from surface wave dispersion analysis 1 group and phase velocities of fundamental mode rayleigh waves in the period range of 10 to 70 s are obtained for southern and northern tibet significant variations in crustal velocity structure are found the group velocity minimum for tibet occurs at 33 s and the minimum is 0 12 km s lower for southern tibet than for northern tibet at periods greater than 50 s however group velocities are up to 0 2 km s faster in southern tibet the group and phase velocities are inverted for layered s wave models the dispersion observations in southern tibet can only be fit with a low velocity layer in the middle crust in contrast the velocity models for northern tibet do not require any lowvelocity zone in the crust the s wave velocity of the lower crust of southern tibet is 0 2 km s faster than the lower crust of northern tibet in southern tibet the sub moho velocity increases with a positive gradient that is similar to a shield while there is no velocity gradient beneath northern tibet the high velocity lower crust of southern tibet is consistent with the underthrusting of indian continental lithosphere the most plausible explanation of the mid crustal low velocity zone is the presence of crustal melt resulting from h2o saturated melting of the interplate shear zone between the underthrusting indian crust and overflowing asian crust the lack of a pronounced crustal low velocity zone in northern tibet is an indication of a relatively dry crust the low s wave velocity in the lower crust of northern tibet is interpreted to be due to a combination of compositional differences high temperatures presumably caused by a high mantle heat flux and possibly small amounts of partial melt combined with all available observations in tibet the new surface wave results are consistent with a hot and weak upper mantle beneath northern tibet index terms 7205 seismology continental crust 1242 7218 seismology lithosphere and upper mantle 7255 seismology surface waves and free oscillations 8102 tectonophysics continental contractional orogenic belts keywords tibet crustal velocity structure surface wave rayleigh waves continental collision

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

the october 6 2008 mw 6 3 magnitude damxung earthquake yadong gulu rift tibet and implications for present day crustal deformation within tibet abstract a mw 6 3 magnitude earthquake occurred on october 6 2008 in southern damxung county within the n s trending yangyi graben which forms the northern section of the yadong gulu rift of south central tibet the earthquake had a maximum intensity of ix at the village of yangyi also yangying 29 43 3 n 90 23 6 e and resulted in 10 deaths and 60 injured in this sparsely populated region field observations and focal mechanism solutions show normal fault movement occurred along the nne trending western boundary fault of the yangyi graben in agreement with the felt epicenter pattern of the isoseismal contours and distribution of aftershocks the earthquake and its tectonic relations were studied in detail to provide data on the seismic hazard to the nearby city of lhasa the damxung earthquake is one of the prominent events along normal and strike slip faults that occurred widely about tibet before and after the 2008 mw 7 9 magnitude wenchuan earthquake analysis of these recent m 5 0 earthquake sequences demonstrate a kinematic relation between the normal strike slip and reverse causative fault movements across the region these earthquakes are found to be linked and the result of eastward extrusion of two large structural blocks of central tibet the reverse and oblique slip surface faulting along the longmenshan thrust belt at the eastern margin of the tibetan plateau causing the wenchuan earthquake was the result of eastward directed compression and crustal shortening due to the extrusion prior to it east west extensional deformation indicated by normal and strike slip faulting events across central tibet had led to a build up of the compression to the east the subsequent renewal of extensional deformational events in central tibet appears related to some drag effect due to the crustal shortening of the wenchuan event unraveling the kinematical relation between these earthquake swarms is a very helpful approach for understanding the migration of strong earthquakes across tibet

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