dislocation models of interseismic deformation in the western united states 1 the gps derived crustal velocity field of the western united states is used to construct dislocation models in a viscoelastic medium of interseismic crustal deformation the interseismic velocity field is constrained by 1052 gps velocity vectors spanning the 2500 km long plate boundary zone adjacent to the san andreas fault and cascadia subduction zone and extending 1000 km into the plate interior the gps data set is compiled from u s geological survey campaign data plate boundary observatory data and the western u s cordillera velocity field of bennett et al 1999 in the context of viscoelastic cycle models of postearthquake deformation the interseismic velocity field is modeled with a combination of earthquake sources on 100 known faults plus broadly distributed sources models that best explain the observed interseismic velocity field include the contributions of viscoelastic relaxation from faulting near the major plate margins viscoelastic relaxation from distributed faulting in the plate interior as well as lateral variations in depth averaged rigidity in the elastic lithosphere resulting rigidity variations are consistent with reduced effective elastic plate thickness in a zone a few tens of kilometers wide surrounding the san andreas fault saf system primary deformation characteristics are captured along the entire saf system eastern california shear zone walker lane the mendocino triple junction the cascadia margin and the plate interior up to 1000 km from the major plate boundaries

aseismic slip during the 1996 earthquake swarm in and around the onikobe geothermal area ne japan abstract in august 1996 an earthquake swarm including 4 earthquakes of magnitudes greater than 5 occurred in and around the onikobe geothermal area northeast japan while earlier studies detected ground displacements by l band jers radar interferograms there remained certain puzzling discrepancies between the observations and the predictions from a seismologically inferred model and no satisfactory models have yet been proposed here by identifying that a steep gradient in the radar line of sight changes exists in seismicity gaps to the east and west of the torage area just to the north of the onikobe caldera we propose two aseismic reverse faults which turn out to contribute to a local topographic growth as well as explaining the pre existing discrepancies another significant signal is detected in a region in which no large earthquakes occurred we account for this signal by another aseismic fault this fault adds to another evidence for the recent hypothesis that aseismic fault motion drives earthquake swarm

the postseismic response to the 2002 m 7 9 denali fault earthquake constraints from insar 2003 2005 summary insar is particularly sensitive to vertical displacements which can be important in distinguishing between mechanisms responsible for the postseismic response to large earthquakes afterslip viscoelastic relaxation we produce maps of the surface displacements resulting from the postseismic response to the 2002 denali fault earthquake using data from the canadian radarsat 1 satellite from the periods summer 2003 summer 2004 and summer 2005 a peak to trough signal of amplitude 4 cm in the satellite line of sight was observed between summer 2003 and summer 2004 by the period between summer 2004 and summer 2005 the displacement rate had dropped below the threshold required for observation with insar over a single year the insar observations show that the principal postseismic relaxation process acted at a depth of 50 km equivalent to the top of the mantle however the observations are still incapable of distinguishing between distributed viscoelastic relaxation and localized afterslip deformation the imposed coseismic stresses are highest in the lower crust and assuming a maxwell rheology a viscosity ratio of at least 5 between lower crust and upper mantle is required to explain the contrast in behaviour the lowest misfits are produced by mixed models of viscoelastic relaxation in the mantle and shallow afterslip in the upper crust profiles perpendicular to the fault show significant asymmetry which is consistent with differences in rheological structure across the fault

northwest basin and range tectonic deformation observed with the global positioning system 1999 2003 1 we use geodetic velocities obtained with the global positioning system gps to quantify tectonic deformation of the northwest basin and range province of the western united states the results are based on gps data collected in 1999 and 2003 across five new quasi linear networks in northern nevada northeast california and southeast oregon the velocities show 3 mm yr westward movement of northern nevada with respect to stable north america west of longitude 119 w the velocities increase and turn northwest parallel to sierra nevada great valley microplate motion and similar to velocities previously obtained to the south the observations are explained by a kinematic model with three domains that rotate around euler poles in eastern oregon and western idaho northeast california experiences internal dextral shear deformation 11 2 3 6 nstrain yr subparallel to pacific north america motion relative motions of the domains imply 2 5 mm yr approximately east west extension in northwest nevada and 1 4 mm yr approximately north south contraction near the california oregon border the northward decreasing approximately east west extension in northwest nevada is consistent with the northern termination of basin and range deformation faulting and characteristic topography no significant extension is detected in the oregon basin and range the oregon cascade arc moves north at 3 5 mm yr and is possibly influenced by the approximately eastward motion of the juan de fuca plate these results disagree with secular northwest trenchward motion of the oregon forearc inferred from paleomagnetic rotations south of latitude 43 however trenchward motion exists and is consistent with block rotations approximately east west basin and range extension and northwest sierra nevada translation

viscosity estimates for the crust and upper mantle from patterns of lacustrine shoreline deformation in the eastern great basin the deformed shorelines of lake bonneville constitute a classic source of information on lithospheric elastic thickness and upper mantle viscosity we describe and apply a new model to a recently augmented data set new data better constrain both the complex spatio temporal pattern of the lake load and the crustal deformation response to that load the history of lake level fluctuations has been significantly refined and somewhat modified this is due to both more radiocarbon dates from within the bonneville basin and to an improved calibration of the radiocarbon timescale itself the data which constrain the crustal deformation pattern consist of ages and shoreline elevations from several hundred points which sample three major levels of lake bonneville and corresponding elevations from the high stands of three smaller lakes situated to the west of lake bonneville the data from the smaller lakes help elucidate the pattern of deflection which occurred beyond the edge of the big lake the geometry of the earth model incorporates an arbitrary number of layers overlying a half space and the rheology of each level can accommodate an arbitrary number of maxwell viscoelastic elements in parallel the inverse modeling comprises three complementary approaches for the simplest configurations we performed a direct search of the parameter space and delineated the irregular boundary of the subspace of acceptable models for more complex configurations we constrained the elastic parameters to their seismically determined values and then solved for viscosity versus depth profiles by either expressing the log viscosity versus log depth profile as a series of specially constructed orthogonal polynomials or by allowing each of 8 10 layers plus the half space to have an independently determined viscosity we found that the data do not strongly support nor can they conclusively exclude a more complex rheology than simple maxwell viscoelasticity the orthogonal polynomial solution exhibits an essentially monotonic decrease in viscosity with depth the most rapid change occurs at shallow depths decreasing from 1023 pa s at 3 km to 102o pa s at 30 km the decrease is much more gradual below with only another factor of 5 decrease between 30 and 300 km depth the unconstrained solution exhibits a rapid decrease in viscosity with depth from 2x 10 24 pa s in the top 10 km to 4x 1017 pa s at a depth of 40 km a nearly isoviscous asthenospheric region extends from 40 to 150 km and is underlain by a mantle lithospheric region with increased viscosity 2x 102o pa s extending from 150 to 300 km depth and by a uniform viscosity 1019 pa s half space below

transient deformation in california from two decades of gps displacements implications for a three dimensional kinematic reference frame our understanding of plate boundary deformation has been enhanced by transient signals observed against the backdrop of time independent secular motions we make use of a new analysis of displacement time series from about 1 000 continuous global positioning system gps stations in california from 1999 to 2018 to distinguish tectonic and nontectonic transients from secular motion a primary objective is to define a high resolution three dimensional reference frame datum for california that can be rapidly maintained with geodetic data to accommodate both secular and time dependent motions to this end we compare the displacements to those predicted by a horizontal secular fault slip model for the region and construct displacement and strain rate fields over the past 19 years california has experienced 19 geodetically detectable earthquakes and widespread postseismic deformation we observe postseismic strain rate variations as large as 1 000 nstrain year with moment releases equivalent up to an mw6 8 earthquake we find significant secular differences up to 10 mm year with the fault slip model from the mendocino triple junction to the southern cascadia subduction zone the northern basin and range and the santa barbara channel secular vertical uplift is observed across the transverse ranges coastal ranges sierra nevada as well as large scale postseismic uplift after the 1999 mw7 1 hector mine and 2010 mw7 2 el mayor cucapah earthquakes we also identify areas of vertical land motions due to anthropogenic natural and magmatic processes finally we demonstrate the utility of the kinematic datum by improving the accuracy of high spatial resolution 12 day repeat cycle sentinel 1 interferometric synthetic aperture radar displacement and velocity maps

earthquake processes in the rainbow mountain fairview peak dixie valley nevada region 1954 1959 the 1954 rainbow mountain fairview peak dixie valley nevada sequence produced the most extensive pattern of surface faults in the intermountain region in historic time five earthquakes of m 6 0 occurred during the first 6 months of the sequence including the december 16 1954 fairview peak m 7 1 and dixie valley m 6 8 earthquakes three 5 5 m 6 5 earthquakes occurred in the region in 1959 but none exhibited surface faulting the results of the modeling suggest that the m 6 5 earthquakes of this sequence are complex events best fit by multiple source time functions although the observed surface displacements for the july and august 1954 events showed only dip slip motion the fault plane solutions and waveform modeling suggest the earthquakes had significant components of right lateral strike slip motion rakes of 135 to 145 all of the earthquakes occurred along high angle faults with dips of 40 to 70 seismic moments for individual subevents of the sequence range from 8 0 1017 to 2 5 1019 n m stress drops for the subevents including the fairview peak subevents were between 0 7 and 6 0 mpa

identification of sublimation type thermal contraction crack polygons at the proposed nasa phoenix landing site implications for substrate properties and climate driven morphological evolution 1 we identify a surface within the nasa phoenix landing site area d characterized by boulder topped polygonally patterned mounds comparable in radius and cross sectional morphology to terrestrial sublimation polygons found in antarctica both martian and antarctic polygons display topographic asymmetry with shallow equator facing slopes and steep pole facing slopes interpreted to indicate insolation dependent differential sublimation of buried ice on the basis of morphological similarities we classify the phoenix box 1 polygons as sublimation polygons terrestrial sublimation polygons form where ice volumes exceeding available pore space occur in the shallow subsurface and where near surface conditions are too cold and dry to permit the development of saturated active layers conditions comparable to those recently modeled for mars in the phoenix landing site area d box 1 the identification of sublimation polygons on mars would provide direct evidence for shallow ground ice exceeding pore ice volumes and shed light on the emplacement mechanism of this ice

accommodation of missing shear strain in the central walker lane western north america constraints from dense gps measurements abstract we present 264 new interseismic gps velocities from the mobile array of gps for nevada transtension magnet and continuous gps networks that measure pacific north american plate boundary deformation in the central walker lane relative to a north america fixed reference frame northwestward velocities increase smoothly from 4 mm yr in the basin and range province to 12 2 mm yr in the central sierra nevada resulting in a central walker lane deformation budget of 8 mm yr we use an elastic block model to estimate fault slip and block rotation rates and patterns of deformation from the gps velocities right lateral shear is distributed throughout the central walker lane with strike slip rates generally

geophysical confirmation of low angle normal slip on the historically active dixie valley fault nevada the december 16 1954 dixie valley earthquake ms 6 8 followed the nearby fairview peak earthquake ms 7 2 by 4 min 20 s waveforms from the fairview peak event contaminate those from the dixie valley event making accurate fault plane solutions impossible a recent geologic study of surface rupture characteristics in southern dixie valley suggests that the dixie valley fault is low angle 30 along a significant portion of the 1954 rupture to extend these observations into the subsurface we conducted a seismic reflection and gravity experiment our results show that a portion of the dixie valley ruptures occurred along a fault dipping 25 to 30 as such the dixie valley event may represent the first large low angle normal earthquake on land recorded historically our high resolution seismic reflection profile images the rupture plane from 5 to 50 m depth medium resolution reflections as well as refraction velocities show a smoothly dipping fault plane from 50 to 500 m depth stratigraphic truncations and rollovers in the hanging wall show a slightly listric fault to 2 km depth gravity profiles conservatively constrain maximum basin depth and define overall geometry extension along the low angle section may have occurred in two phases during the cenozoic current fault motion postdates a 13 to 15 ma basalt imaged in the hanging wall and inherits from a fault formed during an earlier extensional pulse concentrated at 24 2 to 24 4 ma the earlier extension suggests extraordinary slip rates as high as 18 mm yr resulting in the formation of the low angle fault break sections of the dixie valley fault where there is no evidence for current low angle slip correlate well with areas where no pre 15 ma slip has been documented

faults shear zones in the earth s mantle abstract geodetic data support a short term continental deformation localized in faults bounding lithospheric blocks whether major faults observed at the surface affect the lithospheric mantle and if so how strain is distributed are major issues for understanding the mechanical behavior of lithospheric plates a variety of evidence from direct observations of deformed peridotites in orogenic massifs ophiolites and mantle xenoliths to seismic reflectors and seismic anisotropy beneath major fault zones consistently supports prolongation of major faults into the lithospheric mantle this review highlights that many aspects of the lithospheric mantle deformation remain however poorly understood coupling between deformation in frictional faults in the uppermost crust and localized shearing in the ductile crust and mantle is required to explain the post seismic deformation but mantle viscosities deduced from geodetic data and extrapolated from laboratory experiments are only reconciled if temperatures in the shallow lithospheric mantle are high 800 c at the moho seismic anisotropy especially shear wave splitting provides strong evidence for coherent deformation over domains several tens of km wide in the lithospheric mantle beneath major transcurrent faults yet it cannot detect narrow strain localization zones or shallowly dipping faults seismic profiling images shallow dipping seismic reflectors in the lithospheric mantle interpreted as the continuation of normal or less frequently inverse faults in the mantle however the nature of these reflectors is poorly understood there is a large discrepancy between the scale at which deformation processes are studied a few kilometers at most due to the limited size of continuous mantle exposures at the earth s surface and the scale inferred for strain localization in the mantle from geophysical observations tens of kilometers combining data on deformation microstructures and crystal preferred orientations in naturally deformed peridotites and seismologic observations allows nevertheless discussing strain localization processes that may play a role on the development of mantle shear zones

vertical deformation associated with normal fault systems evolved over coseismic postseismic and multiseismic periods vertical deformation of extensional provinces varies significantly and in seemingly contradictory ways sparse but robust geodetic seismic and geologic observations in the basin and range province of the western united states indicate that immediately after an earthquake vertical change primarily occurs as subsidence of the normal fault hanging wall a few decades later a 100 km wide zone is symmetrically uplifted the preserved topography of long term rifting shows bent and tilted footwall flanks rising high above deep basins we develop finite element models subjected to extensional and gravitational forces to study time varying deformation associated with normal faulting we replicate observations with a model that has a weak upper mantle overlain by a stronger lower crust and a breakable elastic upper crust a 60 dipping normal fault cuts through the upper crust and extends through the lower crust to simulate an underlying shear zone stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift under the footwall the breakable upper crust is a necessary model feature to replicate footwall bending over the observed width 10 km which is predicted to take place within 1 2 decades after each large earthquake thus the best preserved topographic signature of rifting is expected to occur early in the postseismic period the relatively stronger lower crust in our models is necessary to replicate broader postseismic uplift that is observed geodetically in subsequent decades

gps constraints on vertical crustal motion in the northern basin and range 1 we estimated vertical velocities using an array of 12 continuous gps stations forming part of the pbo nucleus network we analyzed data spanning the period 1996 through 2006 the array has an aperture 400 km and crosses a major active intracontinental normal fault system in the northern basin and range province the root mean square rms of vertical rates relative to a local no net vertical frame is 0 3 mm yr indicating high relative rate precision the rms difference between rates based on t 7 year sub strands of the total data set and the full 10 year rate estimates varies as 2 4 t 1 3 mm yr the net vertical rate observed across the greater wasatch fault zone is consistent with the predictions of elastic half space dislocation models only when the deep slipping part of the fault has very shallow dip 30

postearthquake relaxation evidence for laterally variable viscoelastic structure and water content in the southern california mantle i reexamine the lower crust and mantle relaxation following two large events in the mojave desert the 1992 m7 3 landers and 1999 m7 1 hector mine california earthquakes time series from continuous gps sites out to 300 km from the ruptures are used to constrain models of postseismic relaxation crustal motions in the mojave desert region are elevated above background for several years following each event to account for broadscale relaxation of the lower crust and mantle the burgers body model is employed involving transient and steady state viscosities joint afterslip postseismic relaxation modeling of the gps time series up to one decade following the hector mine earthquake reveals a significant rheological contrast between a northwest trending southwest domain that envelopes the san andreas fault system and western mojave desert and an adjacent northeast domain that envelopes the landers and hector mine rupture areas in the central mojave desert the steady state viscosity of the northeast domain mantle asthenosphere is inferred to be 4 times greater than that of the southwest domain this pattern is counter to that expected for regional heat flow which is higher in the northeast domain but it is explicable by means of a nonlinear rheology that includes dependence on both strain rate and water concentration i infer that the southwest domain mantle has a relatively low steady state viscosity because of its high strain rate and water content the relatively low mantle water content of the northeast domain is interpreted to result from the continual extraction of water through igneous and volcanic activity over the past 20 myr

source parameters of earthquakes in the nevada seismic zone 1915 1943 the nevada seismic zone has historically been one of the most active seismic regions of the intermountain west although all large m 7 0 earthquakes located within this zone occurred prior to the establishment of a worldwide seismograph network most have been well recorded instrumentally this study uses available instrumental data to determine the source parameters for some of the earliest earthquakes occurring within the region namely the 1915 m 7 6 pleasant valley and 1932 m 7 2 cedar mountain earthquakes and several smaller events of 5 5 m 6 5 occurring within the cedar mountain region between 1934 and 1943 results of body waveform inversions suggest that the pleasant valley earthquake at the northern end of the nevada seismic zone is a complex event best fit by a multiple source time function waveform and first motion information for the cedar mountain earthquake located within the walker lane suggest the earthquake was composed of two events each having significant components of right lateral strike slip motion rakes of 176 to 179 waveforms of the m 6 5 excelsior mountain earthquake located only 40 km southwest of cedar mountain suggest the earthquake was a simple rupture along a normal fault rake of 90 20 although surface faulting indicates that the event had a component of left lateral strike slip motion

modeling the holocene slip history of the wasatch fault utah coseismic and postseismic coulomb stress changes and implications for paleoseismicity and seismic hazard

reevaluation of the viscoelastic and elastic responses to the past and present day ice changes in southeast alaska abstract we have reevaluated the viscoelastic and elastic responses to the past and present day ice changes in southeast alaska se ak based on a gps data set by combining the data previously published in 2005 with additional uplift rates compiled recently there are 22 new gps sites yielding a total of 91 sites the mean observation epoch of the data sets is the middle of 2003 here we considered three ice unloading effects due to the last glacial maximum lgm the little ice age lia and the present day ice melting pdim we also examined the dependency of the estimated lithospheric thickness and the asthenospheric viscosity on pdim models for this test two pdim models were used one is a model called here the uaf05 ice model whose mean epoch is the mid 1970s and the other is a model called here the uaf07 model whose mean epoch is the mid 1980s statistical examinations of the misfits between observations and model predictions indicate that uaf07 gives much more consistent results than uaf05 based on the magnitude of the minimum 2 and the agreement of the residual distribution with a gaussian function we have tested two different kinds of mantle viscosity structure a 2 layer model similar to the model used the paper previously published in 2005 and a 4 layer model for the 2 layer model at the 95 confidence level the optimum values for the lithospheric thickness and the asthenospheric viscosity with a thickness of 110 km are 54 45 65 km and 5 58 4 0 12 0 in unit of 10 18 pa s respectively on the other hand for the 4 layer model the best values were 60 42 63 km and 10 0 3 0 13 in unit of 10 18 pa s respectively the comparison between the analysis results for gps data and the model computations indicates that the observations detect not only the uplift rates in se ak but also their time variations which are considered to be due to the glacier changes after the 1990s

new perspectives on geological strain rates calculated from both naturally deformed and actively deforming rocks abstract a value of 10 14 s 1 is commonly cited as an average geological strain rate this value was first suggested for finite strain across an orogen but based on more limited information than the combined geophysical geological and experimental data now available on active and ancient rock deformation thus it is timely to review the data constraining strain rates in the continents and to consider the quantifiable range of crustal strain rates here where resolution allows both spatial and temporal strain rate variations are explored this review supports that a strain rate of 10 14 1 s 1 arises from geological estimates of bulk finite strains microstructural arguments combining laboratory derived piezometers and viscous flow laws however imply local rates that are orders of magnitude faster geodetic rates in contrast are typically 10 15 s 1 in actively deforming areas about an order of magnitude slower than the bulk rates estimated from geological observations this difference in estimated strain rates may arise from either low spatial resolution or the fact that surface velocity fields can not capture strain localisation in the mid to lower crust integration of geological and geodetic rates also shows that strain rates can vary in both space and time over both single and multiple earthquake cycles overall time averaged geological strain rates are likely slower than the strain rates in faults and shear zones that traverse the crust or lithosphere

surface faulting of the 1954 fairview peak ms 7 2 and dixie valley ms 6 8 earthquakes central nevada abstract the 1954 fairview peak earthquake was followed 4 min and 20 sec later by the dixie valley earthquake surface ruptures were distributed among six different faults that define a complex north trending zone 100 km long and over 15 km wide the rupture sequence progressed from south to north the initial event produced a 32 km rupture of right oblique slip along the east dipping fairview fault where the components of right lateral offset and vertical separation reached 2 9 and 3 8 m respectively the northernmost ruptures occurred during the subsequent event along a 46 km portion of the east dipping dixie valley fault where the sense of slip was normal and reached a maximum vertical separation of 2 8 m average surface offset for both events is about 1 2 m the west dipping west gate louderback mountains and gold king faults also ruptured during the earthquake sequence these faults form a complex structural linkage within a 15 km left step that separates the surface traces of the fairview and dixie valley faults the west dipping faults likely played an important role in the redistribution of static stress from the fairview peak earthquake and subsequent triggering of the dixie valley earthquake right lateral offsets of more than a meter occurred along both the west gate and louder back mountains faults slip was limited to normal motion of 1 m or less along the gold king fault the change from right oblique motion along the fairview fault to pure normal motion on the dixie valley fault may reflect the transition from principally northwest extension in the south to more westerly extension in the north alternatively slip at the latitude of the dixie valley fault may be partitioned between pure normal slip along the dixie valley fault and strike slip motion on faults immediately to the west observations of fault dip provide insight to the complex three dimensional geometry of the rupture sequence of particular note a significant section of the dixie valley fault appears to be characterized by dip angles as low as 25 at the surface slip variation or earthquake endpoints do not generally appear to have been influenced by changes in bedrock type we do not observe systematic relations between slip variation and aspects of fault trace geometry such as salients and reentrants yet the relative competence of footwall bedrock appears to have influenced the long term development of large salients and reentrants along both the dixie valley and the fairview faults as well as the style of rupture along the southern portion of the dixie valley fault

gravitational viscoelastic postseismic relaxation on a layered spherical earth viscoelastic relaxation of a ductile asthenosphere underlying a purely elastic plate is a strong candidate process for explaining anomalous rates of crustal deformation observed following large earthquakes the nongravitational treatment of pollitz 1992 which is valid on a global scale and includes the effects of compressibility is here extended to permit the calculation of gravitational viscoelastic relaxation for a specified spherically layered viscoelastic rheology following an earthquake in an elastic layer the simple approximations we adopt make the resulting treatment particularly suitable for near field calculations for an asthenosphere with a maxwell rheology the effect of gravitational coupling is manifested only many relaxation times after the earthquake as obtained by previous investigators its effect is generally to speed up the long wavelength component of the relaxation process and attenuate the overall vertical displacement pattern several subtle features common to the relaxation behavior from several different fault types thrust rift and strike slip are identified the effect of gravitational coupling on horizontal displacements is consistent with flexure of the upper elastic plate driven by the corresponding effects on the vertical displacement stress diffusion away from the source region generally exhibits pulse like behavior which is dispersive in both space and time if the asthenosphere is confined to a relatively narrow channel then the dispersion branches governing relaxation are radically altered and stress diffusion effects far from the coseismic rupture zone exhibit a complicated time dependence reflecting the competing tendencies of toroidal and spheroidal mode relaxation

geometry of the 1954 fairview peak dixie valley earthquake sequence from a joint inversion of leveling and triangulation data in 1954 four earthquakes greater than ms 6 0 occurred within a 30 km radius and in a period of 6 months elevation and angle changes calculated from repeated leveling and triangulation surveys which span the coseismic period provide constraints on the fault geometries and coseismic slip of the faults which were activated the quality of the coseismic geodetic data is assessed corrections are applied to the leveling data for subsidence due to groundwater withdrawal in the fallon area and a rod miscalibration error of 150 30 ppm is isolated in leveling surveys made in 1967 the leveling and triangulation observations are then simultaneously inverted using the single value decomposition svd inversion method to determine fault geometries and coseismic slip using svd it is possible to determine on which faults slip is resolvable given the data distribution the faults are found to dip between 50 and 80 and extend to depths of 5 to 14 km the geodetically derived slip values are generally equal to or greater than the maximum observed displacement along the surface scarps where slip is resolvable the geodetic data indicates the 1954 sequence contained a significant component of right lateral slip this is consistent with the n15 w trending shear zone which geodetic surveys have detected in western nevada

effects of lithospheric viscoelastic relaxation on the contemporary deformation following the 1959 mw 7 3 hebgen lake montana earthquake and other areas of the intermountain seismic belt 1 the 1959 mw 7 3 hebgen lake mt normal faulting earthquake occurred in an extensional stress regime near the yellowstone volcanic field time dependent crustal deformation data following this major earthquake were acquired by precise trilateration and gps surveys from 1973 to 2000 around the hebgen lake fault zone modeling the changes of baseline lengths across and near the fault reveals a lateral variation of transient rheology in which the lithosphere is stronger near the hebgen lake fault zone than in the vicinity of the yellowstone volcano system the models also imply that the lower crust is stronger than the upper mantle in agreement with results from studies of postseismic and post lake filling relaxations 100 years in addition evaluations of the postseismic motion produced by the hebgen lake and the 1983 mw 6 9 borah peak id earthquakes indicate that horizontal transient motion of up to 1 mm yr contribute significantly to the contemporary regional crustal deformation near the epicentral areas for the eastern basin and range 500 km south of the hebgen lake fault similar rheologic models were derived from the observed uplift associated with the lake bonneville rebound and were used to evaluate the postseismic deformation associated with six most recent paleoearthquakes of the wasatch fault zone and three m 5 6 historic earthquakes of northern utah the results show 0 1 mm yr of horizontal postseismic motion at present time that are within the horizontal uncertainties of continuous gps velocity from the basin and range and significantly smaller than the contemporary extension of 1 3 mm yr in the wasatch front

slip rate variations on faults during glacial loading and post glacial unloading implications for the viscosity structure of the lithosphere abstract many active faults in extensional and contractional tectonic settings experienced a slip rate increase after the last glacial period when the volume of nearby glaciers and lakes decreased this post glacial slip rate increase is caused by transient stresses that are generated by the unloading induced rebound and superimposed on the tectonic background stress field as the latter is different for normal and thrust faults the response to loading and unloading should depend on the fault type here we use finite element models including a fault in rheologically layered lithosphere to explore the conditions under which both normal and thrust faults experience a post glacial slip rate increase the results show that a post glacial slip rate increase occurs on normal faults if the lower crust is stronger than the lithospheric mantle whereas thrust faults accelerate if the lower crust is weaker than the lithospheric mantle these findings imply that the response of faults to mass fluctuations on the earth9s surface may provide constraints on the rheological stratification of the lithosphere we use our results to make predictions on the viscosity structure of the basin and range province and northern scandinavia where palaeoseismological data document a pronounced increase in seismicity as a result of post glacial unloading and rebound

tectono stratigraphic setting of the moreton s harbour group and its implications for the evolution of the laurentian margin notre dame bay newfoundland1this article is one of a series of papers published in this cjes special issue in honour of ward neale on the theme of appalachian and grenvillian geology the moreton s harbour group lies along the red indian line the fundamental iapetus suture that separates rocks of peri laurentian affinity with rocks of peri gondwanan affinity in the newfoundland appalachians characterization of age and environment of formation of the moreton s harbour group is an important constraint on evolution of the laurentian margin during ordovician closure of iapetus ocean and associated marginal basins the moreton s harbour group comprises a fault bounded ophiolitic sequence of layered gabbro sheeted diabase pillow basalt and felsic intrusive rocks it is offset by high angle shear zones that were contemporaneous with a 477 4 0 4 ma syn tectonic and syn magmatic suite of trondhjemite and tonalite trace element data from the felsic suite indicate formation in a supra subduction zone setting although isotopic data from the felsic intrusive rocks end 5 02 to 10 53 tdm 1200 1800 ma indicate a significant amount of contamination from mesoproterozoic or older contin

postseismic relaxation across the central nevada seismic belt 1 two gps geodetic surveys across the basin and range br province of western north america have detected an anomalous compression east of the central nevada seismic belt cnsb the first network installed by the u s geological survey along an east west trending transect across the br at approximately 40 n consisted of 63 monuments observed campaign style in 1992 1996 and 1998 the second network installed by the california institute of technology consisted of 50 continuously operating gps receivers 18 of which were roughly along the same transect as the campaign survey we have used a viscoelastic postseismic relaxation model of the four largest earthquakes in the cnsb on the pleasant valley fault in 1915 the cedar mountain fault in 1932 and on the fairview peak and dixie valley faults in 1954 to interpret the geodetic velocities observed across the cnsb a model of postseismic relaxation with a lower crustal maxwell viscosity of 5 50 1018 pa s can explain the apparent compression regardless of the assumed mantle viscosity the geodetic velocities that we determined after removing the postseismic contribution indicate that within current gps detection limits the br is stable east of the cnsb and is undergoing rapid right lateral shear west of the cnsb

pattern and rates of faulting in the central nevada seismic belt and paleoseismic evidence for prior beltlike behavior the central nevada seismic belt cnsb is a concentration of historical 1915 1932 1954 surface faulting in the western basin and range province forming a linear nearly continuous 300 km long rupture zone previous results are integrated in this study with new paleoseismic and exploratory trenching data from the historical zones to look for evidence of older similar beltlike patterns or elevated slip rates that could indicate whether the cnsb is a zone of focused long term crustal strain the data show that the continuous rupture belt produced by the seven earthquakes occurring between 1915 and 1954 is unique in the available paleoseismic record at the 1954 fairview peak fault the lack of prehistorical faulting in deposits containing the wilson creek bed 19 tephra eliminates the possibility of an identical seismic belt in the past 35 4 ka our studies also show that the faults have net slip rates ranging from a low of 0 09 mm yr on the fairview peak fault to a high of 0 7 mm yr on the 1932 cedar mountain fault these are considered moderate to low rates that are similar to most late quaternary faults in the western basin and range province a space time comparison shows that the paleoseismic histories for these multiple rupture zones are diverse and the number and timing of events in each of the zones indicate that there is little evidence for older contemporaneous ruptures of these same faults based on these results we reach several conclusions regarding the longer term holocene behavior of the cnsb although paleoseismic data preclude an older identical rupture belt among the historical zones consideration of associated holocene faults within the greater cnsb region indicates that several similar but not identical beltlike rupture patterns are plausible during the past 13 ka although each requires seismic gaps in the along strike pattern although long term strain represented by density of young faults does appear to increase from east to west into the cnsb the slip rate data demonstrate that the cnsb is not a belt of concentrated or elevated crustal strain compared with areas that extend west to the sierra nevada the increase in the distribution of holocene fault activity from east to west into the cnsb is consistent with a marked increase in the 1992 2002 gps velocity field at the latitude of the 1954 rupture sequence however a comparison of the geologic rates across the belt at this same latitude indicates that the extension rates 0 59 1 37 mm yr are systematically lower than both the campaign and continuous gps rates 2 20 3 13 mm yr by factors of 2 5 these discrepancies may be due to postseismic strain or to some form of off fault deformation we conclude that the results of our study of fault behavior in the cnsb best support the belt migration model proposed by wallace 1987 for the western basin and range province in which temporal tectonic pulses are believed to migrate regionally activating different beltlike combinations of late quaternary faults in an as yet unknown pattern of migration

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

multiscale insar time series mints analysis of surface deformation 1 we present a new approach to extracting spatially and temporally continuous ground deformation fields from interferometric synthetic aperture radar insar data we focus on unwrapped interferograms from a single viewing geometry estimating ground deformation along the line of sight our approach is based on a wavelet decomposition in space and a general parametrization in time we refer to this approach as mints multiscale insar time series the wavelet decomposition efficiently deals with commonly seen spatial covariances in repeat pass insar measurements since the coefficients of the wavelets are essentially spatially uncorrelated our time dependent parametrization is capable of capturing both recognized and unrecognized processes and is not arbitrarily tied to the times of the sar acquisitions we estimate deformation in the wavelet domain using a cross validated regularized least squares inversion we include a model resolution based regularization in order to more heavily damp the model during periods of sparse sar acquisitions compared to during times of dense acquisitions to illustrate the application of mints we consider a catalog of 92 ers and envisat interferograms spanning 16 years in the long valley caldera ca region mints analysis captures the ground deformation with high spatial density over the long valley region

three dimensional numerical modeling of slip rate variations on normal and thrust fault arrays during ice cap growth and melting 1 changes in the volumes of ice caps considerably alter the stress state of the lithosphere by generating a transient signal that is added to the tectonic background stress field these stress field changes in turn affect crustal deformation and in particular the slip behavior of existing faults here we use three dimensional finite element models to investigate how arrays of normal and thrust faults near a growing and subsequently melting ice cap are influenced in their slip evolution the results show that regardless of fault dip both types of faults experience a decrease in their slip rate during ice cap advance and an increase in their slip rate during ice cap retreat if they are located beneath the ice cap in contrast faults outside the ice cap that are loaded on their footwall or hanging wall only show the opposite pattern their slip rate increases during glacial loading and decreases during subsequent unloading if the load is located along strike of the fault that is at one of its tips the slip behavior of normal and thrust faults is different the normal fault shows a slip rate increase during unloading the thrust fault during loading our results explain the location and timing of deglaciation induced paleoearthquakes in scandinavia and the contrasting slip histories reported from normal faults in the basin and range province which are located at different positions relative to the former yellowstone ice cap more generally our findings imply that a uniform slip behavior of faults in formerly glaciated regions should not be expected

strain accumulation and rotation in western nevada 1993 2000 1 the positions of 44 gps monuments in an array extending from the sierra nevada at the latitude of reno to near austin nevada have been measured several times in the 1993 2000 interval the western half of the array spans the walker lane belt whereas the eastern half spans the central nevada seismic zone cnsz the principal strain rates in the walker lane belt are 29 6 5 3 nstrain yr 1 n88 4 e 5 4 and 12 8 6 0 nanostrain yr 1 n01 6 w 5 4 extension reckoned positive and the clockwise as seen from above the earth rotation rate about a vertical axis is 13 6 4 0 nrad yr 1 the quoted uncertainties are standard deviations the motion in the walker lane belt can then be represented by a zone striking n35 w subject to 16 8 4 9 nstrain yr 1 extension perpendicular to it and 19 5 4 0 nstrain yr 1 right lateral simple shear across it the n35 w strike of the zone is the same as the direction of the local tangent to the small circle drawn about the pacific north america pole of rotation the principal strain rates for the cnsz are 46 2 11 0 nstrain yr 1 n49 9 w 6 0 and 13 6 6 1 nstrain yr 1 n40 1 e 6 0 and the clockwise rotation rate about a vertical axis is 20 3 6 3 nrad yr 1 the motion across the cnsz can then be represented by a zone striking n12 e subject to 32 6 11 0 nstrain yr 1 extension perpendicular to it and 25 1 6 3 nstrain yr 1 right lateral simple shear across it the n12 e strike of the zone is similar to the strikes of the faults rainbow mountain fairview peak and dixie valley within it

space geodetic observations and models of postseismic deformation due to the 2005 m7 6 kashmir pakistan earthquake we use the l band advanced land observing satellite alos and c band envisat interferometric synthetic aperture data and campaign gps observations to study the postseismic deformation due to the 2005 magnitude 7 6 kashmir pakistan earthquake that occurred in the northwestern himalaya envisat data are available from both the descending and ascending orbits and span a time period of 4 5 years immediately following the earthquake 2005 2010 with nearly monthly acquisitions however the envisat data are highly decorrelated due to high topography and snow cover alos data are available from the ascending orbit and span a time period of 2 5 years between 2007 and 2009 over which they remain reasonably well correlated we derive the mean line of sight los postseismic velocity maps in the epicentral area of the kashmir earthquake using persistent scatterer method for envisat data and selective stacking for alos data los velocities from all data sets indicate an uplift decrease in radar range primarily in the hanging wall of the earthquake rupture over the entire period of synthetic aperture radar observations 2005 2010 models of poroelastic relaxation predict uplift of both the footwall and the hanging wall while models of viscoelastic relaxation below the brittle ductile transition predict subsidence increase in radar range in both the footwall and the hanging wall therefore the observed pattern of surface velocities indicates that the early several years of postseismic deformation were dominated by afterslip on the fault plane possibly with a minor contribution from poroelastic rebound kinematic inversions of interferometric synthetic aperture radar and gps data confirm that the observed deformation is consistent with afterslip primarily downdip of the seismic asperity to place constraints on the effective viscosity of the ductile substrate in the study area we subtract the surface deformation predicted by stress driven afterslip model from the mean los velocities and compare the residuals to models of viscoelastic relaxation for a range of assumed viscosities we show that in order to prevent surface subsidence the effective viscosity has to be greater than 1019 pa s

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

historic surface faulting and paleoseismicity in the area of the 1954 rainbow mountain stillwater earthquake sequence central nevada the rainbow mountain area was the site of three surface rupturing earthquakes on 6 july and 23 august 1954 more than 50 field measurements of surface offsets constrain the distribution of slip along the discontinuous and distrib uted rupture zone that formed during the earthquake sequence vertical offsets reach a maximum of 0 8 m with the average vertical offset being 0 2 m in contrast to original reports we see evidence for a right lateral component of slip along portions of the rupture zone including offset stream channels 0 5 1 0 m left stepping en echelon scarps and a well preserved 100 m long mole track the right slip com ponent is consistent with focal plane solutions for the events and recent geodetic results previously unmapped surface ruptures now extend the known rupture length of the sequence by 25 km to a total of 70 km surface ruptures along the previously unmapped fourmile flat fault are subparallel to and form a 10 km left step to the southeast of the rainbow mountain fault event locations and anecdotal information indicate that the fourmile flat ruptures represent minor primary surface rupture associated with the large 6 july aftershock triggered 11 hr after the initial 6 july rainbow mountain event the paleoseismic histories of the rainbow mountain and fourmile flat faults as recorded in natural and trench exposures are different although both faults experi enced three post 15 ka surface rupturing events including 1954 bracketing ages for triultimate events on both faults do not overlap however constraints on the penultimate event for the rainbow mountain and triultimate event for the fourmile flat fault do overlap slightly allowing the possibility that they may have ruptured close in time as in 1954 the holocene slip rate for the fourmile flat fault 0 40 mm yr is similar to the post latest pleistocene rate for the rainbow mountain fault 0 20 0 46 mm yr even though the total length of the fourmile flat 10 km is much shorter than the overall length of the rainbow mountain rupture zone 60 km indicating that even minor faults can be important for assessing regional strain rates and patterns

cyclic ductile and brittle deformation related to coseismic thrust fault propagation structural record at the base of a basement nappe preveli crete 1 the structural record at the base of a basement nappe preveli nappe crete greece thrust upon sedimentary rocks is investigated aimed on understanding mechanisms which result in decoupling of the thrust sheet from its original substratum we identify several superimposed deformation stages each with characteristic structural style and indications of episodic deformation at initially high differential stress the final stage involves formation of a matrix supported breccia transected by pseudotachylytes comprising the lowermost 30 m of the nappe brecciation and pseudotachylyte formation occurred in a single event and structures were not modified afterward complete induration of breccia and composition of phengite crystallized during devitrification of pseudotachylytes place the sequence of events into the middle crust we propose a model relating episodic deformation and cyclic stress history to propagation of a thrust fault in a limited number of seismic events terminal brecciation and frictional fusion record passage of the fault front beneath the site of observation and decoupling of the thrust sheet absence of discernible further deformation is consistent with negligible basal friction during transport as a nappe brecciation and pseudotachylyte formation mark the switch from a history of repeated coseismic loading and postseismic stress relaxation in the plastosphere driven by seismic events on the approaching thrust fault to passive transport with deformation localized in a weak thrust plane for a sequence of superimposed ductile to brittle structures our model provides an alternative to progressive cooling and exhumation concomitant with deformation over millions of years

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

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

surface faulting and paleoseismic history of the 1932 cedar mountain earthquake area west central nevada and implications for modern tectonics of the walker lane the 1932 cedar mountain earthquake m s 7 2 was one of the largest historical events in the walker lane region of western nevada and it produced a complicated strike slip rupture pattern on multiple quaternary faults distributed through three valleys primary right lateral surface ruptures occurred on north striking faults in monte cristo valley small scale lateral and normal offsets occurred in stewart valley and secondary normal faulting occurred on north northeast striking faults in the gabbs valley epicentral region a reexamination of the surface ruptures provides new displacement and fault zone data maximum cumulative offset is estimated to be 2 7 m and newly recognized faults extend the maximum width and end to end length of the rupture zone to 17 and 75 km respectively a detailed quaternary allostratigraphic chronology based on regional alluvial geomorphic relationships tephrochronology and radiocarbon dating provides a framework for interpreting the paleoseismic history of the fault zone a late wisconsinan alluvial fan and piedmont unit containing a 32 36 ka tephra layer is a key stratigraphic datum for paleoseismic measurements exploratory trenching and radiocarbon dating of tectonic stratigraphy provide the first estimates for timing of late quaternary faulting along the cedar mountain fault zone three trenches display evidence for six faulting events including that in 1932 during the past 32 36 ka radiocarbon dating of organic soils interstratified with tectonically ponded silts establishes best fit ages of the pre 1932 events at 4 5 12 15 and 18 ka each with 2 ka uncertainties on the basis of an estimated cumulative net slip of 6 12 m for the six faulting events minimum and maximum late quaternary slip rates are 0 2 and 0 7 mm yr respectively and the preferred rate is 0 4 0 5 mm yr the average recurrence interseismic interval is 3600 yr the relatively uniform thickness of the ponded deposits suggests that similar size characteristic rupture events may characterize late quaternary slip on the zone a comparison of event timing with the average late quaternary recurrence interval indicates that slip has been largely regular periodic rather than temporally clustered to account for the spatial separation of the primary surface faulting in monte cristo valley from the epicenter and for a factor of two to three disparity between the instrumentally and geologically determined seismic moments associated with the earthquake we hypothesize two alternative tectonic models containing undetected subevents either model would adequately account for the observed faulting on the basis of wrench fault kinematics that may be associated with the walker lane the 1932 cedar mountain earthquake is considered an important modern analogue for seismotectonic modeling and estimating seismic hazard in the walker lane region in contrast to most other historical events in the basin and range province the 1932 event did not occur along a major range bounding fault and no single throughgoing basement structure can account for the observed rupture pattern the 1932 faulting supports the concept that major earthquakes in the basin and range province can exhibit complicated distributive rupture patterns and that slip rate may not be a reliable criterion for modeling seismic hazard

omori like decay of postseismic velocities following continental earthquakes various mechanisms have been proposed to explain the transient enhanced surface deformation rates following earthquakes unfortunately these different mechanisms can produce very similar surface deformation patterns leading to difficulty in distinguishing between them here we return to the observations themselves and compile near field postseismic velocity measurements following moderate to large continental earthquakes we find that these velocities have a remarkably consistent pattern with velocity inversely proportional to time since the earthquake this suggests that postseismic velocities show an omori like decay and that postseismic displacements increase logarithmically over time these observations are inconsistent with simple linear maxwell or burgers body viscoelastic relaxation mechanisms but are consistent with rate and state frictional afterslip models and power law shear zone models the results imply that near field postseismic surface deformation measurements are primarily the result of fault zone processes and therefore that the inference of lower crustal viscosities from near field postseismic deformation requires care

mining related ground deformation in crescent valley nevada implications for sparse gps networks 1 we use the small baseline subset sbas insar algorithm to obtain radar line of sight deformation velocities for two adjacent sar swaths and invert the data for the 2 d velocity field in vertical and ground range direction the analysis reveals areas of rapid deformation caused by mining and agricultural activities in the crescent valley nevada usa the los displacements of up to 25 centimeters during the 1992 2002 period are caused by vertical and horizontal deformation about 8 mm yr horizontal velocity is detected 10 km from the bargen gps site lewi suggesting that the gps station may be moving in response to the water pumping in the basin and range anthropogenic ground deformation can extend several tens of kilometers from the basins into the bedrock of the ranges

holocene slip rate of the wasatch fault zone utah from geodetic data earthquake cycle effects 1 gps data define a broad zone of present day deformation in the eastern basin and range province western us using finite element models with elastic upper crust over viscoelastic lower crust upper mantle and incorporating earthquake cycle effects we show that these data are consistent with a model whereby most contemporary fault slip is focused on the wasatch fault zone modeled rates of horizontal extension are 3 0 4 5 mm yr in agreement with holocene geologic data the models are non unique in part because much of the wasatch fault is in the late stages of the earthquake cycle when surface velocity gradients across the fault are low

tectonic implications of isotopic variation among jurassic and early cretaceous plutons klamath mountains jurassic and early cretaceous plutons in the klamath mountains province of california and oregon were intruded both before and after thrusting during the nevadan orogeny ca 155 148 ma plutons intruded before nevadan thrusting range from calc alkalic to calcic and display a range of compositions that changes consistently with time among this group rb k 2 o and initial 87 sr 86 sr sr i range 0 7034 to 0 7047 decrease and nd range 2 0 to 4 8 increases in younger plutons within individual plutons sr i varies considerably whereas nd is nearly constant the sr and nd isotopic data typically plot to the right of the mantle array 18 o values in these plutons are greater than 8 0 tonalitic and trondhjemitic plutons intruded after nevadan thrusting are typically calcic contain low rb and k 2 o contents and have 18 o less than 8 0 these plutons have a narrow range of sr i 0 7033 0 7036 and nd 4 7 to 7 4 values that plot in the mantle array the isotopic compositions of the pre nevadan plutons requires assimilation of metasedimentary rocks or mixing with crustal melts at deep crustal levels the deep crustal component is not exposed in the province and was presumably truncated during nevadan thrusting post nevadan plutons show little evidence of assimilation of metasedimentary crust but display trace element evidence low k 2 o rb and rare earth element concentrations consistent with an origin by partial melting of young ophiolitic rocks underthrust during the nevadan orogeny

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

intraplate deformation and microplate tectonics of the yellowstone hot spot and surrounding western u s interior 1 contemporary deformation of the yellowstone hot spot and surrounding western united states is analyzed using tectonic microplate modeling employing constraints from gps observations corrected for postseismic deformation of m7 earthquakes fault slip rates and earthquake focal mechanisms we focus primarily on the kinematics of the yellowstone hot spot and the eastern snake river plain volcanic field esrp and secondarily on basin range and columbia plateau provinces our results reveal southwest motion of the yellowstone plateau excluding localized volcanic deformation at 0 9 0 1 mm a that decreases to 0 8 0 1 mm a in the esrp block the southwest to west motion of the yellowstone esrp introduces shear in the northern rocky mountain block which is translating east at 0 78 0 08 mm a there is 0 5 mm a differential motion between the esrp and the block at its northern boundary and none at the southern boundary the eastern basin range block moves west at 3 0 0 1 to 4 6 0 1 mm a while velocities of the western basin range microplates rotate to a northwest direction accompanied by a transition from normal to oblique shear deformation columbia plateau block velocities are notably eastward an effect enhanced by postseismic relaxation following the m9 1700 cascadia subduction zone paleoearthquake this study reveals that the overall motion of the western united states is characterized by clockwise rotation with westward extension and northwest shear in the basin range province northeast to east contraction in the columbia plateau and southwest extension of the yellowstone snake river plain block that is driven by the high gravitational potential of the yellowstone swell

slow earthquake in afghanistan detected by insar 1 the chaman fault system forms a prominent 900 km long left lateral transform plate boundary between the indian and eurasian plates in afghanistan and pakistan here we show satellite radar interferometry data that revealed an afterslip or slow earthquake signal following an earthquake of magnitude 5 0 this slow slip episode lasted for more than a year and accompanied a widespread creep signal that occurred at least 50 km along the fault we detected no surface slip before the earthquake during the 1 5 years sampled by our data this finding of long lasting widespread afterslip demonstrates that the plate motion along the chaman fault is accommodated by slow slip episodes following moderate earthquakes and suggests that a potential for magnitude 7 class earthquakes was significantly reduced the duration and moment release of the detected afterslip do not fit the recently proposed scaling law for slow earthquakes

from coseismic offsets to fault block mountains in the basin and range extensional province of the western united states coseismic offsets under the influence of gravity display predominantly subsidence of the basin side fault hanging wall with comparatively little or no uplift of the mountainside fault footwall a few decades later geodetic measurements gps and interferometric synthetic aperture radar insar show broad 100 km aseismic uplift symmetrically spanning the fault zone finally after millions of years and hundreds of fault offsets the mountain blocks display large uplift and tilting over a breadth of only about 10 km these sparse but robust observations pose a problem in that the coesismic uplifts of the footwall are small and inadequate to raise the mountain blocks to address this paradox we develop finite element models subjected to extensional and gravitational forces to study time varying deformation associated with normal faulting stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift which is predicted to take place within one to two decades after each large earthquake thus the best preserved topographic signature of earthquakes is expected to occur early in the postseismic period

slip rate variations on faults in the basin and range province caused by regression of late pleistocene lake bonneville and lake lahontan late pleistocene regression of two large pluvial lakes lake bonneville and lake lahontan caused considerable lithospheric rebound in the basin and range province usa here we use finite element models to show how lake growth and regression affect the temporal and spatial slip evolution on faults near the former lakes our results show that fluctuations in the volume of lake bonneville caused along strike slip variations on the wasatch normal fault with a pronounced slip rate increase on its northern and central parts during lake regression the response of normal and strike slip faults near the ring shaped lake lahontan depends on their location within the rebound area faults located in the centre of rebound show a slip rate increase during lake regression whereas strike slip faults at the periphery decelerate all slip rate variations are caused by differential stress changes owing to changing lake levels regardless of the individual fault response

interferometric synthetic aperture radar observations of the 1994 double spring flat nevada earthquake m5 9 main shock accompanied by triggered slip on a conjugate fault 1 the 1994 double spring flat dsf earthquake m5 9 was the largest earthquake to strike nevada in more than 30 years it occurred in the sierra nevada basin and range transition zone within a step over region between two major normal faults descending and ascending ers interferograms show a maximum range change of 8 5 cm which is the coseismic ground displacement associated with this normal oblique slip moderatesized earthquake elastic inverse modeling and surface displacements across coseismic ground cracks suggest that two different event sources could account for the observed deformation the first source was the main shock with right oblique slip on the northnorthwest striking dsf fault the second source was normal faulting on a shallow northnortheast striking elongated plane conjugate to the dsf fault these two sources are consistent with the pattern of postevent seismicity and we suggest that the second source represents seismic and aseismic slip triggered by the main shock calculations of changes in coulomb failure stress show that the main shock encouraged normal slip on this plane index terms 1206 geodesy and gravity crustal movements interplate 8155 1241 geodesy and gravity satellite orbits 1242 geodesy and gravity seismic deformations 7205 1299 geodesy and gravity general or miscellaneous 7212 seismology earthquake ground motions and engineering

contemporary vertical velocity of the central basin and range and uplift of the southern sierra nevada 1 we estimate the present day vertical velocity field in the central basin and range and sierra nevada mountains and consider causative processes we analyzed data from 16 continuously operating global positioning system stations finding that relative vertical velocity precision wrms scatter is 0 25 mm yr these data demonstrate that the southern sierra nevada is experiencing uplift of 0 5 mm yr relative to a local reference frame in southern nevada and 1 mm yr relative to stations in the northern mojave desert as a possible source of these motions we explored post seismic viscoelastic relaxation following the 1872 owens valley and 1952 kern county earthquakes with models of laterally homogeneous lower crust and upper mantle viscosity post seismic deformation from these two earthquakes cannot entirely explain the data set lateral variations in viscosity or contributions from other regional earthquakes may also be important

subcontinental scale crustal velocity changes along the pacific north america plate boundary transient tectonic deformation has long been noted within approx100 km of plate boundary fault zones and within active volcanic regions but it is unknown whether transient motions also occur at larger scales within plates relatively localized transients are known to occur as both seismic and episodic aseismic events and are generally ascribed to motions of magma bodies aseismic creep on faults or elastic or viscoelastic effects associated with earthquakes however triggering phenomena and systematic patterns of seismic strain release at subcontinental 1 000 km scale along diffuse plate boundaries have long suggested that energy transfer occurs at larger scale such transfer appears to occur by the interaction of stresses induced by surface wave propagation and magma or groundwater in the crust or from large scale stress diffusion within the oceanic mantle in the decades following clusters of great earthquakes here we report geodetic evidence for a coherent subcontinental scale change in tectonic velocity along a diffuse 1 000 km wide deformation zone our observations are derived from continuous gps global positioning system data collected over the past decade across the basin and range province which absorbs approximately 25 per cent of pacific north america relative plate motion the observed changes in site velocity define a sharp boundary near the centre of the province oriented roughly parallel to the north northwest relative plate motion vector we show that sites to the west of this boundary slowed relative to sites east of it by 1 mm yr 1 starting in late 1999

satellite geodetic imaging reveals internal deformation of western tibet 1 it is often assumed that the majority of the interseismic strain accumulates around the major mapped geological block boundaries however numerous recent earthquakes in the continents have occurred on faults that were previously unidentified existing deformation data from tibet are insufficiently dense to map the distribution of interseismic strain here we combine 265 interferograms formed from 166 radar images with gps data to constrain a high resolution velocity field covering 200 000 km2 of western tibet we confirm that the slip rate of the karakoram fault is low 6 mm yr but show that areas of focused strain do not coincide with the major fault structures some of this strain is due to postseismic relaxation after a mw 6 8 earthquake that occurred in 1996 on a structure that is difficult to identify in satellite imagery models of seismic hazard that rely on imperfect knowledge of the boundaries of crustal blocks can therefore underestimate hazard from unknown faults

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