characterization of site specific gps errors using a short baseline network of braced monuments at yucca mountain southern nevada 1 we use a short baseline network of braced monuments to investigate site specific gps effects the network has baseline lengths of 10 100 and 1000 m baseline time series have root mean square rms residuals about a model for the seasonal cycle of 0 05 0 24 mm for the horizontal components and 0 20 0 72 mm for the radial seasonal cycles occur with amplitudes of 0 04 0 60 mm even for the horizontal components and even for the shortest baselines for many time series these lag seasonal cycles in local temperature measurements by 23 43 days this could suggest that they are related to bedrock thermal expansion both shorter period signals and seasonal cycles for shorter baselines to rep2 the one short braced monument in our network are correlated with temperature with no lag time differences between rep2 and the other stations which are deep braced should reflect processes occurring in the upper few meters of the ground these correlations may be related to thermal expansion of these upper ground layers and or thermal expansion of the monuments themselves even over these short distances we see a systematic increase in rms values with increasing baseline length this and the low rms levels suggests that site specific effects are unlikely to be the limiting factor in the use of similar gps sites for geophysical investigations

tectonic implications of a dense continuous gps velocity field at yucca mountain nevada 1 a dense continuous gps network was established in the yucca mountain area in 1999 to provide the most reliable measurements possible of geodetic strain patterns across the nation s only proposed permanent repository for high level radioactive waste the network lies astride a boundary between the geodetically stable central great basin and the active western great basin which at the latitude of yucca mountain is undergoing distributed right lateral shear at a rate of 60 nstrain yr monitoring from 1999 to 2003 3 75 years yields a velocity field characterized by nearly homogenous n20 w rightlateral shear of 20 2 nstrain yr net velocity contrast of 1 2 mm yr across a 60 km aperture in the vicinity of the proposed repository site comparison of time series of continuous results with earlier campaign surveys indicating 50 nstrain yr of westnorthwest extension from 1991 to 1997 suggests that the more rapid rates were in part transient motions associated with the 1992 ms 5 4 little skull mountain earthquake postseismic motions do not appear to affect the 1999 2003 velocity field in either campaign or continuous data the magnitude of the velocity contrast across the area the overall linearity of the gradient and the large area of undeforming crust to the east of yucca mountain are difficult to explain by elastic bending of the crust associated with the death valley fault zone a major right lateral strike slip fault about 50 km west of the repository site these observations along with apparent local variations in the velocity gradient suggest that significant right lateral strain accumulation with displacement rate in the 1 mm yr range may be associated with structures in the yucca mountain area the absence of structures in the area with equivalent late quaternary displacement rates underscores the problem of reconciling discrepancies between geologic and geodetic estimates of deformation rates index terms 1208 geodesy and gravity crustal movements intraplate 8110 1243 geodesy and gravity space geodetic surveys 8107 tectonophysics continental neotectonics 8109 tectonophysics continental tectonics extensional 0905 keywords geodesy tectonics yucca mountain

steady contemporary deformation of the central basin and range province western united states we use data from western u s gps networks to estimate the rate pattern and style of tectonic deformation of the central basin and range province brp previous geodetic investigations have found the crust of eastern nevada and western utah to act as a rigid microplate with zero deformation rates to within measurement uncertainty observed transients in gps time series have led others to propose a megadetachment model predicting that the central brp behaves as a microplate but with time varying translation here we reassess these hypotheses benefiting from a significant increase in gps stations and time span and innovations in analysis techniques our results show that the brp crust deforms everywhere and all the time in a group of 24 stations between longitude 113 5 and 116 8 we find strain rates of 1 9 0 2 10 9 yr 1 extension directed n55 w and 2 2 0 2 10 9 yr 1 contraction directed n35 e inconsistent with microplate behavior the linearity of time series of strain from gps station triplets is inconsistent with episodic translation of quasi rigid domains one exception is station egan that exhibits nonlinear motion not found in adjacent stations the dominant signal in nevada is distributed shear consistent with pacific north america relative plate motion suggesting that stresses are transmitted through the lithosphere at least 800 km from the plate boundary the observed active extension is consistent with earthquake focal mechanisms and is in agreement with integrated rates estimated from earthquake geology our results do not support the proposed megadetachment in the brp

martian north polar cap summer water cycle abstract a key outstanding question in martian science is are the polar caps gaining or losing mass and what are the implications for past current and future climate to address this question we use observations from the compact reconnaissance imaging spectrometer for mars crism of the north polar cap during late summer for multiple martian years to monitor the summertime water cycle in order to place quantitative limits on the amount of water ice deposited and sublimed in late summer we establish here for the first time the summer cycle of water ice absorption band signatures on the north polar cap we show that in a key region in the interior of the north polar cap the absorption band depths grow until l s 120 when they begin to shrink until they are obscured at the end of summer by the north polar hood this behavior is transferable over the entire north polar cap where in late summer regions flip from being net sublimating into net condensation mode this transition or mode flip happens earlier for regions closer to the pole and later for regions close to the periphery of the cap the observations and calculations presented herein estimate that on average a water ice layer 70 microns thick is deposited during the l s 135 164 period this is far larger than the results of deposition on the south pole during summer where an average layer 0 6 6 microns deep has been estimated by brown et al 2014 earth planet sci lett 406 102 109

assessment of gps velocity accuracy for the basin and range geodetic network bargen we assess the accuracy of horizontal velocity estimates from the basin and range geodetic network bargen a continuous gps network that has been in operation since 1996 to make this quantitative assessment we use a procedure that we term the whole error method in this method the measure of the velocity errors is the root mean square rms residual velocity relative to a simple geophysical model this method produces a conservative estimate of the uncertainties since errors in the geophysical models also contribute to the rms residual using estimates from two different bargen subnetworks the northern basin and range and the yucca mountain cluster we determine velocity uncertainties of 0 1 0 2 mm yr 1 since bargen covers a significant fraction of area of the proposed plate boundary observatory component of earthscope our results indicate a good ability of this project to determine highly accurate long term horizontal crustal velocities and deformation rates in this region

influence of lithospheric thickness variations on 3 d crustal velocities due to glacial isostatic adjustment 1 predictions of 3 d crustal velocities driven by glacial isostatic adjustment gia have generally been based on spherically symmetric earth models we adopt a finite volume formulation to explore the impact of lateral variations in elastic plate strength including lithospheric thickness changes across the continent ocean interface and plate boundary weak zones on these predictions weak zones introduce horizontal rate perturbations with a plate scale coherency and amplitudes reaching 1 2 mm yr radial velocity perturbations can be as large but are geographically isolated to the weak zones specifically the north atlantic ridge a discontinuity in ocean continent lithospheric thickness significantly impacts rates along continental margins order 1 mm yr for radial rates and generally about half this for tangential rates we conclude that lateral variations in lithospheric strength should be included in future gia analyzes of space geodetic survey results and in assessing the impact of gia on the stability of geodetic reference frames

increasing long wavelength relief across the southeastern flank of the sierra nevada california abstract a high degree of correlation between present day relative rock uplift measured using continuous gps geodesy and spatially averaged surface elevations suggests that long wavelength topographic relief is presently increasing along the southeastern flank of the sierra nevada range and within an adjacent portion of the northern basin and range province current estimates for erosion rate are an order of magnitude smaller than the relative rates determined by geodesy thus although the uplift serves to enhance long wavelength relief it cannot be explained entirely as an isostatic response to erosion if uplift rates have been constant through time the duration over which the uplift could have been active

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

mars south polar hood as observed by the mars climate sounder 1 we have used observations from the mars climate sounder to investigate south polar hood water ice clouds at 12 m including the first systematic examination of the vertical 5 km resolution and nighttime structure we find that the structure and evolution of the polar hood is controlled more strongly by atmospheric temperature variations than by intrinsic fluctuations in water vapor abundance the clouds form as a belt during ls 10 70 phase 1 and ls 100 200 phase 2 during phase 1 the cloud belt extends over a wide latitude range between 30 s and 75 s with a visible column optical depth between 0 075 and 0 15 the cloud belt then evaporates as temperatures warm during phase 2 the cloud belt reappears due to an increase in water vapor as a partial band of low opacity clouds south of the tharsis region and eventually becomes continuous in longitude with a visible column opacity between 0 125 and 0 25 as the southern spring equinox approaches the cloud belt shifts southward following the seasonal cap edge from ls 140 to ls 200 the daytime belt lies about 15 farther south than the nighttime belt due to tidally driven diurnal temperature differences the vertical structure of the cloud belt is consistent within and between the two seasonal phases and is characterized by a thick lower cloud deck and an upper layer whose altitude shifts between the nighttime and daytime because of thermal tidal control of the condensation altitudes overall the southern polar hood is observed to rapidly form and dissipate as the temperature crosses the saturation point of water vapor

contemporary deformation of the wasatch fault utah from gps measurements with implications for interseismic fault behavior and earthquake hazard observations and kinematic analysis 1 contemporary strain accumulation rates of the 350 km long wasatch fault utah have been determined by gps measurements and provide key data for evaluating normal fault behavior and related earthquake hazard assessment this paper presents a complete description of the wasatch gps network data archiving and processing and the measured ground deformation the network spans the wasatch fault in an area 300 km long and 200 km wide in north and central utah and consists of 43 gps sites surveyed in 1992 1993 1994 1995 1999 2001 and 2003 plus 8 permanent gps stations operating continuously beginning 1997 observations across a 65 km wide area centered on the wasatch fault indicate the principal horizontal extension rate of 24 6 nstrain yr with the direction nearly perpendicular to the fault this strain rate corresponds to a horizontal displacement rate of 1 6 0 4 mm yr accommodating 50 of the crustal deformation across the 200 km wide eastern basin range analysis of the spatial variation of the strain rate field reveals that the strain accumulation is concentrated near the wasatch fault which suggests an abrupt transition in the horizontal deformation at the fault between the eastern basin range and the rocky mountains we employed a finite strain model that accounts for simple shear deformation of the hanging wall to compare horizontal extension rates measured by gps with vertical fault displacement rates determined by geologic data our results suggest that the average holocene strain release rate is higher than the contemporary strain loading rate for the wasatch fault if the fault dips less than 30 w but these two rates are consistent if the fault dips more steeply

comparison of geodetic and geologic data from the wasatch region utah and implications for the spectral character of earth deformation at periods of 10 to 10 million years the wasatch fault and adjacent fault zones provide an opportunity to compare present day deformation rate estimates obtained from space geodesy with geologic displacement rates over at least four temporal windows ranging from the last millennium up to 10 myr the three easternmost gps sites of the basin and range geodetic network bargen at this latitude define a 130 km wide region spanning three major normal faults extending east west at a total rate of 2 7 0 4 mm yr with an average regional strain rate estimated to be 21 4 nstrain yr about twice the basin and range average on the wasatch fault the vertical component of the geologic displacement rate is 1 7 0 5 mm yr since 6 ka 0 6 mm yr since 130 ka and 0 5 0 7 mm yr since 10 ma however it appears likely that at the longest timescale rates slowed over time from 1 0 to 1 4 mm yr between 10 and 6 ma to 0 2 to 0 3 mm yr since 6 ma the cumulative vertical displacement record across all three faults also shows time variable strain release ranging from 2 to 4 mm yr since 10 ka to 1 mm yr averaged over the past 130 kyr conventional earthquake recurrence models reid type behavior would require an accordingly large variation in strain accumulation or loading rate on a 10 kyr timescale for which there appears to be no obvious geophysical explanation alternatively seismic strain release given a wide range of plausible constitutive behaviors for frictional sliding may be clustered on the 10 kyr timescale resulting in the high holocene rates with comparatively low uniform strain accumulation rates on the 100 kyr timescale wallace type behavior the latter alternative combined with observations at the million year timescale and the likelihood of a significant contribution of postseismic transients implies maxima of spectral amplitude in the velocity field at periods of 10 myr variations in tectonic loading 10 kyr clustered strain release and of 100 years postseismic transients if so measurements of strain accumulation and strain release may be strongly timescale dependent for any given fault system

glacial isostatic adjustment on 3 d earth models a finite volume formulation summary we describe and present results from a finite volume fv parallel computer code for forward modelling the maxwell viscoelastic response of a 3 d self gravitating elastically compressible earth to an arbitrary surface load we implement a conservative control volume discretization of the governing equations using a tetrahedral grid in cartesian geometry and a low order linear interpolation the basic starting grid honours all major radial discontinuities in the preliminary reference earth model prem and the models are permitted arbitrary spatial variations in viscosity and elastic parameters these variations may be either continuous or discontinuous at a set of grid nodes forming a 3 d surface within the regional or global modelling domain in the second part of the paper we adopt the fv methodology and a spherically symmetric earth model to generate a suite of predictions sampling a broad class of glacial isostatic adjustment gia data types 3 d crustal motions long wavelength gravity anomalies these calculations based on either a simple disc load history or a global late pleistocene ice load reconstruction ice 3g are benchmarked against predictions generated using the traditional normal mode approach to gia the detailed comparison provides a guide for future analyses e g what grid resolution is required to obtain a specific accuracy and it indicates that discrepancies in predictions of 3 d crustal velocities less than 0 1 mm yr 1 are generally obtainable for global grids with 3 106 nodes however grids of higher resolution are required to predict large amplitude 1 cm yr 1 radial velocities in zones of peak post glacial uplift e g james bay to the same level of absolute accuracy we conclude the paper with a first application of the new formulation to a 3 d problem specifically we consider the impact of mantle viscosity heterogeneity on predictions of present day 3 d crustal motions in north america in these tests the lateral viscosity variation is constructed with suitable scaling from tomographic images of seismic s wave heterogeneity and it is characterized by approximately 2 orders of magnitude peak to peak lateral variations within the lower mantle and 1 order of magnitude variations in the bulk of the upper mantle below the asthenosphere we find that the introduction of 3 d viscosity structure has a profound impact on horizontal velocities indeed the magnitude of the perturbation of order 1 mm yr 1 is as large as the prediction generated from the underlying 1 d radial reference model and it far exceeds observational uncertainties currently being obtained from space geodetic surveying the relative impact of lateral viscosity variations on predicted radial motions is significantly smaller

bargen continuous gps data across the eastern basin and range province and implications for fault system dynamics we collected data from a transect of continuous global positioning system gps sites across the eastern basin and range province at latitude 39 n from 1997 2000 intersite velocities define a region 350 km wide of broadly distributed strain accumulation at 10 nstr yr 1 on the western margin of the region site egan 10 km north of ely nevada moved at a rate of 3 9 0 2 mm yr 1 to the west relative to site cast which is on the colorado plateau velocities of most sites to the west of ely moved at an average rate of 3 mm yr 1 relative to cast defining an area across central nevada that does not appear to be extending significantly the late quaternary geological velocity field derived using seismic reflection and neotectonic data indicates a maximum velocity of egan with respect to the colorado plateau of 4 mm yr 1 also distributed relatively evenly across the region the geodetic and late quaternary geological velocity fields therefore are consistent but strain release on the sevier desert detachment and the wasatch fault appears to have been anomalously high in the holocene previous models suggesting horizontal displacement rates in the eastern basin and range near 3 mm yr 1 which focused mainly along the wasatch zone and intermountain seismic belt may overestimate the holocene wasatch rate by at least 50 per cent and the quaternary rate by nearly an order of magnitude while ignoring potentially major seismogenic faults further to the west

testing for fault activity at yucca mountain nevada using independent gps results from the bargen network 1 data from bargen gps stations around yucca mountain ym have been independently processed using gipsy oasis and gamit globk the rms velocity differences between these solutions is 0 06 mm yr east component and 0 10 mm yr north indicating an ability to resolve tectonic signals 0 3 mm yr with high confidence inversion of gps station velocities for eastern california shear zone ecsz fault parameters produces an unreasonably deep locking depth of 30 km for the death valley furnace creek fault system contradicting seismological evidence the gps cluster locally west of ym observes a strain rate of 17 0 1 8 ns yr marginally higher than our ecsz model predicts 13 9 0 7 ns yr significantly the cluster to the east observes 22 3 2 1 ns yr which is 6 2 higher than the model 8 6 0 7 ns yr suggesting that additional sources of strain more local to ym 0 7 mm yr

active megadetachment beneath the western united states geodetic data interpreted in light of seismic imaging seismicity xenolith studies and the late quaternary geologic history of the northern great basin suggest that a subcontinental scale extensional detachment is localized near the moho to first order seismic yielding in the upper crust at any given latitude in this region occurs via an m7 earthquake every 100 years here we develop the hypothesis that since 1996 the region has undergone a cycle of strain accumulation and release similar to slow slip events observed on subduction megathrusts but yielding occurred on a subhorizontal surface 5 10 times larger in the slip direction and at temperatures 800 c net slip was variable ranging from 5 to 10 mm over most of the region strain energy with moment magnitude equivalent to an m7 earthquake was released along this megadetachment primarily between 2000 0 and 2005 5 slip initiated in late 1998 to mid 1999 in northeastern nevada and is best expressed in late 2003 during a magma injection event at moho depth beneath the sierra nevada accompanied by more rapid eastward relative displacement across the entire region the event ended in the east at 2004 0 and in the remainder of the network at about 2005 5 strain energy thus appears to have been transmitted from the cordilleran interior toward the plate boundary from high gravitational potential to low via yielding on the megadetachment the size and kinematic function of the proposed structure in light of various proxies for lithospheric thickness imply that the subcrustal lithosphere beneath nevada is a strong thin plate even though it resides in a high heat flow tectonic regime a strong lowermost crust and upper mantle is consistent with patterns of postseismic relaxation in the southern great basin deformation microstructures and low water content in dunite xenoliths in young lavas in central nevada and high temperature microstructures in analog surface exposures of deformed lower crust large scale decoupling between crust and upper mantle is consistent with the broad distribution of strain in the upper crust versus the more localized distribution in the subcrustal lithosphere as inferred by such proxies as low p wave velocity and mafic magmatism

strain accumulation near yucca mountain nevada 1993 1998 a 50 km aperture geodetic network centered on the proposed high level radioactive waste disposal site at yucca mountain nevada was surveyed with gps in 1993 and 1998 the average deformation rate across the area is described by the principal strain rates 22 8 8 8 nstrain yr 1 n77 6 w 13 5 and 8 8 11 9 nstrain yr 1 n12 5 e 13 5 extension reckoned positive and a clockwise rotation rate about a vertical axis of 9 6 7 4 nrad yr 1 relative to fixed north america quoted uncertainties are standard deviations those strain rates are consistent with the geodetic strain rates 2 12 nstrain yr 1 n87 12 w and 22 12 nstrain yr 1 n03 12 e previously reported by savage et al 1999 for the 1983 1998 interval and with the low extension rate 5 20 nstrain yr 1 marrett et al 1998 inferred from the geologic record none of those strain rates is consistent with the 50 9 nstrain yr 1 n65 w extension rate for the area reported by wernicke et al 1998

correlated errors in geodetic time series implications for time dependent deformation analysis of frequent trilateration observations from the two color electronic distance measuring networks in california demonstrate that the noise power spectra are dominated by white noise at higher frequencies and power law behavior at lower frequencies in contrast earth scientists typically have assumed that only white noise is present in a geodetic time series since a combination of infrequent measurements and low precision usually preclude identifying the time correlated signature in such data after removing a linear trend from the two color data it becomes evident that there are primarily two recognizable types of time correlated noise present in the residuals the first type is a seasonal variation in displacement which is probably a result of measuring to shallow surface monuments installed in clayey soil which responds to seasonally occurring rainfall this noise is significant only for a small fraction of the sites analyzed the second type of correlated noise becomes evident only after spectral analysis of line length changes and shows a functional relation at long periods between power and frequency of 1 where is frequency and 2 with 2 this type of correlated noise is termed random walk noise and its source is mainly thought to be small random motions of geodetic monuments with respect to the earth s crust though other sources are possible because the line length changes in the two color networks are measured at irregular intervals power spectral techniques cannot reliably estimate the level of 1 noise rather we also use here a maximum likelihood estimation technique which assumes that there are only two sources of noise in the residual time series white noise and random walk noise and estimates the amount of each from this analysis we find that the random walk noise level averages about 1 3 mm yr and that our estimates of the white noise component confirm theoretical limitations of the measurement technique in addition the seasonal noise can be as large as 3 mm in amplitude but typically is less than 0 5 mm because of the presence of random walk noise in these time series modeling and interpretation of the geodetic data must account for this source of error by way of example we show that estimating the time varying strain tensor a form of spatial averaging from geodetic data having both random walk and white noise error components results in seemingly significant variations in the rate of strain accumulation spatial averaging does reduce the size of both noise components but not their relative influence on the resulting strain accumulation model

an introduction to the global positioning system and some geological applications receivers equipped to measure dual frequency carrier phase signals from satellites of the global positioning system gps have been capable under special conditions of determining relative horizontal positions among stations separated by one to a few hundred kilometers with a precision of one to several millimeters since the early 1980s the major obstacles to making this capability routine extending it to all parts of the globe and extending it to longer station separations have been equipment cost limitations in the gps satellite constellation arduous data analysis uncertainties in satellite orbits uncertainties in propagation delays associated with variable tropospheric water vapor and difficulties in resolving carrier phase cycle ambiguities recent improvements have occurred in all these areas the increasing ease and reduced cost of gps data acquisition and analysis are having a significant impact on studies of near fault crustal deformation and earthquake processes until recently the province of conventional terrestrial geodetic techniques the enhanced satellite constellation improved models and establishment of global tracking networks have extended several millimeters horizontal positioning capability to station separations of 1000 km or more in virtually all parts of the world this enables study of new classes of tectonic problems that previously were difficult to attack with any geodetic technique examples include a complete kinematic description of ongoing crustal deformation in broad complex continental plate boundary zones and measurement of relative plate motion at convergent boundaries where global models may be poorly constrained

seasonally chemical weathering and co2 consumption flux of lake qinghai river system in the northeastern tibetan plateau the major cation and anion compositions of waters from the lake qinghai river system lqrs in the northeastern tibetan plateau were measured the waters were collected seasonally from five main rivers during pre monsoon late may monsoon late july and post monsoon middle october the lqrs waters are all very alkaline and have high concentrations of tds total dissolved solids compared to rivers draining the himalayas and the southeastern tibetan plateau seasonal variations in the water chemistry show that except the daotang river the tds concentration is high in october and low in july in the lqrs waters the forward models were used to quantify the input of three main rivers buha river shaliu river and hargai river from rain halite carbonates and silicates the results suggest that 1 atmospheric input is the first important source for the waters of the buha river and the shaliu river contributing 36 57 of the total dissolved cations 2 carbonate weathering input and atmospheric input have equal contribution to the hargai river water 3 carbonate weathering has higher contribution to these rivers than silicate weathering and 4 halite is also important source for the buha river the daotang river water is dominated by halite input owing to its underlying old lacustrine sediments the water compositions of the heima river are controlled by carbonate weathering and rainfall input in monsoon season and groundwater input may be important in pre monsoon and post monsoon seasons after being corrected the atmospheric input average co2 drawdown via silicate weathering in the lqrs is 35 103 mol km2 per year with highest in monsoon season lower than himalayas and periphery of tibetan plateau rivers but higher than some rivers draining shields

a new global mode of earth deformation seasonal cycle detected we have detected a global mode of earth deformation that is predicted by theory precise positioning of global positioning system sites distributed worldwide reveals that during february to march the northern hemisphere compresses and the southern hemisphere expands such that sites near the north pole move downward by 3 0 millimeters and sites near the equator are pulled northward by 1 5 millimeters the opposite pattern of deformation occurs during august to september we identify this pattern as the degree one spherical harmonic response of an elastic earth to increased winter loading of soil moisture snow cover and atmosphere data inversion shows the load moment s trajectory as a great circle traversing the continents peaking at 6 9 1022 kilogram meters near the north pole in winter indicating interhemispheric mass exchange of 1 0 1016 0 2 1016 kilograms

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

a unified analysis of crustal motion in southern california 1970 2004 the scec crustal motion map 1 to determine crustal motions in and around southern california we have processed and combined trilateration data collected from 1970 to 1992 vlbi data from 1979 to 1992 and gps data from 1986 to 2004 a long temporal coverage required in part by the occurrence of several large earthquakes in this region from a series of solutions for station positions we have estimated interseismic velocities coseismic displacements and postseismic motions within the region from 31 n to 38 n and east to 114 w the final product includes estimated horizontal velocities for 1009 gps 190 trilateration and 16 vlbi points with ties between some of these used to stabilize the solution all motions are relative to the stable north american reference frame snarf as realized through the velocities of 20 gps stations this provides a relatively dense set of horizontal velocity estimates with well tested errors for the past quarter century over the plate boundary from 31 n to 36 5 n these velocities agree well with those from the plate boundary observatory which apply to a later time period we also estimated vertical velocities 533 of which have errors below 2 mm yr most of these velocities are less than 1 mm yr but they show 2 4 mm yr subsidence in the ventura and los angeles basins and in the salton trough our analysis also included estimates of coseismic and postseismic motions related to the 1992 landers 1994 northridge 1999 hector mine and 2003 san simeon earthquakes postseismic motions increase logarithmically over time with a time constant of about 10 days and generally mimic the direction and relative amplitude of the coseismic offsets

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

improved stability of a deeply anchored geodetic monument for deformation monitoring a test of two different monument designs used in geodetic networks shows that monuments installed to depths of 5 to 10 meters and laterally braced exhibit less environmentally caused displacement than those installed to 2 meters depth at parkfield california we have been monitoring the lengths of 17 baselines over the past decade with a 2 to 3 day interval between measurements using a two color geodimeter with a nominal precision of 0 5 mm over 5 km long baselines significant variations are observed on many of these baselines which appear to be related to the seasonally occurring rainfall with the larger variations approaching 10 mm over the past decade to test whether we could improve upon the measurements on some of the more susceptible lines at two sites we installed new monuments within about 30 meters of the original monuments after 1 5 years of measurements it is evident that the new monuments significantly attenuate the seasonal displacements to less than 1 mm the use of deeply anchored monuments should improve the ability of fault scale geodetic monitoring arrays to detect small tectonic displacements

late quaternary slip rates along the sierra nevada frontal fault zone california slip partitioning across the western margin of the eastern california shear zone basin and range province new geologic mapping tectonic geomorphologic and cosmogenic radionuclide geochronologic data provide the fi rst numerical constraints on late quaternary vertical slip and horizontal extension rates across the southern sierra nevada frontal fault zone california this fault zone exposes numerous nnw striking east facing normal fault scarps that offset seven distinct quaternary alluvial surfaces and a rockslide deposit beryllium 10 cosmogenic radionuclide surface exposure dating of these surfaces provides surface abandonment model ages of 123 7 16 6 ka 60 9 6 6 ka 25 8 7 5 ka 4 4 1 1 ka and 4 1 1 0 ka on alluvial fan surfaces and 18 7 3 9 ka on the rockslide deposit these age constraints combined with measurements of vertical surface offset across fault scarps yield preferred late pleistocene to holocene vertical and horizontal extensional slip rates of 0 2 0 3 mm yr and 0 1 0 2 mm yr vertical slip rate estimates in this study are comparable to late pleistocene vertical slip rate estimates across other prominent range front normal faults within the basin and range province these geologic and geochronologic results indicate that the eastern escarpment of the southern sierra nevada has remained tectonically active throughout the late quaternary combining our data with slip data from the owens valley and lone pine faults implies that slip along the eastern escarpment of the sierra nevada block is partitioned into three components dominantly dextral slip along the owens valley fault intermediate oblique slip along the lone pine fault and subordinate normal slip along the sierra nevada frontal fault zone these observations are consistent with global positioning system gps data which indicate that dextral shear strain accumulation dominates today along the western boundary of the eastern california shear zone and basin and range province

tide gauge and gps measurements of crustal motion and sea level rise along the eastern margin of adria 1 we use observations from tide gauges and colocated continuous gps cgps stations to investigate crustal deformation and sea level changes along the eastern margin of the adriatic sea we develop a new method to separate common mode relative sea level from spatially variable signals precise vertical crustal motions determined by cgps allow us to further separate relative sea level into absolute sea level changes and crustal motions with respect to a local central mediterranean fixed gps defined reference frame from the tide gauge data we find fairly uniform relative sea level rise along the coast with mean rate of 0 84 0 04 mm yr and weighted rms variation about this mean of 0 2 mm yr this rate is a factor of 2 4 lower than estimates for global average sea level rise in contrast vertical motion of coastal rocks determined by cgps vary appreciably from an average of 1 7 0 4 mm yr in southern adria to 0 0 0 4 mm yr in northern adria this difference in crustal motion between the northern and southern regions is independent of our ability to separate sea level from crustal motion and may be explained by crustal strain associated with an active thrust fault accommodating southern adria microplate convergence with eurasia enigmatically the combination of tide gauge and cgps measurements shows that absolute sea level relative to the gps determined reference frame varies by as much as 1 8 mm yr along the croatian coast in such a way that the relative sea level remains roughly constant there are several potential explanations for this result deriving from ocean atmosphere and solid earth dynamics

vertical distribution of dust and water ice aerosols from crism limb geometry observations 1 near infrared spectra taken in a limb viewing geometry by the compact reconnaissance imaging spectrometer for mars crism on board the mars reconnaissance orbiter provide a useful tool for probing atmospheric structure specifically the observed radiance as a function of wavelength and height above the limb enables the vertical distribution of both dust and water ice aerosols to be retrieved more than a dozen sets of crism limb observations have been taken so far providing pole to pole cross sections spanning more than a full martian year radiative transfer modeling is used to model the observations taking into account multiple scattering from aerosols and the spherical geometry of the limb observations both dust and water ice vertical profiles often show a significant vertical structure for nearly all seasons and latitudes that is not consistent with the well mixed or conrath v assumptions that have often been used in the past for describing aerosol vertical profiles for retrieval and modeling purposes significant variations are seen in the retrieved vertical profiles of dust and water ice aerosol as a function of season dust typically extends to higher altitudes 40 50 km during the perihelion season than during the aphelion season 20 km and the hellas region consistently shows more dust mixed to higher altitudes than other locations detached water ice clouds are common and water ice aerosols are observed to cap the dust layer in all seasons

interseismic strain and rotation rates in the northeast mojave domain eastern california 1 the northeast mojave domain a type locality for bookshelf faulting is a region of east striking left lateral faults in the northeast corner of the mojave block a block otherwise dominated by n40 w striking right lateral faults paleomagnetic evidence suggests that blocks within the domain have rotated clockwise about a vertical axis as much as 60 since 12 8 ma schermer et al 1996 in 1994 and again in 2002 the u s geological survey surveyed an array of 14 geodetic monuments distributed across the northeast mojave domain the 2002 survey results were adjusted to remove the coseismic offsets imposed by the nearby hector mine earthquake 16 october 1999 mw 7 1 the adjusted deformation across the array appears to be uniform and can be approximated by the principal strain rates e1 28 9 9 1 n77 2 w 4 8 and e2 48 2 8 9 n12 8 e 4 8 nstrain yr 1 extension reckoned positive and quoted uncertainties are standard deviations that strain accumulation could be released by slip on faults striking n32 w but not by bookshelf faulting on the east striking faults alone the vertical axis rotation rate of the northeast mojave domain as a whole relative to fixed north america is 71 0 6 4 nrad yr 1 4 07 0 37 myr 1 clockwise about twice the maximum tensor shear strain rate the observed rotation rate acting over 12 8 myr would produce a clockwise rotation of 52 1 4 7 exclusive of possible coseismic rotations that rotation is in rough agreement with the paleomagnetic rotation accumulated in the individual fault blocks within the northeast mojave domain since 12 8 ma

weathering sr fluxes and controls on water chemistry in the lake qinghai catchment ne tibetan plateau strontium sr concentrations and isotopic ratios have been measured in a series of water and rock samples from most of the major tributaries of the lake qinghai basin on the north eastern tibetan plateau dissolved sr and 87sr 86sr show ranges of 488 12 240 nmol l and 0 710497 0 716977 respectively these data together with measurements of major cations and anions in rivers and their tributaries and various lithologies of the catchment were used to determine the contributions of sr and its isotopic expense to rivers and lakes our results demonstrate that the chemical components and 87sr 86sr ratios of the alkaline waters are derived from mixing of carbonate and silicate sources with the former contributing 72 18 dissolved sr to rivers the difference in tributary compositions stems from the lithology of different river systems and low weathering intensity under a semi arid condition variation in 87sr 86sr ratios places constraint on the sr isotopic compositions of the main tributaries surrounding lake qinghai the water chemistry of the buha river the largest river within the catchment underlain by the late paleozoic marine limestone and sandstones dominates sr isotopic composition of the lake water being buffered by the waters from the other rivers and probably by groundwater however the characteristic chemical composition of the lake itself differs remarkably from the rivers which can be attributed to precipitation of authigenic carbonates low magnesium calcite aragonite and dolomite though this does not impact the sr isotope signature which may remain a faithful indicator in paleo records regarding the potential role of groundwater input within the lake qinghai systems in the water budget and water chemistry we have also determined the sr concentration and 87sr s6sr ratio of groundwater from diverse environments this has allowed us to further constrain the sr isotope systematic of this source a steady state calculation gives an estimate for the groundwater flux of 0 19 0 03 108 m3 yr accounting for about 8 of contemporary lake sr budget copyright 2010 john wiley sons ltd

anomalous strain accumulation in the yucca mountain area nevada global positioning system gps surveys from 1991 to 1997 near yucca mountain nevada indicate west northwest crustal elongation at a rate of 1 7 0 3 millimeters per year 1 over 34 kilometers or 50 9 nanostrain per year global positioning system and trilateration surveys from 1983 to 1997 on a 14 kilometer baseline across the proposed repository site for high level radioactive waste indicate that the crust extended by 0 7 to 0 9 0 2 millimeter per year 50 to 64 14 nanostrain per year depending on the coseismic effect of the m s 5 4 1992 little skull mountain earthquake these strain rates are at least an order of magnitude higher than would be predicted from the quaternary volcanic and tectonic history of the area

constraints on vertical crustal motion for long baselines in the central mediterranean region using continuous gps abstract gps determination of vertical crustal velocity relative to a globally defined reference frame is limited by the accuracy of the reference frame origin and scale however the precision of relative vertical rates at regional distance scales remains largely unexplored we investigated the precision of regional scale vertical velocity estimates using data from seven continuously operating gps stations located in the central mediterranean the stations form a network of aperture 500 km and each has been in operation for at least 5 yr we used published constraints on recent crustal uplift inferred from late quaternary shoreline data to aid in the definition of a local vertical reference frame for gps rates to facilitate an assessment of gps vertical precision we explored different methods of defining the local reference frame the simplest method involves the estimation of a single scalar translation parameter adjusting the reference frame by this simple method yields agreement between cgps and holocene shoreline data sets at the level of 0 2 to 0 4 mm yr relative rates determined using cgps are also consistent with tide gauge records and sea level determined by satellite altimetry at the level of about 0 2 mm yr these results suggest that regional scale relative velocity precision well below the mm yr level is now possible using continuous gps

geologic context of geodetic data across a basin and range normal fault crescent valley nevada geodetic strain and late quaternary faulting in the basin and range province is distributed over a region much wider than historic seismicity which is localized near the margins of the province in the relatively aseismic interior both the magnitude and direction of geodetic strain may be inconsistent with the holocene faulting record we document the best example of such a disagreement across the ne striking 55 nw dipping crescent normal fault where a nw oriented 70 km geodetic baseline records contemporary shortening of 2 mm yr orthogonal to the fault trace in contrast our geomorphic paleoseismic and geochronologic analyses of the crescent fault suggest that a large extensional rupture occurred during the late holocene epoch an excavation across the fault at fourmile canyon reveals that the most recent event occurred at 2 8 0 1 ka with net vertical tectonic displacement of 4 6 0 4 m at this location corresponding to the release of 3 m of accumulated nw se extension measured alluvial scarp profiles suggest a minimum rupture length of 30 km along the range front for the event implying a moment magnitude m w of at least 6 6 no prior event occurred between 2 8 ka and 6 4 0 1 ka the 14 c calender age of strata near the base of the exposed section assuming typical slip rates for basin and range faults 0 3 mm yr these results imply that up to one third or 1 m of the extensional strain released in the previous earthquake could have reaccumulated across the fault since 2 8 ka however the contemporary shortening implies that the fault is unloading due to a transient process whose duration is limited to between 6 years geodetic recording time and 2 8 ka the age of the most recent event these results emphasize the importance of providing accurate geologic data on the timescale of the earthquake cycle in order to evaluate geodetic measurements

summer evolution of the north polar cap of mars as observed by omega mars express the observatoire pour la mineralogie l eau les glaces et l activite omega visible infrared imaging spectrometer extensively observed regions of mars with latitudes above 70 n in late 2004 heliocentric longitude from ls 93 to ls 127 the extent of water ice at the surface and the size of ice grains were monitored as a function of time bright small grained frost which initially covered a large fraction of the polar cap waned in favor of large grained ice in outlying regions dominated by large grained ice the albedo increased over the period evaluating the dust content was model dependent however contamination of ice by dust was low

effect of viscoelastic postseismic relaxation on estimates of interseismic crustal strain accumulation at yucca mountain nevada 1 we estimate the long term crustal strain rate at yucca mountain ym nevada from gps velocities taking into account viscoelastic relaxation following recent earthquakes to remove bias associated with transient deformation the ym data reveal postseismic relaxation in time series non linearity and geographic variation of the transient signal from the data we estimate best fitting lower crust and upper mantle viscosities of 1019 5 pa s and 1018 5 pa s respectively once the relaxation model predictions are subtracted from the data the long term shear strain accumulation rate is between 16 3 and 25 1 nanostrains year ns yr to 99 confidence a range much larger than the formal uncertainties from gps measurement we conclude that 1 a maxwell viscoelastic model cannot explain all the deformation observed at ym 2 uncertainty in viscosities dominates uncertainty in ym strain rates and 3 the effects of large recent earthquakes must be accounted for in seismic hazard studies using gps

the frequency area distribution of volcanic units on venus implications for planetary resurfacing the areas of volcanic units on venus have been measured on the 1 5000000 geological maps published by nasa usgs these data were used to obtain a frequency area distribution the cumulative frequency area distribution of 1544 specific occurrence of units cover six orders of magnitude from the largest unit 30 106 km2 to the smallest 20 km2 the probability distribution function has been calculated the medium and large volcanic units correlate well with a power law fractal relation for the dependence of frequency on area with a slope of 1 83 there are fewer small units than the expected values provided by the power law relation our measurements cover 21 02 of the planetary surface 3 59 of the study area was found to be tessera terrain and is excluded from this study of volcanism the measurements were restricted to areas where geological maps have been published the analysis was performed on two independent areas of the planet with a complete coverage of published maps in both areas the largest volcanic unit covers a significant portion of the surface 58 75 and 63 64 respectively for the total measured volcanic units excluding tessera these two largest units that could correspond to the same unit or not cover the 61 18 and they are stratigraphically superimposed on older volcanic units which cover 3 37 of the area the remaining area 35 45 is occupied by younger volcanic units stratigraphically superimposed on the large volcanic unit s these results are based on the independent mapping of a large number of geologists with different ideas about the geodynamical evolution of venus and different criteria for geological mapping despite this fact the presence of these very large units is incompatible with the equilibrium resurfacing models because their generation at different ages would destroy the crater randomness our frequency area distribution of the mapped volcanic units supports a catastrophic resurfacing due to the emplacement of the largest unit s followed by a decay of volcanism our data for the frequency area distribution of volcanic units provide new support for catastrophic resurfacing models it is difficult to make our observations compatible with equilibrium steady state resurfacing models

southern california permanent gps geodetic array error analysis of daily position estimates and site velocities we analyze time series of daily positions estimated from data collected by 10 continuously monitoring global positioning system gps sites in southern california during the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes each time series exhibits a linear tectonic signal and significant colored noise spectral power at frequencies in the range 5 yr 1 to 0 5 d 1 is dominated by white noise or possibly fractal white noise and is several orders of magnitude higher than what would be expected from random walk noise in this short period range attributed by others to geodetic monument motions estimating a single slope for the time series power spectra suggests fractal white noise processes with spectral indices of about 0 4 site velocity uncertainties assuming this fractal white noise model are 2 4 times larger than uncertainties obtained assuming a purely white noise model a combination white noise plus flicker noise spectral index of 1 model also fits the data and suggests that the velocity uncertainties should be 3 6 times larger than for the white noise model we cannot adequately distinguish between these two noise models nor can we rule out the possibility of a random walk signal at the lowest frequencies these questions await the analysis of longer time series in any case reducing the magnitude of low frequency colored noise is critical and appears to be best accomplished by building sites with deeply anchored and braced monuments otherwise rate uncertainties estimated from continuous gps measurements may not be improved significantly compared to those estimated from infrequent campaign mode measurements

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

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

crustal deformation across the sierra nevada northern walker lane basin and range transition western united states measured with gps 2000 2004 1 global positioning system gps data collected in campaigns in 2000 and 2004 were processed and interpreted with other gps data in the western basin and range province to provide new constraints on the rate style and pattern of deformation of the central and northern walker lane wl which lies near the western boundary of the basin and range across the central wl near 38n latitude the velocities with respect to north america increase westward by 10 mm yr inducing dextral shear farther north between 40 and 41n latitude a western zone of 7 mm yr relative motion undergoes dextral shear and an eastern zone of 3 mm yr relative motion undergoes extension and shear these data show that the northern wl is essentially a dextral shear zone experiencing minor net dilatation ed 2 6 0 8 nstrain yr near most holocene normal faults dilatation inferred from the velocity field is not greater than the uncertainties however near the central nevada seismic belt we detect significant dilatation expressed as extension in a direction approximately normal to the range fronts ed 23 0 3 9 nstrain yr some of which is attributable to transient postseismic deformation following large historic earthquakes a block model constrained by velocities corrected for transient effects shows that the sum of dextral slip rates across the honey lake warm springs east pyramid fault system and mohawk valley faults is 7 mm yr the wl is a zone whose width and dilatation rate increase northwestward consistent with counterclockwise rotation of the sierra nevada microplate and transfer of deformation into the pacific northwest

crustal loading near great salt lake utah two sites of the bargen gps network are located 30 km south of great salt lake gsl lake level records since mid 1996 indicate seasonal water elevation variations of 0 3 m amplitude superimposed on a roughly decadal feature of amplitude 0 6 m using an elastic green s function and a simplified load geometry for gsl we calculate that these variations translate into radial crustal loading signals of 0 5 mm seasonal and 1 mm decadal the horizontal loading signals are a factor of 2 smaller despite the small size of the expected loading signals we conclude that we can observe them using gps time series for the coordinates of these two sites the observed amplitudes of the variations agree with the predicted decadal variations to 0 5 mm the observed annual variations however disagree this difference may be caused by some combination of local precipitation induced site motion unmodeled loading from other nearby sources errors in the gsl model and atmospheric errors