active deformation near the nicoya peninsula northwestern costa rica between 1996 and 2010 interseismic megathrust coupling 1 we use campaign and continuous gps measurements at 49 sites between 1996 and 2010 to describe the long term active deformation in and near the nicoya peninsula northwestern costa rica the observed deformation reveals partial partitioning of the cocos caribbean oblique convergence into trench parallel forearc sliver motion and less oblique thrusting on the subduction interface the northern costa rican forearc translates northwestward as a whole ridge block at 11 1 mm yr relative to the stable caribbean the transition from the forearc to the stable caribbean occurs in a narrow deforming zone of 16 km wide subduction thrust earthquakes take 2 3 of the trench parallel component of the plate convergence however surface deformation caused by interseismic megathrust coupling is primarily trench normal two fully coupled patches one located offshore nicoya centered at 15 km depth and the other located inland centered at 24 km depth are identified in nicoya with the potential to generate an mw 7 8 1950 type earthquake another fully coupled patch se of nicoya coincides with the rupture region of the 1990 nicoya gulf earthquake interface microearthquakes non volcanic tremor low frequency earthquakes and transient slow slip events generally occur in the intermediately to weakly coupled regions

seasonal and interannual global surface mass variations from multisatellite geodetic data 1 monthly global surface mass distribution changes are estimated in the spherical harmonic domain with a complete spectrum up to degree and order 50 the estimates are derived by inverting gps displacement series measured at roughly 450 continuously tracking sites and ocean bottom pressure obp estimates of a data assimilated ocean circulation model from 1993 to 2004 the inversion uses a hybrid estimator after singular value decomposition of the normalized measurement equations with reduced reliance on a priori spectral information the results are then compared and combined with gravity recovery and climate experiment grace gravity data to provide enhanced spectral and geographic coverage high fidelity degree 1 surface mass variation coefficients are recovered corresponding to equivalent geocenter motion with better than 0 5 mm annual amplitude precisions in all three components a clear annual surface mass cycle occurs in both gps obp and grace derived results there is very good agreement among the low degree spherical harmonic coefficients and in global geographic pattern but with significant regional differences in amplitudes annual variations of average mass over the global oceans antarctica and greenland are then derived total surface mass over both antarctica and greenland peak in their respective summers due to increased atmospheric mass large interannual variations have also been found involving several continents in the 11 year gps obp solution the patterns of variation suggest that the recent satellite laser ranging slr observation of a reversal in trend of the earth s oblateness may be largely an interannual surface mass cycle with considerable contribution from the northern continents

estimates of vertical crustal motion derived from differences of topex poseidon and tide gauge sea level measurements 1 we have computed estimates of the rate of vertical crustal motion from differences of sea level measurements made by the topex poseidon radar altimeter and a globally distributed network of 114 tide gauges a rigorous error analysis was performed which suggests the accuracy of the estimated vertical rates is approximately 1 2 mm year for roughly half of the tide gauges which is sufficiently accurate to detect a variety of geophysical phenomena while only a cursory analysis of the estimated crustal motion rates was performed we observed many interesting phenomena including significant uplift at volcanic islands in the pacific and uplift of 7 9 mm year along the southwest coast of alaska the results reported here will be useful in a variety of geophysical studies as well as for validation of similar estimates of vertical crustal motion provided by precise geodetic techniques such as slr doris gps and vlbi

new slip rate estimates for the creeping segment of the san andreas fault california new continuous and differential global positioning system gps measurements of recent slip rates and 30 yr alignment array offsets from the central creeping segment of the san andreas fault yield a maximum right lateral slip rate of 25 1 mm yr this slip rate is 20 slower than the 30 mm yr slip rate accepted for this segment of the fault and 35 slower than the 39 mm yr slip rate predicted between the sierra nevada great valley block and the pacific plate new continuous gps measurements between pairs of sites that flank the creeping segment at intersite distances of 1 0 km and 70 km give relative fault parallel slip rates of 28 2 and 30 2 mm yr respectively these observations indicate that right lateral deformation rates increase with distance from the fault possible explanations for the gradient observed in the geodetic data are elastic strain accumulation along the creeping segment or significant distributed deformation on off fault structures

a geodetic study of the 2003 january 22 tecoman colima mexico earthquake we use coseismic displacements and aftershock information from global positioning system gps measurements at 27 sites in western mexico and a 12 station local seismic network to determine the characteristics of the 2003 january 22 m w 7 2 subduction thrust earthquake near tecoman colima mexico estimates of the earthquake moment slip direction and best fitting slip distribution are derived by optimizing the fit to the gps displacements for a 3 d finite element mesh that simulates the study area the calculated moment release is 9 1 10 19 n m m w 7 2 with maximum slip of 2 m at a depth of 24 km and a maximum rupture depth of 35 40 km the inversion indicates that coseismic rupture extended downdip from depths of 9 to 40 km along a 80 km along strike region that is bounded by the edges of the manzanillo trough the optimal solution is robust with respect to plausible changes in the subduction interface geometry and differing subsets of the data a comparison of the cumulative post seismic slip that can be inferred separately from earthquake aftershocks and gps measurements within a year of the earthquake indicates that 95 per cent or more of the post seismic deformation was aseismic near term post seismic measurements indicate that slip propagated downdip to areas of the subduction interface beneath the coastline within days following the earthquake as also occurred after the nearby m w 8 0 colima jalisco subduction earthquake in 1995 the similar behaviours and locations of the 1995 2003 earthquake sequence to two earthquakes in june of 1932 suggests that thrust earthquakes along the subduction interface northwest of the manzanillo trough may trigger earthquakes in the vicinity of the manzanillo trough however our modelling of coulomb stress changes caused by the 1995 earthquake indicate that it induced only modest unclamping of the subduction interface in the vicinity of the tecoman rupture in addition gps measurements indicate that elastic shortening characterized areas onshore from the tecoman rupture from mid 1997 up until the time of the rupture consistent with progressively stronger clamping of the subduction interface during this period this precludes any obvious triggering relationship with the 1995 earthquake the apparent coincidence of the edge of both the 1932 and 1995 2003 rupture sequences with the edge of the manzanillo trough may indicate that the trough is a mechanical barrier to along strike rupture propagation this implies a limit to the area of potential slip and hence rupture magnitude during future large earthquakes in this region

realizing a terrestrial reference frame using the global positioning system we describe a terrestrial reference frame trf realization based on global positioning system gps data alone our approach rests on a highly dynamic long arc 9 day estimation strategy and on gps satellite antenna calibrations derived from gravity recovery and climate experiment and topex poseidon low earth orbit receiver gps data based on nearly 17 years of data 1997 2013 our solution for scale rate agrees with international terrestrial reference frame itrf 2008 to 0 03 ppb yr 1 and our solution for 3 d origin rate agrees with itrf2008 to 0 4 mm yr 1 absolute scale differs by 1 1 ppb 7 mm at the earth s surface and 3 d origin by 8 mm these differences lie within estimated error levels for the contemporary trf

thirty five year creep rates for the creeping segment of the san andreas fault and the effects of the 2004 parkfield earthquake constraints from alignment arrays continuous global positioning system and creepmeters we present results from differential global positioning system gps surveys of seven alignment arrays and four continuous gps sites along the creeping segment of the san andreas fault surveys of four alignment arrays from the central creeping segment yield 33 to 36 year average minimum slip rates of 21 26 mm yr these rates are consistent with previous alignment array surveys spanning a 10 year period and with rates determined by creepmeters indicating approximate steady state creep along the central creeping segment for at least 35 years motion between continuous gps sites that span the central creeping segment is 28 2 0 5 mm yr for two sites that are 1 km apart and 33 6 1 mm yr for two sites that are 70 km apart slip rates therefore increase with distance from the creeping segment of the san andreas fault all rates reported here are significantly slower than the 39 2 mm yr rate predicted for motion between the sierra nevada great valley block and the pacific plate repeat surveys of three alignment arrays following the 2004 parkfield earthquake demonstrate that its coseismic and short term postseismic offsets decrease rapidly with distance from the epicenter from 150 mm to 15 mm to 5 mm at respective distances of 9 36 and 54 km to the northwest continuous gps data confirm that little coseismic and postseismic slip occurred along the central creeping segment geodetic and geologic slip rates are compared and different models for the accommodation of transcurrent deformation across the creeping segment are discussed

ground deformation at soufriere hills volcano montserrat during 1998 2000 measured by radar interferometry and gps abstract we examine the motion of the ground surface on the soufriere hills volcano montserrat between 1998 and 2000 using radar interferometry insar to minimise the effects of variable atmospheric water vapour on the insar measurements we use independently derived measurements of the radar path delay from six continuous gps receivers the surfaces providing a measurable interferometric signal are those on pyroclastic flow deposits mainly emplaced in 1997 three types of surface motion can be discriminated firstly the surfaces of thick valley filling deposits subsided at rates of 150 120 mm year in the year after emplacement to 50 30 mm year two years later this must be due to contraction and settling effects during cooling the second type is the near field motion localised within about one kilometre of the dome both subsidence and uplift events are seen and though the former could be due to surface gravitational effects the latter may reflect shallow

global geodesy using gps without fiducial sites baseline lengths and geocentric radii have been determined from gps data without the use of fiducial sites data from the first gps experiment for the iers and geodynamics gig 91 have been analyzed with a no fiducial strategy a baseline length daily repeatability of 2 mm 4 parts per billion was obtained for baselines in the northern hemisphere comparison of baseline lengths from gps and the global vlbi solution glb659 caprette et al 1990 show rms agreement of 2 1 parts per billion the geocentric radius mean daily repeatability for all sites was 15 cm comparison of geocentric radii from gps and sv5 murray et al 1990 show rms agreement of 3 8 cm given n globally distributed stations the n n 1 2 baseline lengths and n geocentric radii uniquely define a rigid closed polyhedron with a well defined center of mass geodetic information can be obtained by examining the structure of the polyhedron and its change with time

an integrated crustal velocity field for the central andes 1 we present an integrated velocity field for the central andes derived from gps observations collected between january 1993 and march 2001 that eliminates the velocity bias between the south america nazca plate project snapp and central andes gps project cap velocity fields published by norabuena et al 1998 and bevis et al 1999 the reference frame is realized by minimizing the motion of eight continuous gps stations and one rover gps station located in the stable core of the south american plate the rms horizontal motion of these stations is just 1 1 mm yr the amplitude of these residual motions is roughly compatible with expected levels of measurement error in our new solution five of the six snapp stations located just outside the orogenic belt are effectively stationary and the velocities for adjacent cap and snapp stations now agree at a level consistent with their formal uncertainties

external validation of the grace ggm01c gravity field using gps and doris positioning results 1 we have used the new gravity field model ggm01c derived from grace data to reanalyze doris data from 1993 0 to 2003 2 using the gipsy oasis software and a free network approach we have estimated the position and velocity of each doris station in itrf2000 in order to test the accuracy of these results we have compared them to the positions and velocities of 43 collocated gps stations using local ties and covariance information doris results computed using the ggm01c gravity field instead of the egm96 gravity field show a significantly improved external agreement with gps position agreement of 12 26 mm was reduced to 10 13 mm and velocity agreement of 3 3 3 7 mm yr was reduced to 2 4 3 3 mm yr this can be interpreted as an external test of the accuracy of the new ggm01c gravity field

interplate coupling and transient slip along the subduction interface beneath oaxaca mexico summary we describe and model gps measurements of surface deformation from the oaxaca segment of the mexican subduction zone to characterize interseismic strain accumulation and episodic transient slip in this region and test seismologically based models of strain accumulation and release along subduction interfaces deformation measured from 2001 to 2007 within our dense 31 station gps array has consisted of 1 trench normal horizontal contraction at rates that decrease monotonically inland from the coast 2 rapid coastal subsidence that changes gradually to slow uplift at locations more than 100 km inland and 3 periods of transient slip that interrupt the otherwise steady deformation inverse modelling of transient station offsets in 2004 and 2006 indicates that transient slip along the subduction interface occurred downdip from the rupture limits of previous large earthquakes in this region in both 2004 and 2006 gps site velocities that are corrected for the effects of this transient slip vary significantly over distances of only tens of kilometres both along the coastline and inland implying that similar spatial variations occur in the degree of locking across the subduction interface deformation rates measured along the coast reach their maximum above the core of the rupture zone of the 1978 ms 7 8 shallow thrust earthquake and generally decrease outwards towards the edges of the rupture zone bounded value inverse modelling of the interseismic gps velocity field with a finite element mesh that simulates the study region indicates that much of the rupture zone of the 1978 shallow thrust earthquake is fully locked at the plate convergence rate but that this region is surrounded by weakly locked areas of the subduction interface which may slow or arrest the propagation of future earthquakes much of the deeper region of transient slip downdip from the seismogenic zone is also fully locked between the episodes of transient slip however the elastic energy that accumulated due to locking of this deeper transitional zone between 2002 and 2006 appears to have been mostly or completed released by the 2004 and early 2006 transient slip events the approximately balanced energy budget for the deeper zone of transient slip implies that this region is unlikely to contribute significant elastic energy to future earthquakes that originate along the seismogenic zone our results support a model in which seismic asperities coincide with regions of strong locking between earthquakes the potential elastic energy that has re accumulated since 1978 in the seismogenic zone is already sufficient to cause a repeat of the 1978 earthquake

slow slip transients along the oaxaca subduction segment from 1993 to 2007 summary we use data from 12 continuous gps stations in southern mexico including eight new stations to better characterize transient slip episodes along the mexican subduction zone continuous gps recording in oaxaca that began 14 years ago constituting the longest continuous gps record in southern mexico defines nine distinct episodes of transient slip from 1993 to 2007 including previously unreported transient slip episodes in early 1995 and 2006 all transient slip episodes recorded in oaxaca city were also recorded at a gps site 400 km away in the state of guerrero after measurements began there in early 1997 demonstrating that transient slip affects widespread areas of southern mexico well recorded transients in 2004 and 2006 appear to have originated along the oaxaca trench segment hundreds of kilometres from the potentially hazardous guerrero seismic gap during the 2004 slip transient displacements of more than 20 mm were recorded at stations in the oaxaca gps array a factor of 2 3 larger than at sites in guerrero elastic half space modelling of the 2004 displacements at sites throughout southern mexico indicates that most slip was focused beneath oaxaca in deeper areas of the subduction interface immediately downdip from previous megathrust rupture zones but that slip also may have extended significantly updip into a seismic gap along the oaxaca coast the best fitting model is also able to explain transient vertical offsets of up to 30 mm observed during this event shortly before the onset of transient slip in 2004 a pair of moderate m w 5 1 5 5 earthquakes ruptured the downdip end of the seismogenic zone immediately east of the oaxaca seismic gap suggesting a possible relationship between the two in 2006 transient slip began 1 3 months earlier in oaxaca than in other areas offering the clearest evidence to date for the existence of one or more source regions for transient slip outside the guerrero seismic gap where large amplitude transient slip originated in 2002 the still limited data indicate that transient slip that originates elsewhere in mexico may trigger aseismic slip in guerrero and further indicate that transient slip beneath oaxaca is limited to areas of the subduction interface that surround the rupture zones of previous large shallow thrust earthquakes

geologic versus geodetic deformation adjacent to the san andreas fault central california we combine geologic and global positioning system gps data to characterize the style and magnitude of off fault deformation across the san andreas fault system in central california geologic structures record 12 km of both fault parallel and fault perpendicular displacements across creeping and locked portions of the san andreas fault analysis of 150 gps site velocities suggests that the borderlands record 4 6 mm yr of fault parallel and 3 5 mm yr of fault perpendicular motion alongside the creeping segment where elastic strain is minimized the distribution of both long term geologic and short term geodetic deformation is affected by basement type where more deformation is concentrated northeast of the san andreas fault on franciscan basement we suggest that at least half the fault parallel gps deformation measured by gps bordering the creeping segment must be accommodated by geologic structures this permanent deformation needs to be incorporated into dynamic models of the fault system elastic modeling of the san andreas fault in central california which incorporates its well known transition from locked to creeping behavior near parkfield predicts first order variations in the gps velocity field along the fault and corresponding variations in dilatational strain rates the strain rate pattern is dominated by a large contractional region northeast of the transition from locked to creeping behavior and a large extensional region southwest of the transition the former coincides with the coalinga and kettleman hills anticlines the growth and development of which seem to have occurred under at least two kinematic conditions we suggest that the onset of fault creep in central california promoted the growth of these folds by implication fault creep has been active over geologic time scales

dependence of the water retention curve of snow on snow characteristics the water retention curve wrc which shows the relationship between the volumetric liquid water content v and suction h is a fundamental part of the characterization of hydraulic properties therefore the formulation of the wrc as a function of snow characteristics is essential for establishing a model of water movement through the snow cover in this study we measured the wrc of several snow samples which had different characteristics grain size bulk dry density and grain type using a gravity drainage column experiment and then analysed these data using the van genuchten soil physics model vg model the shape of the wrc depended strongly on both the sample grain size d and bulk dry density p therefore we introduced the parameter d to model the wrc of snow the relationships between the parameters and n of the vg model and d change with grain type for melt forms a which is related to the inverse value of the air entry suction increases quickly as d decreases whereas n which is related to the gradient of v vs h increases with d conversely neither of these parameters of the vg model for rounded grains showed obvious dependence on d these results suggest that water movement through snow cover can be modelled using grain size bulk dry density and grain type based on the soil physics model

neotectonics of puerto rico and the virgin islands northeastern caribbean from gps geodesy the boundary between the north american and caribbean plates is characterized primarily by left lateral motion along predominantly east west striking faults seismicity and marine geophysical survey data are consistent with at least two and possibly three microplates in the diffuse boundary zone in the northeastern caribbean 1 the gonave 2 the hispaniola and 3 the puerto rico northern virgin islands prvi we discuss results from gps geodetic measurements acquired since 1994 to test the microplate hypothesis define prvi translation and rotation within the boundary zone and constrain prvi neotectonics gps derived velocities are analyzed with respect to both north american and caribbean plate reference frames integrated displacements across prvi are limited to a few millimeters per year consistent with a rigid prvi and permitting calculation of an average velocity for prvi the motions of prvi relative to north america and the caribbean are 16 9 1 1 mm yr toward n68 e 3 1 and 2 4 1 4 mm yr toward s79 w 26 1 respectively in contrast with some recent models ongoing rotation of prvi about a nearby 25 distant vertical axis is not supported by the geodetic data in addition we argue against eastward tectonic escape of prvi and favor a simple progressive increase in velocity across the plate boundary zone requiring that the summed magnitude of strike slip fault slip rates will equal the total plate motion rate between the caribbean and north america gps data are consistent with components of left lateral strike slip faulting along the muertos trough south of puerto rico and shortening across the puerto rico trench comparison of gps velocities for prvi with respect to north america with total north america caribbean relative motion suggests up to 85 of north american caribbean plate motion is accommodated by the puerto rico trench and offshore faults north of puerto rico differences in gps derived velocities from hispaniola and prvi yield east west extension across the n s trending mona rift of a few millimeters per year when estimated elastic strain accumulation effects along the north hispaniola deformed belt and the septentrional fault zone are considered the opening rate implies an age of the mona rift of 2 3 million years agreeing with marine geophysical data that support a young age for the structure

climate driven deformation of the solid earth from grace and gps 1 grace data indicate large seasonal variations in gravity that are assumed to be related to climate driven fluxes of surface water seasonal redistribution of surface mass should deform the earth and our calculations using grace data suggest vertical deformations of 13 mm in the region of greatest flux the amazon river basin to test the grace gravity hydrology connection we analyzed gps data acquired from sites in this region after accounting for degree 1 variations not observable with grace we find that annual deformation measured with gps correlates highly with predictions calculated from grace measurements these results confirm the variations in surface water sensed by grace which are significantly larger than those predicted by some hydrology models the results also demonstrate that grace can be an important tool for monitoring deformation of the earth and suggest that combined analysis of grace and gps may be a useful approach for estimation of geocenter variations

a gps and modelling study of deformation in northern central america summary we use gps measurements at 37 stations in honduras and el salvador to describe active deformation of the western end of the caribbean plate between the motagua fault and central american volcanic arc all gps sites located in eastern honduras move with the caribbean plate in accord with geologic evidence for an absence of neotectonic deformation in this region relative to the caribbean plate the other stations in the study area move west to west northwest at rates that increase gradually from 3 3 0 6 mm yr 1 in central honduras to 4 1 0 6 mm yr 1 in western honduras to as high as 11 12 mm yr 1 in southern guatemala the site motions are consistent with slow westward extension that has been inferred by previous authors from the north striking grabens and earthquake focal mechanisms in this region we examine the factors that influence the regional deformation by comparing the new gps velocity field to velocity fields predicted by finite element models fems that incorporate the regional plate boundary faults and known plate motions our modelling suggests that the obliquely convergent 20 direction of caribbean north american plate motion relative to the motagua fault west of 90 w impedes the ene directed motion of the caribbean plate in southern guatemala giving rise to extension in southern guatemala and western honduras the fem predictions agree even better with the measured velocities if the plate motion west of the central american volcanic arc is forced to occur over a broad zone rather than along a single throughgoing plate boundary fault our analysis confirms key predictions of a previous numerical model for deformation in this region and also indicates that the curvature of the motagua fault causes significant along strike changes in the orientations of the principal strainrate axes in the fault borderlands in accord with earthquake focal mechanisms and conclusions reached in a recent synthesis of the structural and morphologic data from honduras poor fits of our preferred models to the velocities of gps sites near the gulf of fonseca may be an artefact of the still short gps time series in this region or the simplifying assumptions of our fems

present day crustal deformation in china constrained by global positioning system measurements global positioning system gps measurements in china indicate that crustal shortening accommodates most of india s penetration into eurasia deformation within the tibetan plateau and its margins the himalaya the altyn tagh and the qilian shan absorbs more than 90 of the relative motion between the indian and eurasian plates internal shortening of the tibetan plateau itself accounts for more than one third of the total convergence however the tibetan plateau south of the kunlun and ganzi mani faults is moving eastward relative to both india and eurasia this movement is accommodated through rotation of material around the eastern syntaxis the north china and south china blocks east of the tibetan plateau move coherently east southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year respectively with respect to the stable eurasia

origin of the international terrestrial reference frame 1 with recent improvements in space geodesy the earth s center of mass cm and center of figure cf are no longer indistinguishable the current origin of the international terrestrial reference frame itrf is defined as the cm which shows measured seasonal variations of several millimeters to 1 cm with respect to true cm as scientists study earth s dynamic deformations on seasonal and shorter timescales and begin to compare observed geocenter motion with predictions from geophysical models the reference frame origin presents significant error due to missing the geocenter motion this paper discusses the nature of the origin of the itrf and explores the sensitivity of gps measurements to geocenter motion we find that since the values of nonlinear geocenter motion are not included in the positions of the itrf sites the behavior of the current itrf origin reflects cm on secular timescale but reflects cf on seasonal and short timescales the nature of the itrf origin depends on both the adopted kinematic model and unmodeled network motion the realized itrf origin should be defined by a new nomenclature to reflect its nature accurately by the new nomenclature the origin will maintain its current long term stability while improving its stability on seasonal timescales to the submillimeter level with the degree 1 deformation approach gps measurements are able to provide potentially valuable information on geocenter variations on seasonal and short timescales

rate change observed at jplm after the northridge earthquake geodetic time series determined with the global positioning system indicate that the geodetic rate of a permanent site in pasadena california jplm changed significantly after the 17 january 1994 northridge california earthquake subtracting the pre quake rate and co seismic offset leaves 30 4 mm of integrated eastward excess motion observed in the three years following the earthquake north and vertical components show excess motion of 11 plusmn 3 mm and 25 11 mm respectively local surveys to three additional points near jplm changed by no more than 6 mm e 3 mm n and 15 mm v during the two years after the earthquake ruling out the possibility of a local effect at the jplm monument the direction and size of the post seismic displacements at jplm are not consistent with additional slip on the fault which ruptured the most rapid accumulation of excess motion occurs immediately after the earthquake suggesting a relationship between the two events

transient deformation in southern mexico in 2006 and 2007 evidence for distinct deep slip patches beneath guerrero and oaxaca 1 we model three slow slip events in 2006 and 2007 recorded by continuous gps stations in central and southern mexico to test for overlap between their source regions along the mexican subduction interface and whether they intrude upward into the rupture zones of previous large earthquakes inverse modeling yields source regions beneath central oaxaca for two of the three slow slip events sse where a previously described sse occurred in 2004 and beneath guerrero for the third where slip events previously occurred in 2001 2002 and possibly 1998 along with previously published results our work suggests there are persistent differences between the depths and magnitudes of transient slip beneath oaxaca and guerrero transient slip beneath oaxaca in 2004 2006 and 2007 had a common source region downdip from the seismogenic zone and released elastic strain energy equivalent to mw 7 0 earthquakes equaling most or all energy that accumulated below the seismogenic zone transient slip beneath guerrero in 2006 had a larger moment magnitude mw 7 3 and extended somewhat farther updip possibly to seismogenic depths transient slip thus appears to relieve some elastic strain that accumulates at shallow levels in the guerrero seismic gap we find no evidence for spatial or temporal correlations of slow slip along these two widely separated source regions although better data are needed to test more definitively for any interaction between them

relative motion between the caribbean and north american plates and related boundary zone deformation from a decade of gps observations global positioning system gps measurements in 1986 1994 and 1995 at sites in dominican republic puerto rico cuba and grand turk define the velocity of the caribbean plate relative to north america the data show eastward motion of the caribbean plate at a rate of 21 1 mm yr 1 standard error in the vicinity of southern dominican republic a factor of 2 higher than the nuvel 1a plate motion model prediction of 11 3 mm yr independent measurements on san andres island and an euler vector derived from these data also suggest a rate that is much higher than the nuvel 1a model available data combined with simple elastic strain models give the following slip rate estimates for major left lateral faults in hispaniola 1 the north hispaniola fault offshore the north coast of hispaniola 4 3 mm yr 2 the septentrional fault in northern dominican republic 8 3 mm yr and 3 the enriquillo fault in southern dominican republic and haiti 8 4 mm yr the relatively high plate motion rate and fault slip rates suggested by our study combined with evidence for strain accumulation and historical seismicity imply that seismic risk in the region may be higher than previous estimates based on low plate rate low fault slip rate models and the relatively low rate of seismicity over the last century

crustal velocity field of mexico from continuous gps measurements 1993 to june 2001 implications for the neotectonics of mexico 1 we combine velocities for 14 continuous gps stations spanning mexico and 173 additional continuous gps sites on the north american and pacific plates to study the large scale deformation of mexico the new station velocities which are derived from more than 6000 days of previously unused gps data provide the first ever view of the crustal velocity field of mexico key results are as follows 1 areas north of the mexican volcanic belt not including baja california move with the north american plate interior within the 1 2 mm yr 1 station velocity uncertainties station velocities for the mexican basin and range are consistent with no present day extension and yield an upper 95 limit of 1 3 mm yr 1 for any regional extension 2 south of the mexican volcanic belt five of the six sites move significantly relative to the north american plate all sites in the yucatan peninsula move toward the east at 3 4 mm yr 1 possibly defining an independent yucatan block 3 site velocities are consistent with limits of 0 4 mm yr 1 for present slip across the mexican volcanic belt 4 tampico on the gulf coast exhibits eastward motion consistent with gravity sliding known to occur in the adjacent mexican ridges fold belt 5 southeastward motion of la paz relative to the pacific plate is consistent with the hypothesis that the baja peninsula is not fully attached to the pacific plate 6 residual velocities for 160 north american plate gps stations outside of mexico exhibit no coherent regional patterns indicative of internal plate deformation

the effect of tracking network configuration on gps baseline estimates for the casa uno experiment geodetic monitoring of subduction of the nazca and cocos plates is a goal of the casa central and south america global positioning system gps experiments and requires measurement of intersite distances baselines in excess of 500 km the major error source in these measurements is the uncertainty in the position of the gps satellites at the time of observation a key aspect of the first casa experiment casa uno was the initiation of a global network of tracking stations to minimize these errors we studied the effect of using various subsets of this global tracking network on long 100 km baseline estimates in the casa region best results were obtained with a global tracking network consisting of three u s fiducial stations two sites in the southwest pacific and two sites in europe relative to smaller subsets this global network improved baseline repeatability resolution of carrier phase cycle ambiguities and formal errors of the orbit estimates describing baseline repeatability for horizontal components as a2 b2l2 1 2 where l is baseline length we obtained a 4 and 9 mm and b 2 8 10 8 and 2 3 10 8 for north and east components respectively on casa baselines up to 1000 km in length with this global network

daily estimates of the earth s pole position with the global positioning system daily estimates of the earth s pole position have been obtained with measurements from a worldwide network of global positioning system gps receivers obtained during the three week gig 91 experiment in january february 1991 for this short term study the gps based polar motion series agrees with the other space based geodetic techniques very long baseline interferometry and satellite laser ranging to 0 4 mas rms after the removal of mean biases of order 1 3 mas the small error in day to day variability is not sensitive to the fiducial strategy used nor are fiducial sites even necessary for monitoring high frequency pole position variability the small biases indicate that the applied reference frames of the three geodetic techniques are nearly aligned that the gps fiducial errors are small and that systematic errors in gps are also small of order 5 ppb a well determined reference frame is necessary for monitoring the long term stability of polar motion and for separating it from other long term signals such as tectonic motion and internal systematic errors

regional coseismic deformation from the june 28 1992 landers california earthquake results from the mojave gps network the 1992 landers california earthquake sequence and its aftershocks delineate an active part of the eastern california shear zone the surface rupture lies within the mojave desert providing a unique opportunity to characterize far field deformation with a regional global positioning system gps network that was installed and occupied in may 1991 with uncertainties of less than 1 cm on interstation baseline vectors changes in absolute displacement vectors on the decimetre and centimetre level were determined for individual sites providing more samples of the sparsely sampled landers displacement field measured displacements result from secular strain across the mojave desert coseismic elastic recovery and postseismic deformation during the six weeks between the earthquake and the gps experiment secular strain and postseismic displacement are relatively small thus first order modeling of these fields allows calculation and subtraction of their signals leaving a coseismic residual field the gps determined far field coseismic displacements differ significantly from elastic half space models offering new insight on the role of regional scale heterogeneity in crustal structure

nature of magmatism and sedimentation at a columbia active margin insights from combined u pb and lu hf isotope data of detrital zircons from nw india abstract detrital zircons from a palaeoproterozoic quartzite deposited between 1 85 and 1 82 ga in the northern aravalli orogen of nw india show a distinctive age peak of ca 1 85 ga and variable but largely subchondritic ehf1 85 ga between 1 3 and 21 0 corresponding to hafnium model ages of 2 5 to 3 6 ga these data indicate an important period of reworking of ancient eo to neoarchaean strongly heterogeneous continental crust at this time prevalence of ca 1 85 ga subduction related granitoids almost identical u pb age spectra and ehft of detrital zircons in ca 1 85 ga metasedimentary rocks in the aravalli orogen and the inner lesser himalaya indicate similar sediment provenances and thus a geological connection between these two terranes during late palaeoproterozoic all together the data constrain a rapid succession of sedimentation metamorphism and subduction related magmatic activity and support the interpretation of an active geodynamic realm along the entire north indian margin at ca 1 85 ga comparison of detrital zircon data in conjunction with published paleomagnetic data from north india and other crustal blocks of the columbia supercontinent additionally suggest a close affinity of north india with madagascar the cathaysia block of south china and south korea during columbia times

recent geodetic results in the azores triple junction region gps global positioning system observations started to be carried out in the azores region under the scope of the tango transatlantic network for geodesy and oceanography project in 1988 the measurements carried out between 1993 and 2000 five campaigns on nine gps sites one per island were reprocessed using two state of the art software packages different methodologies were applied to compute each campaign solution and the derived velocity field the velocity fields including the motions of two permanent stations recently installed in the azores were computed within the most recent geodetic reference frame itrf2000 international terrestrial reference frame solution 2000 they are compared with the motions of the stable rigid tectonic plates using as reference deos2k a global tectonic model developed using geodetic data the relative motions between the western and central groups of islands yield to evaluate the opening rate of the mid atlantic ridge boundary between the north american plate and the eurasian and african plates concerning the boundary between the eurasian and african plates the motion of the tango sites in the central and eastern groups clearly identifies the transition pattern between those two plates two of the sites are considered to be located in the stable part of these plates whereas the remaining five are within the deformation region of the eurasia africa boundary the conclusions are analyzed in view of the different deformation models derived from geodynamic or geophysical data that have been proposed for the region

continuous gps measurements of postglacial adjustment in fennoscandia 1 geodetic results 1 data collected under the auspices of the bifrost gps project yield a geographically dense suite of estimates of present day three dimensional 3 d crustal deformation rates in fennoscandia johansson et al 2002 a preliminary forward analysis of these estimates milne et al 2001 has indicated that models of ongoing glacial isostatic adjustment gia in response to the final deglaciation event of the current ice age are able to provide an excellent fit to the observed 3 d velocity field in this study we revisit our previous gia analysis by considering a more extensive suite of forward calculations and by performing the first formal joint inversion of the bifrost rate estimates to establish insight into the physics of the gia response in the region we begin by decomposing a forward prediction into the three contributions associated with the ice ocean and rotational forcings from this analysis we demonstrate that recent advances in postglacial sea level theory in particular the inclusion of rotational effects and improvements in the treatment of the ocean load in the vicinity of an evolving continental margin involve peak signals that are larger than the observational uncertainties in the bifrost network the forward analysis is completed by presenting predictions for a pair of fennoscandian ice histories and an extensive suite of viscoelastic earth models the former indicates that the bifrost data set provides a powerful discriminant of such histories the latter yields bounds on the assumed constant upper and lower mantle viscosity nu um nu lm specifically we derive a 95 confidence interval of 5 x 10 20 less than or equal to nu um less than or equal to 10 21 pa s and 5 x 10 21 less than or equal to nu lm less than or equal to 5 x 10 22 pa s with some preference for elastic lithospheric thickness in excess of 100 km the main goal of the bayesian inverse analysis is to estimate the radial resolving power of the bifrost gps data as a function of depth in the mantle assuming a reasonably accurate ice history we demonstrate that this resolving power varies from similar to 200 km near the base of the upper mantle to similar to 700 km in the top portion of the lower mantle we conclude that the bifrost data are able to resolve structure on radial length scale significantly smaller than a single upper mantle layer however these data provide little constraint on viscosity in the bottom half of the mantle finally elements of both the forward and inverse analyses indicate that radial and horizontal velocity estimates provide distinct constraints on mantle viscosity

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

extent and duration of the 2003 cascadia slow earthquake 1 inversion of continuous gps measurements from the pacific northwest show the 2003 cascadia slow earthquake to be among the largest of ten transients recognized here twelve stations bracketing slow slip indicate transient slip propagated bi directionally from initiation in the southern puget basin reaching 300 km along strike over a period of seven weeks this event produced for the first time resolvable vertical subsidence and horizontal displacement reaching six mm in southern washington state inverted for non negative thrust slip a maximum of 3 8 cm of slip is inferred centered at 28 km depth near the sharp arch in the subducting juan de fuca plate nearly all slip lies shallower than 38 km inverted slip shows a total moment release equal to mw 6 6 and a high degree of spatial localization rather than near uniform slip this suggests rupture concentrated along asperities holds for slow earthquakes as well as conventional events

plate motion and crustal deformation estimated with geodetic data from the global positioning system we use geodetic data taken over four years with the global positioning system gps to estimate 1 motion between six major plates and 2 motion relative to these plates of ten sites in plate boundary zones the degree of consistency between geodetic velocities and rigid plates requires the one dimensional standard errors in horizontal velocities to be 2 mm yr each of the 15 angular velocities describing motion between plate pairs that we estimate with gps differs insignificantly from the corresponding angular velocity in global plate motion model nuvel 1a which averages motion over the past 3 m y the motion of the pacific plate relative to both the eurasian and north american plates is observed to be faster than predicted by nuvel 1a supporting the inference from very long baseline interferometry vlbi that motion of the pacific plate has sped up over the past few m y the eurasia north america pole of rotation is estimated to be north of nuvel 1a consistent with the independent hypothesis that the pole has recently migrated northward across northeast asia to near the lena river delta victoria which lies above the main thrust at the cascadia subduction zone moves relative to the interior of the overriding plate at 30 of the velocity of the subducting plate reinforcing the conclusion that the thrust there is locked beneath the continental shelf and slope

initial results from wing the continuous gps network in the western pacific area to investigate tectonic deformation in the western pacific a continuous gps tracking network has been established and named the western pacific integrated network of gps wing between 1995 and march 1997 we establised ten new sites data for the period july 1995 to october 1996 were analyzed together with data from international gps service for geodynamics igs global sites to estimate daily coordinates a fiducial free approach was used to obtain the most accurate baseline estimates to fix the estimated coordinates to the terrestrial reference frame the tsukuba igs site is assumed to be moving westward relative to the stable eurasian continent at 2 cm yr according to heki s 1996 estimate we find that 1 velocities of sites well within oceanic plates are in good agreement with rigid plate motion models 2 sites close to plate boundaries are all affected by the deformation at those boundaries among which back arc rifting spreading is clearly visible at the mariana and okinawa troughs 3 sites in eastern asia are moving east to east southeast relative to the stable eurasian continent suggesting long distance effects of the northward collision of india with asia

geodetic teleseismic and strong motion constraints on slip from recent southern peru subduction zone earthquakes we use seismic and geodetic data both jointly and separately to constrain coseismic slip from the 12 november 1996 m w 7 7 and 23 june 2001 m w 8 5 southern peru subduction zone earthquakes as well as two large aftershocks following the 2001 earthquake on 26 june and 7 july 2001 we use all available data in our inversions gps interferometric synthetic aperture radar insar from the ers 1 ers 2 jers and radarsat 1 satellites and seismic data from teleseismic and strong motion stations our two dimensional slip models derived from only teleseismic body waves from south american subduction zone earthquakes with m w 7 5 do not reliably predict available geodetic data in particular we find significant differences in the distribution of slip for the 2001 earthquake from models that use only seismic teleseismic and two strong motion stations or geodetic insar and gps data the differences might be related to postseismic deformation or more likely the different sensitivities of the teleseismic and geodetic data to coseismic rupture properties the earthquakes studied here follow the pattern of earthquake directivity along the coast of western south america north of 5 s earthquakes rupture to the north south of about 12 s directivity is southerly and in between earthquakes are bilateral the predicted deformation at the arequipa gps station from the seismic only slip model for the 7 july 2001 aftershock is not consistent with significant preseismic motion

contribution of glacial isostatic adjustment to the geocenter motion abstract the geocenter motion describes the surface net displacement of the entire solid earth with respect to the center of mass of the entire earth including surface masses therefore it resembles an integrative quantity of surface displacement and mass redistribution inside the earth as well as at its surface seasonal variations of this quantity are understood to originate mainly from mass redistribution in the water cycle in contrast a secular trend of the geocenter motion is possible to result also from the dynamics of the earth s interior one mechanism inducing a secular geocenter motion is the glacial isostatic adjustment describing the deformation and mass redistribution in the earth s interior due to glaciations during the pleistocene focusing on this contribution we compute the geocenter motion from the displacement and gravity potential fields calculated for a spherical self gravitating incompressible and viscoelastic earth model loaded by the last pleistocene glacial cycle we discuss the fluid core approximation usually adopted and assess the influence of a list of modelling parameters which are the upper and lower mantle viscosity lithosphere thickness and glaciation history we find a rather robust geocenter motion with respect to parameter variations which is directed towards northeast canada and shows velocities that vary between 0 1 and 1 mm yr depending on the adopted earth model and glaciation history parameterizations

gps measurement of relative motion of the cocos and caribbean plates and strain accumulation across the middle america trench global positioning system gps measurements in 1988 and 1991 on cocos island cocos plate san andres island caribbean plate and liberia caribbean plate mainland costa rica provide an estimate of relative motion between the cocos and caribbean plates the data for cocos and san andres islands both located more than 400 km from the middle america trench define a velocity that is equivalent within two standard errors 7 mm yr rate 5 degrees azimuth to the nuvel 1 plate motion model the data for liberia 120 km from the trench define a velocity that is similar in azimuth but substantially different in rate from nuvel 1 the discrepancy can be explained with a simple model of elastic strain accumulation with a subduction zone that is locked to a relatively shallow 20 z 5 km depth

sub milliarcsecond determination of pole position using global positioning system data the determination of pole position variations from the analysis of 23 days of global positioning system gps data continuously collected with a globally distributed 21 station network is discussed the comparison of the estimated pole positions from these data with results from 11 very long baseline interferometry vlbi experiments conducted during this same interval yields weighted root mean square differences about the mean differences of 0 5 mas for both x and y pole position estimates from an analysis using single day arcs and 1 0 and 0 8 mas from an analysis using three weekly multiday arcs these results are of sufficient quality that gps could provide an alternative technique to vlbi and satellite laser ranging for regular monitoring of high time resolution variations in the position of the earth s rotation axis

seismic cycle and plate margin deformation in costa rica gps observations from 1994 to 1997 global positioning system gps observations in costa rica from 1994 to 1997 reveal a complex pattern of motion consistent with the superposition of seismic cycle and secular plate margin deformation in the south velocity vectors are consistent with motion of the panama block plus postseismic deformation following the 1991 limon earthquake and interseismic strain due to partial locking of the middle america trench mat thrust in the northwest sites west of the volcanic arc are moving to the nw as a forearc sliver superimposed on this sliver motion are vertical and horizontal interseismic deformations from the adjacent nicoya segment of the mat we apply two different inverse methods to understand the source of the seismic strain in nw costa rica we compare fault locking models derived using a singular value decomposition inversion with that of a simulated annealing global optimization approach both methods yield similar models for partial locking of the thrust interface beneath the nicoya peninsula our results define an area of nearly fully locked fault beneath the outer coast of the southern portion of the peninsula with somewhat lower coupling beneath the northern half and with low coupling elsewhere these initial results show the promise for detailed imaging of the locked portion of a thrust interface responsible for future large subduction zone earthquakes

inversion of earth s changing shape to weigh sea level in static equilibrium with surface mass redistribution 1 we develop a spectral inversion method for mass redistribution on the earth s surface given geodetic measurements of the solid earth s geometrical shape using the elastic load love numbers first spectral coefficients are geodetically estimated to some degree spatial inversion then finds the continental surface mass distribution that would force geographic variations in relative sea level such that it is self consistent with an equipotential top surface and the deformed ocean bottom surface and such that the total ocean plus continental mass load has the same estimated spectral coefficients applying this theory we calculate the contribution of seasonal interhemispheric degree 1 mass transfer to variation in global mean sea level and nonsteric static ocean topography using published gps results for seasonal degree 1 surface loading from the global igs network our inversion yields ocean continent mass exchange with annual amplitude 2 92 0 14 1015 kg and maximum ocean mass on 25 august 3 days after correction for the annual variation in global mean vertical deformation of the ocean floor 0 4 mm amplitude we find geocentric sea level has an amplitude of 7 6 0 4 mm consistent with topex poseidon results minus steric effects the seasonal variation in sea level at a point strongly depends on location ranging from 3 to 19 mm the largest being around antarctica in mid august seasonal gradients in static topography have amplitudes of up to 10 mm over 5000 km which may be misinterpreted as dynamic topography peak continental loads occur at high latitudes in late winter at the water equivalent level of 100 200 mm

precise determination of earth s center of mass using measurements from the global positioning system global positioning system gps data from a worldwide geodetic experiment were collected during a 3 week period early in 1991 geocentric station coordinates were estimated using the gps data thus defining a dynamically determined reference frame origin which should coincide with the earth center of mass or geocenter the 3 week gps average geocenter estimates agree to 7 13 cm with geocenter estimates determined from satellite laser ranging a well established technique the rms of daily gps geocenter estimates were 4 cm for x and y and 30 cm for z

a numerical model to simulate snow cover stratigraphy for operational avalanche forecasting laws of snow metamorphism have been introduced in a numerical model which simulates the evolution of temperature density and liquid water profiles of snow cover as a function of weather conditions to establish these laws the authors have summarized previous studies on temperature gradient and on wet snow metamorphism and they have also conducted metamorphism experiments on dry or wet fresh snow samples an original formalism was developed to allow a description of snow with parameters evolving continuously throughout time the introduction of laws of metamorphism has improved significantly the derivation of the settlement of internal layers and of snow covered albedo which depend on the simulated stratigraphy i e the type and size of snow grains of different layers of the snow cover the model was tested during a whole winter season without any re initialization comparison between the simulated characteristics of the snow cover and the observations made in the field are described in detail the model proved itself to be very efficient in simulating accurately the evolution of the snow cover stratigraphy throughout the whole winter season

deformation of jamaica and motion of the gonâve microplate from gps and seismic data summary we use velocities from 20 gps sites on the island of jamaica and seismic data from the jamaican seismic network to quantify motion of the proposed gonave microplate and study deformation and earthquake hazard in jamaica all 20 jamaican gps sites move significantly relative to both the caribbean and north american plates thereby confirming the existence of the gonave microplate in a caribbean plate reference frame the fastest site velocities in jamaica are 8 1m m yr 1 representing a minimum estimate for the rate of gonave caribbean plate motion we estimate a firm upper limit of 13 1m m yr 1 for gonave caribbean plate motion assuming that additional elastic or permanent deformation occurs north of jamaica beyond the reach of our gps network the range of estimates for gonave caribbean plate motion exceeds the 3 7m m yr 1 range of geologically derived rates for post 10 ma fault slip in jamaica suggesting that motion has either increased relative to the long term deformation rate or that estimates of the long term deformation rate are too slow minimum and maximum rates for gonave north america plate motion are 6 1m m yr 1 and 11 1m m yr 1 based on the differences between the estimated gonave caribbean rates and a recent gps based estimate of 19 3 1m m yr 1 of caribbean north american plate motion in jamaica these are slower than 15 20 mm yr 1 published estimates of the long term seafloor spreading rate across the cayman spreading centre which records gonave north american plate motion our observations are thus consistent with a model in which gonave caribbean plate motion has increased through time while gonave north america plate motion has decreased possibly reflecting a progressive transfer of slip from plate boundary structures that accommodate gonave north america motion to faults that carry gonave caribbean plate motion in jamaica gps site directions in both the caribbean and north american plate reference frames are parallel to the caribbean north america plate slip direction and are only 10 20 different from the azimuths of the island s major strike slip faults the mean p and t axes for 48 earthquakes since 1941 have near horizontal plunges and are oriented 45 from the predicted plate slip direction the kinematic and seismic data thus indicate that deformation on the island is dominated by left lateral shear along largely e w trending strike slip faults relative to the caribbean plate the jamaican gps velocities exhibit a nearly monotonic increase in site velocities from south to north along a transect orthogonal to the island s major e w faults this velocity gradient likely reflects the accumulation of elastic strain due to frictional locking of the major e w faults velocities however also increase monotonically from the wsw to ene along a transect orthogonal to the island s numerous nnw striking faults consistent with the accumulation of significant elastic shortening along those faults and supportive of an interpretation of those faults as restraining bends seismic hazard assessment based on the gps derived deformation budget likely maximum fault rupture lengths and the historical seismic record suggests approximate repeat times of one to several centuries for earthquakes of maximum magnitudes of m w 7 0 7 3 the strain that has accumulated since the destructive 1692 earthquake near the capital city of kingston is presently sufficient to release a m w 7 2 earthquake in eastern jamaica

deformation of mexico from continuous gps from 1993 to 2008 1 we combine the velocities of 13 continuous global positioning system stations from mexico and 448 north american plate stations to better understand deformation and earthquake cycle effects in mexico velocities estimated at the mexican sites from high quality gps data collected since 2003 show no evidence for a previously reported eastward bias at sites in and near the yucatan peninsula the new velocities are compared to the predictions of two models one in which all motion in mexico is attributed to north american plate motion and the second of which attributes site motions to a combination of plate motion and the elastic effects of frictional coupling along the mexican subduction zone and faults in the gulf of california the second model fits the velocities within their estimated uncertainties mainland mexico thus moves with the north american plate to within 1 mm per year and undergoes elastic interseismic deformation far into its interior two stations inland from the guerrero and oaxaca segments of the mexican subduction zone have alternated between several year long periods of landward motion and several month long periods of trenchward motion frequently since 1993 consistent with previously described repeating transient slip events along the subduction interface the motions of two stations inland from the rivera plate subduction zone are dominated by the coseismic and postseismic effects of the m 8 0 9 october 1995 colima jalisco earthquake and m 7 5 22 january 2003 tecoman earthquake offshore from western mexico

continuous monitoring of surface deformation at long valley caldera california with gps continuous global positioning system gps measurements at long valley caldera an active volcanic region in east central california have been made on the south side of the resurgent dome since early 1993 a site on the north side of the dome was added in late 1994 special adaptations for autonomous operation in remote regions and enhanced vertical precision were made the data record ongoing volcanic deformation consistent with uplift and expansion of the surface above a shallow magma chamber measurement precisions 1 standard error for absolute position coordinates i e relative to a global reference frame are 3 4 mm north 5 6 mm east and 10 12 mm vertical using 24 hour solutions corresponding velocity uncertainties for a 12 month period are about 2 mm yr in the horizontal components and 3 4 mm yr in the vertical component high precision can also be achieved for relative position coordinates on short 10 km baselines using broadcast ephemerides and observing times as short as 3 hours even when data are processed rapidly on site comparison of baseline length changes across the resurgent dome between the two gps sites and corresponding two color electronic distance measurements indicates similar extension rates within error 2 mm yr once we account for a random walk noise component in both systems that may reflect spurious monument motion both data sets suggest a pause in deformation for a 3 5 month period in mid 1995 when the extension rate across the dome decreased essentially to zero three dimensional positioning data from the two gps stations suggest a depth 5 8 1 6 km and location west side of the resurgent dome of a major inflation center in agreement with other geodetic techniques near the top of a magma chamber inferred from seismic data gps systems similar to those installed at long valley can provide a practical method for near real time monitoring and hazard assessment on many active volcanoes

geodesy using the swedish permanent gps network effects of signal scattering on estimates of relative site positions this paper presents results from a study of elevation angle dependent systematic effects on estimates of relative site positions within the swedish permanent global positioning system gps network two months of data from 16 sites have been analyzed with three different elevation cutoff angles namely 10 15 and 20 we present offsets between these solutions and demonstrate that estimates of the vertical component of several baselines strongly depend on the minimum elevation angle elevation cutoff angle of the data analyzed offsets of 22 3 1 6 mm in the vertical component are evident when the elevation cutoff angle is changed from 10 to 20 we investigate these offsets and conclude that a significant part is due to differential phase errors caused by scattering from structures associated with the mounting of the antenna to the pillar and with the pillar itself the horizontal components of baseline are less affected we found however that the offsets in the horizontal components increase with baseline length for the longest baselines 1500 km offsets of more than 5 mm are evident in the north component when the elevation cutoff angle is changed from 10 to 20 these offsets are most likely due to differential phase errors caused by nonuniform antenna phase patterns an effect that presumably increases with baseline length and which also might increase because of scattering from the pillars and the antenna mounts we identify the scattering structure and reduce associated errors in the vertical component of baseline to a significant degree on one of the sites by using microwave absorbing material the results presented are of importance for those analyzing data from existing networks and for those who intend to establish permanent gps geodetic networks

kinematics of the pacific north america plate boundary zone northern california we measured motions of 54 sites in an east west transect across northern california at 38 40 north by global positioning system gps observations over a 4 year we estimate the total slip rate on the san andreas fault system to be 39 6 0 6 1 5 mm yr 68 6 upper and lower confidence intervals from a nonlinear inversion are indicated by superscripts and subscripts slip rates on the individual faults are determined less precisely due to the high correlations between the estimated parameters our best fitting model fits the fault parallel velocities with a mean square error of 1 04 and the following estimated fault slip rates all in mm yr san andreas 17 4 3 1 2 5 ma acama 13 9 2 8 4 1 and bartlett springs 8 2 1 9 2 1 the data are fit best by models in which the san andreas fault is locked to 14 9 7 1 12 5 km the ma acama fault locked to 13 4 4 8 7 4 km except for shallow creep in the upper 5 km and the bartlett springs fault creeping at all depths the ma acama fault most likely poses a significant seismic hazard as it has a high slip rate and has accumulated a slip deficit large enough to generate a magnitude 7 earthquake we find little evidence for contraction across coast ranges except at western edge of great valley where 1 3 mm yr of shortening is permitted by the data no strain is observed within the great valley or sierra nevada except that associated with right lateral strike slip on the san andreas fault system this is consistent with models of the pacific north america plate boundary zone in which the relative plate motion is partitioned into two domains one strike slip and one dominantly extensional separated by the elastically deforming sierra nevada great valley block

effects of atmospheric pressure loading and seven parameter transformations on estimates of geocenter motion and station heights from space geodetic observations 1 variations in fluid loads such as the oceans and the atmosphere deform the surface of the earth the accuracy of station coordinates in particular heights that can be estimated depends on how well one can separate these surface deformations from the associated translational motion between the center of mass of the solid earth and the total earth cm we applied simulated atmospheric pressure loading effects to the coordinates of sites in the cm frame to explore to what level of accuracy both geocenter motion and accurate station coordinates can actually be recovered from geodetic analyses we found that standard seven parameter transformations three rotations three translations scale generally recover about 80 of the geocenter motion however the inclusion of a scale factor permits the aliasing of surface loading deformation introducing scale errors of up to 0 3 ppb and daily height errors as large as 4 mm this limits the geophysical studies that can be performed accurately using the results of geodetic analyses where the magnitudes of the signals are small e g tectonic movement of tide gauges uplift rates for interpreting glacial isostatic adjustment the quality of the geodetic results is extremely sensitive to the number and distribution of sites used to estimate the transformations and becomes worse when regional rather than global sets of sites are used if the scale factor parameter is omitted then the amount of aliasing of surface loading effects is reduced considerably and more accurate site velocities and geocenter motion estimates are achieved

vertical land motion in the southwest and central pacific from available gnss solutions and implications for relative sea levels s u m m a r y coastal populations are impacted by relative sea level variations which consist both of absolute sea level variations and of vertical land motions this paper focuses on the southwest and central pacific region a recognized vulnerable region to sea level rise and where a large range of vertical land motion dynamics is observed we analyse vertical displacement rates obtained from global navigation satellite systems gnss by different analysis centres we study the role played by modelled parameters such as step discontinuities due to equipment changes earthquakes etc in the position time series analysis we propose a new modelling approach based on a joint inversion of gnss position time series from different analysis centres the final uncertainty on the vertical land motion rates is estimated as a combination of the uncertainty due to the gnss data processing itself and the uncertainty due to the stability of the reference frame in which the gnss data are expressed we find that the dominant trend in the southwest and central pacific is a moderate subsidence with an average rate of 1 1 mm yr 1 but significant variations are observed with displacement rates varying from an uplift of 1 6 0 3 mm yr 1 to a subsidence of 5 4 0 3 mm yr 1 taking into account the geodynamic context we assess for each station the relevance of current estimates of linear vertical displacement rate and uncertainty for forecasting future coastal sea levels

long term strain oscillations related to the hydrological interaction between aquifers in intra mountain basins a case study from apennines chain italy abstract we analyze the multiyear strain cycle of a network of continuous gps stations in the l aquila intra mountain basin in central apennines italy the basin is bounded by two aquifers nuria velino and gran sasso hosted in two tectonically active mountain ranges all stations show coherent displacements mostly in the horizontal plane and orthogonal to the normal fault zones of the apennine mountain range the displacement repeats back and forth roughly every 4 5 years with elongation up to 6 mm the deformation occurs in the region bounded by the two aquifers and the displacement amplitude decreases with distance as predicted by two tensile sources acting in an elastic medium we interpret this type of deformation as induced by the opening of pre existing fractures related to two different fault systems as a response to hydrostatic pressure variations the strain cycle follows the average multiyear rainfall cycle and foresees a dilatation phase during high rainy seasons and a contraction during drier periods the estimated depth of the equivalent tensile sources ranges from 1 2 to 1 5 km affecting stations at distances up to 20 km away gps data show the cumulated movement induced by the two nearby aquifers and suggest a mutual interaction in the elastic space related to the different average annual rainfall and effective infiltration we fit two tensile sources located along the main faults affecting the aquifers the eastern source corresponds to the major active fault system affecting the gran sasso range while the western one includes the sub parallel active faults of the mt ocre in the nuria velino range where carbonate rocks show a higher structural permeability and effective infiltration these fault systems affect jurassic miocene limestones and dolomites inducing parallel fracturation style of the rock matrix and favoring a strong anisotropy allowing a prevalent lateral expansion as a reaction to pore pressure variations the recorded hydrological signal may hamper other geophysical signals in gps time series thus the measure of tectonic strains requires a careful mapping and modeling of major aquifers

relative motions of the australian pacific and antarctic plates estimated by the global positioning system gps measurements spanning 3 years have been used to determine velocities for 7 sites on the australian pacific and antarctic plates the site velocities agree with both plate model predictions and other space geodetic techniques we find no evidence for internal deformation of the interior of the australian plate wellington new zealand located in the australian pacific plate boundary zone moves 20 5 mm yr west southwest relative to the australian plate its velocity lies midway between the predicted velocities of the two plates relative euler vectors for the australia antarctica and pacific antarctica plates agree within one standard deviation with the nuvel 1a predictions

kalref a kalman filter and time series approach to the international terrestrial reference frame realization the current international terrestrial reference frame is based on a piecewise linear site motion model and realized by reference epoch coordinates and velocities for a global set of stations although linear motions due to tectonic plates and glacial isostatic adjustment dominate geodetic signals at today s millimeter precisions nonlinear motions due to earthquakes volcanic activities ice mass losses sea level rise hydrological changes and other processes become significant monitoring these sometimes rapid changes desires consistent and precise realization of the terrestrial reference frame trf quasi instantaneously here we use a kalman filter and smoother approach to combine time series from four space geodetic techniques to realize an experimental trf through weekly time series of geocentric coordinates in addition to secular periodic and stochastic components for station coordinates the kalman filter state variables also include daily earth orientation parameters and transformation parameters from input data frames to the combined trf local tie measurements among colocated stations are used at their known or nominal epochs of observation with comotion constraints applied to almost all colocated stations the filter smoother approach unifies different geodetic time series in a single geocentric frame fragmented and multitechnique tracking records at colocation sites are bridged together to form longer and coherent motion time series while the time series approach to trf reflects the reality of a changing earth more closely than the linear approximation model the filter smoother is computationally powerful and flexible to facilitate incorporation of other data types and more advanced characterization of stochastic behavior of geodetic time series

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

accuracy of high rate gps for seismology 1 we built a device for translating a gps antenna on a positioning table to simulate the ground motions caused by an earthquake the earthquake simulator is accurate to better than 0 1 mm in position and provides the ground truth displacements for assessing the technique of high rate gps we found that the root mean square error of the 1 hz gps position estimates over the 15 min duration of the simulated seismic event was 2 5 mm with approximately 96 of the observations in error by less than 5 mm and is independent of gps antenna motion the error spectrum of the gps estimates is approximately flicker noise with a 50 decorrelation time for the position error of 1 6 s we find that for the particular event simulated the spectrum of surface deformations exceeds the gps error spectrum within a finite band more studies are required to determine whether a generally optimal bandwidth exists for a target group of seismic events

geocenter location and variations in earth orientation using global positioning system measurements we have studied the use of global positioning system gps ground and flight tracking data to measure short period earth orientation variations and changes in earth s center of mass location the geocenter ground based gps estimates of daily and subdaily changes in earth orientation presently show centimeter level precision comparisons between gps estimated earth rotation variations ut1 utc and those calculated from ocean tide models suggest that observed subdaily variations in earth rotation are dominated by oceanic tidal effects our preliminary gps estimates for geocenter location from a 3 week experiment agree with an independent satellite laser ranging estimates to 10 15 cm covariance analysis predicts that temporal resolution of gps estimates for earth orientation and geocenter improves significantly when data collected from low earth orbiting satellites as well as from ground sites are combined the low earth gps tracking data enhance the accuracy and resolution for measuring high frequency global geodynamical signals over time scales less than 1 day low earth orbiters such as topex poseidon carrying gps flight receivers will provide opportunities to demonstrate these enhancements

gps applications for geodynamics and earthquake studies geodetic measurements obtained with the global positioning system gps are increasingly more widely applied in geophysical studies in this paper we review the changes to the technology of gps geodesy over the last five years that are responsible for this increased applicability we survey geophysical investigations employing gps to measure coseismic postseismic and interseismic deformation plate motion and crustal deformation at plate boundaries volcano deformation and the deformation associated with glacial isostatic adjustment and its application to sea level studies we emphasize the use of gps determinations for the modeling of this wide variety of geophysical phenomena we also discuss the recent advent of permanent gps networks for regional geophysical studies as well as the possible future of gps surveying in light of the recent advances

inflation of long valley caldera from one year of continuous gps observations a permanent global positioning system receiver at casa diablo hot springs long valley caldera california was installed in january 1993 and has operated almost continuously since then the data have been transmitted daily to the jet propulsion laboratory for routine analysis with data from the fiducial laboratories for an international natural sciences network flinn by the jpl flinn analysis center results from these analyses have been used to interpret the on going deformation at long valley with data excluded from periods when the antenna was covered under 2 5 meters of snow and from some periods when anti spoofing was enforced on the gps signal the remaining time series suggests that uplift of the resurgent dome of long valley caldera during 1993 has been 2 5 1 1 cm yr and horizontal motion has been 3 0 0 7 cm yr at s53w in a no net rotation global reference frame or 1 5 0 7 cm yr at s14w relative to the sierra nevada block these rates are consistent with uplift predicted from frequent horizontal strain measurements spectral analysis of the observations suggests that tidal forcing of the magma chamber is not a source of the variability in the 3 dimensional station location these results suggest that remotely operated continuously recording gps receivers could prove to be a reliable tool for volcano monitoring throughout the world