recovering seismic displacements through combined use of 1 hz gps and strong motion accelerometers retrieving displacement from seismic acceleration records is often difficult because unknown small baseline offsets in the acceleration time series will contaminate the doubly integrated record with large quadratic errors one hertz global positioning system gps position estimates and collocated seismic data are available from the 2003 m w 8 tokachi oki hokkaido earthquake after a process of correcting for possible misorientation of the seismic sensors an inversion method is used to simultaneously solve for ground displacement with both data sets as input constraints this inversion method takes into account the presence of unknown offsets in the acceleration record and the relatively large uncertainties in the estimated 1 hz gps positions in this study 117 channels of seismic data were analyzed only 5 of the time does the static displacement retrieved from traditional baseline correction processing without gps information agree with the absolute displacement measured with 1 hz gps to within the errors of the gps data in solving simultaneously for constrained displacements that agree with both the seismic and gps data sets an optimal solution was found that included only one or two step functions in the acceleration records potential explanations for the offsets are analyzed in terms of tilt of the sensor or electronic noise for nine stations clear misorientations of the seismic sensors of more than 20 deg from the reported orientation were found for this size event the 30 sec sampled gps solutions were also a sufficient constraint for establishing the offset errors and recovering reliable displacements the results significantly extend the frequency band over which accelerometer data are reliable for source inversion studies online material plots of constrained seismograms with metadata

love wave dispersion in central north america determined using absolute displacement seismograms from high rate gps 1 we use seismic array processing of high rate gps hrgps displacement time series from the great 2004 mw 9 sumatra andaman earthquake recorded at over 90 nonuniformly distributed hrgps stations in central north america to determine the fundamental love wave phase velocity dispersion curve there these measurements were performed using frequency domain beam forming which we show reduces the effects of gps multipath and common mode noise on the measurement of surface wave phase velocity and azimuth our hrgps based results for surface wave phase velocity agree well with those obtained from 28 broadband seismometers between periods of 20 to 300 s by separating waves based on their apparent velocity beam forming supports the simple model for relative displacement hrgps time series as being the difference between the reference and kinematic station s absolute displacements beam forming also demonstrates that for differential gps processing the infinite apparent velocity beam of an array is composed of the sum of common mode noise and the reference station s absolute displacements multipath and noise we show the infinite apparent velocity beam which we call the generalized spatial filter is similar to the spatial filter commonly used to remove common mode noise from hrgps seismograms and can be used to produce absolute displacement time series for the kinematic stations with reduced common mode noise beam forming also suggests a filtering method complimentary to sidereal filtering to produce gps multipath reduced hrgps time series

very high rate 10 hz gps seismology for moderate magnitude earthquakes the case of themw6 3 l aquila central italy event accepted for publication in journal of geophysical research copyright 2010 american geophysical union

gps seismology application to the 2002 mw 7 9 denali fault earthquake abstract the 2002 denali fault alaska earthquake m w 7 9 caused one or more components of most broadband seismometers in western canada to clip yet did not trigger strong motion instruments thus leaving a substantial gap in the seismic record of this event however the large amplitude surface waves generated by this event were well recorded by the global positioning system gps in the same region out to epicentral distances of more than 3000 km in this article we explore the capabilities of gps seismology specifically how the relative strengths of gps and seismic data sets can be exploited in order to more effectively study earthquake source characteristics and wave propagation effects high rate 1 hz gps data from 23 stations throughout western north america have been analyzed to derive displacement waveforms for this event and the impact of instrumentation gps receiver model and error reduction strategy modified sidereal and spatial filtering on the noise characteristics of displacement time series at each gps site was assessed after applying error reduction methods to gps displacements the final average noise floors of 0 5 cm in the horizontal and 1 5 cm in the vertical indicate that large dynamic displacements are observable by gps we validate the gps displacements by comparing broadband seismic recordings integrated to displacement with gps recordings for four effectively colocated sets of instruments we show excellent agreement between the unclipped seismic and gps recordings of the surface waves from the denali earthquake over the period range of 10 50 sec and for ground displacements exceeding about 1 0 cm thus a large gps displacement data set is now available for western north america an area where records of this event were previously missing or incomplete the final gps seismograms are archived at incorporated research institutions for seismology iris for public use in future studies of the 2002 denali earthquake

modeling the rupture process of the 2003 september 25 tokachi oki hokkaido earthquake using 1 hz gps data received 10 september 2004 accepted 3 october 2004 published 3 november 2004 1 high rategpshasthepotentialtorecoverbothdynamic and static displacements accurately we analyze 1 hz gps data recorded during the 2003 tokachi oki earthquake the 1 hz gps displacement waveforms show good agreement with integrated accelerometer records except for low frequency noise that are inherently present in integrated seismic records the gps waveforms were inverted to model the spatio temporal evolution of the fault slip during the rupture the slip is found to propagate downdip in the subduction zone with largest moment release 50 km northwest of the hypocenter the region of largest slip agrees in general with traditional seismic studies indicating that 1 hz gps can be used for finite fault studies the 1 hz gps slip model shows clearer contrast with afterslip distributions than those inferred from strong motion data possibly because 1 hz gps is more sensitive to cumulative slip distribution index terms 1294 geodesy and gravity instruments and techniques 7209 seismology earthquake dynamics and mechanics 7212 seismology earthquake ground motions and engineering citation miyazaki s k m larson k choi k hikima k koketsu p bodin j haase g emore and a yamagiwa 2004 modeling the rupture process of the 2003 september 25 tokachi oki hokkaido earthquake using 1 hz gps data geophys res lett 31 l21603 doi 10 1029 2004gl021457

array analysis using circular wave front geometry an application to locate the nearby seismo volcanic source summary the zero lag cross correlation technique used for array analysis in the hypothesis of plane waves has been modified to allow the wave front to be circular synthetic tests have been performed to check the capability of the method which returns the input test data when the source array distances are not greater than two or three times the array aperture for this distance range the method furnishes an estimate of the apparent velocity and the epicentral coordinates of the source for more distant sources the method becomes equivalent to that based on the planar wave approximation which gives an estimate of the backazimuth to the source and the apparent velocity the method has been applied to seismic data recorded at the active volcano located at deception island antarctica 35 volcanic long period events occurring in a small swarm were selected results show that the epicentres are close to the array between 0 4 and 2 km and aligned in a sw direction in agreement with one of the main directions of the fracture system of deception volcano

using 1 hz gps data to measure deformations caused by the denali fault earthquake the 3 november 2002 moment magnitude 7 9 denali fault earthquake generated large permanent surface displacements in alaska and large amplitude surface waves throughout western north america we find good agreement between strong ground motion records integrated to displacement and 1 hertz global positioning system gps position estimates collected 140 kilometers from the earthquake epicenter one hertz gps receivers also detected seismic surface waves 750 to 3800 kilometers from the epicenter whereas these waves saturated many of the seismicinstruments in the same region high frequency gps increases the dynamic range and frequency bandwidth of ground motion observations providing another tool for studying earthquake processes

the 2011 magnitude 9 0 tohoku oki earthquake mosaicking the megathrust from seconds to centuries geophysical observations from the 2011 moment magnitude m w 9 0 tohoku oki japan earthquake allow exploration of a rare large event along a subduction megathrust models for this event indicate that the distribution of coseismic fault slip exceeded 50 meters in places sources of high frequency seismic waves delineate the edges of the deepest portions of coseismic slip and do not simply correlate with the locations of peak slip relative to the m w 8 8 2010 maule chile earthquake the tohoku oki earthquake was deficient in high frequency seismic radiation a difference that we attribute to its relatively shallow depth estimates of total fault slip and surface secular strain accumulation on millennial time scales suggest the need to consider the potential for a future large earthquake just south of this event

an integrated global model of present day plate motions and plate boundary deformation summary in this paper we present a global model gsrm 1 of both horizontal velocities on the earth s surface and horizontal strain rates for almost all deforming plate boundary zones a model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field in our model we perform a least squares fit between model velocities and observed geodetic velocities as well as between model strain rates and observed geological strain rates model velocities and strain rates are interpolated over a spherical earth using bi cubic bessel splines we include 3000 geodetic velocities from 50 different mostly published studies geological strain rates are obtained for central asia only and they are inferred from quaternary fault slip rates for all areas where no geological information is included a priori constraints are placed on the style and direction but not magnitude of the model strain rate field these constraints are taken from a seismic strain rate field inferred from normalized focal mechanisms of shallow earthquakes we present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones generally the strain rate tensor field is consistent with geological and seismological data with the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs we find that in general there is a good agreement between the present day plate motions we obtain and longterm plate motions but a few significant differences exist the rotation rates for the indian arabian and nubian plates relative to eurasia are 30 13 and 50 per cent slower than the nuvel1a estimate respectively and the rotation rate for the nazca plate relative to south america is 17 per cent slower on the other hand caribbean north america motion is 76 per cent faster than the nuvel 1a estimate while crustal blocks in the india eurasia collision zone move significantly and self consistently with respect to bounding plates only a very small motion is predicted between the nubian and somalian plates by integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in for instance redefining a no net rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation

5hz gps seismology of the el mayor cucapah earthquake estimating the earthquake focal mechanism summary high rate 5hz gps records observed in the near field following the magnitude 7 2 el mayor cucapah earthquake that occurred in northern mexico on 2010 april 4 are compared with broad band seismograms the high rate gps displacement records are consistent with the twice integrated strong motion seismic records in the near field where broad band seismograms are clipped due to strong shaking agreement degrades at distances greater than about 150 km from the epicentre where displacement amplitudes approach the noise level of gps seismograms using high rate gps data the focal mechanism of the main shock is estimated and is shown to be consistent with teleseismic estimates the result is seen as confirmation that high rate gps observed at near field stations can be applied together with teleseismic seismometers to yield better information about earthquake rupture properties and parameters

a large slow slip event and the depth of the seismogenic zone in the south central alaska subduction zone abstract we modeled crustal deformation before during and after a slow slip event sse on the plate interface in southern alaska we divided the gps time series into three time periods before 1998 1998 to 2001 and 2001 2002 the first and last periods represent the steady deformation while the middle period represents the sse we found a stationary zone of 100 slip deficit in the shallow part of the seismogenic zone to depths of 25 30 km which we identify with the main asperity that ruptured in 1964 earthquake the sse occurs downdip of the asperity on a section that accumulated some slip deficit during the steady time periods during the sse 20 000 sq km of the plate interface slipped 10 cm for a cumulative moment magnitude of m w 7 2 the area of the sse did not have a significant slip in the 1964 earthquake compared to the slip of the main asperity we propose that between earthquakes this zone fails repeatedly in sses and remains at relatively low shear stress compared to the main asperity up dip of it

crustal motion in the southern andes 26 36 s do the andes behave like a microplate 1 a new global positioning system gps derived velocity field for the andes mountains 26 36 s allows analysis of instantaneous partitioning between elastic and anelastic deformation at the orogen s opposing sides adding an andes microplate to the traditional description of nazca south america plate convergence provides the kinematic framework for nearly complete explanation of the observed velocity field the results suggest the oceanic nazca boundary is fully locked while the continental backarc boundary creeps continuously at 4 5 mm yr the excellent fit of model to data 1 7 mm yr rms velocity misfit and the relative aseismicity of the upper crust in the interior andean region in comparison with its boundaries supports the notion that the mountains are not currently accruing significant permanent strains additionally the model implies permanent deformation is not accumulating throughout the backarc contractional wedge but rather that the deformation is accommodated only within a narrow deformational zone in the backarc

detection of arbitrarily large dynamic ground motions with a dense high rate gps network 1 we describe the detection of teleseismic surface waves from the 3 november 2002 mw 7 9 denali fault earthquake in alaska with a dense network of 1 hz gps stations in southern california about 3900 km from the event relative horizontal displacements with amplitudes in excess of 15 mm and duration of 700 seconds agree with integrated velocities recorded by nearby broadband seismometers with an rms difference of 2 3 mm the displacements are derived from independent 1 hz instantaneous positions demonstrating that a gps network can provide direct measurements of arbitrarily large dynamic and static ground horizontal displacements at periods longer than 1 s and amplitudes above 2 mm with an inherent precision signal to noise that improves indefinitely with amplitude without clipping and in real time high rate real time gps networks can enhance earthquake detection and seismic risk mitigation and support other applications such as intelligent transportation and civil infrastructure monitoring

detecting multiple surface waves excited by the 2011 tohoku oki earthquake from geonet observations abstract multiple surface waves circling the earth excited by the 2011 m w 9 0 tohoku oki earthquake were well recorded by both global and regional broadband bb seismometer networks in this study we explore the ability of kinematic solutions of global positioning system gps observations from geonet to reveal the phases of multiple surface waves even though multipath effects and common mode errors are not reduced the wave packages of g 2 g 3 of love waves and r 2 r 3 of rayleigh waves are clearly identified from the raw gps displacement time series in the 100 500 s periods which show great coherency with bb seismograms in both amplitude and time the arrival times of these wave packages tally with the synthetic value by the group velocities from the global dispersion model we consider that kinematic solutions of continuous gps measurement can act as a supplementary tool for studying global surface wave dispersion

centroid moment tensor inversions using high rate gps waveforms displacement time series recorded by global positioning system gps receivers are a new type of near field waveformobservation of the seismic source we have developed an inversion method which enables the recovery of an earthquake s mechanism and centroid coordinates from such data our approach is identical to that of the classical centroid moment tensor cmt algorithm except that we forward model the seismic wavefield using a method that is amenable to the efficient computation of synthetic gps seismograms and their partial derivatives we demonstrate the validity of our approach by calculating cmt solutions using 1 hz gps data for two recent earthquakes in japan these results are in good agreement with independently determined source models of these events with wider availability of data we envisage the cmt algorithm providing a tool for the systematic inversion of gps waveforms as is already the case for teleseismic data furthermore this general inversion method could equally be applied to other near field earthquake observations such as those made using accelerometers

millimeter level ultra long period multiple earth circling surface waves retrieved from dense high rate gps network abstract high rate gps networks have proven to be capable of continuously recording strong ground motion which is valuable for studying earthquake rupture processes and seismic hazard mitigation previous studies of high rate gps usually resolved dynamic ground displacements of some major seismic phases stronger than a few millimeters in this study we explore the feasibility of retrieving much weaker ground motions sub millimeter in long duration records by stacking high rate gps network we processed data of the 2011 tohoku oki earthquake recorded by more than 600 high rate gps stations of the plate boundary observatory pbo and analyzed kinematic displacement results with seismic array methods from these high rate gps seismograms we identified abundant seismic phases not only including clear body waves such as multiple s waves s ss sss ssss traveling along minor major great circle arc and ssssss beyond 360 degrees but also the r1 r5 rayleigh waves and g1 g6 love waves some of which travel around the earth multiple times many of these seismic phases have not been reported by previous high rate gps studies the group velocity dispersion curves extracted from multiple earth circling love waves of high rate gps are consistent with those of broadband seismic records in the period from 150 to 600 s which can sample the mantle structure down to top of the lower mantle thus important for understanding interaction between upper mantle and lower mantle so the dense high rate gps networks should be useful for deep mantle research as an additional valuable dataset with the development of multi system gnss and the more precise modeling of error sources high rate gnss data should have great potential for accurately detecting more geodynamic processes with much wider bandwidth in geoscience studies

loading mechanism and scaling relations of large interplate earthquakes we have done a numerical simulation of tectonic loading at transform plate boundaries with a lithosphere asthenosphere coupling model subject to steady relative plate motion in this model a seismic fault is represented by a locked patch with a finite length on an infinitely long vertical dislocation surface cutting the entire lithosphere through the numerical simulation we have obtained the following results stress accumulation on the fault is partly due to viscous drag at the base of the lithosphere base loading and partly due to dislocation pile ups at horizontal edges of the fault edge loading if the viscosity of the asthenosphere is less than 1018 pa s the base loading is not effective since its rate exponentially decays very soon if the viscosity of the asthenosphere is greater than 1020 pa s both types of loading are effective and then the stress accumulation rate in the early stage of loading is formally written as d dt vpl a bl where vpl is a rate of relative plate motion and l is a fault length when the fault length l is small the effect of edge loading the second term is dominant and the stress accumulation rate is in proportion to the inverse of l when the fault length l is large the effect of base loading the first term becomes dominant and the stress accumulation rate is independent of l it is well known that the general l cubed dependence of seismic moment m0 breaks for large interplate earthquakes this break in the moment length relation can be ascribed to difference in loading mechanism between small and large earthquakes from the results of numerical computation if interplate earthquakes have the same stress drop regardless of their fault lengths we may derive a l squared dependence of m0 for large interplate earthquakes and a linear l dependence of m0 for very large interplate earthquakes

stratigraphic and environmental control on marine benthic community change through the early toarcian extinction event iberian range spain abstract in the early jurassic 183 ma ago global warming and associated environmental changes coincided with an extinction event in the marine realm early toarcian extinction event anoxia was previously considered to have been the main cause of extinction but extinctions also occur at localities that remained oxygenated throughout the event suggesting that other factors such as temperature may have played a major role to test this hypothesis we integrated quantitative analyses of benthic macro invertebrates with high resolution geochemical proxies on the bulk rock toc 13c 18o and on belemnites and brachiopod shells 13c 18o from two sections from the iberian range spain with no black shale deposition the sections are orientated se nw along an onshore offshore gradient deepening to the north the dominant benthic groups bivalves and brachiopods show a different response to the extinction brachiopods go through a complete species level turnover while many bivalve species range through the event in the shallower section changes in richness and evenness correlate with toc total organic carbon suggesting that variations in nutrient input from runoff and the possible local onset of low redox conditions toc 4 wt controlled faunal diversity in contrast at the deeper section community change correlates with changes in 18o indicating that temperature variations might have influenced faunal change different stratigraphic patterns of extinction occur between the two localities with last occurrences clustering at the maximum flooding surface in the shallower section and at the transgressive surface in the deeper one the observed differences between the two localities highlight the important role of local sedimentary and stratigraphic processes in controlling the shape of the geochemical and fossil record and the need for studying multiple sections along onshore offshore gradients in order to extrapolate regional and global patterns

co seismic displacements of the 1992 landers earthquake sequence we present co seismic displacement vectors derived from global positioning system gps measurements of 92 stations in southern california these gps results are combined with five well determined gps displacement vectors from continuously tracking stations of the permanent gps geodetic array as well as line length changes from usgs geodolite and two color laser trilateration observations to determine a self consistent set of geodetic data for the earthquake these combined displacements are modeled by an elastic dislocation representation of the primary fault rupture planes on average the model residuals are about twice the estimated measurement errors

slip history of the 2003 san simeon earthquake constrained by combining 1 hz gps strong motion and teleseismic data 1 the slip history of the 2003 san simeon earthquake is constrained by combining strong motion and teleseismic data along with gps static offsets and 1 hz gps observations comparisons of a 1 hz gps time series and a co located strong motion data are in very good agreement demonstrating a new application of gps the inversion results for this event indicate that the rupture initiated at a depth of 8 5 km and propagated southeastwards with a speed 3 0 km sec with rake vectors forming a fan structure around the hypocenter we obtained a peak slip of 2 8 m and total seismic moment of 6 2 10 18 nm we interpret the slip distribution as indicating that the hanging wall rotates relative to the footwall around the hypocenter in a sense that appears consistent with the shape of the mapped fault trace index terms 1242 geodesy and gravity seismic deformations 7205 7212 seismology earthquake ground motions and engineering 8123 tectonophysics dynamics seismotectonics citation ji c k m larson y tan k w hudnut and k choi 2004 slip history of the 2003 san simeon earthquake constrained by combining 1 hz gps strong motion and teleseismic data geophys res lett 31 l17608 doi 10 1029 2004gl020448

surface waves of the 2011 tohoku earthquake observations of taiwan s dense high rate gps network 1 surface waves generated by the 2011 mw 9 0 tohoku japan earthquake were recorded by both the high rate gps and broadband seismic stations in taiwan in this study we investigate the precision of high rate gps displacements and estimate the feasibility of using gps for seismology study in taiwan one hertz observations of 210 continuous gps stations in taiwan and neighboring islands were processed using a precise point positioning technique to estimate the absolute epoch by epoch positions generated by the tohoku earthquake modified sidereal filtering was used to correct for near daily periodical variations of high rate position time series that may be influenced by multipath effects and a band pass filter was used to remove noises from marginal frequencies for all the 210 stations the gps precision after modified sidereal filtering improved from 8 2 to 7 4 mm in the horizontal and from 19 5 to 12 7 mm in the vertical components except for about 20 of the data with large position errors after applying the band pass filter in the teleseismic frequency band 0 008 0 08 hz excluding 54 stations with noisy data 156 continuous gps stations were selected surface wave displacements derived from both high rate gps and broadband seismometers are highly consistent and the correlation coefficients are enhanced by a band pass filter 0 008 0 08 hz from 0 85 to 0 95 in the horizontal and from 0 58 to 0 85 in the vertical components we consider continuous gps can be used as an alternative approach to study characteristics of surface wave propagation in taiwan

comparisons of ground motions from colocated and closely spaced one sample per second global positioning system and accelerograph recordings of the 2003 m 6 5 san simeon california earthquake in the parkfield region the 2003 san simeon california earthquake m 6 5 generated a set of colocated and closely spaced high rate 1 sample per second global positioning system gps positions and ground motions from digital accelerographs in the park field region at epicentral distances of 50 to 70 km the waveforms of displacements derived from the 13 gps receivers in the region have dominant periods between about 7 and 18 sec the waveforms are similar in shape with a systematic change in waveform as a function of distance from the source the gps motions are smaller than the accelerograph motions for periods less than about 2 sec from this we conclude that the 1 sample per sec gps receivers provide a good representation of ground motion at periods longer than about 2 sec perhaps more important for earth quake engineering is that the accelerograph data are similar to the gps data for periods as long as 30 sec if not longer this means that data from digital accelero graphs can provide reliable relative displacement response spectra at the periods needed in the design of large structures at least for earthquakes with magnitudes of 6 5 or above at distances within 70 km we combine the colocated or very closely spaced gps and accelerograph data sets in the frequency domain to obtain a single broadband time series of the ground motion at each accelerograph station these broadband ground motions may be useful to seismologists in unraveling the dynamic process of fault rupture and to engineers for designing large structures with very long period response

instantaneous geodetic positioning at medium distances with the global positioning system we evaluate a new method of global positioning system gps data analysis called instantaneous positioning at spatial scale lengths typical of interstation spacings in a modern crustal motion network this method is more precise and versatile than traditional gps static and kinematic processing of multi epoch batches of data the key to instantaneous positioning is the ability to resolve integer cycle phase ambiguities with only a single epoch of dual frequency phase and pseudorange data rendering receiver cycle slips irrelevant we estimate three dimensional relative coordinates and atmospheric zenith delay parameters independently every 30 s over a 12 week period for baseline distances of 50 m 14 km and 37 km horizontal precision of a single epoch coordinate solution is about 15 mm and vertical precision is about 7 8 times worse removing that component of each time series which repeats with a period of exactly 1 sidereal day and thus manifests signal multipath reduces the scatter by about 50 in all components solution averaging of the high frequency time series can be performed using any number of measurement epochs to further improve coordinate precision we demonstrate that the daily coordinates estimated with instantaneous positioning are more precise by 20 50 per coordinate component than those estimated with 24 hour batch processing spectral analysis of the single epoch solutions indicates that the flicker noise characteristic of gps time series observed in lower frequency bands also affects gps solutions in the frequency band 0 01 mhz to 10 mhz we argue that the flicker noise is induced by tropospheric effects since modern gps receivers are capable of observing at frequencies as high as 10 hz our technique significantly overlaps and complements the frequency band of broadband seismology and benefits other research areas such as earthquake geodesy volcanology and gps meteorology

southern california permanent gps geodetic array spatial filtering of daily positions for estimating coseismic and postseismic displacements induced by the 1992 landers earthquake the june 28 1992 m w 7 3 landers california earthquake was the first earthquake to be surveyed by a continuously operating global positioning system gps array the coordinate time series of seven sites are evaluated for station displacements during an interval of 100 days centered on the day of the earthquake we employ a new spatial filtering technique that removes common mode errors from the coordinate time series this approach provides precise estimates of site specific displacements compared to the cumbersome method of analyzing baselines between pairs of stations all sites indicate significant coseismic horizontal displacements of 5 65 mm with uncertainties of 1 2 mm horizontal displacements are in general agreement with elastic dislocation models in particular for sites closer to the epicenter vertical displacements range from 13 to 7 mm with uncertainties of 2 4 mm the observed vertical displacements in all cases show 5 10 mm more subsidence than expected from geodetic and seismic geologic models significant postseismic horizontal displacements totaling 6 2 mm 10 20 of the coseismic displacement are detected at the three sites closest to the epicenter these displacements are modeled as a short term exponential relaxation with a decay time of 22 10 days superimposed on a longer term linear interseismic trend scaling the observed coseismic and postseismic displacements at one of the sites with the distance to the epicenter provides a measure of site strain which agrees well with the direction and magnitude determined from more precise laser strain meter data the time series do not show any detectable preseismic displacements

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

rapid resolution of crustal motion at short ranges with the global positioning system on the basis of the analysis of global positioning system gps data collected at the u s geological survey kennedy ranch house alinement array near parkfield california in november 1990 and february 1991 we assess the temporal resolution of crustal deformation for gps receiver systems operating as strain meters and provide guidelines for achieving millimeter level precision with short range kinematic type gps measurements site occupation of about one half hour is sufficient for day to day repeatability of submillimeter precision in relative position during good satellite geometry signal multipath effects which dominate dispersive baseline errors are essentially averaged out and need not be modeled however as occupation times decrease baseline solutions are increasingly sensitive to multipath effects which together with nondispersive receiver measurement noise are of millimeter to centimeter magnitude in epoch by epoch solutions on repeatedly monitored baselines we can account for both of these noise sources separately the mostly random receiver noise is effectively suppressed by low pass filters with corner frequencies of about 20 mhz the multipath noise is filtered using the fact that it essentially repeats from day to day residual errors in filtered 1 s epoch by epoch solutions are below 2 mm during periods of good satellite geometry hence for a continuously monitored baseline actual deformation in excess of this threshold can be detected with a time lag comparable to the group delay of the low pass filter i e typically within a minute in terms of strain along a typical short baseline of 1 km sampled once per second we can detect 1 2 s in l min with multipath modeling without multipath modeling it takes 10 min to resolve the same magnitude of deformation in 30 min we can detect 0 1 s independent of multipath modeling these results have important implications for kinematic type gps surveys for millimeter level precision without impractical multipath modeling it is necessary to occupy a site during good satellite geometry for a period longer than that of the multipath signature our experience in both benign and difficult multipath environments indicates that approximately 10 min are sufficient the measurements at the kennedy ranch house alinement array suggest that this segment of the san andreas fault appears to be virtually locked at the surface during the 3 month period between the two surveys

seismic wave observations with the global positioning system we describe the direct measurement of ground displacement caused by the hector mine earthquake in southern california m w 7 1 october 16 1999 we use a new method of instantaneous positioning which estimates site coordinates from only a single epoch of global positioning system gps data to measure dynamic as well as static displacements at 24 stations of the southern california integrated gps network scign with epicentral distances from 50 to 200 km for sites outside the los angeles basin the observed displacements are well predicted by an elastic half space model with a point shear dislocation within the sedimentary basin we observe large displacements with amplitudes up to several centimeters that last as long as 3 4 min since we resolve the gps phase ambiguities and determine site coordinates independently at each epoch the gps solution rate is the same as the receiver sampling rate for the scign data this is 0 033 hz once per 30 s though sample rates up to 2 hz are possible with the scign receivers since the gps phase data are largely uncorrelated at 1 s a higher sampling rate would offer improved temporal resolution of ground displacement so that in combination with inertial seismic data instantaneous gps positioning would in many cases significantly increase the observable frequency band for strong ground motions

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses