global positioning system measurements of strain accumulation across the imperial valley california 1986 1989 global positioning system gps data collected in southern california from 1986 to 1989 indicate considerable strain accumulation across the imperial valley displacements are computed at 29 stations in and near the valley from 1986 to 1988 and at 11 sites from 1988 to 1989 the earlier measurements indicate 5 9 1 0 cm yr right lateral differential velocity across the valley although the data are heavily influenced by the 1987 superstition hills earthquake sequence the 1988 1989 gps displacements are best modeled by 5 0 0 9 cm yr of valley crossing deformation but rates calculated from 15 years of terrestrial geodetic measurements 3 7 0 1 cm yr fit the data nearly as weh1 the relatively high gps rates are suspect because some measurements especially the east trending displacements have large errors there is evidence from gps and very long baseline interferometry observations that the present strain rate along the southern san andreas fault is smaller than the long term geologic estimate suggesting a lower earthquake potential than is currently assumed correspondingly a higher earthquake potential is suggested for the san jacinto fault

north american pacific relative plate motion in southern california from interferometry very long baseline interferometry measurements of baselines crossing the san andreas fault zone in southern california have provided observational constraints on rates of elastic tectonic strain accumulation the single site located near this fault the jet propulsion laboratory site moves in a direction concordant with the pacific plate motion vector but at approximately half the net rate relative to north america this motion agrees approximately in amount with geologically determined displacement rates on the san andreas fault alone but not with the local strike of the fault when considered together with complementary geodetic data these results suggest a complex relation between the short term accumulation of elastic strain and its permanent accommodation on existing faults

application of the global positioning system to crustal deformation measurement 2 the influence of errors in orbit determination networks global positioning system gps measurements of a geodetic network in southern and central california have been used to investigate the errors introduced by adopting different sets of stations as fixed such fixed points called fiducial stations are necessary to eliminate the errors of imprecise satellites orbits which otherwise would dominate the error budget for distances greater than tens of kilometers these fiducial stations also define the reference frame of the crustal deformation network establishing the magnitude of the effect of changing the fiducial network is essential for crustal deformation studies so that these artifacts of the differences between fiducial networks used for the data analyses are not interpreted as geophysical signals solutions for a crustal deformation network spanning distances up to 350 km were computed with a variety of fiducial networks we use fiducial coordinates determined from very long baseline interferometry vlbi we compare these solutions by computing the equivalent uniform strain and rotation that best maps one solution into another if we use a continental scale fiducial network with good geometry the distortions between the solutions are about 10 8 largely independent of the exact choice of stations the one case of a large scale fiducial network where the distortions are larger is when the three fiducial stations chosen all lie close to a great circle use of a fiducial network no larger than the crustal deformation network tan produce apparent strains of up to 10 7 our work suggests that fiducial coordinates determined from gps data analysis may be used although they should be determined using a consistent reference frame such as provided by vlbi and satellite laser ranging

geodetic methods for detecting volcanic unrest a theoretical approach in this paper we study the application of different geodetic techniques to volcanic activity monitoring using theoretical analysis this methodology is very useful for obtaining an idea of the most appropriate and efficient monitoring method mainly when there are no records of geodetic changes previous to volcanic activity the analysis takes into account the crustal structure of the area its geology and its known volcanic activity to estimate the deformation and gravity changes that might precede eruptions the deformation model used includes the existing gravity field and vertical changes in the crustal properties both factors can have a considerable effect on computed deformation and gravity changes topography should be considered when there is a steep slope greater than 10 the case study of teide stratovolcano tenerife canary islands for which no deformation or gravity changes are available is used as a test to avoid considering topography we worked at the lowest level of las canadas and examined a smaller area than the whole caldera or island therefore the results are only a first approach to the most adequate geodetic monitoring system the methodology can also be applied to active areas where volcanic risk is not associated with a stratovolcano but instead with monogenetic scattered centers especially when sites must be chosen in terms of detection efficiency or existing facilities the canary islands provide a good example of this type of active volcanic areas and we apply our model to the island of lanzarote to evaluate the efficiency of the monitoring system installed at the existing geodynamic station on this island topography is not important the results of our study show clearly that the most appropriate geodetic volcano monitoring system is not the same for all different volcanic zones and types and the particular properties of each volcano zone must be taken into account when designing each system

vector constraints on western u s deformation from space geodesy neotectonics and plate motions the rate of slip vector on the san andreas fault in central california estimated from geodetic and holocene geological data 34 3 mm yr n41 w 2 is inconsistent with the prediction of rigid plate models such as rm2 56 3 mm yr n35 w 2 this well known san andreas discrepancy is diagnostic of plate deformation distributed both east of the fault in the basin and range and west of the fault along the california continental margin we construct constraints on the integrated deformation rates across these two regions consistent with 1 the kinematical boundary conditions imposed by the rigid plate model 2 neotectonic and paleoseismic estimates of deformation rates 3 ground based geodetic measurements and 4 rates of change observed by very long baseline interferometry along seven baselines to western u s sites the space geodetic data on basin and range extension taken over a 4 year interval are compatible with geological observations averaged over the holocene the best estimate of its integrated deformation rate provided by the joint inversion of both data types is 9 7 2 1 mm yr n56 w 10 too small and in the wrong direction to account entirely for the san andreas discrepancy we therefore attribute much of it to deformation west of the sierra nevada great valley block accommodated for example on faults such as the san gregorio hosgri system of coastal california the integral of this deformation estimated by subtracting the basin and range contribution from the discrepancy vector requires significant right lateral shear parallel to the san andreas 13 5 mm yr and some compression perpendicular to it 9 3 mm yr

first gps baseline results from the north andes the casa uno gps global positioning system experiment january february 1988 has provided the first epoch baseline measurements for the study of plate motions and crustal deformation in and around the north andes two dimensional horizontal baseline repeatabilities are as good as 5 parts in 108 for short baselines 100 1000 km and better than 3 parts in 108 for long baselines 1000 km vertical repeatabilities are typically 4 6 cm with a weak dependence on baseline length the expected rate of plate convergence across the colombia trench is 6 8 cm yr which should be detectable by the repeat experiment planned for 1991 expected deformation rates within the north andes are of the order of 1 cm yr which may be detectable with the 1991 experiment

present day crustal deformation and geodetic strain in the vicinity of dholavira harappan civilization site kachchh western part of the indian plate abstract to understand the geodynamics in the vicinity of dholavira a harappan civilization site hcs in kachchh western india gps data from 2009 to 2015 were processed and analyzed tectonically this part of northern kachchh is in the influence of island belt fault ibf and allah bund fault abf and is seismically one of the most active intra plate regions of india the motion with respect to indian plate is used for the estimation of deformation and strain rate while fault associated slip rate has been estimated by inverse modeling of observed site motions the analysis reveals that the abf deforms with an average rate of 1 8 mm yr however the segmented ibf has a maximum deformation rate of 2 9 mm yr towards the pachham island and minimum towards the khadir island the computation discloses a maximum seismic moment m0 of 2 1 1024 dyne cm in this part which corresponds to an earthquake of mw 6 0 the calculated maximum strain of 0 04 micro strain year is low but significant in the intra plate region the postseismic deformation after the mw 7 7 2001 bhuj earthquake is estimated to be low in this part the reverse along with strike slip motion of faults builds up stress in the area and accumulating more strain

evaluation of gps estimates of relative positions from central california 1986 1988 i report estimates of long term precision and accuracy of interstation vectors using the global positioning system gps precision is estimated from three experiments conducted in central california over a period of 1 2 years horizontal precision is 3 to 8 mm for baseline vectors between 100 and 450 km in length and the vertical precision ranges from 11 to 33 mm accuracy is assessed by comparing vlbi estimates with results from 6 gps experiments conducted at mojave and palos verdes over a period of 2 2 years rates for all vector components agree with vlbi within one standard deviation

global positioning system reoccupation of early triangulation sites tectonic deformation of the southern coast ranges we study tectonic deformation in the southern coast ranges california we use triangulation and astronomic azimuth data collected since 1875 trilateration since 1970 and global positioning system data collected from 1986 to 1987 two modeling techniques have been used an elastic block fault model is applied to study the tectonic motion of the san andreas fault and the san gregorio hosgri fault station velocities are modeled to study regional deformations results show that the regional deformation is predominantly controlled by deep strike slip motion along the san andreas fault at a rate of 33 2 mm yr deep slip along the san gregorio hosgri fault is about 0 4 mm yr assuming a locked fault to a depth of 20 km convergence normal to the san andreas fault in the southern coast ranges is not greater than 0 02 rad yr

casa uno gps orbit and baseline experiments casa uno data from sites distributed in longitude from australia to europe have been used to determine orbits of the gps satellites the characteristics of the orbits determined from double difference phase have been evaluated through comparisons of two week solutions with one week solutions and by comparisons of predicted and estimated orbits evidence of unmodeled effects is demonstrated particularly associated with the orbit planes that experience solar eclipse the orbit accuracy has been assessed through the repeatability of unconstrained estimated baseline vectors ranging from 245 km to 5400 km both the baseline repeatability and the comparison with independent space geodetic methods give results at the level of 1 2 parts in 108 in addition the mojave owens valley 245 km and kokee park ft davis 5409 km estimates agree with vlbi and slr to better than 1 part in 108

preliminary determination of pacfic north america relative motion in the southern gulf of calfornia using the global positioning system global positioning system gps data from experiments conducted in 1985 and 1989 in the southern gulf of california mexico allow a determination of relative motion between the pacific and north american plates the data indicate motion of cabo san lucas on the pacific plate relative to north america at a rate of 47 7 mrn yr and azimuth of 57 6 west of north 1 errors equivalent within uncertainties to the nuvel 1 global plate motion model

crustal deformation measurements in central japan determined by a global positioning system fixed point network a global positioning system gps fixed point network has been operating in the kanto and tokai districts of central japan since april 1988 to detect crustal deformation associated with the convergence of the eurasian pacific north american and philippine sea plates and to monitor the deformation cycles of frequent large interplate and intraplate earthquakes this 10 station network established by the national research institute for earth science and disaster prevention nied is the first continuously monitoring network of its kind we determine deformation within the network using two consecutive days of data every 2 weeks for the first 17 months of operations we use a station and orbit relaxation method which relies exclusively on data collected within the nied network except for 1 week of global gps tracking data which is used to determine initial station positions with respect to the global reference frame we detect relative to a station on the eurasian plate in central japan significant westward motion of 28 mm yr of the northern tip of the philippine sea plate which is subducting beneath the eurasian plate at the suruga trough our results support finite element models of collision of the izu block with the eurasian plate based on earthquake focal mechanisms and plate block motions of the japanese archipelago determined from conventional geodetic measurements over the last century we detect southwestward motion of 18 mm yr of the southeastern tip of the eurasian plate confirming expected surface extension of the subducted plate parallel to the suruga trough axis significant vertical uplift with a velocity of 20 mm yr is suggested at a site inland of the tokai district located in the akaishi uplift zone and at a site on hatsushima island in sagami bay the general tendency of vertical movements of the other sites agrees with vertical velocities obtained from 70 years of geodetic leveling and with quaternary vertical displacements determined from geomorphological and other geological evidence we detect no significant crustal motion across the fossa magna tectonic zone in central japan often considered a plate boundary across the tokyo metropolitan area nor across the sagami trough associated with the subduction of the philippine sea plate beneath northeast japan our results demonstrate the power of regionally based continuously monitoring gps networks for obtaining temporally dense measurements of small horizontal and vertical crustal movements across plate boundary zones

recent plate motions and crustal deformation reports by u s workers on geodetic measurements of recent plate motions or crustal deformation published in 1987 1990 are reviewed the review begins with global plate motions proceeds through plate boundaries in california alaska and the pacific northwest and finishes with volcanic phenomena monument stability and longevity and gps relative position measurements 184 refs

evaluation of the 1984 alaska global positioning system campaign with the bernese gps software during the summer of 1984 five ti 4100 global positioning system gps receivers were used to measure an eight station network in alaska and canada previously measured with mobile very long baseline interferometry vlbi systems with baselines ranging from 300 km to almost 2700 km the observations have been processed in the network mode with the bernese gps software using orbit improvement techniques the comparisons of the gps and vlbi solutions established through a seven parameter helmert transformation show an agreement of the order of 0 1 ppm for all solutions no significant scale factor between gps and vlbi coordinates could be detected these results demonstrate for the first time the power of orbit improvement in conjunction with network processing of gps phase observations

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

determining the sula block kinematics in the triple junction area in indonesia by gps summary the point of convergence of the eurasian philippine and australian plates is situated adjacent to the island of sulawesi indonesia the relative plate velocities are estimated by nuvel1 to be 7 to 9 cm yr 1 the complex tectonic mechanism of the triple junction has been studied over a two year period in the course of the geodyssea southeast asian project the gps investigations concentrate on measurements of both the sulawesi eastern indonesia part of the inter regional geodyssea network and a local subnetwork on sulawesi motions derived using data from the subnetwork con rm what the results of the inter regional geodyssea network have suggested that is that current deformation is high and there are distinct deformation domains in the study area on sulawesi the tectonic mechanism of the triple junction has been analysed using a rigid microblock model the triple junction area can best be interpreted as a headland of the australian plate de ected by its collision with the philippine plate thereby identifying the driving forces of the current deformation the northern part is dominated by the sula domain which shows clockwise rotation to the south it is connected to the australian plate by an ensemble of microblocks undergoing counterclockwise rotation in addition to the above our tectonic model permits the determination of the local in uence of two large earthquakes m 7 8 1996 january 1 and m 7 0 1996 july 22 on the motion of the station tomini north sulawesi more observations and a denser gps network are planned in order to study the behaviour of the palu koro fault the main fault on the western limit of the sula block

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

establishment of three dimensional geodetic control by interferometry with the global positioning system we consider the theoretical and the practical aspects of using radiointerferometric observations of the global positioning system gps satellites to establish a three dimensional multistation geodetic control network we discuss various ways of processing gps data and try them with observations from a 35 station network in germany we examine the reproducibility of interferometric determinations of individual baseline vectors and the three dimensional vector closure of subnetworks and the whole network we compare these measures of precision with corresponding predictions based on statistics of interferometric phase residuals we conclude that the relative positions of stations in the network were determined by gps interferometry within about 1 part per million ppm in both horizontal coordinates and about 1 6 ppm in the vertical as an external test of horizontal accuracy we compare baseline lengths with electro optical distance measurements the vertical accuracy is tested against determinations by means of spirit leveling and gravimetry of the height differences between stations the differences between the interferometric and the independent determinations are consistent with the uncertainties of the latter interferometry with gps is by far the most efficient method of establishing geodetic control on local and regional scales this is already true even though the constellation of satellites is incomplete the accuracy of regional control by gps should improve to about 0 1 ppm when interferometry is also used to determine the satellite orbits

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

global positioning system network analysis with phase ambiguity resolution applied to crustal deformation studies in california a 5 year campaign is in progress in central and southern california to monitor tectonic motions using observations of the global positioning system gps satellites evidence from geological and space geodetic data indicates that significant horizontal deformations of order 10 mm yr are occurring west of the san andreas fault along the california margin we demonstrate using data from initial epoch measurements in january 1987 that the goal of measuring horizontal deformations with an accuracy of 5 mm yr over the duration of the campaign should be readily achievable the gps network was designed to span a wide range of baseline lengths within california and across north america to aid in phase ambiguity resolution an important factor in achieving highest accuracy baseline determinations we present an efficient algorithm for multisession network analysis of gps data with simultaneous orbit determination and ambiguity resolution using this algorithm with the california data we demonstrate the improvement obtained in station position and satellite orbit estimation when the phase ambiguities are resolved we demonstrate several millimeters 1 part in 108 short term repeatability over five single session daily analyses for horizontal baseline components and length and several tens of millimeters for the vertical comparison with the independently determined very long baseline interferometry baseline between mojave and owens valley suggests that the accuracy is at the same level as the repeatability we show that simultaneous multisession analyses with ambiguity resolution improve the baseline and satellite orbit estimates compared to the single session analyses with the single session analyses we were able to resolve all phase ambiguities on baselines within california with the multisession analyses we were able to resolve the phase ambiguities for most of the network over regional and continental scales

space geodetic measurement of crustal deformation in central and southern california 1984 1992 we estimate the velocity field in central and southern california using global positioning system gps observations from 1986 to 1992 and very long baseline interferometry vlbi observations from 1984 to 1991 our core network includes 12 gps sites spaced approximately 50 km apart mostly in the western transverse ranges and the coastal borderlands the precision and accuracy of the relative horizontal velocities estimated for these core stations are adequately described by a 95 confidence ellipse with a semiminor axis of approximately 2 mm yr oriented roughly north south and a semimajor axis of approximately 3 mm yr oriented east west

geodetic measurement of deformation in the ventura basin region southern california we have measured the deformation in the ventura basin region southern california with global positioning system gps measurements carried out over 4 6 years between 1987 and 1992 the deformation within our network is spatically variable on scales of tens of kilometers with strain rates reaching 0 6 1 micro rad yr in the east central basin blocklike rotations are observed south and northwest of the basin where the maximum shear strain rates are an order of magnitude lower 0 06 1 micro rad yr to the south we also observed clockwise rotations of 1 deg 7 deg m y shear strain rates determined by comparing angle changes from historical triangulation spanning several decades and gps measurements give consistent though less precise results the geodetic rates of shortening across the basin and western transverse ranges are lower than those estimated from geological observations but the patterns of deformation from the two methods agree qualitatively

near inertial motions over a mid ocean ridge effects of topography and hydrothermal plumes we investigate the spatial structure of near inertial motions in the vicinity of the endeavour segment of juan de fuca ridge approximately 48 n 129 w in the northeast pacific ocean on the basis of time series current and water property data collected from september 1984 to september 1987 near inertial motions are ubiquitous features of the 2200 m water column with root mean square rms current speeds comparable to those of the dominant m2 tidal currents within the lower 1000 m of the water column where most of the observations were obtained near inertial oscillations have rms current speeds of o 1 cm s and vertical isotherm displacements of o 10 m the fluctuations are confined to the frequency band 0 966 1 079 f f is the local coriolis parameter and have characteristic event durations of 1 week although the spectra of subsurface motions are dominated by the blue shifted superinertial band significant spectral peaks are found also in the subinertial and inertial frequency bands marked alteration of the near inertial current amplitudes occurs over two well defined depth zones within the study region within the 200 m zone immediately above the 2100 m ridge crest current amplitudes are amplified by a factor of 1 2 1 7 because of bottom reflection and or scattering of the downward propagating energy evidence that the amplification may be linked to bottom reflection rather than to scattering is provided by flattening and cross slope rotation of the near inertial current ellipses with increased proximity to the top of the ridge reflection would occur at grazing angles of less than 1 and would be associated with surface generated waves originating at distances of over 100 km from the observational site in contrast to the enhanced amplitudes immediately above the top of the ridge near inertial currents within the 1600 to 1800 m depth range undergo pronounced attenuation and frequency alteration amplitude attenuation is especially pronounced for motions in the superinertial band and may arise through critical layer absorption of downward propagating waves as they encounter increased vertical shear in the background flow the increased shear is most likely associated with buoyancy induced flow formed by the extensive hydrothermal plume emanating from vent sites in the axial valley along the ridge crest but it could also be related to bottom trapped oscillations over the steep ridge topography near inertial motions are estimated to have vertical coherence scales of the order of 10 100 m while horizontal coherence scales exceed the 50 km separation between the mooring locations minimum vertical and horizontal coherences are found for the depth zone 1600 1800 m while maximum correlation occurs for near bottom motions immediately above the crest of the ridge weak near inertial motions are observed within the 100 m deep axial valley

determination of relative site motions in the western united states using mark iii very long baseline interferometry four years of very long baseline interferometry vlbi measurements involving fixed and mobile stations in the western united states are analyzed using weighted least squares baseline solution time series are used to estimate rates of change of the vector baselines between pairs of vlbi stations horizontal vector motions are determined for 18 sites with respect to a site in the mojave desert six sites west of and two sites just to the east of the san andreas fault show northwestward motion closely parallel to the san andreas fault their motions range from 18 to 43 mm yr and are significant at confidence levels greater than 99 motions in california relative to interior north american plate sites are used to estimate an integrated contribution from basin and range spreading to the total relative pacific plate motion as 9 10 mm yr a maximum relative velocity of 50 51 mm yr is found between the interior north american sites and the western california sites in close agreement with the nuvel i plate motion model

coseismic crustal deformation from the 1994 hokkaido toho oki earthquake monitored by a nationwide continuous gps array in japan using a brand new nationwide continuous gps array we monitored coseismic displacements from the october 4 1994 hokkaido toho oki kurile islands earthquake mjma 8 1 based on 2 week time series of site coordinates of 21 gps stations we present a coseismic deformation field of whole hokkaido within 1 cm precision for example the station at nemuro 170 km west of the epicenter moved 44 cm to the east and subsided 10 cm even stations in southern hokkaido 600 km apart from the epicenter moved a few cm horizontally toward the epicenter we compare the gps result with displacements calculated from two preliminary models assuming fault planes parallel or perpendicular to the kurile trench since the observed were far field displacements on land both models can explain the gps result

a kinematic model of southern california we propose a kinematic model for southern california based on late quaternary slip rates and orientations of major faults in the region internally consistent motions are determined assuming that these faults bound rigid blocks relative to north america most of california west of the san andreas fault is moving parallel to the san andreas fault through the transverse ranges and not parallel to the motion of the pacific plate this is accomplished by counterclockwise rotation of california south of the san andreas fault and by the westward movement of central california north of the gar lock fault the velocities of the blocks are calculated along several paths in southern california that begin in the mojave desert and end off the california coast a path that crosses the western transverse ranges accumulates the accepted relative north america pacific plate velocity whereas paths to the north and south result in a significant missing component of motion this implies the existence of a zone of active deformation in southern california that is interpreted to include the western transverse ranges and northwest trending predominately strike slip faults close to the coast both north and south of the transverse ranges strain on this system accounts for about a third of the total north america pacific plate motion

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

central and south america gps geodesy casa uno in january 1988 scientists from over 25 organizations in 13 countries and territories cooperated in the largest global positioning system gps campaign in the world to date table 1 43 gps receivers collected approximately 590 station days of data in american samoa australia canada colombia costa rica ecuador new zealand norway panama sweden united states west germany and venezuela the experiment was entitled casa uno an acronym for central and south america and uno is the spanish word for one designating first epoch measurements the casa uno experiment was the first civilian effort implementing a global gps satellite tracking network scientific goals of the project include measurement of strain in the northern andes measurement of subduction rates for the cocos and nazca plates beneath central and south america and measurement of relative motion between the caribbean plate and south america a second set of measurements are planned in 1991 casa dos and should provide preliminary estimates of crustal deformation and plate motion rates in the region the casa series of experiments are intended to be carried out over at least one decade

earthquakes and sea level space and terrestrial metrology on a changing planet the complacency with which man inhabits continent ocean margins or plate boundaries is based on the assumption that sea level rise and periodic seismicity are acceptable risks the forecast of future sea level or future seismicity is essential for informed assessment of these risks the historical data from which forecasts may be derived are in each case of limited antiquity and uneven spatial distribution developments in space geodesy and crustal deformation metrology in the past two decades offer the means to acquire a homogeneous global data set for monitoring relative vertical and horizontal motions of the earth s surface to within several millimeters these new tools are reviewed in terms of their application to forecasting trends in sea level rise and forecasting damaging earthquakes

world peat occurrence and the seasonality of climate and vegetation abstract the climatic controls on present day peat formation are examined in order to develop a uniformitarian tool for refining paleoclimate studies and to create a retrodictive model for the coals of the geologic record a peat database has been compiled for the world and the resulting patterns are compared with aspects of precipitation and temperature drawn from a gridded data set precipitation continuity through the annual cycle is important for biologic productivity in the terrestrial realm it is expressed in terms of the number of months with average precipitation above 40 mm temperature is limiting at higher latitudes where the potential growing season may be defined by the number of months with mean temperature exceeding 10 c a map predicting the growing season has been constructed from these rainfall and temperature statistics which compares very well with actual vegetation persistence through the year as measured directly from satellite instruments however biologic production will not result in peat accumulation unless groundwater levels are maintained through the growing season our peat prediction map therefore shows the percentage of time that precipitation occurs during the potential growing season present day peat accumulations are well predicted by this map

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

a revised estimate of pacific north america motion and implications for western north america plate boundary zone tectonics for the past 20 years much effort has been directed to determining the present day relative motion of the pacific and north american plates using two independent approaches one uses geologic observations and geodetic measurements along the san andreas fault and other faults in the plate boundary zone the other is based on plate motion models that incorporate spreading rates from marine magnetic anomalies transform azimuths and earthquake slip vectors geologic and geodetic studies find two principal elements of deformation slip along the san andreas of 34 mm yr directed n41 w and extension across the basin and range province of about 10 mm yr directed n56 w in contrast plate motion studies find 56 60 mm yr directed n35 w the discrepancy between these estimates a vector of about 15 mm yr oriented nearly due north is often attributed to a combination of slip along faults parallel to the san andreas and shortening normal to it here we revise the estimate of pacific north america motion by analyzing marine magnetic profiles from the gulf of california since 3 ma spreading has averaged 48 mm yr 10 mm yr slower than estimated before and consistent with the 49 mm yr spreading predicted by a new global plate motion model derived without any data along the pacific north america boundary the discrepancy with geodetic and geologic estimates is thus reduced to only 5 mm yr parallel to the san andreas 60 less than estimated before and 7 mm yr of shortening across the san andreas similar to prior estimates these results suggest that strike slip motion on faults west of the san andreas is less than thought before a conclusion consistent with geodetic seismological and other geologic observations

determination of vertical deflections using the global positioning system and geodetic leveling the capabilities of the global positioning system gps for accurately determining geodetic quantities are well established nevertheless no comparison between deflections of the vertical as determined through gps with leveling and values conventionally computer by astrogeodetic methods has yet been published this investigation demonstrates that the accurate deflections of the vertical components eta xi can be obtained independently of classical astronomic observations by combining geodetic leveling with satellite gos positioning the approach uses a radial configuration of baselines to determine the best in a least square sense values of eta xi at the central station

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

postseismic deformation following the landers earthquake california 28 june 1992 accelerated strain followed the landers and big bear earthquakes returning to the normal rate only after a period of several months we observed this strain throughout most of southern california using the global positioning system gps three gps receivers operating continuously in fixed positions at pinyon flat jet propulsion laboratory pasadena and goldstone all recorded postseismic deformation in a relative sense in addition we established 16 sites where we deployed portable receivers occasionally over a period of about 6 months near the rupture zones of the earthquakes anomalous postseismic displacements ranged from 55 mm near the epicenter to a few millimeters far from the fault we modeled the displacements using dislocation theory as due to variable slip on the faults that were displaced at the times of the earthquakes the model suggests that the postseismic strain released the equivalent of about 15 of the seismic moment of the mainshock while the strain released from the upper 10 km is about the same as what can be explained by direct effects of aftershocks the major contribution of strain release comes from the lower layer below 10 km depth significant afterslip or viscous relaxation must have occurred below 10 km depth to explain the observed deformation more than 100 km from the fault one interpretation is that high stress on the margin of the co seismic rupture zone drives the rupture to extend itself into urbroken rock below and along the initial rupture zone

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

precise regional baseline estimation using a priori orbital information a solution using gps measurements acquired during the casa uno campaign has resulted in 3 4 mm horizontal daily baseline repeatability and 13 mm vertical repeatability for a 729 km baseline located in north america the agreement with vlbi is at the level of 10 20 mm for all components the results were obtained with the gipsy orbit determination and baseline estimation software and are based on five single day data arcs spanning the 20 21 25 26 and 27 of january 1988 the estimation strategy included resolving the carrier phase integer ambiguities bias fixing utilizing an optimal set of fixed reference stations fiducials and constraining gps orbit parameters by applying a priori information derived from initial multi day trajectory fits to broadcast ephemeris data a multi day january 20 27 gps orbit and baseline solution has yielded similar 2 4 mm horizontal daily repeatabilities for the same baseline consistent with the constrained single day arc solutions the application of weak constraints to the orbital state for single day data arcs produces solutions which approach the precise orbits obtained with unconstrained multi day arc solutions this work suggests that the general availability of nominal ephemerides based on many days of global tracking data would be very valuable and practical for regional geodesy allowing for high precision with single day network solutions when combined with a continental scale fiducial network

crustal deformation across and beyond the los angeles basin from geodetic measurements we combine 6 years of global positioning system gps data with 20 years of trilateration data and a century of triangulation taped distance and astronomic azimuth measurements to derive 66 interseismic station velocities in the greater los angeles region we interpolate the velocities to construct a regional strain rate map beyond the los angeles basin our results generally agree with the model proposed by the working group on california earthquake probabilities in 1995 important regional findings of this study are as follows 1 there is a significant n s convergence and e w extension about 0 22 and 0 17 0 05 strain yr respectively for the two components along the southern frontal fault system of the san gabriel mountains 2 the crustal deformation around the big bend of the san andreas fault saf cannot be explained solely by wrench style motion across the saf remaining motion could be part of a nw se extension which is the response to nfsw compression in the central transverse ranges region alternatively it could be caused by left lateral faulting on an oblique blind thrust beneath the san gabriel mountains 3 low strain rates axe found along the elsinore fault and newport inglewood 4 north south compression decreases from the raymond hill fault westward to the santa monica fault there is little east west extension along this fault system