radar interferometric mapping of deformation in the year after the landers earthquake although the 1992 landers california earthquake sequence occurred in an area well sampled by geodetic networks1 3 the postseismic deformation in the months following the earthquake has been measured at only 15 geodetic stations4 another shortcoming in the geodetic coverage occurs west of the primary rupture where the existing geodetic observations suggest but cannot resolve sympathetic slip on secondary faults1 such measurements which are needed to place the landers earthquake sequence in the context of a recurring seismic cycle in california can be obtained with the dense spatial coverage provided by satellite radar interferometry5 9 here we present radar maps of the surface deformation field which reveal features that would otherwise have been poorly sampled particularly if the earthquake had occurred in a less accessible area we see triggered slip at the level of several centimetres as far as 100 km from the primary rupture and can resolve the geodetic signal of at least one small magnitude 5 aftershock the amount of surface slip following the main shock is less than a decimetre and is consistent with an exponential decay time of several months for the postseismic deformation

detection of a volcanic fracture opening in japan using global positioning system measurements the global positioning system gps is a powerful tool for detecting crustal deformation1 for example the technique has been used to detect plate boundary movements in california2 here we report observations of crustal deformation associated with seismic swarm and sea floor volcanic activity off the east coast of the izu peninsula japan in july 1989 using a fixed point gps network these measurements have enabled us to capture some rarely observed features of seismic and volcanic activity we have for the first time used gps fixed point measurements to follow the evolution with time of the crustal movements such measurements provide a continuous uninterrupted record of deformation our observations were supported by independent data from other sources thus providing further evidence for the utility of the gps

investigation of nearfield postseismic slip following the mw 7 3 landers earthquake sequence of 28 june 1992 california repeated precise surveys of six nearfield trilateration arrays reveal that minor horizontal displacements occurred across the several fault ruptures in the five months following the landers earthquake sequence the displacements range from 0 2 mm on the camp rock and emerson faults to 3 2 mm on the landers fault to 9plusmn 2 mm on the johnson valley fault to 40 5 mm on the eureka peak fault consistent in magnitude and duration with gps and creepmeter measurements by other investigators the relative lack of afterslip at all sites except across the eureka peak fault is probably due to the lack of a thick alluvial cover concomitant precise resurveys of level lines across the san andreas fault in coachella valley and of a trilateration array at durmid hill south easternmost san andreas fault failed to reveal vertical or horizontal displacements greater than the allowable uncertainty 1 mm for leveling 2 mm 2 ppm for trilateration therefore the landers earthquake sequence did not perturb the san andreas in any way that was evident from our measurements of near surface strain

the loma prieta earthquake 1989 and earth strain tidal amplitudes an unsuccessful search for associated changes the loma prieta earthquake of 1989 pro vided an opportunity for a sensitive test of suggestions that earthquakes may be preceded by variations in earth tidal strain amplitudes such variations have been pro posed as providing an advantageous technique for detect ing precursory chkuges in elastic parameters in a seismo genic zone we have analyzed data from two borehole strainmeters continuously operating within 40 km of the epicenter and within about 10 km of the southern end of the rupture we are unable to identify any precursory changes in m2 and o 1 tidal amplitudes and estimate that any large scale changes in young s modulus must have been less than about 2 if these results apply gener ally we would conclude that variations in elastic material properties prior to earthquakes do not occur throughout substantial volumes of the subsequent hypocentral region

application of the global positioning system to crustal deformation measurement 1 precision and accuracy in this paper we assess the precision and accuracy of interstation vectors determined using the global positioning system gps satellites these vectors were between stations in california separated by 50 450 km using data from tracking the seven block i satellites in campaigns from 1986 through 1989 we examine the precision of gps measurements over time scales of a several days and a few years we characterize gps precision by constant and length dependent terms the north south component of the interstation vectors has a short term precision of 1 9 mm 0 6 parts in 108 the east west component shows a similar precision at the shortest distances 2 1 mm with a larger length dependence 1 3 parts in 108 the vertical precision has a mean value of 17 mm with no clear length dependence for long term precision we examine interstation vectors measured over a period of 2 2 to 2 7 years when we include the recent results of davis et al 1989 for distances less than 50 km we can describe long term gps precision for baselines less than 450 km in length as 3 4 mm 1 2 parts in 108 5 2mm 2 8 parts in 108 11 7mm 13 parts in 108 in the north south east west and vertical components accuracy has been determined by comparing gps baseline estimates with those derived from very long baseline interferometry vlbi a comparison of eight interstation vectors shows differences ranging from 5 to 30 mm between the mean gps and mean vlbi estimates in the horizontal components and less than 80 mm in the vertical a large portion of the horizontal differences can be explained by local survey errors at two sites in california a comparison which suffers less from such errors is between the rates of change of the baselines the horizontal rates estimated from over 4 years of vlbi data agree with those determined with 1 2 years of gps data to within one standard deviation in the vertical both gps and vlbi find insignificant vertical motion

the 1989 loma prieta earthquake imaged from inversion of geodetic data we invert geodetic measurements of coseismic deformation from the 1989 ms7 1 loma prieta earthquake to determine the geometry of the fault and the distribution of slip on the fault plane the data include electronic distance measurements global positioning system and very long baseline interferometry vectors and elevation changes derived from spirit leveling the fault is modeled as a rectangular dislocation surface in a homogeneous elastic half space first we assume that the slip on the fault is uniform and estimate the position orientation and size of the fault plane using a nonlinear quasi newton algorithm the best fitting dislocation strikes n48 4 w and dips 76 9 sw consistent with the trend of the aftershock zone and moment tensor solutions bootstrap resampling of the data is used to graphically illustrate the uncertainty in the location of the rupture plane the 95 confidence envelope overlaps the aftershock zone arguing that there is not a significant discrepancy between the geodetic data and the aftershock locations second we estimate the slip distribution using the best fitting uniform slip fault orientation but increase the fault length to 40 km and the downdip width to 18 km the fault is divided into 162 subfaults 18 along strike and 9 along dip each subfault is allowed to have constant right lateral and reverse components of slip we then solve for the slip on each subfault that minimizes a linear combination of the norm of the weighted data residual and the roughness of the slip distribution the smoothing parameter which determines the relative weight put on fitting the data versus smoothing the slip distribution is chosen by cross validation simulations indicate that cross validation estimates of the smoothing parameter are nearly optimal the preferred slip distribution is very heterogeneous with maximum strike slip and dip slip of about 5 and 8 m respectively located roughly 10 km north of the hypocenter there is insignificant dip slip in the southeastern most part of the fault causing the rake to vary from nearly pure right lateral in the southeast to oblique right reverse in the northwest the change in rake is consistent with a uniform stress field if the fault dip increases by about 10 toward the southeast as indicated by the aftershock locations there was little slip above 4 km depth consistent with the observation that there was little if any surface rupture

spectral comparison of continuous global positioning system and strainmeter measurements of crustal deformation temporal power spectral density models of noise in continuous crustal deformation measurements obtained with the global positioning system gps and high quality strainmeters are compared the crossover frequency at which gps measurement noise is less than that of strainmeters is determined assuming gps precision of 0 1 to 1 cm in horizontal components for baselines up to 100 km in length local deformation monitoring with gps may be preferable to strainmeters for observations of short term deformation in under 6 months of continuous at least daily measurements short period tropospheric path delays and multipath effects which may obscure gps determined strain signals in local network measurements also are discussed

seismicity and geometry of a 110 km long blind thrust fault 2 synthesis of the 1982 1985 california earthquake sequence during 1982 1985 three 5 4 mw 6 5 earthquakes migrated 65 km along the north half of a string of quaternary folds at the east front of the california coast ranges there is no surface fault associated with these earthquakes but the fold chain oriented parallel to the san andreas fault 30 km to the west takes up contraction normal to the san andreas fault identification of active blind thrust faults is hindered by the absence of a fault trace but may be revealed by the presence of growing folds at the surface and by earthquakes at depth because of excellent seismic geodetic and geologic data this earthquake sequence illuminates the geometry of the blind faults and enables us to probe their mechanics we relocate seismicity and compute focal mechanisms in a three dimensional velocity space and model the vertical deformation associated with the 1983 m 6 5 coalinga earthquake the aftershock zones abut at echelon offsets in the fold axes and the mainshocks display reverse slip perpendicular to the axes suggesting that the folds conceal a contiguous segmented thrust fault background seismicity concentrates at bends and breaks in the fold chain sites that may correspond to tears and ramps in the thrust fault at depth seismic reflection profiles reveal thrust and reverse faults dipping toward the san andreas fault at depths of 5 10 km with several kilometers of cumulative slip and high angle reverse faults in the anticlines with several hundred meters cumulative slip coseismic fold uplift accompanied the coalinga and kettleman hills north dome earthquakes suggesting that fold growth is episodic and coupled closely to repeated earthquakes on the underlying thrusts the north half of the fold chain has been the site of several 6 m 6 5 earthquakes since 1885 thus kettleman hills middle dome the next fold segment to the south has an elevated seismic potential the aftershock zones of the three main shocks are diffuse and occupy a region much larger than the site of seismic slip aftershocks occur 5 7 km from the fault regions where on the basis of a boundary element model the shear strain increase caused by the fault slip exceeds 20 ppm equivalent to about 0 7 mpa we argue that the broad aftershock zone is a product of high sustained off fault stress caused by repeated displacement on faults that do not cut the earth s surface the fault tip stresses lead to the formation of secondary faults which can become sites of aftershocks and postseismic creep

the displacement field of the landers earthquake mapped by radar interferometry geodetic data obtained by ground or space based techniques can be used to infer the distribution of slip on a fault that has ruptured in an earthquake although most geodetic techniques require a surveyed network to be in place before the earthquake1 3 satellite images when collected at regular intervals can capture co seismic displacements without advance knowledge of the earthquake s location synthetic aperture radar sar interferometry first introduced4 in 1974 for topographic mapping5 8 can also be used to detect changes in the ground surface by removing the signal from the topography9 10 here we use sar interferometry to capture the movements produced by the 1992 earthquake in landers california11 we construct an interferogram by combining topographic information with sar images obtained by the ers 1 satellite before and after the earthquake the observed changes in range from the ground surface to the satellite agree well with the slip measured in the field with the displacements measured by surveying and with the results of an elastic dislocation model as a geodetic tool the sar interferogram provides a denser spatial sampling 100 m per pixel than surveying methods1 3 and a better precision 3 cm than previous space imaging techniques12 13

strain measurements and the potential for a great subduction earthquake off the coast of washington geodetic measurements of deformation in northwestern washington indicate that strain is accumulating at a rate close to that predicted by a model of the cascadia subduction zone in which the plate interface underlying the continental slope and outer continental shelf is currently locked but the remainder of the interface slips continuously presumably this locked segment will eventually rupture in a great thrust earthquake with a down dip extent greater than 100 kilometers

coseismic displacements 1992 landers california earthquake the rupture associated with the 1992 landers earthquake ms 7 5 extended along the west edge of a 60 50 km trilateration network that had been surveyed two months before the earthquake and was resurveyed a month after it the coseismic displacement field within the network was calculated from the changes observed in the trilateration network supplemented by the displacements measured at four gps stations and other less timely trilateration measurements stations near the rupture were displaced by as much as 3 m the observed changes are reproduced reasonably well by dislocation modeling in which the landers rupture is represented by 8 vertical fault segments each extending from the surface to 9 km depth two additional segments represent the big bear and eureka peak faults the average modeled right lateral slip on the landers rupture is about 5 m however the residuals for the best fit slip distribution are about four times greater than expected from measurement error given that uncertainty a broad range of slip models furnish acceptable fits to the data the large residuals are attributed to inelastic deformation principally sympathetic slip on numerous unmodeled faults within the fault blocks assumed to be elastic in the model

hydraulic fracturing water use variability in the united states and potential environmental implications until now up to date comprehensive spatial national scale data on hydraulic fracturing water volumes have been lacking water volumes used injected to hydraulically fracture over 263 859 oil and gas wells drilled between 2000 and 2014 were compiled and used to create the first u s map of hydraulic fracturing water use although median annual volumes of 15 275 m3 and 19 425 m3 of water per well was used to hydraulically fracture individual horizontal oil and gas wells respectively in 2014 about 42 of wells were actually either vertical or directional which required less than 2600 m3 water per well the highest average hydraulic fracturing water usage 10 000 36 620 m3 per well in watersheds across the united states generally correlated with shale gas areas versus coalbed methane tight oil or tight gas where the greatest proportion of hydraulically fractured wells were horizontally drilled reflecting that the natural reservoir properties influence water use this analysis also demonstrates that many oil and gas resources within a given basin are developed using a mix of horizontal vertical and some directional wells explaining why large volume hydraulic fracturing water usage is not widespread this spatial variability in hydraulic fracturing water use relates to the potential for environmental impacts such as water availability water quality wastewater disposal and possible wastewater injection induced earthquakes

global positioning system measurements of deformations associated with the 1987 superstition hills earthquake evidence for conjugate faulting large station displacements observed from imperial valley global positioning system gps campaigns are attributed to the november 24 1987 superstition hills earthquake sequence thirty sites from a 42 station gps network established in 1986 have been reoccupied during 1988 and or 1990 displacements at three sites within 3 km of the surface rupture approach 0 5 m eight additional stations within 20 km of the seismic zone are displaced at least 10 cm this is the first occurrence of a large earthquake ms 6 6 within a preexisting gps network best fitting uniform slip models of rectangular dislocations in an elastic half space indicate 130 8 cm right lateral displacement along the northwest trending superstition hills fault and 30 10 cm left lateral displacement along the conjugate northeast trending elmore ranch fault the geodetic moments are 9 4 1025 dyn cm and 2 3 1025 dyn cm for the superstition hills and elmore ranch faults respectively consistent with teleseismic source parameters the data also suggest that postseismic slip along the superstition hills fault is concentrated at shallow depths distributed slip solutions using singular value decomposition indicate near uniform displacement along the elmore ranch fault and concentrated slip to the northwest and southeast along the superstition hills fault a significant component of nonseismic secular displacement is observed across the imperial valley which is attributed to interseismic plate boundary deformation

discrepancy between geological and geodetic deformation rates in the ventura basin space geodesy provides a new tool for measuring neotectonic deformation which when combined with geological and geophysical observations and models can be used to infer rates and styles of deformation in the ventnra basin region of southern california the geodetically measured convergence rates of 7 10 mm yr 1 ref 1 are significantly lower than the 20 25 mm yr 1 estimated from geological data2 3 here we investigate the possible implications of this discrepancy it might be for example that temporal variations cause the short and long term convergence rates to differ but if this were the case we would expect to observe the long term rate by extending the geodetic measurements over a broader region yet only 11 3 mm yr 1 of regional convergence is observed4 our preferred explanation of the discrepancy is that the geological models require revision and to this end we present two deformation models that satisfy both the geological and geodetic constraints our modelling suggests that the faults bounding the basin are locked at the surface but are slipping at depths below 2 5 km

tide gage measurements of uplift along the south coast of alaska annual mean sea levels along the south coast of alaska are used to measure uplift along the alaska aleutian subduction zone oceanographic effects are removed from the observed annual mean sea levels by subtracting a correction that is proportional to the sea level fluctuations observed in southeast alaska that correction is effective in reducing fluctuations in the observed annual mean sea level as far west as the tip of alaska peninsula additional corrections to remove the eustatic rise in sea level and the apparent fall in sea level due to postglacial isostatic rebound of the land are introduced this corrected sea level record should provide a measure of tectonic subsidence in the area affected by the 1964 alaska earthquake postseismic uplift occurs where coseismic subsidence was observed and postseismic subsidence occurs where coseismic uplift was observed the immediate postseismic response is damped out within the first decade and the subsequent uplift rates appear to be steady over the 1974 1989 interval however some of those rates seem to be too high to be sustained over the 1000 year earthquake recurrence interval appropriate to this area if the interseismic deformation is only to recover the coseismic displacement thus a long term 100 years relaxation in uplift rates is postulated the immediate time constant 5 years postseismic relaxation is attributed to postseismic slip on the plate interface directly downdip from the coseismic rupture the long term time constant 100 years relaxation is attributed to flow in the asthenosphere

modeling of postseismic relaxation following the great 1857 earthquake southern california abstract repeated first order triangulation measurements made from 15 monuments in central and southern california are used to explore the structure of the crust and upper mantle beneath southern california as well as to estimate the distribution of slip during the great 1857 earthquake the monuments are divided into two subnetworks with repeated observations covering the respective time intervals from 1884 to 1923 and from 1898 to 1923 the angle changes occurring within these times are modeled as a sum of two contributions postseismic displacements following the 1857 earthquake and plate tectonic loading the postseismic displacements have been calculated using a elastic viscoelastic coupling model that for any fault geometry yields the exact displacements on a spherically stratified earth the southern california crust and upper mantle are modeled as an upper elastic plate underlain by a viscoelastic asthenosphere for several different combinations of structural parameters inversions are performed for the slip distribution of the 1857 earthquake in general the best fits to the data are achieved with a triangular slip distribution an elastic plate thickness of 16 km a crustal thickness of 16 to 33 km and a mantle viscosity of 0 4 to 0 8 10 19 pa s although these inversions identify the best rheological models they lead to observed residuals that are inconsistent with a normally distributed data set a preferred model of slip is constructed that accounts for the budget of total slip during the earthquake cycle and satisfies a normally distributed data set the preferred slip distribution is similar in shape to the mapped surface slip distribution but is greater in amplitude by a factor of 1 5 to 2 in addition the san jacinto fault which has no known surface slip associated with the 1857 earthquake is inferred to have accommodated 1 to 3 m of slip during the 1857 earthquake and appears to be the favored site for tectonic strain accumulation since 1857 inferred fault slip exceeding known surface slip implies either unrecognized secondary faulting or a slip deficit at the surface relative to the slip at depth

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

a fault model for the 1989 kilauea south flank earthquake from leveling and seismic data the geometry of the fault that ruptured during the m6 1 south flank earthquake on kilauea volcano in 1989 is determined from leveling data the elastic dislocation in a homogeneous elastic half space that best fits the data is found using a nonlinear inversion procedure the best fitting model is a gently dipping thrust fault that lies at 4 km depth this is significantly shallower than the 9 km hypocentral depth determined from the local seismic network two dimensional finite element calculations indicate that at least part of this discrepancy can be attributed to the focusing of the surface deformation by the upper few kilometers of compliant low density lavas we conclude that it is important to include realistic elastic structure to estimate source geometry from geodetic data

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

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

baseflow recession analysis in a large shale play climate variability and anthropogenic alterations mask effects of hydraulic fracturing abstract water resources development and landscape alteration exert marked impacts on water cycle dynamics including areas subjected to hydraulic fracturing hf for exploitation of unconventional oil and gas resources found in shale or tight sandstones here we apply a conceptual framework for linking baseflow analysis to changes in water demands from different sectors e g oil gas extraction irrigation and municipal consumption and climatic variability in the semiarid eagle ford play in texas usa we hypothesize that in water limited regions baseflow q b changes are partly due along with climate variability to groundwater abstraction for a more realistic assessment the analysis was conducted in two different sets of unregulated catchments located outside and inside the eagle ford play three periods were considered in the analysis related to hf activities pre development 1980 2000 moderate 2001 2008 and intensive 2009 2015 periods results indicate that in the eagle ford play region temporal changes in baseflow cannot be directly related to the increase in hydraulic fracturing instead substantial baseflow declines during the intensive period of hydraulic fracturing represent the aggregated effects from the combination of 1 a historical exceptional drought during 2011 2012 2 increased groundwater based irrigation and 3 an intensive hydraulic fracturing activity

record warming in the south pacific and western antarctica associated with the strong central pacific el nino in 2009 10 1 satellite data for the past three decades reveal a record high sea surface temperature sst anomaly within a large mid latitude region of the south central pacific scp during the mature phase of the 2009 10 el nino with a peak magnitude that is 5 times the standard deviation of local sst anomaly and is warmer than the concurrent tropical pacific sst anomaly the scp oceanic warming was confined to the upper 50 meters and is associated with an extreme and persistent anticyclone wind changes associated with the anticyclone caused the oceanic warming with surface heat flux and ocean processes playing equally important roles the anticyclone diverted circumpolar westerlies and warm air towards antarctica austral summer sst in the bellingshausen sea also reached a three decade high the extreme atmospheric and oceanic anomalies in the south pacific may have been fueled by the 2009 10 el nino because of its record high sst anomaly in the central equatorial pacific

earthquakes quaternary faults and seismic hazard in california data describing the locations slip rates and lengths of quaternary faults are the primary basis in this work for constructing maps that characterize seismic hazard in california the expected seismic moment m0e and the strength of ground shaking resulting from the entire rupture of each mapped fault or fault segment are estimated using empirical relations between seismic moment m0 rupture length source to site distance and strong ground motions assuming a fault model whereby the repeat time t of earthquakes on each fault equals m0e m0g where the moment rate m0g is proportional to fault slip rate it is observed that the moment frequency distribution of earthquakes predicted from the geologic data agrees well with the distribution determined from a 150 year historical record the agreement is consistent with the argument that the geologic record of quaternary fault offsets contains information sufficient to predict the average spatial and size distribution of earthquakes through time in california the estimates of t for each fault are the foundation for constructing maps that depict the average return period of 0 1g peak horizontal ground accelerations and the horizontal components of peak acceleration peak velocity and the pseudovelocity response at 1 period and 5 damping expected to occur at the level of 0 1 probability during a 50 year period of time a map is also formulated to show the probability that 0 1g horizontal ground accelerations will occur during the next 50 years the maps serve to illustrate the potential value of quaternary fault studies for assessing seismic hazard interpretation of available slip rates indicates that the largest and most frequent occurrence of potentially destructive strong ground motions are associated principally with the san andreas san jacinto calaveras hayward and ventura basin fault zones other regions of similarly high hazard may yet remain unrecognized this inadequacy results primarily from an incomplete data set numerous faults for example are mapped along the coastal region of northern california and within the modoc plateau but relatively few studies relating to fault slip rate are reported a similar problem exists for other stretches of coastal california where marine reflection studies provide evidence of active faulting offshore yet yield little or no information of fault slip rate geological and geophysical field studies can work to remove these deficiencies a concerted effort to locate and define rates of activity on all faults in california is the most promising means to further quantify present levels of seismic hazard in california

recent ground movement and seismic activity in campi flegrei southern italy episodic growth of a resurgent dome leveling surveys in campi flegrei an active volcanic caldera in southern italy show that this caldera has undergone both subsidence and uplift of a few meters during the past 85 years a single source located at a depth of about 3 km beneath the center of the caldera can account for almost all elevation changes recorded in campi flegrei since the first leveling survey conducted in 1905 1907 this includes leveling surveys that span periods of subsidence such as between 1905 1907 and 1919 and between january 1985 and october 1986 and periods of rapid uplift between march 1970 and october 1971 and between january 1981 and december 1984 a possible geometry for the source of uplift and subsidence beneath campi flegrei is a rectangular horizontal sheet located at a depth of about 3 km and centered a few hundred meters east of the city of pozzuoli the horizontal dimensions of this sheet are about 1 5 km by 3 0 km the long axis is oriented n70 w this sheet lies adjacent to the most intense area of seismicity that occurred from mid 1983 to december 1984 during an uplift episode this sheet may represent the top of a magma body undergoing internal pressure changes possibly by intrusion of additional magma subsidence is caused by groundwater removal from the water saturated deposits that fill this caldera to a depth of a few kilometers a temporary increase in subsidence rate after an uplift episode is caused by increased rate of groundwater removal from newly fractured regions that lie immediately above the magma body the close proximity of this water saturated region and the magma body makes it impossible to separate the depth to these two sources from the results of leveling surveys two observations indicate that uplift has occurred in the center of campi flegrei for at least the past several thousand years first marine deposits in the center of campi flegrei were uplifted at least 40 m between 4000 and 8000 years ago second continuous seismic profiles of the undersea portion of campi flegrei have identified only one region where rocks are fractured and faulted adjacent to the uplifted marine deposits that surround the point of maximum uplift indicated by recent leveling surveys on the basis of these observations and the historical record of activity we suggest that campi flegrei caldera is in a stage of growing a resurgent dome the present diameter of the resurgent dome is about 4 km and the maximum amount of vertical uplift during the past 10 000 years has probably not exceeded 100 m the episodes of rapid uplift and shallow earthquake swarms during the past 20 years are probably related to the growth of this resurgent dome

strain accumulation in the shumagin islands results of initial gps measurements deformation in the shumagin seismic gap has been monitored with repeated trilateration edm in the 1980 1987 interval and with the global positioning system gps in the 1987 1991 interval the geodetic network extends for 100 km across the shumagin islands to the alaska peninsula results from the gps surveys are consistent with those previously reported for the edm surveys we failed to detect significant strain accumulation in the n30 w direction of plate convergence using the method of simultaneous reduction for position and strain rates we found the average rate of extension in the direction of plate convergence to be 25 25 nanostrain yr nstrain yr during the 1987 1991 interval of gps surveys compared with 20 15 nstrain yr during the 1981 1987 interval of complete edm surveys we found a marginally significant 26 12 nstrain yr extension rate in the 1981 1991 interval covered by the combined edm and gps surveys strain rates are higher but not significantly so in the part of the network closest to the trench spatial variation in the deformation is observed in the 1980 1991 average station velocities where three of the four stations closest to the trench have an arcward velocity of a few mm yr the observed strain rates are an order of magnitude lower than the 200 nstrain yr rate predicted by dislocation models

baseflow recession and recharge as nonlinear storage processes discharge in many rivers is often fed by outflow from a shallow groundwater reservoir it is becoming clear that the outflow from this aquifer is not linearly proportional to storage as is commonly assumed in many algorithms numerical analysis of flow recession curves from about 100 river gauging stations instead reveals a nonlinear relationship between baseflow q and storage s for which the equation s aqb was adopted values of the exponent b are found by calibration to be between 0 and 1 but with a high concentration around 0 5 which is in accordance with the findings of other studies and theoretical approaches yielding b 0 5 for unconfined aquifers and relating the coefficient a to catchment properties primarily area and shape of basin pore volume and transmissivity this non linear reservoir function is proposed as a more realistic alternative to the linear reservoir function the relatively fast response of groundwater flow to rainfall is mainly a result of the increase of hydraulic head of the groundwater reservoir accelerating the exfiltration of old pre event water into the river bed as fissure and pore volumes communicate hydraulically it appears physically reasonable to model the system by one non linear reservoir for catchments or parts of them instead of applying independent parallel linear reservoirs the non linear reservoir algorithms are supported by an analytical derivation they are extended for the automatic separation of baseflow from a time series of daily discharge in rivers and the computation of storage and effective recharge of groundwater in river basins by inverse nonlinear reservoir routing the time series obtained allow the identification and quantification of long term changes to the water balance relationships between computed groundwater storage and observed groundwater level can also be established copyright 1999 john wiley sons ltd

monitoring co and pre seismic motion by geodetic techniques a recently built extensometer which is based on a highly stable capacitance transducer as well as a liquid bubble hughes tiltmeter are discussed in view of monitoring strain and deformations at the earth s surface these instruments are being used to control local variations whereas regional and global changes including gravity variations are monitored using repeated gps and very precise relative gravimetry with sufficient exterior control such as absolute gravimetry for calibration tidal measurements for separating tidal from other effects we will acquire a more or less complete system in combination with local leveling etc as used by several other authors as well for determination of time dependent phenomena

surface displacement of the 17 may 1993 eureka valley california earthquake observed by sar interferometry satellite synthetic aperture radar sar interferometry shows that the magnitude 6 1 eureka valley earthquake of 17 may 1993 produced an elongated subsidence basin oriented north northwest parallel to the trend defined by the aftershock distribution whereas the source mechanism of the earthquake implies a north northeast striking normal fault the 3 millimeter accuracy of the radar observed displacement map over short spatial scales allowed identification of the main surface rupture associated with the event these observations suggest that the rupture began at depth and propagated diagonally upward and southward on a west dipping north northeast fault plane reactivating the largest escarpment in the saline range

on the derivation of coseismic displacement fields using differential radar interferometry the landers earthquake we present a map of the coseismic displacement field resulting from the landers california june 28 1992 earthquake derived using data acquired from an orbiting high resolution radar system we achieve results more accurate than previous space studies and similar in accuracy to those obtained by conventional field survey techniques data from the ers 1 synthetic aperture radar instrument acquired in april july and august 1992 are used to generate a high resolution wide area map of the displacements the data represent the motion in the direction of the radar line of sight to centimeter level precision of each 30 m resolution element in a 113 km by 90 km image our coseismic displacement contour map gives a lobed pattern consistent with theoretical models of the displacement field from the earthquake fine structure observed as displacement tiling in regions several kilometers from the fault appears to be the result of local surface fracturing comparison of these data with global positioning system and electronic distance measurement survey data yield a correlation of 0 96 thus the radar measurements are a means to extend the point measurements acquired by traditional techniques to an area map format the technique we use is 1 more automatic 2 more precise and 3 better validated than previous similar applications of differential radar interferometry since we require only remotely sensed satellite data with no additional requirements for ancillary information the technique is well suited for global seismic monitoring and analysis

absolute far field displacements from the 28 june 1992 landers earthquake sequence on 28 june 1992 the largest earthquake in california in 40 years surface wave magnitude ms 7 5 occurred near the small town of landers in southeastern california and was followed three hours later by the nearby ms 6 5 big bear earthquake1 fortuitously the landers earthquake sequence coincided with the first week of the official three month test period of the international global positioning system and geodynamics service2 igs giving us an unprecendented opportunity to detect absolute pre co and post seismic displacements at a distance of 50 200 km from the main rupture with millimetre level precision mutual and independent confirmation of some of our geodetic results are demonstrated by bock et al in this issue3 for the landers earthquake the observed displacements indicate that the depth of the bottom of the rupture is shallower towards the northern end displacements were dominantly symmetric and the rupture extended further south on the johnson valley fault than has been mapped on the basis of surface ground offsets the combined geodetic moment for the landers and big bear earthquakes 1 1 1020 n m 1 agrees well with teleseismic estimates

deformation from 1973 through 1991 in the epicentral area of the 1992 landers california earthquake ms 7 5 deformation of a 50 60 km trilateration network that spans the epicenter of the 1992 landers earthquake ms 7 5 was measured by seven surveys over the 19 years preceding the earthquake three moderate earthquakes 1979 homestead valley ms 5 6 1986 north palm springs ms 6 0 and 1992 joshua tree ms 6 1 occurred within the network during those 19 years here we use geodetic and seismic data to construct a dislocation model for each of the three moderate earthquakes coseismic changes due to these three moderate earthquakes as predicted by the dislocation models are then removed from the trilateration data the residual geodetic changes appear to be uniform in time we take those changes to represent secular strain accumulation this strain accumulation clearly shows right lateral shear across the san andreas fault but also suggests a northwest southeast extension northeast of the eastern end of the big bend of the san andreas fault the landers earthquake ruptured along a north northwest trend across this region of northwest southeast extension

strain accumulation north of los angeles california as a function of time 1977 1992 no significant change in the rate of strain accumulation in a 40 120 km trilateration network spanning the san gabriel mountains was observed from 1977 5 to 1991 8 despite an apparent increase in seismicity ml 4 5 beginning in late 1987 in the northern los angeles basin immediately to the south the observed deformation 0 13 0 01 strain yr right lateral shear across a vertical plane striking n63 w 1 can be attributed to strain accumulation on the san andreas fault local strike n65 w no significant accumulation of compression normal to the strike of the san andreas fault was observed in the network as a whole

deformation from 1973 to 1987 in the epicentral area of the 1959 hebgen lake montana earthquake ms 7 5 a 40 km aperture trilateration network centered on the 1959 hebgen lake earthquake epicenter has been surveyed in 1973 1974 1976 1978 1981 1984 and 1987 the deformation inferred from those surveys is described roughly by a uniaxial 0 266 0 014 strain yr n15 e 1 extension that is uniform in both time and space that extension is orthogonal to the strike n78 w 5 of the 1959 rupture plane inferred from focal mechanism solutions the absence of strain accumulation in the n75 w direction suggests that the source of deformation must be greatly elongated in that direction looked at in greater detail the deformation is found to be concentrated in the northern part of the network the zone of concentrated deformation coincides with a part of a well defined trend in seismicity that extends at least 100 km n75 w from the sour creek resurgent dome in the yellowstone caldera extension perpendicular to that trend is indicated by focal mechanism solutions thus the zone of rifting identified within the hebgen lake network apparently extends east southeast to the yellowstone caldera about 8 mm yr extension is observed across a 20 km width within the zone

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

estimation of depth dependent fault slip from measured surface deformation with application to the 1906 san francisco earthquake we estimate the depth distribution of slip in the 1906 san francisco earthquake by applying new inversion methods to triangulation data collected near point arena california modeling crustal deformation from antiplane slip in a half space we define three regularizing functionals to produce minimum norm inverse problems these functionals measure components of the coseismic change in elastic strain energy stress magnitude and stress variability and are all quadratic in slip orthogonality conditions define finite dimensional representations of slip estimates coefficients of basis functions in these representations are estimated by damped least squares with damping parameter and faulting depth chosen by cross validation the best resulting estimates exhibit right lateral slip to depths of 15 to 20 km with about 6 m of surface slip this is consistent with directly observed offsets of cultural landmarks at the surface and indicates deeper faulting than has been previously inferred for the 1906 earthquake

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

vegetation and climate change in west java indonesia during the last 135 000 years abstract sedimentological and palynological analyses of two sediment cores from the intramontane bandung basin java indonesia provide the first palaeoclimatic record for the indonesian region covering the last 135 000 years our data indicate anomalously dry conditions for the penultimate glacial and very warm and humid conditions during the last interglacial during the last glacial period fresh water swamp forests of the bandung plain were replaced by open swamp vegetation dominated by grasses and sedges indicating a change to considerably drier climatic conditions possibly as a consequence of lower sea levels at the onset of glacial conditions for the last glacial maximum temperatures 4 7 c lower than at present are recorded

postseismic deformation following the 1989 m 7 1 loma prieta california earthquake postseismic deformation along a 90 km profile bisecting the projected surface trace of the coseismic rupture of the 1989 loma prieta earthquake has been monitored by frequent gps surveys for 3 3 years following the earthquake in addition to the expected deformation associated with secular strain accumulation on the san andreas and calaveras faults deformation associated with postseismic readjustment has been detected most of that deformation can be attributed to 1 5 m right lateral and 0 9 m reverse postseismic slip on a 5 km wide downdip extension of the loma prieta rupture in addition there seems to be a 0 1 m postseismic collapse of the loma prieta rupture zone in the direction perpendicular to the plane of the rupture the fault normal n48 e surface displacements plotted as a function of time exhibit a curvature suggesting a relaxation time of about 1 4 years similar plots of the fault parallel n42 w displacement components do not exhibit significant curvature presumably the deformation shown in those plots is dominated by secular strain accumulation along the san andreas and calaveras faults rather than postseismic relaxation

crustal deformation of the yellowstone caldera from first gps measurements 1987 1989 a global positioning system gps network was established in 1987 in order to measure crustal deformation across the yellowstone plateau centered on the yellowstone caldera and adjacent teton wyoming and hebgen lake montana fault zones forty four gps stations in the yellow stone network were re surveyed in 1989 and station coordinates using broadcast orbits were obtained these results were used to assess the precision and accuracy of the gps surveys and to identify areas of rapid crustal deformation on the yellowstone plateau the gps measured displacements between 1987 and 1989 were calculated relative to a station at the eastern edge of the 100 km wide network the relative horizontal displacements have an average magnitude of 15 10 mm the relative vertical displacements are generally less than 25 mm about an average near zero and with an uncertainty of 20 mm comparisons with leveling and trilateration measurements taken nearly simultaneously suggest that the accuracy of these gps measurements is at the level of the above uncertainties gps measured vertical displacements across the northern part of the yellowstone caldera and 1st order leveling results show up to 20 mm of subsidence between 1987 and 1989 this subsidence is part of a six year period of caldera deflation that began in 1985 in addition up to 66 mm of uplift is observed with gps at the northwest edge of the yellowstone caldera and may be associated with processes following an intense earthquake swarm in 1985 86 and with caldera subsidence

motion of kilauea volcano during sustained eruption from the puu oo and kupaianaha vents 1983 1991 kilauea erupted almost continuously from january 1983 through 1991 although the summit began subsiding during the rift zone dike intrusion that initiated this eruption remarkably steady ground surface motions began in late 1983 after a magnitude 6 6 earthquake beneath the slopes of nearby mauna loa volcano and continued until the onset of brief upper east rift zone earthquake swarms in late 1990 during these 7 years the summit and upper rift zones subsided up to 10 11 and 4 8 cm yr 1 respectively and summit baselines contracted up to 6 cm yr 1 baselines directed northward from the summit to stations on mauna loa extended at rates up to 7 cm yr 1 and a baseline from south of the summit to mauna loa extended 4 cm yr 1 much of this extension is inconsistent with deformation caused solely by summit magma reservoir collapse and more likely reflects rifting as the south flank of the volcano moved seaward from the summit and rift zones farther from the summit baselines crossing the south flank extended up to 2 cm yr 1 and a south flank tide gauge rose 2 cm yr 1 the lower east rift zone 40 50 km from the summit subsided about 2 cm yr 1 motion on kilauea then is broadly consistent with slip along low angle south flank faults generating subsidence that is focused at the summit and along the rift system behind the faulting and uplift along the coastal south flank ahead of it dislocation models that combine these elements show that much of kilauea s edifice migrated seaward producing ground surface motions along the south flank of up to about 6 cm yr 1 the magnitude 6 1 earthquake of 1989 punctuated these motions along the eastern south flank producing more than 25 cm of seaward displacement and 15 km east of the epicenter up to 24 cm of subsidence south of the lower east rift zone unlike the magnitude 7 2 south flank earthquake of 1975 the 1989 event was preceded neither by summit magma reservoir inflation nor by rift zone dike intrusions and accompanying compression of the south flank deformation was probably caused by the weight of the volcanic overburden and by ongoing dilation and slip within the rift system

earthquake geodesy and hazard monitoring catastrophic events such as major earthquakes and volcanic eruptions result when the earth s crust fails in response to accumulated deformation the accumulation of deformation results from ongoing processes such as aseismic deformation of subcrustal rock associated with relative plate motions or the ascent of magma through a volcanic plumbing system geodetic measurements document the crustal deformation leading to these failures and the deformation resulting from them providing unique insight into the physical processes involved by virtue of the space and time domains of ground deformation detected with geodetic measurements geodesy is a useful tool in monitoring active tectonic and volcanic regimes for a wide range of natural events including earthquakes aseismic fault motions and volcanic events geodetic measurements constrain physical models of the processes that cause such events because these geodetic studies probe the underlying processes leading to and culminating in catastrophic natural events many such studies are directly applicable to earthquake and volcano hazard assessment

detection of crustal deformation from the landers earthquake sequence using continuous geodetic measurements the measurement of crustal motions in technically active regions is being performed increasingly by the satellite based global positioning system gps 1 2 which offers considerable advantages over conventional geodetic techniques3 4 continuously operating gps arrays with ground based receivers spaced tens of kilometres apart have been established in central japan5 6 and southern california to monitor the spatial and temporal details of crustal deformation here we report the first measurements for a major earthquake by a continuously operating gps network the permanent gps geodetic array pgga 7 9 in southern california the landers magnitude afw of 7 3 and big bear mw 6 2 earthquakes of 28 june 1992 were monitored by daily observations ten weeks of measurements centred on the earthquake events indicate significant coseismic motion at all pgga sites significant post seismic motion at one site for two weeks after the earthquakes and no significant preseismic motion these measurements demonstrate the potential of gps monitoring for precise detection of precursory and aftershock seismic deformation in the near and far field

the faulting process of tangshan earthquake inverted simultaneously from the teleseismic waveforms and geodesic deformation data abstract it is well known that for natural earthquakes the faulting processes are highly complicated to study such processes all of the different types of data that can be acquired should be incorporated into the investigations in accordance with this consideration the faulting process of the tangshan earthquake m s 7 8 on 27 july 1976 is investigated first the geometrical attitude of the fault is determined by analysing the geological structure intensity distribution locations of the aftershocks and geodesic data collectively then the faulting process is simultaneously inverted from 14 wwssn long period teleseismic waveforms and 70 horizontal geodesic static deformation data the results show that the tangshan earthquake is one of the strongest intraplate earthquakes with a complex faulting process the dimension of the main fracture is approximately 100 km by 15 km with a change in direction at the central part of the fault the southern segment strikes at about ne30 becoming 50 60 for the northern segment the total seismic moment inverted is 2 0 10 20 nm and the dislocation was relatively concentrated near the central part of the fault where the slip elapsed for a longer time these results suggest that near the city of tangshan there might be a strong unbroken block and the fault changes its trend there hence the fault system was locked before the earthquake when the regional stress increased and exceeded the strength limit the fracture initiated from this location and extended bilaterally

horizontal deformation in the cascadia subduction zone as derived from serendipitous geodetic data abstract data from recent global positioning system gps surveys are combined with triangulation trilateration data to estimate horizontal shear strain rates for two regions in the cascadia subduction zone near bellingham washington we estimate that the maximum horizontal shear rate equals 0 116 0 089 rad yr and the direction of maximum horizontal contraction orients n71 e 21 for data spanning the 1905 1985 interval the corresponding estimates for a region near portland oregon are 0 057 0 027 rad yr and n95 e 14 for data spanning the 1881 1988 interval these estimates are consistent with estimates from independent geodetic data in the area moreover the estimates for are consistent with the n68 e direction of ongoing convergence between the juan de fuca plate and the north american plate as predicted by the nuvel 1 plate motion model this consistency between estimates and the direction of plate convergence supports the argument for the possibility of a great subduction earthquake occurring in the cascadia subduction zone the low shear rates however imply that the recurrence interval between such earthquakes would be several centuries long

analysis of coseismic surface displacement gradients using radar interferometryc new insights into the landers earthquake the map of the coseismic displacement field generated by interferometric processing of synthetic aperture radar lsarr images taken before and after the june 28 1992 landers earthquake sequence brings new insights into the nature of deformation caused by these earthquakes we use the interferometric map generated by massonnet et al l1993r to analyze the surface displacement field in the vicinity of the fault trace complexities in the fringe pattern near the fault reflect shorthwavelength variations of the surface rupture and slip distribution and attest to large displacement gradients along two sections of the fault characteristic fringe patterns can be recognized contrasting in density and direction with patterns observed away from the rupture in order to understand the observed fringe patterns we compute synthetic interferograms in three simple cases l1r rigidhbody rotations about a vertical axis l2r about a horizontal axis ltiltr and l3r distributed simple shear the orientation and spatial separation of interferometric fringes predicted by these models help constrain nearhfield deformation and rupture parameters where the kickapoo fault connects with the homestead valley fault the interferogram shows a clear pattern of parallel n20 w fringes separated by about 160 m this pattern and vertical offsets measured along the kickapoo fault suggest that the block between this fault and the johnson valley fault may have been tilted down to the west a 5hkm block lifted by l m on one side would be tilted by an angle of 0 01 l190 radr producing fringes separated by about 160 m parallel to the tilt axis such a tilt parallel to a n20 w direction would account for the gradual northward increase of the vertical slip component observed along the kickapoo fault this tilt may also explain the 1 m of reverse slip observed along the slip gap section of the homestead valley break between the southern end of the johnson valley fault and the eureka peak fault where no surface rupture has been mapped the dense pattern of fringes implies distributed shear probably resulting from fault slip at depth the density and direction of the fringes in the gap are consistent with a righthlateral slip of 1 2 3 8 m on a blind fault locked above the depth of 1 5 2 km such observations of small wavelength features in the sar interferogram bring new insights into the nearhfield displacement gradient and thus on response of the uppermost crust to seismic rupture

interseismic deformation at the nankai trough japan subduction zone uplift along the coast of southwestern japan following the 1944 tonankai ms 8 0 and 1946 nankaido ms 8 2 earthquakes has been inferred from the 1950 1985 tide gage records although uplift rates vary with geographic position the temporal dependence at each site can be described as the superposition of an exponentially decaying time constant 5 years transient significant only in the first decade postseismic and a steady interseismic rate the steady interseismic uplift rate is defined only over the 1956 1985 interval but the linearity in time ofthat uplift record is such that uplift over the remainder of the interseismic cycle 80 years might reasonably be expected to occur at the same rate moreover the spatial pattern and magnitude of the steady uplift rate are reasonably close to those predicted by a simple dislocation model of subduction however the currently observed steady uplift rate is not consistent with the uplift rate inferred from geodetic leveling for the final half of the previous earthquake cycle thus either the hypothesis of a steady interseismic uplift rate after the first decade postseismic is wrong or the strain accumulation pattern for one earthquake need not be the same as for the preceding earthquake on the same segment

near field investigations of the landers earthquake sequence april to july 1992 the landers earthquake which had a moment magnitude m w of 7 3 was the largest earthquake to strike the contiguous united states in 40 years this earthquake resulted from the rupture of five major and many minor right lateral faults near the southern end of the eastern california shear zone just north of the san andreas fault its m w 6 1 preshock and m w 6 2 aftershock had their own aftershocks and foreshocks surficial geological observations are consistent with local and far field seismologic observations of the earthquake large surficial offsets as great as 6 meters and a relatively short rupture length 85 kilometers are consistent with seismological calculations of a high stress drop 200 bars which is in turn consistent with an apparently long recurrence interval for these faults