determining vertical leakage from the great artesian basin australia through up scaling field estimates of phreatic evapotranspiration summary understanding the water balance of large groundwater systems is fundamental for the sustainable management of the resource the vertical leakage i e discharge to upper aquifers or the unconfined water table component of the great artesian basin gab is an example of a poorly constrained but large component of the water balance of australia s largest groundwater resource field estimates of phreatic evapotranspiration et were made at discharge zones along the southwestern margin of the gab using eddy covariance station and micro lysimeter measurements and inversion of chloride isotope soil profile measurements the field estimates were assigned to three major landforms associated with areas of increasingly higher evaporative discharge and progressively decreasing depths to the water table these landforms were mapped using remote sensing and digital elevation data with characteristically higher soil moisture salt precipitation and lower surface temperature compared to areas distal to discharge zones based on the field measurements broad ranges of phreatic et 0 5 10 10 100 and 100 300 mm y 1 were assigned to the major land types the higher phreatic et discharge zones mapped by supervised classification of satellite data are 8 28 of the total regional vertical leakage component estimated by numerical modelling of the gab in comparison the higher discharge zones estimated by landform mapping are 73 251 of the total vertical leakage component estimated by modelling the mapped distribution of the high discharge areas has important implications for modelling of the gab in the western sub basin most of the estimated recharge can be accounted for by phreatic et in the high discharge zones located around the basin margins implying that vertical leakage rates distal to the margins are very low and that discharge may exceed current recharge in contrast the results for the eastern sub basin suggest that vertical leakage rates around the south australian portion of the basin margin are low and that more of the vertical leakage component in the eastern sub basin is occurring distal to the basin margins consequently the pathways for vertical leakage in the eastern sub basin are likely to be more complex than for the western sub basin

present day crustal motion along the longitudinal valley fault eastern taiwan abstract the nne striking longitudinal valley fault lvf in eastern taiwan is an extremely active high angle thrust fault it bounds the coastal range and the longitudinal valley which is considered a collision boundary between the philippine sea and the eurasian plates repeated gps data in the longitudinal valley area from 1992 to 1999 are utilized to study the spatial variation of crustal motion along the lvf with respect to penghu in the chinese continental margin velocities for stations on the western side of the lvf longitudinal valley and eastern central range are 18 35 mm yr in directions 283 311 whereas those on the eastern side of the lvf the coastal range are 28 68 mm yr in directions 303 324 a major discontinuity of about 30 mm yr on the rate of crustal motion across the longitudinal valley is attributed to the aseismic slip along the lvf as revealed by trilateration data previously to the south of fengping the block motions of the coastal range are 31 40 mm yr in 317 330 relative to the central range while the near fault motions are 13 33 mm yr in 309 336 various partitions on the left lateral strike slip and convergent components along the lvf are found in the southern longitudinal valley crustal motion is mainly accommodated on the lvf and the luyeh fault in contrast those in the central and northern longitudinal valley are partly taken up on the faults to the east of the lvf or result in the elastic deformation of the coastal range the crustal motion in the northern longitudinal valley area is likely to be distributed in the several ne striking thrusts in a horsetail pattern and obliquely cut the northern coastal range with a small portion of fault slips along the lvf data from dense deployed gps networks across the lvf can be employed to give better estimates of near fault motions and delineate the surface traces of the lvf repeated gps and leveling data from two stations on both ends of the yuli bridge that are 575 m apart clearly indicate that the surface trace of the lvf passes beneath the bridge with oblique horizontal motion of 23 mm yr in 306 and uplift rate of 24 mm yr

watching the hayward fault the hayward fault located on the east side of the san francisco bay represents a natural laboratory for seismologists because it does not sleep silently between major earthquakes in his perspective simpson discusses the study by ba rgmann et al who have used powerful new techniques to study the fault the results indicate that major earthquakes cannot originate in the northern part of the fault however surface rupturing earthquakes have occurred in the area suggesting that they originated to the north or south of the segment studied by ba rgmann et al fundamental questions remain regarding the mechanism by which plate tectonic stresses are transferred to the hayward fault

using repeating earthquakes to correct high precision earthquake catalogs for time dependent station delays waveform cross correlation allows one to measure the relative arrival times of similar microearthquakes with errors of less than 1 10 of 1 sample location algorithms based on these measurements have greatly improved images of earthquake distribution for the northern california seismic network catalog however the relative location errors implied by the scatter of relocated repeating earthquakes sometimes 10s of meters is often considerably larger than the errors estimated from monte carlo simulations meters using a priori estimates of the cross correlation errors i find that most of this discrepancy arises from unmodeled time varying station delays by identifying many clusters of repeating earthquakes presumed to rupture the same source and assuming the measured arrival time differences between event pairs to be due to the difference in origin time plus the difference in station delay it is possible to invert for time dependent station corrections the method is robust in that these corrections are consistent over many kilometers of fault and greatly reduce the scatter and residuals when relocating earthquake clusters not used in the station correction determination many of the largest delay changes some approaching 2 samples 20 ms are associated with changing station electronics at several stations an annual cycle is also clearly seen with amplitudes up to 0 5 samples some m 4 7 earthquakes have produced comparable transient delay changes after applying the station corrections the scatter within clusters of repeating earthquakes is reduced to a few meters and the apparent seismogenic thickness of many kilometer long sections of faults is only 10 20 m manuscript received 31 may 2001

surface creep along the longitudinal valley fault taiwan from insar measurements 1 we use interferometric synthetic aperture radar insar analysis in eastern taiwan to study reverse creep on the longitudinal valley fault lvf a stack of the three highest quality image pairs spanning 1997 2000 shows sharp range change offsets along the eastern side of the longitudinal valley suggesting 11 35 mm yr of surface creep between 23 and 23 4 n no shallow slip was observed along the northern or southern ends of the valley nor on mapped fault traces on the western edge of the valley the width of the zone of deformation varied suggesting distributed shear in shallow sediments above the creeping fault in some places the insar results support the view that although surface creep is rapid in certain locations significant portions of the lvf are locked and thus represent a substantial seismic hazard

interplate quasi static slip off sanriku ne japan estimated from repeating earthquakes 1 space time distribution of quasi static slip on the plate boundary off sanriku northeastern ne japan was estimated by using small repeating earthquakes we found 2509 repeating earthquakes occurring on the plate boundary for the last 17 years based on the interpretation that these events are caused by repeating slips of small asperities surrounded by stable sliding area we regarded these repeating events as creepmeters embedded on the plate boundary the results show that deeper portions of the plate boundary are sliding almost stably and earthquakes with magnitudes more than 6 are accompanied by quasi static slips in the surrounding areas

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

continuous monitoring of an active fault in a plate suture zone a creepmeter study of the chihshang fault eastern taiwan abstract data from continuously monitored creepmeters across the active chihshang fault in eastern taiwan are presented the chihshang fault is an active segment of the longitudinal valley fault the main suture between the converging philippine and eurasian plates in taiwan since the 1951 earthquake mw 7 0 no earthquake larger than magnitude 6 0 occurred in the chihshang area at least during the last 20 years the chihshang fault underwent a steady creep movement resulting in numerous fractures at the surface five creepmeters were installed in 1998 at two sites tapo and chinyuan within the chihshang active fault zone one year results from august 1998 to july 1999 show a horizontal shortening of 19 4 0 3 mm and 17 3 0 7 mm at tapo and chinyuan respectively these annual shortening rates are in a good agreement with other estimates of strain rate independently obtained from geodetic measurements and geological site investigation the creepmeter measurements were made on a daily basis providing accurate information on the previously unknown evolution of creep during the year the records of fault creep at the tapo site thus revealed close seasonal correlation with average rainfall the period of high creep rate coincides with the wet season whereas that of low creep rate coincides with the dry season also in comparison with the tapo site the creep behaviour as a function of time is complex at the chinyuan site possible factors of irregularity are under investigation thermal effect acting on the concrete basement of the creepmeters earth tide effect water table variations in a nearby rice field and rainfall the comparison between gps measurements across the longitudinal valley 31 mm year of horizontal displacement and the creepmeter measurement across the chihshang fault zone 17 19 mm year of horizontal displacement suggests that there exists other shortening deformation across the active fault zone in addition to those we have measured from the creepmeters

characteristic repeating earthquakes in an arc continent collision boundary zone the chihshang fault of eastern taiwan abstract creeping crustal faults often generate a large number of microearthquakes and less commonly they may also produce major earthquakes that rupture the brittle crust the chihshang fault in eastern taiwan is characterized by such behavior and has been known to undergo 2 3 cm yr surface creep making it one of the most active creeping thrust faults known in the world it gives an excellent opportunity to study how a creeping fault can generate large earthquakes however the understanding of fault behavior at depth in this area has been limited due to sparse sampling from seismic and geodetic stations in this study we determine and evaluate a population of repeating earthquakes to improve the understanding of deep fault deformation we propose a repeating sequence identification scheme in the region where the station coverage is sparse and one sided using this identification method we found 30 m 2 3 characteristic repeating sequences under the northern half of the chihshang fault at 7 23 km depth slip estimates from these sequences indicate an average slip rate of 3 cm yr which is consistent with the rate inferred from surface geodetic measurements we infer that the 30 km long chihshang fault is creeping along its northern half and locked in the south consistent with the occurrence of the 2003 ml 6 4 earthquake on the southern fault section

stability of coda wave attenuation during the loma prieta california earthquake sequence the loma prieta california earthquake occurred in a densely instrumented region with a history of microearthquake recording beginning more than a decade before the october 1989 mainshock this affords an unprecedented opportunity to detect changes in seismic wave propagation in the earth s crust associated with a major earthquake in this study we use pairs of nearly identical earthquakes doublets to search for temporal changes of coda attenuation in the vicinity of the loma prieta earthquake we analyze 21 earthquake doublets recorded from 1978 to 1991 that span the preseismic coseismic and postseismic intervals and measure the change in coda q using a running window ratio of the doublet spectral amplitudes in three frequency bands from 2 to 15 hz this method provides an estimate of changes in coda q that is insensitive to other factors that influence coda amplitudes our observations place an upper bound of about 5 on preseismic coseismic and postseismic changes of coda q in the epicentral region of the loma prieta earthquake even at this low level the changes are neither spatially coherent nor correlated between adjacent frequency bands the only hint of a signal is in the preseismic data where there is a possible precursory increase in coda q of approximately 5 in the two years before the mainshock the stability of coda q throughout the loma prieta sequence is in sharp contrast to other studies that have reported much larger precursory changes in coda q for other earthquakes

repeating earthquakes as low stress drop events at a border between locked and creeping fault patches the source of repeating earthquakes on creeping faults is modeled as a weak asperity at a border between much larger locked and creeping patches on the fault plane the x 1 2 decrease in stress concentration with distance x from the boundary is shown to lead directly to the observed scaling t m 1 6 between the average repeat time and average scalar moment for a repeating sequence the stress drop in such small events at the border depends on the size of the large locked patch for a circular patch of radius r and representative fault parameters 7 6 m r 3 5 mpa which yields stress drops between 0 08 and 0 5 mpa 0 8 5 bars for r between 2 km and 100 m these low stress drops are consistent with estimates of stress drop for small earthquakes based on their seismic spectra however they are orders of magnitude smaller than stress drops calculated under the assumption that repeating sources are isolated stuck asperities on an otherwise creeping fault plane whose seismic slips keep pace with the surrounding creep rate linear streaks of microearthquakes observed on creeping fault planes are trivially explained by the present model as alignments on the boundaries between locked and creeping patches

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

variability of fault slip behavior along the san andreas fault in the san juan bautista region an improved understanding of the time history of fault slip at depth is an essential step toward understanding the underlying mechanics of the faulting process using a waveform cross correlation approach we document spatially and temporally varying fault slip along the northernmost creeping section of the san andreas fault near san juan bautista sjb california by systematically examining spatiotemporal behaviors of characteristically repeating earthquakes cres the spatial distribution of pre 1998 sjb earthquake 1984 1998 fault slip rate inferred from the cres reveals a 15 km long low creep or partially locked section located near the 1998 mw 5 1 sjb earthquake rupture a finite fault slip inversion reveals that the rupture of the 1998 sjb earthquake is characterized by the failure of a compact 4 km2 asperity with a maximum slip of about 90 cm and corresponding peak stress drop of up to 50 mpa whereas the mean stress drop is about 15 mpa following the 1998 earthquake the cre activity was significantly increased in a 5 10 km deep zone extending 2 7 km northwest of the main shock which indicates triggering of substantial aseismic slip the postseismic slip inferred from the cre activity primarily propagated to the northwest and released a maximum slip of 9 cm in this 5 10 km depth range the estimated postseismic moment release is 8 6 1016 n m which is equivalent to mw 5 22 the aseismic slip distribution following the 1998 earthquake is not consistent with coseismic stress driven afterslip but represents a triggered long lasting slow earthquake

dislocation model for crustal deformation in the longitudinal valley area eastern taiwan abstract three trilateration and leveling networks traversing the longitudinal valley eastern taiwan have been surveyed frequently during 1983 1988 average rates of length change on each line and height difference on each leveling section are used to study the crustal deformation of this area we model the aseismic deformation near the fault as the sum of a steady rigid block motion and the effect of an upper locked crust due to frictional resistance the effect of the locked part is equivalent to that of a negative dislocation on the fault for the northernmost hualien and central yuli networks we simply assume two blocks and one fault patch while the southernmost taitung network is modeled by three blocks and three fault patches the fault aforementioned is presumed to be the main trace of the longitudinal valley fault lvf we invert the geodetic data to determine the block motion and dislocation model parameters by utilizing a bayesian nonlinear inversion method parameters to be estimated include the three components of velocity for each block and the vertical and horizontal dislocation rates dip angle and width of each rectangular fault patch the estimated block motion parameters and fault widths are mostly well resolved by the observed data the fault widths are all very shallow tectonophysics vol 42 is concentrated on a quite narrow zone several kilometers wide centered at the lvf however due to the limited aperture of our geodetic networks the total width of the deformation zone and the velocity of relative plate motion at this active collision boundary are not resolved the new gps satellite survey technique can be used to solve this ambiguity

coseismic deformation revealed by inversion of strong motion and gps data the 2003 chengkung earthquake in eastern taiwan summary a moderate earthquake of mw 6 8 occurred on 2003 december 10 it ruptured the chihshang fault in eastern taiwan which is the most active segment of the longitudinal fault as a plate suture fault between the luzon arc of the philippine sea plate and the eurasian plate the largest coseismic displacements were 13 cm horizontal and 26 cm vertical we analyse 40 strong motion and 91 gps data to model the fault geometry and coseismic dislocations the most realistic shape of the chihshang fault surface is listric in type the dipping angle of the seismic zone is steep about 60 70 at depths shallower than 10 km and then gradually decreases to 40 50 at depths of 20 30 km thus the polygonal elements in poly3d are well suited for modelling complex surfaces with curving boundaries using the strong motion data the displacement reaches 1 2 m dip slip on the chihshang fault and decreases to 0 1 m near surface the slip averages 0 34 m releasing a scalar moment of 1 6e26 dyne cm for gps data our model reveals that the maximal dislocation is 1 8 m dip slip the dislocations decrease to 0 1 m near the surface the average slip is 0 48 m giving a scalar moment of 2 2e26 dyne cm regarding post seismic deformation a displacements of 0 5 m were observed near the chihshang fault indicating the strain had not been totally released as a probable result of near surface locking of the fault zone

earthquake potential along the northern hayward fault california the hayward fault slips in large earthquakes and by aseismic creep observed along its surface trace dislocation models of the surface deformation adjacent to the hayward fault measured with the global positioning system and interferometric synthetic aperture radar favor creep at 7 millimeters per year to the bottom of the seismogenic zone along a 20 kilometer long northern fault segment microearthquakes with the same waveform repeatedly occur at 4 to 10 kilometer depths and indicate deep creep at 5 to 7 millimeters per year the difference between current creep rates and the long term slip rate of 10 millimeters per year can be reconciled in a mechanical model of a freely slipping northern hayward fault adjacent to the locked 1868 earthquake rupture which broke the southern 40 to 50 kilometers of the fault the potential for a major independent earthquake of the northern hayward fault might be less than previously thought

the long recurrence intervals of small repeating earthquakes may be due to the slow slip rates of small fault strands observations since 1998 have revealed that repeating earthquakes and particularly small repeating earthquakes occur less often than expected given their seismically derived slip and the regional fault slip rate here we test the hypothesis that small repeaters occur infrequently because they occur on fault segments or strands with low slip rates we analyze the recurrence interval moment scaling of earthquake sequences near parkfield california we find that closely spaced sequences which likely occur on the same fault strand and respond to the same slip rate follow a scaling consistent with seismic slip rates while widely spaced sequences which likely occur on different strands follow a scaling consistent with the previous counter intuitive observations these results suggest that spatially varying slip rates could create the recurrence interval scaling though we cannot exclude other explanations

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

shear concentration in a collision zone kinematics of the chihshang fault as revealed by outcrop scale quantification of active faulting longitudinal valley eastern taiwan abstract repeated measurements of active deformation were carried out at three sites along the active chihshang fault a segment of the longitudinal valley fault zone of eastern taiwan the present day plate boundary between the philippine sea plate and eurasia reliable annual records of displacement along an active fault were obtained based on detailed surveys of faulted concrete structures along the active chihshang fault striking n18 e we determined average motion vectors trending n37 w with an average shortening of 2 2 cm yr thus the transverse component of motion related to westward thrusting is 1 8 cm yr whereas the left lateral strike slip component of motion is 1 3 cm yr the fault dips 39 45 to the east so that the vertical displacement is 1 5 3 cm yr and the actual oblique offset of the fault increases at a rate of 2 7 3 7 cm yr this is in good agreement with the results of regional geodetic and tectonic analyses in taiwan and consistent with the n54 w trend of convergence between the northernmost luzon arc and south china revealed by gps studies our study provides an example of extreme shear concentration in an oblique collision zone at chihshang the whole horizontal shortening of the longitudinal valley fault 2 2 cm yr on average occurs across a single narrow fault zone so that the whole reverse slip about 2 7 3 7 cm yr depending on fault dip was entirely recorded by walls 20 200 m long where faults are tightly localized this active faulting accounts for more than one fourth 27 of the total shortening between the luzon arc and south china recorded through gps analyses further surveys should indicate whether the decreasing shortening velocity across the fault is significant revealing increasing earthquake risk due to stress accumulation or not revealing continuing fault creep and weak behaviour of the chihshang fault

clustering and periodic recurrence of microearthquakes on the san andreas fault at parkfield california the san andreas fault at parkfield california apparently late in an interval between repeating magnitude 6 earthquakes is yielding to tectonic loading partly by seismic slip concentrated in a relatively sparse distribution of small clusters 20 meter radius of microearthquakes within these clusters which account for 63 of the earthquakes in a 1987 92 study interval virtually identical small earthquakes occurred with a regularity that can be described by the statistical model used previously in forecasting large characteristic earthquakes sympathetic occurrence of microearthquakes in nearby clusters was observed within a range of about 200 meters at communication speeds of 10 to 100 centimeters per second the rate of earthquake occurrence particularly at depth increased significantly during the study period but the fraction of earthquakes that were cluster members decreased

quantitative analysis of surface coseismic faulting and postseismic creep accompanying the 2003 mw 6 5 chengkung earthquake in eastern taiwan 1 on the basis of field observations and geodetic measurements we analyzed coseismic and postseismic deformation of the 2003 mw 6 5 chengkung earthquake across the rupture trace of the chihshang fault which lies along the suture zone between the philippine sea plate and the eurasian plate in eastern taiwan at three of our investigation sites along the chihshang fault the earthquake deformation was exhibited by fresh fractures within the 150 to 200 m wide surface fault zone reactivating preexisting fractures in most cases in addition to daily recorded creep meter data geodetic measurements including leveling distance and angle electronic distance meters and gps measurements were carried out during surveys 20 25 days before 20 25 days after and 120 125 days after the earthquake the near fault surface deformation is mainly characterized by anticlinal folding in the hanging wall and minor gentle synclinal folding in the footwall the geodetic data show that within our 150 to 250 m wide networks the coseismic deformation of the main shock produced only about 1 2 cm of horizontal shortening and vertical offset across the fault zone a larger additional displacement of about 7 9 cm for both the horizontal shortening and the vertical offset occurred as postseismic creep during the 120 125 days following the main shock we interpret the predominant folding and the rather large postseismic creep as a result of strong velocity strengthening along the fault plane near the surface which caused locking or coupling effect during the coseismic rupturing the depth of locked segment along which the coseismic and postseismic slip decreased dramatically upward is estimated to be 25 100 m depending on the site we interpreted the velocity strengthening and coupling effect at the shallow level as viscoelastic behavior of unconsolidated deposits in the footwall and melange mudstone in the hanging wall by incorporating far fault continuous gps data it was found that minor but significant deformation occurred outside of the surface ruptures zone of the chihshang fault in addition a possible back thrust or back fold might have occurred in the hanging wall we note that the chengkung earthquake occurred during the dry season this is consistent with the fact that the mechanical coupling of the fault at shallow depth is higher during drier periods inferred from the previous seasonal creep data at outcrop scale regarding damage of construction such as a concrete retaining wall most of the coseismic and postseismic horizontal shortening was essentially absorbed by multiple distributed brittle ruptures which deserves attention in terms of earthquake hazard mitigation

periodic pulsing of characteristic microearthquakes on the san andreas fault deep fault slip information from characteristically repeating microearthquakes reveals previously unrecognized patterns of extensive large amplitude long duration quasiperiodic repetition of aseismic events along much of a 175 kilometer segment of the central san andreas fault pulsing occurs both in conjunction with and independent of transient slip from larger earthquakes it extends to depths of 10 to 11 kilometers but may be deeper and it may be related to similar phenomena occurring in subduction zones over much of the study area pulse onset periods also show a higher probability of larger earthquakes which may provide useful information for earthquake forecasting

asperity model of an earthquake dynamic problem a previous study that presented the static solution for an asperity model of an earthquake is extended to solve the dynamic problem that develops when failure occurs on the boundary of an asperity patch and then spreads over the surrounding displacement shadow region the boundary integral equation method is coupled with basic constitutive equations for failure and friction to solve the dynamic problem with different parameters used for the strong asperity patch and weak shadow region no friction displacement weakening friction and velocity strengthening friction are all investigated depending on the type and amount of friction that is present the dynamic solutions for slip on the fault exhibit a range of different features including overshoot of the static solution and oscillation rupture front velocities that may be greater than or less than the s velocity and change with position and either total or partial release of the static moment common characteristics of the solutions are that failure on the asperity patch is almost independent of failure on the shadow region and that the displacement deficit on the shadow region is released by propagating slip pulses the stress concentrations of the asperity model are sufficient to produce nonlinear elastic effects in a region extending outward from the fault to distances comparable with the dimensions of the shadow region beginning with the solutions for slip on the fault waveforms are simulated for an earthquake of magnitude m w 1 44 and compared with data recorded at a distance of 8 65 km simulations that contain both source and propagation effects are capable of explaining most of the basic features of the observational data including general agreement with the shape of the waveforms in the time domain the levels and slopes of the spectra at low frequencies less than 10 hz and at high frequencies greater than 100 hz and some of the interference effects present in both the time and frequency domains

characteristic small earthquake sequence off sanriku northeastern honshu japan 1 we found eight similar earthquakes of m4 8 regularly occurring from 1957 to 1995 on the plate boundary off sanriku northeastern japan the mean recurrence interval of the events is 5 35 years and its standard deviation is only 0 53 years these events have the same focal mechanisms of low angle thrust fault type and their source sizes are estimated to be around 1 km the slip of each event is comparable to the cumulative amount of relative plate motion in the inter seismic period thus these events are probably caused by repeating slip at a small but strong asperity surrounded by creeping zone on the plate boundary the next event was expected to occur by the end of november 2001 with 99 probability and actually m4 7 event occurred on november 13 2001

seismological studies at parkfield vi moment release rates and estimates of source parameters for small repeating earthquakes abstract waveform data from a borehole network of broadband seismographic stations have been used to study microearthquakes along the parkfield segment of the san andreas fault saf analysis of almost 10 years of such data demonstrates that much of the seismicity in this region consists of repeating sequences quasiperiodic sequences of earthquakes that are essentially identical in terms of waveform size and location scalar seismic moments have been estimated for 53 of these repeating sequences and combined with equivalent estimates from 8 similar but larger event sequences from the stone canyon section of the fault and the main parkfield sequence these estimates show that seismic moment is being released as a function of time in a very regular manner measurements of the moment release rate combined with an assumed tectonic loading rate lead to estimates of the seismic parameters source area slip and recurrence interval such parameters exhibit a systematic dependence upon source size over a range of 10 10 in seismic moment that can be described by three simple scaling relationships several implications of these scaling relationships are explored including the repeat time of earthquakes average stress drop strength of the fault and heat generated by earthquakes what emerges from this analysis of moment release rates is a quantitative description of an earthquake process that is controlled by small strong asperities that occupy less than 1 of the fault area this means that the fault is highly heterogeneous with respect to stress strength and heat generation such heterogeneity helps to explain many of the apparent contradictions that are encountered in the study of earthquakes such as why faults appear weak why significant heat flow is not observed how significant high frequencies can be generated by large earthquakes and how various geologic features such as pseudotachylytes might form

vertical crustal movements in eastern taiwan and their tectonic implications abstract leveling surveys along several routes and tidal observations at various points in eastern taiwan demonstrate rapid vertical crustal movements and they provide an effective means for monitoring the effects of collision between the philippine sea plate and the eurasian plate rapid elevation changes were detected in the southern section of the longitudinal valley repeated releveling along three routes since 1984 reveals that the coastal range was uplifted with respect to the longitudinal valley floor at a rate of about 3 0 cm yr this deformation is found to be confined within a very narrow zone along the east coast of taiwan two surveys 1984 and 1987 revealed that the coast is also undergoing uplift but at different rates from 0 cm yr to 3 5 cm yr the point of the most rapid uplift is located near 23 n and the rate generally diminishes towards the north the changes in rates may be controlled by the movements across faults tidal observations while providing a local datum show that uplift of the tidal station has occurred significant horizontal creep has been observed across many faults but rapid vertical creep as observed in the longitudinal valley is not very common

plate boundary slip associated with the 2003 off tokachi earthquake based on small repeating earthquake data 1 plate boundary slip associated with the 2003 off tokachi earthquake northern japan is determined by analysis of repeating earthquakes in the source region a total of 251 repeating earthquake groups consisting of 666 events are identified in and around the aftershock region from october 1 2000 to may 31 2004 although a number of the repeating earthquakes in this region occurred before the main shock there are many events that occurred after the main event the repeating earthquakes are located in the major afterslip region and distributed to the southeast based on this analysis it is estimated that the areas to the east and southeast of the coseismic area undergone approximately 50 cm of slip over three months following the earthquake and less than 5 cm over the three years prior to the earthquake repeating earthquakes can provide afterslip data in offshore areas where resolution from land based gps is poor

active fault creep variations at chihshang taiwan revealed by creep meter monitoring 1998 2001 1 the daily creep meter data recorded at chihshang in 1998 2001 are presented the chihshang creep meter experiment was set up across the chihshang thrust fault the most active segment of the longitudinal valley fault which is the present day plate suture between the eurasian and the philippine sea plates in eastern taiwan near continuous data recording at two sites revealed different surface fault motions yet similar annual shortening rates 16 2 mm at the tapo site comprising two connected creep meters and 15 0 mm at the chinyuan site three creep meters straddling parallel fault branches four of the five creep meters showed a seasonal variation with the fault moving steadily during the rainy season from april to october and remaining quiescent during the rest of the year the only exception was recorded by the creep meter located on a melange composed hillslope where local gravitational landsliding played an additional role other than tectonic faulting through comparison with daily precipitation data we inferred that moderate rainfall suffices to trigger or facilitate slippage on the surface fault during the transition period of the dry wet season during the observation period from 1998 to 2001 the subsurface seismicity exhibited clusters of microearthquakes on the chihshang fault at depths of 10 25 km recurrent earthquakes occurred regardless of whether the season was wet or dry indicating that the stress relaxation associated with seismicity in the seismogenic zone did not transfer immediately up to the surface the accumulated strain on the chihshang fault at shallow surface levels was released through creep during the wet season in addition to these short term seasonal variations an apparent decrease in the annual slipping rate on the chihshang fault during the last few years deserves further investigation in order to mitigate against seismic hazard

fault structure and mechanics of the hayward fault california from double difference earthquake locations 1 the relationship between small magnitude seismicity and large scale crustal faulting along the hayward fault california is investigated using a double difference dd earthquake location algorithm we used the dd method to determine high resolution hypocenter locations of the seismicity that occurred between 1967 and 1998 the dd technique incorporates catalog travel time data and relative p and s wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events the relocated seismicity reveals a narrow near vertical fault zone at most locations this zone follows the hayward fault along its northern half and then diverges from it to the east near san leandro forming the mission trend the relocated seismicity is consistent with the idea that slip from the calaveras fault is transferred over the mission trend onto the northern hayward fault the mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the calaveras fault at calaveras reservoir in some locations discrete structures adjacent to the main trace are seen features that were previously hidden in the uncertainty of the network locations the fine structure of the seismicity suggests that the fault surface on the northern hayward fault is curved or that the events occur on several substructures near san leandro where the more westerly striking trend of the mission seismicity intersects with the surface trace of the aseismic southern hayward fault the seismicity remains diffuse after relocation with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation the seismicity is highly organized in space especially on the northern hayward fault where it forms horizontal slip parallel streaks of hypocenters of only a few tens of meters width bounded by areas almost absent of seismic activity during the interval from 1984 to 1998 when digital waveforms are available we find that fewer than 6 5 of the earthquakes can be classified as repeating earthquakes events that rupture the same fault patch more than one time these most commonly are located in the shallow creeping part of the fault or within the streaks at greater depth the slow repeat rate of 2 3 times within the 15 year observation period for events with magnitudes around m 1 5 is indicative of a low slip rate or a high stress drop the absence of microearthquakes over large contiguous areas of the northern hayward fault plane in the depth interval from 5 to 10 km and the concentrations of seismicity at these depths suggest that the aseismic regions are either locked or retarded and are storing strain energy for release in future large magnitude earthquakes

fault slip rates at depth from recurrence intervals of repeating microearthquakes unique attributes in sequences of recurring similar microearthquakes at parkfield california provide a means for inferring slip rate at depth throughout the active fault surface from the time intervals between sequence events application of the method using an 11 year microseismicity record revealed systematic spatial and temporal changes in the slip rate that were synchronous with earthquake activity and other independent measures of fault zone slip if this phenomenon is found to be generally common behavior in active faults it forms the basis for a method to monitor the changing strain field throughout a seismogenic fault zone

coseismic versus interseismic ground deformations fault rupture inversion and segmentation revealed by 2003 mw 6 8 chengkung earthquake in eastern taiwan 1 the 2003 chengkung earthquake mw 6 8 provided diagnostic evidence for a source model showing the deformation process of the seismogenic chihshang fault in eastern taiwan the aftershocks show a fault bend at a depth of 18 km coseismic ground displacements recorded by strong motion records allow us to deduce instant rupturing of this event our resulting model shows a fault length of 33 km and dip slip dominant rupture on fault plane deeper than 18 km estimated coseismic displacements constrain two fault planes one at 5 18 km depth dipping 60 e and 18 36 km depth dipping 45 e the uppermost fault plane of the chihshang fault 0 5 km did not break immediately after the main shock however it may have a major role in after slip and even interseismic ground deformation the taiyuan basin developed in the hanging wall is a geomorphic feature consistent with and adequately explained by coseismic ground displacements

repeating earthquakes and interplate coupling along the western part of the north anatolian fault abstract the sea of marmara accommodates segments of the north anatolian fault naf in turkey and remains the only part of the western naf that has not ruptured during the last century at its nearest the segment is 20 km from istanbul the largest city in turkey thus it is important to understand the locking state of the fault since it illuminates the strain accumulation rate along the fault segments which in turn is an important input parameter in seismic hazard studies to infer the interplate locking state we used repeating earthquakes that indicate fault creep in the surrounding area using long term april 2005 to may 2013 seismic observations at 12 broadband seismic stations operated by bogazici university kandilli observatory and earthquake research institute we defined repeating earthquakes from waveform coherences that were 0 95 for 40 second long waveforms of the vertical component using the selection procedure we found 21 repeating earthquakes with magnitude 2 3 to 3 2 that are grouped into 9 sequences they are distributed along the main naf comprising three groups of activity one group in the sea of marmara and a group either side to the east and west the three groups are located near the boundary of previous large earthquake ruptures suggesting relatively weak coupling there we also estimated the fault creep rate from the cumulative slip of the repeating earthquakes using a scaling relationship between repeating earthquakes moment and slip the slip rate for these three groups are similar 3 4 cm yr and comparable to albeit slightly higher than those expected from global plate models 2 4 cm yr this suggests relatively weak locking around the groups the relocation results of the repeating earthquake hypocenters in the sea of marmara suggest the creep is occurring at 10 to 20 km depth these results suggest heterogeneous coupling in the segment

behavior of repeating earthquake sequences in central california and the implications for subsurface fault creep repeating earthquakes res are sequences of events that have nearly identical waveforms and are interpreted to represent fault asperities driven to failure by loading from aseismic creep on the surrounding fault surface at depth we investigate the occurrence of these res along faults in central california to determine which faults exhibit creep and the spatiotemporal distribution of this creep at the juncture of the san andreas and southern calaveras paicines faults both faults as well as a smaller secondary fault the quien sabe fault are observed to produce res over the observation period of march 1984 through may 2005 res in this area reflect a heterogeneous creep distribution along the fault plane with significant variations in time cumulative slip over the observation period at individual sequence locations is determined to range from 5 5 58 2 cm on the san andreas fault from 4 8 14 1 cm on the southern calaveras paicines fault and from 4 9 24 8 cm on the quien sabe fault creep at depth appears to mimic the behaviors seen for creep on the surface in that evidence of steady slip triggered slip and episodic slip phenomena are also observed in the re sequences for comparison we investigate the occurrence of res west of the san andreas fault within the southern coast range events within these re sequences occurred only minutes to weeks apart from each other and then did not repeat again over the observation period suggesting that res in this area are not produced by steady aseismic creep of the surrounding fault surface

southern california hypocenter relocation with waveform cross correlation part 2 results using source specific station terms and cluster analysis we obtain precise relative relocations for more than 340 000 southern california earthquakes between 1984 and 2002 by applying the source specific station term ssst method to existing p and s phase picks and a differential lo cation method to about 208 000 events within similar event clusters identified with waveform cross correlation the entire catalog is first relocated by using existing phase picks a reference 1d velocity model and the ssst method of richards dinger and shearer 2000 we also perform separate relocations of imperial valley events by using a velocity model more suited to this region next we apply cluster analysis to the waveform cross correlation output to identify similar event clusters we re locate earthquakes within each similar event cluster by using the differential times alone keeping the cluster centroid fixed to its initial ssst location we estimate standard errors for the relative locations from the internal consistency of differential locations between individual event pairs these errors are often as small as tens of meters in many cases the relocated events within each similar event cluster align in planar features suggestive of faults we observe a surprising number of such faults at small scales that strike nearly perpendicular to the main seismicity trends in general the fine scale details of the seismicity reveal a great deal of structural com plexity in southern california fault systems

variations in rupture process with recurrence interval in a repeated small earthquake in theory and in laboratory experiments friction on sliding surfaces such as rock glass and metal increases with time since the previous episode of slip1 this time dependence is a central pillar of the friction laws widely used to model earthquake phenomena2 3 on natural faults other properties such as rupture velocity4 5 porosity and fluid pressure6 11 may also vary with the recurrence interval eighteen repetitions of the same small earthquake separated by intervals ranging from a few days to several years allow us to test these laboratory predictions in situ the events with the longest time since the previous earthquake tend to have about 15 larger seismic moment than those with the shortest intervals although this trend is weak in addition the rupture durations of the events with the longest recurrence intervals are more than a factor of two shorter than for the events with the shortest intervals both decreased duration and increased friction are consistent with progressive fault healing during the time of stationary contact

inferred depth of creep on the hayward fault central california a relation between creep rate at the surface trace of a fault the depth to the bottom of the creeping zone and the rate of stress accumulation on the fault is derived from weertman s 1964 friction model of slip on a fault a 5 1 km depth for the creeping zone on the hayward fault is estimated from the measured creep rate 5 mm yr at the fault trace and the rate of stress increase on the upper segment of the fault trace inferred from geodetic measurements across the san francisco bay area although fault creep partially accommodates the secular slip rate on the hayward fault a slip deficit is accumulating equivalent to a magnitude 6 6 earthquake on each 40 km segment of the fault each century thus the current behavior of the fault is consistent with its seismic history which includes two moderate earthquakes in the mid 1800 s