repeating earthquakes associated with the wfsd 1 drilling site abstract we cross correlated three component seismic waveforms to find repeating events among the aftershocks of the 2008 wenchuan earthquake centered at the wfsd 1 drilling site during and after the drilling the aftershocks selected occurred from 2008 10 01 to 2011 09 15 with a magnitude range of ml 1 4 5 5 using the 1 10 hz bandpass filtered waveforms recorded by the regional and mobile seismic stations 518 repeating events are identified with the criterion that for at least one station the three components of seismograms all have cross correlation coefficients larger than 0 8 using 12 repeating multiplets defined by the criterion that each pair of events in the multiplet must be repeating pairs fault slip rates are estimated slip rate was averaged at about 5 mm year being within the range of the deformation rate before the wenchuan earthquake obtained by repeating earthquakes with a weak attenuating trend and a suspected disturbance by a strong aftershock

temporal changes of shallow seismic velocity around the karadere duzce branch of the north anatolian fault and strong ground motion we analyze temporal variations of seismic velocity along the karadere duzce branch of the north anatolian fault using seismograms generated by repeating earthquake clusters in the aftershock zones of the 1999 mw7 4 izmit and mw7 1 duzce earthquakes the analysis employs 36 sets of highly repeating earthquakes each containing 4 18 events the events in each cluster are relocated by detailed multi step analysis and are likely to rupture approximately the same fault patch at different times the decay rates of the repeating events in individual clusters are compatible with the omori s law for the decay rate of regional aftershocks a sliding window waveform cross correlation technique is used to measure travel time differences and evolving decorrelation in waveforms generated by each set of the repeating events we find clear step like delays in the direct s and early s coda waves sharp seismic velocity reduction immediately after the duzce main shock followed by gradual logarithmic type recoveries a gradual increase of seismic velocities is also observed before the duzce main shock probably reflecting post seismic recovery from the earlier izmit main shock the temporal behavior is similar at each station for clusters at various source locations indicating that the temporal changes of material properties occur in the top most portion of the crust the effects are most prominent at stations situated in the immediate vicinity of the recently ruptured fault zones and generally decrease with normal distance from the fault a strong correlation between the co seismic delays and intensities of the strong ground motion generated by the duzce main shock implies that the radiated seismic waves produced the velocity reductions in the shallow material

plate interactions crustal deformation and magmatism along the eastern margins of the tibetan plateau abstract in order to investigate the deep structure and dynamics of the triangular colliding system of the eastern tibetan plateau tp as well as the yangtze platform and the qinling dabie fold belt a large number of p and s wave arrival times from both local and teleseismic earthquakes were used to generate high resolution tomographic images beneath the eastern margins of tp the results of this study show that the western margin of the minjiang fault is characterized by low velocity low v anomalies in sharp contrast to the high velocity high v anomalies that are derived from the eastern part this means that the minshan uplift zone is imaged as high v and acts as a barrier to the eastward escape crustal flow which leads to obvious segmentation of the longmenshan fault lmsf zone between velocity belts that are concatenated into the minjiang fault because high v anomalies are clearly imaged in this study to extended depths of ca 450 km we consider the yangtze platform containing the sichuan basin to comprise craton like lithosphere this study reveals the presence of a low v belt extending to a depth of ca 250 km between the sichuan basin and the ordos block which probably represents the migration pathway of upwelling asthenosphere materials from tibet at the same time low v zone with a downdip depth of ca 500 km accompanied by an approximately 400 km rectangular high v body is imaged under the tengchong volcano we interpret the high v body and the low v zone as evidence for the subducted indian plate and the volcanic magma source respectively the results of this study reveal a number of new features of structural heterogeneities relative to deep coupling between the tibet and the yangtze platform as well as the relationship between the sichuan basin and the ordos block and the original source of the tengchong volcano the results presented here enable us a better understanding of the plate interaction crustal deformation and magmatism of the tengchong volcano along the eastern margins of tp

slip parallel seismic lineations on the northern hayward fault california a high resolution relative earthquake location procedure is used to image the fine scale seismicity structure of the northern hayward fault california the seismicity defines a narrow near vertical fault zone containing horizontal alignments of hypocenters extending along the fault zone the lineations persist over the 15 year observation interval implying the localization of conditions on the fault where brittle failure conditions are met the horizontal orientation of the lineations parallels the slip direction of the fault suggesting that they are the result of the smearing of frictionally weak material along the fault plane over thousands of years

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

systematic search for repeating earthquakes along the haiyuan fault system in northeastern tibet repeating earthquakes have been found at many faults around the world and they provide valuable information on diverse faulting behavior at seismogenic depth the haiyuan fault is a major left lat

deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of kilauea dense microearthquake swarms occur in the upper south flank of kilauea providing multiplets composed of hundreds of events the similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters a simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically relocation of these events greatly improves the definition of the seismic image of the fault that generates them indeed relative relocations define a plane dipping about 6 northward although corresponding absolute locations are widely dispersed in the swarm a composite focal mechanism built from events providing a correct spatial sampling of the multiplet also gives a well constrained northward dip of about 5 to the near horizontal plane this technique thus collapses the clouds of hypocenters of single event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies we cannot conclude that all south flank earthquakes collapse to a single plane there may locally be several planes perhaps with different dips and depths throughout the south flank volume the 6 northward dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of hawaii this plane is probably an important feature that characterizes the basal slip layer below the upper south flank of kilauea volcano differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane the present work illustrates how high precision relative relocations of similar events in dense swarms combined with the analysis of geodetic measurements can help to describe deep fault plane geometry systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well instrumented highly seismic areas to provide reliable basic information especially useful for understanding of earthquake generation processes

contemporary crustal deformation around the southeast borderland of the tibetan plateau 1 we derive a detailed horizontal velocity field for the southeast borderland of the tibetan plateau using gps data collected from the crustal motion observation network of china between 1998 and 2004 our results reveal a complex deformation field that indicates that the crust is fragmented into tectonic blocks of various sizes separated by strike slip and transtensional faults most notably the regional deformation includes 10 11 mm yr left slip across the xianshuihe fault 7 mm yr left slip across the anninghe zemuhe xiaojiang fault zone 2 mm yr right slip across a shear zone trending northwest near the southern segment of the lancang river fault and 3 mm yr left slip across the lijiang fault deformation along the southern segment of the red river fault appears not significant at present time the region south and west of the xianshuihexiaojiang fault system whose eastward motion is resisted by the stable south china block to the east turns from eastward to southward motion with respect to south china resulting in clockwise rotation of its internal subblocks active deformation is detected across two previously unknown deformation zones one is located 150 km northwest of and in parallel with the longmenshan fault with 4 6 mm yr right slip and another is continued south southwestward from the xiaojiang fault abutting the red river fault with 7 mm yr left slip while both of these zones are seismically active the exact locations of faults responsible for such deformation are yet to be mapped by field geology comparing our gps results with predictions of various models proposed for tibetan plateau deformation we find that the relatively small sizes of the inferred microblocks and their rotation pattern lend support to a model with a mechanically weak lower crust experiencing distributed deformation underlying a stronger highly fragmented upper crust

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

present day kinematics at the india asia collision zone the collision of the indian subcontinent with asia drives the growth and evolution of the greater tibetan plateau region fault slip rates resulting from the relative motion between crustal blocks can provide a kinematic description of the distribution of presentday deformation i construct a three dimensional regional scale elastic block model of the india asia collision zone that is consistent with geodetic observations of interseismic deforma tion mapped fault system geometry historical seismicity and the mechanics of the earthquake cycle this mechanical model of the elastic upper crust yields a set of kinematically consistent fault slip rates and block motions that may serve to constrain dynamic models of continental crustal dynamics

active tectonics of the beichuan and pengguan faults at the eastern margin of the tibetan plateau the steep high relief eastern margin of the tibetan plateau has undergone rapid cenozoic cooling and denudation yet shows little evidence for large magnitude shortening or accommodation generation in the foreland basin we address this paradox by using a variety of geomorphic observations to place constraints on the kinematics and slip rates of several large faults that parallel the plateau margin the beichuan and pengguan faults are active dominantly dextral slip structures that can be traced continuously for up to 200 km along the plateau margin both faults offset fluvial fill terraces that yield inheritance corrected cosmogenic 10be exposure ages of 15 kyr indicating latest pleistocene activity the pengguan fault appears to have been active in the holocene at two sites along strike latest quaternary apparent throw rates on both faults are variable along strike but are typically 1 mm yr 1 rates of strike slip displacement are likely to be several times higher probably 1 10 mm yr 1 but remain poorly constrained late quaternary folding and dextral strike slip has also occurred along the western margin of the sichuan basin particularly associated with the present day mountain front these observations support models for the formation and maintenance of the eastern plateau margin that do not involve major upper crustal shortening they also suggest that activity on the margin parallel faults in eastern tibet may represent a significant seismic hazard to the densely populated sichuan basin

reconstruction of drought variability in north china and its association with sea surface temperature in the joining area of asia and indian pacific ocean abstract using tree ring data from the northernmost marginal area of the east asian summer monsoon easm in north china may july mean palmer drought severity index pdsi was reconstructed back to 1767 ad the reconstruction captured 52 8 of the variance over the calibration period from 1945 to 2005 ad and showed pronounced pluvial periods during 1850 1905 1803 1811 and 1940 1961 and dry periods during 1814 1844 1916 1932 and 1984 2012 these anomalous periods have previously been reported in other parts of north china spatial correlation analyses and comparisons with other hydroclimatic indices in north china indicated that our new pdsi reconstruction could represent spatial and temporal drought variability in this region well our work also suggested that the drying tendency currently observed in the northern part of north china including the study area is consistent with the weakening of the easm meanwhile the drying trend was seemingly restrained at present in the southern part of north china spatial correlation patterns with global sea surface temperature sst indicated that the regional hydroclimatic variability in north china was tightly linked to sst over the joining area of asia and indian pacific ocean aipo especially over the tropical western pacific when sst from prior november to current july nj sst in the aipo area was anomalously high low the thermal contrast between asian land and ocean was weakened strengthened and the easm was correspondingly weakened strengthened thereby causing droughts pluvials in north china the results of this study do not only provide useful information for assessing the long term climate change in north china but also suggest that abnormal variability in nj sst over the aipo area could be used to forecast hydroclimatic conditions in north china

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

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

earth science microseismicity data forecast rupture area on 28 september 2004 there was an earthquake of magnitude 6 0 at parkfield california here we show that the size distribution of the micro earthquakes recorded in the decades before the main shock occurred allowed an accurate forecast of its eventual rupture area applying this approach to other well monitored faults should improve earthquake hazard assessment in future

high resolution image of calaveras fault seismicity 1 by measuring relative earthquake arrival times using waveform cross correlation and locating earthquakes using the double difference technique we are able to reduce hypocentral errors by 1 to 2 orders of magnitude over routine locations for nearly 8000 events along a 35 km section of the calaveras fault this represents 92 of all seismicity since 1984 and includes the rupture zone of the m 6 2 1984 morgan hill california earthquake the relocated seismicity forms highly organized structures that were previously obscured by location errors there are abundant repeating earthquake sequences as well as linear clusters of earthquakes large voids in seismicity appear with dimensions of kilometers that have been aseismic over the 30 year time interval suggesting that these portions of the fault are either locked or creeping the area of greatest slip in the morgan hill main shock coincides with the most prominent of these voids suggesting that this part of the fault may be locked between large earthquakes we find that the calaveras fault at depth is extremely thin with an average upper bound on fault zone width of 75 m given the location error however this width is not resolvably different from zero the relocations reveal active secondary faults which we use to solve for the stress field in the immediate vicinity of the calaveras fault we find that the maximum compressive stress is at a high angle only 13 from the fault normal supporting previous interpretations that this fault is weak

a gravity study of the longmenshan fault zone new insights into the nature and evolution of the fault zone and extrusion style growth of the tibetan plateau since 40 ma

repeating volcano tectonic earthquakes at mt etna volcano sicily italy during 1999 2009 abstract repeating volcano tectonic vt earthquakes taking place at mt etna during 1999 2009 were detected and analyzed to investigate their behavior we found 735 families amounting to 2479 vt earthquakes representing 38 of all the analyzed vt earthquakes the number of vt earthquakes making up the families ranges from 2 to 23 over 70 of the families comprise 2 or 3 vt earthquakes and only 20 families by more than 10 events the occurrence lifetime is also highly variable ranging from some minutes to ten years in particular more than half of the families have a lifetime shorter than 0 5 day and only 10 longer than 1 year on the basis of these results most of the detected families were considered burst type i e show swarm like occurrence and hence their origin cannot be explained by a temporally constant tectonic loading indeed since the analyzed earthquakes take place in a volcanic area the rocks are affected not only by tectonic stresses related to the fairly steady regional stress field but also by local stresses caused by the volcano such as magma batch intrusions movements and gravitational loading we focused on the five groups of families characterized by the longest repeatability over time namely high number of events and long lifetime located in the north eastern eastern and southern flanks of the volcano unlike the first four groups which similarly to most of the detected families show swarm like vt occurrences group v located in the north eastern sector exhibits a more tectonic behavior with the events making up such a group spread over almost the entire analyzed period it is clear how both occurrence and slip rates do not remain constant but vary over time and such changes are time related to the occurrence of the 2002 2003 eruption finally by fpfit algorithm a good agreement between directions identified by nodal planes and the earthquake epicentral distribution was generally found

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

repeating earthquakes and seismic potential along the northern longitudinal valley fault of eastern taiwan 1 the northern longitudinal valley fault in eastern taiwan creeps at the surface with a small rate of 1 cm yr but slips in large earthquakes to improve seismic hazard assessment it is important to comprehend the slip deficit rate distribution at depth we discovered 25 ml 2 1 4 6 repeating earthquakes in this area and inverted gps measurements for producing an image of the along strike spatial distribution of deep fault slip rates the repeating events are located at the depths of 10 22 km with 24 9 77 5 mm yr slip rates which are comparable with the gps derived slip rates of 47 5 5 8 mm yr at similar depth ranges based on distribution of gps derived slip deficits since 1951 the northern longitudinal valley fault has become capable of releasing stored strain in a future mw 7 3 earthquake

variations in seismic velocity and attenuation associated with seismogenesis a numerical verification using ambient noise abstract seismic velocity variations associated with the seismogenic process have been studied worldwide for almost half a century since the dilatancy hypothesis proposed in early 1970s however the reports in seismogenesis associated variations in attenuation are rare reports on simultaneous variation of velocity and attenuation are even rarer the conventional way to obtain the seismogenic temporal variation in velocity and attenuation is through the observation of travel time and amplitude variations of microseismicity in a seismogenic zone anyhow for some major earthquakes there may not always be microseismicity prior to the mainshock thus obtaining a complete record of seismic velocity and attenuation variation from microseismicity is severely limited if pre mainshock microseismicity exists in contrast seismic ambient noise is an ideal source for crustal stimulation for monitoring temporal variations in velocity and attenuation in a seismogenic zone in this paper the seismogenesis associated seismic velocity and attenuation variations shown as some observable parameters in ambient noise measurements are verified using a numerical simulation approach first based on the temporal variation in seismic velocity observed along the longmenshan fault associated with the 2008 wenchuan earthquake we divided the seismogenic process into six phases upon velocity drop stages in an elliptic area in the crust second using finite difference time domain method we generated 30 minute low frequency ambient noise over a vertical profile of 200 45 km and recorded it with a 90 station array on the surface next we processed the synthetic ambient noise records to get the auto correlation function acf cross correlation function ccf rayleigh wave dispersion curve and horizontal to vertical spectral ratio h v finally we examined the temporal variation of these parameters versus the phases of the seismogenic process and found the most pronounced changes occur in the phase with the largest velocity drop and the recovery phase directly before the mainshock

deep slip rates along the longmen shan fault zone estimated from repeating microearthquakes 1 we investigated deep slip rates along the longmen shan fault zone where the devastating 2008 m7 9 wenchuan earthquake occurred using repeating earthquake data recorded by two digital seismic networks near the fault using cross correlation analysis of waveform data we identified a total of 231 doublets and 224 multiplets that have highly similar waveforms most of these sequences are aperiodic with recurrence intervals varying from a few minutes to hundreds of days for each multiplet we first constructed a reference seismogram at each station and used it to measure the delay time of the p and s waves of each event within the cluster we used the delay times to determine the relative distances between each event and the cluster centroid the relative distances were used in screening repeating events in each multiplet we identified a total of 12 repeating earthquake clusters in the source region of the m7 9 wenchuan earthquake most of the clusters are located at the edge of locked areas where large coseismic slips were observed during the 2008 wenchuan earthquake suggesting a close spatial relationship between microearthquakes and impending large devastating earthquakes the measured in situ deep slip rates appeared to increase with depth and varied from 3 5 to 9 6 mm yr at depth range of 4 18 km they are approximately twice as large as those inferred from surface gps and geological data our results here have significant implications to the understanding of faulting as well as risk assessment of seismic hazards

slip maxima at fault junctions and rupturing of barriers during the 2008 wenchuan earthquake the devastating wenchuan earthquake in 2008 struck along a fault zone that showed low rates of deformation analysis of gps and insar data suggests that as structural barriers failed during a single earthquake the rupture cascaded across multiple fault segments which may explain the high magnitude of the event

the magnitude frequency distribution of earthquakes recorded with deep seismometers at cajon pass southern california abstract the cumulative b value the slope of the gutenberg richter relationship between earthquake occurrence rate and magnitude is commonly found to be constant 1 network catalogues however reveal a decrease at small magnitudes b value is not just an artifact of catalogue incompleteness but that small earthquakes are really not as numerous as a constant b value extrapolated from larger events would predict in the cajon pass area southern california the b value of seismicity recorded by the local network scsn appears to decrease below about m l 1 6 in order to investigate whether this decrease is real or simply represents the network detection threshold we use seismicity recorded by the deep 1 5 and 2 5 km seismometers deployed in the cajon pass scientific drillhole between april 1992 and october 1994 the maximum amplitudes recorded downhole are compared to scsn magnitudes for events recorded by the network to determine the relationship between amplitude and m l as a function of hypocentral distance from the borehole magnitudes are then calculated for 1300 earthquakes which occurred within 40 km of the borehole magnitude frequency curves are calculated for those events within 18 km of the borehole and a constant b value is observed to m l 0 5

coseismic reverse and oblique slip surface faulting generated by the 2008 mw 7 9 wenchuan earthquake china the mw 7 9 wenchuan china earthquake ruptured two large thrust faults along the long menshan thrust belt at the eastern margin of the tibetan plateau this earthquake generated a 240 km long surface rupture zone along the beichuan fault and an additional 72 km long surface rupture zone along the pengguan fault maximum vertical and horizontal offsets of 6 5 m and 4 9 m respectively were measured along the beichuan fault a maximum vertical offset of 3 5 m was measured along the pengguan fault coseismic surface ruptures integrated with aftershocks and industry seismic profiles show that two imbricate structures have ruptured simultaneously resulting in the largest continental thrust event ever documented large oblique thrusting observed during this earthquake indicates that crustal shortening is an important process responsible for the high topography in the region as everywhere along the edge of tibetan plateau

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

systematic variations in recurrence interval and moment of repeating aftershocks 1 the recurrence intervals for 194 repeating clusters on the calaveras fault follow a power law decay relation with elapsed time after the 1984 m6 2 morgan hill california mainshock the decay rates of repeating aftershocks in the immediate vicinity of a high slip patch that failed during the mainshock systematically exceed those that are farther away the trend between relative moment and recurrence interval which is a measure of the fault healing rate varies systematically with depth and changes from negative to positive value as the distance between the repeating aftershock and the mainshock slip patch increases we speculate that high strain rate in the early postseismic period may cause transient embrittlement and strengthening of the deep repeating clusters in the areas adjacent to the mainshock slip patch resulting in large moments that decrease with time as the strain rate diminishes our observations suggest that systematic behavior of repeating aftershocks reflect variations in the fault zone rheology

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

the influence of landscape connectivity and landslide dynamics upon channel adjustments and sediment flux in the liwu basin taiwan catchment scale analyzes of spatial and temporal variability in landscape connectivity are critical considerations in appraisals of landscape evolution and disaster mitigation in tectonically active mountain belts such as taiwan this study uses historical aerial photographs flow discharge and seismic data to analyze landslide changes and channel adjustments over a 30 year period in the liwu basin recurrent earthquakes and typhoon events trigger frequent landslide activity channel adjustment and sediment reworking in this system spatial variability in magnitude frequency relations of hillslope valley floor lateral and upstream downstream longitudinal connectivity during the study period are shown to reflect annual reworking in source and accumulation zones while partly confined valleys in the mid catchment area trap sediment behind landslide induced dams that are formed and breached on an approximately decadal basis this promotes partial longitudinal connectivity in these areas landscape responses to disturbance events were especially pronounced following combinations of seismic and typhoon events prior to the 1998 and 2005 images although single high magnitude events and series of moderate events affect patterns of landscape connectivity in the liwu basin residence times for sediment storage are very short in this highly connected river system where confined valley settings extend virtually to the coast copyright 2014 john wiley sons ltd

rapid channel response to variability in sediment supply cutting and filling of the tarndale fan waipaoa catchment new zealand abstract in the headwaters of the waipaoa catchment fluvio mass movement gully complexes are currently significant contributors of sediment delivery of which is buffered by fans which have developed in the small tributaries that lead from the gully complexes biannual channel cross section surveys made since 1983 show seasonal aggradation incision cycles channels generally incise in summer and infill during the winter months this seasonal pattern of cutting and filling is driven by variations in sediment supply from the gully complexes in this paper to better understand patterns and processes of sediment delivery at the top of the sediment cascade we examine cut and fill cycles on the 11 ha tarndale fan over a two and a half year period analysis of sequential dems compiled from survey data obtained between december 2004 and august 2007 indicates cutting and filling may involve up to 47 000 tonnes of sediment over as little as three months during discrete severe rainstorm and or wet weather periods mass movements in the gully complex are enhanced and contribute large quantities of sediment to the fan via debris flows and landslides which infill channels during drier periods mass movement activity is inhibited and runoff incises the feeder channels

the geological evolution of the tibetan plateau the geological evolution of the tibetan plateau is best viewed in a context broader than the india eurasia collision zone after collision about 50 million years ago crust was shortened in western and central tibet while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western pacific and indonesia cessation of rapid pacific trench migration 15 to 20 million years ago coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern tibet the latter appear to result from rapid eastward flow of the deep crust probably within crustal channels imaged seismically beneath eastern tibet these events mark a transition to the modern structural system that currently accommodates deformation within tibet

spatial clustering and repeating of seismic events observed along the 1976 tangshan fault north china 1 spatial and temporal features of the seismicity occurring along the tangshan fault in 2001 2006 were investigated with data recorded by the beijing metropolitan digital seismic network the relocated seismicity with the double difference method clearly exhibits a dextral bend in the middle of the fault more than 85 of the earthquakes were found in the two clusters forming the northern segment where relatively small coseismic slips were observed during the 1976 m7 8 earthquake the b values calculated from the seismicity occurring in the northern and southern segment are 1 03 0 02 and 0 85 0 03 respectively the distinct seismicity and b values are probably the collective effect of the fault geometry and the regional stress field that has an ene wsw oriented compression using cross correlation and fine relocation analyses we also identified a total of 21 doublets and 25 multiplets that make up 50 of the total seismicity most of the sequences are aperiodic with recurrence intervals varying from a few minutes to hundreds of days based on a quasi periodic sequence we obtained a fault slip rate of 2 6 mm yr at 15 km which is consistent with surface gps measurements

depth dependence of post seismic velocity changes in and near source area of the 2013 m7 0 lushan earthquake revealed by s coda of repeating events abstract i investigated postseismic velocity changes within focal area of the 2013 m 7 0 lushan earthquake using coda wave data of repeating small earthquakes i employed template matching and grid search methods to identify well defined repeating earthquakes in order to minimize artifacts induced by variations in source location i identified a total of 3 isolated patches in a two month period after the m 7 0 mainshock i applied the coda wave interferometry technique to the waveform data of the identified repeating earthquakes to estimate velocity changes between the first and subsequent events in each cluster up to 0 1 0 2 velocity increase is observed from the s coda of repeating events occurred at regions surrounding the large coseismic slip area at seismogenic depths my observations suggest that a large percent of velocity changes may occur at surface near the stations or shallow however healing along the propagation paths in the deep 5 20 km is likely have contributed to the amount of velocity changes observed after the lushan earthquake

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

similar microearthquakes observed in western nagano japan and implications for rupture mechanics 1 we have applied a waveform cross correlation technique to study the similarity and the repeatability of more than 21 000 microearthquakes 0 m 4 5 in the aftershock zone of the 1984 western nagano earthquake in central japan we find that the seismicity in this particular intraplate fault essentially consists of no repeating earthquakes that occurred on the same patch of the fault in a quasiperiodic manner in the study period between 1995 and 2001 on the other hand we identify a total of 278 doublets and 62 multiplets 807 events that occurred consecutively within seconds to days on the basis of the relative arrival times of the p and s waves we have obtained precise relative locations of these consecutive events with an error between several meters to a few tens of meters there is a clear lower bound on the distances measured between these consecutive events and the lower bound appears to be proportional to the size of the first events this feature is consistent with what rubin and gillard 2000 have observed near the san juan bautista section of the san andreas fault shear stress increases at the edge of an earthquake rupture and the rupture edge becomes the most likely place where the second events are initiated the observed minimum distance thus reflects the rupture size of the first events the minimum distance corresponds to the rupture size calculated from a circular fault model with a stress drop of 10 mpa we found that using different time windows results in a slight difference in the delay time estimates and the subsequent projection locations which may reflect the finite size nature of earthquake ruptures

geomorphic and sedimentological controls on the effectiveness of an extreme flood the 1993 flood on the upper mississippi river was a rare large magnitude hydrological event field and aerial survey analyses and landsat 5 thematic mapper data were used to appraise the thickness of overbank deposits on leveed and unleveed reaches results indicate that minimal 5 mm overbank sedimentation occurred except in the immediate vicinity of a levee break unleveed sections also lacked overbank sedimentation little geomorphological or sedimentological evidence of this extreme event is likely to be preserved this raises questions about the completeness of the stratigraphic record in situations where wide floodplains with cohesive soils provide effective resistance and dissipate energy so that erosion is minimized and or sediment supply is limited by event timing or sequencing a large flood may leave little or no substantive evidence of its occurrence

inversion for the composite moment tensor abstract the composite moment tensor is defined in analogy to the composite focal mechanism as the averaged representative seismic moment tensor characteristic for a focal area under study in contrast to the composite focal mechanism which provides information on shear faulting the composite moment tensor can provide additional information on nonshear rupture mode and on physical conditions along the fault the composite moment tensor is calculated by a joint inversion of multiple earthquakes associated with the same fault system and displaying a similar focal mechanism the method utilizes amplitudes of p and or s waves or full waveforms because the inversion is linear it is fast and applicable to datasets of many earthquakes the method is particularly suitable for the analysis of microseismicity earthquake swarms or aftershock sequences where observations of multiple earthquakes are available the composite moment tensor can be retrieved even when the station configuration or data quality prevent inversion for the full moment tensors of individual earthquakes

postseismic response of repeating aftershocks the recurrence intervals of repeating earthquakes on the san andreas fault in the loma prieta aftershock zone follow the characteristic 1 t decay of omori s law a model in which these earthquakes occur on isolated patches of the fault that fail in stick slip with creep around them can explain this observation in this model the recurrence interval is inversely proportional to the loading rate due to creep logarithmic velocity strengthening friction predicts 1 t decay in creep rate following the mainshock the time dependence of recurrence is inconsistent with a simple viscous constitutive relationship which predicts an exponential decay of loading rate thus our observations imply postseismic slip at seismogenic depth under a power law rheology the time dependence of postseismic deformation measured geodetically may be diagnostic of whether postseismic deformation is caused by creep or possible viscoelastic deformation at greater depths

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