evidence for widespread nonlinear strong ground motion in the mw 6 9 loma prieta earthquake we exploit 55 repeating microearthquake sequences on the san andreas fault just south of the rupture zone of the 1989 m w 6 9 loma prieta earthquake to search for time dependent properties of the earth s crust using moving window waveform cross correlation we identify clear and systematic delays as large as 20 msec for the direct s wave and exceeding 50 msec in the early s wave coda following the loma prieta mainshock others have also identified phase delays velocity reductions associated with damaging earthquakes and they have suggested a myriad of possible causal mechanisms here we present new evidence for a mechanism to produce velocity reductions correlated in time and space with an earthquake a strong correlation between the spatial patterns of s delays and the intensity of strong ground motion in the loma prieta earthquake suggests that physical damage the formation or growth of cracks during strong ground motion to the earth s shallow crust is responsible for the observed velocity reductions the strong spatial variability in s delays over short distances and the strong correlation of the magnitude of delays with surface geology indicate that the phase delays accumulate primarily near the receiver the effect is stronger at stations on young soft rocks than at stations on old hard rock disproportionately larger s coda delays than p coda delays suggest that the cracks formed by the strong shaking are fluid filled in the 10 years after loma prieta the initial increase in travel times reduces logarithmically with respect to time often back to the premainshock levels we attribute this behavior to the same slow dynamic healing observed in laboratory studies of the recovery of materials from transient nonlinear strain manuscript received 14 january 2004

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

waveform retrieval and phase identification for seismic data from the cass experiment the little destruction to the deployment site and high repeatability of the controlled accurate seismic source cass shows its potential for investigating seismic wave velocities in the earth s crust however the difficulty in retrieving impulsive seismic waveforms from the cass data and identifying the seismic phases substantially prevents its wide applications for example identification of the seismic phases and accurate measurement of travel times are essential for resolving the spatial distribution of seismic velocities in the crust until now it still remains a challenging task to estimate the accurate travel times of different seismic phases from the cass data which features extended wave trains unlike processing of the waveforms from impulsive events such as earthquakes or explosive sources in this study we introduce a time frequency analysis method to process the cass data and try to retrieve the seismic waveforms and identify the major seismic phases traveling through the crust we adopt the wigner ville distribution wvd approach which has been used in signal detection and parameter estimation for linear frequency modulation lfm signals and proves to feature the best time frequency convergence capability the wigner hough transform wht is applied to retrieve the impulsive waveforms from multi component lfm signals which comprise seismic phases with different arrival times we processed the seismic data of the 40 ton cass in the field experiment around the xinfengjiang reservoir with the wvd and wht methods the results demonstrate that these methods are effective in waveform retrieval and phase identification especially for high frequency seismic phases such as pmp and sms with strong amplitudes in large epicenter distance of 80 120 km further studies are still needed to improve the accuracy on travel time estimation so as to further promote applicability of the cass for and imaging the seismic velocity structure

assessments of serious anthropogenic land subsidence in yunlin county of central taiwan from 1996 to 1999 by persistent scatterers insar article i nfo anthropogenic ground subsidence due to massive pumping of groundwater is one of the severe environmen tal hazards in taiwan the yunlin county located in the southwestern coastal region of taiwan is one of the most counties with serious land subsidence because of the agricultural needs in certain areas of the region the subsidence rate reaches as much as 14 3 cm yr the severe land subsidence gives rise to the risk of flood hazard and damage of infrastructures in this area we represented a persistent scatterers insar psinsar results deduced from 1996 to 1999 time span for monitoring of land subsidence in this area the psinsar results show that baojhou tuku and yuanchang townships reveal a maximum subsidence rate of about 7 8 cm yr along the los and lunbei township located on the northern yunlin reveals a subsidence rate of 3 5 cm yr which is quite coincident with the precise leveling result this result has proven that the effective reduction of labor and cost could be achieved by using this technique on monitoring land subsidence in

spurious velocity changes caused by temporal variations in ambient noise frequency content ambient seismic noise cross correlations are now being used to detect temporal variations of seismic velocity which are typically on the order of 0 1 per cent at this small level temporal variations in the properties of noise sources can cause apparent velocity changes for example the spatial distribution and frequency content of ambient noise have seasonal variations due to the seasonal hemispherical shift of storms here we show that if the stretching method is used to measure time shifts then the temporal variability of noise frequency content causes apparent velocity changes due to the changes in both amplitude and phase spectra caused by waveform stretching with realistic seasonal variations of frequency content in the los angeles basin our numerical tests produce about 0 05 per cent apparent velocity change comparable to what meier et al observed in the los angeles basin we find that the apparent velocity change from waveform stretching depends on time windows and station pair distances and hence it is important to test a range of these parameters to diagnose the stretching bias better understanding of spatiotemporal noise source properties is critical for more accurate and reliable passive monitoring

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

atmospheric effects in interferometric synthetic aperture radar surface deformation and topographic maps interferogram images derived from repeat pass spaceborne synthetic aperture radar systems exhibit artifacts due to the time and space variations of atmospheric water vapor other tropospheric variations such as pressure and temperature also induce distortions but the effects are smaller in magnitude and more evenly distributed throughout the interferogram than the wet troposphere term spatial and temporal changes of 20 in relative humidity lead to 10 cm errors in deformation products and perhaps 100 m of error in derived topographic maps for those pass pairs with unfavorable baseline geometries in wet regions such as hawaii these are by far the dominant errors in the spaceborne imaging radar c and x band synthetic aperature radar sir c x sar interferometric products the unknown time delay from tropospheric distortion is independent of frequency and thus multiwavelength measurements such as those commonly used to correct radar altimeter and global positioning system gps ionospheric biases cannot be used to rectify the error in the topographic case the errors may be mitigated by choosing interferometric pairs with relatively long baselines as the error amplitude is inversely proportional to the perpendicular component of the interferometer baseline for the sir c x sar hawaii data we found that the best longest baseline pair produced a map supporting 100 m contouring whereas the poorest baseline choice yielded an extremely noisy topographic map even at this coarse contour interval in the case of deformation map errors the result is either independent of baseline parameters or else very nearly so here the only solution is averaging of independent interferograms so in order to create accurate deformation products in wet regions many multiple passes may be required rules for designing optimal data acquisition and processing sequences for interferometric analyses in nondesert parts of the world are 1 to use the longest radar wavelengths possible within ionospheric scintillation and faraday rotation limits 2 for topography maximize interferometer baseline within decorrelation limits and 3 for surface deformation use multiple observations and average the derived products following the above recipe yields accuracies of 10 m for digital elevation models and 1 cm for deformation maps even in very wet regions such as hawaii

origin of the west taiwan basin by orogenic loading and flexure of a rifted continental margin 1 seismic and well data suggest that the west taiwan basin developed by orogenic loading and flexure of a rift type continental margin the most likely source of the loading is taiwan where oblique convergence between the eurasian and philippine sea plates has produced an orogenic belt up to 300 km in length 100 km in width and 4 km in height flexure modeling shows that surface loading is unable to explain the depth of the west taiwan basin other subsurface or buried loads are required combined surface and buried loading explains the depth and width of the basin it also accounts for a bouguer gravity anomaly high and flanking low over the orogenic belt a lateral offset of 20 30 km between the peak topography and the maximum depth to the seismic moho and evidence for tectonic uplift in the penghu islands the depth of the base of the foreland sequence in the northern part of the west taiwan basin can be explained well by an elastic plate model with an effective elastic thickness te of 13 km while this value is low when compared to most other foreland basins it is within the range of values derived from rifted continental margins the northern part of the west taiwan basin unconformably overlies a passive margin sequence and therefore appears to have inherited the long term 1 myr flexural properties of the margin in the southern part of the basin however the depth to the base of the foreland sequence dips too steeply to be explained by elastic plate models this part of the basin therefore appears to be yielding rather than flexing differences in the flexural behavior along strike of the west taiwan foreland basin lithosphere are reflected in seismicity patterns west of the thrust front the northern part of the basin is associated with a low level of seismic activity while the south correlates with an abundance of earthquakes especially at shallow 25 km depths there is a cluster of earthquakes along two extensional faults that were active during rifting of the underlying margin therefore lithospheric flexure and fault reactivation may be important contributors to the seismicity of the taiwan region

reply to comment on near surface location geometry and velocities of the santa monica fault zone los angeles california by r d catchings g gandhok m r goldman d okaya m j rymer and g w bawden by t l pratt and j f dolan in a comment on our 2008 paper catchings gandhok et al 2008 on the santa monica fault in los angeles california pratt and dolan 2010 herein referred to as p d cite numerous objections to our work inferring that our study is flawed however as shown in our reply their objections contradict their own published works published works of others and proven seismic methodologies rather than responding to each repeated invalid objection we address their objections by topic in the subsequent sections in catchings gandhok et al 2008 we presented high resolution seismic reflection images that showed two near surface faults in the upper 50 m beneath the grounds of the wadsworth veterans administration hospital wvah although p d suggest we effectively duplicated their seismic acquisition our survey was not a duplication of their efforts rather we conducted a seismic imaging survey over a similar profile as pratt et al 1998 but used a different data acquisition system and different data processing methods to evaluate methods of seismically imaging blind faults in the wake of the 17 january 1994 m 6 7 northridge earthquake we used an acquisition method that provides both tomographic seismic velocities and reflection images our combined data approach allowed for shallower imaging 2 5 m minimum than the 20 m minimum of pratt et al 1998 clearer images of the fault zone and more accurate depth determinations rather than time images in processing the reflection images we used prestack depth migration which is generally accepted as the only proper imaging method for imaging subsurface structures with strong lateral velocity variations versteeg 1993 a condition shown to exist at the wvah site we correlated our reflection images with refraction tomography images borehole lithology and velocity data interferometric synthetic aperture radar images and changes in groundwater depths except for some minor differences our seismic reflection images coincide with previously published seismic reflection

holocene uplift and subsidence along an active tectonic margin southwestern taiwan abstract taiwan is located along a convergent plate boundary where the luzon arc collides with the eurasia continental margin the tainan plain of southwestern taiwan is incorporated into and deformed by a regional fold and thrust belt associated with this convergent plate margin in this study we establish a tentative regional holocene relative sea level curve that allows us to analyze crustal uplift and subsidence rates of the tainan plain the maximum holocene uplift rates on the tainan plain occur on the tainan tableland and the chungchou terrace these two areas have experienced long term holocene uplift rates of 5 and 7 mm yr respectively the tawan lowland located between these two areas is subsiding at a long term rate of about 1 mm yr based on this pattern of the crustal movement the tainan tableland is interpreted as a mud diapiric dome and the chungchou terrace as the product of a blind thrust fault the holocene reference sea level curve proposed in this study can be used to determine the pattern of crustal movements elsewhere in taiwan it also can suggest that the holocene terrace development does not occur in area where the uplift rate exceeds 8 mm yr while late holocene regression the general trend around the western pacific is not recorded where the rate of subsidence is lower than 1 mm yr

rupture process of the 2004 sumatra andaman earthquake the 26 december 2004 sumatra andaman earthquake initiated slowly with small slip and a slow rupture speed for the first 40 to 60 seconds then the rupture expanded at a speed of about 2 5 kilometers per second toward the north northwest extending 1200 to 1300 kilometers along the andaman trough peak displacements reached 15 meters along a 600 kilometer segment of the plate boundary offshore of northwestern sumatra and the southern nicobar islands slip was less in the northern 400 to 500 kilometers of the aftershock zone and at least some slip in that region may have occurred on a time scale beyond the seismic band

radar interferometry and its application to changes in the earth s surface geophysical applications of radar interferometry to measure changes in the earth s surface have exploded in the early 1990s this new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times the resulting interferogram is a contour map of the change in distance between the ground and the radar instrument these maps provide an unsurpassed spatial sampling density 100 pixels km 2 a competitive precision 1 cm and a useful observation cadence 1 pass month 1 they record movements in the crust perturbations in the atmosphere dielectric modifications in the soil and relief in the topography they are also sensitive to technical effects such as relative variations in the radar s trajectory or variations in its frequency standard we describe how all these phenomena contribute to an interferogram then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments including the four satellites currently in orbit ers 1 ers 2 jers 1 and radarsat the next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement respecting the limits of the technique assessing its uncertainty recognizing artifacts and discriminating different types of signal we then review the geophysical applications published to date most of which study deformation related to earthquakes volcanoes and glaciers using ers 1 data we also show examples of monitoring natural hazards and environmental alterations related to landslides subsidence and agriculture in addition we consider subtler geophysical signals such as postseismic relaxation tidal loading of coastal areas and interseismic strain accumulation we conclude with our perspectives on the future of radar interferometry the objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it

coda wave interferometric detection of seismic velocity changes associated with the 1999 m 3 6 event at mt vesuvius 1 we detect seismic wave velocity changes at mt vesuvius using doublets and the coda wave interferometry method the high sensitivity of multiply scattered coda waves to temporal changes in the medium allows us to detect velocity variation smaller than 0 4 we use 17 doublets some of them grouped in families of multiplets spanning january 1996 to december 1999 data show a systematic increase in velocity from 1996 to end september 1999 followed by a rapid drop in velocity this drop immediately precedes a sustained swarm of vt type earthquakes including the 9th october 1999 m 3 6 event the largest in the region since at least 1972 we propose a long term fluid pressurization followed by influx as a possible causative mechanism

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

long term volcanic hazard forecasts based on somma vesuvio past eruptive activity distributions of pyroclastic deposits from the main explosive events at somma vesuvio during the 8 000 year b p a d 1906 time span have been analysed to provide maps of volcanic hazard for long term eruption forecasting in order to define hazard ratings the spatial distributions and loads kg m2 exerted by the fall deposits on the roofs of buildings have been considered a load higher than 300 kg m2 is defined as destructive the relationship load frequency the latter defined as the number of times that an area has been impacted by the deposition of fall deposits is considered to be a suitable parameter for differentiating among areas according to hazard rating using past fall deposit distributions as the basis for future eruptive scenarios the total area that could be affected by the products of a future vesuvio explosive eruption is 1 500 km2 the perivolcanic area 274 km2 has the greatest hazard rating because it could be buried by pyroclastic flow deposits thicker than 0 5 m and up to several tens of metres in thickness currently the perivolcanic area also has the highest risk because of the high exposed value mainly arising from the high population density

synthetic aperture radar interferometry to measure earth s surface topography and its deformation synthetic aperture radar interferometry insar from earth orbiting spacecraft provides a new tool to map global topography and deformation of the earth s surface radar images taken from slightly different viewing directions allow the construction of digital elevation models of meter scale accuracy these data sets aid in the analysis and interpretation of tectonic and volcanic landscapes if the earth s surface deformed between two radar image acquisitions a map of the surface dis placement with tens of meters resolution and subcentimeter accuracy can be con structed this review gives a basic overview of insar for earth scientists and presents a selection of geologic applications that demonstrate the unique capabilities of insar for mapping the topography and deformation of the earth

temporal changes of surface wave velocity associated with major sumatra earthquakes from ambient noise correlation abstract detecting temporal changes of the medium associated with major earthquakes has implications for understanding earthquake genesis here we report temporal changes of surface wave velocity over a large area associated with 3 major sumatra earthquakes in 2004 2005 and 2007 we use ambient noise correlation to retrieve empirical green s function egf of surface waves between stations because the process is completely repeatable the technique is powerful in detecting possible temporal change of medium we find that 1 excellent station pair psi in indonesia and chto in thailand shows significant time shifts up to 1 44 s after the 2004 and 2005 events in the rayleigh waves at 10 20 s but not in the love waves suggesting that the rayleigh time shifts are not from clock error the time shifts are frequency dependent with the largest shifts at the period band of 11 16 s we also observe an unusual excursion 1 month before the 2004 event we obtain a total of 17 pairs for june 2007 to june 2008 which allow us to examine the temporal and spatial variation of the time shifts we observed strong anomalies up to 0 68 s near the epicenter after the 2007 event but not in the region further away from the source or before the event or 3 months after the event the observations are interpreted as stress changes and subsequent relaxation in upper mid crust in the immediate vicinity of the rupture and the broad area near the fault zone

active deformation of tainan tableland of southwestern taiwan based on geodetic measurements and sar interferometry the d insar technique is applied to detect the active fault related folding structure of the tainan tableland near the deformation front in sw taiwan by using ers sar images during 1996 2000 the tainan tableland is located in between a blind fault in the west and the houchiali fault in the east thus the tainan tableland is interpreted as a pop up structure in a fold thrust belt at active tectonic margin interferometric processing of six sar images reveals the average slant range deformation srd as 12 5 mm yr the uplift rate is higher in eastern tainan tableland than that in western tainan tableland and it increases from west edge of tainan tableland and decreases across the houchiali fault the campaign mode gps data set from 1999 to 2003 indicate an average horizontal movement of 12 4 mm yr in the direction of n44 w for the tainan tableland with respect to western coastline furthermore 5 precise leveling surveys across tainan tableland over a period of 2 years show an uplift rate of 14 mm yr for the benchmarks on the tableland based on the 2 d analytical solution with the constraint of he inferred fault geometry the slip rate along the inferred tainan fault is 16 mm yr 10 mm yr along the houchiali fault and 25 mm yr along the inferred chungchou fault consequently we propose that active deformation of the tainan tableland is likely resulted from the freely slipping of the tainan fault and the houchiali fault the locking depth should be located on the deeper part of decollement eastern of the chungchou fault in addition the combination of d insar gps data and the precise leveling data reveals that the short term deformation rate is larger than long term deformation rate which implies that a destructive seismic event could occur in the eastern tainan area

coseismic displacements of the footwall of the chelungpu fault caused by the 1999 taiwan chi chi earthquake from insar and gps data abstract the differential sar interferometry technique interferometric synthetic aperture radar insar is applied on the chelungpu fault surface rupture zone of the september 20 1999 taiwan chi chi earthquake using six ers 2 images covering the period from february 1999 to january 2000 as compared with available geodetic data insar measurements result in more extensive analysis because of high spatial sampling and centimetric accuracy however coseismic displacements can be evaluated only on the footwall of the fault the analysis of interferograms shows the existence of a linear trend in phase difference mainly caused by orbital errors which we removed from interferograms using gps data the corrected interferograms provide a precise map of the insar component of the coseismic displacement showing a continuous decrease over the footwall from a maximum of 36 7 cm at the fault east of taichung city to a value of about 5 cm at the coastline 30 km further west the map analysis reveals that the changhua fault whose surface trace is located about 20 km west of the chelungpu one and the tuntzuchio fault influence the displacement field we interpret this in terms of minor reactivation of these faults triggered by the earthquake a 1 7 cm uncertainty estimated from the gps data is proposed to quantify the precision of the map beyond this single value we highlight the interest of having several coseismic interferograms to evaluate the reliability of the map in a more comprehensive way comparisons with displacements inferred from models of slip distribution inverted without insar data highlight the advantage of carrying out a joint inversion including our results as new constraints

surface deformation from persistent scatterers sar interferometry and fusion with leveling data a case study over the choushui river alluvial fan taiwan abstract the choushui river alluvial fan craf one of the most important agricultural areas in taiwan suffers severe subsidence caused by groundwater withdrawal we use 20 envisat images from 2006 to 2008 to derive vertical deformation over craf by persistent scatterer interferometry psi which effectively reduces errors affecting conventional dinsar techniques the pixel density over craf is 107 6 pixels km 2 compared to 0 19 points km 2 of the leveling benchmarks psi yields vertical displacements matching the leveling result to 0 6 cm year rms and provides a higher spatial resolution of subsidence than the latter we also develop a data fusion method that considers the high precision low point density leveling result as a smoothed correction to the psi result the combined field is more representative of overall deformation characteristics than the psi only or leveling only field and it is better suited for the assessment of the impact of subsidence over craf

3d shear wave velocity structure beneath the southeastern tibetan plateau from ambient noise we perform high resolution 3d shear wave structures of the crust and upper mantle using continuous wave data recorded at 170 stations from national and regional networks in the southeastern tibetan plateau first empirical green s functions are obtained between all the possible station pairs then rayleigh wave group velocity and phase velocity dispersion curves are retrieved using the frequency time analysis method the rayleigh wave group velocity images at periods from 8 to 50 s and phase velocity images at periods from 8 to 40 s are inverted on a 1 1 grid finally the 1d shear wave structure beneath each grid and the 3d shear wave velocity structure are acquired by linear interpolation our results indicate that low velocity layers lvls are ubiquitous in the middle lower crust beneath the southeastern tibetan plateau but vary in depth 20 35 km thickness 5 20 km and strength 5 4 10 8 velocity reduction in different blocks the 3d geometry of the lvls is complex and cannot be interpreted as a model with a uniform flow channel the shear velocity in the chuandian block is unevenly distributed indicating that the block is inhomogeneous the 12 may 2008 wenchuan and 20 april 2013 lushan earthquake sequences m s 3 0 all occurred in the crustal layers in which lvls are inhibited by the strong sichuan basin and in which the topography and crustal thickness vary sharply this formed the earthquake preparation environment of the two earthquakes the ningnan qiaojia pull apart region is characterized by low shear wave velocity in the shallow crust which agrees well with the sedimentary features of the upper crust a relatively high velocity is observed in the central part of the low velocity sichuan basin in the shallow layers indicating the basement beneath the sichuan basin may be uplifted around the central part of the basin

evidence for an independent 26 s microseismic source near the vanuatu islands the 26 s peak in the ambient seismic noise spectrum is persistently excited and observed at stations globally using noise cross correlation functions ncfs the location suggests that the source could be situated in the gulf of guinea and fiji basin however the fiji basin was proposed to be the mirror site near antipode of the gulf of guinea source instead of an independent source assuming that the surface waves more efficiently propagate along the major arc paths of oceanic movements to investigate the propagation of the rayleigh waves along continental and oceanic paths we analyzed the surface wave data recorded from an earthquake near the gulf of guinea and found that rayleigh waves travel along continental minor arc paths more efficiently than along oceanic major arc paths we then located the source in the western pacific ocean from group velocities measured with earthquake data by using the travel time misfit in ncfs after calibration and concluded that the source is in the vanuatu islands moreover the temporal variation of the 26 s microseismic peak observed in the western pacific seismic stations is very different from that in stations near the gulf of guinea which suggests that they are excited by independent sources therefore the vanuatu source should be an independent microseismic source as it is close to volcanoes in the vanuatu islands the pacific 26 s microseismic source might be excited by magmatic processes which are also responsible for very long period volcanic tremors

uplift of tainan tableland sw taiwan revealed by sar interferometry interferometric processing of five sar ers images reveals uplift of the tainan tableland sw of taiwan during the period 1996 1998 the maximum measured ground motion for these two years is 2 8 cm along the radar line of sight towards the satellite indicating for the displacement vector a vertical component of 3 2 cm and a horizontal component of 1 6 cm towards the wsw considering additional information from gps data the reconstructed displacement field is consistent with the geological interpretation of the tainan tableland as an actively growing anticline connected to the taiwan fold and thrust belt this implies that the deformation front is located farther west than usually assumed in the tainan area the large tainan city is thus located in an active deformation zone seismic hazard assessment is however difficult because the mechanisms and kinematics are not known in detail

damage to the shallow landers fault from the nearby hector mine earthquake crustal faults have long been identified as sites where localized sliding motion occurs during earthquakes which allows for the relative motion between adjacent crustal blocks although there is a growing awareness that we must understand the evolution of fault systems on many timescales to relate present day crustal stresses and fault motions to geological structures formed in the past fault zone damage and healing have been documented quantitatively in only a few cases we have been monitoring the healing of damage on the shallow johnson valley fault after its rupture in the 1992 magnitude 7 3 landers earthquake and here we report that this healing was interrupted in 1999 by the magnitude 7 1 hector mine earthquake rupture which occurred 20 30 km away the hector mine earthquake both strongly shook and permanently strained the johnson valley fault adding damage discernible as a temporary reversal of the healing process the fault has since resumed the trend of strength recovery that it showed after the landers earthquake these observations lead us to speculate that fault damage caused by strong seismic waves may help to explain earthquake clustering and seismicity triggering by shaking and may be involved in friction reduction during faulting

fifteen years of surface deformation in western taiwan insight from sar interferometry abstract geodetically measured surface displacements are produced by a combination of underlying deformation processes acting at different spatial and temporal scales a complete history of surface measurements in an area can help discriminate contributions from tectonic hydrologic and anthropogenic processes in this study we use synthetic aperture radar sar images of the active mountain front and adjacent coastal plain of southwestern taiwan to generate time series of surface deformation from 1995 to 2001 and from 2005 to 2008 based on the insar small baseline method the insar measurements agree well with los motions estimated from continuous gps measurements of 3d displacements between 2006 and 2008 a significant range increase in line of sight los is dominated by land subsidence in the coastal area of western and southwestern taiwan subsidence rates vary with annual periods and are highly correlated with seasonal precipitation which are likely associated with groundwater recharge and withdrawal the long term deformation is dominated by long term tectonic loading in sw taiwan during the interseismic period of the earthquake cycle including elastic strain along or continuous creep on the active faults our results show the ability of insar to reveal spatiotemporal crustal deformation in western taiwan with high spatial resolution and accuracy which is potentially important for evaluating seismic hazards

depth extent of damage zones around the central calaveras fault from waveform analysis of repeating earthquakes summary we systematically investigate spatial variations of temporal changes and depth extent of damage zones along the calaveras fault that ruptured during the 1984 morgan hill earthquake by the waveform analysis of 333 sets of repeating earthquakes we use a sliding window waveform cross correlation technique to measure traveltime changes in waveforms generated by each repeating cluster we find clear traveltime delays in the s and early s coda waves for events immediately after the morgan hill main shock the amplitudes of the time delays decrease logarithmically with time since the main shock indicating a time dependent recovery healing process following the abrupt coseismic temporal changes the largest temporal changes are observed at station cco that is the closest to the rupture zone of the morgan hill main shock the time delays at this station are larger for clusters in the top 6 km and decrease systematically at larger depth in comparison the time delays observed at other five stations are much smaller and do not show clear relationship with hypocentral depth we suggest that the temporal changes at these five stations mostly occur in the top few hundred metres of the near surface layers while the temporal changes at station cco are likely associated with the damage zone around the calaveras fault that is well developed in the top few kilometres of the upper crust our results are consistent with the inference of a widespread damage and non linearity in the near surface layers associated with strong ground motions of nearby large earthquakes and localized damages and flower type structures around active faults based on previous studies of fault zone structures and recent 3 d numerical simulations

temporal changes of seismic velocity associated with the 2006 mw 6 1 taitung earthquake in an arc continent collision suture zone 1 to detect temporal changes of elastic properties associated with the 2006 mw 6 1 taitung earthquake in southeast taiwan whereby the collision between the luzon arc riding on the philippine sea plate and the asian margin is taking place we construct the green s functions from auto and cross correlation function acf and ccf of continuous ambient noise between stations time lapse changes in the retrieved coda arrivals are estimated for monitoring spatiotemporal variations of seismic velocities around the ruptured fault zones to the south of the main shock epicenter where the earthquake may have ruptured along two perpendicularly intersecting fault planes resulting in intense coseismic slip and widely dispersed aftershocks the acfs 2 8 hz at nearby stations reveal a large sudden velocity drop of over 1 after the event occurrence the ccfs 0 1 0 9 hz also show moderate reduction about 0 1 for the interstation paths traveling through the southeast quadrant of the focal sphere which has experienced the maximum peak ground acceleration and dilatational strain change the intense seismic shaking combined with the rupture induced damage near the junction of the two faults is the most plausible cause for such localized but significant coseismic velocity reduction the response of groundwater levels to precipitation is in phase correlated with velocity variations over 3 years of investigation unlike the postseismic surface displacements gradually relaxed the velocity remained slow until october 2006 due to the typhoon induced heavy rains between may and september

pliocene pleistocene initiation style and sequencing of deformation in the central tien shan in response to the indo asian collision deformation of the tien shan initiated at 25 ma along the northwestern margin of the tarim basin 300 km north the kyrgyz range began deforming 15 ma later although multiple intervening structures across the tien shan are currently active the sequencing of initial deformation across the orogen s entire width remains poorly known to determine whether deformation migrated sequentially northward or developed less predictably we documented deformation patterns within the naryn basin in south central kyrgyzstan detailed mapping and a published balanced cross section across the naryn basin suggest that deep seated relatively steeply dipping thrust faults have disrupted the basin during late cenozoic deformation dating of deformed fluvial terraces with ages between 10 and 250 ka constrains the rate of deformation across relatively young structures in the tien shan interior based on geodetic surveys of dated terraces local rates of relative rock uplift span from 0 3 to 3 5 mm yr folding rates and patterns are temporally persistent at a given site moreover they mimic modern geodetic rates measured from interferometric synthetic aperture radar extrapolating these rates into the past suggests that structures within the interior of the naryn basin formed in the last 1 myr whereas the ranges surrounding the basin initiated at least 1 4 myr earlier hence within the naryn basin itself deformation has migrated from margins to interior similarly these new chronologies indicate that at least some deformation in the interior of the tien shan initiated millions of years later than along either orogenic margin 2014 american geophysical union all rights reserved

a growing structure near the deformation front in sw taiwan as deduced from sar interferometry and geodetic observation 1 we apply the d insar technique to monitor the active growing structure on the tainan tableland near the deformation front in sw taiwan using ers sar images in the period of 1996 2000 interferometric processing of six sar images reveals the average slant range displacement srd to be 12 5 mm yr and it increases from the west edge of the tainan tableland and decreases across the houchiali fault the gps campaign data indicate an average horizontal movement of 12 4 mm yr in the direction of n44 w for the tainan tableland with respect to the western coastline five precise leveling surveys across the tainan tableland over two years show an uplift rate of 14 mm yr for the benchmarks on the tableland by combining the horizontal velocity of gps data and the srd of d insar we transfer the srd into vertical deformation and discuss the deformation pattern and seismic hazards in the tainan area

temporal velocity changes in the crust associated with the great sumatra earthquakes abstract co and postseismic slip of the great earthquakes can give rise to temporal changes in the medium either due to strong ground motion damaging near surface sediment layer or stress perturbations modulating crack density and or fluid movement at depth such time varying crustal properties can result in fractional change in seismic velocity that can be probed from cross correlating waveforms and measuring their time lags within a repeating earthquake sequence this study analyzes lag times of high frequency 0 5 2 0 hz p and s coda waves as well as long period 0 03 0 1 hz surface waves from repeating aftershock sequences of the great 2004 sumatra andaman and 2005 nias simeulue earthquakes the observed lag times reveal several major characteristics 1 lag time series t of s coda for the 2004 sequences fluctuate around zero and are sometimes negative as a function of lapse time whereas t of s coda for the 2005 sequences exhibit a monotonic increase as a function of lapse time 2 average velocity reduction of s coda v s is about two times larger than that of p coda v p average velocity reduction of rayleigh waves v lr is 3 4 times larger than that of love waves v lq and 3 v s and v lr display temporal velocity recovery with calendar time especially for the 2005 sequences the form of temporal velocity recovery of v s of the 2005 sequences is similar to available displacement time series of the nearby geodetic station whereas we discuss potential artifacts such as source separation temporal changes of the noise field and instrument response observations collectively point to nonuniform temporal velocity reduction in the crust modulated by co or and postseismic slip of the 2004 2005 great earthquakes online material table of source parameters and figure showing tests on lag time measurements of long period rayleigh waves

traveltime measurements from noise correlation stability and detection of instrumental time shifts we test the feasibility of using green s functions extracted from records of ambient seismic noise to monitor temporal changes in the earth crust properties by repeated measurements at regional distances we use about 11 yr of continuous recordings to extract surface waves between three pairs of stations in california the correlations are computed in a moving 1 month window and we analyse the temporal evolution of measured interstation traveltimes the comparison of the arrival times in the positive and negative correlation time of rayleigh and love waves allows us to separate time shifts associated with any form of physical change in the medium those resulting from clock drift or other instrumental errors and those due to change in the localization of the noise sources this separation is based on the principle of time symmetry when possible we perform our analysis in two different period bands 5 10 and 10 20 s the results indicate that significant instrumental time errors 0 5 s are present in the data these time shifts can be measured and tested by closure relation and finally corrected independently of any velocity model the traveltime series show a periodic oscillation that we interpret as the signature of the seasonal variation of the region of origin of the seismic noise between 1999 and 2005 the final arrival time fluctuations have a variance of the order of 0 01 s this allows us to measure interstation traveltimes with errors smaller than 0 3 per cent of the interstation traveltime and smaller than 1 per cent of the used wave period this level of accuracy was not sufficient to detect clear physical variation of crustal velocity during the considered 11 yr between the three stations in california such changes may be more easily detectable when considering pairs of stations more closely located to each other and in the vicinity of tectonically active faults or volcanoes

extracting earth s elastic wave response from noise measurements recent research has shown that noise can be turned from a nuisance into a useful seismic source in seismology and other fields in science and engineering the estimation of the system response from noise measurements has proven to be a powerful technique to convey the essence of the method we first treat the simplest case of a homogeneous medium to show how noise measurements can be used to estimate waves that propagate between sensors we provide an overview of physics research dating back more than 100 years showing that random field fluctuations contain information about the system response this principle has found extensive use in surface wave seismology but can also be applied to the estimation of body waves because noise provides continuous illumination of the subsurface the extracted response is ideally suited for time lapse monitoring we present examples of time lapse monitoring as applied to the softening of soil after the 2011 tohoku oki earthquake the detection of a precursor to a landslide and temporal changes in the lunar soil

seismic velocity changes in the backarc continental crust after the 2011 mw 9 0 tohoku oki megathrust earthquake the 2011 mw 9 0 tohoku oki megathrust earthquake accompanied coseismic and postseismic displacements around the eastern eurasian continental plate noise cross correlations produced transient seismic waveforms along interstation paths in the korean peninsula we measured the traveltime changes of the fundamental mode rayleigh waves over the range of 0 03 0 08 hz after the megathrust earthquake the temporal seismic velocity changes in the lower crust were assessed from the traveltime changes the traveltimes increased instantly after the megathrust earthquake and were gradually recovered over several hundreds to thousands of days the instant shear wave velocity decreases ranged between 0 731 0 057 and 4 068 0 173 the temporal medium perturbation might be caused by the transient uniaxial tensional stress due to the coseismic and postseismic displacements the medium properties may be recovered by progressive stress field reconstruction

azimuthal seismic anisotropy in the upper crust of the japanese islands induced by the 2011 tohoku oki megathrust earthquake

lithological control on the deformation mechanism and the mode of fault slip on the longitudinal valley fault taiwan the longitudinal valley fault lvf in taiwan is creeping at shallow depth along its southern half where it is bounded by the lichi melange by contrast the northern segment of the lvf is locked where it is bounded by forearc sedimentary and volcanoclastic formations structural and petrographic investigations show that the lichi melange most probably formed as a result of internal deformation of the forearc when the continental shelf of south china collided with the luzon arc as a result of the subduction of the south china sea beneath the philippine sea plate the forearc formations constitute the protolith of the lichi melange it seems improbable that the mechanical properties of the minerals of the matrix illite chorite kaolinite in themselves explain the aseismic behavior of the lvf microstructural investigations show that deformation within the fault zone must have resulted from a combination of frictional sliding at grain boundaries cataclasis responsible for grain size comminution and pressure solution creep responsible for the development of the scaly foliation and favored by the mixing of soluble and insoluble minerals the microstructure of the gouge formed in the lichi melange favors effective pressure solution creep which inhibits strain weakening brittle mechanisms and is probably responsible for the dominantly aseismic mode of fault slip since the lichi melange is analogous to any unlithified subduction melanges this study sheds light on the mechanisms which favor aseismic creep on subduction megathrust

convenient formulas for determining dip slip fault parameters from geophysical observables abstract simple equations are presented for estimating slip magnitude fault dip angle width of the zone of compression and other co seismic parameters from geologic seismic and geodetic observations made in subduction zone and continental dip slip environments these equations are easy to memorize and use without computational aids

near surface evidence of recent taiwan orogeny detected by a shallow seismic method abstract collision between the philippine plate and the eurasian plate has caused recent tectonics in the southwestern alluvial plain of taiwan a fold which is the near surface evidence of this recent tectonics has been found using a shallow seismic method the fold passes through 23 13 83 n and 120 07 54 e and strikes about n10w nearly parallel to the taiwan strait coastline the fold is only a few kilometres away the fold is in unconsolidated sediments and is possibly an extension of a blind thrust fault folding of near surface strata suggests deformation within the last 10 ka consistent with the proposition of biq ti chi 12 1992 1 12 that the recent taiwan orogeny is at its early stage this recent tectonics also provides evidence that the plate boundary in taiwan is migrating northwestward

what caused the mysterious eighteenth century tsunami that struck the southwest taiwan coast several different historical records allude to a disastrous tsunami on the southwestern taiwan coast sometime between 1781 and 1782 with a reported death toll of more than 40 000 despite consistent reports from southwest taiwan no corroborative information exists for neighboring shorelines in southeast china or northwest luzon philippines and a plausible source of this tsunami has never been identified neither a large earthquake from the manila trench and active thrust faults nor a submarine volcanic eruption from the northern luzon arc can explain the very localized area affected and the physical phenomena described in the historical records comparing the results of 13 numerical models of tsunamis generated from different sources earthquake volcano and submarine mass failure we therefore suggest that a seismically triggered submarine mass failure on the upper portion of the continental slope offshore from southwestern taiwan is the most likely source of the eighteenth century event