signals of extreme weather conditions in central europe in grace 4 d hydrological mass variations we report evidence of observed extreme weather fluctuations in central europe by satellite gravimetry during the last five years heat waves droughts excessive rain snowfall and floodings occurred frequently during the study period such phenomena are primarily associated with hydrological mass variations that are manifested in the changes of the earth s gravity field sensitive to the ka band satellite to satellite ranging kbr measurements onboard of the gravity field mission grace twin satellites 2002 2007 in our contribution we perform a regional analysis of grace data over europe based on spherical wavelet b spline and global spherical harmonic solutions resulting temporal gravity field variations are expressed in terms of equivalent water mass variations which are subsequently compared and in balance with the net effect of precipitation and evaporation from the atmospheric flux convergence reduced by runoff from river gauge data for seven central european river basins

directional properties of van s ses and ulf mt signals at ioannina greece abstract in order to examine the validity of the earthquake prediction technique developed in greece by van varotsos alexopoulos and nomicos and elucidate the underlying physical processes we performed a magnetotelluric mt recording of the ulf band 3 200 s in the vicinity of van s sensitive station ioannina ioa by comparing mt electric field of ionospheric or magnetospheric origin electric field of lightning origin and van s seismic electric signals ses the following facts were revealed 1 the mt electric field always varies in the ene wsw direction indicating existence of significant electrical conductivity contrast near the site 2 the lightning electric field orientation is somewhat more scattered but still holds the same preferred direction as that of the mt electric field the scatter is larger for larger lightning field probably due to closer location of lightning stroke to the station and or due to no linear saturation of the recording signals 3 the ses electric field orientation is even more scattered than that of the lightning origin these observations suggest that the sources of the ses are in the neighborhood of the station it is still unclear how the ses associated with distant earthquakes are emitted from the sources near the ioa station

grace measurements of mass variability in the earth system monthly gravity field estimates made by the twin gravity recovery and climate experiment grace satellites have a geoid height accuracy of 2 to 3 millimeters at a spatial resolution as small as 400 kilometers the annual cycle in the geoid variations up to 10 millimeters in some regions peaked predominantly in the spring and fall seasons geoid variations observed over south america that can be largely attributed to surface water and groundwater changes show a clear separation between the large amazon watershed and the smaller watersheds to the north such observations will help hydrologists to connect processes at traditional length scales tens of kilometers or less to those at regional and global scales

size and geometry of microearthquake seismic ruptures from p and s pulse width data summary we propose a method to estimate the radius dip and strike of a circular seismic rupture through the inversion of first p and s wave pulse widths measured on microearthquake records the method is based on quite general numerically calibrated relationships relating source and q parameters under the assumption that the waves are radiated by a circular crack propagating at a constant rupture velocity to study the influence of both the source and receiver configuration and the properties of seismic rupture a detailed resolution study on synthetic data has been carried out for a microearthquake rupture the pulse width variations with azimuths depend critically on the fault plane orientation and the resolution on fault angle parameters can be qualitatively assessed by the parameter defined as the relative variation of the take off angles with respect to their average value a statistical approach based on mapping random deviations on data in the parameter space has been adopted to quantify the uncertainty affecting the fault plane estimates the method is applied to estimate the source parameters of an ml 3 1 event recorded during the 1997 umbria marche earthquake sequence for the considered event the fault plane solution is in good agreement with the estimates obtained by the method of the joint inversion of p polarities and s polarizations

source and qp parameters from pulse width inversion of microearthquake data in southeastern sicily italy 1 source and qp parameters were estimated from the inversion of first arrival p waveform durations of about 300 microearthquakes recorded at a digital seismic network operating in southeastern sicily the average risetime and pulse width at each station do not show large differences allowing us to exclude significant differential attenuation site effects a first qp estimate was obtained by applying the classical risetime method under the assumption of a point like source time function in order to investigate the effect of directivity due to the finiteness of seismic sources new nonlinear relationships based on a circular crack model rupturing at a constant velocity were numerically built these relationships were used to formulate a nonlinear inverse method for retrieving source radius dip and strike of the circular crack and qp parameters from the inversion of risetime and pulse width data the application of the method produced a better fit of the observed data and a qp value higher than that obtained by applying the risetime method the discrepancy between the different q estimates may be due to a trade off among source dimension and qp as we inferred from a test on a subset of low magnitude events ml 2 5 a good agreement with independent estimates of fault plane solutions as inferred from p polarities and s polarizations was found the estimated stress drops are generally very low 0 1 10 bars this suggests that the background seismic activity in southeastern sicily is related to fault segments and or weakened zones where great stress accumulations are hindered

attenuation and source properties at the coso geothermal area california we use a multiple empirical green s function method to determine source properties of small m 0 4 to 1 3 earthquakes and p and s wave attenuation at the coso geothermal field california source properties of a previously identified set of clustered events from the coso geothermal region are first analyzed using an empirical green s function egf method stress drop values of at least 0 5 1 mpa are inferred for all of the events in many cases the corner frequency is outside the usable bandwidth and the stress drop can only be constrained as being higher than 3 mpa p and s wave stress drop estimates are identical to the resolution limits of the data these results are indistinguishable from numerous egf studies of m 2 5 earthquakes suggesting a similarity in rupture processes that extends to events that are both tiny and induced providing further support for byerlee s law whole path q estimates for p and s waves are determined using the multiple empirical green s function megf method of hough 1997 whereby spectra from clusters of colocated events at a given station are inverted for a single attenuation parameter with source parameters constrained from egf analysis the estimates which we infer to be resolved to within 0 01 sec or better exhibit almost as much scatter as a function of hypocentral distance as do values from previous single spectrum studies for which much higher uncertainties in individual estimates are expected the variability in estimates determined here therefore suggests real lateral variability in q structure although the ray path coverage is too sparse to yield a complete three dimensional attenuation tomographic image we invert the inferred value for three dimensional structure using a damped least squares method and the results do reveal significant lateral variability in q structure the inferred attenuation variability corresponds to the heat flow variations within the geothermal region a central low q region corresponds well with the central high heat flow region additional detailed structure is also suggested

separation of large scale water storage patterns over iran using grace altimetry and hydrological data extracting large scale water storage ws patterns is essential for understanding the hydrological cycle and improving the water resource management of iran a country that is facing challenges of limited water resources the gravity recovery and climate experiment grace mission offers a unique possibility of monitoring total water storage tws changes an accurate estimation of terrestrial and surface ws changes from grace tws products however requires a proper signal separation procedure to perform this separation this study proposes a statistical approach that uses a priori spatial patterns of terrestrial and surface ws changes from a hydrological model and altimetry data the patterns are then adjusted to grace tws products using a least squares adjustment lsa procedure thereby making the best use of the available data for the period of october 2002 to march 2011 monthly grace tws changes were derived over a broad region encompassing iran a priori patterns were derived by decomposing the following auxiliary data into statistically independent components i terrestrial ws change outputs of the global land data assimilation system gldas ii steric corrected surface ws changes of the caspian sea iii that of the persian and oman gulfs iv ws changes of the aral sea and v that of small lakes of the selected region finally the patterns of i to v were adjusted to grace tws maps so that their contributions were estimated and grace tws signals separated after separation our results indicated that the annual amplitude of ws changes over the caspian sea was 152 mm 101 mm over both the persian and oman gulfs and 71 mm for the aral sea since january 2005 terrestrial ws in most parts of iran specifically over the center and northwestern parts exhibited a mass decrease with an average linear rate of 15 mm yr the estimated linear trends of groundwater storage for the drought period of 2005 to march 2011 corresponding to the six main basins of iran khazar persian and oman gulfs urmia markazi hamoon and srakhs were 6 7 6 1 11 2 9 1 3 1 and 4 2 mm yr respectively the estimated results after separation agree fairly well with 256 in situ piezometric observations

new insights on intraplate volcanism in french polynesia from wavelet analysis of grace champ and sea surface data in this paper we discuss the origin of superswell volcanism on the basis of representation and analysis of recent gravity and magnetic satellite data with wavelets in spherical geometry we computed a refined gravity field in the south central pacific based on the grace satellite ggm02s global gravity field and the kms02 altimetric grid and a magnetic anomaly field based on champ data the magnetic anomalies are marked by the magnetic lineation of the seafloor spreading and by a strong anomaly in the tuamotu region which we interpret as evidence for crustal thickening we interpret our gravity field through a continuous wavelet analysis that allows to get a first idea of the internal density distribution we also compute the continuous wavelet analysis of the bathymetric contribution to discriminate between deep and superficial sources according to the gravity signature of the different chains as revealed by our analysis various processes are at the origin of the volcanism in french polynesia as evidence we show a large scale anomaly over the society islands that we interpret as the gravity signature of a deeply anchored mantle plume the gravity signature of the cook austral chain indicates a complex origin which may involve deep processes finally we discuss the particular location of the marquesas chain as suggesting that the origin of the volcanism may interfere with secondary convection rolls or may be controlled by lithospheric weakness due to the regional stress field or else related to the presence of the nearby tuamotu plateau

seismic electric signals ses and earthquakes a review of an updated van method and competing hypotheses for ses generation and earthquake triggering abstract electromagnetic phenomena are sometimes associated with seismic events but earthquake prediction using seismic electric signals ses has not been seriously considered since the early 1990s there are several causes 1 false alarms that have created panics in greece and 2 a strong critique of the varotsos alexopoulos nomicos van method used there an updated van method that includes time series analysis has made successful medium range predictions and short range predictions when coupled with seismic time series analysis four types of potential mechanisms to create precursory ses relying on deformation effects temperature effects ore mineral movement or groundwater variation are reviewed data relevant to each are insufficient to favor a single mechanism records of the number of false positive and missed events for an updated van method have not been well maintained false positives appear to be abundant and render the method unusable co seismic groundwater fluctuations are addressed and two novel hypotheses of earthquake trigger mechanism are also presented ionospherically induced electric and resultant magnetic fields to weaken rock thereby causing failure and volatiles liberated from minerals additionally promoting rock failure recommendations for further study are included

evaluation of new grace time variable gravity data over the ocean 1 monthly grace gravity field models from the three science processing centers csr gfz and jpl are analyzed for the period from february 2003 to april 2005 over the ocean the data are used to estimate maps of the mass component of sea level at smoothing radii of 500 km and 750 km in addition to using new gravity field models a filter has been applied to estimate and remove systematic errors in the coefficients that cause erroneous patterns in the maps of equivalent water level the filter is described and its effects are discussed the grace maps have been evaluated using a residual analysis with maps of altimeter sea level from jason 1 corrected for steric variations using the world ocean atlas 2001 monthly climatology the mean uncertainty of grace maps determined from an average of data from all 3 processing centers is estimated to be less than 1 8 cm rms at 750 km smoothing and 2 4 cm at 500 km smoothing which is better than was found previously using the first generation grace gravity fields

regional surface mass anomalies from grace kbr measurements application of l curve regularization anda priori hydrological knowledge 1 we present a method of directly estimating surface mass anomalies at regional scales using satellite to satellite k band ranging kbr data from the gravity recovery and climate experiment grace twin satellite mission geopotential differences based primarily on kbr measurement are derived using a modified energy integral method with an improved method to calibrate accelerometer measurements surface mass anomalies are computed based on a downward continuation process with optimal regularization parameters estimated using the l curve criterion method we derive the covariance functions in both space and space time domains and use them as light constraints in the regional gravity estimation process in the amazon basin study region the space time covariance function has a time correlation distance of 1 27 months which is evident that observations between neighboring months are correlated and the correlation should be taken into account however most of the current grace solutions did not consider such temporal correlations in our study the artifact in the regional gravity solution is mitigated by using the covariance functions the averaged commission errors are estimated to be only 6 86 and 5 85 for the solutions based on the space covariance function scf and the space time covariance function stcf respectively our regional gravity solution in the amazon basin study region which requires no further post processing shows enhanced regional gravity signatures reduced gravity artifacts and the gravity solution agrees with nasa gsfc s grace mascon solution to about 1 cm rms in terms of water thickness change over the amazon basin study region the regional gravity solution also retains the maximum signal energy while suppressing the short wavelength errors

attenuation structure of coso geothermal area california from wave pulse widths abstract pulse width data are used to invert for attenuation structure in the coso geothermal area california the dataset consists of pulse width measurements of 838 microseismic events recorded on a seismic array of 16 downhole stations between august 1993 and march 1994 the quality factor q correlates well with surface geology and surface heat flow observations a broad region of low q 30 to 37 is located at 0 5 to 1 2 km in depth below devil9s kitchen nicol prospects and coso hot springs a vertical low q 36 in contrast with surrounding rock of 80 region is interpreted as a channel through which hydrothermal energy is transported from depth to the surface the location of the channel is between stations s1 and s4 and its dimension is about 1 km at the deep end of the channel a large broad body of low q is also located at 3 km in depth 2 to 4 km to the southwest of nicol prospects and devil9s kitchen since it lies at the bottom of the target region and beyond the scope of seismicity further research is needed to constrain its extent numerical modeling with a pseudospectral method is also done to investigate the applicability of the inversion scheme to fractured regions a linear relationship between pulse width broadening and travel time is upheld and the proportional constants are estimated

time variability of the earth s gravity field hydrological and oceanic effects and their possible detection using grace the grace satellite mission scheduled for launch in 2001 is designed to map out the earth s gravity field to high accuracy every 2 4 weeks over a nominal lifetime of 5 years changes in the gravity field are caused by the redistribution of mass within the earth and on or above its surface grace will thus be able to constrain processes that involve mass redistribution in this paper we use output from hydrological oceanographic and atmospheric models to estimate the variability in the gravity field i e in the geoid due to those sources we develop a method for constructing surface mass estimates from the grace gravity coefficients we show the results of simulations where we use synthetic grace gravity data constructed by combining estimated geophysical signals and simulated grace measurement errors to attempt to recover hydrological and oceanographic signals we show that grace may be able to recover changes in continental water storage and in seafloor pressure at scales of a few hundred kilometers and larger and at timescales of a few weeks and longer with accuracies approaching 2 mm in water thickness over land and 0 1 mbar or better in seafloor pressure

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

properties of seismic fault zone waves and their utility for imaging low velocity structures a two dimensional solution for the scalar wave equation in a model of two vertical layers between two quarter spaces is used to study properties of seismic waves in a laterally heterogeneous low velocity structure the waves referred to as seismic fault zone waves include head waves internal fault zone reflections and trapped waves the analysis aims to clarify the dependency of the waves on media velocities media attenuation coefficients layer widths and source receiver geometry additional calculations with extreme low velocity layers provide examples that may be relevant for volcanic and geothermal domains the interference patterns controlling seismic fault zone waves change with the number of internal reflections in the low velocity structure this number increases with propagation distance along the structure decreases with fault zone width and increases for given length scales with the velocity contrast the relative lateral position of the source within the low velocity layer modifies die length scales associated with internal reflections and influences the resulting interference pattern low values of q affect considerably the dominant period and overall duration of the waves thus there are significant tradeoffs between propagation distance along the structure fault zone width velocity contrast source location within the fault zone and q the lateral and depth receiver coordinates determine the particular point where the interference pattern is sampled and observed motion is a strong function of both coordinates the zone connecting sources generating fault zone waves and observation points with appreciable wave amplitude can be over an order of magnitude larger than the fault zone width calculations for cases with layer p wave velocity of 200 m s 1 modeling a vertical dike or crack with fluid and gas show conspicuous persisting oscillations the results resemble aspects of seismic data in volcanic domains if these waves exist in observed records their explicit recognition and modeling will help to separate source and structural effects and aid in the interpretation of volcano seismology signals although the tradeoffs in parameters governing seismic fault zone waves are significant each variable has its own signature and the parameters may be constrained by additional geophysical data simultaneous modeling of many waveforms with an appropriate solution can resolve the various parameters and provide a high resolution structural image

improved estimation of terrestrial water storage changes from grace 1 the temporal variations in the earth s gravity field caused by fluctuations in terrestrial water mass can be inferred from changes in grace monthly gravity field solutions such methods have limited spatial resolution due to a necessary and possibly arbitrary truncation and smoothing of the coefficients limiting the temporal resolution to one month was necessary to solve the gravity field by a global representation our alternative method uses grace satellite to satellite tracking and accelerometer data to obtain the along track geopotential differences and directly estimate the temporal gravity variations regionally this method was tested on the estimation of hydrological mass anomaly over the amazon and orinoco river basins compared to conventional spherical harmonic methods the spatial extent of the estimated grace water height anomaly achieved finer resolution and is shown to follow more closely the boundaries of the river basins and significant systematic variation could be discerned at 15 day temporal resolutions

latest aspects of earthquake prediction in greece based on seismic electric signals ii abstract since 1983 continuous monitoring of the electrotelluric field has been carried out using an array of measuring stations located at various sites in greece the basic physical properties of the transient changes seismic electric signals ses in the electrotelluric field that are forerunners of earthquakes were first described six years ago since then a large body of data has been collected resulting in new insight into various aspects of the method the present paper reviews the latest developments in ses based earthquake prediction and describes the current procedures used to predict the epicenter and magnitude of an impending earthquake a detailed list of the predictions officially issued in greece during the past 3 years january 1 1987 november 30 1989 is also given public warnings were issued well before the most destructive seismic activity

empirical green s function analysis of loma prieta aftershocks abstract following the 18 october 1989 loma prieta earthquake an array of 22 three component iris passcal instruments was deployed in the santa cruz mountains we use an empirical green9s function method to study source properties of aftershocks as well as attenuation in the epicentral area using pairs of closely spaced events we show that the largest aftershocks are well modelled by an 2 source spectrum and we obtain estimates of the p wave corner frequency for a total of 15 events brune stress drops are observed to have no systematic variation over the range of moments spanned by the data set down to 10 19 dyne cm there is a suggestion that aftershocks that occurred outside the mainshock rupture have higher stress drops than those that occurred within the mainshock rupture a m l 3 4 foreshock in the subsequence associated with the 18 april 1990 m l 5 4 watsonville earthquake yields a stress drop estimate of 820 bars this value is well outside the stress drops obtained for all other events 6 to 266 bars site specific attenuation parameters suggest large lateral and vertical heterogeneity in p wave q structure station holy in a valley near the surface trace of the san andreas fault is characterized by low q values while stations to the north of the aftershock zone are characterized by the highest q values

empirical green s function analysis of recent moderate events in california i use seismic data from portable digital stations and the broadband terrascope network in southern california to investigate radiated earthquake source spectra and discuss the results in light of previous studies on both static stress drop and apparent stress applying the empirical green s function egf method to two sets of m 4 6 1 events i obtain deconvolved source spectra estimates and corner frequencies the results are consistent with an 2 source model and constant brune stress drop however consideration of the raw spectral shapes of the largest events provides evidence for a high frequency decay more shallow than 2 the intermediate f 1 slope cannot be explained plausibly with attenuation or site effects and is qualitatively consistent with a model incorporating directivity effects and a fractional stress drop rupture process as suggested by haddon 1996 however the results obtained in this study are not consistent with the model of haddon 1996 in that the intermediate slope is not revealed with egf analysis this could reflect either bandwidth limitations inherent in egf analysis or perhaps a rupture process that is not self similar i show that a model with an intermediate spectral decay can also reconcile the apparent discrepancy between the scaling of static stress drop and that of apparent stress drop for moderate to large events

official earthquake prediction procedure in greece abstract since jan 19 1983 the authors have been operating a telemetric network of electrotelluric stations in greece the real time observation of specific pre seismic variations in the electric field of the earth seismic electric signals ses allows us to predict the time epicenter and magnitude of an impending earthquake eq initially the predictions were announced by expediting telegrams prior to the event after the ministry of public works established the earthquake prediction council epc in september 1985 predictions were dealt with in special sessions of the council prior to the occurrence of an earthquake it was decided to announce only eq s with an expected magnitude ms 4 8 for epicenters predicted within or near the perimeter surrounding the network of measuring stations and ms 5 for eq s predicted outside the perimeter this procedure was followed from september 1985 to march 18 1986 with the following results 1 1 within the network only one eq with ms 4 9 occurred during the period mentioned the prediction of the magnitude was accurate to within a few tenths of a magnitude unit while the epicenter was predetermined to within some tens of kilometers no predictions were made that were not followed by earthquakes 2 2 outside the network three eq s with ms 5 4 5 2 and 5 3 occurred on nov 9 dec 18 and dec 23 1985 respectively the first was missed the magnitudes of the other two were predicted to be ms 5 2 and 5 5 respectively the corresponding epicentral coordinates were forecast with an accuracy of 150 and 160 km respectively the sessions were discontinued on march 18 1986 on march 24 1986 a ms 6 1 eq was predicted and directly announced to the ministry of public works the event occurred on march 29 with the predicted magnitude and less than 50 km from the predicted epicenter

comprehensive analysis of earthquake source spectra and swarms in the salton trough california 1 we study earthquakes within california s salton trough from 1981 to 2009 from a precisely relocated catalog we process the seismic waveforms to isolate source spectra station spectra and travel time dependent spectra the results suggest an average p wave q of 340 agreeing with previous results indicating relatively high attenuation in the salton trough stress drops estimated from the source spectra using an empirical green s function egf method reveal large scatter among individual events but a low median stress drop of 0 56 mpa for the region the distribution of stress drop after applying a spatial median filter indicates lower stress drops near geothermal sites we explore the relationships between seismicity stress drops and geothermal injection activities seismicity within the salton trough shows strong spatial clustering with 20 distinct earthquake swarms with at least 50 events they can be separated into early mmax and late mmax groups based on the normalized occurrence time of their largest event these swarms generally have a low skew value of moment release history ranging from 9 to 3 0 the major temporal difference between the two groups is the excess of seismicity and an inverse power law increase of seismicity before the largest event for the late mmax group all swarms exhibit spatial migration of seismicity at a statistical significance greater than 85 a weighted l1 norm inversion of linear migration parameters yields migration velocities from 0 008 to 0 8 km hour to explore the influence of fluid injection in geothermal sites we also model the migration behavior with the diffusion equation and obtain a hydraulic diffusion coefficient of approximately 0 25 m2 s for the salton sea geothermal site which is within the range of expected values for a typical geothermal reservoir the swarms with migration velocities over 0 1 km hour cannot be explained by the diffusion curve rather their velocity is consistent with the propagation velocity of creep and slow slip events these variations in migration behavior allow us to distinguish among different driving processes

source pulse enhancement by deconvolution of an empirical green s function observations of the earthquake source time function are enhanced if path recording site and instrument complexities can be removed from seismograms assuming that a small earthquake has a simple source its seismogram can be treated as an empirical green s function and deconvolved from the seismogram of a larger and or more complex earthquake by spectral division when the deconvolution is well posed the quotient spectrum represents the apparent source time function of the larger event this study shows that with high quality locally recorded earthquake data it is feasible to fourier transform the quotient and obtain a useful result in the time domain in practice the deconvolution can be stabilized by one of several simple techniques in this paper the method is implemented and tested on high quality digital recordings of aftershocks of the jan 9 1982 miramichi new brunswick earthquake in particular seismograms from a jan 17 aftershock 017 13 33 gmt local mag 3 5 exhibit path or site effects which complicate the determination of source parameters after deconvolution the apparent far field source of this event is a simple pulse in displacement with duration 0 07 second for both p and s

apparent break in earthquake scaling due to path and site effects on deep borehole recordings 1 we reexamine the scaling of stress drop and apparent stress rigidity times the ratio between seismically radiated energy to seismic moment with earthquake size for a set of microearthquakes recorded in a deep borehole in long valley california in the first set of calculations we assume a constant q and solve for the corner frequency and seismic moment in the second set of calculations we model the spectral ratio of nearby events to determine the same quantities we find that the spectral ratio technique which can account for path and site effects or nonconstant q yields higher stress drops particularly for the smaller events in the data set the measurements determined from spectral ratios indicate no departure from constant stress drop scaling down to the smallest events in our data set mw 0 8 our results indicate that propagation effects can contaminate measurements of source parameters even in the relatively clean recording environment of a deep borehole just as they do at the earth s surface the scaling of source properties of microearthquakes made from deep borehole recordings may need to be reevaluated

source properties of earthquakes near the salton sea triggered by the 16 october 1999 m 7 1 hector mine california earthquake we analyze the source properties of a sequence of triggered earthquakes that occurred near the salton sea in southern california in the immediate aftermath of the m 7 1 hector mine earthquake of 16 october 1999 the sequence produced a number of early events that were not initially located by the regional network including two moderate earthquakes the first within 30 sec of the p wave arrival and a second approximately 10 minutes after the mainshock we use available amplitude and waveform data from these events to estimate magnitudes to be approximately 4 7 and 4 4 respectively and to obtain crude estimates of their locations the sequence of small events following the initial m 4 7 earthquake is clustered and suggestive of a local aftershock sequence using both broadband trinet data and analog data from the southern california seismic network scsn we also investigate the spectral characteristics of the m 4 4 event and other triggered earthquakes using empirical green s function egf analysis we find that the source spectra of the events are consistent with expectations for tectonic brittle shear failure earthquakes and infer stress drop values of 0 1 to 6 mpa for six m 2 1 to m 4 4 events the estimated stress drop values are within the range observed for tectonic earthquakes elsewhere they are relatively low compared to typically observed stress drop values which is consistent with expectations for faulting in an extensional high heat flow regime the results therefore suggest that at least in this case triggered earthquakes are associated with a brittle shear failure mechanism this further suggests that triggered earthquakes may tend to occur in geothermal volcanic regions because shear failure occurs at and can be triggered by relatively low stresses in extensional regimes

retrieval of large scale hydrological signals in africa from grace time variable gravity fields since its launch in april 2002 the gravity recovery and climate experiment grace mission is recording the earth s time variable gravity field with temporal and spatial resolutions of typically 7 30 days and a few hundreds of kilometers allowing the monitoring of continental water storage variations from both continental and river basin scales we investigate here large scale hydrological variations in africa using different grace spherical harmonic solutions using different processing strategies constrained and unconstrained solutions we compare our grace estimates to different global hydrology models with different land surface schemes and also precipitation forcing we validate grace observations through two different techniques first by studying desert areas providing an estimate of the precision then we compare grace recovered mass variations of main lakes to volume changes derived from radar altimetry measurements we also study the differences between different publicly available precipitation datasets from both space measurements and ground rain gauges and their impact on soil moisture estimates

earthquake prediction a critical review summary earthquake prediction research has been conducted for over 100 years with no obvious successes claims of breakthroughs have failed to withstand scrutiny extensive searches have failed to find reliable precursors theoretical work suggests that faulting is a non linear process which is highly sensitive to unmeasurably fine details of the state of the earth in a large volume not just in the immediate vicinity of the hypocentre any small earthquake thus has some probability of cascading into a large event reliable issuing of alarms of imminent large earthquakes appears to be effectively impossible key word earthquake prediction

regional four dimensional hydrological mass variations from grace atmospheric flux convergence and river gauge data 1 the spatiotemporal behavior of the earth s gravity field is traditionally modeled as a series expansion in terms of spherical harmonics with a number of time dependent coefficients in this contribution we study regional effects namely hydrological mass variations observed by the gravity recovery and climate experiment grace satellite mission since 2002 as compared to the global spherical harmonics scaling and wavelet functions are quasi compactly supported i e highly localizing with respect to space and time consequently they establish a system of base functions well suited for regional modeling we determine a spatiotemporal regional gravity model from grace using the spherical wavelet technique for the spatial part and a one dimensional b spline expansion for the temporal variations that is we end up with a four dimensional multiresolution representation mrr of the geopotential over selected regional areas and time intervals for an exemplary area consisting of three large river basins in south america we compute mass variations expressed in terms of equivalent water heights we demonstrate that a b spline expansion for modeling the temporal behavior is more appropriate than the classical fourier series approach in order to corroborate the results our storage estimates are balanced with the net effect of river discharge from gauges outflow and the difference of precipitation and evaporation inflow from the convergence of vertically integrated water vapor fluxes furthermore our results are compared with monthly mass grids from grace spherical harmonic solution data products we conclude that the mrr means a robust tool to maximize the observational accuracy for grace it considers the spatiotemporal resolution of the observations due to resolution dependent highest levels and it is applicable elsewhere globally to model hydrological or other phenomena of mass change

a delineation of the nojima fault ruptured in the m7 2 kobe japan earthquake of 1995 using fault zone trapped waves we used four linear seismic arrays of portable seismometers at the northern awaji island japan to record fault zone trapped waves from aftershocks of the 1995 m7 2 hyogoken nanbu kobe earthquake from april to june 1996 three arrays were deployed across the nojima fault which ruptured during the mainshock while one array was deployed across the higashiura fault which did not break recently we observed significant fault zone trapped waves with relatively large amplitudes and the long wave train following s waves only when both the stations and aftershocks were located close to the nojima fault the coda normalized spectral amplitudes of trapped waves show a maximum peak at 4 7 hz which decreases rapidly with distance from the fault trace the normalized amplitudes of trapped waves also show a decrease with hypocentral distance along the fault giving an apparent q of approximately 25 at 4 7 hz in comparison the array across the higashiura fault recorded much shorter wave trains with higher frequencies after s arrivals for the same events we simulate these trapped waves as s waves guided in a low velocity waveguide sandwiched between high velocity wall rocks we find an adequate fit by using a waveguide 60 m wide at the northern site and 30 40 m wide elsewhere along the nojima fault a waveguide s velocity of 1 5 1 7 km s and a q value of 25 for the higashiura fault the s velocity is 2 5 km s and the q value is 80 the locations of aftershocks for which we observed fault zone trapped waves show that the nojima waveguide is 9 km long and dips southeastward at 80 85 to a depth of 16 km it extends 6 km farther south westward along the asano fault though there are no obvious surface breaks along it however the waveguide is disconnected from the suma fault on the main island which was also ruptured during the kobe earthquake possibly because of the existence of an offset between the nojima fault and the suma fault

source parameters of small earthquakes recorded at 2 5 km depth cajon pass southern california implications for earthquake scaling a 2 5 km deep triaxial seismometer at cajon pass in southern california has recorded several hundred earthquakes ml4 0 occurring within the san andreas fault system at 2 5 km seismic background noise is below amplifier sensitivity and the 2 250 hz spectral range of recorded seismic motion is wider and higher than that of most natural event catalogs compared with downhole recorded motion seismic amplitudes at the surface are amplified below 10 hz and severely attenuated above 30 hz we estimate that qs is at least 1000 for wave motion at 2 5 km and below and qp is over 2000 the range of source dimensions in the downhole recorded catalog is 10 m to 70 m ml 2 0 mo 108 nm to ml 2 7 mo 1013 nm the plot of log source radius vs log moment has a straight line trend compatible with earthquake scaling at constant stress drop inferred stress drops are scattered between 1 and 500 bars there is no evidence in the catalog for the proposed minimum source dimension at 100 m when the cajon pass borehole catalog containing some of the smallest recorded natural earthquakes is combined with 800 larger events from previous studies the moment radius trend suggests that natural earthquakes are self similar over a magnitude range m 2 to 8 we suggest that inferences of minimum source dimension are more likely due to bias in bandlimited individual catalogs than to properties of the seismic crust

regional high resolution spatiotemporal gravity modeling from grace data using spherical wavelets we determine a regional spatiotemporal gravity field over northern south america including the amazon region using grace inter satellite range rate measurements by application of a wavelet based multiresolution technique a major advantage of this method is that we are able to represent the amazon hydrological signals in form of time series of detail signals with level dependent temporal resolution the coarser structures generally require only ten days whereas the medium and finer details are computable from one month of data to this end we employ the basic property of multiresolution representations which is to split a signal into detail signals each related to a specific resolution level and computable from data covering a specific part of the spectrum our results which for the first time fully exploit the spatial and temporal resolutions of grace data in modeling amazon hydrological fluxes are in good agreement with hydrological models and gps derived height variations

rebuttal to replies i and ii by varotsos et al we show that earthquakes in greece can be predicted much more efficiently than van by anybody using the pde earthquake bulletin our analysis is retrospective but our scheme can be unambiguously tested against future seismicity for the period from jan 1 1987 to june 30 1992 the rule developed in this paper predicts 9 of 12 large events in greece as opposed to at most 4 successes for van

microseismicity stress and fracture in the coso geothermal field california abstract microseismicity stress and fracture in the coso geothermal field are investigated using seismicity focal mechanisms and stress analysis comparison of hypocenters of microearthquakes with locations of development wells indicates that microseismic activity has increased since the commencement of fluid injection and circulation microearthquakes in the geothermal field are proposed as indicators of shear fracturing associated with fluid injection and circulation along major pre existing fractures high seismicity zones are associated with the main fluid flow paths within the geothermal system calculated stress patterns from focal mechanisms provide direct evidence for the boundary between significantly different stress regimes within the coso geothermal field microseismicity in the coso geothermal field is spatially but not temporally related to regional seismicity extending southeast of the field the spatial distribution of these events defines a northwest trending seismic fracture zone consistent with a previously defined northwest striking zone the abrupt decrease of seismicity below this fracture zone may provide seismic evidence for the existence of a brittle and ductile transition zone at shallow depth beneath the coso geothermal field

some relationship between van seismic electric signals ses and earthquake parameters abstract a possible correlation between ses seismic electric signals of the van method characteristics and earthquake parameters is investigated for the period january 1 1983 december 31 1994 for western greece during this period there were total of 55 earthquakes of mb 5 0 in the region of the so called selectivity maps of the ioannina ioa and pirgos pir van stations cmt solutions are available for 29 of these earthquakes eighteen were preceded by ses at ioa and eleven at pir none of them was preceded by simultaneous ses at both stations the main results are as follows 1 the direction of the ses vector at ioa is correlated with the focal position of predicted earthquakes although nearby earthquakes often have ses with dissimilar vector directions 2 the ses of all nine thrust events of the 29 earthquakes were observed at ioa but their vector direction was not unique 3 eleven earthquakes in the zone west of kefallinia to peloponese preceded by ses at pir were of the strike slip type with varying degrees of normal component the vector direction of ses at pir for these earthquakes was predominantly westward 4 the source mechanism changed from largely strike slip type to thrust type in the above zone at the end of 1987 and this coincided with a shift in the sensitive site from pir to ioa indicating a possible correlation between the source mechanism and selectivity characteristics of van stations

estimation of crustal qβ in the ganga basin using teleseismic broad band sh waveforms for the 1988 nepal india border earthquake abstract the average value of the intrinsic shear wave quality factor q has been estimated for the upper 55 km of the earth 47 km of crustal and upper 8 km of the upper mantle thickness in the border region between the ganga basin and himalaya in bihar we have used the teleseismic broad band sh and s sh waveforms of the 1988 nepal india border earthquake 6 4 m b for this purpose the frequency independent average value of q estimated in the range of 0 2 1 5 hz is found to be 1250 158

attenuation and source parameters of shallow microearthquakes at mt etna volcano italy we estimated the attenuation laws of high frequency seismic waves in the shallow crust depth 5 km and earthquake source parameters by using a se lected data set of 320 shallow events 2 6 md 4 2 recorded at mt etna volcano during the last two flank eruptions occurring in 2001 and 2002 2003 the quality factor q was estimated from spectra of p and s waves for 24 stations of the local permanent network by applying a spectral ratio technique the results show varia tions in both qp and qs as a function of frequency according to the power law q q0f n with n ranging between 0 3 and 1 3 for p waves and between 0 2 and 0 9 for s waves as typical of volcanic environments strong azimuthal variations of qp were also found suggesting the presence of local strong lateral heterogeneities and or of fluid filled cracked volumes after correction for attenuation we estimated the source parameters seismic moment source radius and stress drop of a subset of 66 shallow events under the assumption of a circular dislocation the estimated seismic moments m0 range from 10 13 to 10 15 n m the source radii r are confined between 100 and 1000 m and stress drop dr ranges between 0 2 mpa and about 4 mpa combining the source parameters obtained in this study with those calculated by pataneet al 1997 for an old data set of smaller microearthquakes 10 9 m0 10 14 n m recorded in the same area we re evaluated the scaling relationship between seismic moment m 0 and corner frequency f c for the earthquakes with m 0 ranging between 10 13 and 10 15 n m we confirm that microearthquakes at mt etna seem not to obey a

source parameters of the 23 april 1992 m 6 1 joshua tree california earthquake and its aftershocks empirical green s function analysis of geos and terrascope data source parameters of the m 6 1 23 april 1992 joshua tree mainshock and 86 m 1 8 to 4 9 aftershocks are determined using an empirical green s function methodology for the aftershocks deconvolved p and s wave spectra are calculated for 126 pairs of closely spaced events recorded on portable geos stations s wave spectra from the two horizontal components are averaged the deconvolved spectra are fit by a ratio of omega square source models yielding an optimal least squares corner frequency for both the large and the small event in each pair we find no resolved difference between the inferred p and s wave corner frequencies using the standard brune model for stress drop we also find no resolved nonconstant scaling of stress drop with moment although we also conclude that detailed scaling systematics would be difficult to resolve in particular a weak increase of stress drop with moment over a limited moment magnitude cannot be ruled out for magnitudes smaller than m 3 to 3 5 the inferred stress drop values will be limited by the maximum observable corner frequency value of 60 hz for the mainshock source time functions are obtained from mainshock recordings at three terrascope stations pfo pas and gsc using an m 4 3 foreshock as an empirical green s function the results indicate a fairly simple single pulse source time function with clear south to north directivity and an inferred rupture radius of 5 to 6 km the deconvolved source time functions are inverted to obtain a finite rupture model that gives a robust estimate of rupture dimension early aftershocks are found to lie along the perimeters of regions with high mainshock slip the inferred mainshock stress drop value 56 bars is within the range determined for the aftershocks our derived mainshock source spectra do not show resolvable deviation from the omega square model

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

large scale ocean circulation from the grace ggm01 geoid 1 the grace gravity model 01 ggm01 computed from 111 days of grace k band ranging kbr data is differenced from a global mean sea surface mss computed from a decade of satellite altimetry to determine a mean dynamic ocean topography dot as a test of the ggm01 gravity model large scale zonal and meridional surface geostrophic currents are computed from the topography and are compared with those derived from a mean hydrographic surface reduction in residual rms between the two by 30 60 and increased correlation indicates that the ggm01 geoid represents a dramatic improvement over older geoid models which were developed from multiple satellite tracking data altimetry and surface gravity measurements for the first time all major current systems are clearly observed in the dot from space based measurements

source parameters and three dimensional attenuation structure from the inversion of microearthquake pulse width data method and synthetic tests we propose a new method to determine source parameters and attenuation structure of a three dimensional medium based on first p rise time and total pulse width measurements from microearthquake data the effects of fault finiteness on seismic radiation are taken into account by assuming the rupture model for a circular crack of sato and hirasawa 1973 ray theory synthetic seismograms in a constant q anelastic medium are computed to derive a set of nonlinear equations which relate the source and attenuation parameters fault radius orientation of the fault plane and quality factor to the pulse width data half and total duration of the p waveforms the numerically built relationships are used to compute the direct problem in the framework of a nonlinear inversion scheme based on the modified downhill simplex method the validity and robustness of the inversion method are tested by synthetic simulations by assuming the sources and receivers configuration of the seismic passive experiment conducted in the campi flegrei caldera southern italy during the last microearthquake crisis 1982 1984 different heterogeneous q models have been considered in order to assess the uncertainty and resolution of source and attenuation parameters for the given acquisition layout the results of this simulation study indicate that first pulse width data from a local network permit retrieval with sufficient accuracy of the heterogeneous q structure and fault radii a rather dense azimuthal coverage of the sources is instead needed to recover the angles in particular the fault strike which define the fault orientation

p wave velocity variations in the coso region california derived from local earthquake travel times inversion of 4036 p wave travel time residuals from 429 local earthquakes using a tomographic scheme provides information about three dimensional upper crustal velocity variations in the indian wells valley coso region of southeastern california the residuals are calculated relative to a coso specific velocity model corrected for station elevation weighted and back projected along their ray paths through models defined with layers of blocks slowness variations in the surface layer reflect local geology including slow velocities for the sedimentary basins of indian wells and rose valleys and relatively fast velocities for the sierra nevada and argus mountains in the depth range of 3 5 km the inversion images an area of reduced compressional velocity in western and northern indian wells valley but finds no major velocity variations beneath the coso volcanic field to the north these results are consistent with a recent study of anomalous shear wave attenuation in the coso region between 5 and 10 km depth low velocity areas 7 slow appear at the southern end of the coso volcanics reaching east to the coso basin numerical tests of the inversion s resolution and sensitivity to noise indicate that these major anomalies are significant and well resolved while other apparent velocity variations in poorly sampled areas are probably artifacts the seismic data alone are not sufficient to uniquely characterize the physical state of these low velocity regions because of the coso region s history of pleistocene bimodal volcanism high heat flow geothermal activity geodetic deformation and seismic activity one possibility is to link the zones of decreased p velocity to contemporary magmatic activity

comprehensive analysis of earthquake source spectra in southern california we compute and analyze p wave spectra from earthquakes in southern california between 1989 and 2001 using a method that isolates source receiver and path dependent terms we correct observed source spectra for attenuation using both fixed and spatially varying empirical green s function methods estimated brune type stress drops for over 60 000 m l 1 5 to 3 1 earthquakes range from 0 2 to 20 mpa with no dependence on moment or local b value median computed stress drop increases with depth in the upper crust from about 0 6 mpa at the surface to about 2 2 mpa at 8 km where it levels off and remains nearly constant in the midcrust down to about 20 km however the results at shallow depths could also be explained as reduced rupture velocities near the surface rather than a change in stress drop spatially coherent variations in median stress drop are observed with generally low values for the imperial valley and northridge aftershocks and higher values for the eastern transverse ranges and the north end of the san jacinto fault we find no correlation between observed stress drop and distance from the san andreas and other major faults significant along strike variations in stress drop exist for aftershocks of the 1992 landers earthquake which may correlate with differences in main shock slip

antarctic regional ice loss rates from grace abstract using recent improved time variable gravity solutions from the gravity recovery and climate experiment grace we estimate rates of antarctic ice mass change for the period january 2003 through september 2006 combined improvements in data and filtering techniques allow observation of ice loss in the northern antarctic peninsula ap and along the coast of the west and central amundsen sea embayment ase in west antarctica there is also evidence of ice loss along the coast near the stancomb wills sta and jutulstraumen jut glaciers in queen maud land apparent rates are adjusted for influences of limited spatial resolution filtering and estimated postglacial rebound pgr to obtain ice loss rates for the northern ap coastal ase and sta jut of 28 8 7 9 81 17 and 16 7 9 7 km3 yr respectively this is the first estimate for the northern ap from satellite gravity data the ase estimate 81 17 km3 yr is consistent with a previous value 77 14 km3 yr using an earlier grace data release these results indicate significant improvement in grace data quality increased spatial resolution and applicability of grace data to a wider class of problems than previously possible

large earthquakes during hydraulic stimulations at the geothermal site of soultz sous forets abstract several deep wells were drilled in the rhine graben soultz sous forets france to evaluate the geothermal hot dry rock potential of a deep fractured granite reservoir three main boreholes which reached about 5 km depth intersected a crystalline basement overlain by 1 4 km of cenozoic and mesozoic sediments stimulations of these three wells were carried out in 2000 for gpk2 2003 for gpk3 and 2004 and 2005 for gpk4 during these stimulations and other hydraulic activities a seismological surface network was installed in order to monitor the seismicity induced by the massive fluid injection here we analyse the seismicity of magnitude larger than or equal to 1 4 which is the lowest magnitude felt by the population based on a spectral analysis of the displacement recorded by a guralp velocimeter at a depth of 200 m we know that the source dimensions range from tens to hundreds of metres we analyse several parts of the reservoir where obvious correlation between the fluid path and tectonic features has been pointed out based on seismological arguments such as location and focal mechanisms we show that this activity is linked with tectonic features or at least with large fractures that control the behaviour of the geothermal reservoir to constrain the hypothesis we study 391 events and focal mechanisms to argue in favour of the existence and stability of tectonic features that can be compared to geological data we show that the largest events recorded on the site occurred after the shut in their spatial distribution appears not to be random within the reservoir and the focal mechanisms of these events also confirm the non randomness of their distribution given their source dimensions the largest events can only occur on large structures such as tectonic ones therefore the behaviour of the reservoir is controlled by these main fractured zones which either lead the fluid or hinder its path

seismic attenuation tomography of the mariana subduction system implications for thermal structure volatile distribution and slow spreading dynamics 1 the anelastic structure of a subduction zone can place first order constraints on variations in temperature and volatile content we investigate seismic attenuation across the western pacific mariana subduction system using data from the 2003 2004 mariana subduction factory imaging experiment this 11 month experiment consisted of 20 broadband stations deployed on the arc islands and 58 semibroadband ocean bottom seismographs deployed across the fore arc island arc and back arc spreading center we compute amplitude spectra for p and s arrivals from local earthquakes and invert for the path averaged attenuation for each waveform along with the seismic moment and corner frequency for each earthquake additionally we investigate earthquake source parameter assumptions and frequency dependent exponents ranging from 0 to 0 6 tomographic inversion of nearly 3000 t estimates at 0 27 for 2 d qp 1 and qp qs structure shows a 75 km wide columnar shaped high attenuation anomaly with qp 43 60 beneath the spreading center that extends from the uppermost mantle to 100 km depth a weaker high attenuation region qp 56 70 occurs at depths of 50 100 km beneath the volcanic arc and the high attenuation regions are connected at depths of 75 125 km the subducting pacific plate is characterized by low attenuation at depths greater than 100 km but high attenuation is found in the plate between 50 and 100 km depth the fore arc shows high attenuation near the volcanic arc and beneath the serpentinite seamounts in the outer fore arc qs structure is less well resolved than qp because of a smaller data set but qp qs ratios are significantly less than 2 throughout the study region as temperatures estimated from qs 1 are unusually high we interpret the arc and wedge core anomalies as regions of high temperature with enhanced q 1 due to hydration and or melt the slab and fore arc anomalies as indicative of slab derived fluids and or large scale serpentinization and the columnar shaped high qp 1 anomaly directly beneath the back arc spreading center as indicative of a narrow region of dynamic upwelling and melt production beneath the slow spreading ridge axis

source parameters of microearthquakes in southeastern sicily italy we computed the source parameters of 135 local earthquakes that occurred in southeastern sicily italy between 1994 and 2001 magnitudes ranged from 0 6 to 2 5 the source parameters were determined from the spectral analysis of p waves after corrections for attenuation and site effects p wave quality qp and site s factors are known in the two frequency ranges 3 9 hz and 16 27 hz giampiccolo et al 2003 because the correction for qp and s over the whole spectrum could not be performed a new approach to estimate spectral parameters was applied we defined the new notion of holed spectrum to specify a spectrum lacking corrected spectral amplitude values within a certain frequency range whereas we referred to a whole spectrum to specify when the entire analyzed frequency band was used a detailed statistical analysis showed that dealing with the holed spectrum did not lead to significant differences in the estimate of spectral parameters displacement holed spectra corrected by the attenuation and site response were then used to estimate source parameters seismic moments ranged from 1017 to 1020 dyne cm and source dimensions from 150 to 500 m in general the stress drop values obtained analyzing p wave spectra were very low because they mainly span the range of 0 05 5 bars

source parameters of microearthquakes at mount st helens usa summary we estimate the source parameters for a selection of microearthquakes that occurred at mount st helens in the period 1995 1998 excluding the activity of 2004 september this time period includes the most intense episode of earthquake activity since the last dome building eruption in 1986 october 200 seismograms were processed to obtain seismic moments source radii stress drops and average fault slip the source parameters were determined from the spectral analysis of p waves after correction for attenuation and site effects in particular p wave quality qp and site s factors have been previously calculated in the frequency ranges 2 7 hz and 18 30 hz because it was impossible to perform corrections for qp and s over the whole spectrum we applied a new approach based on the notion of holed spectrum to estimate spectral parameters the term holed spectrum indicates a spectrum lacking corrected spectral amplitude values at certain frequencies we carried out a statistical study to verify that dealing with the holed spectrum does not lead to significant differences in the estimates of spectral parameters we also investigated the dependence of spectral parameters low frequency level corner frequency and high frequency decay on the bandwidth of spectral hole and defined the threshold values for three different spectral models displacement holed spectra corrected by attenuation and site response are then used to determine spectral parameters in order to calculate seismic source parameters seismic moments range from 1017 to 1019 dyne cm source dimensions from 100 to 350 m and average fault slip from 0 003 to 0 1 cm self similarity seems to break down in that stress drops are very low 0 1 1 bars we postulate that seismicity is associated with a brittle shear failure mechanism occurring in a highly heterogeneous material under a relatively low stress regime

physical properties of the variations of the electric field of the earth preceding earthquakes i abstract in an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field the present letter clarifies a few points that were not properly emphasized in our previous publications furthermore recent results like that of the destructive kalamata earthquake on september 13 1986 indicate that the duration of a preseismic electric signal may reach considerably high values lasting up to several hours

reservoir characterization using oil production induced microseismicity clinton county kentucky abstract microseismic monitoring tests were conducted from 1993 to 1995 in the seventy six oil field clinton county kentucky oil is produced from low porosity fractured carbonate rocks at 3 no injection operations were conducted gross changes in production rate correlate with event rate event rate lags changes in production rate by 2 to 3 weeks hypocenters and first motion data have revealed previously undetected low angle thrust faults above and below the currently drained depth intervals production history well logs and drill tests indicate that the seismically active faults or fractures are previously drained intervals that have subsequently recovered to hydrostatic pressure via brine invasion storage capacity computed for one of these drained fractures implies that total oil production represents about 20 of total pore volume correlation of older production intervals and well log porosity anomalies with the seismically active faults indicate that the oil reservoir in the study area is primarily a set of compartmentalized low angle thrust faults although low angle fracture sets have not previously been considered in the exploration and development of the area the mapped thrust faults are consistent with other investigators interpretations of oil associated with secondary fracture sets occurring along deeper seated wrench fault structures stress determined from composite focal mechanisms indicates a near surface

empirical green s function analysis taking the next step an extension of the empirical green s function egf method is presented that involves determination of source parameters using standard egf deconvolution followed by inversion for a common attenuation parameter for a set of colocated events recordings of three or more colocated events can thus be used to constrain a single path attenuation estimate i apply this method to recordings from the 1995 1996 ridgecrest california earthquake sequence i analyze four clusters consisting of 13 total events with magnitudes between 2 6 and 4 9 i first obtain corner frequencies which are used to infer brune stress drop estimates i obtain stress drop values of 0 3 53 mpa with all but one between 0 3 and 11 mpa with no resolved increase of stress drop with moment with the corner frequencies constrained the inferred attenuation parameters are very consistent they imply an average shear wave quality factor of approximately 20 25 for alluvial sediments within the indian wells valley although the resultant spectral fitting using corner frequency and is good the residuals are consistent among the clusters analyzed their spectral shape is similar to the the theoretical one dimensional response of a layered low velocity structure in the valley an absolute site response cannot be determined by this method because of an ambiguity between absolute response and source spectral amplitudes i show that even this subtle site response can significantly bias estimates of corner frequency and if it is ignored in an inversion for only source and path effects the multiple egf method presented in this paper is analogous to a joint inversion for source path and site effects the use of colocated sets of earthquakes appears to offer significant advantages in improving resolution of all three estimates especially if data are from a single site or sites with similar site response

shear wave splitting and reservoir crack characterization the coso geothermal field abstract this paper aims to improve current understanding of the subsurface fracture system in the coso geothermal field located in east central california the coso reservoir is in active economic development so that knowledge of the subsurface fracture system is of vital importance for an accurate evaluation of its geothermal potential and day to day production to detect the geometry and density of fracture systems we applied the shear wave splitting technique to a large number of high quality seismograms from local microearthquakes recorded by a permanent 16 station down hole 3 component seismic array running at 480 samples s the analysis of shear wave splitting seismic birefringence provides parameters directly related to the strike of the subsurface fractures and their density number of cracks per unit volume and consequently is an important technique to outline zones of high permeability three major fracture directions n10 30w n0 20e and n40 50e of which the first and the second are the most prominent were identified from the seismograms recorded by the 16 station down hole array all orientations are consistent with the known strike of local sets of faults and fractures in local wells and at the surface as well as with previous analyses of seismic anisotropy in the region the high quality of the recordings has allowed us to launch an unprecedented investigation into the characteristics of the temporal variations in crack polarization and crack density in a producing geothermal environment preliminary results point to significant temporal changes in shear wave time delays probably influenced by temporal changes in crack density within a period of 5 years 1996 2000 they are tentatively interpreted as due to a local 3 increase in shear wave velocity in the southwestern part of the field during 1999

applications of attenuation tomography to imperial valley and coso indian wells region southern california spatial variations in seismic wave attenuation were tomographically imaged from observed s to p wave amplitude ratios in the imperial valley and coso indian wells regions of southern california in the coso indian wells region a highly attenuating body s wave quality factor q 30 coincides with a slow p wave anomaly mapped by walck and clayton 1987 this coincidence suggests the presence of a 3 to 5 km depth magmatic or hydrothermal body in the indian wells region in the imperial alley slow p wave travel time anomalies and highly attenuating s wave anomalies were found in the brawicy seismic zone at a depth of 8 12 kin the effective s wave quality factor is very low q 20 and the p wave velocity is 10 slower than the surrounding area these results suggest either magmatic or hydrothermal intrusions or fractures at depth possibly related to active shear in the brawley seismic zone this attenuation tomographic technique is shown to be useful in delineating the spatial variations in seismic wave attenuation and in estimating the effective seismic quality factor of attenuation anomalies

crustal structure determined from ambient noise tomography near the magmatic centers of the coso region southeastern california we apply seismic ambient noise tomography to image and investigate the shallow shear velocity structure beneath the coso geothermal field and surrounding areas data from a passcal experiment operated within the coso geothermal field between 1998 and 2000 and surrounding broadband stations from the southern california seismic network are acquired and processed daily cross correlations of ambient noise between all pairs of stations that overlapped in time of deployment were calculated and then stacked over the duration of deployment phase velocities of rayleigh waves between 3 and 10 s periods are measured from the resulting cross correlations depending on the period between about 300 and 600 reliable phase velocity measurements are inverted for phase velocity maps from 3 to 10 s periods which in turn are inverted for a 3 d shear velocity model beneath the region the resulting 3 d model reveals features throughout the region that correlate with surface geology beneath the coso geothermal area shear velocities are generally depressed a prominent low velocity anomaly is resolved clearly within the top 2 km no significant anomaly is seen below about 14 km depth and a weakly resolved anomaly is observed between 6 and 12 km depth the anomaly in the top 2 km probably results from geothermal alteration in the shallow subsurface no magmatic body is imaged beneath 14 km depth but the shear velocity anomaly between 6 and 12 km may be attributable to partial melt the thickness and amplitude of the magma body trade off in the inversion and are ill determined low velocities in the regions surrounding coso at depths near 7 km underlie areas with miocene to recent volcanism suggesting that some magmatic processing of the crust could be focused near this depth

a three year continuous sample of officially documented predictions issued in greece using the van method 1987 1989 abstract copies of all officially documented predictions issued in greece using the van method for the period 1987 1989 are presented a correlation between these predictions and earthquakes is attempted selectivity maps based on experimental data are drawn and the selectivity effect with relation to some earthquake source parameters is commented upon finally the quality of the predictions for large earthquakes is discussed

determination of near surface attenuation with κ parameter to obtain the seismic moment stress drop source dimension and seismic energy for microearthquakes in the granada basin southern spain abstract a set of 43 microearthquakes of the granada basin with magnitude duration m d from 1 4 to 3 5 have been spectrally analysed the digital data used in this study was recorded by two short period digital seismic network five permanent stations using andalusian seismic network red sismica de andalucia rsa and three stations of a portable digital seismic network red sismica portatil rsp the displacement spectra for p and s waves were analysed with brune s j geophys res 75 1970 4997 j geophys res 76 1971 5002 source model and the spectra parameters were determined by snoke s model to correct spectra from path attenuation coda q was used for the spectra correction from near surface attenuation parameter was calculated obtaining it from acceleration spectra the values of parameter range from 0 01 to 0 04 s for p waves and from 0 006 to 0 04 s to s waves once the spectra of these attenuation effects was corrected we obtained the seismic moments that range from 5 45 10 17 dyne cm to 1 53 10 20 dyne cm the source radii are between 0 13 and 0 39 km the seismic energy ranges from 7 17 10 3 j to 1 13 10 8 j the stress drop values were below 4 bars the scaling relations between seismic moment and stress drop indicated decreasing stress drop with decreasing seismic moment