analysis of foreshock sequences in california and implications for earthquake triggering we analyze foreshock activity in california and compare observations with simulated catalogs based on a branching aftershock triggering model we first examine foreshock occurrence patterns for isolated m ge 5 earthquakes in southern california from 1981 to 2011 and in northern california from 1984 to 2009 among the 64 m ge 5 mainshocks excluding 3 swarms and 3 doubles 53 of the rest are preceded by at least one foreshock within 30 days and 5 km foreshock occurrence appears correlated with mainshock faulting type and depth foreshock area is correlated with the magnitude of the largest foreshock and the number of foreshocks however it is not correlated with mainshock magnitude we then examine the occurrence pattern of all seismicity clusters without a minimum magnitude requirement and the possibility that they are foreshocks of larger mainshocks only about 30 of the small clusters lead to a larger cluster about 66 of the larger clusters have foreshock activities and the spatial distribution pattern is similar to m ge 5 mainshocks with lower occurrence rates in the transverse range and central california and higher occurrence rates in the eastern california shear zone and the bay area these results suggest that foreshock occurrence is largely controlled by the regional tectonic stress field and fault zone properties in special cases foreshock occurrence may be useful for short term forecasting however foreshock properties are not reliably predictive of the magnitude of the eventual mainshock comparison with simulated catalogs suggest that the swarmy features and foreshock occurrence rate in the observed catalogs are not well reproduced from common statistical models of earthquake triggering

change in the probability for earthquakes in southern california due to the landers magnitude 7 3 earthquake the landers earthquake in june 1992 redistributed stress in southern california shutting off the production of small earthquakes in some regions while increasing the seismicity in neighboring regions up to the present this earthquake also changed the ratio of small to large events in favor of more small earthquakes within about 100 kilometers of the epicenter this implies that the probabilistic estimate for future earthquakes in southern california changed because of the landers earthquake the location of the strongest increase in probability for large earthquakes in southern california was the volume that subsequently produced the largest slip in the magnitude 7 1 hector mine earthquake of october 1999

nonlinear frequency dependence of the effective seabottom acoustic attenuation from low frequency field measurements in shallow water hamilton s seabed geo acoustic model which is widely accepted predicts that the attenuation of sound in marine sediments increases linearly with frequency over the full frequency range of interest in ocean acoustics a few hertz to megahertz however biot stoll s physics based seabed geo acoustic model predicts that the bottom attenuation should exhibit non linear frequency dependence particularly in sandy bottoms since the publication of previous papers zhou j acoust soc am 78 1003 1009 1985 kibblewhite ibid 86 716 738 1989 more low frequency field data collected from different coastal zones around the world have shown inconsistencies with the often used linear frequency dependence this paper attempts to support the non linear frequency dependence of sea bottom attenuation through a review of shallow water acoustic field measurements with a special emphasis on the 50 1000 hz frequency range the relevant measurements include bottom reflection loss sound transmission loss dispersion analysis vertical coherence of both propagation and reverberation normal mode spatial filtering and optimum frequency and transition range of sound propagation a non linear frequency dependence of equivalent bottom acoustic attenuation derived from these measurements will be introduced work supported by onr and nnsf of china

foreshock activity related to enhanced aftershock production foreshock activity sometimes precedes the occurrence of large earthquakes but the nature of this seismicity is still debated and whether it marks transient deformation and or slip nucleation is still unclear we here study at the worldwide scale how foreshock occurrence affects the postseismic phase and find a significant positive correlation between foreshock and aftershock activities earthquakes preceded by accelerating seismicity rates produce 40 more aftershocks on average and the length of the aftershock zone after 20 days is 20 larger these observations cannot be reproduced by standard earthquake clustering models that predict the accelerating pattern of foreshock occurrence but not its impact on aftershock activity this strongly suggests that slow deformation transients possibly related to episodic creep could initiate prior to the main shock and extend past the coseismic phase resulting in compound ruptures that include a very long period up to tens of days component

sequential inversion of modal data for sound attenuation in sediment at the new jersey shelf this paper presents a method for estimating bottom geoacoustic properties especially the sediment attenuation from information contained in normal modes of a broadband signal propagating modes are resolved using the time warping technique applied to signals from light bulb sound sources deployed at ranges of 5 and 7 km in the shallow water 06 experiment a sequential inversion approach is designed that uses specific features of the acoustic data that are highly sensitive to specific geoacoustic model parameters the first feature is the modal group speed which is inverted for seabed sound speed density and sediment thickness the second feature is the modal depth function for inverting receiver depths the third feature is related to the modal coefficient spectra and this is inverted for source depth and sediment attenuation in each subsequent stage estimates from the previous stage s are used as known values the sequential inversion is stable and generates estimates for the geoacoustic model parameters that agree very well with results from other experiments carried out in the same region notably the inversion obtains an estimated attenuation of 0 078 db in the band 120 180 hz for the de watered marine sediment characteristic of the continental shelf at the site

a common origin for aftershocks foreshocks and multiplets we demonstrate that the statistics of earthquake data in the global cen troid moment tensor cmt and national earthquake information center neic catalogs and local california council of the national seismic system cnss catalog are consistent with the idea that a single physical triggering mechanism is responsible for the occurrence of aftershocks foreshocks and multiplets specifically we test the hypothesis that tectonic earthquakes usually show clustering only as a result of an initial earthquake triggering subsequent ones and that the magnitude of each trig gered earthquake is entirely independent of the magnitude of the triggering earth quake therefore a certain percentage of the time as determined by the gutenberg richter magnitude frequency relationship an earthquake should by chance be larger than or comparable in size to the earthquake that triggered it this hypothesis predicts that the number of times foreshocks or multiplets are observed should be a fixed fraction of the number of aftershock observations we find that this is indeed the case in the global cmt and neic catalogs the average ratios between foreshock aftershock and multiplet rates are consistent with what would be predicted by the gutenberg richter relationship with b 1 we give special attention to the solomon islands where it has been claimed that unique fault structures lead to unusually high numbers of multiplets we use monte carlo trials to demonstrate that the solomon islands multiplets may be explained simply by a high regional aftershock rate and earthquake density we also verify our foreshock results from the more complete recordings of small earthquakes available in the california catalog and find that foreshock rates for a wide range of foreshock and mainshock magnitudes can be projected from aftershock rates using the gutenberg richter relationship with b 1 and the relationship that the number of earthquakes triggered varies with triggering earthquake magnitude m as c10m where c is a productivity constant and is equal to 1 finally we test an alternative model that proposes that foreshocks do not trigger their mainshocks but are instead triggered by the mainshock nucleation phase in this model the nucleation phase varies with mainshock magnitude so we would expect mainshock magnitude to be correlated with the magnitude number or spatial extent of the foreshocks we find no evidence for any of these correlations

low frequency sound speed and attenuation in sandy seabottom from long range broadband acoustic measurements a joint china u s underwater acoustics experiment was conducted in the yellow sea with a very flat bottom and a strong and sharp thermocline broadband explosive sources were deployed both above and below the thermocline along two radial lines up to 57 2 km and a quarter circle with a radius of 34 km two inversion schemes are used to obtain the seabottom sound speed one is based on extracting normal mode depth functions from the cross spectral density matrix the other is based on the best match between the calculated and measured modal arrival times for different frequencies the inverted seabottom sound speed is used as a constraint condition to extract the seabottom sound attenuation by three methods the first method involves measuring the attenuation coefficients of normal modes in the second method the seabottom sound attenuation is estimated by minimizing the difference between the theoretical and measured modal amplitude ratios the third method is based on finding the best match between the

comparing foreshock characteristics and foreshock forecasting in observed and simulated earthquake catalogs in this paper we compare the empirical results regarding foreshocks obtained from the japan data with results for synthetic catalogs in order to clarify whether or not the corresponding results are consistent with the description of the seismicity by a superposition of background activity and epidemic type aftershock sequence etas models this question is important because it is still controversially discussed whether the nucleation process of large earthquakes is driven by seismically cascading etas type or by aseismic accelerating processes to explore the foreshock characteristics we first applied the same clustering algorithms to real and synthetic catalogs and analyzed the temporal spatial and magnitude distributions of the selected foreshocks most properties are qualitatively the same in the real data and in synthetic catalogs however we find some quantitative differences particularly in the temporal acceleration spatial convergence and magnitude dependence which also depend on the assumed synthetic catalogs furthermore we calculated forecast scores based on a single link cluster algorithm which could be appropriate for real time applications we find that the japan meteorological agency catalog yields higher scores than all synthetic catalogs and that the etas models having the same magnitude sequence as the original catalog performs better more close to the reality than etas models with randomly picked magnitudes we also find that the etas model that takes account of the triggering effect by small earthquakes below threshold magnitude performs more closely to the reality

triggering of seismicity at short timescales following californian earthquakes 1 a method for measuring seismicity rate changes caused by the occurrence of major earthquakes in the surrounding crust is proposed it is based on a nonstationary poisson modeling of earthquake activity an estimate of the seismicity rate change and a probability measure of seismicity triggering following a large shock are derived and the removal of the influence of independent aftershock sequences of other nearby previous earthquakes is attempted without using more traditional declustering techniques the seismicity rate change estimator is corrected for its natural bias in favor of positive changes at short timescales that has so far strongly hindered measures of seismicity quiescences three californian earthquakes are examined using this method the 1989 m7 1 loma prieta the 1992 m7 3 landers and the 1994 m6 7 northridge earthquakes positive triggering is very commonly observed as expected but quiescence is however more seldomly obtained for timescales up to 100 days after the main shock this relative absence of quiescence as compared to typical predictions of coulomb modeling for example is also independently observed through direct correlation analyses of californian seismicity the possibility that the stresses caused by the main shock are spatially highly variable may explain these observations

a hypothesis for delayed dynamic earthquake triggering 1 it s uncertain whether more near field earthquakes are triggered by static or dynamic stress changes this ratio matters because static earthquake interactions are increasingly incorporated into probabilistic forecasts recent studies were unable to demonstrate all predictions from the static stress change hypothesis particularly seismicity rate reductions however current dynamic stress change hypotheses do not explain delayed earthquake triggering and omori s law here i show numerically that if seismic waves can alter some frictional contacts in neighboring fault zones then dynamic triggering might cause delayed triggering and an omori law response the hypothesis depends on faults following a rate state friction law and on seismic waves changing the mean critical slip distance dc at nucleation zones

statistical features of foreshocks in comparison with other earthquake clusters summary when earthquakes occur in a cluster the probability that they will be foreshocks of a forthcoming significantly larger earthquake appears dependent on the magnitude differences origin time spans and distances between several of the earliest events in a cluster the earthquake catalogue of the japan meteorological agency jma 1926 91 mj 2 4 is decomposed into numbers of clusters in time and space to compare statistical features of foreshocks with those of swarms and main shockaftershock sequences since the number of foreshocks in individual earthquake clusters is usually small two types of data stacking are considered first we consider the spatial and temporal distribution of events relative to the location and time of the coming main shock for the foreshocks a relative doughnut shaped pattern which converges in time to the main shock s epicentre is seen while this pattern is weak for swarms next we consider the temporal spatial and magnitude distributions of events relative to the time location and magnitude of earlier events in every sequence then a statistical discrimination of foreshocks from earthquakes of other types of clusters is explored the search for significant trends of relative frequency of foreshocks in comparison with other cluster types revealed the following features of foreshocks 1 their relative frequency is high when the inter event time span is less than several days but the maximum is attained at about several hours span 2 their relative frequency is high at short distances between epicentres especially within 10 km and then decreases as the distance gets larger and 3 their relative frequency increases as the magnitude increases among the earliest shocks in a cluster the stability of the results is confirmed by finding similar trends using different cluster identification methods and different threshold magnitudes further microearthquakes in the japan university network data file 1983 87 m 2 2 and moderate to large earthquakes in the international seismological centre world catalogue isc 1979 90 mh 2 5 are examined to see some effects of the magnitude thresholds of these catalogues similar features to those obtained in the jma catalogue are also found for these catalogues

triggering of earthquake aftershocks by dynamic stresses it is thought that small static stress changes due to permanent fault displacement can alter the likelihood of or trigger earthquakes on nearby faults many studies of triggering in the near field particularly of aftershocks rely on these static changes as the triggering agent and consider them only in terms of equivalent changes in the applied load on the fault here we report a comparison of the aftershock pattern of the moment magnitude mw 7 3 landers earthquake not only with static stress changes but also with transient oscillatory stress changes transmitted as seismic waves that is dynamic stresses dynamic stresses do not permanently change the applied load and thus can trigger earthquakes only by altering the mechanical state or properties of the fault zone these dynamically weakened faults may fail after the seismic waves have passed by and might even cause earthquakes that would not otherwise have occurred we find similar asymmetries in the aftershock and dynamic stress patterns the latter being due to rupture propagation whereas the static stress changes lack this asymmetry previous studies have shown that dynamic stresses can promote failure at remote distances but here we show that they can also do so nearby

the long precursory phase of most large interplate earthquakes many earthquakes are preceded by foreshocks however the mechanisms that generate foreshocks and the reason why they occur before some earthquakes and not others are unknown here we use seismic catalogues from the best instrumented areas of the north pacific to analyse the foreshock sequences preceding all earthquakes there between 1999 and 2011 of magnitude larger than 6 5 and at depths shallower than 50 km the data set comprises 31 earthquakes at plate boundaries and 31 in plate interiors we find that there is a remarkable contrast between the foreshock sequences of interplate compared with intraplate earthquakes most large earthquakes at plate interfaces in the north pacific were preceded by accelerating seismic activity in the months to days leading up to the mainshock in contrast foreshocks are much less frequent in intraplate settings we suggest that at plate boundaries the interface between the two plates begins to slowly slip before the interface ruptures in a large earthquake this relatively long precursory phase could help mitigate earthquake risk at plate boundaries

estimating marine sediment attenuation at low frequency with a vertical line array this paper presents a method of determining the compressional wave attenuation in marine sediment from a short range measurement the data were collected on a vertical line array at a range of 230 m during the shallow water 2006 experiments the sediment attenuation is extracted from the signal strength ratio of the sea bottom reflection to a sub bottom reflection at different frequencies from 1 75 to 3 15 khz linear frequency dependence of the attenuation is found from the estimation the sediment attenuation estimate is lower than the values estimated from the inversions of acoustic field data previously done in the vicinity

forecasting where larger crustal earthquakes are likely to occur in italy in the near future a forecast of future occurrences of larger m 5 9 crustal earthquakes in italy is made on the basis of historic and instrumental seismicity and following a seismotectonic regionalization recently derived on the basis of geological evidence combined with earthquake epicenters and focal mechanisms completeness problems in the seismic catalog allow one to study only 20 regions out of 58 large crustal seismicity within each seismogenic region is modeled as either a periodic gauss process or a random poisson process according to the experimental coefficient of variation of the series of past occurrences in each region return times are estimated directly from the series of m 4 5 earthquakes if they are sufficient in number or from the gutenberg richter law applied to lower magnitude seismicity m 4 5 otherwise the immediate probability of an m 5 9 crustal seismic event is esti mated to be very low in all regions except southeastern sicily and appennino abrnz zese in the near future next 20 yr the estimated probability is high above 65 also in the appennino forlivese and naso capo d orlando regions in addition to detailed seismic risk reevaluations these regions represent the best bet for a program of intensive monitoring to gather a record of the process of strain accumulation and seismic release

comparative performance of time invariant long range and short range forecasting models on the earthquake catalogue of greece 1 time invariant long range and short range forecasting models were fitted to the earthquake catalogue of greece for magnitudes 4 0 and greater to optimize their ability to forecast events of magnitude 6 0 and greater in the period 1966 1980 the models considered were stationary spatially uniform and spatially varying poisson models a long range forecasting model based on the precursory scale increase phenomenon with every earthquake regarded as a precursor according to scale and epidemic type short range forecasting models with spatially uniform and spatially varying spontaneous seismicity each of the models was then applied to the catalogue for 1981 2002 and their forecasting performance was compared using the log likelihood statistic the long range forecasting model performed substantially better than the time invariant models and the short range forecasting models performed substantially better again the results show that the information value to be gained from modeling temporal and spatial variation of earthquake occurrence rate at both long and short range is much greater than can be gained from modeling spatial variation alone

seismic gap hypothesis ten years after the seismic gap hypothesis states that earthquake hazard increases with time since the last large earthquake on certain faults or plate boundaries one of the earliest and clearest applications of the seismic gap theory to earthquake forecasting was by mccann et al 1979 who postulated zones of high medium and low seismic potential around the pacific rim in the 10 years since there have been over 40 large m 7 0 earthquakes enough to test statistically the earlier forecast we also analyze another forecast of long term earthquake risk that by kelleher et al 1973 the hypothesis of increased earthquake potential after a long quiet period can be rejected with a large confidence the data suggest that contrary to these forecasts places of recent earthquake activity have larger than usual seismic hazard whereas the segments of the circum pacific belt with no large earthquakes in recent decades have remained relatively quiet the clustering of earthquake times does not contradict the plate tectonic model which constrains only the long term average slip rate not the regularity of earthquakes

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

properties of the 2003 lefkada ionian islands greece earthquake seismic sequence and seismicity triggering on 14 august 2003 lefkada island central ionian was strongly af fected by an mw 6 2 earthquake a dense temporary seismic network was installed one day after and accurately located hundreds of aftershocks that defined in detail the main rupture as well as the activity distribution in the neighboring fault segments the main rupture occupied the northwestern part of the coastline and trends north northeast south southwest in agreement with regional tectonics regional network locations were appropriately calibrated using the local network data allowing the relocation of the mainshock and strong m 4 5 or larger aftershocks during the first day intense aftershock activity took place up to 40 km beyond the southern end of the main rupture theoretical static stress changes from the mainshock give a preliminary explanation for the aftershock distribution aside from the main rupture as well as triggering of seismicity in the nearby kefalonia fault providing evidence for future seismic hazard ensuing from this fault

nucleation points of recent mainshocks in southern iceland mapped by b values the earthquake catalog in southern iceland between 20 25 w and 21 3 w is complete down to approximately mw 0 and shows no evidence for mag nitude shifts as a function of time since 1991 this means that 6902 earthquakes m 0 1 depth 20 km are available for studies of seismicity patterns preceding the two ms 6 6 mainshocks in 2000 in their source volumes and vicinity 20 25 w and 20 9 w the power law of the frequency magnitude relationship holds down to m0 detailed mapping including 3d mapping of the b value of the frequency magnitude distribution shows that variations from b 0 6 to 1 4 exist over distances of about 2 km this suggests that the tectonic fabric in southern iceland is hetero geneous on a small scale the hypocenters of the two ms 6 6 mainshocks and one additional m 4 5 mainshock are associated with low b values 0 6 0 8 statistically significantly different from volumes in their vicinity therefore one can expect future mainshocks in southern iceland to also emanate from volumes characterized by low b values however the small dimensions of these asperities may render it difficult to identify them before the mainshocks occur low values of estimated local recur rence times 500 2000 years map the two fault zones that ruptured in 2000 against a background of local recurrence times longer than 5000 years the first of the two m 6 6 mainshocks emanated from a volume of short estimated local recurrence time this supports the hypothesis that asperities with short local recurrence times control locations of major ruptures mapping of b values in cross sections shows anomalies of high b at the bottom of the seismogenic crust correlating with the change of its thickness in the middle of the study area these high b value anomalies and other pockets of such anomalies at shallower depths are best interpreted as caused by high pore pressure because evidence of fluids under high pressure is ubiquitous in this area

stochastic slip predictable model for earthquake occurrences recent geophysical studies have indicated that an earthquake recurrence interval and the size of the preceding event are positively correlated this observation is the basis for the deterministic time predictable recurrence model of shimazaki and nakata using the basic assumptions of the time predictable recurrence model we develop a stochastic model of earthquake occurrence that incorporates temporal dependence this paper discusses the formulation of the model and the effect of including temporal dependence hazard estimates for a section of the san andreas fault near parkfield where data has suggested time predictable behavior are obtained for illustrative purposes comparisons are made with the poisson model results indicate that currently used poisson models may give lower estimates of the seismic hazard when there has been a seismic gap of the various sensitivity analyses performed it is observed that slip rate has the largest effect on exceedence probabilites computed from the stochastic time predictable model therefore accurate determinations of slip rates both seismic and aseismic can substantially reduce the uncertainty in seismic hazard estimates

bayesian geoacoustic inversion in a dynamic shallow water environment this paper presents results for matched field bayesian geoacoustic inversion of multitonal continuous wave data collected on the new jersey continental shelf to account for effects of significant spatial and temporal variation of the water column sound speed the sound speed profile was represented by empirical orthogonal functions data error information for the inversion was estimated from multiple time windows of the data inversion results for the sediment sound speeds at three ranges are in excellent agreement with the ground truth

methods for measuring seismicity rate changes a review and a study of how the m w 7 3 landers earthquake affected the aftershock sequence of the m w 6 1 joshua tree earthquake the development of fault interaction models has triggered the need for an accurate estimation of seismicity rate changes following the occurrence of an earthquake several statistical methods have been developed in the past to serve this purpose each relying on different assumptions e g stationarity gaussianity pertaining to the seismicity process

are aftershocks of large californian earthquakes diffusing we analyze 21 aftershock sequences of california to test for evidence of space time diffusion aftershock diffusion may result from stress diffusion and is also predicted by any mechanism of stress weakening here we test an alternative mechanism to explain aftershock diffusion based on multiple cascades of triggering in order to characterize aftershock diffusion we develop two methods one based on a suitable time and space windowing the other using a wavelet transform adapted to the removal of background seismicity both methods confirm that diffusion of seismic activity is very weak much weaker than reported in previous studies a possible mechanism explaining the weakness of observed diffusion is the effect of geometry including the localization of aftershocks on a fractal fault network and the impact of extended rupture lengths which control the typical distances of interaction between earthquakes

precursory activity before larger events in greece revealed by aggregated seismicity data we investigate the seismicity rate behaviour in and around greece during 2009 seeking significant changes in rate preceding larger events for individual larger events it is difficult to clearly d

relative seismic quiescence before large aftershocks in terms of the modified omori s formula and akaike s information criterion thirteen aftershock sequences have been analysed quantitatively to check if any anomalous change of seismic activity took place before the occurrence of the largest aftershock the analysis follows the method proposed by the epicentre distribution of the main shocks covers the aegean sea greece area and the surrounding regions the earthquakes occurred from 1988 to 1998 although difficulties existed for a quantitative treatment of seismic quiescence the results of the temporal analysis of the aftershock activities seem to be promising in eight of thirteen cases the observed temporal pattern is similar the aftershock activity decreases significantly before the occurrence of the largest aftershock with respect to the level expected according to the modified omori s formula thereafter the activity recovers to its previous level just before or immediately after the occurrence of the main aftershock moreover an estimation of the reliability of the method is made based on the results of this study as well as of previous similar investigations from a total of 41 aftershock sequences which have been analysed following matsu ura s method 29 of them 71 show a remarkable relative quiescence before the occurrence of the main shock although it is difficult to construct a model which explains the precursory pattern the real time monitoring and check for seismic quiescence could at least contribute to a qualitative prediction of the largest aftershock which could at times be as large and disastrous as the main shock

seismicity analysis through point process modeling a review the occurrence times of earthquakes can be considered to be a point process and suitable modeling of the conditional intensity function of a point process is useful for the investigation of various statistical features of seismic activity this manuscript summarizes likelihood based methods of analysis of point processes and reviews useful models for particular analyses of seismicity most of the analyses can be implemented by the computer programs published by the author and collaborators

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

quantifying the uncertainty of geoacoustic parameter estimates for the new jersey shelf by inverting air gun data this paper describes geoacoustic inversion of low frequency air gun data acquired during an experiment on the new jersey shelf hybrid optimization and bayesian inversion techniques based on matched field processing were applied to multiple shots from three air gun data sets recorded by a vertical line array in a long range shallow water geometry for the bayesian inversions full data error covariance matrix was estimated from a set of consecutive shots that had high temporal coherence and small spatial variation in source position the effect of different data error information on the geoacoustic parameter uncertainty estimates was investigated by using the full data error covariance matrix a diagonalized version of the full error covariance and a diagonal matrix with identical variances the comparison demonstrated that inversion using the full data error information provided the most reliable parameter uncertainty estimates the inversions were highly sensitive to the near sea floor geoacoustic parameters including sediment attenuation of a simple single layer geoacoustic model the estimated parameter values of the model were consistent with depth averaged values over wavelength scales of a high resolution geoacoustic model developed from extensive ground truth information the interpretation of the frequency dependence of the estimated attenuation is also discussed

recognition of a hidden mineral deposit by an artificial intelligence program a computer program that uses artificial intelligence techniques has successfully identified the location of a porphyry molybdenum deposit given geological maps of readily available predrilling exploration data for mount tolman in washington state and using rules obtained from a porphyry molybdenum exploration specialist the program called prospector identified the location of previously unknown ore grade mineralization this appears to be the first reported determination of the location of mineralization by such a computer based approach

seabed acoustics of a sand ridge on the new jersey continental shelf acoustic measurements were made on a sand ridge on the new jersey continental shelf data collected on two l arrays separated by 20km from a single multi frequency tow suggest small horizontal environmental variability values for the sound speed structure of the seabed are extracted by first applying a geo acoustic inversion method to broadband and narrowband acoustic data from short range sources then a parabolic equation algorithm is used to properly include the bathymetry and sub bottom layering finally the frequency dependence of the seabed attenuation is inferred by optimizing the model fit to long range transmission loss data in the 50 3000hz band

a premonitory pattern of earthquakes in northern greece on 20 june 1978 at 20 h 03 min 23 s an earthquake of surface wave magnitude 6 5 occurred in the migdonian basin between the lagada and volvi lakes and 26 km from thessaloniki the main shock was preceded by a seismic sequence which started on 8 may the largest earthquake of that sequence occurred on 23 may and had a surface wave magnitude of 5 8 the long duration of this sequence before the main shock of 20 june had tremendous psychological effects on the whole country greek seismologists were in a difficult position during that time 8 may 20 june especially after the earthquake of 23 may when pressed to state whether these earthquakes were foreshocks or aftershocks long lasting seismic sequences with earthquakes of magnitude 6 are common in the aegean area because these sequences are sometimes followed by large earthquakes it is important to see whether the latter can be predicted the may june 1978 seismic sequence provided the opportunity for testing hypotheses about statistical properties which it has been suggested could distinguish between foreshocks and aftershocks this particular sequence has been investigated extensively1 4 and more accurate data are available than for any other sequence around greece focal mechanism studies5 6 and field observations2 showed that the largest earthquakes of the sequence were produced by horizontal extension in a nearly north south direction and that the main rupture occurred on a normal fault which strikes almost east west and dips to the north the fault length of the main shock of 20 june was estimated7 to be 32 km accurate determination of earthquake foci using portable seismographs showed that the earthquakes of this sequence were shallow h 17 km while the distribution of the epicentres had a very clear east west elongation4 5 a migration of the seismic activity from east to west has also been observed between 8 may and 14 july we investigate here the time variation of the average magnitude and the frequency of all the shocks with m 3 0 of this sequence the time variations of these seismic parameters are examined in connection with the distribution of well determined epicentres of 38 earthquakes with m 4 3 in order to search for any premonitory pattern of the 23 may and 20 june major earthquakes

testing the stress shadow hypothesis 1 a fundamental question in earthquake physics is whether aftershocks are predominantly triggered by static stress changes permanent stress changes associated with fault displacement or dynamic stresses temporary stress changes associated with earthquake shaking both classes of models provide plausible explanations for earthquake triggering of aftershocks but only the static stress model predicts stress shadows or regions in which activity is decreased by a nearby earthquake to test for whether a main shock has produced a stress shadow we calculate time ratios defined as the ratio of the time between the main shock and the first earthquake to follow it and the time between the last earthquake to precede the main shock and the first earthquake to follow it a single value of the time ratio is calculated for each 10 10 km bin within 1 5 fault lengths of the main shock epicenter large values of the time ratio indicate a long wait for the first earthquake to follow the main shock and thus a potential stress shadow whereas small values indicate the presence of aftershocks simulations indicate that the time ratio test should have sufficient sensitivity to detect stress shadows if they are produced in accordance with the rate and state friction model we evaluate the 1989 mw 7 0 loma prieta 1992 mw 7 3 landers 1994 mw 6 7 northridge and 1999 mw 7 1 hector mine main shocks for each main shock there is a pronounced concentration of small time ratios indicating the presence of aftershocks but the number of large time ratios is less than at other times in the catalog this suggests that stress shadows are not present by comparing our results to simulations we estimate that we can be at least 98 confident that the loma prieta and landers main shocks did not produce stress shadows and 91 and 84 confident that stress shadows were not generated by the hector mine and northridge main shocks respectively we also investigate the long hypothesized existence of a stress shadow following the 1906 san francisco bay area earthquake we find that while bay area catalog seismicity rates are lower in the first half of the twentieth century than in the last half of the nineteenth this seismicity contrast is also true outside of the bay area in regions not expected to contain a stress shadow this suggests that the rate change is due to a more system wide effect such as errors in the historical catalog or the decay of aftershocks of the larger 1857 fort tejon earthquake

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

statistical analysis of sound transmission results obtained on the new jersey continental shelf experiments have been conducted near the site of amcor borehole 6010 on the new jersey shelf to evaluate propagation predictability in sandy shallow water environments the influence of a nonlinear frequency dependence of the sediment volume attenuation in the uppermost sediment layer at this location is examined previously it was determined that a frequency power law exponent of 1 5 was required for the best modeling of experimental results over the band 50 1000hz the approach here references the attenuation to an accepted value at 1khz and makes extensive comparisons between measurements and calculations to determine a power law exponent of 1 85 0 15

on the preparatory processes of the m6 6 earthquake of june 17th 2000 in iceland 1 a model is proposed to explain the spatial distribution of foreshocks of the june 17th 2000 ms 6 6 earthquake in the south iceland seismic zone sisz and the high stress drop of the mainshock fluids of magmatic origin ascending at near lithostatic pressure through a low permeability layer perturb the regional stress field inhibiting fluid flow laterally where a high strength asperity is left the asperity is modeled as elastic embedded within a medium with low effective rigidity regional stresses due to tectonic motions are perturbed by the presence of the asperity enhancing the production of hydrofractures and foreshocks in the nw and se quadrants and increasing considerably the shear stress within the asperity leading to the ns striking mainshock

seismic potential for large and great interplate earthquakes along the chilean and southern peruvian margins of south america a quantitative reappraisal the seismic potential of the chilean and southern peruvian margins of south america is reevaluated to delineate those areas or segments of the margin that may be expected to experience large or great interplate earthquakes within the next 20 years 1984 2004 long term estimates of seismic potential or the conditional probability of recurrence within a specified period of time are based on 1 statistical analysis of historic repeat time data using weibull distributions and 2 deterministic estimates of recurrence times based on the time predictable model of earthquake recurrence both methods emphasize the periodic nature of large and great earthquake recurrence and are compared with estimates of probability based on the assumption of poisson type behavior the estimates of seismic potential presented in this study are long term forecasts only as the temporal resolution or standard deviation of both methods is taken to range from 15 to 25 of the average or estimated repeat time at present the valparaiso region of central chile 32 35 s has a high potential or probability of recurrence in the next 20 years coseismic uplift data associated with previous shocks in 1822 and 1906 suggest that this area may have already started to rerupture in 1971 1973 average repeat times also suggest this area is due for a great shock within the next 20 years flanking segments of the chilean margin coquimbo illapel 30 32 s and talca concepcion 35 38 s presently have poorly constrained but possibly quite high potentials for a series of large or great shocks within the next 20 years in contrast the rupture zone of the great 1960 earthquake 37 46 s has the lowest potential along the margin and is not expected to rerupture in a great earthquake within the next 100 years in the north the seismic potentials of the mollendo arica 17 18 s and arica antofagasta 18 24 s segments which last ruptured during great earthquakes in 1868 and 1877 are also high but poorly constrained

importance of direct and indirect triggered seismicity in the etas model of seismicity 1 using the simple etas branching model of seismicity which assumes that each earthquake can trigger other earthquakes we quantify the role played by the cascade of triggered seismicity in controlling the rate of aftershock decay as well as the overall level of seismicity in the presence of a constant external seismicity source we show that in this model the fraction of earthquakes in the population that are aftershocks is equal to the fraction of aftershocks that are indirectly triggered and is given by the average number of triggered events per earthquake previous observations that a significant fraction of earthquakes are triggered earthquakes therefore imply that most aftershocks are indirectly triggered by the mainshock

stress transferred by the 1995 mw 6 9 kobe japan shock effect on aftershocks and future earthquake probabilities the kobe earthquake struck at the edge of the densely populated osaka kyoto corridor in southwest japan we investigate how the earthquake transferred stress to nearby faults altering their proximity to failure and thus changing earthquake probabilities we find that relative to the pre kobe seismicity kobe aftershocks were concentrated in regions of calculated coulomb stress increase and less common in regions of stress decrease we quantify this relationship by forming the spatial correlation between the seismicity rate change and the coulomb stress change the correlation is significant for stress changes greater than 0 2 1 0 bars 0 02 0 1 mpa and the nonlinear dependence of seismicity rate change on stress change is compatible with a state and rate dependent formulation for earthquake occurrence we extend this analysis to future mainshocks by resolving the stress changes on major faults within 100 km of kobe and calculating the change in probability caused by these stress changes transient effects of the stress changes are incorporated by the state dependent constitutive relation which amplifies the permanent stress changes during the aftershock period earthquake probability framed in this manner is highly time dependent much more so than is assumed in current practice because the probabilities depend on several poorly known parameters of the major faults we estimate uncertainties of the probabilities by monte carlo simulation this enables us to include uncertainties on the elapsed time since the last earthquake the repeat time and its variability and the period of aftershock decay we estimate that a calculated 3 bar 0 3 mpa stress increase on the eastern section of the arima takatsuki tectonic line attl near kyoto causes fivefold increase in the 30 year probability of a subsequent large earthquake near kyoto a 2 bar 0 2 mpa stress decrease on the western section of the attl results in a reduction in probability by a factor of 140 to 2000 the probability of a mw 6 9 earthquake within 50 km of osaka during 1997 2007 is estimated to have risen from 5 6 before the kobe earthquake to 7 11 afterward during 1997 2027 it is estimated to have risen from 14 16 before kobe to 16 22

hellenic unified seismological network an evaluation of its performance through snes method summary in this paper we analyse the location performance of the hellenic greek unified seismological network husn by seismic network evaluation through simulation method snes this method gives as a function of magnitude hypocentral depth and confidence level the spatial distribution of the number of active stations in the location procedure and their relative azimuthal gaps and confidence intervals in hypocentral parameters regarding both the geometry of the seismic network and the use of an inadequate velocity model greece is located on a tectonically active plate boundary at the convergence of the eurasian and african lithospheric plates and exhibits a high level of seismicity the husn monitors the seismicity in greek territory from 2007 at present it is composed by 88 seismic stations appropriately distribute in the area of greece the application of the snes method permitted us to evaluate the background noise levels recorded by the network stations and estimate an empirical law that links the variance of p and s traveltime residuals to hypocentral distance the statistical analysis of the p and s traveltime residuals allowed us to assess the appropriateness of the velocity model used by the husn in the location routine process we constructed snes maps for magnitudes of 2 2 5 and 3 fixing the hypocentral depth to 10 km and the confidence level to 95 per cent we also investigated by two different vertical sections the behaviour of the errors in hypocentral parameters estimates as function of depth finally we also evaluated fixing the hypocentral depth to 10 km and the confidence level to 95 per cent the magnitude of completeness through the application of the snes method we demonstrate that the husn provides the best monitoring coverage in western greece with errors that for 2 5 are less than 2 and 5 km for epicentre and hypocentral depth respectively at magnitude 2 5 this seismic network is capable of constraining earthquake hypocentres to depths of about 160 km and more and provides a threshold of completeness down to magnitude 2 for most of greek territory we delineate some seismogenic areas of southern greece that probably are not adequately covered by husn use of the snes technique could optimize upgrades of the network in these areas

heightened odds of large earthquakes near istanbul an interaction based probability calculation we calculate the probability of strong shaking in istanbul an urban center of 10 million people from the description of earthquakes on the north anatolian fault system in the marmara sea during the past 500 years and test the resulting catalog against the frequency of damage in istanbul during the preceding millennium departing from current practice we include the time dependent effect of stress transferred by the 1999 moment magnitude m 7 4 izmit earthquake to faults nearer to istanbul we find a 62 15 probability one standard deviation of strong shaking during the next 30 years and 32 12 during the next decade

foreshocks explained by cascades of triggered seismicity 1 the observation of foreshocks preceding large earthquakes and the suggestion that foreshocks have specific properties that may be used to distinguish them from other earthquakes have raised the hope that large earthquakes may be predictable among proposed anomalous properties are the larger proportion than normal of large versus small foreshocks the power law acceleration of seismicity rate as a function of time to the mainshock and the spatial migration of foreshocks toward the mainshock when averaging over many sequences using southern california seismicity we show that these properties and others arise naturally from the simple model that any earthquake may trigger other earthquakes without arbitrary distinction between foreshocks aftershocks and mainshocks we find that foreshock precursory properties are independent of the mainshock size this implies that earthquakes large or small are predictable to the same degree as seismicity rate is predictable from past seismicity by taking into account cascades of triggering the cascades of triggering give rise naturally to long range and long time interactions which can explain the observations of correlations in seismicity over surprisingly large length scales