seismicity rate change before the irpinia m 6 9 1980 earthquake the stability of seismicity rate in central and southern italy was examined in two data sets from 1975 0 to 1995 0 with m 3 4 and from 1987 5 to 1996 0 with m 2 5 these are the approximate minimum magnitudes of complete reporting for the respective periods the first set was used to evaluate the possibility that the 23 november 1980 irpinia m 6 9 earthquake was preceded by precursory seismic quiescence the second was used to evaluate the conditions under which a current seismic quiescence could be detected in central or southern italy during the years before the irpinia earthquake the seismicity rate in the northern half of the rupture area and north of it was low whether this was a case of precursory quiescence or not is subject to interpretation because the background rate cannot be established for the years before 1975 if we accept the relatively constant seismicity rate in the irpinia volume during the decade after the mainshock as representative for the background rate we have a clear case of precursory quiescence lasting at least 1 3 yr up to the mainshock alternatively it can be postulated that the seismicity rate during the decade following this shock was elevated regionally because of the stress redistribution and that the low rates seen before it represent the normal background rate even if this reasoning is accepted the fact remains that a volume including the northern part of the rupture produced no m 3 4 earthquakes during 1 3 yr before the irpinia earthquake but produced 10 earthquakes during the 4 7 previous yr given these facts we favor the interpretation that the irpinia 1980 earthquake was preceded by precursory seismic quiescence in the entire data set there are three other cases of quiescence of higher significance without a mainshock following since no other mainshock with m 6 exists in the data set no missed event exists we propose that in italy precursory seismic quiescence may precede mainshocks and that it may be detected in the future by the improved catalog of the modern data set beginning in 1987 5 major magnitude scale changes give the mistaken appearance that fewer large magnitude earthquakes occur in italy now than in years before 1987 we postulate that the rate of earthquakes has not changed and that the magnitude scale should be adjusted

analyzing earthquake clustering features by using stochastic reconstruction 1 on the basis of the epidemic type aftershock sequence etas model and the thinning procedure this paper gives the method about how to classify the earthquakes in a given catalogue into different clusters stochastically the key points of this method are the probabilities of one event being triggered by another previous event and being a background event making use of these probabilities we can reconstruct the functions associated with the characteristics of earthquake clusters to test a number of important hypotheses about the earthquake clustering phenomena we applied this reconstruction method to the shallow seismic data in japan and also to a simulated catalogue the results show the following assertions 1 the functions for each component in the formulation of the space time etas model are good enough as a first order approximation for describing earthquake clusters 2 a background event triggers less offspring in expectation than a triggered event of the same magnitude 3 the magnitude distribution of the triggered event depends on the magnitude of its direct ancestor 4 the diffusion of the aftershock sequence is mainly caused by cascades of individual triggering processes while no evidence shows that each individual triggering process is diffusive and 5 the scale of the triggering region is still an exponential law as formulated in the model but not the same one for the expected number of offspring

temporal variation of seismic b values beneath northeastern japan island arc 1 analysis of a high quality seismic catalog reveals that the average of seismic b values in the crust beneath most part of northeastern japan island arc decreased from 0 86 between 1984 and 1990 to 0 73 between 1991 and 1995 the two areas with the largest decrease are found to be in the same areas where the coupling between the north american and the pacific plates is the highest as suggested by a recent geodetic study in the same time period the annual seismic moment release increased by 10 times in addition there seems to be a corresponding increase in volcanic activities in the same area one of the most likely interpretations for the observations is an increase in the subduction rate starting from 1991 the timing of this possible increase in subduction rate is consistent with an apparent increase in global seismic activity

three dimensional numerical modelling of wind driven circulation in a shallow homogeneous lake abstract the development validation and application of a three dimensional deterministic numerical model of the wind induced circulation in a shallow homogeneous lake are described the governing equations expressing the conservation of fluid mass and momentum are solved in the model using an implicit finite difference initial value method particular attention is paid to the representation of the bed friction the wind shear stress and turbulent diffusion the model was compared with analytical solutions for three idealised flows before being calibrated and verified with field data from esthwaite water in cumbria the model was tested for stability and parameter sensitivity and then used to generate typical circulation patterns for a variety of steady state conditions comparisons with field measurements suggest that the model is better at predicting water movements in the open water than in the sheltered bays

seismicity change revealed by etas pi and z value methods a case study of the 2013 nantou taiwan earthquake abstract on mar 27 2013 a ml6 2 earthquake occurred in the nantou area of central taiwan which caused one death and nearly 90 injured two months later another ml6 3 earthquake struck the same region on june 2 2013 the epicenter of which is close to the march ml6 2 earthquake seismicity is a sensitive indicator of stress rate and inelastic deformation process in crust therefore examination of temporal changes in seismicity is important to understand the preparatory processes of damaging inland earthquakes in this study we applied the epidemic type aftershock sequences model etas model to the earthquake data covering broader taiwan region which is maintained by the central weather bureau cwb of taiwan to investigate precursory temporal changes in seismicity for the ml6 2 nantou earthquake we regard the march ml6 2 and june ml6 3 earthquakes as an event sequence and especially focus on temporal changes in seismicity prior to the ml6 2 event application of more than one model to an earthquake catalog would be informative in elucidating the relationships between seismicity precursors and the preparatory processes of large earthquakes based on this motivation we further applied two different approaches the pattern informatics pi method and the zmap method which is a gridding technique based on the standard deviate z value test to the same earthquake data of cwb as a result we found that the epicenter of the 2013 ml6 2 nantou earthquake was surrounded by three main seismic quiescence regions prior to its occurrence the assumption that this is due to precursory slip stress drop on fault plane or its deeper extent of the ml6 2 nantou earthquake is supported by previous researches based on seismicity data geodedic data and numerical simulations using rate and state dependent friction laws

earthquake patterns in diverse tectonic zones of the globe we extend existing branching models for earthquake occurrences by incorporating potentially important estimates of tectonic deformation and by allowing the parameters in the models to vary across different tectonic regimes we partition the earth s surface into five regimes trenches including subduction zones and oceanic convergent boundaries and earthquakes in outer rise or overriding plate fast spreading ridges and oceanic transforms slow spreading ridges and transforms active continental zones and plate interiors everything not included in the previous categories our purpose is to specialize the models to give them the greatest possible predictive power for use in earthquake forecasts we expected the parameters of the branching models to be significantly different in the various tectonic regimes because earlier studies bird and kagan in bull seismol soc am 94 6 2380 2399 2004 found that the magnitude limits and other parameters differed between similar categories we compiled subsets of the cmt and pde earthquake catalogs corresponding to each tectonic regime and optimized the parameters for each and for the whole earth using a maximum likelihood procedure we also analyzed branching models for california and nevada using regional catalogs our estimates of parameters that can be compared to those of other models were consistent with published results examples include the proportion of triggered earthquakes and the exponent describing the temporal decay of triggered earthquakes we also estimated epicentral location uncertainty and rupture zone size and our results are consistent with independent estimates contrary to our expectation we found no dramatic differences in the branching parameters for the various tectonic regimes we did find some modest differences between regimes that were robust under changes in earthquake catalog and lower magnitude threshold subduction zones have the highest earthquake rates the largest upper magnitude limit and the highest proportion of triggered events fast spreading ridges have the smallest upper magnitude limit and the lowest proportion of triggered events the statistical significance of these variations cannot be assessed until methods are developed for estimating confidence limits reliably some results apparently depend on arbitrary decisions adopted in the analysis for example the proportion of triggered events decreases as the lower magnitude limit is increased possibly because our procedure for assigning independence probability favors larger earthquakes in some tests we censored earthquakes occurring near and just after a previous event to account for the fact that most such earthquakes will be missing from the catalog fortunately the branching model parameters were hardly affected suggesting that the inability to measure immediate aftershocks does not cause a serious estimation bias we compare our branching model with the etas model and discuss the differences in the models parametrization and the results of earthquake catalogs analysis

cooperative joint inversion of 3d seismic and magnetotelluric data with application in a mineral province abstractthe integration of different geophysical data has the potential to provide more accurate estimate of subsurface rock properties several methodologies and attempts have been developed over the years with the objective of reducing exploration risk we have developed a cooperative joint inversion approach intended to facilitate recovery of acoustic impedance ai using seismic and magnetotelluric mt data in this approach the mt data provided a pathway for iteratively building large scale low frequency information content not directly recoverable from the seismic data themselves the mt data provided complementary information to seismic especially in seismically complex terrains such as overthrust belts subbasalt and subsalt carbonate reefs or for targets below deep cover containing limestone concretionary layers or basalt on the other hand the seismic data provided structural information necessary to derive accurate resistivity models from mt inversion and small scale features during seis

advances in velocity model building technology for subsalt imaging seismic imaging of hydrocarbon accumulations below salt is a formidable challenge because complexly shaped salt bodies severely distort wavefronts or scatter seismic energy we have highlighted some recent advances in building a velocity model for subsalt imaging there are three main stages suprasalt velocity determination salt model definition and subsalt velocity update volumetric high resolution tomography that incorporates high velocity contrast boundaries is used to derive a good sediment velocity model before building a salt model to facilitate integration of interpretation and depth processing beam based interactive imaging is used to refine the salt geometry for subsalt velocity update either subsalt tomography or subsalt scan based techniques can be used depending on the quality of subsalt reflections there are concepts and techniques for attaining subsalt images suitable for hydrocarbon exploration beneath complexly shaped salt bodies

evidence of strain accumulation in the andaman region for the giant 2004 sumatra andaman earthquake abstract we report results of global positioning system gps and tide gauge data from the andaman region that pertain to the period before the 26 december 2004 sumatra andaman earthquake m w 9 2 in the preceding 40 years seismicity in the frontal arc region was generally very low implying locking of the main thrust zone the campaign mode gps data support strain accumulation in the region corresponding to a slip deficit rate of about 3 cm year however the tide gauge data of the preceding three years from the earthquake indicate land subsidence at a rate of about 3 3 cm year whereas uplift was expected in the period prior to the earthquake as the region experienced coseismic subsidence during the earthquake

integrating basin modeling with seismic technology and rock physics we explore the link between basin modelling and seismic inversion by applying different rock physics models this study uses the e dragon ii data in the gulf of mexico to investigate the impact of different rock physics models on the link between basin modelling and seismic inversion we first model relationships between seismic velocities and both 1 porosity and 2 effective stress for well log data using published rock physics models then we build 1d basin models to predict seismic velocities derived from basin modelling with different rock physics models in a comparison with average sonic velocities measured in the wells finally we examine how basin modelling outputs can be used to aid seismic inversion by providing constraints for the background low frequency model for this we run different scenarios of inverting near angle partial stack seismic data into elastic impedances to test the impact of the background model on the quality of the inversion results the results of the study suggest that the link between basin modelling and seismic technology is a two way interaction in terms of potential applications and the key to refine it is establishing a rock physics models that properly describes changes in seismic signatures reflecting changes in rock properties

are spontaneous earthquakes stationary in california 1 aftershocks and some main shocks are triggered with timing controlled by preceding events the remaining spontaneous earthquakes presumably respond to tectonic stresses we consider whether triggered events can be reliably identified whether the rest are stationary and whether external phenomena control them to all three questions some studies of earthquake physics and hazard assume answers many suggest that stress changes from large distant earthquakes can alter the local spontaneous earthquake rate we demonstrate significant differences in the apparent earthquake rate after declustering by different methods and we present criteria for assessing the influence of such distant events the estimated spontaneous earthquake rate depends on the lower magnitude threshold of included events whether spontaneity is treated in binary or probabilistic form as well as assumptions about catalog completeness different statistical tests give different answers to the question of stationarity we examine a reported rate change in southern california and the suggestion that it might have resulted from the 1960 chile and 1964 alaska earthquakes the rate change itself is questionable if it has occurred it was probably not caused by those distant events because the rate change is not present in northern california or in all parts of southern california

precursory seismic anomalies and transient crustal deformation prior to the 2008 mw 6 9 iwate miyagi nairiku japan earthquake 1 the epidemic type aftershock sequence etas model has been widely used for detecting seismicity anomalies such as quiescence and activation during aftershock sequences of large earthquakes and background levels of seismicity the causes of such anomalies are thought to be associated with spatiotemporal changes in stress even tiny perturbation of local stress here we analyze the seismic activity during the decade prior to the 2008 iwate miyagi inland earthquake of m7 2 mw6 9 to fit the etas model to the seismicity from various regions around the source over northern honshu japan from the viewpoint of the analyses with the etas model we find northern honshu is divided into three areas of distinctive behaviors increased seismicity decreased seismicity and normal seismicity relative to the etas prediction as in other previously published papers here we hypothesize that coulomb stress changes caused by a few years of precursory slip of the iwate miyagi earthquake resulted in the seismicity changes in and around the 2008 source region the confirmed significant seismic anomalies in respective regions are consistent with the increments of the coulomb failure stress of the corresponding regions that are calculated by the assumed slow slip on the southern part of the faults of the main shock the local crustal deformations observed from a dense global positioning system network including a station right above the focal fault supports that slow slip on the fault had been taking place for about 5 years prior to the occurrence of the focal earthquake and suggests that the slip terminated or migrated to down dip extension of the fault around 1 year before the rupture

short and long term earthquake forecasts for california and nevada we present estimates of future earthquake rate density probability per unit area time and magnitude on a 0 1 degree grid for a region including california and nevada based only on data from past earthquakes our long term forecast is not explicitly time dependent but it can be updated at any time to incorporate information from recent earthquakes the present version founded on several decades worth of data is suitable for testing without updating over a five year period as part of the experiment conducted by the collaboratory for study of earthquake predictability csep the short term forecast is meant to be updated daily and tested against similar models by csep the short term forecast includes a fraction of our long term one plus time dependent contributions from all previous earthquakes those contributions decrease with time according to the omori law proportional to the reciprocal of the elapsed time both forecasts estimate rate density using a radially symmetric spatial smoothing kernel decreasing approximately as the reciprocal of the square of epicentral distance weighted according to the magnitude of each past earthquake we made two versions of both the long and short term forecasts based on the advanced national seismic system anss and preliminary determinations of epicenters pde catalogs respectively the two versions are quite consistent but for testing purposes we prefer those based on the anss catalog since it covers a longer time interval is complete to a lower magnitude threshold and has more precise locations both forecasts apply to shallow earthquakes only depth 25 km or less and assume a tapered gutenberg richter magnitude distribution extending to a lower threshold of 4 0

introduction to this special section low frequency seismic geophysicists in the seismic exploration industry have long recognized the potential benefits of extending the bandwidth of seismic measurements to well below 10 hz low frequencies generated by a seismic shot travel much farther through the subsurface than do higher frequencies just as the low frequencies in thunder travel farther in the atmosphere thus the amount of power available in the low end of the seismic spectrum is especially important for deep exploration targets such as subsalt and sub basalt plays and for deep crustal studies in many areas of the world higher frequencies are often too attenuated scattered and dispersed to provide useful signal for probing such objectives also low frequencies play a critical role in the inversion process by which seismic data are converted into acoustic impedance sections and ultimately into reservoir properties surface seismic data usually lack low frequencies necessary for accurate inversion so they are commonly augmented by data from well log me

the use of pseudorandom sweeps for vibroseis surveys pseudorandom vibroseis sweeps have long been suggested as an alternative to standard linear sweeps due to their potential for having superior orthogonality a lower likelihood for infrastructure damage and increased low frequency content in the past they were also attractive as they have a better autocorrelation shape although that is less important today their use has been limited but the increasing popularity of simultaneous acquisition techniques has rekindled interest as they offer the ability to reduce interference noise a wide variety of methods for generating pseudorandom sweeps have been developed over the last 45 years this paper gives an overview of the motivations for their use before classifying and describing the different sweep types finally the sweeps will be compared in terms of their major attributes including their suitability for simultaneous surveys

on the relationship between lower magnitude thresholds and bias in epidemic type aftershock sequence parameter estimates 1 modern earthquake catalogs are often described using spatial temporal point process models such as the epidemic type aftershock sequence etas models of ogata 1998 earthquake catalogs often have issues of incompleteness and other inaccuracies for earthquakes of magnitude below a certain threshold and such earthquakes are typically removed prior to fitting a point process model this paper investigates the bias in the parameters in etas models introduced by the removal of the smallest events it is shown that in the case of most of the etas parameters the bias increases approximately exponentially as a function of the lower magnitude cutoff

increased probability of large earthquakes near aftershock regions with relative quiescence it is shown that after a large earthquake of m6 class or over has taken place another event of similar size or larger is relatively more likely in the sense of rate per unit area to occur in the near field than in the far field in particular we show that the aftershock activity of the first event provides useful information for assessing the probability of a following large event in the neighborhood within a distance of a few degrees namely if the aftershock activity from the first event becomes relatively quiet compared to the normal decay the occurrence rate of larger events in the neighborhood is several times higher during the first decade after the main shock than would be the case for normal aftershock activity for measuring such phenomena precisely we need to model the normal aftershock activity in fact many aftershock sequences are more complex than the simple inverse power decay represented by the modified omori formula the epidemic type aftershock sequences etas model is a generalized version of the modified omori formula which fits well with various aftershock sequences including nonvolcanic type swarms using this model aftershock sequences are investigated for the 76 main shocks that occurred in and around japan during the last three quarters of a century the focus is placed on objective examination of whether or not in an aftershock sequence there exists a significant change point followed by relative quiescence that is a significant lowering of the seismicity from that predicted by the etas model relative quiescence can take place regardless of the seismicity level the extent of such quiescence if it exists is seen from the diagrams of cumulative numbers versus the transformed occurrence times based on the predicted occurrence rate by the estimated etas model it is thus demonstrated that relative quiescence can be a helpful factor in detecting anomalous aftershock activity this can then be used to forecast whether or not a large event is more likely to follow shortly within 6 years in the neighborhood within a distance of 3 of the initial event

detection of anomalous seismicity as a stress change sensor 1 anomalous seismicity such as quiescence and activation is defined by a systematic deviation of seismic activity from the predicted rate by the epidemic type aftershock sequence etas model that represents the normal occurrence rate of earthquakes in a region indicating the empirical triggering effect by the previous events the model is fitted to a data set of origin times and magnitudes of earthquakes or aftershocks during may august 2003 in and around northern japan the detected quiescence and activation relative to the predicted seismicity rate are consistent with the coseismic changes of coulomb failure stress cfs in the corresponding regions transferred from certain strong earthquakes few results in this paper agree with the claim that there should be a threshold value of cfs capable of affecting seismic changes thus we expect that significant deviation of actual activity from the predicted rates is sensitive enough to detect a slight stress change furthermore i offer a similar interpretation of the detected seismicity lowering relative to the modeled rates preceding the strong earthquakes assuming some aseismic slips

a non stationary epidemic type aftershock sequence model for seismicity prior to the december 26 2004 m 9 1 sumatra andaman islands mega earthquake 1 we study temporal changes in seismicity in sumatra andaman islands region before the m 9 1 earthquake of december 26 2004 we applied the epidemic type aftershock sequence etas models to the seismicity the two stage non stationary etas model with a single change point provides a better statistical fit to the seismicity data than the stationary etas model throughout the whole period we made further change point analysis of data sets by dividing into two sub regions the best fitted models suggest that the seismic activation relative to the etas rates started in the middle of july 2000 about 4 5 years before the m 9 1 earthquake this includes an increase in the background seismicity rates particularly in the southern part of the seismogenic zone near the epicenter a space time etas model also suggests that the background seismicity throughout the entire sumatra andaman islands area had increased after the change point time

earthquake triggering during preparation for great earthquakes seismic quiescence has been proposed as a precursor to many large earthquakes in this paper we present two cases in which precursory quiescence is interrupted several years prior to great earthquakes by triggered events in the upcoming rupture areas this triggering results in complex precursory patterns which include seismic quiescence and triggered events prior to the kermadec earthquake of 1976 ms 8 0 events in the rupture zone were triggered by a quake on the outer rise and one near the future mainshock epicenter events were triggered by an earthquake on an adjacent segment of the plate interface and by one near the epicenter of the new hebrides earthquake of 1980 ms 8 0 we propose that two preconditions must be fulfilled for triggering to occur first the stress in the region must be close to the failure stress and second nearby events must occur which are large enough to affect the stress field but not large enough to cause an immediate mainshock

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

space time model for regional seismicity and detection of crustal stress changes 1 the regional occurrence rate of earthquakes is modeled as a function of previous activity the specific form of which is based on empirical laws in time and space such as the modified omori formula and the utsu seki scaling law of aftershock area against magnitude respectively its parameters including the p value of the aftershock decay rate vary from place to place in such a way that for example the regional p value at the locations around the main shock is similar to the one estimated from the corresponding individual aftershock sequence the estimated space time model is used to visualize features of the regional seismic activity the utility is demonstrated by applying the model to the events of m 5 in and around japan for the period 1926 1995 among the parameters of the model this paper is particularly concerned with the normalized k value of the modified omori function indicating the aftershock productivity this takes high values around the boundaries of asperities that are estimated in the wide area off the east coast of tohoku district japan by the inversion of historical strong motion seismograms furthermore this space time model enables us to identify the anomalous period and regions where the actual occurrence rates deviate systematically from the modeled one such an anomaly activation and quiescence relative to the model could sensitively reveal the change of stresses in the regions we attempt to relate this relative activation and lowering of the seismicity to the pattern of coulomb stress changes due to a rupture or silent slip elsewhere for example such anomalies seen in the seismic activity in the central japan m 2 5 during 1995 1999 and during 2001 are respectively likely the consequence of the coulomb stress changes due to the 1995 kobe rupture and the interplate aseismic slip during 2001 beneath the western tokai region

pre seismic anomalies in seismicity and crustal deformation case studies of the 2007 noto hanto earthquake of m6 9 and the 2007 chuetsu oki earthquake of m6 8 after the 2004 chuetsu earthquake of m6 8 summary if aseismic slip occured on a fault or its deeper extension both seismicity and crustal deformation around the source would be affected such anomalies are determined from earthquake occurrence data and geodetic records during the periods leading up to the 2007 march noto hanto earthquake of m6 9 and the 2007 july chuetsu oki earthquake of m6 8 which successively occurred after the 2004 october chuetsu earthquake of m6 8 on the japan sea coast assuming such aseismic slips seismic zones corresponding to negative and positive increments of the coulomb failure stress show seismic quiescence and activation respectively relative to the rate predicted by the epidemic type aftershock sequence model these interpretations are further supported by transient crustal movements around the sources preceding the ruptures for example the time series of baseline distances between permanent global positioning system stations deviated from their long term linear trends in a manner that is consistent with the assumed slip in particular this paper emphazes on the investigation of the interacting tectonic processes within such a narrow area and a short period considering the precursory slow slips on the focal faults or their downdip extensions based on the observed anomalies in seismicity and crustal movement

long term earthquake clustering summary we analyse statistically the long term properties of several instrumental earthquake catalogues complete catalogues exhibit both short and long term clustering for earthquakes of all depth ranges after accounting for the effect of short term clustering we find that in residual declustered catalogues long term clustering not periodicity characterizes the occurrence of all earthquakes shallow intermediate and deep the degree of clustering in residual catalogues is the same for earthquakes in different depth ranges circumstantial evidence indicates that the long term v ariation of seismicity is governed by a power law temporal distribution as in short term clustering it is scale invariant the fractal dimension of an earthquake set on the time axis is of the order of 0 8 0 9 therefore mainshock occurrence is closer to a stationary poisson process than standard aftershock sequences of shallow earthquakes

three dimensional modelling of stratified coastal waters abstract an implicit baroclinic 3 d model developed to simulate the circulation in coastal waters is presented the model has hydrodynamic transport and turbulence model components it is a composite finite difference finite element model in the horizontal plane second order central finite differences on a staggered scheme and in the vertical galerkin method with linear shape functions are used implicit equations are solved by crank nicholson method which has second order accuracy in time also developed model predictions are compared with the analytical solutions of steady wind driven circulatory flow and tidal flow model predictions are tested with an experiment performed on the buoyant surface jet discharge then the model is applied to the goksu lagoon system located on the mediterranean coast of turkey where there exist some measurements of salinity temperature and velocity model predictions are in good agreement with the field data

missing links in earthquake clustering models 1 many clustering models imply two kinds of earthquakes spontaneous ones and those triggered by previous earthquakes the pair wise links from earlier to later earthquakes control the estimates of the clustering parameters however earthquake catalogs are limited in time space and magnitude so that triggers of some cataloged earthquakes may be unknown thus some links are unrecognized and some triggered events appear spontaneous here we present a method for identifying such earthquakes and reducing the bias from missing links we treat earthquakes probably affected by missing links as potential triggers but we exclude them in evaluating modeled effects we use an epidemic type aftershock sequence etas model to examine specifics the most affected parameter is the proportion of spontaneous earthquakes the most important missing links apparently follow earthquakes below the magnitude threshold before the start and outside the spatial boundaries of the catalog in that order

three dimensional layer integrated modelling of estuarine flows with flooding and drying abstract details are given of the refinement and application of a thee dimensional 3 d layer integrated numerical model of tidal circulation with the aim of simulating severe tidal conditions for practical engineering applications the mode splitting strategy has been used in the model a set of depth integrated 2 d equations are first solved to give the pressure gradient and the layer integrated 3 d equations are then solved to obtain the vertical distributions of the flow velocities attention has been given to maintaining consistency of the physical quantities derived from the 2 d and 3 d equations a two layer mixing length turbulence model for the vertical shear stress distribution has been included in the model emphasis has been focused on applying the model to a real estuary which is geometrically complicated and has large tidal ranges giving rise to extensive flooding and drying the model has been applied to three examples including wind driven flow in a rectangular lake tidal circulation in a model rectangular harbour and tidal circulation in a large estuary favourable results have been obtained for both the simple and complex flow beds

evidence of clustering and nonstationarity in the time distribution of large worldwide earthquakes 1 the purpose of this paper is to characterize the statistical distribution of worldwide largest earthquakes we analyze the distribution of worldwide shallow events with ms 7 0 since 1900 by following the occam s razor philosophy we start from the simplest possible model stationary poisson process and we inspect more complicated models only if the data show significant departures from the simplest one the results show two important characteristics first worldwide ms 7 0 earthquakes tend to cluster in time and space with features similar to smaller events second for some seismic regions there is evidence in favor of long term fluctuations of the earthquake rate these results support the hypothesis of universality suggesting that an etas model with a background varying with time can be considered reliable to describe the seismicity distribution over a wide space time magnitude window from a practical point of view our findings suggest that the paradigm that seismic zones are stationary systems implicitly assumed in seismic hazard assessment should be regarded with caution

plate boundary deformation associated with the great sumatra andaman earthquake the sumatra andaman earthquake of 26 december 2004 is the first giant earthquake moment magnitude m w 9 0 to have occurred since the advent of modern space based geodesy and broadband seismology it therefore provides an unprecedented opportunity to investigate the characteristics of one of these enormous and rare events here we report estimates of the ground displacement associated with this event using near field global positioning system gps surveys in northwestern sumatra combined with in situ and remote observations of the vertical motion of coral reefs these data show that the earthquake was generated by rupture of the sunda subduction megathrust over a distance of 1 500 kilometres and a width of 150 kilometres megathrust slip exceeded 20 metres offshore northern sumatra mostly at depths shallower than 30 kilometres comparison of the geodetically and seismically inferred slip distribution indicates that 30 per cent additional fault slip accrued in the 1 5 months following the 500 second long seismic rupture both seismic and aseismic slip before our re occupation of gps sites occurred on the shallow portion of the megathrust where the large aceh tsunami originated slip tapers off abruptly along strike beneath simeulue island at the southeastern edge of the rupture where the earthquake nucleated and where an m w 7 2 earthquake occurred in late 2002 this edge also abuts the northern limit of slip in the 28 march 2005 m w 8 7 nias simeulue earthquake

a great earthquake doublet and seismic stress transfer cycle in the central kuril islands temporal variations of the frictional resistance on subduction zone plate boundary faults associated with the stick slip cycle of large interplate earthquakes are thought to modulate the stress regime and earthquake activity within the subducting oceanic plate here we report on two great earthquakes that occurred near the kuril islands which shed light on this process and demonstrate the enhanced seismic hazard accompanying triggered faulting on 15 november 2006 an event of moment magnitude 8 3 ruptured the shallow dipping plate boundary along which the pacific plate descends beneath the central kuril arc the thrust ruptured a seismic gap that previously had uncertain seismogenic potential although the earlier occurrence of outer rise compressional events had suggested the presence of frictional resistance within minutes of this large underthrusting event intraplate extensional earthquakes commenced in the outer rise region seaward of the kuril trench and on 13 january 2007 an event of moment magnitude 8 1 ruptured a normal fault extending through the upper portion of the pacific plate producing one of the largest recorded shallow extensional earthquakes this energetic earthquake sequence demonstrates the stress transfer process within the subducting lithosphere and the distinct rupture characteristics of these great earthquakes illuminate differences in seismogenic properties and seismic hazard of such interplate and intraplate faults

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

a long term seismic quiescence before the 2004 sumatra mw 9 1 earthquake the 2004 sumatra m w 9 1 earthquake was preceded by a seismic quiescence that began 13 years before the mainshock an earthquake catalog created by the international seismological centre is analyzed in the study area 80 110 e 10 s 20 n between 1964 and 2004 including 1153 earthquakes shallower than 100 km with body wave magnitude of 5 0 m b 6 7 a detailed analysis of the earthquake catalog using a gridding technique zmap shows the quiescent area is located between 3 and 6 n which covers the southeastern part of the focal area including the rupture initiation point of the 2004 sumatra earthquake the observed spatial pattern of quiescence can be explained by stress perturbation due to a long term slow slip located on the deeper edge of the mainshock fault which is predicted by a numerical simulation based on a laboratory derived friction law although the quiescence is not significant statistically it may still be considered unlikely that such an anomalous quiescence would occur at almost the same time and location as other long term anomalies reported in the previous studies including decreases in b value and tidal triggering

seismicity associated with the sumatra andaman islands earthquake of 26 december 2004 the u s geological survey national earthquake information center usgs neic had computed origins for 5000 earthquakes in the sumatra andaman islands region in the first 36 weeks after the sumatra andaman islands mainshock of 26 december 2004 the cataloging of earthquakes of m b usgs 5 1 and larger is essentially complete for the time period except for the first half day following the 26 december mainshock a period of about two hours following the nias earthquake of 28 march 2005 and occasionally during the andaman sea swarm of 26 30 january 2005 moderate and larger m b 5 5 aftershocks are absent from most of the deep interplate thrust faults of the segments of the sumatra andaman islands subduction zone on which the 26 december mainshock occurred which probably reflects nearly complete release of elastic strain on the seismogenic interplate thrust during the mainshock an exceptional thrust fault source offshore of banda aceh may represent a segment of the interplate thrust that was bypassed during the mainshock the 26 december mainshock triggered a high level of aftershock activity near the axis of the sunda trench and the leading edge of the overthrust burma plate much near trench activity is intraplate activity within the subducting plate but some shallow focus near trench reverse fault earthquakes may represent an unusual seismogenic release of interplate compressional stress near the tip of the overriding plate the interplate thrust nias earthquake of 28 march 2005 in contrast to the 26 december aftershock sequence was followed by many interplate thrust aftershocks along the length of its inferred rupture zone

indonesian earthquake earthquake risk from co seismic stress last year s indonesian earthquake has increased seismic hazard in the region the scale of death and destruction caused by the recent sumatra andaman islands earthquake and its tsunami has raised concerns that another earthquake might be triggered on the contiguous sunda trench subduction zone a new calculation of stress distribution here and on the neighbouring sumatra fault reveals stress build up on both structures severe enough to increase the already high earthquake hazard this finding makes the need for an indian ocean tsunami warning system all the more pressing following the massive loss of life caused by the sumatra andaman earthquake in indonesia and its tsunami the possibility of a triggered earthquake on the contiguous sunda trench subduction zone is a real concern we have calculated the distributions of co seismic stress on this zone as well as on the neighbouring vertical strike slip sumatra fault and find an increase in stress on both structures that significantly boosts the already considerable earthquake hazard posed by them in particular the increased potential for a large subduction zone event in this region with the concomitant risk of another tsunami makes the need for a tsunami warning system in the indian ocean all the more urgent

an experiment in earthquake prediction and the 7 may 1986 andreanof islands earthquake abstract the occurrence of the 7 may 1986 andreanof islands earthquake provides the opportunity to evaluate the earthquake forecast and specific prediction that had been formulated and promulgated starting more than 2 yr before the prediction experiment was based on the observation of seismic quiescence in the part of the aleutian subduction zone monitored by the central aleutians adak seismic network the magnitude estimate m s 7 to 7 5 was based on the size of the quiescent zone and the seismic history of the adak region since 1900 the time of occurrence was predicted as a test of the discovery by habermann of a quiescence lasting about 3 yr prior to the 2 may 1971 adak canyon event and the hypothesis that a characteristic precursor time is a valid concept the place was originally forecast as near adak island then specified with epicenter at the eastern margin of adak canyon rupturing to the west under the canyon the 7 may 1986 earthquake had magnitude m s 7 7 m w 8 0 with epicenter 140 km east of the predicted place rupturing east of adak canyon and stopping in the area predicted as the nucleation point the time of this event was 6 months later than predicted thus the specifically predicted event has not happened the largest part of the rupture did go through the segment that had been most active before the onset of quiescence and which experienced the sharpest and most persistent quiescence a cause and effect relation between preparation for this earthquake and the quiescence is still to be firmly established but the distribution of the pattern of quiescence relative to the epicentral location and the site of the greatest moment release suggest a physical connection between earthquake and seismicity patterns the predictions of location and time were acknowledged throughout as highly speculative no firm basis exists for quantitative estimation of the uncertainties to be assigned to the elements of an intermediate term prediction this experiment lends support to the validity of quiescence as a precursor at least for some earthquakes and demonstrates the need for local network data to provide the high resolution of seismicity required for prediction efforts based on seismicity patterns

seismicity rate variations and systematic changes in magnitudes in teleseismic catalogs abstract seismicity rate variations are commonplace in teleseismic catalogs these changes have two possible causes they could be real or they could be related to changes in the networks used to detect the events it is clearly important to differentiate between these two possibilities we demonstrate a technique for making this differentiation using uniform data generated with known rates and magnitude shifts we then apply this technique to data from large regions of the world all of these regions show significant variations in seismicity rates for sets with magnitude cutoffs of 5 0 and 5 5 we show that most of these changes have distributions in the magnitude domain which are consistent with systematic changes in magnitudes of between 0 1 and 0 2 units these results suggest that most observed rate variations in teleseismic sets with high magnitude cutoffs are related to systematic changes in magnitudes and are therefore not real this result has important implications for earthquake prediction and tectonic studies which interpret these variations

synthetic aperture controlled source electromagnetics controlled source electromagnetics csem has been used as a de risking tool in the hydrocarbon exploration industry although there have been successful applications of csem this technique is still not widely used in the industry because the limited types of hydrocarbon reservoirs csem can detect in this paper we apply the concept of synthetic aperture to csem data synthetic aperture allows us to design sources with specific radiation patterns for different purposes the ability to detect reservoirs is dramatically increased after forming an appropriate synthetic aperture antenna consequently the types of hydrocarbon reservoirs that csem can detect are significantly extended because synthetic apertures are constructed as a data processing step there is no additional cost for the csem acquisition synthetic aperture has potential for simplifying and reducing the cost of csem acquisition we show a data example that illustrates the increased sensitivity obtained by applying synthetic aperture csem source

two dimensional horizontal modeling of fine sediment transport at the south channel north passage of the partially mixed changjiang river estuary china tidal flow and fine sediment transport at the south channel north passage of the partially mixed changjiang river estuary were studied using a two dimensional horizontal 2dh numerical model this 2dh model was achieved by depth integrating the momentum and convection diffusion equations the alternating direction implicit scheme was used to solve the governing equations the iterative method was adopted for the calculation of convection and diffusion terms of momentum equation comparisons between calculated and measured results tidal elevations and depth averaged velocities have shown reasonable agreement horizontal distributions of tidal current velocity and suspended sediment concentration were qualitatively consistent with observations those modeled results were analyzed to elucidate the mechanisms for the formation of the turbidity maximum and intratidal variations in fine sediment transport processes

predictive modeling of the seismic cycle of the greater san francisco bay region the seismic cycle for the san francisco bay region is synthesized by a model combining the pre and post 1906 seismic histories the long term acceleration of seismic release seismic moment benioff strain release or event count in the seismic cycle and the shorter term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique called time to failure analysis in which rate of seismic release is proportional to an inverse power of the remaining time to failure the exponent of time to failure in the accelerating sequences appears to be scale invariant and the length of the full cycle is estimated at 269 50 years the 1989 loma prieta earthquake which is the culmination of the first subcycle in the present long term seismic cycle should have been predictable with an uncertainty of 2 years in time and 0 5 in magnitude although the specific location at loma prieta was not predictable by this technique if our model is correct and if the loma prieta earthquake is the culmination of a subcycle the san francisco bay region should be entering a relatively long 20 50 years period of seismic quiescence above magnitude 6 a great earthquake such as the 1906 san francisco event would appear to be more than a century in the future

comparison of short term and time independent earthquake forecast models for southern california we have initially developed a time independent forecast for southern california by smoothing the locations of magnitude 2 and larger earthquakes we show that using small m 2 earthquakes gives a reasonably good prediction of m 5 earthquakes our forecast outperforms other time independent models kagan and jackson 1994 frankel et al 1997 mostly because it has higher spatial resolution we have then developed a method to estimate daily earthquake probabilities in south ern california by using the epidemic type earthquake sequence model kagan and knopoff 1987 ogata 1988 kagan and jackson 2000 the forecasted seismicity rate is the sum of a constant background seismicity proportional to our time independent model and of the aftershocks of all past earthquakes each earthquake triggers aftershocks with a rate that increases exponentially with its magnitude and decreases with time following omori s law we use an isotropic kernel to model the spatial distribution of aftershocks for small m 5 5 mainshocks for larger events we smooth the density of early aftershocks to model the density of future aftershocks the model also assumes that all earthquake magnitudes follow the gutenberg richter law with a uniform b value we use a maximum likelihood method to estimate the model parameters and test the short term and time independent forecasts a retro spective test using a daily update of the forecasts between 1 january 1985 and 10 march 2004 shows that the short term model increases the average probability of an earthquake occurrence by a factor 11 5 compared with the time independent forecast

a three dimensional simulation of the hudson raritan estuary part i description of the model and model simulations abstract a time dependent three dimensional finite difference simulation of the hudson raritan estuary is presented the calculation covers july september 1980 the model estuary is forced by time dependent observed winds tidal elevation at open boundaries and river and sewage discharges turbulence mixing coefficients in the estuary are calculated according to a second moment turbulence closure submodel horizontal diffusivities are zero in the simulation and small scale eddies produced by the interaction of unsteady three dimensional velocity and salinity fields with coastline and bottom bathymetry were resolved by the model these eddies are important physical elements in shear dispersion processes in an estuary model results show unstably stratified water columns produced by advection of waters of different densities these instabilities produce intense mixing with vertical eddy diffusivities reaching 2 3 times their neutral values they occur most frequently at slack currents during initial s

detecting precursory earthquake migration patterns using the pattern informatics method 1 in this paper we analyze the evolution of seismic activity using a dynamic modification of the pattern informatics method this method identifies locations that have systematic fluctuations in seismicity on pi maps by investigating the evolution of hotspot configurations on the pi map and calculating the distance between hotspots and the epicenter of the impending large earthquake a migrating pattern of increasing or decreasing precursory change in seismicity is revealed we find that hotspots on the pi map appear increasingly closer to the epicenter as the time of the forthcoming earthquake is approached implying the existence of an earthquake preparation process the migration pattern and associated decreasing distance is confirmed by a stochastic test and therefore we conclude that a preparation process prior to large earthquakes can be detected

global omori law decay of triggered earthquakes large aftershocks outside the classical aftershock zone 1 triggered earthquakes can be large damaging and lethal as evidenced by the1999 shocks in turkey and the 2001 earthquakes in el salvador in this study earthquakes with ms 7 0 from the harvard centroid moment tensor cmt catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected about 61 of earthquakes that occurred near defined as having shear stress change 0 01 mpa the ms 7 0 shocks are associated with calculated shear stress increases while 39 are associated with shear stress decreases if earthquakes associated with calculated shear stress increases are interpreted as triggered then such events make up at least 8 of the cmt catalog globally these triggered earthquakes obey an omori law rate decay that lasts between 7 11 years after the main shock earthquakes associated with calculated shear stress increases occur at higher rates than background up to 240 km away from the main shock centroid omori s law is one of the few time predictable patterns evident in the global occurrence of earthquakes if large triggered earthquakes habitually obey omori s law then their hazard can be more readily assessed the characteristic rate change with time and spatial distribution can be used to rapidly assess the likelihood of triggered earthquakes following events of ms 7 0 i show an example application to the m 7 7 13 january 2001 el salvador earthquake where use of global statistics appears to provide a better rapid hazard estimate than coulomb stress change calculations

far field triggering of foreshocks near the nucleation zone of the 5 september 2012 m w 7 6 nicoya peninsula costa rica earthquake abstract on 5 september 2012 a moment magnitude mw 7 6 earthquake occurred directly beneath the nicoya peninsula an area with dense seismic and geodetic network coverage the mainshock ruptured a portion of a previously identified locked patch that was recognized due to a decade long effort to delineate the megathrust seismic and aseismic processes in this area here we conduct a comprehensive study of the seismicity prior to this event utilizing a matched filter analysis that allows us to decrease the magnitude of catalog completeness by 1 unit we observe a statistically significant increase in seismicity rate below the nicoya peninsula following the 27 august 2012 mw 7 3 el salvador earthquake about 450 km to the northwest and 9 days prior to the nicoya earthquake additionally we identify a cluster of small magnitude

likelihood analysis of earthquake catalogues summary we apply several classes of stochastic multidimensional models to statistical analysis of earthquake catalogues using likelihood methods we investigate the importance of including different earthquake parameters in the model epicentral coordinates hypocentral depth time limits for interearthquake interaction and especially spatial distribution of earthquakes as well as spatial aftershock patterns results of this study combined with other investigations suggest that most distributions controlling earthquake interaction have a fractal or scale invariant form developed models are used for statistical analysis of several earthquake catalogues to evaluate parameters of earthquake occurrence these parameters are shown to be similar for shallow earthquakes of different magnitude ranges and seismogenic regions confirming self similarity of the earthquake process whereas intermediate earthquakes seem to emulate the pattern of shallow earthquake occurrence albeit at a much smaller aftershock rate deep earthquakes differ significantly in their properties predictability of standard shallow earthquake catalogues has been analysed we present evidence that for the best availabfe catalogues the predictability is close to 10 bits per earthquake several synthetic earthquake catalogues have been created and processed through the likelihood inversion scheme the results from likelihood analysis of these catalogues confirm our approach

simulation of the great bay estuarine system tides with tidal flats wetting and drying 1 realistic lunar tides of the great bay estuarine system have been simulated using a fixed boundary finite element numerical model as described by ip et al 1998 it is a two dimensional nonlinear time stepping model with a groundwater component coupled to a kinematic force balance to facilitate the realistic drainage and filling of elements during ebb and flood respectively the numerical model reproduces the observed m2 tides as described by swift and brown 1983 and it successfully captures qualitatively correct residual currents and transports realistic mass conserving flooding and dewatering of the tidal flats and current asymmetry between flood and ebb the simulation results were sensitive to local bathymetry and the implemented friction law the accuracy of the model is demonstrated by comparison with the 1975 great bay study swift and brown 1983 in terms of tidal elevations at 14 tidal stations and 4 cross sectionally averaged current measurements in the estuary quantitatively the model results show good agreement with observations displaying correlation coefficients of 0 96 in surface elevation and 0 95 in averaged current with average rms errors of 0 12 m and 0 26 m s 1 respectively in addition tidal flat hydrodynamics characteristic distributions of residual current sediment bed load transport and influence of topography on the overall circulation in the region are also discussed