analysis of the completeness magnitude and seismic network coverage of japan abstract a reliable estimate of completeness magnitude m c above which all earthquakes are considered to be detected by a seismic network is vital for seismicity related studies we show a comprehensive analysis of m c in japan we use the catalog maintained by the japan meteorological agency jma and also available information on seismic stations that report to jma for computing m c we adopt a commonly used method based on the gutenberg richter frequency magnitude law presently m c 1 0 might be typical in the mainland but to have a complete catalog one needs to use earthquakes with magnitudes of 1 9 or larger comparison with the southern california seismic network scsn suggests that the recent event detectability in the mainland generally shows similar completeness levels to that in the authoritative region of scsn we argue that the current m c of japan is due to the success of network modernization over time particularly we show that the spatiotemporal change of m c closely matches the addition of the hi net borehole stations to enhancing seismic station density it started in october 1997 in southwestern japan continuing to northeastern japan until 2002 as suggested from this matching we confirm that m c inversely correlates with station density further we find that irrespective of the network change after 1997 this correlation is unchanged in time demonstrating that the influence on m c from factors beyond station density does not vary in time contrary to alaska and california wiemer and wyss 2000 our results do not attribute such factors simply to anthropogenic noise because this is due to the borehole stations that reduce ambient noise we conclude that in japan the anthropogenic noise has an insignificant effect on m c

modeling seismicity rate changes during the 1997 umbria marche sequence central italy through a rate and state dependent model 1 we model the spatial and temporal pattern of seismicity during a sequence of moderate magnitude normal faulting earthquakes which struck in 1997 the umbria marche sector of northern apennines italy by applying the dieterich 1994 rate and state dependent constitutive approach the goal is to investigate the rate of earthquake production caused by repeated coseismic stress changes computed through a 3 d elastic dislocation model in a homogeneous half space the reference seismicity rate is assumed time independent and it is estimated by smoothing the seismicity that occurred in the previous decade without declustering we propose an analytical relation for deriving the stressing rate directly from the reference seismicity rate this allows us to perform a tuning of the constitutive parameter a where a accounts for the direct effect of friction in the rate and state dependent model and is the effective normal stress into the dieterich model through a maximum likelihood method which yields for this seismic sequence a best fitting value equal to 0 04 mpa our computations show that although seven out of eight main shocks are located in areas of increased rate of earthquake production numerous aftershocks are located in seismicity shadows our simulations point out that the adopted value of a strongly affects the pattern of both seismicity shadow and areas of enhanced rate of earthquake production we conclude that solely accounting for static stress changes caused by the main shocks of this seismic sequence is not sufficient to forecast the complex spatial and temporal evolution of seismicity

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

toggling of seismicity by the 1997 kagoshima earthquake couplet a demonstration of time dependent stress transfer 1 two m 6 well recorded strike slip earthquakes struck just 4 km and 48 days apart in kagoshima prefecture japan in 1997 providing an opportunity to study earthquake interaction aftershocks are abundant where the coulomb stress is calculated to have been increased by the first event and they abruptly stop where the stress is dropped by the second event this ability of the main shocks to toggle seismicity on and off argues that static stress changes play a major role in exciting aftershocks whereas the dynamic coulomb stresses which should only promote seismicity appear to play a secondary role if true the net stress changes from a sequence of earthquakes might be expected to govern the subsequent seismicity distribution however adding the stress changes from the two kagoshima events does not fully capture the ensuing seismicity such as its rate change temporal decay or migration away from the ends of the ruptures we therefore implement a stress transfer model that incorporates rate state friction in which seismicity is treated as a sequence of independent nucleation events that are dependent on the fault slip slip rate and elapsed time since the last event the model reproduces the temporal response of seismicity to successive stress changes including toggling decay and aftershock migration nevertheless the match of observed to predicted seismicity is quite imperfect due perhaps to inadequate knowledge of several model parameters however to demonstrate the potential of this approach we build a probabilistic forecast of larger earthquakes on the expected rate of small aftershocks taking advantage of the large statistical sample the small shocks afford not surprisingly such probabilities are highly time and location dependent during the first decade after the main shocks the seismicity rate and the chance of successive large shocks are about an order of magnitude higher than the background rate and are concentrated exclusively in the stress triggering zones

aftershocks halted by static stress shadows the role of permanent versus transient crustal stress changes in triggering earthquakes is debated analysis of the stress imparted by the joshua tree and nearby landers earthquakes in california in 1992 implies that a permanent drop in stress can halt aftershocks so such static stress changes should be incorporated into seismic hazard assessments

predicted tortuosity of muds tortuosity figures prominently in geochemical hydrological and geophysical calculations concerned with sediments but it is a difficult parameter to measure past theoretical models for predicting the tortuosity from porosity data do not work with marine muds and scientists and engineers have had to resort to entirely empirical models without a mechanistic explanation and with unknown predictive power we offer the first geometric model for the dependence of tortuosity on porosity in marine muds the model is based on the tortuosity of separated layers of nonoverlapping disks the fitted geometric constant in this model indicates that natural marine sediments act as if their fabric were made of disks with thickness diameter ratios very close to 1 2 which indicates a blocklike fabric with respect to diffusion the model was also applied to predict the tortuosity of a variety of sediments and soils not in the original database and it provides a satisfactory prediction of the mean trend in these data

aftershock modeling based on uncertain stress calculations 1 we discuss the impact of uncertainties in computed coseismic stress perturbations on the seismicity rate changes forecasted through a rate and state dependent frictional model we aim to understand how the variability of coulomb stress changes affects the correlation between predicted and observed changes in the rate of earthquake production we use the aftershock activity following the 1992 m7 3 landers california earthquake as a case study to accomplish these tasks we first analyze the variability of stress changes resulting from the use of different published slip distributions we find that the standard deviation of the uncertainty is of the same size as the absolute stress change and that their ratio the coefficient of variation cv is approximately constant in space this uncertainty has a strong impact on the forecasted aftershock activity if a rate and state frictional model is considered we use the early aftershocks to invert for friction parameters and the coefficient of variation by means of the maximum likelihood method we show that when the uncertainties are properly taken into account the inversion yields stable results which fit the spatiotemporal aftershock sequence the analysis of the 1992 landers sequence demonstrates that accounting for realistic uncertainties in stress changes strongly improves the correlation between modeled and observed seismicity rate changes for this sequence we measure a friction parameter asn 0 017 mpa and a coefficient of stress variation cv 0 95

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

further applications of the stochastic stress release model to historical earthquake data abstract the stochastic stress release model provides a stochastic version of the elastic rebound model which may be used to fit simulate and forecast occurrence of large earthquakes within a seismic region this paper reviews its applications to historical earthquakes from china iran and japan thereby extending and supporting earlier work on the chinese historical data the model generally provides an improvement in fit over poisson models with either constant rate or linear trend a crucial factor is the identification of suitable subregions which can act as largely independent seismic units in northern china divisions into two and four such units are considered based on recognized geophysical subdivisions in iran the best results are obtained from a subdivision into three such units the situation in japan seems more complex a preliminary model with two units gives a significant improvement of fit in one out of the two cases in all regions treating the subregions separately gives marked improvements over treating the whole region as a single unit however the quality of fit within subregions differs sharply from case to case pointing to substantial differences in the seismic regimes as reflected in the historical data

bias in fitting the etas model a case study based on new zealand seismicity summary we fit various forms of the etas model to a large region that includes all of the most seismically active areas of new zealand the etas model contains two components a component describing background or immigrant events and a part describing aftershocks of the background events and aftershocks of the aftershocks we refer to the first part as the background part and the second as the etas part generally all of the sophistication and the bulk of the model parameters lies in the etas part of the model the background component is generally treated as a nuisance component and is often very simplistic while the main interest lies in the etas part of the model the poor model description of the background part imposes considerable bias on the etas part of the model for example a poorly specified spatial density of the background events causes many of the background events to be seen as etas events it can also cause the estimated omori power law decay p to be too small and hence the aftershock sequences appear to continue for too long on the other hand the boundary of the observation region can impose a reverse bias which causes aftershocks that are close but within the boundary to be seen as background events in almost all of the large nz event sequences since 1965 the model consistently under fits these sequences consequently it over fits those space time regions where there is normal seismicity with no major events present this may indicate that the space time region of a major event sequence is much closer to criticality in that aftershock events appear to be much more easily initiated the standard etas model does not reflect this observation

finding realistic dike models from interferometric synthetic aperture radar data the february 2000 eruption at piton de la fournaise dike intrusions often cause complex ground displacements that are not sufciently explained by simple analytical models we develop a method to nd complex and realistic dike geometries and overpressures from interferometric synthetic aperture radar insar data this method is based on a combination of a boundary element method with realistic topography and a neighbourhood algorithm inversion dike model geometry is roughly a quadrangle with its top reaching the ground the inversion has two stages search and appraisal the appraisal stage involves calculations of model marginal probability density functions using mist val ues calculated during the search stage the mist function takes into account the variance and correlation of data noise synthetic tests show that a model is successfully retrieved within predicted narrow condence intervals we apply the method on insar data of the february 2000 ank eruption at piton de la fournaise and get a trapezoid dike dipping seaward 61 0 n 67 3 with its bottom passing 800n1000 m beneath the summit a model with a basal slip plane does not better explain observed asymmetric displacements and thus this asymmetry is solely attributed to the dipping dike the dike lies above a narrow band of pre eruption seis micity suggesting that lateral magma propagation occurred neglecting topography results in poor modeling at depth and in overestimations of overpressure or opening height both about 30 and volume about 20

afterslip and aftershocks in the rate and state friction law istituto nazionale di geofisica e vulcanologia italy ingv centre national de la recherche scientifique cnrs exxonmobil upstream research company

impact of the receiver fault distribution on aftershock activity 1 aftershock models are usually based either on purely empirical relations ignoring the physical mechanism or on deterministic calculations of stress changes on a predefined receiver fault orientation here we investigate the effect of considering more realistic fault systems in models based on static coulomb stress changes for that purpose we perform earthquake simulations with elastic half space stress interactions rate and state dependent frictional earthquake nucleation and extended ruptures with heterogeneous fractal slip distributions we find that the consideration of earthquake nucleation on multiple receiver fault orientations does not influence the shape of the temporal omori type aftershock decay but changes significantly the predicted spatial patterns and the total number of triggered events so called stress shadows with decreased activity almost vanish and activation decays continuously with increasing distance from the main shock rupture the total aftershock productivity which is shown to be almost independent of the assumed background rate increases significantly if multiple receiver fault planes exist the application to the 1992 m7 3 landers california aftershock sequence indicates a good agreement with the locations and the total productivity of the observed directly triggered aftershocks

continuous gps array and present day crustal deformation of japan a gps array with about 1 000 permanent stations is under operation in japan the gps array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the japanese islands based on daily coordinate data of the gps stations strain rate distribution is estimated most regions with a large strain rate are related to plate boundaries and active volcanoes in addition the niigata kobe tectonic zone nktz is recognized as a region of large strain rate along the japan sea coast and in the northern chubu and kinki districts this newly found tectonic zone may be related to a hypothetical boundary between the eurasian or amurian and the okhotsk or north america plates precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations

vail s sea level curves aren t going away academic researchers are beginning to gather support for exxon s new stratigraphic organizing scheme as its interpretation becomes more sophisticated

can coseismic stress variability suppress seismicity shadows insights from a rate and state friction model 1 the paucity of detectable seismicity shadows in the days months following a main shock has raised the question as to whether dynamic rather than static triggering could be the main mechanism driving the seismicity at these timescales the lack of correlation between the stress unloading of the main fault and the typically vigourous aftershock production taking place on it however suggests that the spatial heterogeneity of the coseismic stress change could also be a factor in the apparent suppression of seismicity shadows at least on the main fault here we study whether this stress variability can indeed be an important aspect in the stress modeling of earthquake sequences a rate and state friction model of seismicity is used in conjunction with realistic levels of stress heterogeneity at the earthquake nucleation scale 1 10 m as predicted from these friction laws based on scale invariant models of coseismic slip distribution in this model a relatively weak on fault quiescence is delayed by months to years because of the high stress heterogeneity delayed quiescences due to slip heterogeneity are similarly predicted at distances of up to about half the rupture length away from the fault we also postulate that off fault seismicity can be significantly controlled by stress variability that originates from small scale crustal heterogeneity and the complexity in fault geometries rather than mapping stress changes by providing a single stress value at every grid point these results suggest that an estimate of the likely stress variability acting at the nucleation scale is also needed especially when trying to account for the seismicity occurring at relatively short timescales

implications of rate and state friction for properties of aftershock sequence quasi static inherently discrete simulations 1 dieterich 1994 modeled the response to a stress step of a population of faults governed by rate and state dependent friction this model assumes that aftershocks nucleate over areas on the fault that at the time of the main shock are already accelerating toward failure and disregards the effect of interactions among aftershocks the main objective of this study is to examine consequences of relaxing these underlying assumptions aftershock activity is simulated using an inherently discrete earthquake fault model with a fault surface governed by an approximate constitutive friction law similar to the one used by dieterich we find that the governing equations in nondimensional form are a function of three main parameters and explore the effect of these parameters on the simulated catalogs we derive a simple expression for the time dependent seismicity response to a stress step that approximates the effect of multiple interactions among aftershocks as a time dependent stressing rate close match is found between the simulated seismicity response to a stress step and that predicted analytically however the numerical simulations show that the effect of the main shock is not only to raise the local seismicity rate but also to systematically modify the earthquake size distribution as a result the actual seismicity rate change early during the aftershock sequence may be higher than that predicted whereas seismicity rate late in the sequence may be lower than that predicted such a modification of the earthquake size distribution can explain observations of lower b values immediately following a stress step

low detection capability of global earthquakes after the occurrence of large earthquakes investigation of the harvard cmt catalogue summary we investigated the detection capability of global earthquakes immediately after the occurrence of a large earthquake we stacked global earthquake sequences after occurrences of large earthquakes obtained from the harvard centroid moment tensor catalogue and applied a statistical model that represents an observed magnitude frequency distribution of earthquakes to the stacked sequence the temporal variation in model parameters which corresponds to the detection capability of earthquakes was estimated using a bayesian approach we found that the detection capability of global earthquakes is lower than normal for several hours after the occurrence of large earthquakes for instance the duration of lowered detection capability of global earthquakes after the occurrence of an earthquake with a magnitude of seven or larger is estimated to be approximately 12 hr

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

a variety of aftershock decays in the rate and state friction model due to the effect of secondary aftershocks implications derived from an analysis of real aftershock sequences the model based on rate and state dependent friction law reproduces the temporal decay of an aftershock sequence with the p value of the omori utsu law equal to 1 if we simply assume a constant stress rate over time however because p values vary in real aftershock sequences this model requires some modification this study examined the effect of secondary aftershocks on the variety of the p value a large aftershock causes a stepwise stress increase in the aftershock area and the expected seismicity rate derived from the friction law also increases abruptly these multiple increases in the seismicity rate during its decay following a mainshock could cause variation in the apparent p value in this study a model incorporating this idea is applied to two aftershock sequences observed in japan and is shown to substantially modify the modeling of aftershock activity