the effect of rupture complexity on estimates of source size a general technique is proposed for estimating rupture geometry from measurements of body wave durations wherein measurements of the overall signal duration or the duration of a single pulse identified in all of the arrivals are inverted to estimate the geometry of the overall rupture or of a specific subevent respectively the complexity of a waveform is determined by comparing the overall signal duration to the duration of the most prominent pulse in the waveform this complexity is used to estimate the ratio of the average rupture velocity to the subevent rupture velocity the shear waves radiated by eight moderate 3 6 ml 4 9 multiply recorded aftershocks of the 1975 oroville california earthquake are analyzed using measurements of the corner frequency the characteristic frequency the pulse duration and the signal duration comparison of these four different estimates of source size indicates that the corner frequency and the characteristic frequency are more sensitive to the dominant subevent size than to the overall event size the difference between the estimates of source size determined from the signal duration measurements and the spectral measurements increases as the rupture complexity increases

earthquake nests as natural laboratories for the study of intermediate depth earthquake mechanics article the physical mechanism of intermediate depth earthquakes is still under debate in contrast to conditions in the crust and shallow lithosphere at temperatures and pressures corresponding to depths 50 km rocks ought to yield by creep or flow rather than brittle failure some physical process has to enable brittle or brittle like failure for intermediate depth earthquakes the two leading candidates for that are dehydration embrittlement and ther mal shear runaway given their great depth intermediate depth earthquake processes can t be observed direct ly insteadwe must relyona combination ofseismologyand thestudy of laboratory analogs tounderstand them earthquake nests are regions of highly concentrated seismicity that are isolated from nearby activity in this paper we focus on three intermediate depth earthquake nests vrancea hindu kush and bucaramanga and what they reveal about the mechanics of intermediate depth earthquakes we review published studies of tectonic setting focal mechanisms precise earthquake locations and earthquake source physics at these locations with an emphasis on the bucaramanga nest all three nests are associated with subducting litho sphere and at least two of the nests have consistently larger stress drops compared to shallow seismicity in contrast the bucaramanga nest has a larger b value larger variability of focal mechanisms and shows no evidence of aftershock sequences unlike the other two we also report for the first time finding a signifi cant number of repeating earthquakes some with reverse polarity

decomposition of surface drifter observations in the atlantic ocean 1 surface drifter observations are decomposed into mean seasonal annual and semiannual and eddy components via gauss markov estimation this approach helps separate seasonal fluctuations and mean values in the observationally sparse tropical and south atlantic where monthly mean values cannot be calculated at the spatial scale of the major currents in some regions large differences are found between these means and those obtained by simple binned averaging the differences are attributed to inhomogeneous sampling of seasonal variability and to the inherent bias of lagrangian observations towards periods of low velocity the analysis reveals strong seasonal variations of some surface currents including a significant late spring reversal of the western north equatorial counter current

artificial tracers for geothermal reservoir studies safe disposal of thermally spent geothermal brines that contain environmentally hazardous constituents is commonly obtained by reinjection the reinjection process also serves to maintain reservoir pressure enhance thermal recovery and eliminate possible compactional subsidence to avoid premature thermal breakthrough of reinjected fluids tracer tests are employed for detection and evaluation of preferential path networks in this paper some promising tracers that have not received much attention in geothermal reservoir studies are discussed and a comprehensive tabulation of field sites of artificial tracer utilization is presented chemical and transport processes responsible for tracer retention by the formation of reservoir solids as well as available tracer detection techniques are emphasized

seismicity and detection location threshold in the southern great basin seismic network a spatially varying model of the detection location capabilities of the southern great basin seismic network sgbsn has been derived that is based on simple empirical relations and statistics this permits use of almost all the catalog data gathered instead of ignoring data that are below the threshold of completeness a spatially varying threshold model is developed so that subregions having lower completeness levels than the network as a whole can be outlined and the completeness level of each sub region determined such a model is required to unambiguously identify regions that are aseismic due to natural processes rather than to limited detection and or location capabilities accounting for spatial variations in detection location threshold is also important for studies in which magnitude frequency distributions are interpreted in terms of source scaling properties the characteristics of the spatial distribution of earthquakes where earthquake clusters and aseismic regions locate appear to be stable at all magnitude levels so that inferences about where strain is being accommodated will be the same whether numbers of earthquakes or strain estimated from seismic moments are examined for the southern great basin region these principal characteristics include clusters at the northern end of the furnace creek fault and in the pahranagat shear zone and a relatively large number of earthquakes in the northern and southeastern portions of the nevada test site these clusters cover regions much larger than the surface projections of any of the mapped faults the extent to which seismicity is induced by nuclear testing is unclear the predominantly aseismic regions include the area west of the death valley furnace creek fault system and an almost complete absence of events at yucca mountain finally a considerable number of isolated events in the sgbsn catalog cannot be correlated with mapped faults

nonaqueous liquid pool dissolution in three dimensional heterogeneous subsurface formations a three dimensional numerical flow and contaminant transport model is developed to investigate the effect of variable hydraulic conductivity on average mass transfer coefficients associated with the dissolution of dense nonaqueous phase liquid dnapl pools in heterogeneous water saturated subsurface formations randomly generated three dimensional hydraulic conductivity fields are used to represent a heterogeneous confined aquifer model simulations indicate that the average mass transfer coefficient is inversely proportional to the variance of the log transformed hydraulic conductivity a power law correlation relating the sherwood number to the variance of the log transformed hydraulic conductivity and appropriate peclet numbers is developed a reasonable fit between predicted and numerically determined mass transfer coefficients is observed

source parameters of intermediate depth vrancea romania earthquakes from empirical green s functions modeling abstract several source parameters source dimensions slip particle velocity static and dynamic stress drop are determined for the moderate size october 27th 2004 mw 5 8 and the large august 30th 1986 mw 7 1 and march 4th 1977 mw 7 4 vrancea romania intermediate depth earthquakes for this purpose the empirical green s functions method of irikura e g irikura k 1983 semi empirical estimation of strong ground motions during large earthquakes bull dis prev res inst kyoto univ 33 part 2 no 298 63 104 irikura k 1986 prediction of strong acceleration motions using empirical green s function in proceedings of the 7th japan earthquake engineering symposium 151 156 irikura k 1999 techniques for the simulation of strong ground motion and deterministic seismic hazard analysis in proceedings of the advanced study course seismotectonic and microzonation techniques in earthquake engineering integrated training in earthquake risk reduction practices kefallinia 453 554 is used to generate synthetic time series from recordings of smaller events with 4 mw 5 in order to estimate several parameters characterizing the so called strong motion generation area which is defined as an extended area with homogeneous slip and rise time and for crustal earthquakes corresponds to an asperity of about 100 bar stress release miyake h t iwata and k irikura 2003 source characterization for broadband ground motion simulation kinematic heterogeneous source model and strong motion generation area bull seism soc am 93 2531 2545 the parameters are obtained by acceleration envelope and displacement waveform inversion for the 2004 and 1986 events and msk intensity pattern inversion for the 1977 event using a genetic algorithm the strong motion recordings of the analyzed vrancea earthquakes as well as the msk intensity pattern of the 1977 earthquake can be well reproduced using relatively small strong motion generation areas which corresponds to small asperities with high stress drops 300 1200 bar and high particle velocities 3 5 m s these results imply a very efficient high frequency radiation which has to be taken into account for strong ground motion prediction and indicate that the intermediate depth vrancea earthquakes are inherently different from crustal events

mining induced microseismicity monitoring and applications of imaging and source mechanism techniques the study of microseismicity in mines provides an ideal method for remote volumetric sampling of rock masses the nature and uniqueness of microseismic monitoring is outlined in the context of acquisition hardware and software requirements several topics are used to highlight the potential for novel applications of microseismicity and to outline areas where further study is required these topics reflect some of the current interest areas in seismology namelyb values and source parameters fault plane solutions modes of failure and moment tensor inversion imaging and seismicityvelocity correlations these studies suggest potential correlations between zones of high seismic velocity high microseismic activity and maximal stress drops which can be interpreted spatially to be the locations of highly stressed ground with a potential for rock bursting fault plane solutions are shown to be useful in determining the slip potential of various joint sets in a rock mass source parameter studies and moment tensor analysis clearly show the importance of non shear components of failure andb values for microseismicity appear to be magnitude limited and related to spatial rather than temporal variations in effective stress levels

statistical analysis of the central europe seismicity abstract the aim of this paper is to characterize the spatio temporal distribution of central europe seismicity specifically by using a non parametric statistical approach the proportional hazard model leading to an empirical estimation of the hazard function we provide some constrains on the time behavior of earthquake generation mechanisms the results indicate that the most conspicuous characteristics of mw 4 0 earthquakes is a temporal clustering lasting a couple of years this suggests that the probability of occurrence increases immediately after a previous event after a few years the process becomes almost time independent furthermore we investigate the cluster properties of the seismicity of central europe by comparing the obtained result with the one of synthetic catalogs generated by the epidemic type aftershock sequences etas model which previously have been successfully applied for short term clustering our results indicate that the etas is not well suited to describe the seismicity as a whole while it is able to capture the features of the short term behaviour remarkably similar results have been previously found for italy using a higher magnitude threshold

application of pattern recognition techniques to earthquake catalogs generated by model of segmented fault systems in three dimensional elastic solids techniques and seismicity parameters described by eneva and ben zion 1997 are used to examine synthetic earthquake catalogs generated by ben zion 1996 for precursory patterns of large model events different model realizations represent various levels of fault zone disorder these include models with uniform properties u a parkfield type asperity a fractal brittle properties f and multi size scale heterogeneities m the seismicity parameters used are based on information contained in typical earthquake catalogs reflecting earthquake distribution in space time and size the analysis highlights the complexity of the information content of the synthetic earthquake catalogs simple repetitive precursory signals have not been found however local extrema in the examined parameters are found to have significant association in time with large events thus our techniques and parameters may be useful for intermediate term earthquake prediction especially when parameters are used in combinations some analysis results are the same for all model realizations and some depend on the model features characterizing all catalogs are as follows 1 large model events are statistically predictable on the basis of patterns in the distribution of smaller events 2 for a given parameter the type of precursory extrema maxima or minima is the same for all models 3 the interparameter correlation for any parameter pair has the same sign positive or negative in all models 4 the large events are neither slip nor time predictable based on previous large events results that differ from model to model include the following 1 the degree of predictability of large events correlates with the degree of regularity in the assumed fault properties following the order u f a and m 2 there is no one to one correlation between type of precursory extrema maxima or minima and type of precursory trends increase or decrease this produces great variations in observable trends for any given parameter both from model to model and for different events in the same model 3 the interparameter correlations vary among models with the highest correlations in model f most discussed patterns are in agreement with observations from seismically active zones laboratory models and mining induced seismicity

seismicity in deep gold mines of south africa implications for tectonic earthquakes we have studied induced seismicity associated with five deep gold mines located in the far west rand district republic of south africa focusing on the digital data recorded from january 1994 until february 2000 by in mine arrays of three component geophones the observed seismicity which exceeds 1 000 events per day can be divided into two kinds of events designated as types a and b type a events are tightly clustered in time and space and generally occur within 100 m of an active mining face or development tunnel their spectra are comparatively enriched in high frequencies and they have an upper moment magnitude cutoff at mmax 1 we associate these events with the fracture dominated rupture of com petent rock induced by dynamic stresses during blasting and quasi static stress per turbations from the excavation and closure of individual stopes in contrast type b events are temporally and spatially distributed throughout the active mining region they represent friction dominated slip in existing shear zones such as faults or dikes and have source scaling properties that agree well with extrapolations from tectonic earthquakes in the far west rand region type b events can have large magnitudes m 3 but they show a distinct lower magnitude cutoff at mmin 0 we interpret this cutoff in terms of a critical patch size for nucleation of shear failure and we show that the data are consistent with a rate and state dependent friction model in which the critical slip distance d c 10 4 m both the spectral predictions of this model and accelerograms of type b events agree that f max 200 hz

dissolution of a well defined trichloroethylene pool in saturated porous media experimental design and aquifer characterization a unique three dimensional bench scale model aquifer is designed and constructed to carry out dense nonaqueous phase liquid dnapl pool dissolution experiments the model aquifer consists of a rectangular glass tank with internal dimensions 150 0 cm length 21 6 cm width and 40 0 cm height the formation of a well defined circular pool with a perfectly flat pool water interface is obtained by a bottom plate with a precise cutout to contain the dnapl the aquifer is packed with a well characterized relatively uniform sand a conservative tracer is employed for the determination of the longitudinal and transverse aquifer dispersivities the dissolution studies are conducted using a circular trichloroethylene tce pool the sorption characteristics of tce onto the aquifer sand are independently determined from a flow through column experiment steady state dissolved tce concentrations at specific downstream locations within the aquifer are collected under three different interstitial velocities an appropriate overall mass transfer coefficient is determined from each data set the data collected in this study are useful for the validation of numerical and analytical dnapl pool dissolution models

the polymodal frequency magnitude relationship of earthquakes earthquake frequency magnitude relationships can be well described as a polymodal composite of normal distributions a pattern consistent with varying causal mechanisms in different tectonic settings and or magnitude ranges but a pattern also in conflict with the assumption of self similarity or the fractal nature of earthquakes from the giardini catalog 4660 deep 350 km worldwide earthquakes presumably homogeneous with respect to causal mechanism are well described as a single normally distributed population analysis of 10 341 earthquakes ranging in magnitude from 2 0 to 8 2 from the 1989 to 1991 national earthquake information center quick epicenter determination catalogue yields three populations each of whose magnitude frequency is expressed in terms of probability some nonsimilar frequency magnitude distributions for low magnitudes are also explicable as the result of one or more normally distributed populations in our model b is a measure of the dispersion of the population

a method for multidimensional analysis of earthquake frequency magnitude distribution with an application to the vrancea region of romania abstract a novel method is proposed for the time space analysis of the frequency magnitude distribution of earthquakes fmd the fmd is calculated using a non parametric technique based on the nearest neighbourhood statistics and the fmd parameters namely the occurrence rate at a reference magnitude and the b value are subsequently estimated by a parametric log linear regression the method s potential is examined by using a microearthquake catalogue of the intermediate depth h 60 km seismicity in the vrancea region romania spanning 18 yr for the magnitude intervals of ml 2 8 4 0 and 4 0 5 2 the calculated occurrence rates exhibited different linear decays with increasing magnitude on a log linear scale quasi linear correlations were found between the fmd parameters over selected time space intervals in several cases the results showed that changes in the b values were inversely related to changes in the occurrence rates of magnitudes at the limits of the first magnitude interval the three large events mw 7 reported in the catalogue were preceded by time space regions of relatively low b values lasting for a few years at the depth of these events three episodes of distinct behaviour were identified i b values are inversely related to changes in the occurrence rates of magnitudes at the limits of the first study range ml 2 8 and 4 0 ii a decrease in the b value occurs when an increase in the occurrence rate of relatively larger magnitude events ml 4 0 is observed iii the occurrence rate of larger events tends to saturate whereas the rate of small events tends to fluctuate the results suggest that multi dimensional b values and occurrence rates over selected magnitudes have the potential to outline characteristic trends in the recorded seismicity and provide relative constraints for the modelling of the earthquake cycle

scaling of source parameters for vrancea romania intermediate depth earthquakes the stress drop scaling of the vrancea romania intermediate depth earthquakes with seismic moments from 10 to 20 dyne cm is investigated the empirical green s function technique is used in order to retrieve the seismic source parameters for the smaller earthquakes 1021 1026 dyne cm available source parameters for the major vrancea earthquakes that occurred in 1940 1977 1986 and 1990 mw 6 9 as determined from teleseismic and local data were included a circular source model approximates well the deconvolved source time functions and source spectra for the analyzed earthquakes in case of the large earthquakes an equivalent circular area is considered corresponding to the zone of aftershocks the static stress drop is determined from seismic moment and source radius for brune s model a dependence of the stress drop on the seismic moment as m140 is outlined over the entire magnitude range

magnitude frequency relation for small earthquakes a clue to the origin of ƒmax of large earthquakes in order to test the hyothesis that the max of large earthquakes is due to the source effect and is causally related to the corner frequency of small earthquakes when it becomes constant below magnitude about 3 we constructed the frequency magnitude relation for earthquakes with magnitude range from 1 3 to 4 recorded at a borehole seismograph station operated by the university of southern california at baldwin hills in the middle of the newport inglewood fault a procedure was developed for an accurate estimation of moment magnitude from the measurement of coda amplitude as a function of lapse time the cumulative number of earthquakes per unit time period and area was estimated by finding the detection limit for ts p for each magnitude we found a clear depature of the observed log frequency magnitude relation for m 3 the observed frequency of earthquakes with m 0 5 is almost 10 times less than that expected from the extrapolation of empirical relation for earthquakes with magnitudes larger than 3 we conclude that the observed frequency magnitude relation departs from self similarity for earthquakes with magnitude smaller than about 3 this departure coincides with the widely observed departure of the moment corner frequency relation from self similarity these observations are consistent with the interpretation of max of large earthquakes in terms of the slip weakening instability model in which the critical slip may be a few tenths of a meter to a few meters and the cohesive zone size may be a few hundred meters to a few kilometers

a statistical procedure for the analysis of seismotectonically induced hydrochemical signals a case study from the eastern carpathians romania changes in the stress field of an aquifer system induced by seismotectonic activity may change the mixing ratio of groundwaters with different compositions in a well leading to hydrochemical signals which in principle could be related to discrete earthquake events due to the complexity of the interactions and the multitude of involved factors the identification of such relationships is a difficult task in this study we present an empiric statistical approach suitable to analyse if there is an interdependency between changes in the chemical composition of monitoring wells and the regional seismotectonic activity of a considered area to allow a rigorous comparison with hydrochemistry the regional earthquake time series was aggregated into an univariate time series this was realized by expressing each earthquake in form of a parameter beq taking into consideration both energetic magnitude of a seismic event and spatial parameters position of epi hypocentrum relative to the monitoring site the earthquake and the hydrochemical time series were synchronised aggregating the e parameters into bearthquake activityq functions e which takes into account the time of sampling relative to the earthquakes which occurred in the considered area for the definition of the aggregation functions a variety of different beq parameters were considered the set of earthquake functions e was grouped by means of factor analysis to select a limited number of significant and representative earthquake functions e to be used further on in the relation analysis with the multivariate hydrochemical data set from the hydrochemical data a restricted number of hydrochemical factors were extracted factor scores allow to represent and analyse the variation of the hydrochemical factors as a function of time finally regression analysis was used to detect those hydrochemical factors which significantly correlate with the aggregated earthquake functions this methodological approach was tested with a hydrochemical data set collected from a deep well monitored for two years in the seismically active vrancea region romania three of the hydrochemical factors were found to correlate significantly with

nonlinear frequency magnitude relationships for the hokkaido corner japan abstract frequency magnitude relationships are determined for a source region defined by a circular epicentral area of 50 km radius centered on the carnegie broadband seismograph at kmu in the southeast corner of hokkaido island japan within this region bounded by a maximum depth of 125 km more than 11 100 earthquakes were detected and cataloged by the hokkaido university network during the period july 1976 through january 1987 the seismicity is divided into two effectively decoupled suites crustal eurasian plate and subduction pacific plate the frequency magnitude recurrence distributions exhibit departures from linearity which are statistically significant below m d 2 5 for the crustal data suite and m d 3 5 for the subduction data suite three independent tests show the nonlinearity is not caused by incompleteness the catalog is complete down to magnitude 2 0 or less for both data suites these observations are therefore inconsistent with the linear gutenberg richter relationship which is assumed to be valid over any magnitude range for which the data are complete there are relatively more large events and fewer small events in the subduction suite the logarithm of the ratio of the number of crustal events to the number of subduction events versus magnitude is monotonically decreasing and remarkably linear over the magnitude range 1 0 to 5 0 this suggests that the observed nonlinearity of these two frequency magnitude relationships has a common origin

a reinterpretation of the precursory seismic b value anomaly from fracture mechanics summary a new model is presented which can explain the major temporal fluctuations in seismic b value in terms of the underlying physical processes of time varying applied stress and crack growth under conditions of constant strain rate the model predicts two minima in the b value separated by a temporary maximum of inflexion point a corollary being that a single broad maximum would be expected in scattering attenuation these fluctuations in b value are consistent with reported intermediate term and short term earthquake precursors separated by a period of seismic quiescence we present preliminary results from controlled laboratory experiments and report recent field observations both of which are consistent with the predicted form and in particular exhibit the distinctive second short term anomaly which reaches a value bc 0 5 during the critical phase

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

multifractal and chaotic analysis of vrancea romania intermediate depth earthquakes investigation of the temporal distribution of events the vrancea seismic region contains an isolated cluster of events beneath the carpathian arc bend in romania dipping to about 200 km depth seismic activity mainly occurs at intermediate depths h 60 km the main goal of the paper is to perform an in depth complex analysis of the occurrence times of these intermediate depth events we also try to show the versatility of the methods used to characterize different aspects of the seismicity evolution and to offer a user friendly software toolbox to do most of the related computations the earthquake catalog used in this study spans from 1974 to 2002 and includes only the intermediate depth events in the first part of the paper we analyze the multifractal characteristics of the temporal distribution of earthquakes the study reveals two distinct scaling regimes at small scales we found a clear nonhomogeneous multifractal pattern while at large scales the temporal distribution of events shows a monofractal and close to poissonian random behavior the multifractal behavior at small scales minutes hours is shown to be clearly an effect of the short aftershock sequences that occurred after some major vrancea earthquakes in the second part of the paper we analyze whether our temporal series shows a persistent or anti persistent long term behavior by using the detrended fluctuation analysis dfa method the results suggest that the analyzed temporal series of vrancea earthquakes is a non correlated process in part three of the paper we seek to determine whether the dynamics of our earthquake system described by the occurrence time of vrancea earthquakes is deterministically chaotic deriving from a rather simple evolution law or whether it is stochastic and is generated by a system that possesses many degrees of freedom the results suggest that our signal is stochastic probably does not possess an attractor the limited time span of the catalog and the analysis performed in this paper cannot rule out the emergence of an interesting quasi deterministic and low dimensional structure in the case of major vrancea earthquakes

asperity distribution and percolation as fundamentals of an earthquake cycle abstract a seismic cycle model is proposed based on the existence of an asperity space strength distribution along the fault plane and the applicability of the percolation theory to earthquakes as suggested by vrancea seismotectonic data two seismic regions somewhat decoupled are emphasized in the lower lithosphere roughly between 80 and 110 km and between 120 and 170 km depth and an asperity magnitude quasi independent dimension of 0 3 0 4 km is determined for small to moderate earthquakes accordingly two concepts are introduced 1 the active zone a distinct fault region able to generate a major earthquake by percolation and characterized by a specific background seismicity total area and maximum possible magnitude 2 the asperity cell an elementary local stress inhomogeneity of an active zone generating weak to moderate events percolation requires the presence of a critical stress free surface 44 of the active zone area the model explains the non linearity of the frequency magnitude relationship and enables the estimation of the major earthquake magnitude domain in each zone the computed maximum possible magnitudes are mw 7 6 and mw 7 8 respectively in agreement with historical data a complex form of the recurrence period of earthquakes in the major magnitude domain is determined ranging from about 40 to 100 years irrespective of the seismic zone it follows that the seismic activity per unit area is invariant in both zones this result is considered to be a consequence of an intrinsic material property the scale invariance of the fragmentation process in the lithospheric material different aspects related to the discrete structure of the active zone and the fractal dimension of faulting are also discussed from the point of view of this model

some source and medium properties of the vrancea seismic region romania abstract simple spectral theory of seismic sources was used to determine source parameters directly related to medium properties stress drop seismic efficiency and fracture energy and quality factors of the vrancea romania seismic region the results show an increase in maximum static stress drop maximum seismic efficiency and fracture energy with depth the seismic efficiency is magnitude independent but the stress drop is magnitude independent only for events with ml 3 8 below this value the logarithm of stress drop increases quasi linearly with magnitude in the depth interval 50 160 km the stress drop increases with a slope of about 2 3 bar km the fracture energy per unit area of the fault has values of the order of 105 108 erg cm2 the frequency independent quality factors indicate that the attenuation of p waves is generally higher than that of s waves and that qp values are in agreement with recent tectonic models for the vrancea region total decoupling of the slab now sinking gravitationally is present only in the southwestern part of the vrancea region as suggested by the spatial position of intermediate depth hypocenters

rupture characteristics and tomographic source imaging of ml 3 earthquakes near anza southern california the rupture characteristics of several ml 3 earthquakes near anza california are determined from time domain analysis of path corrected displacement pulses these pulses are corrected for propagation effects apparent attenuation scattering site resonance using the waveforms of adjacent small events ml 2 1 as empirical green s functions the earthquakes studied occurred during two swarm sequences near cahuilla in an area characterized by swarm activity at shallow depth 5 km the data consist of seismograms recorded by the anza seismic network a high dynamic range local array with digital telemetry the waveforms of adjacent small events ml 2 1 are deconvolved from those of the ml 3 events to yield the source time functions of the larger earthquakes the ml 3 earthquakes display a variety of rupture modes similar to those reported for large shocks but over much shorter time scales and distances events with single and multiple ruptures are observed relative locations of the subevents are obtained from azimuthal differences in the time separation of pulses in the deconvolved displacement waveforms some events as small as ml 2 4 display unilateral rupture propagation as manifested by azimuthal variations in the pulse widths of the deconvolved displacement pulses a tomographic back projection technique is applied to the deconvolved displacement pulses to image the slip velocity on the fault as a function of time after nucleation and distance along the fault using a one dimensional fault model the tomographic inversion for one of the events ml 2 4 reveals a unilateral rupture with rupture velocity about equal to the shear wave velocity vs and fault length of 300 m a similar inversion for an ml 3 7 event resolves two subevents separated by about 200 m and yields an average rupture velocity of 0 8vs these rupture velocities are similar to those reported for large earthquakes indicating that rupture velocity is independent of seismic moment down to 3 1 1019 dyn cm the smallest event studied there are clear variations in pulse width for neighboring events with similar seismic moments implying significant differences in static stress drops factor of five variations in stress drop 11 61 bars are calculated for events within 200 m of each other thus the stress and or strength along this fault zone varies considerably over distances of hundreds of meters

the theoretical seismicity of asperity models an application to the coast of oaxaca summary we solve the statistical dynamical equations of an asperity model to obtain both the time dependent seismicity and the stationary seismicity with its associated magnitude frequency relation the parameters of the model are chosen to reproduce the seismicity of the oaxaca region on the western coast of mexico the observed enhancement of the seismicity in the high magnitude range is well reproduced and the calculated b value of about 7 is also acceptable the predicted features of the time dependent seismicity are as follows there is an enhancement of the small scale seismicity immediately following a characteristic earthquake this enhancement approximately doubles the rate of occurrence of small events relative to the stationary values both intermediate and characteristic earthquakes present a gap with a subsequent enhancement of the seismicity superior to long term averages there are strong correlations between the characteristic and intermediate seismicities indicating that the latter have premonitory value

non similar frequency magnitude distribution for m 1 seismicity a series of 1503 induced seismic events ranging in magnitude from 2 to 1 as computed based on a locally calibrated seismic moment scale were located within a well defined volume at depth the seismicity analysis was carried out over 2 months and included events recorded before during and following the after shock period of a mn 2 6 rockburst a non similar pattern was clearly apparent for both cumulative and non cumulative frequency magnitude distributions showing a relative enhancement of seismicity between magnitudes 0 5 and 0 this supports the existence of non similar scaling at these magnitudes the time variation of the b value as computed for a limited self similar magnitude domain 1 1 to 0 4 did not appear to be related to the rockburst instead it is suggested that the rockburst perturbed the local stress field and consequently the distribution of the very small events no correlations were found between b and space clustering

hierarchy in earthquake size distribution abstract we propose a fault model in which there are a finite number of characteristic lengths between the smallest and the largest scales e g between a grain size and a size of great earthquakes a fault plane in one scale is segmented into blocks of statistically similar sizes by the barriers of statistically similar heights rupture expands by successively climbing the barriers the average barrier height is proportional to the average block size which defines the characteristic length of the relevant scale stresses before and after rupturing are assumed to be independent of earthquake size with these assumptions the probability for rupture to grow further is shown to be independent of the scale of barrier structure the rupture in one scale however tends to grow more easily as it grows so that once the rupture exceeds some critical size it no longer stops until it encounters the barriers in the next larger scale rupture grows by repeating this cycle which starts with rupturing of a unit block in one scale and ends with one in the next larger scale our model involves two parameters which must be determined empirically one is the length ratio r between two successive scales the other is the critical number of blocks n c which defines the critical size for unstable rupture growth in one scale we suggest values of 5 for both r and n c with these values our model explains a diversity of earthquake phenomena such as the magnitude frequency relation the seismic gap and the magnitude gap the magnitude difference between a main shock and its largest aftershock the occurrence of multiplet earthquakes the generation of high frequency seismic waves the incoherency of the near field acceleration and the recent observation by furumoto and nakanishi that the main rupture is often preceded by a precursory rupture whose time duration in general scales with seismic moment

on the recurrence time of earthquakes insight from vrancea romania intermediate depth events summary the statistics of earthquake inter occurrence times in broad areas have been reported to obey universal scaling laws e g by bak et al and corral we investigate the recurrence times of intermediate depth vrancea earthquakes depth 60km taking advantage of the scarcity of aftershocks for deeper events we use a complete earthquake catalogue m 2 8 spanning from 1974 to 2002 the analysis of the probability density distribution of the recurrence times for the entire catalogue reveals a power law regime at small scales in order better to understand this scaling we also analyse declustered catalogues from which the distinct aftershock sequences following the 1977 1986 and 1990 major earthquakes have been removed and a time period without large events for these data sets the recurrence times follow an exponential distribution at all scales this observation suggests that deviations from the exponential model characteristic of the scaling laws recently proposed result primarily from short term aftershock clustering

a characteristic earthquake model of the seismicity preceding the eruption of mount st helens on 18 may 1980 abstract the two classes of earthquakes which preceded the explosive eruption of mount st helens washington on 18 may 1980 can be related to two different forms of energy release this is manifest both in the predominant periods of the two classes of seismic energy release at 1 0 and 0 55 s and in the ratio of their source dimensions in the range 2 1 to 6 1 inferred from characteristic magnitudes of the two possible classes of earthquakes apparent in the discrete frequency magnitude distribution the observed increase in the ratio of long to short period amplitudes of surface waves recorded on mso a local wwssn station can be numerically related to the growth of a magma chamber or conduit within which are generated the transient oscillations thought to be responsible for volcanic tremor these calculations predict an increase in the chamber s diameter at a rate of 2 7 m day 1 at depth in the 2 months preceding the eruption and this is consistent with an observed growth rate of 2 m day 1 of the precursory bulge which appeared at the surface on the mountain s north flank at the time the frequency magnitude distribution is analysed in two parts corresponding to a power law at low magnitudes and a gaussian distribution of typical fault lengths at high magnitudes an extension of the characteristic earthquake model first developed for individual fault zones the power law can in general have a non integer exponent which can be equated to a fractal self similarity dimension d temporal changes in d which is proportional to the seismic b value are proposed as an alternative and complementary description of the way seismic energy is released to the more commonly used viewpoints of changes in stress and heterogeneity despite a reassessment of the completeness of the magnitude catalogue no clear seismic precursor to the explosive eruption is observed in the b value although an earlier phase of phreatic eruptions was strongly associated with a b value anomaly

classification of seismic patterns in a hierarchical model of rupture a new phase diagram for seismicity summary i present a detailed description of the temporal properties of seismicity in a hierarchical model of rupture incorporating healing and faulting at the microscopic scale a stochastic process controls transitions between a solid and a broken state with respect to the local stress from the distribution of broken elements geometric rules of interaction determine the state of fracturing of domains of larger dimensions and the shape of the stress redistribution then any point in space evolves with respect to its state of stress and its state of fracturing measured at different length scales applied to a single fault zone under a constant loading rate this model of seismicity reproduces the main characteristics of the seismic catalogues gutenberg richter law for the magnitude frequency relationship omori law for the aftershock decay rate clustering of major events swarms of earthquakes seismicity of creeping segment and seismic noise i infer that the control parameter is the dimensionless parameter a the ratio between a characteristic time of healing and a characteristic time of loading following the magnitude of a different seismic scenarios emerge if a 1 the system is in a critical state and largest events can occur over a wide range of timescales e g clustering of major events if a 1 the system is in subcritical states controlled by healing and the fault zone may be creeping one particular feature is that the amplitude of the stress stored in the fault zone decreases and the frequency of large events increases as the critical state is approached this can be interpreted as a weakening process i propose a new phase diagram of seismicity to illustrate an alternative to the classical seismic cycle picture

aftershocks of the 13 may 1993 shumagin alaska earthquake the 13 may 1993 ms 6 9 shumagin earthquake had an aftershock sequence of 247 earthquakes with magnitudes greater than or equal to 1 5 by 1 june 1993 of these aftershocks 79 were located by using s p travel times at the only two stations within 570 km of the mainshock epicenter the rupture area inferred from the aftershocks is about 600 km2 and we estimate for the mainshock a mean fault displacement of 1 0 m and a 28 bar stress drop the magnitude frequency plots give a b value for the aftershock sequence of about 0 4 which is low compared to the background value of approximately 0 8 the decay of the aftershock sequence followed the modified omori law with a p value of 0 79 which is also lower than the typical values of about 1 1 observed in alaska both of these facts can be interpreted as indicating relatively high ambient stress in the shumagin seismic gap and the possibility that the 13 may earthquake was a foreshock to a larger gap filling event to occur within the next few years

wavelet based multiscale resolution analysis of real and simulated time series of earthquakes summary this study introduces a new approach based on the continuous wavelet transform modulus maxima method to describe qualitatively and quantitatively the complex temporal patterns of seismicity their multifractal and clustering properties in particular firstly we analyse the temporal characteristics of intermediate depth seismic activity m 2 6 events in the vrancea region romania from 1974 to 2002 the second case studied is the shallow crustal seismicity m 1 5 events which occurred from 1976 to 1995 in a relatively large region surrounding the epicentre of the 1995 kobe earthquake mw 6 9 in both cases we have declustered the earthquake catalogue and selected only the events with m mc where mc is the magnitude of completeness before analysis the results obtained in the case of the vrancea region show that for a relatively large range of scales the process is nearly monofractal and random does not display correlations for the second case two scaling regions can be readily noticed at small scales i e hours to days the series display multifractal behaviour while at larger scales days

slip patterns and earthquake populations along different classes of faults in elastic solids numerical simulations of slip instabilities on a vertical strike slip fault in an elastic half space are performed for various models belonging to two different categories the first category consists of inherently discrete cellular fault models such are used to represent fault systems made of segments modeled by numerical cells that can fail independently of one another their quasi independence is assumed to provide an approximate representation of strong fault heterogeneity due to geometric or material property disorder that can arrest ruptures at segment boundaries the second category consists of models having a well defined continuum limit these involve a fault governed by rate and state dependent friction and are used to evaluate what types of property heterogeneity could lead to the quasi independent behavior of neighboring fault segments assumed in the first category the cases examined include models of a cellular fault subjected to various complex spatial distributions of static to kinetic strength drops and models incorporating rate and state dependent friction subjected to various spatial distributions of effective stress normal stress minus pore pressure the results indicate that gradual effective stress variations do not provide a sufficient mechanism for the generation of observed seismic response strong and abrupt fault heterogeneity as envisioned in the inherently discrete category is required for the generation of complex slip patterns and a wide spectrum of event sizes strong fault heterogeneity also facilitates the generation of rough rupture fronts capable of radiating high frequency seismic waves the large earthquakes in both categories of models occur on a quasi periodic basis the degree of periodicity increases with event size and decreases with model complexity however in all discrete segmented cases the models generate nonrepeating sequences of earthquakes and the nature of the large quasi periodic events is highly variable the results indicate that expectations for regular sequences of earthquakes and or simple repetitive precursory slip patterns are unrealistic the frequency size fs statistics of the small failure episodes simulated by the cellular fault models are approximately self similar with b 1 2 and ba 1 where b and ba are b values based on magnitude and rupture area respectively for failure episodes larger than a critical size however the simulated statistics are strongly enhanced with respect to self similar distributions defined by the small events this is due to the fact that the stress concentrated at the edge of a rupture expanding in an elastic solid grows with the rupture size when the fault properties e g geometric irregularities are characterized by a narrow range of size scales the scaling of stress concentrations with the size of the failure zone creates a critical rupture area terminating the self similar earthquake statistics in such systems events reaching the critical size become on the average unstoppable and they continue to grow to a size limited by a characteristic model dimension when however the system is characterized by a broad spectrum of size scales the above phenomena are suppressed and the range of apparent self similar fs statistics is broad and characterized by average b and ba values of about 1 the simulations indicate that power law extrapolations of low magnitude seismicity will often underestimate the rate of occurrence of moderate and large earthquakes the models establish connections between features of fs statistics of earthquakes range of self similar regimes local maxima and structural properties of faults dominant size scales of heterogeneities dimensions of coherent brittle zones the results suggest that observed fs statistics can be used to obtain information on crustal thickness and fault zone structure

depth distribution of local stress inhomogeneities in the vrancea region romania corrected displacement amplitude spectra of weak and moderate ml 2 5 5 0 vrancea earthquakes h 0 201 km exhibit an obvious shape with two comer frequencies and two slopes this behavior is related to local inhomogeneities within the seismic zone and a heterogeneity parameter e is defined as the fraction of the complete stress drop released during earthquake barrier model or the ratio of the asperity to source radii asperity model the parameter e is evaluated as the ratio of the first corner frequency versus the second one and it ranges from 0 50 to 0 15 the heterogeneity appears to increase with increasing magnitude e decreases suggesting that the earthquakes represent the failure of asperities this behavior is not evident for the events in the 30 50 km depth interval a mostly crack origin of earthquakes in this zone is suggested this region is found to be more homogeneous and able to decouple the seismic activities in the crust and sinking slab the depth distribution of local inhomogeneities within the region is heterogeneous the crust and two intermediate depth intervals 90 110 km and 120 160 km are the most heterogeneous and have occurrence potential for moderate earthquakes the two intermediate zones show the highest activities which are slightly decoupled due to a more homogeneous layer 110 120 km

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

earthquake failure sequences along a cellular fault zone in a three dimensional elastic solid containing asperity and nonasperity regions numerical simulations of earthquake failure sequences along a discrete cellular fault zone are performed for a three dimensional 3 d model representing approximately the central san andreas fault the model consists of an upper crust overlying a lower crust and mantle region together defining an elastic half space with a vertical half plane fault the fault contains a region where slip is calculated on a uniform grid of cells governed by a static kinetic friction law and regions where slip is prescribed so as to represent tectonic loading aseismic fault creep and adjacent great earthquakes the computational region models a 70 km long and 17 5 km deep section of the san andreas fault to the nw of the great 1857 rupture zone different distributions of stress drops on failing computational cells are used to model asperity parkfield asperity and nonasperity fault regions the model is inherently discrete and corresponds to a situation in which a characteristic size of geometric disorder within the fault i e cell size here a few hundreds of meters is much larger than the nucleation size of the order of tens of centimeters to tens of meters based on slip weakening or state evolution slip distances the computational grid is loaded by a constant plate motion imposed at the lower crust upper mantle and creeping fault regions and by a staircase slip history imposed at the 1857 and 1906 rupture zones stress transfer along and outside the fault due to the imposed loadings and failure episodes along the computational grid is calculated using 3 d elastic dislocation theory the resulting displacement field in the computational region is compatible with geodetic and seismological observations only when the asperity and nonasperity regions are characterized by significantly different average stress drops the frequency magnitude statistics of the simulated failure episodes are approximately self similar for small events with b 1 2 the b value of statistics based on rupture area ba is about 1 but are strongly enhanced with respect to self similarity for events larger than a critical size this is interpreted as a direct manifestation of our 3 d elastic stress transfer calculations beyond certain rupture area and potency seismic moment divided by rigidity release values the event is usually unstoppable and it continues to grow to a size limited by a characteristic model dimension this effect is not accounted for by cellular automata and block spring models in which the adopted simplified stress transfer laws fail to scale properly with increasing rupture size the simulations suggest that local maxima in observed frequency magnitude statistics correspond to dimensions of coherent brittle zones such as the width of the seismogenic layer or the length of a fault segment bounded by barriers the analysis indicates that a single cell size representing approximately a single scale of geometric disorder cannot induce self similarity in a 3 d elastic model over a broad range of magnitudes a representation of geometric disorder covering a range of scales may thus be required to generate a wide domain of self similar gutenberg richter statistics our simulations show a great diversity in the mode of failure of the parkfield asperity the earthquakes themselves define an irregular sequence of events the modeling like many other discrete fault models suggests that expectations for periodic parkfield earthquakes and or simple precursory patterns repeating from one event to the other are unrealistic

frequency magnitude distribution of earthquakes in vrancea relevance for a discrete model a high resolution analysis of a homogeneous and complete data set of intermediate depth microearthquakes h 60 km extending over an interval of 9 3 years emphasizes a significant deviation at low magnitudes ml 4 in a linear frequency magnitude distribution it appears as a distinct change in the slope of the cumulative distribution and as a seismicity deficit followed by a relative enhancement in the corresponding noncumulative curve this is in agreement with the presence of two characteristic mechanisms and allows the identification of both the magnitude threshold of asperity like earthquakes and the transition zone ml 3 3 3 9 from crack like earthquakes background seismicity to asperity like events these features are better pointed out on well individualized active zones the background seismicity shows a tremendeous decrease in its b slope from 1 03 to 0 57 during a 6 year interval before the occurrence of a major earthquake in 1986 mw 7 3 followed by a fast recovery to 1 03 in 2 years after this event such a behavior could be correlated to the continuous growth of the shear stress free surface on the fault as in a percolation process followed by its sudden diminution due to the locking of the fault the above results provide relevance for the discrete character of faulting and enable a coherent modeling of the earthquake generation process from microearthquake to major event scale lengths

geodynamics and intermediate depth seismicity in vrancea the south eastern carpathians current state of the art abstract the vrancea region of the south eastern carpathians is a remarkable site of intra continental intermediate depth seismicity a large set of geological geophysical and geodetic observations has been accumulated for the last few decades and utilised to improve our knowledge of the shallow and deep structures beneath vrancea the crustal and mantle dynamics and the linkage between deep and surface processes in the region in this article we review geology and tectonics of the vrancea region including post collisional to recent deformations syn to post collisional magmatism and orogenic exhumation along the east and south carpathians the regional seismicity is analysed and the recent seismic studies including reflection refraction body and surface wave tomography are reviewed we discuss new geodetic measurements of horizontal and vertical movements in the region geoelectric studies density gravity and thermal modelling qualitative and quantitative including retrospective geodynamic models developed for vrancea are analysed the knowledge of regional tectonics geodynamics seismicity lithospheric deformation and stress regime in the vrancea earthquake prone region assists in an assessment of strong ground motion seismic hazard and risk the earthquake simulation seismic hazard and earthquake forecasting models have also been reviewed providing a link between deep geodynamic processes and their manifestation on the surface finally we discuss unresolved problems in vrancea in order to improve our understanding of the regional evolution present tectonics mantle dynamics intermediate depth seismicity and surface manifestations of the lithosphere dynamics and to enhance our ability to forecast strong earthquakes in the vrancea region the problems to be solved include i the origin of the high velocity body revealed by seismic tomography studies oceanic versus continental ii the lithospheric scale mechanism driving the miocene subsidence of the transylvania basin iii sub crustal structure between 40 and 70 km iv contemporary regional horizontal and vertical movements and v a comprehensive seismic hazard assessment in the region

numerical simulation of the earthquake generation process a numerical algorithm is proposed for the simulation of the earthquake process during a seismic cycle the algorithm is based on a heterogeneous discrete model of the fault plane and assumes there are two kinds of seismicity background crack like earthquakes and asperity like events an active zone of the fault contains an asperity distribution with a characteristic elementary area the background seismicity randomly develops shear stress free surfaces which tend to surround the asperities as in a 2d percolation process the model parameters are taken from observations on the vrancea romania intermediate depth seismic region the results emphasize the significant role of the geometry in the mechanism of the seismic failure the algorithm predicts the nonlinear behavior in the frequency magnitude distribution the decrease of theb slope associated with the asperity like events the magnitude range of major earthquakes and their recurrence times