self driven mode switching of earthquake activity on a fault system theoretical results based on two different modeling approaches indicate that the seismic response of a fault system to steady tectonic loading can exhibit persisting fluctuations in the form of self driven switching of the response back and forth between two distinct modes of activity the first mode is associated with clusters of intense seismic activity including the largest possible earthquakes in the system and frequency size event statistics compatible with the characteristic earthquake distribution the second mode is characterized by relatively low moment release consisting only of small and intermediate size earthquakes and frequency size event statistics following a truncated power law the average duration of each activity mode scales with the time interval of a large earthquake cycle in the system the results are compatible with various long geologic paleoseismic and historical records the mode switching phenomenon may also exist in responses of other systems with many degrees of freedom and nonlinear dynamics 1999 elsevier science b v all rights reserved

stress drops of the 1997 1998 colfiorito central italy earthquakes hints for a common behaviour of normal faults in the apennines stress drop estimates of moderate magnitude earthquakes in the umbria marche region in the northern apennines exhibit a large scatter for the two mw 5 7 and 6 0 main shocks of 26 september 1997 near colfiorito several papers resulted in stress drop estimates of 20 mpa but values as low as 2 3 mpa were proposed as well also for the largest aftershocks mw 4 estimates spread from 1 mpa up to values ten times larger we have critically revisited methods and data used in the literature we have specifically faced the trade off between source and propagation effects as we believe that it is responsible for a part of the large scatter to keep this trade off under control we have applied a methodology that combines the best fit of both source spectra after empirical green s function egf deconvolution and observed ground motion spectra finding that the results of the two different data sets converge independently at the same solution we have used ground motions observed in the colfiorito basin where an accelerograph and a co located seismological broad band station recorded three clusters of earthquakes in a broad magnitude interval 1 7 mw 6 0 we have found that the mainshock aftershock sequences result in stress drops of 2 5 mpa at mw 5 6 with an average tendency to decrease at smaller magnitudes where stress drop variability increases these findings confirm the source scaling recently assessed through empirical green s function deconvolution for another well monitored seismic sequence of normal faulting earthquakes which struck the city of l aquila in the central apennines in april 2009 the similar scaling law of the two areas suggests common mechanisms of stress release for the shallow normal faults in the apennines the propensity of smaller earthquakes to increase in variability with a tendency toward smaller stress drops may reflect an effect of fault strength heterogeneities for smaller size ruptures

seismic and aseismic preparatory processes before large stick slip failure natural earthquakes often have very few observable foreshocks which significantly complicates tracking potential preparatory processes to better characterize expected preparatory processes before failures we study stick slip events in a series of triaxial compression tests on faulted westerly granite samples we focus on the influence of fault roughness on the duration and magnitude of recordable precursors before large stick slip failure rupture preparation in the experiments is detectable over long time scales and involves acoustic emission ae and aseismic deformation events preparatory fault slip is found to be accelerating during the entire pre failure loading period and is accompanied by increasing ae rates punctuated by distinct activity spikes associated with large slip events damage evolution across the fault zones and surrounding wall rocks is manifested by precursory decrease of seismic b values and spatial correlation dimensions peaks in spatial event correlation suggest that large slip initiation occurs by failure of multiple asperities shear strain estimated from ae data represents only a small fraction 1 of total shear strain accumulated during the preparation phase implying that most precursory deformation is aseismic the relative contribution of aseismic deformation is amplified by larger fault roughness similarly seismic coupling is larger for smooth saw cut faults compared to rough faults the laboratory observations point towards a long lasting and continuous preparation process leading to failure and large seismic events the strain partitioning between aseismic and observable seismic signatures depends on fault structure and instrument resolution

earthquake activity related to seismic cycles in a model for a heterogeneous strike slip fault we investigate the evolution of seismicity within large earthquake cycles in a model of a discrete strike slip fault in elastic solid the model dynamics is governed by realistic boundary conditions consisting of constant velocity motion of regions around the fault static kinetic friction and dislocation creep along the fault and 3d elastic stress transfer the fault consists of brittle parts which fail during earthquakes and undergo small creep deformation between events and aseismic creep cells which are characterized by high ongoing creep motion this mixture of brittle and creep cells is found to generate realistic aftershock sequences which follow the modified omori law and scale with the mainshock size furthermore we find that the distribution of interevent times of the simulated earthquakes is in good agreement with observations the temporal occurrence however is magnitude dependent in particular the small events are clustered in time whereas the largest earthquakes occur quasiperiodically averaging the seismicity before several large earthquakes we observe an increase of activity and a broadening scaling range of magnitudes when the time of the next mainshock is approached these results are characteristics of a critical point behavior the presence of critical point dynamics is further supported by the evolution of the stress field in the model which is compatible with the observation of accelerating moment release in natural fault systems

stress slip and earthquakes in models of complex single fault systems incorporating brittle and creep deformations numerical simulations of slip evolution along a cellular vertical strike slip fault in an elastic half space are performed for several models representing discrete fault systems embedded in three dimensional elastic continua the geometry and imposed boundary conditions correspond approximately to the central san andreas fault the simulations incorporate brittle and creep deformations in series the net fault zone deformation rate is the sum of creep rate and frictional slip rate brittle fault properties are given by various distributions of earthquake stress drops on failing segments numerical cells the assumed distributions represent two idealized situations corresponding to different extreme states along an evolutionary path of a fault 1 a strongly disordered state characterized by a wide range of size scales representing immature fault zones and extended spatial domains and 2 a relatively regular state having a narrow range of size scales representing mature highly slipped faults the assumed creep properties are identical in all cases these are prescribed in terms of coefficients characterizing a power law dependency of creep slip rate on stress the combined brittle creep process and employed parameters lead to an overall pine tree stress depth profile with a brittle ductile transition depth of about 12 5 km and variable stress along strike profiles with brittle creep transition around 65 km nw of the 1857 rupture the spatial patterns of simulated hypocenters are statistically similar to observed data the results indicate that the range of size scales characterizing strong fault zone heterogeneities has important manifestations on the seismic response of a fault system a narrow range of size scales leads to frequency size statistics of earthquakes resembling the characteristic earthquake distribution and quasi periodic temporal distribution of large events as in the seismic gap hypothesis on the other hand a wide range of size scales leads to gutenberg richter power law frequency size statistics and random or clustered temporal distribution of large events the simulations demonstrate that treatment of the various observed forms of frequency size and temporal statistics of earthquakes can be unified through the concept of range of size scales characterizing fault zone heterogeneities this has a clear physical interpretation in terms of structural properties of a given fault zone or broad lithospheric domain and is supported by observed earthquake and fault data in some simulated cases the frequency size statistics of small earthquakes fall sharply below the self similar gutenberg richter line the results indicate that small earthquakes prepare the fault for the occurrence of a large event by smoothing during gradual tectonic loading the long wavelength components of stress on the fault this is done through short wavelength stress roughening associated with the numerous ruptures of the small events the above pattern of smoothing roughening of long short wavelengths of stress on the fault is reversed during large scale ruptures of the big events

accelerating seismic release from a self correcting stochastic model 1 we investigate the conditions under which the stress release model a stochastic version of the elastic rebound model produces synthetic earthquake sequences characterized by accelerating seismic release asr in this model the level or stress of the process accumulates linearly with time through tectonic input and decreases as the result of earthquakes these stress drops correspond to some power of the energy released in the earthquakes either e0 5 benioff strain or e seismic moment earthquakes occur in a point process with rate controlled by the level of the process we hypothesize that the critical factor in the appearance of asr is the manner in which the event sizes depend on the level of the process this is modeled by the square root of energy released following either a tapered pareto or truncated gutenberg richter distribution with maximum earthquake size controlled by a tail off or truncation point as the tail off point becomes large so does the average size corresponding to an acceleration to criticality of the system we found that those cases where the underlying level of the process corresponded to accumulated seismic moment produced numerous asr sequences whereas those cases using accumulated benioff strain as the level did not these results suggest that the occurrence of asr is strongly dependent on how large earthquakes affect the dynamics of the fault system in which they are embedded and hopefully provide some insight into the mechanics of acceleration to criticality i e on the possible causes of occurrence nonoccurrence of asr

statistical physics seismogenesis and seismic hazard the scaling properties of earthquake populations show remarkable similarities to those observed at or near the critical point of other composite systems in statistical physics this has led to the development of a variety of different physical models of seismogenesis as a critical phenomenon involving locally nonlinear dynamics with simplified rheologies exhibiting instability or avalanche type behavior in a material composed of a large number of discrete elements in particular it has been suggested that earthquakes are an example of a self organized critical phenomenon analogous to a sandpile that spontaneously evolves to a critical angle of repose in response to the steady supply of new grains at the summit in this stationary state of marginal stability the distribution of avalanche energies is a power law equivalent to the gutenberg richter frequency magnitude law and the behavior is relatively insensitive to the details of the dynamics here we review the results of some of the composite physical models that have been developed to simulate seismogenesis on different scales during 1 dynamic slip on a preexisting fault 2 fault growth and 3 fault nucleation the individual physical models share some generic features such as a dynamic energy flux applied by tectonic loading at a constant strain rate strong local interactions and fluctuations generated either dynamically or by fixed material heterogeneity but they differ significantly in the details of the assumed dynamics and in the methods of numerical solution however all exhibit critical or near critical behavior with behavior quantitatively consistent with many of the observed fractal or multifractal scaling laws of brittle faulting and earthquakes including the gutenberg richter law some of the results are sensitive to the details of the dynamics and hence are not strict examples of self organized criticality nevertheless the results of these different physical models share some generic statistical properties similar to the universal behavior seen in a wide variety of critical phenomena with significant implications for practical problems in probabilistic seismic hazard evaluation in particular the notion of self organized criticality or near criticality gives a scientific rationale for the a priori assumption of stationarity used as a first step in the prediction of the future level of hazard the gutenberg richter law a power law in energy or seismic moment is found to apply only within a finite scale range both in model and natural seismicity accordingly the frequency magnitude distribution can be generalized to a gamma distribution in energy or seismic moment a power law with an exponential tail this allows extrapolations of the frequency magnitude distribution and the maximum credible magnitude to be constrained by observed seismic or tectonic moment release rates the answers to other questions raised are less clear for example the effect of the a priori assumption of a poisson process in a system with strong local interactions and the impact of zoning a potentially multifractal distribution of epicentres with smooth polygons the results of some models show premonitory patterns of seismicity which could in principle be used as mainshock precursors however there remains no consensus on both theoretical and practical grounds on the possibility or otherwise of reliable intermediate term earthquake prediction

a note on adding viscoelasticity to earthquake simulators abstract here i describe how time dependent quasi static stress transfer can be implemented in an earthquake simulator code that is used to generate long synthetic seismicity catalogs most existing seismicity simulators use precomputed static stress interaction coefficients to rapidly implement static stress transfer in fault networks with typically tens of thousands of fault patches the extension to quasi static deformation which accounts for viscoelasticity of earth s ductile lower crust and mantle involves the precomputation of additional interaction coefficients that represent time dependent stress transfer among the model fault patches combined with defining and evolving additional state variables that track this stress transfer the new approach is illustrated with application to a california wide synthetic fault network

8000 years of environmental evolution of barrier lagoon systems emplaced in coastal embayments nw iberia the rocky and indented coast of nw iberia is characterized by the presence of highly valuable and vulnerable small and shallow barrier lagoon systems structurally controlled the case study was se

critical behaviour and the evolution of fault strength during earthquake cycles the problem of how fault rheology and heterogeneity interact to produce the observed scaling of earthquakes such as the power law moment frequency relationship remains largely unsolved rock friction experiments have elucidated the properties of smooth faults1 2 3 but seem insufficient to explain the observed complexity of real fault dynamics4 5 the recognition of a connection between fault related processes and critical phenomena in other physical systems together with numerical models of repeated earthquakes have resulted in significant progress in the theoretical interpretation of earthquake scaling4 5 6 7 8 9 10 11 12 13 14 but fault rheology and heterogeneity have so far been treated separately here i attempt to unify the requirements of fault rheology and heterogeneity using numerical calculations of quantized slip in an elastic continuum i show that cyclical fault strength evolves naturally by means of a statistical selection for high strength fault patches asperities resulting in the accumulation and eventual failure of those asperities the applicability of these results to real fault systems is supported by a recent analysis of time dependent earthquake statistics15 these results imply that self similarity and criticality on a fault emerge during an earthquake cycle and suggest that the character of local seismicity can be useful in earthquake forecasting by revealing how advanced a fault is within its cycle

a systematic spatiotemporal test of the critical point hypothesis for large earthquakes 1 the critical point hypothesis for large earthquakes predicts two different precursory phenomena in space and time an accelerating moment release and the growth of the spatial correlation length the objective of this work is to investigate both methods with respect to their predictive power a systematic statistical test based on appropriate random earthquake catalogs allows to quantify the correlations of a precursory pattern with the subsequent mainshock activity the analysis of target earthquakes in california since 1960 with magnitudes m mcut reveals that these correlations increase systematically with growing mcut and correlations at greater than 95 confidence are observed for mcut 6 5 in the case of the spatial correlation length in particular the seismicity patterns are found to be significantly correlated with each of the largest earthquakes m 7 0 individually the acceleration of the moment release has a similar trend but is less significant

examination of scaling between proposed early signals in p waveforms and earthquake magnitudes summary we examine seismic waveforms generated by clusters of similar earthquakes and additional events located on the karadere duzce branch of the north anatolian fault to investigate possible scaling between proposed early signals in the p waveforms and magnitudes the employed signals can be divided into two classes the first is associated with ellsworth beroza and iio type signals that are assumed to reflect signatures of seismic nucleation phases the second are associated with nakamura type period and wu zhao type maximum displacement in the early waveforms that are related to measures of the corner frequency and local magnitude respectively the impact on each signal of artefacts generated by the finite impulse response fir filter is also examined the use of repeating event clusters reduces considerably the variability of path and site effects compared to previous regional and global studies this allows us to focus more accurately on variations of the potential scaling parameters with the source magnitude however the magnitude range of the employed events is limited to about 4 units the fir filter artefacts can generate spurious signals prior to the p wave arrival potentially affecting the ellsworth beroza type signals but are not a significant influence on any of the other measurements the results indicate that candidates for the ellsworth beroza signals associated with identification of a weak arrival before the main p phase exist in less than 20 per cent of the cases the iio type signals can be determined by definition on all waveforms both of these potential signatures of nucleation phases show little or no scaling with the final event size in the examined data in contrast the nakamura and wu zhao type signals in the first few seconds which can also be determined by definition on all waveforms appear to scale with the final event magnitude albeit with large scatter the relatively large time windows used in the analysis compared to the rupture time of the employed events implies that the results provide little if any information on the physical process of the rupture initiation the scaling of the nakamura and wu zhao type early signals with the final event size may be explained by statistical tendency of stronger initial rupture phases to propagate larger distances

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

episodic tremor and slip on a frictional interface with critical zero weakening in elastic solid summary non volcanic tremor nvt and related relatively weak and slow slip events termed episodic tremor and slip ets are observed below the seismogenic sections of numerous subduction zones and several major strike slip faults these events have various characteristics that distinguish them from regular tectonic earthquakes here we show that a frictional fault in elastic solid with a region below the seismogenic zone having on average a critical near zero weakening during slip provides a simple unified explanation for the diverse observed phenomenology of nvt ets the results imply that nvt ets have little predictive power on the occurrence of large events in the overriding seismogenic zone additional model predictions that may be tested with future high resolution observations are fractal slip distributions and failure areas discrete power law frequency moment statistics with exponent 3 2 and exponential tapering overall scale invariant potency moment magnitude time histories triggered periodic nvt with evolving size and rate correlated with the stressing rate of the periodic triggering mechanisms and parabolic or exponential source time functions for event sizes measured by duration or moment potency

evolving towards a critical point a review of accelerating seismic moment energy release prior to large and great earthquakes there is growing evidence that some proportion of large and great earthquakes are preceded by a period of accelerating seismic activity of moderate sized earthquakes these moderate earthquakes occur during the years to decades prior to the occurrence of the large or great event and over a region larger than its rupture zone the size of the region in which these moderate earthquakes occur scales with the size of the ensuing mainshock at least in continental regions a number of numerical simulation studies of faults and fault systems also exhibit similar behavior the combined observational and simulation evidence suggests that the period of increased moment release in moderate earthquakes signals the establishment of long wavelength correlations in the regional stress field the central hypothesis in the critical point model for regional seismicity is that it is only during these time periods that a region of the earth s crust is truly in or near a self organized critical soc state such that small earthquakes are capable of cascading into much larger events the occurrence of a large or great earthquake appears to dissipate a sufficient proportion of the accumulated regional strain to destroy these long wavelength stress correlations and bring the region out of a soc state continued tectonic strain accumulation and stress transfer during smaller earthquakes eventually re establishes the long wavelength stress correlations that allow for the occurrence of larger events these increases in activity occur over longer periods and larger regions than quiescence which is usually observed within the rupture zone of a coming large event the two phenomena appear to have different physical bases and are not incompatible with one another

a physical model for strain accumulation in the san francisco bay region stress evolution since 1838 1 understanding of the behavior of plate boundary zones has progressed to the point where reasonably comprehensive physical models can predict their evolution the san andreas fault system in the san francisco bay region sfbr is dominated by a few major faults whose behavior over about one earthquake cycle is fairly well understood by combining the past history of large ruptures on sfbr faults with a recently proposed physical model of strain accumulation in the sfbr we derive the evolution of regional stress from 1838 until the present this effort depends on 1 an existing compilation of the source properties of historic and contemporary sfbr earthquakes based on documented shaking geodetic data and seismic data bakun 1999 and 2 a few key parameters of a simple regional viscoelastic coupling model constrained by recent gps data pollitz and nyst 2004 although uncertainties abound in the location magnitude and fault geometries of historic ruptures and the physical model relies on gross simplifications the resulting stress evolution model is sufficiently detailed to provide a useful window into the past stress history in the framework of coulomb failure stress we find that virtually all m 5 8 earthquakes prior to 1906 and m 5 5 earthquakes after 1906 are consistent with stress triggering from previous earthquakes these events systematically lie in zones of predicted stress concentration elevated 5 10 bars above the regional average the sfbr is predicted to have emerged from the 1906 shadow in about 1980 consistent with the acceleration in regional seismicity at that time the stress evolution model may be a reliable indicator of the most likely areas to experience m 5 5 shocks in the future index terms 1206 geodesy and gravity crustal movements interplate 8155 1236 geodesy and gravity rheology of the lithosphere and mantle 8160 1243 geodesy and gravity space geodetic surveys keywords crustal deformation plate boundary zones viscoelastic relaxation san francisco bay region

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

dynamic simulations of slip on a smooth fault in an elastic solid we report on numerical simulations of slip evolution along a two dimensional slip varies only with depth vertical strike slip fault in an elastic half space using a framework incorporating full inertial elastodynamics the model is a follow up on earlier quasi static and quasi dynamic simulations of deformations along smooth fault systems in elastic continua the fault is driven below a crustal depth of 24 km by a constant plate velocity of 35 mm yr deformation at each fault location in the crustal zone is the sum of slip rate contributions from rate and state dependent friction and power law creep where both processes have temperature dependent and hence depth varying coefficients and both take place locally under the same stress the simulations employ two versions of rate and state dependent friction a slip law which requires nonzero velocity for state evolution and an ageing slowness law which incorporates state evolution and restrengthening in stationary contact the assumed constitutive laws and distribution of frictional parameters are compatible with laboratory experiments the elastodynamic calculations are based on spectral representations of variables and a new algorithm providing a unified computational framework for calculations of long deformational histories containing short periods of rapid instabilities the simulations show dynamic rupture propagation and wave phenomena not accounted for in the previous quasi static and quasi dynamic works however the results are qualitatively similar to those obtained by corresponding quasi static and quasi dynamic calculations slip histories along a smooth fault simulated here with full elastodynamics for various constitutive laws and model parameters consist mostly of quasi periodic large events this finding indicates that inertial dynamics does not provide a generic mechanism for generating spatio temporal complexities of slip on the other hand calculations done for cases representing approximately strongly disordered systems do show rich slip histories with a range of event sizes this result is compatible with our previous conclusions that the origin of observed broad distributions of earthquake sizes is strong fault zone heterogeneities the fully dynamic calculations illustrate the evolution of nucleation phases of instabilities associated with accelerating and expanding creep final slip values of model earthquakes in full elastodynamic calculations are larger than those of corresponding quasi static and quasi dynamic events the dynamic overshoot in simulations with the slip version of friction is larger than in those employing the ageing slowness law

seismicity in a model governed by competing frictional weakening and healing mechanisms summary observations from laboratory field and numerical work spanning a wide range of space and time scales suggest a strain dependent progressive evolution of material properties that control the stability of earthquake faults the associated weakening mechanisms are counterbalanced by a variety of restrengthening mechanisms the efficiency of the healing processes depends on local material properties and on rheologic temperature and hydraulic conditions we investigate the relative effects of these competing non linear feedbacks on seismogenesis in the context of evolving frictional properties using a mechanical earthquake model that is governed by slip weakening friction weakening and strengthening mechanisms are parametrized by the evolution of the frictional control variable the slip weakening rate r using empirical relationships obtained from laboratory experiments in our model weakening depends on the slip of an earthquake and tends to increase r following the behaviour of real and simulated frictional interfaces healing causes r to decrease and depends on the time passed since the last slip results from models with these competing feedbacks are compared with simulations using non evolving friction compared to fixed r conditions evolving properties result in a significantly increased variability in the system dynamics we find that for a given set of weakening parameters the resulting seismicity patterns are sensitive to details of the restrengthening process such as the healing rate b and a lower cutoff time t c up to which no significant change in the friction parameter is observed for relatively large and small cutoff times the statistics are typical of fixed large and small r values respectively however a wide range of intermediate values leads to significant fluctuations in the internal energy levels the frequency size statistics of earthquake occurrence show corresponding non stationary characteristics on time scales over which negligible fluctuations are observed in the fixed r case the progressive evolution implies that except for extreme weakening and healing rates faults and fault networks possibly are not well characterized by steady states on typical catalogue time scales thus highlighting the essential role of memory and history dependence in seismogenesis the results suggest that an extrapolation to future seismicity occurrence based on temporally limited data may be misleading due to variability in seismicity patterns associated with competing mechanisms that affect fault stability

techniques and parameters to analyze seismicity patterns associated with large earthquakes a pattern recognition algorithm is developed to provide potential improvements over existing earthquake prediction practices the parameters employed in the analysis include degree of spatial nonrandomness in two distance ranges spatial correlation dimension spatial repetitiveness of earthquakes with a similar size average depth of events time interval for the occurrence of a constant number of events and ratio of the numbers of events in two magnitude intervals the parameter temporal variations are compared quantitatively with the time series of large events using a technique of association in time the significance of the association frequencies is evaluated by comparison with chance associations estimated from corresponding simulated random time series the developed techniques differ from existing approaches in the following aspects the parameters here emphasize the spatial distribution of earthquakes possible correlations among the parameters are evaluated to determine the final set of parameters to be monitored threshold values for the assumed anomalies are chosen with consideration of properties of the available earthquake catalogs such as the number of large events to be retrospectively predicted equal weight is given to both locally high and locally low parameter values care is taken to distinguish between anomalies preceding large events and those following previous events it is shown that the relationship between precursory local extrema and precursory trends is nonunique with precursory local extrema of the same type frequently associated with opposite observable precursory trends the application of the seismicity parameters and pattern recognition techniques is demonstrated using synthetic earthquake catalogs generated by models of segmented fault systems in a three dimensional elastic solid ben zion 1996

earthquake cycle fault zones and seismicity patterns in a rheologically layered lithosphere we study the coupled evolution of earthquakes and faults in a model consisting of a seismogenic upper crust governed by damage rheology over a viscoelastic substrate the damage rheology has two types of functional coefficients 1 a generalized internal friction separating states associated with material degradation and healing and 2 damage rate coefficients for positive degradation and negative healing changes the evolving damage modifies the effective elastic properties of material in the upper crust as a function of the ongoing deformation this simulates the creation and healing of fault systems in the upper seismogenic zone in addition to the vertically averaged thin sheet approximation we introduce a green function for three dimensional elastic half space for the instantaneous component of deformation the formulation accounts in an internally consistent manner for evolving deformation fields evolving fault structures aseismic energy release and spatiotemporal seismicity patterns these developments allow us to simulate long histories of crustal deformation and to study the simultaneous evolution of regional earthquakes and faults for various model realizations to focus on basic features of a large strike slip fault system we first consider a simplified geometry of the seismogenic crust by prescribing initial conditions consisting of a narrow damage zone in an otherwise damage free plate for this configuration the model generates an earthquake cycle with distinct interseismic preseismic coseismic and postseismic periods model evolution during each period is controlled by a subset of physical properties which may be constrained by geophysical geodetic rock mechanics and seismological data in the more generic case with a random initial damage distribution the model generates large crustal faults and subsidiary branches with complex geometries the simulated statistics depend on the space time window of the observational domain the results indicate that long healing timescale h describing systems with relatively long memory leads to the development of geometrically regular fault systems and the characteristic frequency size earthquake distribution conversely short h relatively short memory leads to the development of a network of disordered fault systems and the gutenberg richter earthquake statistics for intermediate values of h the results exhibit alternating overall switching of response from periods of intense seismic activity and the characteristic earthquake distribution to periods of low seismic activity and gutenberg richter statistics

a physical model for strain accumulation in the san francisco bay region summary strain accumulation in tectonically active regions is generally a superposition of the effects of background tectonic loading steady state dislocation processes such as creep and transient deformation in the san francisco bay region sfbr the most uncertain of these processes is transient deformation which arises primarily in association with large earthquakes as such it depends upon the history of faulting and the rheology of the crust and mantle which together determine the pattern of longer term decade scale post seismic response to earthquakes we utilize a set of 102 gps velocity vectors in the sfbr in order to characterize the strain rate field and construct a physical model of its present deformation we first perform an inversion for the continuous velocity gradient field from the discrete gps velocity field from which both tensor strain rate and rotation rate may be extracted the present strain rate pattern is well described as a nearly uniform shear strain rate oriented approximately n34 w 140 nanostrain yr 1 plus a n56 e uniaxial compression rate averaging 20 nanostrain yr 1 across the shear zone we fit the velocity and strain rate fields to a model of time dependent deformation within a 135 km wide arcuate shear zone bounded by strong pacific plate and sierra nevada block lithosphere to the sw and ne respectively driving forces are purely lateral consisting of shear zone deformation imposed by the relative motions between the thick pacific plate and sierra nevada block lithospheres assuming a depth dependent viscoelastic structure within the shear zone we account for the effects of steady creep on faults and viscoelastic relaxation following the 1906 san francisco and 1989 loma prieta earthquakes subject to constant velocity boundary conditions on the edges of the shear zone fault creep is realized by evaluating dislocations on the creeping portions of faults in the fluid limit of the viscoelastic model a priori plate boundary pb parallel motion is set to 38 mm yr 1 ag rid search based on fitting the observed strain rate pattern yields a mantle viscosity of 1 2 10 19 p as and a pb perpendicular convergence rate of 3m m yr 1 most of this convergence appears to be uniformly distributed in the pacific sierra nevada plate boundary zone

implications of a statistical physics approach for earthquake hazard assessment and forecasting there is accumulating evidence that distributed seismicity is a problem in statistical physics seismicity is taken to be a type example of self organized criticality this association has important implications regarding earthquake hazard assessment and forecasting a characteristic of a thermodynamic system is that it exhibits a background noise that is self organized in the case of a dilute gas this self organization is the maxwell boltzmann distribution of molecular velocities in seismicity it is the gutenberg richter frequency magnitude scaling this scaling is fractal observations favor the hypothesis that smaller earthquakes in moderate sized regions occur at rates that are only weakly dependent on time thus the rate of occurrence of smaller earthquakes can be extrapolated to assess the hazard of larger earthquakes in a region we obtain the rate of occurrence of earthquakes with m 4 in 1 1 areas from the neic catalog using only this data we produce global maps of the seismic hazard observations also favor the hypothesis that the stress level at which an earthquake occurs is a second order critical point as a critical point is approached correlations extend over increasingly larger distances in terms of seismicity the approach to a critical point is associated with an increase in the rate of occurrence of intermediate sized earthquakes prior to a large earthquake this precursory activation has been shown to exhibit power law scaling and to occur over a region about ten times larger than the rupture length of the large earthquake analyses of the spinoidal behavior associated with second order critical points predict the power law increase in seismic activity prior to a characteristic earthquake this precursory activation provides the basis for intermediate range earthquake forecasting

probabilistic prediction of rupture length slip and seismic ground motions for an ongoing rupture implications for early warning for large earthquakes earthquake earlywarning eew predicts future ground shaking based on presently available data long ruptures present the best opportunities for eew since many heavily shaken areas are distant from the earthquake epicentre and may receive long warning times predicting the shaking from large earthquakes however requires some estimate of the likelihood of the future evolution of an ongoing rupture an eew system that anticipates future rupture using the present magnitude or rupture length together with the gutenberg richter frequencysize statistics will likely never predict a large earthquake because of the rare occurrence of extreme events however it seems reasonable to assume that large slip amplitudes increase the probability for evolving into a large earthquake to investigate the relationship between the slip and the eventual size of an ongoing rupture we simulate suites of 1 d rupture series from stochastic models of spatially heterogeneous slip we find that while large slip amplitudes increase the probability for the continuation of a rupture and the possible evolution into a big one the recognition that rupture is occurring on a spatially smooth fault has an even stronger effect we conclude that aneewsystem for large earthquakes needs some mechanism for the rapid recognition of the causative fault e g from real time gps measurements and consideration of its smoothness an eew system for large earthquakes on smooth faults such as the san andreas fault could be implemented in two ways the system could issue a warning whenever slip on the fault exceeds a few metres because the probability for a large earthquake is high and strong shaking is expected to occur in large areas around the fault a more sophisticated eew system could use the present slip on the fault to estimate the future slip evolution and final rupture dimensions and using this information could provide probabilistic predictions of seismic ground motions along the evolving rupture the decision on whether an eew system should be realized in the first or in the second way or in a combination of both is user specific

seismicity on a fault controlled by rate and state dependent friction with spatial variations of the critical slip distance 1 we perform systematic simulations of slip using a quasi dynamic continuum model of a two dimensional 2 d strike slip fault governed by rate and state dependent friction the depth dependence of the a b and l frictional parameters are treated in an innovative way that is consistent with available laboratory data and multidisciplinary field observations various realizations of heterogeneous l distributions are used to study effects of structural variations of fault zones on spatiotemporal evolution of slip we demonstrate that such realizations can produce within the continuum class of models realistic features of seismicity and slip distributions on a fault we explore effects of three types of variable l distributions 1 a depth dependent l profile accounting for the variable width of fault zones with depth 2 uncorrelated 2 d random distributions of l with different degrees of heterogeneity and 3 a hybrid distribution combining the depth dependent l profile with the 2 d random l distributions the first type of l distribution with relatively small l over the depth range corresponding to the seismogenic zone and larger l elsewhere generates stick slip events in the seismogenic zone and ongoing creep above and below that region the 2 d heterogeneous parameterizations generate frequency size statistics with event sizes spanning 4 orders of magnitude our results indicate that different degrees of heterogeneity of l distributions control 1 the number of simulated events and 2 the overall stress level and fluctuations other observable trends are 3 the dependency of hypocenter location on l and 4 different nucleation phases for small and large events in heterogeneous distributions

discriminating characteristics of tectonic and human induced seismicity we analyze statistical features of background and clustered subpopulations of earthquakes in different regions in an effort to distinguish between human induced and natural seismicity analysis of end member areas known to be dominated by human induced earthquakes the geyser geothermal field in northern california and tautona gold mine in south africa and regular tectonic activity the san jacinto fault zone in southern california and the coso region excluding the coso geothermal field in eastern central california reveals several distinguishing characteristics induced seismicity is shown to have 1 higher rate of background events both absolute and relative to the total rate 2 faster temporal offspring decay 3 higher rate of repeating events 4 larger proportion of small clusters and 5 larger spatial separation between parent and offspring compared to regular tectonic activity these differences also successfully discriminate seismicity within the coso and salton sea geothermal fields in california before and after the expansion of geothermal production during the 1980s online material figures of examined regions earthquake epicenters and joint distributions of the time and space components of the nearest neighbor distance

seismicity and stress evolution in heterogeneous faults with various degrees of roughness abstract we investigate the effects of the spatial distribution of stress drop ratios sdrs on the fault of an earthquake sequence as well as stress evolution to achieve this we test four fault models each with its own sdrs which differ with regard to wavelength components roughness but which share first order similarity and the same mean value we assume rupture processes are quasi static and fluid controlled the evidence clearly shows that the locations of large earthquakes are more sensitive to distribution than to the values of the sdrs for this reason it is expected that reducing fault roughness should increase the number of large earthquakes but decrease the number of small ones it is also clearly apparent that a clustered distribution of large earthquakes should be more frequently observed on heterogeneous faults especially in areas with small gradient values of the sdrs these phenomena are consistent with our finding that long wavelength components of stress usually develop in areas with low gradients of the sdrs a fault with a smoother distribution of sdrs should therefore exhibit a greater likelihood to generate large earthquakes by contrast in that a rough fault covers a smaller area on which long wavelengths can develop it should result in fewer large earthquakes but a much more highly clustered distribution

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

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

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

the seismic cycle and the difference between foreshocks and aftershocks in a mechanical fault model 1 we examine the evolution of and the exchange between two forms of elastic energies stored in the quasi static fault model of ziv and rubin 2003 the first etect is due to the integrated slip deficit accumulated between the plate boundaries and the fault surface and the second efault is the result of differential slip along the fault surface the results of our analysis reveal cyclic exchange between the two energies on a efault versus etect plot the seismic cycle has a triangular shape with the large earthquakes occurring at the top corner of the triangle where efault is maximum and the foreshocks and the aftershocks occupying the right side and left side respectively while both foreshocks and aftershocks dissipate tectonic energies the cumulative effect of the foreshocks is to increase the potential elastic energy along the fault plane and the cumulative effect of the aftershocks is to reduce it

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

physical basis for statistical patterns in complex earthquake populations models predictions and tests understanding the physics of earthquakes and the space time patterns they produce is illuminated by the use of coarse grained models and simulations that capture the basic physical processes and that are amenable to analysis we present a summary of ideas that describe the nucleation growth and arrest of earthquakes on individual faults under shear loading we find that faults reside in a metastable state near a classical spinodal that governs the nucleation and growth of slip events the roughness of an associated stress distribution field x t determines whether slip events are confined within the initial high stress patch or break away and grow to become very large we find a critical value of roughness that is associated with a first order order disorder transition we also give a number of predictions examples and applications of these ideas and indicate how they might be tested through systematic observational programs

dilatancy controlled spatiotemporal slip evolution of a sealed fault with spatial variations of the pore pressure summary a range of observations suggest the formation and maintenance of sealed and hence overpressured compartments in fluid infiltrated fault zones it is assumed that hydromechanical properties of regions with variable pore pressure states control the fault s stability and thus its characteristic response that is seismic or aseismic slip accumulation we investigate in a systematic parameter space study the effects of spatial variations in pore pressure on spatiotemporal slip evolution along a hydraulically isolated fault plane the 3 d continuum model is governed by rate and state friction and constitutive laws for porosity reduction we show that the model response is sensitive to the degree of overpressurization and the efficiency of dilatant hardening mechanisms low pore pressures and small dilatancy effects result in unstable response types whereas high pore pressures and large dilatant effects lead to stable and aseismic creep regions with an unstable response are shown to support most of the stresses accumulated during interseismic periods accelerated slip nucleates preferably in regions of low pore pressure statistical properties of model seismicity produce a wide range of event sizes for moderate and large earthquakes in the case where dilatant mechanisms are inefficient in case of efficient slip rate controlled porosity increase less instabilities grow into large earthquakes final slip maps demonstrate the applicability of the chosen method to model seismicity controlled by frictional and hydraulic processes on a planar fault plane the evolution of governing variables that depend on the pore pressure environment provide a conceptual basis for the interpretation of observed response characteristics

statistics of earthquake stress drops on a heterogeneous fault in an elastic half space we investigate properties of earthquake stress drops in simulations of evolving seismicity and stress field on a heterogeneous fault the model consists of an inherently discrete strike slip fault surrounded by a 3d elastic half space we consider various spatial distributions of frictional properties and analyze results generated by 150 300 model years in all cases the self organized heterogeneous initial stress distributions at the times of earthquake failure lead to stress drops that are systematically lower than those predicted for a homogeneous process in particular the large system sized events have stress drops that are consistently 25 of predictions based on the average fault strength the type and amount of assumed spatial heterogeneity on the fault affect the stress drop statistics of small earthquakes m l 5 more than those of the larger events this produces a decrease in the range of stress drops as the earthquake magnitudes increase the results can resolve the discrepancy between traditional estimates of stress drops and seismological observations the general tendency for low stress drops of large events provides a rationale for reducing the statistical estimates of potential ground motion associated with large earthquakes

quantifying focal mechanism heterogeneity for fault zones in central and southern california summary we present a statistical analysis of focal mechanism orientations for nine california fault zones with the goal of quantifying variations of fault zone heterogeneity at seismogenic depths the focal mechanism data are generated from first motion polarities for earthquakes in the time period 1983 2004 magnitude range 0 5 and depth range 0 15 km only mechanisms with good quality solutions are used we define fault zones using 20 km wide rectangles and use summations of normalized potency tensors to describe the distribution of double couple orientations for each fault zone focal mechanism heterogeneity is quantified using two measures computed from the tensors that relate to the scatter in orientations and rotational asymmetry or skewness of the distribution we illustrate the use of these quantities by showing relative differences in the focal mechanism heterogeneity characteristics for different fault zones these differences are shown to relate to properties of the fault zone surface traces such that increased scatter correlates with fault trace complexity and rotational asymmetry correlates with the dominant fault trace azimuth these correlations indicate a link between the long term evolution of a fault zone over many earthquake cycles and its seismic behaviour over a 20 yr time period analysis of the partitioning of san jacinto fault zone focal mechanisms into different faulting styles further indicates that heterogeneity is dominantly controlled by structural properties of the fault zone rather than time or magnitude related properties of the seismicity

large earthquake cycles and intermittent criticality on heterogeneous faults due to evolving stress and seismicity 1 we analyze evolving stress and seismicity generated by three realizations of a discrete model of a strike slip fault in a three dimensional 3 d elastic half space using five functions of stress and five functions of seismicity the first model f has realistic dynamic weakening static minus dynamic frictions the second fc has zero critical dynamic weakening and the third sys is constrained to produce only system size events the results for model f show cyclical development saturation and destruction of fluctuations and long range correlations on the fault punctuated by the system size events the development stage involves evolution of stress and seismicity to distributions having broad ranges of scales evolution of response functions toward scale invariant behavior increasing seismicity rate and event sizes and increasing hypocenter diffusion most functions reach asymptotically stable values around 2 3 of the cycle and then fluctuate until one event cascades to become the next large earthquake in model fc the above evolution is replaced by scale invariant statistical fluctuations while in model sys the signals show simple cyclic behavior the results suggest that large earthquake cycles on heterogeneous faults with realistic positive dynamic weakening are associated with intermittent criticality produced by spontaneous evolution of stress heterogeneities toward a critical level of disorder having a broad range of scales the stress evolution and development of large earthquake cycles may be tracked with seismicity functions

objective estimation of spatially variable parameters of epidemic type aftershock sequence model application to california the etas model is widely employed to model the spatio temporal distribution of earthquakes generally using spatially invariant parameters we propose an efficient method for the estimation of spatially varying parameters using the expectation maximization em algorithm and spatial voronoi tessellation ensembles we use the bayesian information criterion bic to rank inverted models given their likelihood and complexity and select the best models to finally compute an ensemble model at any location using a synthetic catalog we also check that the proposed method correctly inverts the known parameters we apply the proposed method to earthquakes included in the anss catalog that occurred within the time period 1981 2015 in a spatial polygon around california the results indicate significant spatial variation of the etas parameters we find that the efficiency of earthquakes to trigger future ones quantified by the branching ratio positively correlates with surface heat flow in contrast the rate of earthquakes triggered by far field tectonic loading or background seismicity rate shows no such correlation suggesting the relevance of triggering possibly through fluid induced activation furthermore the branching ratio and background seismicity rate are found to be uncorrelated with hypocentral depths indicating that the seismic coupling remains invariant of hypocentral depths in the study region additionally triggering seems to be mostly dominated by small earthquakes consequently the static stress change studies should not only focus on the coulomb stress changes caused by specific moderate to large earthquakes but also account for the secondary static stress changes caused by smaller earthquakes

mississippi valley type mineralization in the silurian paleoaquifer central appalachians this study used lead and sulfur isotope tracers to determine the nature and geometry of mvt related brine flow in the silurian paleoaquifer of the central appalachians although the stratigraphy and lithology of this sedimentary package is similar to that of the important lower cambrian mvt hosting paleoaquifer of the southern appalachians it lacks important mineralization lead isotope compositions from mvt deposits in the lockport dolomite in the upper part of the silurian paleoaquifer form a cluster at about 206pb204pb 18 3 207pb204pb 15 6 and 208pb204pb 38 2 which is similar in form but slightly different in composition from those seen in deposits in underlying clastic rocks sulfur isotope compositions for lockport mvt sulfides range from 19 to 6 and have lower 34s values than mvt sulfides hosted by underlying clastic rocks these relations in combination with na cl br compositions of fluid inclusion leachates suggest that mvt deposits in the lower part of the paleoaquifer formed when rising metal bearing brines intersected reduced sulfur of probable thermogenic origin whereas deposits in the upper part of the paleoaquifer lockport dolomite formed where metal bearing brines intersected reduced sulfur of biogenic origin that was dissolved from sulfate evaporites in the overlying salina group and transported downward into the lockport