earthquake rupture complexity due to dynamic nucleation and interaction of subsidiary faults we numerically study the dynamic interaction of propagating cracks it is assumed that propagating cracks can nucleate and drive subsidiary cracks because of shear strain enhancement near the propagating crack tips the critical strain fracture criterion is assumed in the analysis intense interaction is expected to occur among the cracks all the cracks are assumed to be parallel and antiplane strain deformation is assumed in the computation

fractal structure of spatial distribution of microfracturing in rock summary a constant stress fracture experiment of oshima granite was carried out at the confining pressure of 40mpa hypocentres of 2064 acoustic emissions were located during the experiment using the correlation integral we found that the spatial distribution of hypocentres of acoustic emission is a fractal and that the fractal dimension decreases with the evolution of rock fracturing the spatial distribution of earthquake s hypocentres reveals fractals ranging from regional to worldwide distribution if we extrapolate from laboratory measurements it is possible to predict the occurrence of large earthquakes by the decrease in the fractal dimension

dynamic nucleation process of shallow earthquake faulting in a fault zone two distinct phases are commonly observed at the initial part of seismograms of large shallow earthquakes low frequency and low amplitude waves following the onset of a p wave p1 are interrupted by the arrival of the second impulsive phase p2 enriched with high frequency components this observation suggests that a large shallow earthquake involves two qualitatively different stages of rupture at its nucleation we propose a theoretical model that can naturally explain the above nucleation behaviour the model is 2 d and the deformation is assumed to be anti plane a key clement in our model is the assumption of a zone in which numbers of pre existing cracks are densely distributed this cracked zone is a model for the fault zone dynamic crack growth nucleated in such a zone is intensely affected by the crack interactions which exert two conflicting effects one tends to accelerate the crack growth and the other tends to decelerate it the accelerating and decelerating effects are generally ascribable to coplanar and non coplanar crack interactions respectively we rigorously treat the multiple interactions among the cracks using the boundary integral equation method biem and assume the critical stress fracture criterion for the analysis of spontaneous crack propagation our analysis shows that a dynamic rupture nucleated in the cracked zone begins to grow slowly due to the relative predominance of non coplanar interactions this process radiates the p1 phase if the crack continues to grow coalescence with adjacent coplanar cracks occurs after a short time then coplanar interactions suddenly begin to prevail and crack growth is accelerated the p2 phase is emitted in this process it is interpreted that the two distinct phases appear in the process of the transition from non coplanar to coplanar interaction predominance

dynamic modeling of slow slip coupled with tremor 1 we theoretically study the generation mechanism of slow slip in a dynamical framework assuming a fault in a fluid saturated thermoporoelastic medium the fluid flow is taken into consideration dynamic slip is assumed to create pores and cause shear heating on the fault key parameters in the modeling are su and su the nondimensional parameter su represents the relative dominance of the effect of pore creation on the fluid pressure change over that of shear heating while su is associated with the dominance of fluid flow effect over the effect of shear heating our calculation shows that we have to assume su 1 and relatively small values for su to simulate rupture speed that is negligibly small compared to the shear wave velocity although this was also found in our former paper our new finding here is the simulation of slow slip coupled with tremor we find that frozen slip is reactivated sporadically because the fluid inflow triggered by the pore creation elevates the fluid pressure on the fault the slip reactivation actually occurs if su is smaller than a threshold such sporadic reactivation of slips can be a model for slow slip coupled with tremor we also show that the moment evolution curves are categorized into two separate groups when su 0 1 one of them represents slow slips while the other represents ordinary earthquakes

image ray tomography abstract seismic tomography is a well established approach to invert smooth macro velocity models from kinematic parameters such as traveltimes and their derivatives which can be directly estimated from data tomographic methods differ more with respect to data domains than in the specifications of inverse problem solving schemes typical examples are stereotomography which is applied to prestack data and normal incidence point wave tomography which is applied to common midpoint stacked data one of the main challenges within the tomographic approach is the reliable estimation of the kinematic attributes from the data that are used in the inversion process estimations in the prestack domain weak and noisy signals as well as in the post stack domain occurrence of triplications and diffractions leading to numerous conflicting dip situations may lead to parameter inaccuracies that will adversely impact the resulting velocity models to overcome the above limitations a new tomographic procedure applied in the time migrated domain is proposed we call this method image incident point wave tomography the new scheme can be seen as an alternative to normal incidence point wave tomography the latter method is based on traveltime attributes associated with normal rays whereas the image incidence point wave technique is based on the corresponding quantities for the image rays compared to normal incidence point wave tomography the proposed method eases the selection of the tomography attributes which is shown by synthetic and field data examples moreover the method provides a direct way to convert time migration velocities into depth migration velocities without the need of any dix style inversion

3d tomographic velocity model estimation with kinematic wavefield attributes a tomographic inversion method is presented that uses kinematic information in the form of zero offset traveltimes and kinematic wavefield attributes first and second spatial traveltime derivatives to determine smooth laterally inhomogeneous 3d subsurface velocity models for depth imaging the kinematic wavefield attributes can be extracted from the seismic prestack data by means of the common reflection surface crs stack the input for the tomography is then taken from the resulting attribute volumes at a number of pick locations in the crs stacked zero offset volume as a smooth model description based on b splines is used and reflection points are treated independently of each other only locally coherent events in the stacked volume are required and very few picks are needed thus picking is considerably simplified during the iterative inversion process the required forward modelled quantities are obtained by dynamic ray tracing along normal rays pertaining to the input data points frechet derivatives for the tomographic matrix are calculated with ray perturbation theory the inversion algorithm is demonstrated on a 3d synthetic data example where the kinematic wavefield attributes have directly been obtained by forward modelling

archaeological formation theory and geoarchaeology state of the art in 2016 since the influential work of michael b schiffer on formation processes has been published in 1987 much has advanced on the part of environmental formation processes also known as n transforms most new knowledge is the result of research conducted by geoarchaeologists on the theoretical level a huge leap forward was made with the realization that occupation deposits are artifacts of human activity the focus of formation theory thus shifted from the artifact to the deposit methodological innovations and a geoarchaeological tool kit notably including the contextual technique of micromorphology followed empirical studies of archaeological occupation deposits contributed new spatial and stratigraphic knowledge and understanding a holistic middle range methodology termed geo ethnoarchaeology was developed whereby macroscopic and microscopic artifacts are studied together with their associated sediments in ethnographic contexts providing contextual social information about the relationship between artifacts and the surrounding sediments as archaeological assemblages form this method is especially powerful when sequentially dated abandoned settlements or features are studied to provide mechanistic understanding of assemblage and or site formation through degradation because geo ethnoarchaeology is based on general chemical biological and physical laws the resultant mechanistic models are applicable globally for any time period culture and environment the new tools and mechanistic understanding by which n transforms are currently studied provide means to more reliably interpret the archaeological record which is crucial for the credibility of archaeology therefore when studying archaeological assemblages one should utilize the tool kit developed by geoarchaeologists to first assess the states of preservation of the various material assemblages macroscopic and microscopic as it should be borne in mind that assemblages identified to be well preserved will produce the most reliable archaeological interpretation the theory and method of geoarchaeology have matured enough to allow responsible archaeological research into the meaning of spatial and temporal stratigraphic patterns at any given site

the structural evolution of the messinian evaporites in the levantine basin abstract the levantine basin in the south eastern mediterranean sea is a world class site for studying the initial stages of salt tectonics driven by differential sediment load because the messinian evaporites are comparatively young the sediment load varies along the basin margin they are hardly tectonically overprinted and the geometry of the basin and the overburden is well defined in this study we analyse depositional phases of the evaporites and their structural evolution by means of high resolution multi channel seismic data the basinal evaporites have a maximum thickness of about 2 km precipitated during the messinian salinity crisis 5 3 5 9 ma ago the evaporite body is characterized by 5 transparent layers sequenced by four internal reflections we suggest that each of the internal reflection bands indicate a change of evaporite facies possibly interbedded clastic sediments which were deposited during temporal sea level rises all of these internal reflections are differently folded and distorted proving that the deformation was syn depositional thrust angles up to 14 are observed backstripping of the pliocene quaternary reveals that salt tectonic is mainly driven by the sediment load of the nile cone the direction of lateral salt displacement is mainly ssw nne and parallel to the bathymetric trend apparent rollback anticlines off israel result rather from differential subsidence than from lateral salt displacement in the south eastern basin margin the deposition of the isreali slump complex isc is coeval with the onset of salt tectonic faulting suggesting a causal link between slumping processes and salt tectonics the superposition of thin skinned tectonics and thick skinned tectonics becomes apparent in several locations the fold belt off the israeli mediterranean slope mainly results from active strike slip tectonics which becomes evident in faults which reach from the seafloor well below the base of the evaporites owing to the wrenching of the crustal segments which are bounded by deep rooted fault lines like the damietta latakia pelusium and shelf edge hinge line the setting is transpressional south of 32 n where the fault lines bend further towards the west this adds a component of thick skinned transpression to the generally thin skinned compressional regime in the basin above 1 5 km of evaporites a mud volcano is observed with the mud source seemingly within the evaporite layer at the eastern cyprus arc the convergence zone of the african and the anatolian plates deep rooted compression heavily deformed the base of the evaporites whereas at the eratosthenes seamount mainly superficial compression affecting the post messinian sediments and the top of the evaporites is observed

precursory seismic quiescence seventeen cases of precursory seismic quiescence to mainshocks with magnitudes fromml 4 7 toms 8 0 are summarized the amount of rate decrease ranges from 45 to 90 the significance of these changes varies between 90 and 99 99 the assumption that the background rate is approximately constant is fulfilled in most crustal volumes studied all quiescence anomalies seem to have abrupt beginnings and the rate during the anomalous period is fairly constant the duration of the precursors ranges from 15 to 75 months and it is not clear what factors determine that time at least three successful predictions have been based on seismic quiescence these cases have shown that mainshocks can be predicted based on quiescence but they have also shown that the interpretation of the data in real time is difficult and nonunique if a false alarm is defined as a period of quiescence with a significance level larger than a precursory quiescence in the same tectonic area then we estimate based on searches in four areas that the false alarm rate may be on the order of 50 failure to predict may be expected in perhaps 50 of mainshocks even in carefully monitored areas quiescence cannot be used as a precursor in tectonic environments with low seismic activity most characteristics of the phenomenon are still poorly defined but data exist which probably permit at least a doubling of the presently available data on case histories

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

estimation of geological dip and curvature from time migrated zero offset reflections in heterogeneous anisotropic media starting from a given time migrated zero offset data volume and time migration velocity recent literature has shown that it is possible to simultaneously trace image rays in depth and reconstruct the depth velocity model along them this in turn allows image ray migration namely to map time migrated reflections into depth by tracing the image ray until half of the reflection time is consumed as known since the 1980s image ray migration can be made more complete if besides reflection time also estimates of its first and second derivatives with respect to the time migration datum coordinates are available such information provides in addition to the location and dip of the reflectors in depth also an estimation of their curvature the expressions explicitly relate geological dip and curvature to first and second derivatives of reflection time with respect to time migration datum coordinates such quantitative relationships can provide useful constraints for improved construction of reflectors at depth in the presence of uncertainty furthermore the results of image ray migration can be used to verify and improve time migration algorithms and can therefore be considered complementary to those of normal ray migration so far image ray migration algorithms have been restricted to layered models with isotropic smooth velocities within the layers using the methodology of surface to surface paraxial matrices we obtain a natural extension to smooth or layered anisotropic media

mechanisms of seismic quiescences in the past decade there have been major advances in understanding the seismic cycle in terms of the recognition of characteristic patterns of seismicity over the entire tectonic loading cycle the most distinctive types of patterns are seismic quiescences of which three types can be recognized post seismic quiescence which occurs in the region of the rupture zone of an earthquake and persists for a substantial fraction of the recurrence time following the earthquake intermediate term quiescences which appear over a similar region and persist for several years prior to large plate rupturing earthquakes andshort term quiescences which are pronounced lulls in premonitory swarms that occur in the hypocentral region hours or days before an earthquake although the frequency with which intermediate term and short term quiescences precede earthquakes is not known and the statistical significance of some of the former has been challenged there is a need if this phenomena is to be considered a possibly real precursor to consider physical mechanisms that may be responsible for them the characteristic features of these quiescences are reviewed and possible mechanisms for their cause are discussed post seismic quiescence can be readily explained by any simple model of the tectonic loading cycle as due to the regional effect of the stress drop of the previous principal earthquake the other types of quiescence require significant modification to any such simple model of the possibilities considered only two seem viable in predicting the observed phenomena dilatancy hardening and slip weakening intermediate term quiescences typically occur over a region equal to or several times the size of the rupture zone of the later earthquake and exhibit a relationship between the quiescence duration and size of the earthquake they thus involve regional hardening or stress relaxation and agree with the predictions of the dilatancy diffusion theory short term quiescences on the other hand are more likely explained by fault zone dilatancy hardening and or slip weakening within a small nucleation zone because seismicity is a locally relaxing process seismicity should follow a behaviour known in rock mechanics as the kaiser effect in which only a very slight increase in strength due to dilatancy hardening or decrease in stress due to slip weakening is required to cause quiescence this is in contrast to other precursory phenomena predicted by dilatancy which require large dilatant strains and complete dilatancy hardening

models of aftershock occurrence summary the omori formula for aftershock activity can be shown to be a consequence of each of two models of a complex earthquake in the first case aftershocks are assumed to be caused by subsequent slip on asperities of a fault which are locked during the fracture in the main shock in the second aftershocks are caused by catastrophic coalescence of nearby small fractures with the fracture surface of the main shock hence the first source model describes aftershock activity in the interior of a main shock rupture zone while the second describes aftershock activity near the outer boundary of a main shock rupture zone stress corrosion cracking is assumed to be the physical cause of the quasistatic growth of the main fracture zone at the expense of the area of the locked patches in the first model and is also the cause of the growth of the small satellite fractures in the second

numerical modelling of space and time variations of seismic activity before major earthquakes summary the spatial and temporal variations of seismic activity before large earthquakes including precursory swarm earthquakes clustering pre seismic quiescence in the epicentral area doughnut patterns and foreshocks are numerically modelled by quasi static and dynamical rupture processes on three dimensional heterogeneous faults with various types of non uniform strength distributions the main physical parameters that could yield these precursory changes of seismicity patterns are the form of distributions of static and sliding frictional strengths and their spatial variations over the fault and also the rate of increase of tectonic stress for weakly heterogeneous faults a large scale main shock rupturing the entire fault surface occurs without any precursory indications if the fault has moderately to heavily non uniform strengths on a small scale gradually increasing activity tends to occur over a long period prior to a main event with no swarms or quiescence for extremely heterogeneous faults including a number of small to moderate size asperities with medium to high strengths a typical sequence appears with swarms quiescence foreshocks and a main shock event the temporal behaviour of these events seems to depend primarily on the form of distribution of the strengths if the fault includes a large size asperity with medium to high strengths in its central part a doughnut pattern of seismicity repeatedly appears with high activity and quiescence in the surrounding and central asperity regions if a belt like barrier region with extremely high strengths lies in the central part of the fault dividing the entire region into two sections large scale shocks take place successively in the adjacent unruptured regions at slightly different times and a main shock event rupturing the entire fault occurs after a long period of quiescence these results from numerical simulations could provide possible explanations of observed seismicity patterns prior to major earthquakes

seismicity simulation with a mass spring model and a displacement hardening softening friction law dieterich simulated aftershocks numerically using a one dimensional mass spring model with a time dependent friction law but an important precursory phenomenon called quiescence cannot be produced by this model unless as mikumo and miyatake showed with a three dimensional continuum model a somewhat arbitrary bimodal distribution of frictional strength is assumed here we used the friction law proposed by stuart which is a displacement hardening softening model and simulated the quiescence by varying the parameters of the friction law in our mass spring model we found a variety of seismicity patterns when we choose extremely large critical displacement we get a recurrent sequence of creep followed by mainshock without small earthquakes but when we choose a critical displacement in the same order of magnitude as the slip weakening critical displacement estimated by papageorgiou and aki from strong motion data we get a normal seismicity pattern including quiescence before large events this simple model points to a promising approach for the interpretation of the rupture process during an earthquake by the same physical model

generation of microcracks by dynamic shear rupture and its effects on rupture growth and elastic wave radiation laboratory and field observations suggest that dynamically propagating earthquake faults generate a large number of tensile microcracks in their vicinity which will contribute to the formation of fault zones intense interactions are expected to occur between such microcracks and a dynamically propagating fault which will complicate the fault growth near field seismic waves will also be affected by the generation of microcracks we numerically study how such tensile microcracks are generated and how dynamic growth of a macroscopic shear rupture and near field elastic waves are affected by the distribution of generated microcracks it is essential to consider a large number of microcracks in such studies so that it is impractical to consider each microcrack individually from the viewpoint of computation time and memory we overcome this difficulty by representing the microcrack distribution by anisotropic properties of the overall elastic coefficients on the basis of hudson s 1980 study our simulations show that the decrease in the microcrack density is approximated well by a logarithmic function of the distance from the rupture plane microcracks on the dilational side of the rupture plane are shown to make larger angles to the rupture plane than on the compressive side these are consistent with field and laboratory observations it is also shown that dynamically generated microcracks tend to reduce the rupture tip shear stress this implies that the dynamic growth of a shear rupture is more decelerated when microcracks are generated than when the shear rupture is isolated in an isotropic and homogeneous medium if the dynamic rupture growth is arrested suddenly an abrupt expansion of the distribution zone of microcracks is shown to occur near the arrested rupture tip aftershocks are expected to cluster in this zone because of the shear stress enhancement there and the high density of distributed microcracks which facilitates aftershock occurrence due to dynamic coalescence of microcracks our simulations also show that the component of radiated displacement waves perpendicular to the rupture plane is much more affected by the generation of microcracks than the parallel component

application of fracture mechanics to the simulation of seismicity and recurrence of characteristic earthquakes on a fault we present a fault model consisting of a large number of collinear cracks and intervening asperities for the simulation of seismicity and recurrence of large earthquakes on a fault we apply fracture mechanics to the analysis of the interaction of cracks and to the consideration of fracture condition our fault model gives rise to a complex frequency distribution of event sizes even if no externally imposed spatial inhomogeneity is assumed for the distribution of cracks and asperities and a homogeneous statistical distribution is assumed for fracture strengths the frequency distribution of event sizes is found to be bimodal with no intermediate size event in all the calculations for the smaller events the frequency distribution shows a power law behavior whereas the larger size events denote ones that rupture the whole fault statistically the same frequency distributions are obtained for inhomogeneous distributions of crack lengths and fracture strengths the occurrence of events that rupture the whole fault is shown to be periodic when the fault is isolated the magnitudes of these large events generally increase with increasing recurrence period for given fault length and rate of remote loading the events having a longer recurrence period have a shorter fault length for given magnitude and rate of remote loading if there are fault interactions the periodicity in the recurrence of the large events that would be observed for the isolated fault disappears and the recurrence of the large events becomes complex

possible mechanisms of dynamic nucleation and arresting of shallow earthquake faulting abstract the nucleation and arresting mechanisms of large shallow earthquakes are investigated from both observational and theoretical viewpoints we show that two distinct phases are commonly observed at the initial part of seismograms of large shallow earthquakes the first phase denotes the onset of the p wave which shows a very gradual increase in amplitude with time this gradual change is interrupted by the arrival of the second phase which causes an abrupt change in the amplitude our seismological observation shows that the time interval between the onset of the two phases is strongly correlated with the magnitude of the earthquake it is probable that the above two phases are related to some aspect of inhomogeneities in the earth s crust one of the important sources of such inhomogeneities is known to be preexisting cracks and their interactions we theoretically show in this paper that a rupture occurring in a zone of densely distributed cracks radiates elastic waves that can simulate the features of the above two phases note that such a rupture is considerably affected by crack interactions theoretical calculation is also carried out to investigate the effect of crack interactions on the arresting of rupture propagation a propagating crack can excite subsidiary cracks ahead of its crack tip which gives rise to crack interactions we show that these interactions sometimes facilitate the arresting of rupture propagation

model for intermediate term precursory clustering of earthquakes a causal sequence of an earthquake swarm extended quiescence foreshocks and main shock can be understood in terms of an aggregation model of crack growth and ultimate fusion on a multiplanar earthquake fault system the rheological model is one of accelerated crack growth under conditions of slip weakening coupled with a slow recovery of static friction after fracture once a slip feature has been generated that spans a large part of the available geometry a stress shadow is cast on other neighboring cracks that strongly retards and inhibits crack growth thus initiating the quiescent phase abruptly the success of the model depends on the assumption that nonlinear rheology regulates the rate of slip and that earthquake faults are not simply connected surfaces but instead have many strands

foreshock and aftershock sequence of the 1998 m 5 0 sendai northeastern japan earthquake and its implications for earthquake nucleation we investigated foreshock and aftershock sequences of a m 5 0 earthquake that occurred on 15 september 1998 near the nagamachi rifu fault an active fault crossing the urban area of sendai city northeastern japan the focal mechanism of this event was a reverse fault type with a nearly horizontal p axis parallel to the plate conversion direction aftershock distribution located by the homogeneousstation method delineates the fault plane of this event dipping to the northwest at an angle of 30 in the depth range of 10 12 km the location of the fault plane and the slip direction thus estimated suggest that this event was a slip at a deep portion of the nagamachi rifu fault three days prior to the mainshock many foreshocks with similar waveforms started to occur very close to the mainshock hypocenter we estimated relative locations of these similar foreshocks based on crossspectrum analyses of waveforms recorded at nearby stations they are located at the deepest portion of the mainshock fault plane and just above the mainshock hypocenter migration of the foreshocks is observed from deeper to shallower depths cumulative coulomb stress changes caused by preceding events show negative values at hypocenters of similar waveform foreshocks our results do not support the cascade model for the process of foreshock generation nucleation phase prior to the high speed rupture of the mainshock is observed in seismograms at nearby stations the initial point of the nucleation phase is located on a deeper extension of the foreshock area the high speed breakout point is located in the area where a large amount of seismic moment release was estimated from waveform inversions these observations probably reflect an underlying aseismic nucleation process preceding the main dynamic rupture of the m 5 0 event

precursory seismic quiescence past present and future precursory seismic quiescence has played a major role in most of the succesful earthquake predictions made to date in addition to these successes the number of detailed post mainshock documentations of precursory quiescence is steadily growing these facts suggest that precursory quiescence will play an important role in earthquake prediction programs of the future for this reason it is important to critically evaluate the present state of knowledge concerning this phenomenon the history of observations of precursory seismic quiescence includes work on seismic gaps and seismic preconditions as well as actual studies of temporal quiescence these papers demonstrated the importance of quantitative evaluation of seismicity rates and the benefits of systematic analysis during the early 1980 s the impact of man made effects on seismicity rates was demonstrated for the first time despite progress in catalog understanding the identification and correction of man made seismicity changes remains as the major barrier to earthquake prediction using these data effects of man made changes are apparent in many past studies of seismicity patterns making the results difficult to evaluate recent experience with real time anomalies has demonstrated the necessity of determining the false alarm rates associated with quiescence precursors determination of false alarm rates depends on quantitative definitions of anomalies and statistical evaluations of their significance a number of successful predictions which have been made on the basis of seismic quiescence provide important lessons for present and future work there are many presently unanswered questions regarding seismic quiescence which must be answered before we can determine the reliability of this phenomena as a precursor

analysis of the static stress field around faults lying along and intersecting a bimaterial interface summary major faults are known to lie along material interfaces including plate interfaces and tectonic lines recent high precision observations have revealed that there are also faults in the vicinity of material interfaces this suggests that slip on a fault and stress changes near one can be affected significantly by the presence of a material interface in this paper we develop a new mathematical framework to derive an expression for a static slip response function by drawing on properties of complex functions our method is characterized by its unique ability to analyse both a fault lying along a material interface and a fault intersecting a material interface under a unified framework a few previous studies have theoretically dealt with the problem of slip on a fault that intersects a material interface but their mathematical techniques were so complicated that they had only limited utility for seismological applications by contrast our mathematical framework has a simple structure thanks to the characteristics of the complex functions using our formula one can easily calculate the fault slip and the static stress changes nearby if only the stress drop on the fault is given the static stress is represented as a sum of stress changes due to the slip and a background stress that is generally discontinuous across a material interface understanding of the static stress state around a fault has important implications for evaluating the likelihood of secondary failures we find that when the fault is located along or in the vicinity of a material interface the background stress plays a key role in the formation of the stress state around a fault and accordingly also in the triggering of secondary failures

long term seismogenic process for major earthquakes in subduction zones abstract a qualitative physical process for the long term seismogenesis of major earthquakes in subduction zones is proposed on the basis of quantitative empirical evidence that swarms mainshocks and aftershocks are closely related phenomena the relations which have been identified in the comprehensive long term catalogues of new zealand and japan represent swarms as predictors of mainshocks with respect to location time and magnitude clustering of swarms and of mainshock aftershock events is allowed for with a database of 15 sequences of swarms mainshocks and aftershocks tests are being conducted with the object of refining the relations and evaluating them as a possible means of practical synoptic forecasting three sequences have culminated in major earthquakes since the tests began and the systematic study now relates a total of 36 swarms with 29 mainshock aftershock events these empirical results strengthen and quantify the connection between swarms and major earthquakes which several authors have demonstrated by means of numerical physical modelling the proposed seismogenic process includes swarms mainshocks and aftershocks as separate event stages which are related by predictability interevent conditions are specified according to the mogi criteria for the medium cracks at which fractures subsequently occur constitute nonuniformity in the mogi sense and post earthquake healing restores uniformity where the gutenberg richter relation occurs it is accepted as possible evidence of deterministic chaos and unpredictability as a corollary the process is noncyclical the principle of scaling is held to apply except when modified by large scale boundaries in the medium subduction zones and some other localities where water is abundant are indicated by the main empirical studies as favourable to the occurrence of swarms fluid overpressuring is therefore proposed as a mechanism for the self triggering of swarms and this is supported by additional examples of the predictive relations occurring in conditions of high fluid pressure including the vicinity of large man made reservoirs the process can be tested by systematic studies in other subduction regions given adequate catalogues for quantifying the algorithm it also has implications for other tectonic environments with swarms replaced by cognate more protracted seismicity precursors

fractal geometry in the san andreas fault system it has been noted that the spatial distribution of earthquakes and the mode of strain release in the san andreas fault system is related to the complexity of fault geometry because of their rough appearance over many length scales faults can be regarded as fractal surfaces direct estimates of fractal dimension d of portions of the san andreas fault system between the northern gabilan range and the salton sea including the postulated extent of the great 1857 fort tejon earthquake are obtained from measured fault lengths analogous to the lengths of coastlines as discussed by mandelbrot regions characterized by complicated fault geometry are associated with larger values of d based on fault traces mapped at a scale of 1 750 000 d is 1 3 for this reach of the fault defined as a 30 km wide band about a main fault trace for that part near parkfield which could be associated with the nucleation of the 1857 earthquake d is 1 1 at this same scale d is 1 4 for the san andreas and related faults near san bernardino where the 1857 rupture stopped compared to 1 2 for the san andreas san juan fault segments near the point of arrest of the 1966 parkfield earthquake at finer map scales 1 24 000 and 1 62 500 critical lengths of 500 m and 1 km are identified which might relate to the extent of off san andreas fault offsets the critical lengths also suggest that fault geometry is not self similar if this fractal geometry persists through the seismic cycle it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault

mainshocks are aftershocks of conditional foreshocks how do foreshock statistical properties emerge from aftershock laws 1 the inverse omori law for foreshocks discovered in the 1970s states that the rate of earthquakes prior to a mainshock increases on average as a power law 1 tc t p of the time to the mainshock occurring at tc here we show that this law results from the direct omori law for aftershocks describing the power law decay 1 t tc p of seismicity after an earthquake provided that any earthquake can trigger its suit of aftershocks in this picture the seismic activity at any time is the sum of the spontaneous tectonic loading and of the activity triggered by all preceding events weighted by their corresponding omori law the inverse omori law then emerges as the expected in a statistical sense trajectory of seismicity conditioned on the fact that it leads to the burst of seismic activity accompanying the mainshock in particular we predict and verify by numerical simulations on the epidemic type aftershock sequence etas model that p is always smaller than or equal to p and a function of p of the b value of the gutenberg richter law gr and of a parameter quantifying the number of direct aftershocks as a function of the magnitude of the mainshock the often documented apparent decrease of the b value of the gr law at the approach to the mainshock results straightforwardly from the conditioning of the path of seismic activity culminating at the mainshock however we predict that the gr law is not modified simply by a change of b value but that a more accurate statement is that the gr law gets an additive or deviatoric power law contribution with exponent smaller than b and with an amplitude growing as a power law of the time to the mainshock in the space domain we predict that the phenomenon of aftershock diffusion must have its mirror process reflected into an inward migration of foreshocks toward the mainshock in this model foreshock sequences are special aftershock sequences which are modified by the condition to end up in a burst of seismicity associated with the mainshock foreshocks are not just statistical creatures but are genuine forerunners of large shocks as shown by the large prediction gains obtained using several of their qualifiers

prestack time migration by common migrated reflector element stacking abstracttime migration is an attractive tool to produce a subsurface image because it is faster and less sensitive to velocities errors than depth migration however a highly focused time image is only achievable with well determined time migration velocities therefore a refinement of the initial time migration velocities often is required we introduced a new technique for prestack time migration based on the common migrated reflector element stack of common scatterpoint gathers including an automatic update of time migration velocities the common scatterpoint gathers are generated using a new formulation of the double square root equation that is parametrized with the common offset apex time the common migrated reflector element stack is a multiparameter stacking technique based on the taylor expansion of traveltimes of time migrated reflections in the paraxial vicinity of the image ray our 2d synthetic and field data examples demonstrated that the proposed method provides updated time migration

image ray tracing for joint 3d seismic velocity estimation and time to depth conversion seismic time migration is known for its ability to generate well focused and interpretable images based on a velocity field specified in the time domain a fundamental requirement of this time migration velocity field is that lateral variations are small in the case of 3d time migration for symmetric elementary waves e g primary pp reflections diffractions for which the incident and departing elementary waves at the reflection diffraction point are pressure p waves the time migration velocity is a function depending on four variables three coordinates specifying a trace point location in the time migration domain and one angle the so called migration azimuth based on a time migration velocity field available for a single azimuth we have developed a method providing an image ray transformation between the time migration domain and the depth domain the transformation is obtained by a process in which image rays and isotropic depth domain velocity parameters for their propagation are estimated simultaneously the depth domain velocity field and image ray transformation generated by the process have useful applications the estimated velocity field can be used for example as an initial macrovelocity model for depth migration and tomographic inversion the image ray transformation provides a basis for time to depth conversion of a complete time migrated seismic data set or horizons interpreted in the time migration domain this time to depth conversion can be performed without the need of an a priori known velocity model in the depth domain our approach has similarities as well as differences compared with a recently published method based on knowledge of timemigration velocity fields for at least three migration azimuths we show that it is sufficient as a minimum to give as input a time migration velocity field for one azimuth only a practical consequence of this simplified input is that the image ray transformation and its corresponding depth domain velocity field can be generated more easily

a model of foreshock occurrence summary we have constructed a model for the occurrence of foreshocks and foreshock sequences the foreshocks as well as the main shock are assumed to occur because of the abrupt coalescence of pre existing cracks coalescence occurs if the stress intensity factors at the crack tips exceed a certain critical value in the sub critical state each crack undergoes accelerated extension quasi statically due to stress corrosion until it reaches the critical state at which point growth becomes catastrophic the rate of foreshock occurrence increases as the time of the main shock approaches and is described by a power law function of time the exponent in the power law is independent of the distributions of crack sizes spacings and fracture strengths this universality implies that foreshock patterns should be useful identifiers for the prediction of the occurrence times of large earthquakes however we find that there is considerable diversity in the patterns of energy release nevertheless there is some hope that the magnitudes of large earthquakes can be predicted from the magnitudes of the events in the foreshock sequences if one has a priori information describing the distributions of barrier strengths and geometries

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

theoretical and numerical stress analysis at edges of interacting faults application to quasi static fault propagation modelling summary we study theoretically and numerically the process of fault interactions within a quasi static faulting model at long tectonic timescale the model handles birth growth and sliding of multiple straight but non coplanar interacting faults regardless of any coseismic dynamic slip events the study is restricted to the 2 d elastic antiplane case an idealization of the normal faulting process the model handles a general slip dependent friction law for faults to take into account a possible long term fault weakening process at fault tips finite stress and progressive weakening lead to fault tip cohesive zones and ensure stability we introduce a new numerical method based on a series development of slip profiles using a chebyshev basis which provides an accurate computation of large stress gradients at fault tips here simulations are limited to two parallel faults which is enough to investigate many important features such as slip partitioning between faults variable fault tip velocities and the state of stress in fault relay zones responsible for the fault linking process we study both a quasi static problem and the associated spectral problem and show the link between them we compare our quasi static simulations with experimental results concerning the acceleration deceleration of fault tips submitted to stress interaction and concerning the geometrical parameters that favour the linking of two normal faults we find that the linking coalescence process should most likely occur during the deceleration phase of the faults tips subject to stress shadowing in the fault relay furthermore for large ratios of fault lengths to separation the linking process should begin for fault overlaps comparable to the values observed by soliva benedicto in small natural fault relays typically 2 9 times the fault separation

premonitory transformation of steel fracturing and seismicity abstract transformation of microfracturing preceding the break up of steel and rock samples is similar to transformation of earthquakes flow prior to strong earthquakes in southern california the break up in a sample is preceded by transition from formation of new microcracks to coalescence or expansion of existing cracks this is reflected in the relation between the length and the number of the cracks similar transformation of seismicity precedes southern california earthquakes with magnitude m 6 6 1935 1994 specifically magnitude frequency relation bends downward for magnitudes from 3 to 4 5 and upward for magnitudes from about 4 5 to 6 in the usual notations the b value becomes larger in the first interval and smaller in the second one this transformation is accompanied by the increased share of aftershocks in the earthquakes flow in such a way the approach of a strong earthquake is reflected in both major traits of seismicity magnitude frequency relation and earthquake clustering imprecision of the earthquake catalog and reasonable variations in its analysis do not change our conclusions this phenomenon explains so far qualitatively a wide set of premonitory seismicity patterns we give it a formal definition allowing to test whether it takes place in other seismic regions