rank ordering statistics of extreme events application to the distribution of large earthquakes rank ordering statistics provide a perspective on the rare largest elements of a population whereas the statistics of cumulative distributions are dominated by the more numerous small events the exponent of a power law distribution can be determined with good accuracy by rank ordering statistics from the observation of only a few tens of the largest events using analytical results and synthetic tests we quantify the systematic and the random errors we also study the case of a distribution defined by two branches each having a power law distribution one defined for the largest events and the other for smaller events with application to the worldwide harvard and southern california earthquake catalogs in the case of the harvard moment catalog we make more precise earlier claims of the existence of a transition of the earthquake magnitude distribution between small and large earthquakes the b values are b2 2 3 0 3 for large shallow earthquakes and b1 1 00 0 02 for smaller shallow earthquakes however the crossover magnitude between the two distributions is ill defined the data available at present do not provide a strong constraint on the crossover which has a 50 probability of being between magnitudes 7 1 and 7 6 for shallow earthquakes this interval may be too conservatively estimated thus any influence of a universal geometry of rupture on the distribution of earthquakes worldwide is ill defined at best we caution that there is no direct evidence to confirm the hypothesis that the large moment branch is indeed a power law in fact a gamma distribution fits the entire suite of earthquake moments from the smallest to the largest satisfactorily there is no evidence that the earthquakes of the southern california catalog have a distribution with two branches or that a rolloff in the distribution is needed for this catalog b 1 00 0 02 up to the largest magnitude observed mw 7 5 hence we conclude that the thickness of the seismogenic layer has no observable influence whatsoever on the frequency distribution in this region

the evolution of regional seismicity between large earthquakes 1 we describe a simple model that links static stress coulomb modeling to the regional seismicity around a major fault unlike conventional coulomb stress techniques which calculate stress changes we model the evolution of the stress field relative to the failure stress background seismicity is attributed to inhomogeneities in the stress field which are created by adding a random field that creates local regions above the failure stress the inhomogeneous field is chosen such that when these patches fail the resulting earthquake size distribution follows a gutenburg richter law immediately following a large event the model produces regions of increased seismicity aftershocks where the overall stress field has been elevated and regions of reduced seismicity where the stress field has been reduced stress shadows the high stress levels in the aftershock regions decrease due to loading following the main event combined with the stress shadow from the main event this results in a broad seismically quiet region of lowered stress around the epicenter pre event seismicity appears as the original stress shadows finally fill as a result of loading the increase in seismicity initially occurs several fault lengths away from the main fault and moves inward as the event approaches as a result of this effect the seismic moment release in the region around the future epicenter increases as the event approaches synthetic catalogues generated by this model are virtually indistinguishable from real earthquake sequences in california and washington

inversion for seismic slip rate history and distribution with stabilizing constraints application to the 1986 andreanof islands earthquake we develop and present a method of inverting seismograms including their absolute amplitudes to obtain the complete seismic slip time history and distribution using the method of linear programming a rectangular fault is discretized into cells and the source duration into time steps the inversion for the slip rate distribution on the fault as a function of time reduces to the solution of a system of linear equations the influence on the solution of constraining different source parameters such as the sign of the slip rate and the seismic moment is investigated it is found that the constraint of positiveness of slip rate and the constraint that the seismic moment determined from the solution should be close to that obtained from the centroid moment tensor cmt solution are very strong constraints and are essential to obtaining a physically reasonable solution since the inverse problem is unstable instead of presenting only one particular solution we examine several solutions equally well fitting the data for all practical purposes we find that when both constraints are applied the solution becomes quite stable the method is applied to a data set consisting of the vertical component of available digitally recorded teleseismic p waves at stations within a chosen distance window for the 1986 andreanof islands earthquake mw 8 0 the preferred solution is the one in which the slip rate is constrained to be positive and the moment is set to the cmt value the average rupture speed in the 90 km segment to the east of the hypocenter was 3 2 km s and in the 190 km section to the west was 2 km s the maximum slip in the area of large moment release to the west was 5 m and the maximum slip rate which occurs in the same place as the maximum slip was 6 5 m s the slip distribution on the fault shows a corrugated pattern with the long axis in the direction of the plate convergence rather than normal to the arc which was the slip vector direction for the earthquake with most of the slip occurring pn a region of the fault to the west of the rupture nucleation zone this region continued to slip for about 55 s the total source duration being about 80 s the results of this analysis suggest that the long term motion on this portion of the aleutian arc is indeed in the direction of plate convergence

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

aftershocks of the andreanof islands earthquake of june 10 1996 and local seismotectonics three questions have been addressed in connection with an mw 7 7 earthquake that occurred in the andreanof islands alaska on june 10 1996 first was there any variation in seismic activity rate during the previous five years that might have been diagnostic of the imminent occurrence of this event the answer based on the usgs pde catalog is no second though there were abundant pre event earthquakes and aftershocks on both sides of adak canyon why was there very little activity under the canyon itself a property that has been observed previously it is not possible to resolve the cause of the behavior with existing seismological data finally how does one explain the eastern group of aftershocks which fell within the zone of abundant aftershocks of the 1986 mw 8 andreanof islands earthquake when very little of the 1996 mainshock moment was released under or to the east of adak canyon one explanation of these aftershocks is that the recent aftershocks are late aftershocks of 1986 whose occurrence within a short time was induced by the stress pulse but not seismic slip from the 1996 earthquake though large earthquakes in the aleutians occur in distinct tectonic blocks the boundaries of these blocks may not always be defined reliably by aftershock zones

test of the predictability of the pi method for recent large earthquakes in and near tibetan plateau five large earthquakes of m 7 0 based on the magnitude scale of the china earthquake networks center occurred in and near the tibetan plateau during 2008 2014 including the wenchuan m8 0 earthquake on may 12 2008 bjt in this paper the tibetan plateau was chosen to be the study region and calculating parameters of pattern informatics pi method with grid of 1 1 and forecasting time interval of 8 years were employed for the retrospective study according to the previous studies for m7 earthquake forecasting the sliding step of forecasting interval was 1 year and the hotspot diagrams of each forecasting interval since 2008 were obtained year by year the relationships among the hotspots and the m 7 0 earthquakes that occurred during the forecast intervals were studied the predictability of pi method was tested by verification of receiveroperating characteristic curve roc and r score the results show that the successive obvious hotspots occurred during the sliding forecasting intervals before four of the five earthquakes while hotspots only occurred in one forecasted interval without successive evolution process before one of the five earthquakes which indicates that four of the five large earthquakes could be forecasted well by pi method test results of the predictability of pi method by roc and r score show that positive prospect of pi method could be expected for long term earthquake forecast

a synthetic seismicity model for southern california cycles probabilities and hazard the absence of a long historical catalog of observed seismicity with which to constrain earthquake recurrence behaviors is a fundamental stumbling block to earthquake prediction in california conceding that this limitation is not likely to relax in the foreseeable future alternative approaches must be sought to extend the catalog artificially in this article i evaluate the long term behaviors of earthquakes on a map like set of southern california faults through computer simulations that incorporate the physics of earthquake stress transfer and are constrained by excellent but restricted bodies of geological and seismological data i find that model seismicity fluctuates on both short decades and long centuries timescales but that it possesses a well defined mean and standard deviation seismicity fluctuations correlate across different magnitudes and the long term cycles of smaller events seem to lead cycles of larger events short period seismicity fluctuations do not exhibit this tendency and short term changes in low magnitude m5 seismicity are not likely to be an effective predictor of future large events at least for the region as a whole as do real faults the model faults produce characteristic and power law quakes in variable ratios with diverse periodic and nonperiodic behaviors generally larger events tend to occur quasi periodically and smaller ones tend to cluster however only for a few earthquake classes and certain locations is recurrence notably non poissonian an important use of synthetic seismicity is in the construction of earthquake hazard maps because it firmly grounds previously ad hoc assumptions regarding frequency magnitude distributions multiple segment failure statistics and rupture extents while satisfying a spectrum of geological constraints such as fault slip rate segment recurrence interval and slip per event with its depth of temporal and spatial coverage synthetic seismicity also provides a means to investigate the time dependence of seismic hazard because hazard likelihood is a concatenation of the recurrence statistics from many seismic sources in only about 40 50 of the regions near the major faults do sequences of 0 1 g or 0 2 g exceedances differ from poissonian

seismic activity on neighbouring faults as a long term precursor to large earthquakes in the san francisco bay area activity in moderate size earthquakes accelerated in the several decades before the large california earthquakes of 1989 1906 and 1868 this type of precursor seems to require the presence of several major faults in close enough proximity to one another that moderate size shocks are selectively triggered on surrounding faults during the latter stages of the cycle of strain buildup to large earthquakes it may be possible to use quantitative aspects of similar seismic precursors to make predictions of large earthquakes on timescales of a few years to one decade

stress shadows determined from a phase dynamical measure of historic seismicity the pattern informatics pi technique tiampo et al 2002 is founded on the premise that changes in the seismicity rate are a proxy for changes in the underlying stress these stress changes are correlated over large spatial regions and can be quantified using a phase dynamical analysis of the changes in historic seismicity rates this new approach to the study of seismicity quantifies its local and regional space time patterns and identifies regions of local quiescence or activation here we study those local changes in an attempt to objectively quantify short term stress shadow regions we determine that while persistent stress shadows are detectable with this method they do not occur uniformly throughout the spatio temporal region

increased long range intermediate magnitude earthquake activity prior to strong earthquakes in california we study the space time relationships between strong earthquakes in california and the intermediate magnitude earthquakes that both precede and follow them all 11 earthquakes in california with nominal magnitudes greater than or equal to 6 8 from 1941 to 1993 were preceded by an increase in the rate of occurrence of earthquakes having magnitudes greater than 5 1 ten of the 11 earthquakes occurred when or shortly after the intermediate magnitude activity was greater than its 75th percentile three of these strong earthquakes are in a conventional space time foreshock aftershock relationship with others of the 11 strong events the precursory activity is concentrated in regions having linear dimensions of the order of a few hundred kilometers these dimensions are significantly larger than the estimated fracture lengths of the ensuing strong earthquakes the correlations are ill defined for smaller earthquakes and are almost unidentifiable for earthquakes with magnitudes less than about 4 6 the precursors to the strong earthquakes appear over a time interval of the order of 5 to 10 years before the strong earthquake although the onset was about 25 years before the san francisco earthquake in the case of the loma prieta and san francisco earthquakes the onset of increased activity appears to be relatively abrupt the increased activity is either switched off abruptly to distances of the order of hundreds of kilometers shortly after the occurrence of a strong earthquake or the strong events are themselves part of a precursory pattern of continuing high activity before a second strong earthquake that takes place soon thereafter with subsequent extinction of activity after it thus the intermediate magnitude precursors do not directly influence the time and location of the subsequent strong event but the strong event has a strong influence on the stress field in the vicinity of intermediate magnitude earthquakes to distances of the order of many times the scale size of the strong earthquake

patterns of seismic activity preceding large earthquakes we analyze the patterns of seismic activity which precede large events in a mechanical model of a fault the model generates a statistical distribution of events similar to that observed for a single fault with a scaling region consistent with the gutenberg richter law at small and moderate magnitudes and an excess of events at large magnitudes we find only slight variation in the scaling behavior during a loading cycle however we do observe systematic variations in space and time of the overall rate of activity in the model the activity accelerates dramatically preceding a large event and is usually a maximum hi the neighborhood of the future epicenter these results are compared to california seismicity data where we find that activity patterns vary regionally looking at patterns of activity in the san francisco bay area since 1948 we find an increase of activity on the calaveras fault near san jose beginning in the 1980s which if our model is relevant would forecast a large earthquake in that region the 1989 loma prieta earthquake occurred on the san andreas fault within 30 km of the section of the calaveras fault showing increased activity

imaging b value variation beneath the pamir hindu kush region the frequency magnitude distribution b value for the seismicity of the pamir hindu kush region from august 2008 to june 2010 is analyzed we used a very precisely located earthquake dataset containing 9532 events with a magnitude of completeness of 2 9 we attempted both 1d and 2d approaches to resolve the b value variation as a function of depth several pockets of high b value were detected during the cross sectional analysis that may reflect the changes in the physical properties of the subducting slab with depth under the hindu kush sector a high b value 1 2 is identified at the depth of 150 km but under pamir this zone b 0 9 is apparent at shallower depth an earlier detailed seismic tomography study revealed a low velocity zone beneath hindu kush where the high b value is imaged in the present study this observation is corroborated by the existence of fluid due to the dehydration and increase in pore pressure within the lower portion of the indian lithosphere the relatively high b value at shallower depth could be associated with the higher slab temperature as caused by the slower subduction under pamir

accelerating seismic moment release and outer rise compression possible precursors to the next great earthquake in the alaska peninsula region the moment release rate in the kodiak island ki segment increased prior to the great 1964 prince william sound earthquake mw 9 2 starting in 1983 the moment release rate in the shumagin island si segment shows a similar increase in july 1990 an outer rise reverse earthquake showed arc normal compression at a depth of 42 km seaward of the alaska peninsula ap segment because accelerating moment release and arc normal compression have both been proposed as precursors to large and great earthquakes we suggest this is evidence that the si ap region is nearing the end of the seismic cycle between large thrust earthquakes

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

man made changes of seismicity rates seismicity catalogs contain important information about processes which occur in seismically active regions of the earth many authors have examined these catalogs for patterns and variations in patterns which might reflect changes in these processes we have found that these catalogs include a complex mixture of real and man made changes one must identify and account for the man made changes before the real ones can be identified and understood many man made changes in seismicity catalogs are manifested as changes in seismicity rates and can therefore be identified through careful examination of these rates obvious effects include increases or decreases in the detection and reporting of smaller events which accompany the installation or closure of seismic stations these types of changes can be recognized by examining the distribution of seismicity rate changes in the magnitude domain they are characterized by increases or decreases in the number of small events in the catalog at times when the number of larger events remains constant systematic changes in the magnitudes assigned to events can also be identified by examining seismicity rates because they cause apparent changes in rates of data sets with magnitude cutoffs the sign of the apparent rate change depends on the sign of the magnitude change and the type of cutoff used the effects of detection changes can be easily remedied by using a magnitude cutoff which eliminates the smaller events from consideration the techniques we have developed allow one to determine the optimum cutoff magnitude corrections are necessary for remedying the effects of systematic changes in magnitude estimates these corrections can be determined through modeling of observed rate changes caused by these shifts man made changes are present in all seismicity catalogs whether local regional or teleseismic they must be accounted for if these catalogs are to provide meaningful information on real process changes in the earth

a mathematical formulation of accelerating moment release based on the stress accumulation model large earthquakes can be preceded by a period of accelerating seismic activity of moderate sized earthquakes this phenomenon usually termed accelerating moment release has yet to be clearly understood a new mathematical formulation of accelerating moment release is obtained from simple stress transfer considerations following the recently proposed stress accumulation model this model based on the concept of elastic rebound simulates accelerating seismicity from theoretical stress changes during an idealized seismic cycle in this view accelerating moment release is simply the consequence of the decrease due to loading of the size of a stress shadow due to a previous earthquake we show that a power law time to failure equation can be expressed as a function of the loading rate on the fault that is going to rupture we also show that the m value which is the power law exponent can be defined as m d 3 with d a parameter that takes into account the geometrical shape of the stress lobes and the distribution of active faults in the stress accumulation model the power law is not due to critical processes

increased correlation range of seismicity before large events manifested by earthquake chains earthquake chains are clusters of moderate size earthquakes which extend over large distances and are formed by statistically rare pairs of events that are close in space and time neighbors earthquake chains are supposed to be precursors of large earthquakes with lead times of a few months here we substantiate this hypothesis by mass testing it using a random earthquake catalog also we study stability under variation of parameters and some properties of the chains we found two invariant parameters they characterize the spatial and energy scales of earthquake correlation both parameters of the chains show good correlation with the magnitudes of the earthquakes they precede earthquake chains are known as the first stage of the earthquake prediction algorithm reverse tracing of precursors rtp now tested in forward prediction a discussion of the complete rtp algorithm is outside the scope of this paper but the results presented here are important to substantiate the rtp approach

anomalous seismicity preceding the 1999 izmit event nw turkey summary the 1999 izmit earthquake 1999 august 17 mw 7 4 was one of the largest earthquakes to occur in northwestern turkey during the past 100 yr this earthquake occurred along the izmit sapanca fault within the northern anatolian fault zone variations in the generalized fractal dimensions dq of clustering in time and space the gutenberg richter b value and earthquake frequency n are evaluated in detail over an 8 5 yr time period preceding the izmit event spatial and temporal comparisons of the variations in these parameters reveal anomalous intermediate term behaviour over shorter timescales than previously observed significant correlation is observed between changes in b value with the spatial and temporal fractal dimension of epicentre distribution these correlations oscillate back and forth over 2 3 yr time intervals and suggest occurrence of significant instability in the nature of intermediate term deformation along the fault zone seismotectonic behaviour immediately preceding the izmit event is represented by a significant rise in b value to a maximum of 2 26 accompanied by relatively small increases in d the rapid rise of b is associated with an increased frequency of low magnitude seismicity although d spatial and temporal increase slightly in the 2 3 yr period preceding rupture they remain less than 1 indicating that seismicity remains clustered prior to rupture in areas where earthquake frequency or station density do not permit resolution of short term variations of fractal scaling parameters within a few months of main rupture an accelerated period of low magnitude seismicity high b value concentrated along a fault zone d 1 may suggest heightened probability of a forthcoming large event

probabilities of occurrence of large plate rupturing earthquakes for the san andreas san jacinto and imperial faults california 1983 2003 the san andreas san jacinto and imperial faults in california are divided into 19 segments conditional probabilities are calculated that a particular segment will be the site of a large plate rupturing earthquake i e an event that breaks the entire down dip extent of the seismogenic zone during the next 20 years the sizes of such events which account for most of the slip that occurs seismically appear to vary greatly for different segments of these faults repeat time of large shocks coseismic displacement moment release rupture length and seismic magnitude appear to correlate with one another and to be a function of the tectonic style of different parts of those fault zones tectonic inhomogeneities on a scale of about 1 to 100 km are much larger than displacement in any single seismic event and may be regarded as being invariant in their effects upon earthquake generation over many cycles of large shocks it is this invariance that appears to lead to a given segment of a fault rupturing repeatedly in events of nearly the same size since repeat time varies however for a given segment of a fault a simple probabilistic approach is used to forecast the likelihood of large future earthquakes for each segment using as input the time of the last large shock the average recurrence time and the standard deviation of time intervals between events dates of the last large shocks are available for most of the segments investigated repeat times are estimated from times of historic and prehistoric events tectonic similarity and times calculated from coseismic displacement in the last large shock divided by a rate of fault motion or strain buildup the standard deviation of time intervals divided by the average repeat time is close to 1 3 for three fault segments in california for which data are available on historic and prehistoric earthquakes that normalized value is adopted for all calculations of conditional probability magnitudes and seismic moments of future plate rupturing events are estimated for each fault segment several of the segments have well constrained probabilities for rupture during the next 20 years whereas others have large uncertainties eight of the segments constituting about 40 of the total lengths of the three faults have moderate to high probability and thus should be instrumented and studied extensively so as to provide shorter time warnings in some cases two adjacent segments may be nearly in phase in their loading history and may break in a single event the segment of the san andreas fault from opposite san jose to san juan bautista which ruptured less than 1 5 m in 1906 and which probably also broke in 1838 is calculated to have a moderate to high probability of an earthquake of magnitude 6 to during the next 20 years a 325 km section of the southern san andreas between tejon pass and the salton sea has about a 25 chance of rupturing in a shock of magnitude near 8 during the next 20 years all the other segments have only a small chance i e less than 5 to 10 of rupturing in an event of magnitude near 8 during that interval

cu ni co au bearing massive sulfide deposits associated with mafic ultramafic rocks of the main urals fault south urals geological structures ore textural and mineralogical features comparison with modern analogs abstract cu rich massive sulfide deposits associated with mafic ultramafic rocks in the southern portion of the main urals fault muf are characterized by variable enrichments in ni up to 0 45 wt co up to 10 wt and au up to 16 ppm in individual hand specimens the cu ni co rich composition of muf deposits as opposed to the cu zn rich composition of more eastward massive sulfide deposits of broadly similar age along the western flank of the magnitogorsk arc reflects the abundance of seafloor exposed ni co rich ultramafic rocks in the most external portion of the early devonian magnitogorsk forearc morphological textural and compositional differences between individual deposits are interpreted to be the result of the sulfide deposition style and in part of the original subseafloor lithology one deposit produced by dominantly on seafloor hydrothermal processes is characterized by pyrite marcasite pyrrhotite not so low zn grades occasionally up to 2 wt abundant clastic facies and periodical superficial oxidation deposits produced by dominantly subseafloor hydrothermal processes are characterized by pyrrhotite pyrite very low zn generally

what controls an earthquake s size results from a heterogeneous cellular automaton the controls on an earthquake s size are examined in a heterogeneous cellular automaton that includes stress concentrations which scale with rupture size large events only occur when stress is highly correlated with strength over the entire fault although the largest events occur when this correlation is the highest the magnitude of the correlation has no predictive value as events of all magnitudes occur during times of high stress strength correlation rather the size of any particular event depends on the local stress heterogeneity encountered by the growing rupture patterns of energy release with time for individual ruptures reflect this heterogeneity and many show nucleation type behaviour although there is no relation between the duration of nucleation phase and the size of the event these results support the view that earthquake size is determined by complex interactions between previous event history and dynamic stress concentrations and suggest that deterministic earthquake prediction based on monitoring nucleation zones will not be possible

precursors to a magnitude 4 8 earthquake in the virgin islands spatial clustering of small earthquakes anomalous focal mechanisms and earthquake doublets abstract waveforms of small earthquakes that preceded a magnitude 4 8 earthquake in the virgin islands were studied using digital recordings from a local seismic network during the 10 months prior to the main shock a spatial cluster of five events 1 4 m 2 5 occurred within 3 km of the impending shock variations in the p wave first motions at one station as well as p sv amplitude ratios indicate that the focal mechanisms of the events within the cluster changed 2 months before the main shock the focal mechanism of the later events and of two foreshocks that occurred the day of the main event differed from the typical focal mechanism observed for the area the main event and most of its aftershocks exhibited the normal set of first motions recorded for events in this region the cluster events and the foreshocks occurred in pairs each pair with very similar waveforms cross correlations of these waveforms reveal that the earthquakes in each pair are located within about 110 m of each other each pair can be interpreted as an earthquake doublet that is two similarly sized events with adjacent rupture zones that are related in time the occurrence of doublets is unusual for events in this region and may be indicative of high stress in the vicinity of the impending shock no significant differences were observed between the spectra of the cluster events the foreshocks or the aftershocks

evolution of the stress field in southern california and triggering of moderate size earthquakes a 200 year perspective changes in stress in southern california are modeled from 1812 to 2025 using as input 1 stress drops associated with six large 7 0 7 5 earthquakes through 1995 and 2 stress buildup associated with major faults with slip rates 3 mm yr as constrained by geodetic paleoseismic and seismic measurements evolution of stress and the triggering of moderate to large earthquakes are treated in a tensoffal rather than a scalar manner we present snapshots of the cumulative coulomb failure function acff as a function of time for faults of various strike dip and rake throughout southern california we take acff to be zero everywhere just prior to the great shock of 1812 we find that about 95 of those well located m 6 earthquakes whose mechanisms involve either strike slip or reverse faulting are consistent with the coulomb stress evolutionary model that is they occurred in areas of positive acff the interaction between slow moving faults and stresses generated by faster moving faults significantly advanced the occurrence of the 1933 long beach and 1992 landers events in their earthquake cycles coulomb stresses near major thrust faults of the western and central transverse ranges have been accumulating for a long time future great earthquakes along the san andreas fault especially if the san bernardino and coachella valley segments rupture together can trigger moderate to large earthquakes in the transverse ranges as appears to have happened in the santa barbara earthquake that occurred 13 days after the great san andreas shock of 1812 maps of current acff provide additional guides to long term earthquake prediction

soil creep in a mesotidal salt marsh channel bank fast seasonal and water table mediated abstract muddy banks of marsh channels experience soil creep a viscous like slow deformation resulting in a net downslope transport here we present the first field evidence of soil creep in a mesotidal salt marsh using both pole displacement and high precision measurements of soil deformation taken with a vibrating wire extensometer over two years soil extended 2 4 mm m year in the high marsh platform and 20 40 mm m year in the low marsh bank this was equivalent to a soil diffusivity of about 0 2 m2 year which is much higher than the diffusivity on hillslopes and also matches the high value predicted by long term marsh evolution models high precision 0 03 mm soil deformation measurements shed light on the dynamics of the creep process first the low bank compressed and extended by 5 mm m every tidal cycle suggesting that the diurnal changes in water level play a role in the bank movements second net soil extension took place mostly during fall net soil extension preceded the period of ice formation suggesting that freezing and ice rafting are not a leading cause of soil creep net soil extension was likely triggered by an increase in water table during fall which decreased the effective stress and thus destabilized the bank this high water table was caused by a combination of an abiotic factor the increase in atmospheric precipitation and a biotic factor the decrease in evapotranspiration triggered by vegetation senescence this study confirms that creep is a significant process in marsh morphodynamics and that vegetation can reduce mass wasting in marsh channels

seismicity trends and potential for large earthquakes in the alaska aleutian region the high likelihood of a gap filling thrust earthquake in the alaska subduction zone within this decade is indicated by two independent methods analysis of historic earthquake recurrence data and time to failure analysis applied to recent decades of instrumental data recent may 1993 earthquake activity in the shumagin islands gap is consistent with previous projections of increases in seismic release indicating that this segment along with the alaska peninsula segment is approaching failure based on this pattern of accelerating seismic release we project the occurrence of one or morem 7 3 earthquakes in the shumagin alaska peninsula region during 1994 1996 different segments of the alaska aleutian seismic zone behave differently in the decade or two preceding great earthquakes some showing acceleration of seismic release type a zones while others show deceleration type d zones the largest alaska aleutian earthquakes in 1957 1964 and 1965 originated in zones that exhibit type d behavior type a zones currently showing accelerating release are the shumagin alaska peninsula delarof and kommandorski segments time to failure analysis suggests that the large earthquakes could occur in these latter zones within the next few years

seismic potential of the queen charlotte alaska aleutian seismic zone the 5000 km long queen charlotte alaska aleutian seismic zone is subdivided into 17 unequally sized segments their boundaries are delineated based on the prior distribution of large and great earthquakes the 17 segments are chosen to represent areas likely to be ruptured by characteristic earthquakes this term usually implies repeated breakage of a plate boundary segment by either a large or great earthquake whose source dimensions remain consistent from cycle to cycle this definition does not exclude the possibility that occasionally adjacent characteristic earthquake segments may break together in a single giant event that is larger than the characteristic size outlined conversely a segment can also sometimes break in a series of smaller ruptures formal computations of the conditional probabilities for future large and great earthquakes in the 17 segments of the queen charlotte alaska aleutian seismic zone are based on the following data sets and findings 1 recurrence intervals from historic and geologic data 2 direct recurrence time estimates based on rates of relative plate motion and the size or displacement of the most recent characteristic event in each segment and 3 the application of a lognormal distribution of recurrence times for large and great earthquakes results of these computations indicate seven areas that have high i e 60 conditional probabilities for the recurrence of either large or great earthquakes within the next 20 years 1988 2008 these areas include cape st james yakataga the shumagin islands unimak island and the fox delarof and near islands segments of the aleutian arc when a shorter time interval is considered 1988 1998 those segments more likely to rupture in large ms 7 7 7 rather than great earthquakes have a high conditional probability these areas include the unimak fox and delarof islands segments the largest uncertainties in these forecasts stem from the short historic record providing a single recurrence time estimate for some segments or widely varying estimates for others from the unknown importance of aseismic slip and from a vague definition of characteristic earthquake size in fact characteristic earthquake size may not be a time invariant quantity

intermediate term earthquake prediction using precursory events in the new madrid seismic zone abstract earthquake prediction may be possible for some mainshock events the time to failure method described by varnes 1989 and bufe and varnes 1990 uses precursory events foreshocks to define an accelerated energy release curve by fitting an equation to the data a predicted time of failure and magnitude can be calculated until recently this method has been used in only a few studies in tectonically active areas and for moderate to large magnitude mainshock events using the microearthquake network data set from the new madrid seismic zone nmsz which is reasonably complete for earthquakes of magnitude 1 5 in the area of interest the method has yielded predicted values of past events as small as m b 3 5 the network data set used in this evaluation covers the time interval from 29 june 1974 to 20 july 1995 for the nmsz there have been 36 earthquakes of magnitude 3 5 over the 21 yr period in which the network has been operating because precursory events are required for the application of the time to failure method mainshocks that occurred before 1980 do not have enough data to adequately define the accelerated energy release curve therefore we utilized the 26 earthquakes that occurred after 1980 and that had a magnitude 3 5 sixteen of the 26 mainshock events were modeled in most cases the precursory sequences yielded predicted times of failure and magnitudes that were reasonably close to the actual mainshock values the remaining mainshocks including those occurring before 1980 could not be modeled due to either 1 not enough events to adequately define the precursory sequence or 2 interfering events that disrupt the accelerated energy release curve in addition two events were modeled from the nuttli catalog nuttli 1979 along with one that used a combination of both catalogs nineteen earthquakes with magnitudes 3 5 were evaluated using the time to failure method the first calculation using the time to failure method gave predicted results with large error bounds essentially no upper bound on the predicted magnitude an empirical relationship between parameters has helped to constrain the range of the predicted magnitude and to a lesser extent the estimated time of failure this relationship modifies the time to failure equation and yields predicted values for magnitudes that have an upper limit another empirical relationship suggests that the logarithm of the moment of the mainshock increases linearly with the logarithm of the size of the precursory event search diameter the relative seismicity of the region also influences the optimum search diameter used to find precursory events in addition to the evaluation of the acceleration sequences associated with the mainshocks an analysis of the occurrence of false positive acceleration sequences acceleration sequences that do not end in a mainshock was conducted the preliminary false positive analysis was conducted by randomly selecting potential mainshock locations the results yielded a false positive acceleration sequence occurrence rate of 2 with the incorporation of the empirical relationships into the time to failure method the potential for future intermediate term earthquake predictions for the nmsz is encouraging

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

evolution of moderate seismicity in the san francisco bay region 1850 to 1993 seismicity changes related to the occurrence of large and great earthquakes the rate of seismic activity of moderate size m 5 5 earthquakes in the san francisco bay sfb region has varied considerably during the past 150 years as measured by the rate of seismic moment release seismic activity in the sfb region is observed to accelerate prior to m 7 0 earthquakes in 1868 1906 and 1989 and then to decelerate following them we examine these seismicity changes in the context of the evolution of the stress field in the sfb region as a result of strain accumulation and release using a model of dislocations in an elastic halfspace we use a coulomb failure function cff to take into account changes in both shear and normal stresses on potential failure planes of varying strike and dip in the sfb region we find that the occurrence of a large or great earthquake creates a stress shadow a region where the stress driving earthquake deformation is decreased interseismic strain accumulation acts to reverse this process gradually bringing faults in the sfb region out of the stress shadow of a previous large or great earthquake and back into a state where earthquake failure is possible as the stress shadow generated by a large or great earthquake disappears it migrates inward toward the fault associated with that large or great event the observed changes in the rate of occurrence of moderate earthquakes in the sfb region are broadly consistent with this model in detail the decrease in seismicity throughout most of the sfb region and a localized increase in the monterey bay region following the great 1906 earthquake is consistent with our predicted stress changes the timing and location of moderate size earthquakes when the rate of seismicity increases again in the 1950s is consistent with areas in which the 1906 stress shadow had been eliminated by strain accumulation in the sfb region those earthquakes that are most inconsistent with our stress evolution model including the 1911 earthquake southeast of san jose are found to occur in regions where dip slip faulting is common in addition to strike slip the 1906 earthquake brought that zone of dip slip faulting closer to failure suggesting that the 1911 event may have been a reverse faulting earthquake rather than a strike slip one similar to the 1984 morgan hill earthquake the occurrence of activity on faults very close to the san andreas such as the lake elsman earthquakes of 1988 and 1989 appear to be associated with the last disappearence of the stress shadow on the loma prieta segment of the san andreas fault thus events of that type may represent an intermediate term precursor to a large earthquake such as the 1989 loma prieta event much of the moderate size earthquake activity in the sfb region appears to be modulated in time by the buildup and release of stress in large and great earthquakes a tensorial approach to earthquake prediction i e taking into account changes in the components of the stress tensor has several advantages over examining scalar changes such as those in seismic activity and moment release rates this tensorial approach allows for both activation and quiescence but in different subregions prior to as well as after large earthquakes

frequency of occurrence of moderate to great earthquakes in intracontinental regions implications for changes in stress earthquake prediction and hazards assessments we investigate the departure of shallow intracontinental earthquakes from the frequency magnitude relationship log n m a bm we consider seven large continental regions but exclude subduction zones in each active and stable areas are differentiated within active areas we separately categorize earthquakes on faults with high slip rates we use data sets from 1978 1994 and 1900 1994 which are complete for moment magnitudes mw 5 3 and 7 0 to calculate changes in b value with mw for all active intracontinental regions combined except asia b changes at 98 confidence from 0 90 to 2 1 at a corner magnitude mc of 6 9 to 7 0 the distribution for stable regions indicates a similar change values of mc are associated with downdip widths of rupture of about 23 to 27 km which are smaller than those for subduction zones in each case mc marks a transition from unbounded to bounded earthquakes in asia events from 1958 to 1994 also delineate a similar change near mc 7 0 earthquakes in asia of 7 0 mw 8 1 from 1900 to 1957 however define a b value of 1 0 and a moment release rate 5 6 times higher than that from 1958 to 1994 those anomalous values indicate that a large region of asia was close to failure i e near a self organized critical state during the earlier period we associate those changes with the giant himalayan earthquake in 1950 of mw 8 6 regional variations in seismic strain release rates correlate with the types of processes at adjacent plate boundaries extrapolating rates of activity of the past 95 years to mw 8 0 indicates that such events should be very rare in stable areas

the cyclic and fractal seismic series preceding an mb 4 8 earthquake on 1980 february 14 near the virgin islands summary seismic activity in the 10 months preceding the 1980 february 14 mb 4 8 earthquake in the virgin islands reported on by frankel in 1982 consisted of four principal cycles each cycle began with a relatively large event or series of closely spaced events and the duration of the cycles progressively shortened by a factor of about 3 4 had this regular shortening of the cycles been recognized prior to the earthquake the time of the next episode of seismicity the main shock might have been closely estimated 41 days in advance that this event could be much larger than the previous events is indicated from time to failure analysis of the accelerating rise in released seismic energy using a non linear time and slip predictable foreshock model examination of the timing of all events in the sequence shows an even higher degree of order rates of seismicity measured by consecutive interevent times when plotted on an iteration diagram of a rate versus the succeeding rate form a triangular circulating trajectory the trajectory becomes an ascending helix if extended in a third dimension time this construction reveals additional and precise relations among the time intervals between times of relatively high or relatively low rates of seismic activity including period halving and doubling the set of 666 time intervals between all possible pairs of the 37 recorded events appears to be a fractal the set of time points that define the intervals has a finite non integer correlation dimension of 0 70 in contrast the average correlation dimension of 50 random sequences of 37 events is significantly higher close to 1 0 in a similar analysis the set of distances between pairs of epicentres has a fractal correlation dimension of 1 52 well defined cycles numerous precise ratios among time intervals and a non random temporal fractal dimension suggest that the seismic series is not a random process but rather the product of a deterministic dynamic system

the linked stress release model for spatio temporal seismicity formulations procedures and applications summary the linked stress release model is based on the build up of stress through elastic rebound and its dissipation in the form of earthquakes in addition stress can be transferred between large scale geological or seismic features the model can be statistically fitted to both historical and synthetic seismicity catalogues and through simulation can be used to create probabilistic forecasts of earthquake risk we review the genesis of the model provide some observations on forecasting using the model and follow with a comprehensive review of applications to date a systematic procedure for identification of the best model is illustrated by data from the persian region we then consider the evaluation of fitted models using residual point processes and information gains implications of the use of benioff strain rather than seismic moment are discussed the sensitivity of the model to regionalization magnitude errors catalogue incompleteness catalogue size and declustering magnitude cut off is then considered in detail with reference to data from north china the latter data are also used to illustrate the model evaluation techniques introduced earlier some technical material on numerical fitting simulation and calculation of the information gain is given in an appendix

stress correlation function evolution in lattice solid elasto dynamic models of shear and fracture zones and earthquake prediction it has been argued that power law time to failure fits for cumulative benioff strain and an evolution in size frequency statistics in the lead up to large earthquakes are evidence that the crust behaves as a critical point cp system if so intermediate term earthquake prediction is possible however this hypothesis has not been proven if the crust does behave as a cp system stress correlation lengths should grow in the lead up to large events through the action of small to moderate ruptures and drop sharply once a large event occurs however this evolution in stress correlation lengths cannot be observed directly here we show using the lattice solid model to describe discontinuous elasto dynamic systems subjected to shear and compression that it is for possible correlation lengths to exhibit cp type evolution in the case of a granular system subjected to shear this evolution occurs in the lead up to the largest event and is accompanied by an increasing rate of moderate sized events and power law acceleration of benioff strain release in the case of an intact sample system subjected to compression the evolution occurs only after a mature fracture system has developed the results support the existence of a physical mechanism for intermediate term earthquake forecasting and suggest this mechanism is fault system dependent this offers an explanation of why accelerating benioff strain release is not observed prior to all large earthquakes the results prove the existence of an underlying evolution in discontinuous elasto dynamic systems which is capable of providing a basis for forecasting catastrophic failure and earthquakes

a physical model for earthquakes 2 application to southern california the purpose of this paper is to apply ideas developed in a previous paper to the construction of a detailed model for earthquake dynamics in southern california the basis upon which the approach is formulated is that earthquakes are perturbations on or more specifically fluctuations about the long term motions of the plates this concept is made mathematically precise by means of a fluctuation hypothesis which states that all physical quantities associated with earthquakes can be expressed as integral expansions in a fluctuating quantity called the offset phase while in general the frictional stick slip properties of the complex interacting faults should properly come out of the underlying physics a simplification is made here and a simple spatially varying friction law is assumed together with the complex geometry of the major active faults an assumed spatially varying earth rheology the average rates of long term offsets on all the major faults and the friction coefficients one can generate synthetic earthquake histories for comparison to the real data the result is a set of slip time histories for all of the major faults which are similar to data obtained by geologic trenching studies however the patterns of earthquake occurrence are evidently chaotic in the technical sense meaning that although there is an element of periodicity to the events the patterns shift change and evolve with time time scales for pattern evolution seem to be of the order of a thousand years for average recurrance intervals of a hundred years or so in the synthetic slip histories for the model faults a series of events on the big bend is identified which resembles the pattern of events leading up to the 1857 fort tejon earthquake one of the events is similar enough to the 1857 event that it is taken as a model of that earthquake the horizontal surface deformation 130 years after the model event is calculated for comparison to the data observed by various methods during the past decade in southern california for example horizontal surface rates of strain and velocities are calculated and compared to u s geological survey trilateration data to very long baseline interferometry line length changes and to laser ranging data on the san andreas fault experiment baseline with a few exceptions agreement is good