serial ruptures of the san andreas fault carrizo plain california revealed by three dimensional excavations 1 it is poorly known if fault slip repeats regularly through many earthquake cycles well documented measurements of successive slips rarely span more than three earthquake cycles in this paper we present evidence of six sequential offsets across the san andreas fault at a site in the carrizo plain using stream channels as piercing lines we opened a latticework of trenches across the offset channels on both sides of the fault to expose their subsurface stratigraphy we can correlate the channels across the fault on the basis of their elevations shapes stratigraphy and ages the three dimensional excavations allow us to locate accurately the offset channel pairs and to determine the amounts of motion for each pair we find that the dextral slips associated with the six events in the last millennium are from oldest to youngest 5 4 0 6 8 0 0 5 1 4 0 5 5 2 0 6 7 6 0 4 and 7 9 0 1 m in this series three and possibly four of the six offset values are between 7 and 8 m the common occurrence of 7 8 m offsets suggests remarkably regular but not strictly uniform slip behavior age constraints for these events at our site combined with previous paleoseismic investigations within a few kilometers allow a construction of offset history and a preliminary evaluation of slip and time predictable models the average slip rate over the span of the past five events between a d 1210 and a d 1857 has been 34 mm yr not resolvably different from the previously determined late holocene slip rate and the modern geodetic strain accumulation rate we find that the slip predictable model is a better fit than the time predictable model in general earthquake slip is positively correlated with the time interval preceding the event smaller offsets coincide with shorter prior intervals and larger offset with longer prior intervals

major pathways of atlantic water in the northern north atlantic and nordic seas toward arctic 1 the major pathways of near surface atlantic water in the northern north atlantic and nordic seas are identified as current speeds above 30 cm s using 1014 lagrangian drifters combined with previously published hydrography the inflow over the scotland greenland ridge and establishment of the two branch norwegian atlantic current nwac are described in light of the circulation in the northern north atlantic the western branch of the nwac appears as a jet in the polar front topographically guided from the iceland faroe front through the nordic seas toward fram strait the eastern branch starts as a shelf edge current above the irish scottish continental shelf and after passing through the faroe shetland channel it continues northward along the norwegian shelf edge toward the arctic with a branch bifurcating into the barents sea the nwac appears to maintain its two branch structure throughout the nordic seas with the atlantic water confined to a 200 600 km wide wedge

ages of late holocene earthquakes on the central garlock fault near el paso peaks california a trench across the central garlock fault within a small playa adjacent to el paso mountains revealed buried fissures and fault scarps that provide strong evidence for five surface rupturing earthquakes within the past 5 kyr weaker evidence suggested the possibility of three additional events within this same time period these observations indicate an average recurrence interval of 700 to 1200 years nearly all 28 radiocarbon dates on samples of detrital charcoal wood and shell are in correct stratigraphic order these dates constrain the ages of the individual faulting events and indicate that the recurrence interval is not periodic but is quite irregular individual recurrence intervals range from 190 to 1545 years if all eight events are actual earthquakes or from 190 to 3405 years if only the five well documented events represent earthquakes the two most recent earthquakes occurred within the past 550 years with preferred ages of about a d 1790 and a d 1600 the a d 1790 event ruptured a narrower width of the fault zone and may have been a smaller earthquake than the others the radiocarbon dates from the trench also indicate that the sedimentation rate on the playa has fluctuated within the past 5 kyr low sedimentation rates 0 1 to 0 35 mm yr and infrequent floods 1 per century prevailed from about 2000 b c to a d 100 and from a d 500 to 1300 during the remaining intervals within the past 5 kyr the sedimentation rate averaged 1 0 to 1 7 mm yr and major floods occurred two to four times per century the changes in sedimentation rate and flood frequency may reflect climatic changes or they may simply reflect changes in drainage patterns

holocene rate of slip and tentative recurrence interval for large earthquakes on the san andreas fault cajon pass southern california abstract detailed mapping of the san andreas fault zone where it crosses cajon creek southern california has revealed a number of late quaternary deposits and geomorphological features offset by the fault radiocarbon dates from alluvial and swamp deposits provide a detailed chronology with which to characterize the activity of the san andreas fault four independent determinations of the slip rate on the san andreas fault yield an average rate of 24 5 3 5 mm yr for the past 14 400 years the similarity of the four values which span different intervals of time from 5900 to 14 400 years ago suggest that the slip rate has been constant during this period the slip rate confirms that the san andreas fault is accumulating slip faster than any other fault in the plate boundary throughout california also the sum of the slip rates on the san andreas 24 5 mm yr and the san jacinto 10 mm yr faults south of their junction is the same as the san andreas north of their junction 35 mm yr an excavation provided evidence for at least two and up to four earthquakes that caused rupture on the fault between 1290 and 1805 a d and tentative evidence for six earthquakes in about the last 1000 years both lines of evidence imply an average recurrence interval for large earthquakes of about 1 to 2 centuries combined with the historic record this investigation indicates that the last major earthquake at cajon creek was probably at the beginning or middle of the 18th century while the record at cajon creek may suggest that the next major earthquake on the san andreas fault is overdue the data can be interpreted to indicate that the recurrence interval for earthquakes on the san andreas south of the 1857 rupture is 3 to 4 centuries and that the anticipated event should not be expected until the next century

an application of synthetic seismicity in earthquake statistics the middle america trench this paper demonstrates how synthetic seismicity calculations which are based on the concept of fault segmentation and incorporate the physics of faulting through static dislocation theory can improve earthquake recurrence statistics and hone the probabilities of hazard compared to forecasts constructed from a handful of earthquake recurrence intervals forecasts constructed from synthetic seismicity are more robust in that they embody regional seismicity information over several units of magnitude they can extrapolate seismicity to higher magnitudes than have actually been observed and they are formulated from a catalog which can be extended as long as needed to be statistically significant synthetic seismicity models can also be used to judge the stability of common rate estimates and the appropriateness of idealizations to the earthquake cycle i find that estimates of fault slip rate are unbiased regardless of sampling duration while estimates of earthquake recurrence time are strongly biased recurrence intervals estimated from seismicity samples less than about 10 times the actual recurrence interval will almost certainly be too short for the middle america trench mat it would take 200 and 400 years of monitoring to constrain slip and recurrence rates to 10 events m 6 have as much as a 60 probability of recurrence within 5 years due to the clustering of small earthquakes in foreshocks and aftershocks this probability drops to less than 15 for m 7 events increasing gap time generally increases conditional probability of earthquake occurrence but the effect is weak for the mat the spread parameters of the best fitting lognormal or weibull distributions 0 75 are much larger than the 0 21 intrinsic spread proposed in the nishenko buland hypothesis stress interaction between fault segments disrupts time or slip predictability and causes earthquake recurrence to be far more aperiodic than has been suggested

strain accumulation in western united states this review is principally concerned with recent geodetic strain measure ments in western united states undertaken by the us geological survey as part of the earthquake studies program and as a consequence is heavily biased toward the author s own publications most of the publications reporting crustal strain measurements in western united states prior to about 1968 have been compiled in one volume national geodetic survey 1973 and more recent work with complete bibliographies is summarized in three successive quadrennial reports to the international union of geodesy and geophysics meade 1971 savage 1975 thatcher 1979b the following conventions are employed in this paper strain a dimensionless quantity is reported in units of 10 6 extension is taken as positive to distinguish between engineering and tensor shear strain we denote the former by y and quote the units as j lrad whereas the latter is denoted by e and given the units of j lstrain uncertainties in all cases are quoted as one standard deviation at the present time geodetic techniques furnish the only reliable measure of strain accumulation in the seismic regions of the world the superiority of geodetic techniques derives principally from the long baseline of the measurements difficulties in coupling fiducial marks to the earth have generally made short baseline measurements of strain accumulation questionable wyatt 1982 however long baselines introduce the dis advantage that the measured strain is not closely localized the current technique of measuring strain accumulation involves the

a viscoelastic coupling model for the cyclic deformation due to periodically repeated earthquakes at subduction zones vertical displacements due to periodic reverse faulting events in an elastic plate overlying a viscoelastic maxwell half space are obtained and compared with the observed deformation cycle coseismic strain release postseismic transients interseismic strain accumulation from japan the viscoelastic effects including the influence of buoyant restoring forces are obtained using the method developed by rundle and plate convergence and strain accumulation are incorporated following the procedure suggested by savage the resulting deformation cycle is compared with that of an analogous elastic half space dislocation model in which postearthquake effects are due to transient aseismic slip below the coseismic fault cyclic deformation is similar but not identical for the two models and observations from southwest japan suggest the superiority of the viscoelastic coupling model in particular inclusion of the effects of steady state flow in the asthenosphere overcomes a defect of the elastic half space model and results in agreement with the observed interseismic movement pattern several aspects of the postseismic deformation its landward migration and its transition to the interseismic phase of the cycle are explained as well but the short duration of near trench transients relative to those observed farther inland is not matched the success of a buried slip model in explaining early postseismic near trench movements and asthenospheric flow in accounting for cumulative postearthquake transient motions suggests the existence of a transition zone between lithosphere and asthenosphere whose behavior is brittle elastic in the short term and ductile for longer term deformation and such a modification may reconcile remaining discordant observations however reasonable variations in coupling model parameters cannot account for observed differences in the deformation cycle in other parts of japan and these regional differences remain unexplained

upgrading a synthetic seismicity model for more realistic fault ruptures a quasi static synthetic seismicity model for multiple interacting faults of any orientation is upgraded to include a more realistic rupture model in the original model entire ruptures covering many fault patches occur instantaneously and rupture propagation is ignored now time is introduced into the rupture process via a patch interaction delay in proportion to distance shear wave velocity also to try to mimic observed rise times for real earthquakes a simple time dependent friction law is used comparison of results for the old and new models for a simple case of two strike slip faults show that clustering of large events is somewhat reduced in the new model it remains to be seen if this conclusion will be verified in more complex fault networks the new model takes about twice as much computation time but the results may now be used to calculate synthetic seismograms

a simulation based approach to forecasting the next great san francisco earthquake in 1906 the great san francisco earthquake and fire destroyed much of the city as we approach the 100 year anniversary of that event a critical concern is the hazard posed by another such earthquake in this article we examine the assumptions presently used to compute the probability of occurrence of these earthquakes we also present the results of a numerical simulation of interacting faults on the san andreas system called virtual california this simulation can be used to compute the times locations and magnitudes of simulated earthquakes on the san andreas fault in the vicinity of san francisco of particular importance are results for the statistical distribution of recurrence times between great earthquakes results that are difficult or impossible to obtain from a purely field based approach

role of subsurface loads and regional compensation in the isostatic balance of the transverse ranges california evidence for intracontinental subduction bouguer gravity anomalies in the transverse ranges of southern california show a pronounced asymmetry in north south profiles across the mountains and a characteristic shape which is largely insensitive to variations in the topographic load along strike while individual gravity topography profile pairs could be consistent with a number of isostatic compensation mechanisms the unusual relationship between gravity and topography in the san bernardino mountains severely limits the class of acceptable models if the bouguer gravity field is caused by flexure of the crust mantle boundary the simplest solution consistent with the data in the western transverse ranges the san gabriel mountains and the san bernardino mountains models the great valley and mojave provinces to the north as a 50 km thick elastic plate supporting the mountains which are underthrust by a much weaker plate to the south the best fit to the gravity data in the san bernardino mountains requires a terminal bending moment on the southern plate beneath the mountains the magnitude of the terminal bending moment decreases to the west in the san gabriel and western transverse ranges we equate the load responsible for this terminal moment with the high velocity slablike feature mapped in the upper mantle beneath the transverse ranges using seismic tomography the coupling between the subsurface load and the overlying lithosphere suggests that the slab represents lithospheric subduction with an extremely small density contrast rather than a small scale convective feature

extensional reactivation of an abandoned thrust a bound on shallowing in the brittle regime abstract shallow dip angles 45 suggested by field observations of continental extensional faults are not predicted by classical isotropic mohr coulomb anderson theory earthquake data indicate that normal faults exist in the upper crust with dip angles commonly as shallow as 30 some structural evidence suggests brittle normal faulting with dip angles as shallow as 10 one explanation of the apparent conflict between theory and structural seismic observations is that intrinsically weak shallow dipping pre existing faults are preferentially reactivated any reduction in frictional strength of the pre existing structure below that of surrounding rock increases the likelihood that such structures will be first breaking when extension is initiated enhanced fluid pore pressure on the pre existing fault reduces the effective strength and can further enhance shallow fault reactivation an analytical treatment clarifies the roles of geometry intact pre existing fault strengths and fluid pore pressures frictional strength ratios of 3 or greater could account for extremely shallow normal faults dips 10 20 without consideration of pore pressures in excess of the least principal stress or of principal stress systems rotated away from the gravity vector moderate reduction in friction 3 4 with respect to wall rock can reduce the dip to 30 and can account for shallow normal slip earthquakes

holocene environments of central iturup island southern kuril archipelago russian far east two lake records document holocene changes in sea level vegetation and climate on the okhotsk and pacific sides of central iturup island southern kuril islands the sediment cores originated within tidal flats that subsequently developed into a marine strait which crosscut the island as sea levels rose during the early holocene brackish lagoons and eventually freshwater lakes formed by 7100 cal yr bp associated with warmer than present conditions past vegetation changes indicate a clear holocene thermal maximum recorded on the pacific coast but a less distinct optimum on the western shores 7200 6100 cal yr bp a gradual cooling toward modern levels occurred 6100 3500 cal yr bp four prominent layers of coarse sediment found in mid to late holocene lake deposits may correspond to intervals of climate cooling dune formation previously documented in coastal sections although chronological limitations question the synchronicity of these events across the south russian far east it seems probable that they have a regional signature however the mechanisms responsible for holocene climatic changes are likely the result of complex interactions of hemispheric scale atmospheric patterns marine characteristics and regional feedbacks rather than simply fluctuations in sea levels as suggested in the current interpretative model

gravity changes from a stress evolution earthquake simulation of california 1 the gravity signal contains information regarding changes in density at all depths and can be used as a proxy for the strain accumulation in fault networks a stress evolution time dependent model was used to create simulated slip histories over the san andreas fault network in california using a linear sum of the gravity signals from each fault segment in the model via coseismic gravity green s functions a time dependent gravity model was created the steady state gravity from the long term plate motion generates a signal over 5 years with magnitudes of 2 gal the current limit of portable instrument observations moderate to large events generate signal magnitudes in the range of 10 to 80 gal well within the range of ground based observations the complex fault network geometry of california significantly affects the spatial extent of the gravity signal from the three events studied

strain accumulation in southern california 1973 1984 repeated surveys of selected lines from five trilateration networks along the san andreas fault in southern california have been used to deduce the 1973 1984 strain accumulation records at five localities the secular rate of engineering shear strain accumulation is about 0 3 rad yr with the plane of maximum shear parallel to the local strike of the san andreas fault the secular rate of accumulation of areal dilatation is negligible the data were examined to detect evidence for fluctuations in the rate of strain accumulation for this examination 19 lines were removed from the data set four because they exhibited an obvious coseismic offset and 15 others because they contained at least one very anomalous measurement that could reasonably be attributed to a survey blunder the incidence of such blunders appears to be one in every 75 measurements the remaining data consist of 104 lines with an average of 10 measurements each although the strain accumulation plots for the five networks may exhibit marginally significant temporal fluctuations we are not convinced that those fluctuations are greater than could be attributed to survey error in particular we are unable to demonstrate that the 1973 1979 southern california strain anomaly reported by savage and others is real given the uncertainty in the random and systematic errors in measurement the strain measurements in southern california are marginally consistent with linear in time strain accumulation the strain accumulation plots for the salton network clearly established that unlike the deformation reported after the 1940 imperial valley earthquake no acceleration in the shear strain rate has yet been observed following the 1979 imperial valley earthquake

1855 and 1991 surveys of the san andreas fault implications for fault mechanics two monuments from an 1855 cadastral survey that span the san andreas fault in the carrizo plain have been right laterally displaced 11 0 2 5 m by the 1857 fort tejon earthquake and associated seismicity and afterslip this measurement confirms that at least 9 5 0 5 m of slip occurred along the main fault trace as suggested by measurements of offset channels near wallace creek the slip varied by 2 to 3 m along a 2 6 km section of the main fault trace using radiocarbon dates of the penultimate large earthquake and measurements of slip from the 1857 earthquake we calculate an apparent slip rate for the last complete earthquake cycle that is at least 25 lower than the late holocene slip rate on the main fault trace comparison of short term broad aperture strain accumulation rates with the narrow aperture late holocene slip rate indicates that the fault behaves nearly elastically over a time scale of several earthquake cycles therefore slip in future earthquakes should compensate the slip rate deficit from the 1857 earthquake

near surface circulation in the northern north atlantic as inferred from lagrangian drifters variability from the mesoscale to interannual 1 the near surface circulation of the nordic seas is basically cyclonic and consists of jets and recirculation cells which are tightly linked to the bottom topography variable forcing by the large scale rotation of the wind leads to a modulation in the strength of the gyres and their interconnecting jets this is seen in drifter and altimeter data currents are stronger during winter and during phases of high north atlantic oscillation index the exchanges between the north atlantic and the nordic seas do not seem to be directly affected by this variable forcing the narrow boundary currents and the intergyre jets are subject to instability causing mesoscale current fluctuations which contribute to the stirring and mixing of polar and atlantic water masses

pathways of the greenland sea warming 1 progressive warming of the west spitsbergen current wsc has been observed since 2004 during summer 2006 temperature and salinity of the core of atlantic water aw reached the highest ever observed by the institute of oceanology polish academy of sciences iopas values the structure of the wsc the heat content and the extent of aw in the fram strait fs region has also changed temperature changes resulted from the upstream warming of the norwegian atlantic current nwac the structure of the wsc and its heat content were modified by the northward advection of large mesoscale eddies observed within the western branch of the wsc in summer 2005 these changes may have large impacts on the arctic ocean ao climate and ecosystem

simulation based distributions of earthquake recurrence times on the san andreas fault system earthquakes on a specified fault or fault segment with magnitudes greater than a specified value have a statistical distribution of recurrence times the mean recurrence time can be related to the rate of strain accumulation and the strength of the fault very few faults have a recorded history of earthquakes that define a distribution well for hazard assessment in general a statistical distribution of recurrence times is assumed along with parameter values assumed distributions include the weibull stretched exponential distribution the lognormal distribution and the brownian passage time inverse gaussian distribution the distribution of earthquake waiting times is the conditional probability that an earthquake will occur at a time in the future if it has not occurred for a specified time in the past the distribution of waiting times is very sensitive to the distribution of recurrence times an exponential distribution of recurrence times is poissonian so there is no memory of the last event the distribution of recurrence times must be thinner than the exponential if the mean waiting time is to decrease as the time since the last earthquake increases neither the lognormal or the brownian passage time distribution satisfies this requirement we use the virtual california model for earthquake occurrence on the san andreas fault system to produce a synthetic distribution of earthquake recurrence times on various faults in the san andreas system we find that the synthetic data are well represented by weibull distributions we also show that the weibull distribution follows from both damage mechanics and statistical physics

fault interaction near hollister california a numerical model is used to study fault stress slip near hollister california the geometrically complex system of interacting faults including the san andreas calaveras sargent and busch faults is approximated with a two dimensional distribution of short planar fault segments in an elastic medium the steady stress and slip rate are simulated by specifying frictional strength and stepping the remote stress ahead in time the resulting computed fault stress is roughly proportional to the observed spatial density of small earthquakes suggesting that the distinction between segments characterized by earthquakes and those with aseismic creep results in part from geometry a nonsteady simulation is made by introducing in addition stress drops for individual moderate earthquakes a close fit of observed creep with calculated slip on the calaveras and san andreas faults suggests that many changes in creep rate averaged over several months are caused by local moderate earthquakes in particular a 3 year creep lag preceding the august 6 1979 coyote lake earthquake on the calaveras fault seems to have been a direct result of the november 28 1974 thanksgiving day earthquake on the busch fault computed lags in slip rate preceding some other moderate earthquakes in the area are also duemore to earlier earthquakes although the response of the upper 1 km of the fault zone may cause some individual creep events and introduce delays in others the long term rate appears to reflect deep slip less

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

forecast model for large and great earthquakes in southern california an earthquake instability model is used to compute theoretical fault slip and ground surface deformation before possible future earthquakes on the san andreas fault in southern california the quasistatic model represents the earth s crust by an elastic half space and the san andreas imperial cerro prieto and san jacinto faults by flat rectangular surfaces whose strikes approximate the actual local strikes the seismogenic zone of the san andreas fault is represented by a brittle strain softening patch extending from the ground surface to 11 km depth and from parkfield to the salton sea 500 km the strength of the patch varies along strike and unstable failures of parts of the patch are earthquake analogs failed areas heal immediately after instability for the model to reproduce the lengths slips and times of earthquakes since 1080 a d reported by k sieh and others the patch must be divided into five sections along strike the sections have alternately low and high strength with the two strongest sections being roughly coincident with the major bends of the san andreas fault ten to twenty years before unstable slippage of patch areas portions of the patch bottom begin to fail stably aseismically the stable failure causes accelerating fault slip at depth and at the fault trace as well as anomalous changes in lengthening rates of trilateration lines in the model simulation the next two sections to fail unstably in the future are just north of the salton sea and just south of parkfield rupture lengths are about 100 km and 40 km at favorable locations precursory anomalies of fault slip and trilateration line length become large enough to be detected in field data a few years before each earthquake

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

recurrence time distributions of large earthquakes in eastern iran the eastern part of the iranian plateau is characterized by large and infrequent earthquakes with recurrence intervals of more than several hundred years given that previous observations and paleoseismological studies are insufficient for forecasting large earthquakes we have developed a physics based synthetic seismicity model for the fault system in eastern iran using the virtual quake simulator the model is independent of the seismic catalogs however it is tuned to match available earthquakes records we show that the modeled seismicity rates and empirical frequency magnitude distributions are consistent within the uncertainty of the empirical relations furthermore our synthetic catalog agrees with previous paleoseismological investigations from the resulting catalog we can obtain the statistical distributions of recurrence times and waiting times for large earthquakes in the region as a whole and for the individual faults in agreement with previous earthquake simulator studies we find that the poisson time independent distribution best describes the recurrence times of large earthquakes in the region as a whole large earthquakes on the individual faults show quasi periodic behavior and for most faults can be well represented by the weibull distribution we present the corresponding time dependent conditional probabilities for large earthquakes throughout the region and for a few selected individual faults long term simulations indicate that waiting times for large earthquakes on specific faults are strongly dependent on the fault system configuration faults confined by other active faults or consisting of several segments host large earthquakes with more distributed recurrence times moreover the obtained long term synthetic seismic catalog shows that fault interactions clearly have a major effect on occurrence of large earthquakes and hence should be taken into account for seismic hazard assessment

stratigraphic evidence for seven meters of dextral slip on the san andreas fault during the 1857 earthquake in the carrizo plain the smallest geomorphic offsets along a 35 km section of the san andreas fault in the carrizo plain vary from 7 to 10 m our three dimensional excavation of alluvial deposits a few km southeast of wallace creek confirms that at least 6 6 to 6 9 m of dextral slip occurred there during the latest large earthquake in 1857 dates on detrital charcoal suggest that the last event prior to the 1857 earthquake occurred before a date within the range a d 1305 to 1623 the 3 m range in smallest offsets along this portion of the fault may reflect either a 3 m variation in slip along the san andreas in 1857 or 2 to 3 m of slip during an event prior to 1857 observations made after the recent landers earthquake are compatible with the hypothesis of large local variations in slip during a single earthquake but do not explain the cause of such variations off fault dextral rotations would be one plausible explanation however paleoseismic data in the carrizo plain are too sparse to allow rejection of the alternative hypothesis that slip in the event prior to 1857 was only 2 to 3 m an amount of slip which would be several times too small to fit a time predictable model

stress transfer in earthquakes hazard estimation and ensemble forecasting inferences from numerical simulations abstract observations indicate that earthquake faults occur in topologically complex multi scale networks driven by plate tectonic forces we present realistic numerical simulations involving data mining pattern recognition theoretical analyses and ensemble forecasting techniques to understand how the observable space time earthquake patterns are related to the fundamentally inaccessible and unobservable dynamics numerical simulations can also help us to understand how the different scales involved in earthquake physics interact and influence the resulting dynamics our simulations indicate that elastic interactions stress transfer combined with the nonlinearity in the frictional failure threshold law lead to the self organization of the statistical dynamics producing 1 statistical distributions for magnitudes and frequencies of earthquakes that have characteristics similar to those possessed by the gutenberg richter magnitude frequency distributions observed in nature and 2 clear examples of stress transfer among fault activity described by stress shadows in which an earthquake on one group of faults reduces the coulomb failure stress on other faults thereby delaying activity on those faults in this paper we describe the current state of modeling and simulation efforts for virtual california a model for all the major active strike slip faults in california noting that the working group on california earthquake probabilities wgcep uses statistical distributions to produce earthquake forecast probabilities we demonstrate that virtual california provides a powerful tool for testing the applicability and reliability of the wgcep statistical methods furthermore we show how the simulations can be used to develop statistical earthquake forecasting techniques that are complementary to the methods used by the wgcep but improve upon those methods in a number of important ways in doing so we distinguish between the official forecasts of the wgcep and the research quality forecasts that we discuss here finally we provide a brief discussion of future problems and issues related to the development of ensemble earthquake hazard estimation and forecasting techniques

an efficient numerical method for earthquake cycles in heterogeneous media alternating subbasin and surface rupturing events on faults crossing a sedimentary basin we present an efficient numerical method for earthquake cycle simulations that employs a finite difference discretization of the off fault material to accommodate spatially variable elastic properties the method is developed for the two dimensional antiplane shear problem of a vertical strike slip fault with rate and state friction we compare earthquake cycles in a homogeneous half space with those in which the upper portion of the fault cuts through a sedimentary basin in both cases we assume velocity weakening behavior over the full seismogenic depth even in the basin to isolate the influence of elastic heterogeneity in a homogeneous half space events rupturing the full seismogenic depth occur periodically event sequences are more complex in basin models with one or several subbasin events confined to the lower section of the fault followed by a much larger surface rupturing event that breaks through the basin this phenomenology emerges only for sufficiently compliant and deep basins predicted surface velocities are essentially identical before subbasin events and surface rupturing events suggesting that geodetic observations would not be useful in predicting the rupture mode the alternating sequence of subbasin and surface rupturing events would complicate interpretation of paleoseismic data our results also offer one potential explanation for the shallow slip deficit observed in many recent earthquakes namely that these events which lack appreciable surface slip are simply one style of rupture subsequent events on these faults might be larger with slip extending all the way to the surface the 1940 mw 7 0 and 1979 mw 6 5 imperial valley events might be considered as examples of these two rupture styles

parametrizing physics based earthquake simulations utilizing earthquake source parameter scaling relations we formulate an extensible slip weakening friction law for quasi static earthquake simulations this algorithm is based on the method used to generate fault strengths for a recent earthquake simulator comparison study of the california fault system here we focus on the application of this algorithm in the virtual quake earthquake simulator as a case study we probe the effects of the friction law s parameters on simulated earthquake rates for the ucerf3 california fault model and present the resulting conditional probabilities for california earthquake scenarios the new friction model significantly extends the moment magnitude range over which simulated earthquake rates match observed rates in california as well as substantially improving the agreement between simulated and observed scaling relations for mean slip and total rupture area

an approach to modeling present day deformation in southern california this paper presents an approach to modeling the complete time dependent deformation in southern california we make use of a variety of techniques to include the far field plate motion stress relaxation in the asthenosphere aseismic fault slip within the elastic lithosphere and the complex three dimensional nature of the faults within the southern california region among the conclusions of the work here are the following 1 the data exhibit a marginal preference for a relatively thin lithosphere in southern california 2 the most sensitive determinant for lithospheric thickness and viscosity of the asthenosphere is the rotation rate of the motion vectors toward or away from major faults 3 the major faults in southern california are slipping at depth at or near their average holocene rates 4 a shallow active decollement beneath the transverse ranges is apparently needed to realistically model the strain changes observed there and 5 this modeling technique offers the best approach for understanding the complex deformation field in southern california

pattern dynamics and forecast methods in seismically active regions large extended fault systems such as those in california demonstrate complex space time seismicity patterns which include repetitive events precursory activity and quiescence and aftershock sequences although the characteristics of these patterns can be qualitatively described a systematic quantitative analysis remains elusive our research suggests that a new pattern dynamics methodology can be used to define a unique finite set of seismicity patterns for a given fault system in addition while a long sought goal of earthquake research has been the reliable forecasting of these events very little progress has been made in developing a successful consistent methodology in this report we document the discovery of systematic space time variations in seismicity from southern california using a new technique here we present examples of this analysis technique on data obtained prior to events in seismically active areas that show coherent regions associated with the future occurrence of major earthquakes in the same areas these results strongly support the hypothesis that seismic activity is highly correlated across many space and time scales within large volumes of the earth s crust

earthquakes quaternary faults and seismic hazard in california data describing the locations slip rates and lengths of quaternary faults are the primary basis in this work for constructing maps that characterize seismic hazard in california the expected seismic moment m0e and the strength of ground shaking resulting from the entire rupture of each mapped fault or fault segment are estimated using empirical relations between seismic moment m0 rupture length source to site distance and strong ground motions assuming a fault model whereby the repeat time t of earthquakes on each fault equals m0e m0g where the moment rate m0g is proportional to fault slip rate it is observed that the moment frequency distribution of earthquakes predicted from the geologic data agrees well with the distribution determined from a 150 year historical record the agreement is consistent with the argument that the geologic record of quaternary fault offsets contains information sufficient to predict the average spatial and size distribution of earthquakes through time in california the estimates of t for each fault are the foundation for constructing maps that depict the average return period of 0 1g peak horizontal ground accelerations and the horizontal components of peak acceleration peak velocity and the pseudovelocity response at 1 period and 5 damping expected to occur at the level of 0 1 probability during a 50 year period of time a map is also formulated to show the probability that 0 1g horizontal ground accelerations will occur during the next 50 years the maps serve to illustrate the potential value of quaternary fault studies for assessing seismic hazard interpretation of available slip rates indicates that the largest and most frequent occurrence of potentially destructive strong ground motions are associated principally with the san andreas san jacinto calaveras hayward and ventura basin fault zones other regions of similarly high hazard may yet remain unrecognized this inadequacy results primarily from an incomplete data set numerous faults for example are mapped along the coastal region of northern california and within the modoc plateau but relatively few studies relating to fault slip rate are reported a similar problem exists for other stretches of coastal california where marine reflection studies provide evidence of active faulting offshore yet yield little or no information of fault slip rate geological and geophysical field studies can work to remove these deficiencies a concerted effort to locate and define rates of activity on all faults in california is the most promising means to further quantify present levels of seismic hazard in california

surficial offsets on the central and eastern garlock fault associated with prehistoric earthquakes geomorphic features offset along the central and eastern garlock fault record the amount of surface slip associated with prehistoric earthquakes along the easternmost 90 km of the fault the smallest offsets cluster around 2 3 m of left lateral slip apparently associated with the most recent earthquake on this portion of the fault larger offsets along this part of the fault especially in pilot knob valley cluster around values consistent with 2 4 m of slip in each of the past several events farther west south of el paso mountains offset geomorphic features suggest that each of the past two earthquakes on this stretch of the garlock fault was produced by about 7 m of slip whereas the third event back was produced by about 4 m of slip vertical displacements of geomorphic features range from 0 to 30 of the left lateral offsets within pilot knob valley along the southern side of the slate range vertical displacements are consistently up on the northern side whereas within the avawatz mountains both north and south side up vertical displacements are present on the basis of the geomorphic offsets the geometry of the garlock fault and the precedents set by historical strike slip earthquakes elsewhere a number of different rupture patterns are plausible these range from rupture of the entire garlock fault in a single event with a maximum magnitude of about mw 7 8 to separate rupture of the western segment and of the central and eastern segments combined with approximate magnitudes mw 1 1 and mw 7 5 respectively to separate rupture of even shorter segments producing earthquakes of magnitudes mw 6 6 to mw 7 5 in conjunction with available slip rates for the garlock fault the geomorphic offsets suggest that average recurrence intervals are probably within the range of 600 1200 years south of el paso mountains about 200 750 years in searles valley about 200 1300 years in pilot knob valley and about 200 3000 years near leach lake and in the avawatz mountains

acoustic emission experiments of rock failure under load simulating the hypocenter condition a series of acoustic emission ae experiments of rock failure have been conducted under cyclic load in tri axial stress tests to simulate the hypocenter condition the specimens are loaded by the combined action of a constant stress intended to simulate the tectonic loading and a small sinusoidal disturbance stress analogous to the earth tide induced by the sun and the moon each acoustic emission signal can indicate the occurrence time location and relative magnitude of the damage micro crack in the specimen the experimental results verified some precursors such as lurr load unload response ratio and aer accelerating energy release before macro fracture of the samples a new parameter the correlation between the ae and the load has been proposed to describe the loading history on the eve of some strong earthquakes the correlation between the benioff strain and the coulomb failure stress cfs decreases similar to the variation of lurr prior to strong earthquakes

critical jump distance for propagating earthquake ruptures across step overs the geometry of a strike slip fault system is an important component that influences the kinematics and interactions of the various faults within the system discontinuities and bends in the fault geometry not only determine the types of structures and the physiography that we observe along the fault system but also have a significant influence on the propagation of earthquake ruptures a precise knowledge of the fault geometry especially how it is segmented and other physical parameters is essential for seismic hazard analysis it is known that earthquake ruptures sometimes propagate over multiple faults by jumping from one segment to the next a fault jump is a sudden dynamic coalescence of two faults separated by a step over field observations suggest that a step over width of 5 km is an appropriate maximum jump distance our study shows that between 2 5 and 6 5 km of step over width the probability of fault jump for both releasing and restraining step overs decreases significantly from 100 to 10

virtual california earthquake simulations simple models and their application to an observed sequence of earthquakes summary numerical simulations are routinely used for weather forecasting it is clearly desirable to develop simulation models for regional seismicity one model that has been developed for the purpose is the virtual california vc simulation in order to better understand the behaviour of seismicity simulations we apply vc to three relatively simple problems involving a straight strike slip fault in problem i we divide the fault into two segments with different mean earthquake interval times in problem ii we add a central strong asperity segment and in problem iii we change this to a weak central segment in all cases we observe limit cycle behaviour with a wide range of periods we also show that the historical sequence of 13 great earthquakes along the nankai trough japan exhibits a limit cycle behaviour very similar to our asperity model

how regularly do earthquakes recur a synthetic seismicity model for the san andreas fault we have been attempting to improve estimates of long term earthquake recurrence probabilities along the san andreas fault by means of synthetic seismicity calculations the calculations are based on the concept of fault segmentation and incorporate the physics of static dislocation theory forecasts constructed from synthetic seismicity are robust in that they embody regional seismicity information over several units of magnitude they tie together in a physical manner a spectrum of fault segment features such as length strength characteristic magnitude mean repeat time and slip rate they can reasonably account for fault segment interactions and they are formulated from a catalog which can be extended as long as needed to be statistically significant we contend earthquake recurrence is more aperiodic than previously thought and as a result probabilities of major san andreas earthquakes should be revised downward

seismicity of the garlock fault california the garlock fault is a 265 km long left slip fault striking northeastward from the san andreas fault in southern california relocations of earthquakes that occurred from 1932 to 1981 on and near this major fault were made using the master event technique the spatial distribution of seismicity along the fault is different west and east of its midpoint near rand where the largest en echelon offset and a marked change in strike occur these two segments also display distinct geologic features and different seismic and aseismic behavior the 150 km long segment west of rand has shown continuous low seismic activity during the past 50 yr well documented aseismic creep and has a relatively complex fault trace in contrast the 155 km long segment east of rand has very few small earthquakes no demonstrable creep and a simpler fault trace p wave first motion studies substantiate predominantly left slip motion along the garlock fault overall energy release during this 50 yr period gives a seismic moment rate of 2 75 10 21 dyne cm yr much lower than that inferred from holocene geologic offsets thus indicating that the garlock fault currently represents a temporal seismic gap and that the potential exists for large earthquakes if behavior of the garlock fault is similar to that of the san andreas the western segment of the fault can be compared with the central creeping segment of the san andreas and the eastern segment with those segments broken by the 1857 and 1906 earthquakes thus larger events might be expected on the eastern segment than on the western segment or if the entire fault breaks during a single event larger displacements toward the east

a seismotectonic analysis of the anza seismic gap san jacinto fault zone southern california small earthquake epicenters near the anza seismic gap define a 20 km quiescent segment of fault bounded to the northwest and southeast by areas of relatively high seismicity recent moderate earthquakes on and near the san jacinto fault in the gap and their relatively depressed aftershock activity indicate that the fault is seismogenic and highly stressed but locked by some mechanism the locked nature of the fault may be due to relatively high compressive stress normal to the fault resulting from the convergent geometries of the local active discontinuous faults and the oblique orientation of the regional maximum compressive stress strain is not being relieved by aseismic fault creep a swarm of small earthquakes in the crustal block 13 km southwest of the anza gap beneath the cahuilla valley recently released stress in an area which was previously highly active before the 1918 m 6 8 and 1937 m l 6 0 earthquakes the occurrence of these periods of increased seismicity near cahuilla in the years immediately before the nearby closer than 35 km large earthquakes and the recent swarm suggest that the ground beneath cahuilla may be acting as a stress meter signaling the presence of high stresses before large local earthquakes the length of the quiescent fault segment suggests potential for about an m 6 5 earthquake if the entire segment ruptures at once

eigenpatterns in southern california seismicity 1 earthquakes in seismically active regions of the world are known to be associated with a variety of spatial and temporal patterns examples include precursory quiescence or activation seismic clustering and mogi donuts although the characteristics of these patterns can be qualitatively described a systematic quantitative analysis has proved elusive in this paper we employ a new method developed using numerical simulations that allows a systematic quantification of the spatial and temporal characteristics of the patterns in historic seismicity in southern california this method decomposes a set of boolean activity functions representing historic seismicity into their orthonormal eigenvalues and eigenfunctions here we show the results of this analysis which strongly support the hypothesis that seismic activity is highly correlated across many space scales and timescales within large volumes of the earth s crust

determination of relative site motions in the western united states using mark iii very long baseline interferometry four years of very long baseline interferometry vlbi measurements involving fixed and mobile stations in the western united states are analyzed using weighted least squares baseline solution time series are used to estimate rates of change of the vector baselines between pairs of vlbi stations horizontal vector motions are determined for 18 sites with respect to a site in the mojave desert six sites west of and two sites just to the east of the san andreas fault show northwestward motion closely parallel to the san andreas fault their motions range from 18 to 43 mm yr and are significant at confidence levels greater than 99 motions in california relative to interior north american plate sites are used to estimate an integrated contribution from basin and range spreading to the total relative pacific plate motion as 9 10 mm yr a maximum relative velocity of 50 51 mm yr is found between the interior north american sites and the western california sites in close agreement with the nuvel i plate motion model

a more precise chronology of earthquakes produced by the san andreas fault in southern california improved methods of radiocarbon analysis have enabled us to date more precisely the earthquake ruptures of the san andreas fault that are recorded in the sediments at pallett creek previous dates of these events had 95 confidence errors of 50 100 calendar years new error limits are less than 23 calendar years for all but two of the dated events this greater precision is due to larger sample size longer counting time lower background noise levels more precise conversion of radiocarbon ages to calendric dates and better stratigraphic constraints and statistical techniques the new date ranges with one exception fall within the broader ranges estimated previously but our estimate of the average interval between the latest 10 episodes of faulting is now about 132 years variability about the mean interval is much greater than was suspected previously five of the nine intervals are shorter than a century three of the remaining four intervals are about two to three centuries long despite the wide range of these intervals a pattern in the occurrence of large earthquakes at pallett creek is apparent in the new data the past 10 earthquakes occur in four clusters each of which consists of two or three events earthquakes within the clusters are separated by periods of several decades but the clusters are separated by dormant periods of two to three centuries this pattern may reflect important mechanical aspects of the fault s behavior if this pattern continues into the future the current period of dormancy will probably be greater than two centuries this would mean that the section of the fault represented by the pallett creek site is currently in the middle of one of its longer periods of repose between clusters and sections of the fault farther to the southeast are much more likely to produce the next great earthquake in california the greater precision of dates now available for large earthquakes recorded at the pallett creek site enables speculative correlation of events between paleoseismic sites along the southern half of the san andreas fault a history of great earthquakes with overlapping rupture zones along the mojave section of the fault remains one of the more attractive possibilities

temporal clustering of major earthquakes along individual faults due to post seismic reloading palaeoseismic evidence suggests that earthquake recurrence intervals in some regions can be highly variable with clusters of multiple large events separated by much longer periods of quiescence because post seismic processes have a significant effect on the reloading rate of the coseismic fault we hypothesize that temporal variations in the amount of stress concentrated in the non seismogenic lithosphere can modulate large earthquake recurrence times we explore this hypothesis using simple analogue spring dashpot slider models we find that in the presence of small amounts of environmental noise post seismic stress transfer over timescales much longer than an earthquake cycle may be an important factor in generating clustering behaviour the propensity for the system to be clustered is a function of a non dimensional number that we call the wallace number w w is defined as the average earthquake stress drop divided by the product of the long term geologic strain rate across the fault and the effective viscosity of the system our results indicate that environments with relatively low strain rates and a relatively weak non seismogenic lithosphere are most susceptible to clustering driven by post seismic stress recycling mechanisms

application of an inhomogeneous stress patch model to complex subduction zone earthquakes a discrete interaction matrix approach in recent years it has been recognized that the level of shear and normal stress along a fault can vary thus the stress is spatially and temporally inhomogeneous moreover it has also been suspected that faults might interact in some way with the result that a variety of earthquake magnitudes might be produced along a given length of fault at varying times in order to explore these ideas we have developed a quantitative formalism which we call the interaction matrix method to express the influence of one fault upon another this matrix is calculated by use of the energy change for a system of interacting cracks or faults and therefore gives energy consistent results specifically the interaction matrix relates the area averaged stress on the fault segment to the area averaged slip state on all the other fault segments in the system since any fault can be subdivided into an arbitrary number of fault segments the interaction matrix can have arbitrary dimension in fact the continuum limit is recovered as the dimension of the matrix approaches infinity we combine this matrix method with a segmentation or patch model for earthquakes in which each discrete segment of a fault has the same coseismic stress change defined as the difference between the driving stress at which healing occurs minus the driving stress at which sliding starts each time it slips we show that slip on a patch during an earthquake can vary substantially depending on how it interacts with other nearby patches in this model it is quite possible for the spatial distribution of stress on the fault following an event to be again in a spatially inhomogeneous state rather than in a uniform state as is often assumed hence the seismic moment produced by an earthquake on a given set of patches can vary substantially depending on the sequence of sliding and healing on the different patches to apply these ideas we devised a means to calculate the interaction matrix elements and used them to quantitatively examine earthquake sequences off the colombia ecuador coast and in the nankai trough near japan

synthetic seismicity models of multiple interacting faults a synthetic seismicity model for multiple interacting faults of any strike and dip in a three dimensional elastic half space has been developed the ultimate purpose is to determine how hazard is modified by elastic interactions of events in complex fault systems and to examine the synthetic seismicity for unusual behavior before large events that might be observable in the real world each fault is subdivided into some number of equal sized patches and a coefficient of static friction random within a specified range is assigned to each the patch static strength is then the product of friction and differential normal stress stress both shear and normal accumulates due to some predefined tectonic driving force until one or more patches fail and slip instantaneously the slip can be in any direction within the fault plane and its magnitude is determined by a specified fractional stress drop this initial slip induces shear stress and strength changes on all other patches and faults and perhaps results in other patches failing patches can slip more than once once having failed their strength is reduced resulting in an overshoot that approximates the effect of dynamic stress enhancement an event is over when all patches are stable although present computational constraints do not allow models with more than about 1500 patches or a large number of faults experiments with simple models of two parallel strike slip faults 25 km length 15 km depth 694 m x 714 m patch size driven at different rates and separated by 10 or 15 km give some indicative results a range of friction between 0 1 and 0 2 with a stress drop of 10 about 3 mpa or 30 bars produces a b value 500 000 events close to 1 the models generate a distinct class of large characteristic events that rupture the full fault plane the distribution of interevent times for the background seismicity is very similar to that for a poisson process while the characteristic events are quasi periodic nearly half the larger events directly induce some activity on the other fault the effect of a characteristic event on the occurrence of another characteristic event on the opposite fault is small and depends on the separation at 10 km distance other events are retarded while at 15 km distance they are advanced at 10 km separation the probability of a pair of characteristic events within 1 year is reduced to 0 3 from 1 7 for the case with no interaction consideration of interactions between slip on the faults and the driving mechanism as well as higher stress drops and more overshoot would increase the magnitude of the interaction effects

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

cyclic stressing and seismicity at strongly coupled subduction zones we use the finite element method to analyze stress variations in and near a strongly coupled subduction zone during an earthquake cycle deformation is assumed to be uniform along strike plane strain on a cross section normal to the trench axis and periodic earthquake slip is imposed consistent with the long term rate of plate convergence and degree of coupling simulations of stress and displacement rate fields represent periodic fluctuations in time superimposed on an average field the oceanic plate descending slab and continental lithosphere are assumed here to respond elastically to these fluctuations and the remaining mantle under and between plates is assumed to respond as maxwell viscoelastic in the first part of the analysis we find that computed stress fluctuations in space and time are generally consistent with observed earthquake mechanism variations with time since a great thrust event in particular trench normal extensional earthquakes tend to occur early in the earthquake cycle toward the outer rise but occur more abundantly late in the cycle in the subducting slab downdip of the main thrust zone compressional earthquakes when they occur at all have the opposite pattern our results suggest also that the actual timing of extensional outer rise events is controlled by the rheology of the shallow aseismic portion of the thrust interface the second part of the analysis shows the effects of mantle relaxation on the rate of ground surface deformation during the earthquake cycle models without relaxation predict a strong overall compressional strain rate in the continental plate above the main thrust zone with the strain rate constant between mainshocks however with significant relaxation present a localized region of unusually low compressional or even slightly extensional strain rate develops along the surface of the continental plate above and somewhat inland from the downdip edge of the locked main thrust zone the low strain rate starts in the middle or late part of the cycle depending on position this result suggests that the negligible or small contraction measured on the shumagin islands alaska during 1980 to 1991 may not invalidate an interpretation of that region as being a moderately coupled subduction zone in contrast mantle relaxation causes only modest temporal nonuniformity of uplift rates in the overriding plate and of extensional stress rates in the subducting plate even when the maxwell time is an order of magnitude less than the recurrence interval

vertical deformation 1952 1987 in the salton trough california from water level recordings analysis of 36 years of water level data from three sites on the shore of the salton sea reveals a history of vertical deformation in the salton trough data from two sites allow estimation of tilt along a 36 km nw se baseline between 1952 and 1970 since 1970 the addition of a 13 km wnw ese baseline allows the full tilt vector to be estimated we find down to the southeast tilting at an average rate of about 0 01 0 01 rad yr from the early 1960s to 1987 an anomalous period of more rapid 0 2 0 04 rad yr tilting occurs between the mid 1950s and early 1960s but this coincides with a period from which we have been unable to examine all the original data a previous analysis of the 1952 1978 data suggested a precursory increase in tilt rate prior to the 1968 borrego mountain earthquake and a tilt reversal in 1972 we show that there was no significant tilt change prior to the 1968 earthquake and that the apparent 1972 reversal resulted from uncorrected offsets in the water level observations tilts derived from water level and from reliable first order leveling surveys show limited agreement but the leveling data contain evidence for nonuniform tilting recent analyses of leveling data by others using different techniques show 20 30 cm uplift and subsidence events in the salton trough between 1968 and 1978 our data constrain the relative elevations of the three water level sites to be stable within 1 2 cm during these proposed events

strain rate profile across the elsinore san jacinto and san andreas faults near palm springs california 1973 81 a profile of the strain accumulation rate along a line trending n50 e across the subparallel elsinore san jacinto and san andreas faults near palm springs california has been constructed from trilateration surveys in the 1973 81 interval the strain accumulation is principally right lateral shear across a vertical plane parallel to fault strike n40 w the strain rate profile for that component exhibits two clearly resolved maxima one centered on the san jacinto fault max 0 35 0 02 rad a and the other on the san andreas fault max 0 40 0 02 rad a no maximum is associated with the elsinore fault this result clearly implies that slip at depth on both the san andreas and san jacinto faults is loading the shallower sections of these faults and that eventually rupture can be expected on both

earthquakes and sea level space and terrestrial metrology on a changing planet the complacency with which man inhabits continent ocean margins or plate boundaries is based on the assumption that sea level rise and periodic seismicity are acceptable risks the forecast of future sea level or future seismicity is essential for informed assessment of these risks the historical data from which forecasts may be derived are in each case of limited antiquity and uneven spatial distribution developments in space geodesy and crustal deformation metrology in the past two decades offer the means to acquire a homogeneous global data set for monitoring relative vertical and horizontal motions of the earth s surface to within several millimeters these new tools are reviewed in terms of their application to forecasting trends in sea level rise and forecasting damaging earthquakes

space and time dependent probabilities for earthquake fault systems from numerical simulations feasibility study and first results in weather forecasting current and past observational data are routinely assimilated into numerical simulations to produce ensemble forecasts of future events in a process termed model steering here we describe a similar approach that is motivated by analyses of previous forecasts of the working group on california earthquake probabilities wgcep our approach is adapted to the problem of earthquake forecasting using topologically realistic numerical simulations for the strike slip fault system in california by systematically comparing simulation data to observed paleoseismic data a series of spatial probability density functions pdfs can be computed that describe the probable locations of future large earthquakes we develop this approach and show examples of pdfs associated with magnitude m 6 5 and m 7 0 earthquakes in california

earthquake recurrence time variations with and without fault zone interactions summary the macroscopic behaviour of a fault zone can be described by a classic coulomb friction law and static kinetic rheology the critical failure stress leading to the activation of a single shear zone segment then depends on the normal stress acting on the future fault plane it is known that the seismic cycle on a main fault patch can be modulated by surrounding fault activations leading to interaction with the main segment or by other external stress perturbations the results presented here stem from analytical assessments and 2 d numerical elastic models they show that an earthquake recurrence time variation with continuing deformation system development is not necessarily connected to fault interaction processes under the above assumptions instead aperiodicity can result from a non ideal orientation of the rupture plane in the simplest possible homogeneous stress eld even when constant loading rate and frictional parameters are assumed this eiect can still be found in the multifault geometries we studied where the interaction of segments determines the seismicity patterns of the system to varying extents our results suggest that a stable earthquake periodicity on non changing fault sets will seldom be found in nature we propose a reconsideration of the ideas leading to a hypothesized steady seismic cycle in earthquake prediction models

paleoseismic evidence of clustered earthquakes on the san andreas fault in the carrizo plain california exposures we have excavated across the san andreas fault contradict the hypothesis that part of the fault in the carrizo plain is unusually strong and experiences relatively infrequent rupture the exposures record evidence of at least seven surface rupturing earthquakes which have been approximately dated by accelerated mass spectrometry radiocarbon analysis of detrital charcoal and buried in situ plants five large earthquakes have occurred since 1218 a d the most recent earthquake event a was the 1857 fort tejon earthquake which we have associated with 6 6 10 m of dextral slip along the main fault trace the penultimate earthquake event b most likely occurred within the period a d 1405 1510 slip from either events b and c combined or from event b alone totals 7 11 m three earthquakes events c d and e occurred in a temporal cluster prior to event b and after approximately a d 1218 the average recurrence interval within this cluster is 73 116 years depending on assumptions events f and g occurred after 200 years b c a depositional hiatus between events e and f may hide evidence of additional earthquakes events b and d within the carrizo cluster of a d 1218 1510 may correlate with events t a d 1329 1363 and v a d 1465 1495 at pallett creek on the mojave segment of the fault this suggests two fault ruptures similar in length to that of 1857 events c and e apparently did not rupture the mojave section which suggests that the carrizo segment has ruptured independently or in combination with segments to the north irregular repeat times of large earthquakes suggest a pattern of clustered events at the end of seismic supercycles

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

simulating gravity changes in topologically realistic driven earthquake fault systems first results currently gps and insar measurements are used to monitor deformation produced by slip on earthquake faults it has been suggested that another method to accomplish many of the same objectives would be through satellite based gravity measurements the gravity recovery and climate experiment grace mission has shown that it is possible to make detailed gravity measurements from space for climate dynamics and other purposes to build the groundwork for a more advanced satellite based gravity survey we must estimate the level of accuracy needed for precise estimation of fault slip in earthquakes we turn to numerical simulations of earthquake fault systems and use these to estimate gravity changes the current generation of virtual california vc simulates faults of any orientation dip and rake in this work we discuss these computations and the implications they have for accuracies needed for a dedicated gravity monitoring mission preliminary results are in agreement with previous results calculated from an older and simpler version of vc computed gravity changes are in the range of tens of gal over distances up to a few hundred kilometers near the detection threshold for grace

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

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

new evidence of warming propagating toward the arctic ocean 1 the dramatic changes in the arctic climate observed in recent years have generated an urgent need to investigate the arctic ocean s heat budget mooring data and synoptic observations in the fram strait fs region have shown that increasing amounts of heat have been transported into the arctic ocean ao in recent times here we present results from observations conducted in the west spitsbergen current wsc in summers 2000 2005 the study was motivated by the strong warm anomalies seen in the atlantic water aw layer over a large area of the wsc and changes in the wsc structure we conclude that the warm signal was only approaching the fs and we expect that high heat transport through the strait will continue and be even higher than during the last 6 years mostly due to increasing activity and temperature of the western branch of wsc

the recurrence time of dislocation events on the antitethic margins of an elastic plate welded to a maxwell viscoelastic half space the dynamics of an elastic plate subject to a tectonic stress field and controlled by finite strength boundaries is studied following the stress relaxation in a maxwell asthenosphere due to a long sequence of dislocation events localized on two antitethic transform boundaries the model is plane bidimensional and each dislocation event cutting the whole strike of the boundary is interpreted as a sequence of earthquakes the time of each dislocation event is determined as the time when the overall stress field reaches given threshold values on each boundary if two boundaries only are considered a stationary dislocation cycle is attained only if events on the two boundaries release opposite stress drops if this is not the case very slow diffusion of stress takes place in the medium well beyond the two boundaries and a stationary regime is not achieved even after a time lag greater than the age of the earth a periodic boundary model is then devised which avoids introducing plates with infinite width in this second model stationary dislocation cycles are obtained even if the strength values of the antitethic boundaries are different from each other from these simulations of the earthquake cycles inference could be drawn in principle on tectonic parameters and a formal equivalence can be stated between an elastic lithosphere affected by boundary earthquakes and a viscoelastic continuum lithosphere subjected to the same tectonic stress field even if this plate model cannot be applied to any real plate of the earth nevertheless the role of the finite widths of plates and of stress diffusion from very distant boundaries is proven to be important in modeling the seismic cycle and the deformation of plates however the extreme sensitivity of the model from very distant features and the trade off existing between the long time and the long distance behavior imply that horizontally stratified two dimensional dislocation models cannot be profitably employed to simulate the seismic cycle in realistic situations