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

a synthetic seismicity model for the northwestern portion of the xianshuihe fault southwestern china simulation using the monte carlo method based on historical earthquake data abstract in order to estimate distributions of recurrence intervals and segment interactions across the four fault segments along the northwestern portion of the xianshuihe fault npxf in southwestern china i generate a large number of synthetic earthquake catalogs by sampling recurrence intervals and segment interactions for the four segments within the preferred ranges based on the seismogenic mechanism of fault rupture and interaction the ranges are derived from previous studies those catalogs that are closest to the real historical earthquake catalog consisting of seven strong events of m 6 8 during 1792 1981 along the npxf are then selected to determine the possible distributions of the intervals and interactions finally i create a synthetic earthquake catalog by using monte carlo sampling from the determined distributions of the intervals and interactions the 40 000 year simulated seismic activity shows good agreement with the observed data with respect to the following four statistical features 1 most events are single segment ruptures with few rupturing two or three segments 8 of simulated earthquakes and none breaking all four segments simultaneously 2 the coefficient of variation c v of the recurrence interval tends to increase with the complexity of a segment or fault 3 the brownian passage time distribution represents the best fit for each of the four individual segments whereas the weibull distribution matches the entire npxf best 4 the next strong event is most likely to occur in the eastern part of the southernmost segment of the npxf

stressing of locked patches along a creeping fault an analysis is presented of the stressing of locked patches along a fault zone which is creeping elsewhere the model consists of strike slip faulted elastic lithospheric plates loaded in a manner equivalent to imposition of a remotely uniform tectonic shear stress the fault zone has an inhomogeneous strength distribution both depth wise and along strike it is modeled as being composed of locked patches and freely slipping parts treated as cracks the solution is given with the use of the line spring model which analyzes the problem by thickness averaged plane stress theory for lithospheric plates which slip along a discontinuity cut at the plate boundary as a boundary condition thickness averaged stress and slip at each local section along the cut was related to one another by the result of an antiplane strain analysis of slip for the crack or crack pair which describes the slipping and locked depth ranges at that section the analysis indicates that the slip distribution along creeping parts of the fault as well as the stress distribution along locked patches depends strongly on the geometry of these zones the model is used to examine stress concentrations associated with a slip deficient seismic gap along strike and to study the effect of local irregularities in the margin of a locked region it is also used to simulate slip and stressing processes associated with the creeping portion of the san andreas fault in central california between the presently locked zones of the great 1906 and 1857 ruptures and to constrain the nature of an apparently locked zone at the southeastern end which ruptures in characteristic parkfield earthquakes near fault creep and broadscale displacement data along the fault since the 1966 parkfield earthquake and inferences from seismicity distributions are used limitations of the modeling procedure at short spatial wavelengths prohibit an accurate description of the parkfield locked patch but results suggest that it may be localized and occupy a small fraction of area of the normal seismogenic zone an effective remote stressing rate of order 0 3 10 6 shear modulus yr is inferred together with a less well constrained 30 to 40 km lithospheric thickness for consistency with the displacement data results enable estimates of stress accumulation along the locked 1857 rupture zone and the build up of fracture energy release capability of order 107 j m2 in 150 yr at its lower margin

frictional sliding of dolomite a variation in constitutive behavior fault slip occurs via earthquakes or stable creep depending on the manner in which frictional resistance varies with sliding velocity and displacement if the form of this dependence is a function of rock type observed spatial variations in slip behavior along faults could be explained by lithologic variation we have used a rotary shear apparatus to investigate the frictional response of dolomite marble to changes in sliding velocity we have modeled the results using a state variable constitutive law for rock friction and a numerical method to solve for the interaction between the friction law and the compliance of our machine dolomite marble displays steady state velocity strengthening as contrasted with granite and quartzite which show velocity weakening at the same conditions to model the dolomite results it is necessary to use two state variables and surprisingly the parameters specifying the decay magnitudes associated with these state variables differ in sign from each other the magnitude of the parameter associated with the longer decay is negative leading to a downward decay of frictional strength associated with a decrease in velocity if the shorter decay is of sufficient magnitude as we observe at low velocity it is possible for the machine rock system to exhibit instability and oscillatory behavior even though the steady state response is velocity strengthening another way in which dolomite contrasts with granite and quartzite is that the friction parameters vary strongly with velocity a transition from unstable to stable sliding with increasing velocity has been observed previously and our observed variation of the constitutive parameters with velocity can explain this behavior there is some indication that the evolution of the state variables for dolomite occurs as a function of time rather than displacement in contrast with granite and quartzite the frictional behavior of dolomite shows that the constitutive laws that have been developed based on results from granite and quartzite are inadequate to describe all rock types and that more general laws are required

roughness at the base of the seismogenic zone contributing factors the cutout depth of microseismic activity in continental fault zones appears to correspond to the onset of greenschist metamorphic conditions at about 300 c it can generally be modeled as the transition from frictional to quasi plastic behavior in quartzofeldspathic crust shear resistance increases with depth through the frictional regime to peak at the transition beneath which it falls off exponentially with increasing temperature larger earthquake ruptures ml 5 5 nucleate around this transition depth where the highest concentrations of strain energy may accumulate varying depth and amplitude of the peak shear resistance along strike induce fluctuations in strain energy concentration at the base of the seismogenic zone factors affecting the depth of the transition include crustal composition geometry and mode of faulting fluid pressure levels in the frictional regime and water content in the quasi plastic regime quasi plastic strain rate and geothermal gradient evaluation of their relative importance is complicated because several are interdependent however compositional change may cause abrupt irregularities in seismogenic depth and peak shear resistance while regional variations in heat flow look to be particularly effective in creating long wavelength heterogeneities in strain energy concentration affecting faulting style

how the continents deform the evidence from tectonic geodesy space geodesy now provides quantitative maps of the surface velocity field within tectonically active regions supplying constraints on the spatial distribution of deformation the forces that drive it and the brittle and ductile properties of continental lithosphere deformation is usefully described as relative motions among elastic blocks and is block like because major faults are weaker than adjacent intact crust despite similarities continental block kinematics differs from global plate tectonics blocks are much smaller typically 100 1000 km in size departures from block rigidity are sometimes measurable and blocks evolve over 1 10 ma timescales particularly near their often geometrically irregular boundaries quantitatively relating deformation to the forces that drive it requires simplifying assumptions about the strength distribution in the lithosphere if brittle elastic crust is strongest interactions among blocks control the deformation if ductile lithosphere is the stronger its fl

frictional constraints on crustal faulting we consider how variations in fault frictional properties affect the phenomenology of earthquake faulting in particular we propose that lateral variations in fault friction produce the marked heterogeneity of slip observed in large earthquakes we model these variations using a rate and state dependent friction law where we differentiate velocity weakening behavior into two fields the strong seismic field is very velocity weakening and the weak seismic field is slightly velocity weakening similarly we differentiate velocity strengthening behavior into two fields the compliant field is slightly velocity strengthening and the viscous field is very velocity strengthening the strong seismic field comprises the seismic slip concentrations or asperities the two intermediate fields weak seismic and compliant have frictional velocity dependences that are close to velocity neutral these fields modulate both the tectonic loading and the dynamic rupture process during the interseismic period the weak seismic and compliant regions slip aseismically while the strong seismic regions remain locked evolving into stress concentrations that fail only in main shocks the weak seismic areas exhibit most of the interseismic activity and aftershocks but can also creep seismically this mixed frictional behavior can be obtained from a sufficiently heterogeneous distribution of the critical slip distance the model also provides a mechanism for rupture arrest dynamic rupture fronts decelerate as they penetrate into unloaded complaint or weak seismic areas producing broad areas of accelerated afterslip aftershocks occur on both the weak seismic and compliant areas around a fault but most of the stress is diffused through aseismic slip rapid afterslip on these peripheral areas can also produce aftershocks within the main shock rupture area by reloading weak fault areas that slipped in the main shock and then healed we test this frictional model by comparing the seismicity and the coseismic slip for the 1966 parkfield 1979 coyote lake and 1984 morgan hill earthquakes the interevent seismicity and aftershocks appear to occur on fault areas outside the regions of significant slip these regions are interpreted as either weak seismic or compliant depending on whether or not they manifest interevent seismicity

propagation of the azov sea waters in the black sea under impact of variable winds geostrophic currents and exchange in the kerch strait abstract satellite and hydrological data were used to study the propagation of the azov waters azov plume ap in the black sea its relation to wind forcing eddy dynamics and water balance in the azov and black seas strong north winds increase the inflow of the azov waters in the basin and their further transport to the west along the crimean coast ap usually extends from the kerch strait to the west up to cape chauda and feodosiya bay over the shallow areas less than 30 m deep in winter early spring when northeast storms and the rim current are the most intense they penetrate further up to cape meganom or even to the southwestern crimean coast near the capes ap may detach from the coast and get trapped in the mesoscale anticyclones formed beyond the capes salinity gradients between the ap and the black sea waters induce the formation of frontal geostrophic currents reaching 10 cm s which can constitute half of the total geostrophic velocity in this part of the basin during the strong south winds ap is transported both to the east and west of the kerch strait or the inflow of the azov waters is completely blocked these storms are the reason of the highest turbidity in the vicinity of the kerch strait which is related to the wave induced coastal erosion and resuspension of bottom sediments over the shallow kerch taman shelf altimetry and in situ data on sea level difference in the two basins were used to study the variability of the barotropic transport near the kerch strait and its dependence on the water balance in the two basins wind direction and magnitude the greatest difference between mean sea level in the azov sea and the black sea in winter increases the inflow of the azov waters in cold season rise of the dynamic sea level over the coastal part of the black sea in winter caused by the intensification of cyclonic circulation partly compensates this difference and decreases the exchange north and northwest winds with magnitude 12 16 m s increase the barotropic velocity in the strait by 30 40 cm s while south and southwest winds with the same magnitude decrease it by 20 30 cm s turbidity near the strait that is an indicator of ap has significant interannual variability in 2003 2015 it declines over the whole kerch taman shelf which is related to the decrease of the inflow of the azov waters into the black sea in this period

earthquake recurrence and magnitude and seismic deformation of the northwestern okhotsk plate northeast russia 1 recorded seismicity from the northwestern okhotsk plate northeast asia is currently insufficient to account for the predicted slip rates along its boundaries due to plate tectonics however the magnitude frequency relationship for earthquakes from the region suggests that larger earthquakes are possible in the future and that events of mw 7 5 which should occur every 100 350 years would account for almost all the slip of the plate along its boundaries due to eurasia north america convergence we use models for seismic slip distribution along the bounding faults of okhotsk to conclude that relatively little aseismic strain release is occurring and that larger future earthquakes are likely in the region our models broadly support the idea of a single okhotsk plate with the large majority of tectonic strain released along its boundaries

holocene and latest pleistocene activity on the mesquite lake fault near twentynine palms eastern california shear zone implications for fault interaction paleoseismic data from the mesquite lake fault reveal evidence for up to four prehistoric earthquakes since the latest pleistocene with three large surface rupturing events in about the past 10 2 ka three events were recorded in trenches excavated for this investigation on mesquite lake playa a buried fault scarp brack eted by accelerator mass spectrometer radiocarbon ages of detrital charcoal indicate that a mid to late holocene event occurred between about 2 7 and 7 4 ka most likely between about 3 9 and 4 6 ka an early holocene rupture defined by a subtle buried scarp and upward terminating fissures is bracketed between about 7 7 and 10 2 ka evidence for an inferred late pleistocene event prior to about 10 2 ka includes a subtle scarp upward termination of faults folding and in filled craters and fissures a previous paleoseismic investigation just south 2 km of the playa identified at least one event in the past 1 3 ka although this event was not identified in this study at the playa site apparent vertical offsets of about 1 0 m and 1 2 m for the last two events at the playa site suggest a sequence of similar serial ruptures these separa tions are comparable to the height of surficial scarps just south of the playa because the vertical separations produced by each event are similar the mesquite lake fault at least locally experiences similar slip per event since the initiation of holocene playa development just over 10 2 ka ago we estimate a horizontal slip rate of 0 7 0 9 mm yr 1 that is consistent with slip rates for other faults in the eastern california shear zone despite large uncertainties event stratigraphy at the playa site shows that periods of quiescence up to thousands of years separated large ruptures similar to other faults in the eastern california shear zone comparison of paleoseismic studies in the eastern california shear zone suggest that the mesquite lake and possibly the bullion and lavic lake faults in the eastern part of the shear zone may have failed during periods of seismic quiescence in the western part of the zone at about 1 5 ka this suggests that seismic strain release may vary spatially across the shear zone and that temporal clusters of earthquakes are not necessarily spatially limited to specific regions

constitutive behavior and stability of frictional sliding of granite an understanding of the frictional sliding on faults that can lead to earthquakes requires a knowledge of both constitutive behavior of the sliding surfaces and its mechanical interaction with the loading system we have determined the constitutive parameters for frictional sliding of initially bare surfaces of westerly granite using a recently developed high pressure rotary shear apparatus that allows long distances of sliding and therefore a greater assurance of attaining steady state behavior from experiments conducted at room temperature and normal stresses of 27 84 mpa several important results have been found 1 a gouge layer 100 to 200 m thick was developed from the initially bare rock surfaces after 18 to 70 mm of sliding 2 the steady state frictional resistance attained after about 10 mm of sliding is proportional to the negative of the logarithm of the sliding velocity 3 abrup changes in the velocity of sliding result in initial changes in the frictional resistance which have the same sign as the velocity change and are followed by a gradual decay to a new steady state value over a characteristic distance of sliding this velocity weakening behavior is essentially identical with that found by several previous workers on the same material at lower normal stress 4 our results are well described by a two state variable constitutive law the values of the constitutive parameters are quite similar to those found previously at low normal stress but the characteristic distance is about an order of magnitude smaller than that found at 10 mpa normal stress with thicker layers of coarser gouge 5 we have approximated our results with a one state variable constitutive law and compared the results with the predictions of existing nonlinear stability analysis in addition we have extended the stability analysis to systems possessing two state variables with such formulations good agreement is found between the experimentally observed and theoretically predicted transitions between stable and unstable sliding these results allow a better understanding of the instabilities that lead to earthquakes

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

continental fault structure and the shallow earthquake source plate boundaries in continental crust are generally less sharply defined than in the oceans with seismicity spread over broad areas interplate displacements appear to be largely accommodated by networks of major fault zones a simple 2 level model for these important structures accounts for the depth distribution of most continental earthquakes and for the observed range of faulting styles and associated rock deformation textures the model consists of a seismogenic frictional slip regime overlying quasi plastic mylonite belts wherein shearing is largely accommodated aseismically due mainly to the changing response of quartz to deformation with increasing temperature shear resistance increases with depth to a peak value in the vicinity of the frictiona1 quasi plastic transition and then decreases rapidly the depth to which microseismic activity extends appears inversely related to regional heat flow and can be satisfactorily modelled as the frictional quasi plastic transition for different geotherms using laboratory determined flow laws for quartz bearing rocks larger earthquake ruptures m 5 5 tend to nucleate near the base of the seismogenic regime in the region inferred to have the highest shear resistance and concentration of distortional strain energy consideration is also given to the depression of isotherms and seismic activity in regions of thrusting and to the question of the downward continuation of major fault zones through the lithosphere decoupling of the upper crust on flat lying shear zones may accompany higher level dip slip and perhaps in some circumstances strike slip faulting being favoured by above average continental heat flow and a high quartz content in the middle or deep crust the average level of deviatoric stress within the seismogenic regime remains an outstanding problem

constitutive relations for fault slip and earthquake instabilities constitutive relations for fault slip are described and adopted as a basis for analyzing slip motion and its instability in the form of earthquakes on crustal faults the constitutive relations discussed include simple rate independent slip weakening models in which shear strength degrades with ongoing slip to a residual frictional strength and also more realistic but as yet less extensively applied slip rate and surface state dependent relations for the latter the state of the surface is characterized by one or more variables that evolve with ongoing slip seeking values consistent with the current slip rate models of crustal faults range from simple single degree of freedom spring slider systems to more complex continuous systems that incorporate nonuniform slip and locked patches on faults of depth dependent constitutive properties within elastic lithospheric plates that may be coupled to a viscoelastic asthenosphere

probability of earthquake recurrence with nonuniform stress rates and time dependent failure current methods for calculation of long term probabilities for the recurrence of large earthquakes on specific fault segments are based upon models of the faulting process that implicitly assume constant stress rates during the interval separating earthquakes and instantaneous failure at a critical stress threshold however observations indicate that the process of stress recovery following an earthquake involves rate variations at all time scales in addition to stress steps caused by nearby earthquakes additionally the existence of foreshocks aftershocks and possible precursory processes suggest that there may be significant time dependence of the earthquake nucleation process a method for determining the conditional probabilities for earthquake occurrence under conditions of irregular stressing is developed that could be useful at all time scales including those pertinent to short and intermediate term prediction used with models for earthquake occurrence at a stress threshold the addition of variable stressing introduces a simple scaling of the conditional probabilities by stress level and stress rate a model for the time dependent nucleation of earthquake slip has been proposed recently that is based upon laboratory observations of fault strength this failure criterion results in large but relatively short duration changes in the probability of earthquake recurrence particularly following stress steps applied to populations of earthquakes the models predicts a 1 t decay of seismicity following stress steps as observed for aftershocks and for frequency of foreshock mainshock pairs the model suggests that variations of seismicity rates of small earthquakes in the nucleation zone of the expected earthquake directly indicate variations in probability of recurrence of the large earthquake

geodetic observations of postseismic creep in the decade after the 1999 izmit earthquake turkey implications for a shallow slip deficit the relationship between aseismic slip and tectonic loading is important for understanding both the pattern of strain accumulation along a fault and its ability to generate large earthquakes we investigate the spatial distribution and temporal evolution of aseismic creep on the western north anatolian fault naf using time series analysis of envisat interferometric synthetic aperture radar insar data covering the full extent of the 1999 izmit and duzce earthquake ruptures and spanning 2002 2010 discontinuities in the line of sight velocity across the fault imply that fault creep reaches the earth s surface at an average fault parallel rate of 5 mm yr along an 80 km section of the naf by combining insar and published gps velocities we are able to extract the vertical and east west components of motion and show that the adapazari basin is subsiding at a rate of 6 mm yr vertical motions have biased previous estimates of creep in this region the displacement time series close to the fault is consistent with an afterslip model based on rate and state friction which predicts a rapid deceleration in fault creep rate after the izmit earthquake to a near steady state 5 mm yr after 5 years projecting our model 200 years into the future we find that the cumulative displacement of 1 1 3 m is insufficient to account for the shallow coseismic slip deficit observed in previous studies distributed off fault deformation in the shallow crust or transient episodes of faster slip are likely required to release some of the long term strain during the earthquake cycle

a friction to flow constitutive law and its application to a 2 d modeling of earthquakes establishment of a constitutive law from friction to high temperature plastic flow has long been a challenging task for solving problems such as modeling earthquakes and plate interactions here we propose an empirical constitutive law that describes this transitional behavior using only friction and flow parameters with good agreements with experimental data on halite shear zones the law predicts steady state and transient behaviors including the dependence of the shear resistance of fault on slip rate effective normal stress and temperature it also predicts a change in velocity weakening to velocity strengthening with increasing temperature similar to the changes recognized for quartz and granite gouge under hydrothermal conditions a slight deviation from the steady state friction law due to the involvement of plastic deformation can cause a large change in the velocity dependence we solved seismic cycles of a fault across the lithosphere with the law using a 2 d spectral boundary integral equation method revealing dynamic rupture extending into the aseismic zone and rich evolution of interseismic creep including slow slip prior to earthquakes seismic slip followed by creep is consistent with natural pseudotachylytes overprinted with mylonitic deformation overall fault behaviors during earthquake cycles are insensitive to transient flow parameters the friction to flow law merges christmas tree strength profiles of the lithosphere and rate dependency fault models used for earthquake modeling on a unified basis strength profiles were drawn assuming a strain rate for the flow regime but we emphasize that stress distribution evolves reflecting the fault behavior a fault zone model was updated based on the earthquake modeling

a mechanical model of precursory source processes for some large earthquakes a mechanical model is presented of precursory source processes for some large earthquakes along plate boundaries it is assumed that the pre seismic period consists of the upward progression of a zone of slip from lower portions of the lithosphere towards the earth s surface the slip front is blocked by local asperities of different size and strength these asperities may be zones of real alteration of inherent strength or instead may be zones which are currently stronger due to a local slowdown of a basically rate dependent frictional response such blocking by a single large asperity or array of asperities produces quiescence over a segment of plate boundary until gradual increase of the stress concentration forces the slip zone through the blocked region at one end of the gap thus nucleating a seismic rupture that propagates upwards and towards the other end this model is proposed to explain certain distinctive seismicity patterns that have been observed before large earthquakes notably quiescence over the gap zone followed by clustering at its ends prior to the main event a discussion of mechanical factors influencing the process is presented and some introductory modelling performed with the use of a generalized elsasser model for lithospheric plates and the line spring model for part through flaws slip zones at plate boundaries is outlined briefly

crustal deformation in great california earthquake cycles periodic crustal deformation associated with repeated strike slip earthquakes is computed for the following model a depth l h extending downward from the earth s surface at a transform boundary between uniform elastic lithospheric plates of thickness h is locked between earthquakes it slips an amount consistent with remote plate velocity vpl after each lapse of earthquake cycle time tcy lower portions of the fault zone at the boundary slip continuously so as to maintain constant resistive shear stress the plates are coupled at their base to a maxwellian viscoelastic asthenosphere through which steady deep seated mantle motions compatible with plate velocity are transmitted to the surface plates the coupling is described approximately through a generalized elsasser model we argue that the model gives a more realistic physical description of tectonic loading including the time dependence of deep slip and crustal stress buildup throughout the earthquake cycle than do simpler kinematic models in which loading is represented as imposed uniform dislocation slip on the fault below the locked zone parameters of the model are chosen to fit seismic and geologic constraints and the apparent time dependence of surface strain rates along presently locked traces of the 1857 and 1906 san andreas ruptures we fix vpl 35 mm yr tcy 160 years and l 9 11 km based on earthquake nucleation depths the geodetic data are then found to be described reasonably within the context of a model that is locally uniform along strike and symmetric about a single san andreas fault strand by lithosphere thickness h 20 30 km and elsasser relaxation time tr 10 16 years we therefore suggest that the asthenosphere appropriate to describe crustal deformation on the earthquake cycle time scale lies in the lower crust and perhaps crust mantle transition zone and has an effective viscosity between about 2 1018 and 1019 pa s depending on the thickness assigned to the asthenospheric layer predictions based on the chosen set of parameters are also consistent with data on variations of contemporary surface strain and displacement rates as a function of distance from the 1857 and 1906 rupture traces although the fit is degraded by asymmetry relative to the fault and by slip on adjacent fault strands

coherent high and low latitude climate variability during the holocene warm period a faunal record of sea surface temperature sst variations off west africa documents a series of abrupt millennial scale cooling events which punctuated the holocene warm period these events evidently resulted from increased southward advection of cooler temperate or subpolar waters to this subtropical location or from enhanced regional upwelling the most recent of these events was the little ice age which occurred between 1300 to 1850 a d when subtropical ssts were reduced by 3 to 4 c these events were synchronous with holocene changes in subpolar north atlantic ssts documenting a strong in phase link between millennial scale variations in high and low latitude climate during the holocene

preseismic rupture progression and great earthquake instabilities at plate boundaries we present a procedure for modeling the initially quasi static upward progression of a zone of slip from some depth in the lithosphere toward the earth s surface along a transform plate margin culminating in a great crustal earthquake stress transmission in the lithosphere is analyzed with a generalized elsasser model in which elastic lithospheric plates undergo plane stress deformation and are coupled by an elementary foundation model to a maxwellian viscoelastic asthenosphere upward progression of rupture over a finite length of plate boundary corresponding to a seismic gap along strike is analyzed by a method based on the line spring concept whereby a two dimensional antiplane analysis of the upward progression provides the relation between lithospheric thickness averaged stress and slip used as a boundary condition in the generalized elsasser plate model the formulation results in a nonlinear integral equation for the rupture progression as a function of time and distance along strike a simpler approximate single degree of freedom analysis procedure is described and shown to lead to instability results that can be formulated in terms of the slip softening slope at the boundary falling below the elastic unloading stiffness of the surroundings the results also indicate a delay of ultimate seismic instability due to the stiffer short versus long time asthenospheric response and predict a final period of self driven creep toward instability the procedures for prediction of rupture progression and instability are illustrated in detail for an elastic brittle crack model of slip zone advance and parameters of the model are chosen consistently with great earthquake slips and stress drops for example an effective crack fracture energy of the order 4 106 j m2 at the peak 7 to 10 km below surface of a gaussian bell shaped distribution of fracture energy with depth with variance of the order 5 km simulating strength build up in a seismogenic layer leads to prediction of nominal seismic stress drops of 30 to 60 bars and slips of 2 to 5 m in great strike slip earthquake ruptures breaking 100 to 400 km along strike precursory surface straining in the self driven stage is predicted to proceed at a distinctly higher rate over time intervals beginning 3 to 10 months before such an earthquake this interval being greater for longer distances along strike over which the preseismic upward rupture progression takes place

lateral variation of the cutoff depth of shallow earthquakes beneath the japan islands and its implications for seismogenesis abstract we estimated the spatial distribution of the cut off depth of shallow seismicity beneath the japan islands based on data from a recently constructed nationwide dense seismic network in order to avoid the effect of heterogeneous seismic velocity structure we determined the 3d seismic velocity structure for the whole of japan which was then used to relocate the hypocenters the cut off depth was determined by calculating d90 the depth above which 90 of the earthquakes occur a spatial distribution of estimated d90 values shows a considerable lateral variation ranging from about 5 km to about 40 km the d90 s are deep along the pacific coast of eastern japan locally shallow d90 s extend along belt like stretches of volcanic areas heat flow is low along the pacific coast in eastern japan and high in the volcanic areas this indicates that the lateral variation of d90 s is formed mainly by lateral geotherm variation cooling by the subducting old very cold pacific plate may cause the deep d90 s along the pacific coast in eastern japan heating by magma supplied from the mantle wedge below is considered to be the main cause of the shallow d90 s in the volcanic areas magma and or aqueous fluids derived from solidified magma contribute not only to locally shallow d90 s but also to the weakening of ambient rocks in the lower crust resulting in stress concentrations in the upper crust just above them large shallow inland earthquakes tend to occur in such areas suggesting that a model of shallow earthquake generation applied to tohoku can be used in other areas in japan as well

towards an improved understanding of the mechanical properties and rheology of the lithosphere an introductory article to rock deformation from field experiments and theory a volume in honour of ernie rutter ernie rutter s influential contribution to our understanding of rock deformation spans the whole continental crust from deformation just under the grass e g rutter green 2011 to melt migration in the lower crust e g rutter neumann 1995 ernie has also worked on many aspects of the deformation of oceanic crust rutter brodie 1988 however here we reflect on the wide range of deformation conditions ernie has studied by presenting key aspects of the strength and rheology of the continental lithosphere as we understand it today with the aim of providing the context for the contributions included within this volume the continental crust forms just over a third of the earth s surface and it is different from the crust of any other planet in our solar system it is rich in those elements that partition in a silicate melt and its formation and evolution determined the composition of the mantle and that of the atmosphere hawkesworth 2006 thanks to its physical and chemical fingerprint the earth s crust has sustained life uninterrupted for 3 8 ga and it is the source of major natural resources such as hydrocarbons and mineral deposits and others such as geothermal energy the continental crust is less dense than its oceanic counterpart and is therefore more buoyant it forms a substantial part of the cold thermal layer of the earth and its rheology from greek r1v rhe flow and logia logia study the study of the flow of matter is a key factor controlling plate tectonic processes at the earth s surface and in its interior davies 2011 beneath the continental crust lies the lithospheric mantle and together they form the continental lithosphere considerable variations in structure thickness and composition of the continental lithosphere mean that despite its importance we currently have limited understanding of the rheology of this complex system thatcher pollitz 2008 significant advances in our knowledge of continental rheology have been possible through

stress transfer and seismic phenomena in coupled subduction zones during the earthquake cycle an elementary mechanical model of a coupled subduction zone is presented it is used to study the transfer of extensional stresses along the underthrusting plate and shear stress interactions between the plate itself and its thrust contact zone with the overriding plate during the earthquake cycle the model assumes an elastic plate which deforms one dimensionally has shear drag interactions treated approximately by the elsasser procedure with a maxwellian viscoelastic mantle and is subject to steady gravitational sinking forces great thrust earthquakes are simulated as sudden stress relieving displacements at the contact zone between the slab and overriding plate the model allows analysis of the space and time variable stresses in the main thrust zone the adjacent oceanic plate and the subducting slab over each earthquake cycle stress variations leading to outer rise events are discussed as well as stress changes responsible for intraplate seismicity downdip from the main thrust zone based on simulations of periodic great earthquakes the results of simulated slow progression of deformation slip from below into the thrust contact zone are also presented such preslip occurring over a time scale that is small in comparison with the whole seismic cycle e g of the order of a tenth or so is shown to transiently slow the rate of buildup of or even relieve extensional stresses in the slab in the absence of preslip those stresses build up steadily in time during the latter part of the cycle the results have implications for induction of sesimic quiescence as well as for explaining patterns of seismicity in relation to spatial position along the underthrusting plate and to time throughout the cycle correlations are reported between the model simulations and seismicity observations from coupled subduction zones around the world the observations include tensional outer rise events after large subduction earthquakes and compressional ones in the latter parts of the cycle normal tensional intraplate earthquakes preceding the main thrust events and positioned downdip from the thrust zones and interlaced periods of seismic activity in the lower part of the main thrust zone and in the descending slab

a note on the rate sensitivity of frictional sliding of westerly granite the frictional sliding of simulated faults containing crushed westerly granite was studied in a series of constant stepped velocity experiments confining pressures were varied from 0 00733 to 7 33 m s the strain rate sensitivity b that is the slope of the frictional stress change with the logarithm of the change in velocity log10 v2 v1 was found to be low and pressure dependent increasing with increased confining pressure to a maximum of approximately 0 01 at 300 mpa confining pressure creep curves are available with entire article on microfiche order from the american geophysical union 2000 florida avenue n w washington dc 20009 document b83 011 2 50 payment must accompany order

elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate and state dependent friction we present an efficient and rigorous numerical procedure for calculating the elastodynamic response of a fault subjected to slow tectonic loading processes of long duration within which there are episodes of rapid earthquake failure this is done for a general class of rate and state dependent friction laws with positive direct velocity effect the algorithm allows us to treat accurately within a single computational procedure loading intervals of thousands of years and to calculate for each earthquake episode initially aseismic accelerating slip prior to dynamic rupture the rupture propagation itself rapid post seismic deformation which follows and also ongoing creep slippage throughout the loading period in velocity strengthening fault regions the methodology is presented using the two dimensional 2 d antiplane spectral formulation and can be readily extended to the 2 d in plane and 3 d spectral formulations and with certain modifications to the space time boundary integral formulations as well as to their discretized development using finite difference or finite element methods the methodology can be used to address a number of important issues such as fault operation under low overall stress interaction of dynamic rupture propagation with pore pressure development patterns of rupture propagation in events nucleated naturally as a part of a sequence the earthquake nucleation process earthquake sequences on faults with heterogeneous frictional properties and or normal stress and others the procedure is illustrated for a 2 d crustal strike slip fault model with depth variable properties for lower values of the state evolution distance of the friction law small events appear the nucleation phases of the small and large events are very similar suggesting that the size of an event is determined by the conditions on the fault segments the event is propagating into rather than by the nucleation process itself we demonstrate the importance of incorporating slow tectonic loading with elastodynamics by evaluating two simplified approaches one with the slow tectonic loading but no wave effects and the other with all dynamic effects included but much higher loading rate

earthquake aftereffects and triggered seismic phenomena the physical basis for delayed aftereffects of large crustal earthquakes is analyzed these effects apparently range in scale from typical aftershocks near the source region of a prior earthquake to the triggering of groundwater and deformation related anomalies possibly including other large earthquakes at locations as much as a few hundred kilometers from the source of a great earthquake observational reports of such aftereffects are reviewed and possible mechanisms for their occurrence are discussed

postseismic deformation following the landers earthquake california 28 june 1992 accelerated strain followed the landers and big bear earthquakes returning to the normal rate only after a period of several months we observed this strain throughout most of southern california using the global positioning system gps three gps receivers operating continuously in fixed positions at pinyon flat jet propulsion laboratory pasadena and goldstone all recorded postseismic deformation in a relative sense in addition we established 16 sites where we deployed portable receivers occasionally over a period of about 6 months near the rupture zones of the earthquakes anomalous postseismic displacements ranged from 55 mm near the epicenter to a few millimeters far from the fault we modeled the displacements using dislocation theory as due to variable slip on the faults that were displaced at the times of the earthquakes the model suggests that the postseismic strain released the equivalent of about 15 of the seismic moment of the mainshock while the strain released from the upper 10 km is about the same as what can be explained by direct effects of aftershocks the major contribution of strain release comes from the lower layer below 10 km depth significant afterslip or viscous relaxation must have occurred below 10 km depth to explain the observed deformation more than 100 km from the fault one interpretation is that high stress on the margin of the co seismic rupture zone drives the rupture to extend itself into urbroken rock below and along the initial rupture zone

nucleation and growth of dip slip faults in a stable craton we analyze the conditions for nucleation of a dip slip fault in intact crust and its subsequent growth using linear elastic fracture mechanics and the finite element method we assume a fault can be modeled as a mode ii shear crack in a layered elastic crust and we investigate fault behavior under conditions of a variable dip and shear fracture energy two shear fracture energy gradients gc were evaluated both have surface values of 1 105 j m2 and increase linearly to values of 1 106 or 1 107 j m2 at 15 km depth the base of the seismogenic zone we assume that the vertical and horizontal components of the gravitational stress are both equal to the lithostatic load effectively removing them from the calculation of shear stress on the fault strain required for failure varied with respect to shear fracture energy gradient and rupture direction but not with dip rupture upward from the base of the seismogenic zone required more than twice the initial strain to cause fault growth and would result in very large earthquakes rupture downward in models associated with the higher gc gradient resulted in stable growth of the fault that is additional strain was needed to allow for continuous fault growth from the surface to the base of the seismogenic zone we suggest that fault nucleation and growth are a stable process which would preferentially occur by rupturing downward under stable conditions rerupturing of an established fault may initiate at depth or the surface depending on the degree of healing between rupture events and the tectonic stress available a vast majority of shallow crustal earthquakes nucleate at the base of the seismogenic zone and rupture upwards this suggests that most events are a reactivation of an old established fault and not growth of a new or developing fault

seismicity and thermal structure along the northern san andreas fault system california usa abstract the correlation between depth patterns of seismicity and crustal thermal regime are investigated for the san andreas fault system regions of anomalous behavior include the occurrence of seismicity at temperatures depths substantially greater than or the cessation of seismicity at temperatures depths less than typical values observed in seismically active regions of the continents seismicity at temperatures significantly greater than target values indicate a need to re evaluate the assumed geotherm and crustal lithology model regions where the seismicity cutoff is at temperatures significantly below target values are possible sites for the future occurrence of significantly deeper earthquakes than presently observed such sites need further study for analysis of possible increased earthquake risk comparisons of seismicity patterns with crustal thermal models may also provide a powerful tool in the evaluation of the patterns of heat production and thermal conductivity in heterogeneous continental crust