scaling of the critical slip distance for seismic faulting with shear strain in fault zones theoretical and experimentally based laws for seismic faulting contain a critical slip distance1 5 dc which is the slip over which strength breaks down during earthquake nucleation on an earthquake generating fault this distance plays a key role in determining the rupture nucleation dimension6 the amount of premonitory and post seismic slip7 10 and the maximum seismic ground acceleration1 11 in laboratory friction experiments d c has been related to the size of surface contact junctions2 5 12 thus the discrepancy between laboratory measurements of dc 10 5m and values obtained from modelling earthquakes 10 2m has been attributed to differences in roughness between laboratory surfaces and natural faults5 this interpretation predicts a dependence of dc on the particle size of fault gouge2 breccia and wear material but not on shear strain here we present experimental results showing that dc scales with shear strain in simulated fault gouge our data suggest a new physical interpretation for the critical slip distance in which dc is controlled by the thickness of the zone of localized shear strain as gouge zones of mature faults are commonly 102 103 m thick12 17 whereas laboratory gouge layers are 1 10 mm thick our data offer an alternative interpretation of the discrepancy between laboratory and field based estimates of dc

contents of natural radioactive nuclides in soil in relation to their surface area concentrations of uranium series nuclides 238u 226ra 210pb thorium series nuclides 228ra 212bi and potassium in soil of a granitic belt were examined in relation to their surface area of soil clay mineral composition and the sio2 and fe contents in soil which is less weathered and has a surface area of around 10 m2 g the 238u 226ra 210pb 228ra and 40k contents increase with an increase the sio2 content related to the elemental compositions of their parents rocks in homologous soils resulting from progressive weathering the 238u 226ra 210pb and 228ra contents are found to increase with increasing surface area for an homologous soil which is free from the clay consisting of three layer units the 40k content decrease with increasing surface area however in an homologous soil which contains a clay consisting of three layer units the 40k content is not surface area dependent

interseismic coupling and asperity distribution along the kamchatka subduction zone 1 gps measurements of interseismic horizontal surface velocities reveal the degree of kinematic coupling of the plate boundary thrust along the kamchatka subduction zone from about 51 degrees to 57 degrees n latitude inversions for the distribution of aseismic slip rate along the similar to 15 degrees nw dipping underthrust suggest a nonslipping plate interface in southern kamchatka above similar to 50 km depth along the segment that ruptured in the m w 9 1952 earthquake north of similar to 53 degrees n the subduction interface experiences significant aseismic slip consistent with the lower seismic moment release in m 8 5 earthquakes along this portion of the subduction zone the gps velocities are consistent with a boundary element forward model in which historic earthquake rupture zones are represented as locked asperities surrounded by a zero shear stress subduction interface loaded by plate convergence models in which the complete rupture zones of historic earthquakes are considered locked greatly overpredict the degree of kinematic coupling reducing the area of the locked model asperities to the central 25 area of historic rupture zones fits the data well suggesting that large earthquakes involve small fully locked core asperities surrounded by conditionally stable portions of the plate interface areas of low aseismic slip rate appear to be roughly correlated with areas of low isostatic gravity anomalies over offshore forearc basins while less coupled portions of the kamchatka subduction zone coincide with high gravity anomalies offshore of two peninsulas possibly related to the subduction of the emperor meji seamount chain and the kruzenstern fracture zone

the 1989 loma prieta earthquake imaged from inversion of geodetic data we invert geodetic measurements of coseismic deformation from the 1989 ms7 1 loma prieta earthquake to determine the geometry of the fault and the distribution of slip on the fault plane the data include electronic distance measurements global positioning system and very long baseline interferometry vectors and elevation changes derived from spirit leveling the fault is modeled as a rectangular dislocation surface in a homogeneous elastic half space first we assume that the slip on the fault is uniform and estimate the position orientation and size of the fault plane using a nonlinear quasi newton algorithm the best fitting dislocation strikes n48 4 w and dips 76 9 sw consistent with the trend of the aftershock zone and moment tensor solutions bootstrap resampling of the data is used to graphically illustrate the uncertainty in the location of the rupture plane the 95 confidence envelope overlaps the aftershock zone arguing that there is not a significant discrepancy between the geodetic data and the aftershock locations second we estimate the slip distribution using the best fitting uniform slip fault orientation but increase the fault length to 40 km and the downdip width to 18 km the fault is divided into 162 subfaults 18 along strike and 9 along dip each subfault is allowed to have constant right lateral and reverse components of slip we then solve for the slip on each subfault that minimizes a linear combination of the norm of the weighted data residual and the roughness of the slip distribution the smoothing parameter which determines the relative weight put on fitting the data versus smoothing the slip distribution is chosen by cross validation simulations indicate that cross validation estimates of the smoothing parameter are nearly optimal the preferred slip distribution is very heterogeneous with maximum strike slip and dip slip of about 5 and 8 m respectively located roughly 10 km north of the hypocenter there is insignificant dip slip in the southeastern most part of the fault causing the rake to vary from nearly pure right lateral in the southeast to oblique right reverse in the northwest the change in rake is consistent with a uniform stress field if the fault dip increases by about 10 toward the southeast as indicated by the aftershock locations there was little slip above 4 km depth consistent with the observation that there was little if any surface rupture

displacement across the cholame segment of the san andreas fault between 1855 and 1893 from cadastral surveys changes since 1855 in reported section line lengths and positions of survey monuments that span the san andreas fault saf were used to measure displacement interpreted to be from the 1857 fort tejon earthquake in south central california in 1855 1856 james e freeman established township and range lines across the saf between rancho cholame and the northern carrizo plain at least 26 1 mile sections lines spanned the saf in the area between present day california highways 46 and 58 each section line was marked by monuments at the midpoint and endpoints section lines across portions of the saf were resurveyed in 1893 by j m gore we projected changes in line length onto the fault zone to measure displacement the measurements indicate right lateral displacement of 16 2 6 0 m across the fault zone the resulting tectonic displacement exceeds the maximum reported geomorphic offsets 6 7 m attributed to the 1857 earthquake along the cholame segment although we recognize great uncertainties in the accuracy of our small historical data set we tentatively conclude that total displacement in the 1857 earthquake along the saf over this 2 km wide aperture was significantly greater than the 3 to 6 m slip previously reported for the cholame segment from narrower aperture geomorphic and trenching studies these differences may be compatible if slip along the fault increases down dip rapidly from 3 6 m at the surface to 20 m within several hundred meters of the surface our inference of high slip along this portion of the cholame segment in 1857 is at odds with most rupture models of the central saf and suggests that geomorphic offsets may not represent total displacement across the fault zone

quaternary ostracode and foraminiferal biostratigraphy and paleoceanography in the western arctic ocean abstract the stratigraphic distributions of ostracodes and selected calcareous benthic and planktic foraminiferal species were studied in sediment cores from 700 to 2700 m water depth on the northwind mendeleev and lomonosov ridges in the western arctic ocean microfaunal records in most cores cover mid to late quaternary sediments deposited in the last 600 ka with one record covering the last 1 5 ma results show a progressive faunal turnover during the mid pleistocene transition mpt 1 2 to 0 7 ma and around the mid brunhes event mbe 0 4 ma reflecting major changes in arctic ocean temperature circulation and sea ice cover the observed mpt shift is characterized by the extinction of species that today inhabit the sea ice free subpolar north atlantic and or seasonally sea ice free nordic seas echinocythereis sp rockallia cf enigmatica krithe cf aquilonia pterygocythereis vannieuwenhuisei after a very warm interglacial during marine isotope stage mis 11 dominated by the temperate planktic foraminifer turborotalita egelida the mbe experienced a shift to polar assemblages characteristic of predominantly perennial arctic sea ice cover during the interglacial and interstadial periods of the last 300 ka these include the planktic foraminifera neogloboquadrina pachyderma the sea ice dwelling ostracode acetabulastoma arcticum and associated benthic taxa pseudocythere caudata pedicythere neofluitans and polycope spp several species can be used as biostratigraphic markers of specific intervals such as ostracodes rabilimis mirabilis mis 5 and p vannieuwenhuisei extinction after mis 11 and foraminiferal abundance zones bulimina aculeata late mis 5 and bolivina arctica mis 5 11

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

baffin bay present day analog of the central arctic during late pliocene to mid pleistocene time olive green and olive gray glacial marine sandy clays with rare planktonic foraminifera dominated by a euryhaline and eurytherm species blanket the northern baffin bay floor today these sediments are analogous to those of the central arctic basin deposited between 3 and 0 9 m y ago while today the central arctic is covered with perennial sea ice during part of the gauss and most of the matuyama epochs unit ii hydrological conditions were very similar to those in northern baffin bay today generally ice free year round these data lend support to the hypothesis of an ice free arctic during late pliocene to mid pleistocene time

controls of shear zone rheology and tectonic loading on postseismic creep 1 postseismic deformation is well documented in geodetic data collected in the aftermath of large earthquakes in the postseismic time interval gps is most sensitive to creep in the lower crust or upper mantle activated by earthquake generated stress perturbations in these regions deformation may be localized on an aseismic frictional surface or on a ductile shear zone these two hypotheses imply specific rheologies and therefore time dependence of postseismic creep hence postseismic creep constitutes a potential probe into the rheology of aseismic regions of the lithosphere i present a simple shear zone model of postseismic creep in which the rheology of the creeping element can be varied in the absence of tectonic loading during the postseismic time interval the displacement history of the shear zone obeying a power law rheology with stress exponent n follows an analytical relaxation curve parameterized by 1 n for a frictional surface postseismic creep follows the same relaxation law in the limit 1 n 0 a rough estimate of the apparent stress exponent can be obtained from continuous gps records application to data collected after the 1994 sanriku earthquake yields 1 n 0 1 which is consistent with dislocation creep mechanisms however the records of two other subduction zone events the 2001 peru event and the 1997 kronotski earthquake and a continental strike slip earthquake the 1999 izmit earthquake require negative 1 n rather than characterizing the shear zone rheology these negative exponents indicate that reloading of the shear zone by tectonic forces is important numerical simulations of postseismic deformation with nonnegligible reloading produce curves that are well fit by the generalized relaxation law with 1 n 0 although the actual stress exponent of the rheology is positive while this prevents rheology from being tightly constrained by the studied gps records it indicates that reloading is important in the postseismic time interval in other words the stress perturbation induced by an earthquake is comparable to the stress supported by ductile shear zones in the interseismic period

rapid afterslip following the 1999 chi chi taiwan earthquake 1 postseismic displacements of as much as 14 cm were recorded by gps measurements in the 3 months following the mw 7 6 1999 chi chi taiwan earthquake data from 35 continuous and 90 campaign surveyed stations which show continued east over west thrusting are analyzed to estimate the postseismic slip distribution and fault geometry assuming the shallow fault dips 24 e as determined by numerous studies of the mainshock we invert for the deeper fault structure our results show that the fault dip shallows with depth below the hypocenter merging into a nearly horizontal decollement at a depth of 8 12 km the afterslip distribution shows a maximum slip of 25 cm in the hypocentral region at 7 12 km depth as well as significant slip on the lower decollement afterslip is notably absent in the region of maximum coseismic slip consistent with the afterslip being driven by the mainshock stress change

the resolving power of coseismic surface displacement data for fault slip distribution at depth 1 the spatial slip distribution of the august 17 1999 izmit turkey earthquake has previously been determined from both geodetic and seismological data though the models derived agree on a broad scale they are significantly different in detail these differences could be due to the inversion techniques applied and or additional constraints implemented and or be due to poor resolution it is also conceivable that the relative agreement at larger scales results in part from a resolution artifact common to all models to investigate this we perform a resolution analysis of fault slip models based on the inversion of surface displacement data assuming the theory of elastic dislocations in a half space and adopting a parameterization for which model predictions are capable of fitting the spatial variations of the data the inverse problem proves to be intrinsically ill conditioned

coseismic and initial postseismic deformation from the 2004 parkfield california earthquake observed by global positioning system electronic distance meter creepmeters and borehole strainmeters global positioning system gps electronic distance meter creepmeter and strainmeter measurements spanning the m 6 0 parkfield california earthquake are examined using these data from 100 sec through 9 months following the mainshock the omori s law with rate inversely related to time 1 t p and p ranging between 0 7 and 1 3 characterizes the time dependent deformation during the postseismic period these results are consistent with creep models for elastic solids with an accurate function of postseismic response the coseismic displacements can be estimated from the high rate 1 min sampling gps and the coseismic displacements are approximately 75 of those estimated from the daily solutions consequently fault slip models using daily solutions overestimate coseismic slip in addition at 2 months and at 8 months following the mainshock postseismic displacements are modeled as slip on the san andreas fault with a lower bound on the moment exceeding that of the coseismic moment online material data description and supplementary figures tables and data used in models and time series analysis

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

slip deficit on the san andreas fault at parkfield california as revealed by inversion of geodetic data a network of geodetic lines spanning the san andreas fault near the rupture zone of the 1966 parkfield california earthquake magnitude m 6 has been repeatedly surveyed since 1959 in the study reported here the average rates of line length change since 1966 were inverted to determine the distribution of interseismic slip rate on the fault these results indicate that the parkfield rupture surface has not slipped significantly since 1966 comparison of the geodetically determined seismic moment of the 1966 earthquake with the interseismic slip deficit rate suggests that the strain released by the latest shock will most likely be restored between 1984 and 1989 although this may not occur until 1995 these results lend independent support to the earlier forecast of an m 6 earthquake near parkfield within 5 years of 1988

space time distribution of afterslip following the 2003 tokachi oki earthquake implications for variations in fault zone frictional properties 1 gps time series following the september 25 2003 ut tokachi oki earthquake m w 8 0 reveal significant deformation we use the network inversion filter to invert for the spatial and temporal evolution of afterslip in the 30 days following the earthquake afterslip is concentrated adjacent to the coseismic rupture zone between the 2003 rupture and the inferred source regions of the 1968 tokachi oki and the 1973 nemuro oki earthquakes the inversion shows a rapid decay of slip rate in the 2003 rupture zone with slower deceleration in the surrounding regions the stress velocity paths for the afterslip regions approximately follow d d in v 0 6 mpa suggestive of steady state velocity strengthening friction the complementary spatial pattern of coseismic rupture and afterslip may indicate along strike spatial variations of frictional properties although other interpretations can not be ruled out

frictional properties on the san andreas fault near parkfield california inferred from models of afterslip following the 2004 earthquake the abundance of geodetic and seismic data recording postseismic deformation following the 2004 parkfield earthquake provides an unprecedented opportunity to resolve frictional properties on the parkfield section of the san andreas fault the parkfield segment is a transition between the locked section to the southeast that last ruptured in the 1857 fort tejon earthquake and the creeping section to the northwest we develop three dimensional rate and state dependent friction models of afterslip following the 2004 earthquake to investigate the frictional behavior of the fault it is assumed that the coseismic rupture occurred on an area of the fault surrounded by aseismic creep that accelerated after the earthquake we estimate the distribution of coseismic slip afterslip and rate state frictional parameters by inverting a two step slip model in the model we 1 estimate the coseismic slip distribution from 1 hz global positioning system gps data and 2 use the corresponding coseismic shear stress change on the fault as input into a numerical afterslip model governed by rate state friction we find the rate state frictional parameter a b an indicator of frictional stability is in the range 10 4 10 3 at 50 mpa normal stress which is near the transition from potentially unstable negative a b to nominally stable positive a b friction the estimate of a b values falls within a wide range of experimental values reported for serpentinite which crops out along the san andreas fault zone the critical slip distance d c which characterizes the distance over which strength breaks down during a slip event is in the range 0 01 0 1 m consistent with seismic estimates and a fault gouge thickness of 1 10 m the afterslip model reproduces most features observed in the gps time series data including high surface velocities in the first few months after the earthquake and lower rates at later times as well as the cumulative postseismic displacement the model tends to underpredict the displacement data at later times suggesting that perhaps the modeled afterslip period ends too quickly or an unmodeled deformation process dominates the signal at later times

models of glaciomarine sedimentation and their application to the interpretation of ancient glacial sequences abstract this paper argues that glaciomarine environments can be regarded as special glacially influenced types of continental margin environments e g continental shelf slope rise and basin plain knowledge of the stratigraphic architecture and typical sedimentary sequences of non glacial margins is becoming well known but remains limited for those that have been glacially modified the principal influences on sedimentation in these environments relate to the glacial sediment input controlled by relief of basin margin glacier thermal regime and ice flow dynamics and depositional environments influence of traction currents substrate relief and proximity to nearby ice margins typical ranges of sedimentation rates can be established for glacially influenced continental margin environments and these may provide a framework for ancient sequences starvation of sediment supply to glacially influenced continental margins is common the nature of sub ice shelf sedimentation a model that has been applied to many ancient glacial sequences is critically reviewed the significance of such sedimentation in the rock record has probably been exaggerated because of oversimplistic interpretations of diamictite sequences existing process models of glaciomarine sedimentation derived from study of modern environments are sometimes difficult to employ in investigation of ancient sedimentary sequences because simple lithofacies criteria and typical vertical profiles are not available to aid in interpretation in addition compositional data emphasized by many workers for distinguishing glaciomarine from continental glacial diamict ite s frequently fingerprint sediment source and not mode of deposition the importance of facies analysis methods for isolating depositional environments is illustrated by three examples of ancient glaciomarine sequences these are the early proterozoic gowganda formation 2 3 ga of northern ontario canada the late proterozoic port askaig formation 670 ma of scotland and ireland and the late cenozoic yakataga formation 20 ma to recent of the gulf of alaska these examples illustrate the significance of detailed genetic studies of ancient glacial rocks in the interpretation of palaeogeographic and tectonic settings diamictite units in ancient glaciomarine sequences cannot be easily interpreted in terms of climatic or ice advance retreat cycles because of the varied controls on diamict accumulation and diamictite preservation in marine basins

time dependent distributed afterslip on and deep below the izmit earthquake rupture surface deformation transients measured with the global positioning system during the 87 days between the 17 august 1999 izmit earthquake and the 12 november 1999 duzce earthquake indicate rapidly decaying aseismic fault slip on and well below the coseismic rupture elastic model inversions for time dependent distributed fault slip using a network inversion filter approach show that afterslip was highest between and below the regions of maximum coseismic slip and propa gated downward to or even below the base of the crust maximum afterslip rates decayed from greater than 2 m yr immediately after the i zmit earthquake to about 1 2 m yr just prior to the duzce earthquake maximum afterslip occurred below the eastern karadere rupture segment and near the i zmit hypocenter afterslip in the upper 16 km decayed more rapidly than that below the seismogenic zone these observations are consistent with a phase of rapid aseismic fault slip concentrated near the base of the seismogenic zone continued loading from the rapid deep afterslip along the eastern rupture zone is a plausible mechanism that helped trigger the nearby mw 7 2 12 november duzce earthquake

evidence of power law flow in the mojave desert mantle studies of the earth s response to large earthquakes can be viewed as large rock deformation experiments in which sudden stress changes induce viscous flow in the lower crust and upper mantle that lead to observable postseismic surface deformation laboratory experiments suggest that viscous flow of deforming hot lithospheric rocks is characterized by a power law in which strain rate is proportional to stress raised to a power n refs 2 3 most geodynamic models of flow in the lower crust and upper mantle however resort to newtonian linear stress strain rate relations here we show that a power law model of viscous flow in the mantle with n 3 5 successfully explains the spatial and temporal evolution of transient surface deformation following the 1992 landers and 1999 hector mine earthquakes in southern california a power law rheology implies that viscosity varies spatially with stress causing localization of strain and varies temporally as stress evolves rendering newtonian models untenable our findings are consistent with laboratory derived flow law parameters for hot and wet olivine the most abundant mineral in the upper mantle and support the contention that at least beneath the mojave desert the upper mantle is weaker than the lower crust

coseismic slip distribution of the 2002 mw7 9 denali fault earthquake alaska determined from gps measurements 1 on 3 november 2002 an mw7 9 earthquake occurred in central alaska the earthquake ruptured portions of the susitna glacier denali and totschunda faults inversion of the gps measured displacement field indicates that the event was dominated by a complex right lateral strike slip rupture along the denali fault gps sites closest to the epicenter show the effect of thrust motion on the susitna glacier fault the preferred coseismic slip model with m w 7 8 indicates relatively low slip on the western part of the rupture and high slip from about 60 km east of the hypocenter extending to the junction of the denali and totschunda faults we find mostly shallow slip from the surface to 15 km depth but the inversion suggests one large deep slip patch about 110 km east of the hypocenter our model predicts surface slip in good agreement with surface geological observations where model resolution is good

co seismic slip post seismic slip and largest aftershock associated with the 1994 sanriku haruka oki japan earthquake 1 we analyzed continuous gps data to investigate the spatio temporal distribution of co seismic slip post seismic slip and largest aftershock associated with the 1994 sanriku haruka oki japan earthquake mw 7 7 to get better resolution for co seismic and post seismic slip distribution we imposed a weak constraint as a priori information of the co seismic slip determined by seismic wave analyses we found that the post seismic slip during 100 days following the main shock amount to as much moment release as the main shock and that the sites of co seismic slip and post seismic slip are partitioning on a plate boundary region in complimentary fashion the major post seismic slip was triggered by the mainshock in western side of the co seismic slip and the extent of the post seismic slip is almost unchanged with time it rapidly developed a shear stress concentration ahead of the slip area and triggered the largest aftershock

upper cenozoic history of the labrador sea baffin bay and the arctic ocean a paleoclimatic and paleoceanographic summary foraminifera palynomorphs and stable isotopes in planktonic foraminifera have been studied in piston cores from the northern labrador sea southern baffin bay and the alpha ridge region of the central arctic ocean foraminifera in cores from the labrador sea and southern baffin bay show glacial interglacial 18o values similar to those reported from the norwegian and greenland seas in contrast to the eastern north atlantic ocean however peaks of subarctic foraminifera and dinoflagellates in the western north atlantic cores show that relatively warm atlantic surface water continued to flow into the northern labrador sea during the early glaciation growth phases of isotopic stages 2 4 6 and 8 boreal and subarctic pollen suggest that warm atlantic air flowed into the northern labrador sea and baffin bay during the ice sheet growth phases the advection of warm air masses and the presence of open waters during the summer probably provided moisture for the growth of the laurentide innuitian and greenland ice sheets isotopic and microfossil records in arctic cores can also be tentatively correlated with major high latitude north atlantic glacial interglacial events magnetostratigraphic palynological and amino acid dating however shows that sedimentation on the alpha ridge has been very slow during the past 0 73 m y therefore events of less than 20 000 years duration cannot be clearly discerned interpretation of pre pleistocene paleoenvironments is further limited by the sparseness of calcareous and siliceous microfossils

slip on the san andreas fault at parkfield california over two earthquake cycles and the implications for seismic hazard parkfield california which experienced m 6 0 earthquakes in 1934 1966 and 2004 is one of the few locales for which geodetic observations span multiple earthquake cycles we undertake a comprehensive study of deformation over the most recent earthquake cycle and explore the results in the context of geodetic data collected prior to the 1966 event through joint inversion of the variety of parkfield geodetic measurements trilateration two color laser and global positioning system including previously unpublished two color data we estimate the spatial distribution of slip and slip rate along the san andreas using a fault geometry based on precisely relocated seismicity although the three most recent parkfield earthquakes appear complementary in their along strike distributions of slip they do not produce uniform strain release along strike over multiple seismic cycles since the 1934 earthquake more than 1 m of slip deficit has accumulated on portions of the fault that slipped in the 1966 and 2004 earthquakes and an average of 2 m of slip deficit exists on the 33 km of the fault southeast of gold hill to be released in a future perhaps larger earthquake it appears that the fault is capable of partially releasing stored strain in moderate earthquakes maintaining a disequilibrium through multiple earthquake cycles this complicates the application of simple earthquake recurrence models that assume only the strain accumulated since the most recent event is relevant to the size or timing of an upcoming earthquake our findings further emphasize that accumulated slip deficit is not sufficient for earthquake nucleation online material model fault geometry fit to the data for the inversions and model resolution

on the physical mechanism of silent slip events along the deeper part of the seismogenic zone 1 to investigate the mechanism of recently observed silent slip events we simulated earthquake preparation processes using the dieterich ruina rate and state dependent friction law to ensure realistic modeling of the unstable stable transition we considered small cut off velocity to an evolution effect in the friction law for the transition zone when the cut off velocity to the evolution effect is significantly smaller than that of a direct effect steady state friction behaves as velocity weakening at low slip velocity and velocity strengthening at high slip velocity this frictional behavior was experimentally and theoretically confirmed for the unstable stable transition zone the results of our numerical simulations show that silent slips of which velocity is higher than the velocity of relative plate motion eventually propagates horizontally along the unstable stable transition over a period of several years silent slip events can be interpreted as being caused by the transitional behavior of the fault constitutive law