the key frictional parameters controlling spatial variations in the speed of postseismic slip propagation on a subduction plate boundary abstract we investigate relations between the postseismic slip process effective normal stress and friction parameters for a rate and state dependent law using 3 d numerical simulations of a subduction zone the results show that the postseismic propagation speed largely depends on a a rather than a b a b or d c where a and b are the frictional parameters describing the friction law is the effective normal stress and d c is the characteristic slip distance the duration of the postseismic slip is found to depend on d c and a b considering that postseismic slip propagates faster in shallower regions than in deeper regions for both our numerical simulations and observation off sanriku and that frictional parameter a is not likely to be several times smaller than that estimated from rock laboratory experiments we conclude that effective normal stress mainly controls the spatial variations in the speed of postseismic slip propagation for large earthquakes off sanriku moreover the effective normal stress much lower than lithostatic stress due to high pore pressure may explain the speed of aseismic slip propagation in other subduction zones as well as off sanriku

the critical slip distance for seismic faulting experimentally based friction laws1 2 have been found to predict virtually the entire range of observed behaviour of natural faults3 4 these laws contain a critical slip distance l which plays a key role in determining the degree of fault instability the size of the zone of earthquake nucleation the frictional breakdown width and the proportion of pre and post seismic slip to co seismic slip in laboratory measurements l is found to be about 10 5m but modelling results show that it must be about 10 2m if natural earthquake behaviour is to be simulated the discovery that fault surfaces are fractal over the scale range 10 5 105 refs 5 6 even for faults with large net slip has confused the problem of scaling this parameter from laboratory experiments to natural faults because fractal surfaces have no characteristic length here i show that geometrically unmated fractal surfaces when in contact under a normal load develop a characteristic length in their contact because long wavelength apertures close under load whereas short wavelength apertures may remain open this critical distance may be identified with l and calculations based on fault topography data show that at seismogenic depths it will be in the range anticipated from the earthquake modelling studies

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

space time evolution of crustal deformation related to the mw 6 3 2009 l aquila earthquake central italy from principal component analysis inversion of gps position time series

dynamics of izmit earthquake postseismic deformation and loading of the duzce earthquake hypocenter we have developed dynamic finite element models of izmit earthquake postseismic deformation to evaluate whether this deformation is better explained by afterslip via either velocity strengthening frictional slip or linear viscous creep or by distributed linear viscoelastic relaxation of the lower crust we find that velocity strengthening frictional afterslip driven by coseismic shear stress loading can reproduce time dependent global positioning system data better than either linear viscous creep on a vertical shear zone below the rupture or lower crustal viscoelastic relaxation our best frictional afterslip model fits the main features of postseismic slip inversions in particular high slip patches at and below the hypocenter and on the western karadere segment and limited afterslip west of the hersek delta burgmann et al 2002 the model requires a weakly velocity strengthening fault that is either low effective normal stress in the slipping regions or a smaller value for the parameter describing rate dependence of friction a b than is indicated by laboratory experiments our best afterslip model suggests that the coulomb stress at the duzce hypocenter increased by 0 14 mpa 1 4 bars during the izmit earthquake assuming right lateral slip on a surface dipping 50 to the north and by another 0 1 mpa during the 87 days between the izmit and duzce earthquakes in the marmara sea region within about 160 km of the izmit earthquake rupture this model indicates that the coulomb stresses increased by 15 25 of the coseismic amount during the first 300 days after the earthquake three hundred days after the earthquake postseismic contributions to coulomb stressing rate on the maramara region faults had fallen to values equal to or less than the inferred secular stress accumulation rate our estimates of postseismic coulomb stress are highly model dependent in the marmara region the linear viscous shear zone and viscoelastic lower crust models predict greater postseismic coulomb stresses than the frictional afterslip model near field stress and fault zone rheology estimates are sensitive to the earth9s elastic structure when a layered elastic structure is incorporated in our model it yields a coulomb stress of 0 24 mpa at the duzce hypocenter significantly more than the 0 14 mpa estimated from the uniform elastic model because of the higher near field coseismic stresses the layered elastic model requires a higher value of velocity strengthening parameter a b a b times effective normal stress r to produce comparable postseismic slip a b is estimated at 0 4 and 0 2 mpa respectively for the layered and uniform elastic models these results highlight the importance of understanding the earth9s elastic structure and the mechanism for postseismic deformation if we wish to accurately model coseismic and postseismic crustal stresses

dynamics of a velocity strengthening fault region implications for slow earthquakes and postseismic slip we consider the effect of permanent stress changes on a velocity strengthening rate and state fault through numerical simulations and analytical results on 1 d 2 d and 3 d models we show that slip transients can be triggered by perturbations of size roughly larger than lb gdc b where g is the shear modulus dc and b are the characteristic slip distance and the coefficient of the evolution effect of rate and state friction respectively and is the effective normal stress perturbations that increase the coulomb stress lead to the strongest transients but creep bursts can also be triggered by perturbations that decrease the coulomb stress in the latter case peak slip velocity is attained long after the perturbation so that it may be difficult in practice to identify their origin the evolution of slip in a creep transient shares many features with the nucleation process of a rate and state weakening fault slip initially localizes over a region of size not smaller than lb and then accelerates transiently and finally expands as a quasi static propagating crack the characteristic size lb implies a constraint on the grid resolution of numerical models even on strengthening faults that is more stringent than classical criteria in the transition zone between the velocity weakening and strengthening regions the peak slip velocity may be arbitrarily large and may approach seismic slip velocities postseismic slip may represent the response of the creeping parts of the fault to a stress perturbation of large scale comparable to the extent of the main shock rupture and high amplitude while slow earthquakes may represent the response of the creeping zones to a more localized stress perturbation our results indicate that superficial afterslip observed at usually seismogenic depths is governed by a rate strengthening rheology and is not likely to correspond to stable weakening zones the predictions of the full rate and state framework reduce to a pure velocity strengthening law on a timescale longer than the duration of the acceleration transient only when the triggering perturbation extends over length scales much larger than lb

rate and state friction properties of the longitudinal valley fault from kinematic and dynamic modeling of seismic and aseismic slip the longitudinal valley fault lvf taiwan is a fast slipping fault 5 cm yr which exhibits both seismic and aseismic slip geodetic and seismological observations 1992 2010 were used to infer the temporal evolution of fault slip thomas et al 2014a this kinematic model is used here to estimate spatial variations of steady state velocity dependence of fault friction and to develop a simplified fully dynamic rate and state model of the lvf based on the postseismic slip we estimate that the rate and state parameter a b over bar decreases from 1 2 mpa near the surface to near velocity neutral at 19 km depth the inferred a b values are consistent with the laboratory measurements on clay rich fault gouges comparable to the lichi melange which borders the lvf the dynamic model that incorporates the obtained a b over bar estimates as well as a vw patch with tuned rate and state properties produces a sequence of earthquakes with some realistic diversity and a spatio temporal pattern of seismic and aseismic slip similar to that inferred from the kinematic modeling the larger events have moment magnitude m w 6 7 similar to the 2003 chenkung earthquake with a range of smaller events the model parameterization allows reproducing partial overlap of seismic and aseismic slip before the earthquake but cannot reproduce the significant postseismic slip observed in the previously locked patch we discuss factors that can improve the dynamic model in that regard including the possibility of temporal variations in a b due to shear heating such calibrated dynamic models can be used to reconcile field observations kinematic analysis and laboratory experiments and assess fault behavior

a model for possible crustal deformation prior to a coming large interplate earthquake in the tokai district central japan we perform numerical simulations of a seismic cycle by applying a laboratory derived friction law to evaluate possible crustal deformations prior to the hypothesized tokai earthquake which is expected to occur in the near future along the suruga trough central japan the frictional force obeying a rate and state dependent friction law is assumed to act on the plate interface in a 2d model of the subduction zone we test two versions of the friction law the so called slowness version and the slip version we select model parameters on the basis of historical documents about past large earthquakes in the tokai district and the present coupling state of the plate interface beneath the tokai district estimated by gps observations simulation results for both the slowness and the slip version are as follows 1 the coupling region of the plate interface becomes narrower with time in the interseismic period 2 the inland crust contracts at a nearly constant rate for most of the interseismic period the contraction rate decreases or a change from contraction to extension takes place before the occurrence of a large interplate earthquake 3 significant abnormal crustal deformation precedes the earthquake and maximum amplitudes about one day before the earthquake exceed the noise levels in the case of clear weather of borehole strainmeters installed in the tokai district 4 the spatiotemporal variation of aseismic sliding on the plate interface perturbs the regional stress field around the source volume of the coming earthquake leading possibly to precursory seismic quiescence in the overriding plate and a change in focal mechanisms of small earthquakes in the subducting slab the most significant difference in the results between the slowness version and the slip version of the friction law is that amplitudes of preslip and crustal deformation just before earthquakes are several times larger for the slowness version than for the slip version although some ambiguity remains in the present model mainly because of the incompleteness of the friction law and the deficiency of observational data constraining model parameters the physical model can be improved through the comparison of predicted crustal deformation with observations continuous and concentrated observations of crustal deformation and seismic activity are thus important in the tokai district to understand quantitatively the sliding process preceding a large interplate earthquake there

calculation of aftershock accumulation from observed postseismic deformation m6 2004 parkfield california earthquake 1 the postseismic stress accumulation t over the interval 0 004 to 880 days following the 2004 parkfield earthquake m6 can be inferred from gps measurements of postseismic deformation the stress relaxation t lt where l is the interseismic loading rate and t is the time after the earthquake plotted as a function of the number of m 1 5 aftershocks na t that have occurred by time t is bilinear with the slope of the fit to the first half of the aftershock sequence less than the slope of the fit to the second half thus the aftershock seismicity rate is not proportional to the stress relaxation rate t l over the entire sequence but rather exhibits two distinct proportionalities the observed postearthquake accumulation of m 1 5 earthquakes in the aftershock zone as a function of time can be explained with the rate and state friction relation proposed by dieterich 1994 between the cumulative number of earthquakes and t

adaptation of the near surface wind to the development of sand transport a model of wind blown sand transport is described with particular emphasis on the feedback between the grain cloud and the near surface wind the results from this model are used to develop owen s 1964 hypothesis that the grain layer behaves so far as the flow outside it is concerned as increased aerodynamic roughness whose height is proportional to the thickness of the layer the hypothesis is developed to show the influence this dynamic roughness has on the turbulent boundary layer above the saltation layer two processes are identified which influence the path of the system towards equilibrium the first is the feedback between the near surface wind and the grain cloud in which the quantity of sand transported is limited by the carrying capacity of the wind the second is due to the temporal development of an internal boundary layer in response to the additional roughness imposed on the flow above the grain layer by the grain cloud a similarity is noted between the temporal response of a turbulent boundary layer to sand transport and the spatial response of a turbulent boundary layer downstream of a step increase in surface roughness finally it is noted that the work may have important implications for transport rate prediction in unsteady winds

velocity profile of a sand cloud blowing over a gravel surface particle dynamic analyzer pda measurement technology was used to study the turbulent characteristics and the variation with height of the mean horizontal in the downwind direction and vertical in the upward direction particle velocity of a sand cloud blowing over a gravel surface the results show that the mean horizontal particle velocity of the cloud increases with height while the mean vertical velocity decreases with height the variation of the mean horizontal velocity with height is to some extent similar to the wind profile that increases logarithmically with height in the turbulent boundary layer the variation of the mean vertical velocity with height is much more complex than that of the mean horizontal velocity the increase of the resultant mean velocity with height can be expressed by a modified power function particle turbulence in the downwind direction decreases with height while that in the vertical direction is complex for fine sands 0 2 0 3 mm and 0 3 0 4 mm there is a tendency for the particle turbulence to increase with height in the very near surface layer 4 mm the movement of blown sand particles is very complex due to the rebound of particles on the bed and the interparticle collisions in the air wind starts to accelerate particle movement about 4 mm from the surface the initial rebound on the bed and the interparticle collisions in the air have a profound effect on particle movement below that height where particle concentration is very high and wind velocity is very low

post seismic and interseismic fault creep i model description we present a model of localized aseismic fault creep during the full interseismic period including both transient and steady fault creep in response to a sequence of imposed coseismic slip events and tectonic loading we consider the behaviour of models with linear viscous non linear viscous rate dependent friction and rate and state dependent friction fault rheologies both the transient post seismic creep and the pattern of steady interseismic creep rates surrounding asperities depend on recent coseismic slip and fault rheologies in these models post seismic fault creep is manifest as pulses of elevated creep rates that propagate from the coseismic slip these pulses feature sharper fronts and are longer lived in models with rate state friction compared to other models with small characteristic slip distances in rate state friction models interseismic creep is similar to that in models with rate dependent friction faults except for the earliest periods of post seismic creep our model can be used to constrain fault rheologies from geodetic observations in cases where the coseismic slip history is relatively well known when only considering surface deformation over a short period of time there are strong trade offs between fault rheology and the details of the imposed coseismic slip geodetic observations over longer times following an earthquake will reduce these trade offs while simultaneous modelling of interseismic and post seismic observations provide the strongest constraints on fault rheologies

theoretical analysis of particle number density in steady aeolian saltation abstract particle number density or particle concentration in aeolian saltation is one important input parameter to calculate the sand flux kinetic energy and mid air collision probability in the aeolian saltation and particle concentration is also related to the wind erosion capacity hence in the present paper the vertical distribution of particle number density in steady aeolian saltation is analyzed based on two different types of probability density functions of vertical lift off velocity of saltating particles one is the pdf probability density function of vertical velocity of lift off particles in the three dimensional space defined as a type a pdf which considers the number of particles in various velocity bins per unit volume and the other is the pdf of vertical velocity of lift off particles ejected from the sand bed surface in a period of time as a type b pdf which considers the number flux of particles in various velocity bins per unit surface area these two types of pdfs are from two different perspectives i e volume and surface based perspectives respectively and can be deduced from each other the half normal and exponential distributions are recommended for the type a pdf and the corresponding type b pdf is expressed by rayleigh and gamma 2 distributions the pdf distribution pattern of vertical velocity of lift off particles has an important influence on the vertical profile of particle number density if the type a pdf of vertical velocity of ejected particles is a half normal distribution the particle number density decays exponentially with height if the type a pdf is an exponential distribution the particle number density also decreases with height if the type a pdf is gamma 3 and rayleigh distributions the particle number density first increases then decreases with height the type a and type b height parameters which are calculated according to the mean vertical lift off velocity from the type a and type b pdfs respectively are not simply considered as the actual mean saltation height although if the type a pdf of vertical lift off velocity is half normal pdf the mean dispersion height of particle concentration equals the mean saltation height the vertical distribution of particle number density can determine the dislodgement rate on bed surface which further affects the surface bedforms

interplate coupling beneath ne japan inferred from three dimensional displacement field 1 the northeastern japan arc is located in a typical subduction zone and is a seismically active region where large interplate earthquakes have occurred repeatedly the nationwide gps network has made it possible to investigate the crustal deformation in unprecedented detail however vertical displacements are less accurate than the horizontal ones and have not been used to constrain interplate coupling models in this study gps carrier phase data are analyzed in order to estimate three components of site displacements the result indicates uplift along the japan sea coast and subsidence along the pacific ocean coast using the vertical site velocities together with the horizontal ones as the data for a geodetic inversion method a new model of interplate coupling is constructed to explain both the horizontal and vertical velocities for the interseismic period from 1997 to 2001 the model demonstrates strong coupling in the area off miyagi and in the area off aomori through the area off tokachi including the areas of asperities the downdip limit of the locked fault zone on the plate boundary has been estimated seismologically to be at a depth of 50 60 km in northeastern japan and the distribution of slip deficits derived in this study indicates that the transition zone extends down to a depth of about 100 km

newly imaged shape of the deep seismic zone within the subducting pacific plate beneath the hokkaido corner japan kurile arc arc junction 1 the geometry of the deep seismic zone associated with the subducting pacific plate beneath the north american plate in the hokkaido corner japan kurile arc arc junction has been investigated based on the hypocenters accurately relocated by a dense local seismographic network with three dimensional p and s wave velocity structures the model suggests that the lateral changes in the dip of the subduction zone are more rapid than previously believed we found that the deep seismic zone in the pacific plate dips at 20 to 30 on the side of the japan arc the dip angle increased in a narrow region around 143 144 e by 10 to 20 and the dip was 40 to 50 on the side of the kurile arc in the transitional zone around 143 144 e an unusual distribution of microearthquakes has been discovered within the pacific plate which was located on a near vertical plane with an area of 50 100 km2 with strike that was perpendicular to the kurile trench axis this feature was named the tokachi oki slab cracking zone we suggest that this is a slab cracking zone torn by the extensional stress due to the rapid lateral changes in the dip of the subduction zone the slab cracking zone may possibly grow into the large disruption or tear of the slab in the future

fault friction parameters inferred from the early stages of afterslip following the 2003 tokachi oki earthquake 1 we use subdaily gps time series of positions in the first 5 hours following the 2003 tokachi oki earthquake mw 8 0 located offshore of hokkaido japan to estimate frictional parameters for the afterslip zone on the subduction interface the data show little motion immediately after the earthquake with sudden acceleration at about 1 2 hours after the main shock this coincides with the largest aftershock m 7 4 followed by gradual deceleration we assume that early afterslip is the response of a fault patch to instantaneous stress perturbations caused by the main shock and the largest aftershock early afterslip is modeled with a spring slider system obeying a rate and state dependent friction law we develop and apply an inversion method to estimate friction parameters dc a and a b where is effective normal stress the estimated 95 confidence intervals of dc a and a b are 2 6 10 4 to 1 8 10 3 m 0 29 to 0 43 mpa and 0 214 to 0 220 mpa respectively estimated dc is 10 to 103 times larger than typical laboratory values estimated a and a b values suggest that a and a b are smaller than typical laboratory values and or the pore pressure on the plate boundary is significantly elevated above the hydrostatic value our analyses show that the model can reproduce the observed gps data and that the timing of the rapid acceleration of postseismic deformation is controlled by the frictional properties of the fault and stress change from the main shock not by the timing of the largest aftershock

late summer thermal regime of a small proglacial lake this study was motivated by an interest in understanding the potential effects of climate change and glacier retreat on late summer water temperatures in alpine areas fieldwork was carried out between july and september 2007 at place lake located below place glacier in the southern coast mountains of british columbia place lake has an area of 72 000m2 a single inlet and outlet channel and an approximate residence time of 4 days warming between the inlet and outlet of the lake ranged up to 3 c and averaged 1 8 c which exceeds the amount of warming that occurred over the 1 km reach of place creek between the lake outlet and tree line over a 23 day period net radiation totalled about 210 mj m 2 with sensible heat flux adding another 56 mjm 2 the latent heat flux consumed about 8 of the surface heat input the dominant heat sink was the net horizontal advection associated with lake inflow and outflow early in the study period temperatures between the surface and 6 m depth were dominantly at or above 4 c and were generally neutral to thermally stable whereas temperatures decreased with depth below 6m and exhibited irregular sub diurnal variations the maximum outflow temperature of almost 7 c occurred in this period we hypothesize that turbidity currents associated with cold sediment laden glacier discharge formed an underflow and influenced temperatures in the deeper portion of the lake but did not mix with the upper layers later in the study period the lake was dominantly well mixed with some near surface stability associated with nocturnal cooling further research is required to examine the combined effects of sediment concentrations and thermal processes on mixing in small proglacial lakes to make projections of the consequences of glacier retreat on alpine lake and stream temperatures

experimental investigation of the concentration profile of a blowing sand cloud detailed wind tunnel tests were carried out to establish the mean downwind velocity and transport rate of different sized loose dry sand at different free stream wind velocities and heights as well as to investigate the vertical variation in the concentration of blowing sand in a cloud particle dynamic analyzer pda technology was used to measure the vertical variation in mean downwind velocity of a sand cloud in a wind tunnel the results reveal that within the near surface layer the decay of blown sand flux with height can be expressed using an exponential function in general the mean downwind velocity increases with height and free stream wind velocity but decreases with grain size the vertical variation in mean downwind velocity can be expressed by a power function the concentration profile of sand within the saltation layer calculated according to its flux profile and mean downwind profile can be expressed using the exponential function cz ae bz where cz is the blown sand concentration at height z and a and bare parameters changing regularly with wind velocity and sand size the concentration profiles are converted to rays of straight lines by plotting logarithmic concentration values against height the slope of the straight lines representing the relative decay rate of concentration with height decreases with an increase in free stream wind velocity and grain size implying that more blown sand is transported to greater heights as grain size and wind speed increase

height profile of the mean velocity of an aeolian saltating cloud wind tunnel measurements by particle image velocimetry abstract the velocity of saltating particles is an important parameter in studying the aeolian sand movement we used particle image velocimetry to measure the variation with height of the mean particle velocity of a saltating cloud over a loose sand surface in a wind tunnel the results suggest that both the horizontal and vertical particle velocities fit the gaussian distribution well and that the mean particle velocity of a saltating cloud varies with wind velocity particle size and the height above bed the mean horizontal velocity is mainly the result of acceleration by the wind and increases with an increase in friction wind velocity but decreases with an increase in grain size because greater wind velocity causes more acceleration and finer particles are more easily accelerated at a given wind velocity it also increases with an increase in height by a power function in agreement with previous results obtained by other methods such as the high speed multi flash photographic method and particle dynamics analyzer pda reflecting first the increase in wind velocity with height through the boundary layer and second the longer trajectory particle path length increases with height and affords a longer time for acceleration by the wind an empirical model relating the mean horizontal particle velocity and height friction wind velocity as well as particle size is developed the ratio of the mean horizontal particle velocity to the clean wind velocity at the same height increases with height but decreases with grain size the magnitude of mean vertical velocity is much less one or two orders less compared with the mean horizontal velocity the average movement in the vertical direction of a saltating cloud is upward the mean vertical velocity is positive although the upward velocity of a saltating particle should decrease with height due to gravity the mean vertical upward velocity the average of both ascending and descending particles generally shows a tendency to increase with height it seems that at higher elevations the data are more and more dominated by the high flyers the underlying mechanism for the mean vertical velocity distribution patterns needs to be clarified by further study

fault model for preseismic deformation at parkfield california we construct an earthquake instability model to estimate precursory faulting and ground deformation before the next moderate m 5 5 6 earthquake on the san andreas fault near parkfield california the quasi static model simulates fault slip fault shear stress and ground deformation for all stages of repeated earthquake cycles unstable slip which is the analog of a moderate parkfield mainshock is caused by overall failure of a postulated strong area or patch of the fault zone the brittle patch and surrounding weaker viscous fault are defined by the sign of a spatially varying coefficient of a slip rate dependent fault law stable failure of the patch leading up to mainshock failure causes slip rate to increase at depth amplitudes and timescales of the resulting preseismic deformation anomalies are found for the current earthquake cycle at parkfield starting just after the 1966 mainshock in two ways in the first way we vary parameter values in a sequence of simulations so as to find the simulation giving best agreement with locations moments and recurrence times of past moderate earthquakes and also with fault creep and trilateration line length changes since the 1966 mainshock in the second way we assign values of most parameters from laboratory friction experiments and a temperature depth profile inferred from heat flow data overall agreement between model results and observations is comparable for the two methods in all simulations preseismic deformation anomalies arise from slip rate increase near the model earthquake focus and start several years or less before instability preseismic anomalies in surface fault creep and line length are always too small to detect in current measurements however for some simulations constrained mainly by field data the predicted anomalies in borehole dilatation are large enough to detect

quantitative measure of the variation in fault rheology due to fluid rock interactions we analyze friction data from two published suites of laboratory tests on granite in order to explore and quantify the effects of temperature t and pore water pressure pp on the sliding behavior of faults rate stepping sliding tests were performed on laboratory faults in granite containing gouge granite powder both dry at 23 to 845 c lockner et al 1986 and wet pp 100 mpa at 23 to 600 c blanpied et al 1991 1995 imposed slip velocities v ranged from 0 01 to 5 5 m s and effective normal stresses were near 400 mpa for dried granite at all temperatures and wet granite below 300 c the coefficient of friction shows low sensitivity to v t and pp for wet granite above 350 drops rapidly with increasing t and shows a strong positive rate dependence and protracted strength transients following steps in v presumably reflecting the activity of a water aided deformation process by inverting strength data from velocity stepping tests we determined values for parameters in three formulations of a rate and state dependent constitutive law one or two state variables were used to represent slip history effects each velocity step yielded an independent set of values for the nominal friction level five constitutive parameters transient parameters a b1 and b2 and characteristic displacements dc1 and dc2 and the velocity dependence of steady state friction ss ln v a b1 b2 below 250 data from dry and most wet tests are adequately modeled by using the slip law ruina 1983 and one state variable a 0 003 to 0 018 b 0 001 to 0 018 dc 1 to 20 m dried tests above 250 can also be fitted with one state variable in contrast wet tests above 350 require higher direct rate dependence a 0 03 to 0 12 plus a second state variable with large negative amplitude b2 0 03 to 0 14 and large characteristic displacement dc2 300 to 4000 m thus the parameters a b1 and b2 for wet granite show a pronounced change in their temperature dependence in the range 270 to 350 c which may reflect a change in underlying deformation mechanism we quantify the trends in parameter values from 25 to 600 c by piecewise linear regressions which provide a straightforward means to incorporate the full constitutive response of granite into numerical models of fault slip the modeling results suggest that the succeptibility for unstable stick slip sliding is maximized between 90 and 360 c in agreement with laboratory observations and consistent with the depth range of earthquakes on mature faults in the continental crust

geodetic displacements and aftershocks following the 2001 mw 8 4 peru earthquake implications for the mechanics of the earthquake cycle along subduction zones we analyzed aftershocks and postseismic deformation recorded by the continuous gps station areq following the m w 8 4 23 june 2001 peru earthquake this station moved by 50 cm trenchward in a n235 e direction during the coseismic phase and continued to move in the same direction for an additional 15 cm over the next 2 years we compare observations with the prediction of a simple one dimensional 1 d system of springs sliders and dashpot loaded by a constant force meant to simulate stress transfer during the seismic cycle the model incorporates a seismogenic fault zone obeying rate weakening friction a zone of deep afterslip the brittle creep fault zone bcfz obeying rate strengthening friction and a zone of viscous flow at depth the ductile fault zone dfz this simple model captures the main features of the temporal evolution of seismicity and deformation our results imply that crustal strain associated with stress accumulation during the interseismic period is probably not stationary over most of the interseismic period the bcfz appears to control the early postseismic response afterslip and aftershocks although an immediate increase by a factor of about 1 77 of ductile shear rate is required placing constraints on the effective viscosity of the dfz following a large subduction earthquake displacement of inland sites is trenchward in the early phase of the seismic cycle and reverse to landward after a time t i for which an analytical expression is given this study adds support to the view that the decay rate of aftershocks may be controlled by reloading due to deep afterslip given the ratio of preseismic to postseismic viscous creep we deduce that frictional stresses along the subduction interface account for probably 70 of the force transmitted along the plate interface

offshore geodetic data conducive to the estimation of the afterslip distribution following the 2003 tokachi oki earthquake a cable based seafloor observatory located offshore of hokkaido japan provides the world s first direct observation of offshore post seismic displacement after removing thermal noise this data is used to constrain the distribution of offshore afterslip from a great interplate earthquake mw 8 0 that occurred during 2003 along the southern kuril trench a checkerboard resolution test showed a great contribution of the offshore data to improving the spatial resolution on the plate interface slip near the trench the 1 yr afterslip is distributed in a u shaped pattern encircling its co seismic slip area this result indicates that the stick slip frictional properties of the plate interface are distributed in a patch like pattern as opposed to a banding pattern as previously assumed in young subduction zones

on the mechanics of earthquake afterslip we propose a model for earthquake afterslip based on rate and state variable friction laws in the model afterslip is attributed to the interaction of a velocity weakening region at depth within which earthquakes nucleate with an upper region of velocity strengthening frictional behavior the existence of this upper region is supported by independent seismologic observations and the results of laboratory friction experiments in our model afterslip is the result of relaxation of a stress perturbation within the velocity strengthening region which arises when an earthquake propagates into that region from below we derive the stress perturbation and its decay from the friction constitutive law using a simple 1 degree of freedom approximation for the elastic interaction between the fault and its surroundings this approximation is based on thickness averaged displacements and slip velocities within the velocity strengthening region which is assumed to slip as a rigid block coseismic and postseismic slip are coupled through the thickness averaged stiffness k of the velocity strengthening region we assume k to be inversely proportional to the thickness of this region which means that thicker velocity strengthening regions have a greater tendency to arrest coseismic slip we model the afterslip time histories of the 1966 parkfield and 1987 superstition hills earthquakes and relate the model parameters to physical parameters which may govern the rheologic behavior of the faults in accord with field observations our model predicts 1 that afterslip on some faults scales with the thickness of the unconsolidated sedimentary cover and 2 that proportionally more afterslip occurs for earthquakes in which coseismic surface slip is small compared with coseismic slip at depth velocity strengthening frictional behavior is to be expected for faults within poorly consolidated sediments and for those that contain significant gouge zones about 500 m within their shallow regions 3 5 km combining our results with those of recent laboratory friction studies indicates that relatively young faults with little accumulated fault gouge should exhibit little afterslip

steady state saltation in air coupled equations of motion for steady state saltation over an infinite plane are derived and solved for a simplified model of the grain surface impact process experimentally observed features of the wind velocity profile in saltation are qualitatively reproduced including a diminution of the sub saltation layer mean wind speed as the friction speed increases in this model the surface impact velocity of the saltating grains remains relatively constant over a wide range of free stream shear stresses and the grain mass flux increases with friction speed uf less rapidly than uf3

height profile of particle concentration in an aeolian saltating cloud a wind tunnel investigation by piv msd 1 attempt is made to define the particle concentration in an aeolian saltating cloud and its variation with height using artificial spherical quartz sand in a wind tunnel the height profiles of the relative particle concentration in aeolian saltating cloud at three wind velocities were detected by the state of the art piv particle image velocimetry msd mie scattering diffusion technique and converted to actual concentration based on sand transport rate and the variation with height of velocity of the saltating cloud the particle concentration was found to decay exponentially with height and to increase with wind velocity it decayed more rapidly when the wind velocity decreased the volume volume concentration in the near surface layer was at the order of 10 4 the results obtained by piv msd technique were in good agreement with those derived from the sand flux and velocity profiles the former being about 15 greater than the later

the 2003 m8 0 tokachi oki earthquake how much has the great event paid back slip debts 1 a great earthquake with m8 0 the 2003 tokachi oki earthquake occurred on september 26 2003 on the plate boundary south of hokkaido at about the same epicenter as that of the 1952 m8 2 tokachi oki earthquake we estimated the coseismic slip distribution using gps data to obtain consistent results with that inferred from waveform inversions a maximum slip larger than 5m exists around 30km nne from the epicenter though the slip deficit estimated there 80 mm yr by our recent study is based on a rather short period of observation 5 years to discuss the whole seismic cycle the maximum coseismic slip roughly accounts for the slip deficit accumulated in the past 51 years assuming that the back slip rate has been nearly constant since 1952 besides the area of the largest slip however an accumulated slip deficit still remains and should be released by seismic or aseismic slip which is now actually observed in part as postseismic slip

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

a numerical simulation of earthquake cycles along the nankai trough in southwest japan lateral variation in frictional property due to the slab geometry controls the nucleation position abstract the occurrence pattern of historical great earthquakes along the nankai trough indicates the existence of rupture segments that seem to correlate with 100 km scale lateral variation in the dip angle of the subducting philippine sea plate for instance the latest earthquakes the 1944 tonankai and the 1946 nankai earthquakes initiated their ruptures off kii peninsula where the dip angle of the slab is steeper than in adjacent areas to investigate how such heterogeneity in slab geometry affects the occurrence of earthquakes we conducted a three dimensional 3d numerical simulation of earthquake cycles for a large source area about 700 km long along the trough and 300 km wide in the dip direction based on a rate and state dependent friction law we used a simple flat dipping plane to model the plate boundary frictional parameters and effective normal stress were assumed to depend on the estimated depth of the real plate boundary based on seismic surveys and seismicity data the depth dependent frictional parameters were mapped on the flat model plane this made lateral variation in frictional property due to the variation in the dip angle of the slab the plate convergence rate in the model decreased eastward along the trough consistent with a recent global positioning system gps analysis in the simulation results preslip occurred and rupture started off kii peninsula both effects of a narrower locked area due to the higher dip angle and a higher plate convergence rate caused the highest stress accumulation rate to be in this area promoting slip nucleation our simple simulation suggests that lateral variation in the dip angle of the slab is one of the factors controlling the nucleation position of great interplate earthquakes

postseismic relaxation driven by brittle creep a possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks application to the chi chi earthquake taiwan we evaluate the effect of coseismic stress changes on the fault slip at midcrustal depth assuming a velocity strengthening brittle creep rheology we show that this model can help reconcile the time evolution of afterslip as measured from geodesy with aftershocks decay we propose an analytical expression for slip of the brittle creeping fault zone bcfz that applies to any dynamic or static stress perturbation including shear stress and normal stress changes the model predicts an initial logarithmic increase of slip with time postseismic slip rate decays over a characteristic time t r a that does not depend on the amplitude of the stress perturbation and it asymptotically joins the long term creep imposed by interseismic stress buildup given that the seismicity rate might be considered proportional to the sliding velocity of the bcfz the model predicts a decay rate of aftershocks that follows omori s law with a mathematical formalism identical to that of dieterich 1994 although based on a different mechanical rationale our model also differs from dieterich s model in that it requires that aftershock sequences and deep afterslip as constrained from geodetic measurements should follow the same temporal evolution we test this for the 1999 chi chi earthquake m w 7 6 and find that both sets of data are consistent with a model of afterslip due to the response of the bcfz the inferred relaxation time t r 8 5 years requires a value for a log v being the coefficient of friction in the range between 1 3 10 3 and 10 2

coupled afterslip and viscoelastic flow following the 2002 denali fault alaska earthquake summary models of postseismic deformation following the 2002 m 7 9 denali fault alaska earthquake provide insight into the rheologic structure of the alaskan lithosphere and the physical processes activated following a large earthquake we model coseismic gps displacements and 4 yr of postseismic gps position time series with a coupled model of afterslip on the fault in the lithosphere and distributed viscous flow in the asthenosphere afterslip is assumed to be governed by a simplified version of a laboratory derived rate strengthening friction law that is characterized with a single parameter a b where is the effective normal stress on the fault and a b is a dimensionless empirical parameter afterslip is driven by coseismic stress changes on the fault generated by the main shock the lithosphere is modelled as an elastic plate overlying a linear maxwell viscoelastic asthenosphere we devise a scheme to simultaneously estimate the distributions of coseismic slip and afterslip friction parameters lithosphere thickness and asthenosphere viscosity the postseismic gps time series are best reproduced with a 45 85 km thick elastic lithosphere overlying an asthenosphere of viscosity 0 6 1 5 1019 pa s the 45 85 km elastic lithosphere thickness is greater than or equal to the average crustal thickness in the region suggesting that distributed postseismic flow occurs largely within the mantle while postseismic deformation in the crust is confined largely to slip on a discrete fault penetrating the entire crust and perhaps into the uppermost mantle for typical laboratory values of a b of order 10 2 at temperatures corresponding to the inferred depth of afterslip the estimated effective normal stress on the fault is 50 mpa which is about an order of magnitude lower than effective normal stresses at hydrostatic pore pressure previous studies showed that models with linear newtonian rheology cannot reproduce the observed gps time series but that models incorporating non linear or biviscous flow of the mantle do fit the data we show that a model with afterslip governed by a non linear fault zone rheology coupled to newtonian mantle flow is sufficient to reproduce the gps time series

a comprehensive numerical model of steady state saltation comsalt 1 the blowing of sand by wind known as saltation ejects dust aerosols into the atmosphere creates sand dunes and erodes geological features we present a comprehensive numerical model of steady state saltation comsalt that in contrast to most previous studies can reproduce a wide range of measurements and can simulate saltation over mixed soils comsalt calculates the motion of saltating particles due to gravity fluid drag particle spin fluid shear and turbulence and explicitly accounts for the retardation of the wind due to drag from saltating particles furthermore we included a novel physically based parameterization of the ejection of surface particles by impacting saltating particles which matches experimental results comsalt is the first numerical saltation model to reproduce measurements of the wind shear velocity at the impact threshold i e the lowest shear velocity for which saltation is possible and of the aerodynamic roughness length in saltation it also reproduces a range of other saltation processes including profiles of the wind speed and particle mass flux and the size distribution of saltating particles as such comsalt is the first physically based numerical model to reproduce such a wide range of experimental data since we use a minimum of empirical relations comsalt can be easily adapted to study saltation under a variety of physical conditions such as saltation on other planets saltation under water and saltating snow

the effect of wind speed and bed slope on sand transport this paper reports on a wind tunnel study of the effects of bed slope and wind speed on aeolian mass transport the use of a sloping wind tunnel has enabled estimation of the friction angle to be about 40 for saltating particles in the range 170 540 m a formula relating dimensionless mass transport to friction speed and bed slope is proposed and mass transport data for five uniform sand samples and one non uniform sand sample are shown to fit the equation well in particular the relationship reveals an overshoot in mass transport slightly above threshold collisions a feature also evident when previous experimental data is re examined as the number of mid air collisions between the saltating particles increases greatly with wind speed the overshoot may occur as a result of increasing energy losses resulting from the collisions finally it is demonstrated that data for saltating snow shows a similar overshoot in the dimensionless transport rate

modeling afterslip and aftershocks following the 1992 landers earthquake one way to probe the rheology of the lithosphere and fault zones is to analyze the temporal evolution of deformation following a large earthquake in such a case the lithosphere responds to a known stress change that can be assessed from earthquake slip models constrained from seismology and geodesy here we model the postseismic response of a fault zone that is assumed to obey a rate strengthening rheology where the frictional stress varies as a ln e e being the deformation rate and a 0 a rheological parameter the model is simple enough that these parameters can be estimated by inversion of postseismic geodetic data we apply this approach to the analysis of geodetic displacements following the m w 7 3 1992 landers earthquake the model adjusts well the measured displacements and implies a 0 47 0 53 mpa in addition we show that aftershocks and afterslip follow the same temporal evolution and that the spatiotemporal distribution of aftershocks is consistent with the idea that they are driven by reloading of the seismogenic zone resulting from frictional afterslip

spatio temporal evolution of aseismic slip along the haiyuan fault china implications for fault frictional properties article history we use 20 years of synthetic aperture radar acquisitions by the ers and envisat satellites to investigate the spatial and temporal variations of strain rates along the 35 km long creeping section of the haiyuan fault at the north eastern boundary of the tibetan plateau we then use the derived displacements to infer the fault s frictional properties and discuss the relationship between creep and the seismic behavior of the fault located in between a millennial seismic gap and the 1920 m8 surface rupture trace this section has an average creep rate of 5 1m m yr about the interseismic loading rate the comparison of average surface velocity profiles derived from sar interferometry across the creeping section reveals a creep rate increase and or a creep migration to shallower depth between the 1990s and the 2000s we apply a smoothed time series analysis scheme on envisat insar data to investigate the creep rate variations during the 2004 2009 time period our analysis reveals that the creep rate accelerated in 2007 although data resolution does not allow to better constrain the onset of creep acceleration and its amplitude both decadal and short term transient behaviors are coeval with the largest earthquakes m 4 5 along the fault segment in recent years from the precise mapping of the surface fault trace we use the fault strike variations and the mohr circle construction to compute the along strike distribution of the friction coefficient along the creeping segment and compare it with the observed distribution of the creep rate we find that the creep rate scales logarithmically with the friction coefficient in agreement with the rate and state friction law in a rate strengthening regime the estimated value of log v 2 10 3 indicates that the earthquakes occurring along the creeping section cannot be the cause for a significant change in the overall segment s creep rate and that the recorded micro seismicity is most likely creep driven finally given the size and frictional properties of the creeping section we estimate based on previous models of dynamic rupture simulations a 0 20 probability for a rupture to break through this section together with the geometrical configuration of the haiyuan fault these results suggest that the creeping segment may act as a persistent barrier to earthquake propagation

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

laterally propagating slow slip events in a rate and state friction model with a velocity weakening to velocity strengthening transition we investigate the behavior of simulated slow slip events using a rate and state friction model that is steady state velocity weakening at low slip speeds but velocity strengthening at high slip speeds our simulations are on a one dimensional line fault but we modify the elastic interactions to mimic the elongate geometry frequently observed in slow slip events simulations exhibit a number of small events as well as periodic large events the large events propagate approximately steadily along strike and stress and slip rate decay gradually behind the propagating front their recurrence intervals can be determined by considering what is essentially an energy balance requirement for long distance propagation it is possible to choose the model parameters such that the simulated events have the stress drops slip velocities and propagation rates observed in cascadia

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

on the effect of mid air collisions on aeolian saltation the effect of mid air collisions on aeolian saltation is investigated using concentration profiles and grain velocities predicted by a numerical saltation model the probability of a mid air collision is found to be greater at high wind speeds it is also found that mid air collisions tend to reduce the number of grain bed impacts and thus reduce the number of ejecta near the bed this in turn reduces the intensity of mid air collisions it is suggested that this feed back mechanism significantly influences transport rates at high wind speeds

frictional afterslip following the 2005 nias simeulue earthquake sumatra continuously recording global positioning system stations near the 28 march 2005 rupture of the sunda megathrust moment magnitude m w 8 7 show that the earthquake triggered aseismic frictional afterslip on the subduction megathrust with a major fraction of this slip in the up dip direction from the main rupture eleven months after the main shock afterslip continues at rates several times the average interseismic rate resulting in deformation equivalent to at least a m w 8 2 earthquake in general along strike variations in frictional behavior appear to persist over multiple earthquake cycles aftershocks cluster along the boundary between the region of coseismic slip and the up dip creeping zone we observe that the cumulative number of aftershocks increases linearly with postseismic displacements this finding suggests that the temporal evolution of aftershocks is governed by afterslip

the characteristic of streamwise mass flux of windblown sand movement abstract two patterns have been reported in previous literature about the streamwise mass flux of windblown sand movement in steady state namely the exponential pattern and the stratification pattern although the exponential pattern has been verified by some experimental measurements and numerical simulations an agreed conclusion is not reached yet re evaluating the previous model it can be found that the pattern of the pdf probability density function distribution of the initial liftoff velocity is the key factor that determines whether the stratification happens or not if the number of liftoff grains decreases with the increase in liftoff velocity such as in the case of the exponential distribution the stratification pattern will not appear if the number of liftoff grains increases first and decreases later with the increase in liftoff velocity such as in the case of the log normal distribution gamma distribution and gaussian distribution the stratification pattern will come into existence in addition the hop height for the initial liftoff velocity corresponding to the peak value of its pdf distribution equals the height of the maximum streamwise mass flux on the basis of some deterministic laws from experimental measurements and numerical simulations of grain bed impact a qualitative understanding about the pdf distribution of the liftoff velocity is obtained and the rayleigh distribution is used for reptating grains also included in this paper is a model in which grain bed impact is discussed and the interaction between the grains and the wind is considered it is shown that the stratification pattern composed of a linear increment layer a saturation layer and a monotonic decrement layer indeed exists in the streamwise mass flux of windblown sand movement further as with the average velocity and pdf distribution of the liftoff velocity of the reptating grains which is determined by the characteristics of grains the height of the peak value of the streamwise mass flux is also determined by the property of the grains and will be independent of the wind intensity

frictional slip of granite at hydrothermal conditions sliding on faults in much of the continental crust likely occurs at hydrothermal conditions i e at elevated temperature and elevated pressure of aqueous pore fluids yet there have been few relevant laboratory studies to measure the strength sliding behavior and friction constitutive properties of faults at hydrothermal conditions we slid laboratory granite faults containing a layer of granite powder simulated gouge velocity stepping experiments were performed at temperatures of 23 to 600 c pore fluid pressures ph2o of 0 dry and 100 mpa wet effective normal stress of 400 mpa and sliding velocities v of 0 01 to 1 m s 0 32 to 32 m yr conditions were similar to those in earlier tests on dry granite to 845 c by lockner et al 1986 the mechanical results define two regimes the first regime includes dry granite up to at least 845 and wet granite below 250 c in this regime the coefficient of friction is high 0 7 to 0 8 and depends only modestly on temperature slip rate and ph2o the second regime includes wet granite above 350 c in this regime friction decreases considerably with increasing temperature temperature weakening and with decreasing slip rate velocity strengthening these regimes correspond well to those identified in sliding tests on ultrafine quartz we infer that one or more fluid assisted deformation mechanisms are activated in the second hydrothermal regime and operate concurrently with cataclastic flow slip in the first cool and or dry regime is characterized by pervasive shearing and particle size reduction slip in the second hot and wet regime is localized primarily onto narrow shear bands adjacent to the gouge rock interfaces weakness of these boundary shears may result either from an abundance of phyllosilicates preferentially aligned for easy dislocation glide or from a dependence of strength on gouge particle size major features of the granite data set can be fit reasonably well by a rate and temperature dependent three regime friction constitutive model chester this issue we extrapolate the experimental data and model fit in order to estimate steady state shear strength versus depth along natural slipping faults for sliding rates as low as 31 mm yr we do this for two end member cases in the first case pore pressure is assumed hydrostatic at all depths shallow crustal strength in this case is similar to that calculated in previous work from room temperature friction data while at depths below about 9 13 km depending on slip rate strength becomes less sensitive to depth but sensitive to slip rate in the second case pore pressure is assumed to be near lithostatic at depths below 5 km strength is low at all depths in this case 20 mpa in agreement with observations of weak faults such as the san andreas the predicted depth of transition from velocity weakening to velocity strengthening lies at about 13 km depth for a slip rate of 31 mm yr in rough agreement with the seismic aseismic transition depth observed on mature continental faults these results highlight the importance of fluid assisted deformation processes active in faults at depth and the need for laboratory studies on the roles of additional factors such as fluid chemistry large displacements higher concentrations of phyllosilicates and time dependent fault healing

expansion of aftershock areas caused by propagating post seismic sliding summary it is known that the aftershock areas of large earthquakes often expand over time this expansion indicates that the stress increase associated with a main shock gradually propagates outward from the main shock rupture area it is likely that this propagating stress increase is caused by the propagation of post seismic sliding which has been detected for many large earthquakes from geodetic observations mainly global positioning system gps in the present study i perform a numerical simulation of the expansion of the aftershock area caused by the propagation of post seismic sliding the model fault exists within an infinite elastic medium and is loaded at a constant displacement rate the frictional stress on the fault obeys a laboratory derived rate and state dependent friction law non uniformity of the frictional constitutive parameters is introduced to the model fault plane to represent a large asperity for a large earthquake main shock and many possible nucleus sites for aftershocks around the main shock asperity negative values of a b are assigned to areas of seismic slip for the main shock and aftershocks while positive values of a b are assigned to regions where aseismic sliding occurs here a b is defined by d ss d ln v that describes the velocity v dependence of steady state friction stress ss seismic slip may be nucleated for negative a b and aseismic slip occurs for positive a b slip histories on the model fault plane are simulated through numerical integration of the friction law under the condition of uniform shear loading of a constant velocity the simulation can reproduce aftershocks triggered by stress increases related to postseismic sliding and expansion of the aftershock area the rate of expansion of the aftershock area decreases with increasing distance from the main shock asperity or increasing value of a b in the velocity strengthening region this finding suggests that the a b value for a plate interface can be estimated from aftershock data the simulation indicates that the 7 day and 30 day aftershock areas are 14 22 and 24 39 per cent larger respectively than the 1 day aftershock area these numbers are approximately consistent with observations from large earthquakes at subduction zones

numerical simulation of recurrence of asperity rupture in the sanriku region northeastern japan 1 a numerical simulation study is presented for the recurrence of great earthquakes and aseismic sliding in the sanriku region northeastern japan where the pacific plate subducts beneath northern honshu and m8 class earthquakes have occurred approximately every 100 years the friction on the plate interface is assumed to obey a rate and state dependent friction law and the spatial distribution of constitutive parameters of the friction law is estimated so that the simulated slip histories mimic those estimated from seismic and geodetic observations by introducing two large asperities that have velocity weakening frictional properties earthquakes similar to the 1968 tokachi oki earthquake mw 8 2 and the 1994 sanriku oki earthquake mw 7 7 can be modeled the former broke both the large asperities and the latter broke one of them the ruptures of the two simulated large earthquakes started from almost the same location and their nucleation processes are similar to each other two smaller asperities were introduced to represent smaller earthquakes one of the small asperities is for the largest aftershock mw 6 9 of the 1994 sanriku oki earthquake which was located westward from the 1994 main shock area and took place 10 d after the main shock the present simulation suggests that the largest aftershock was triggered by stress caused by propagation of postseismic sliding in the simulation the area of greatest intensity of postseismic sliding is located in the region between the main shock slip area and the largest aftershock area which is consistent with the estimation from gps data analyses for the postseismic sliding of the 1994 sanriku oki earthquake some important characteristics of seismic and aseismic processes as estimated from observations are reproduced in the model this suggests that spatially nonuniform frictional properties on the plate interface can be estimated to some extent by comparison between model results and observed data

coseismic and early postseismic slip for the 2003 tokachi oki earthquake sequence inferred from gps data 1 early afterslip following the 2003 tokachi oki earthquake is investigated using subdaily gps time series afterslip results are compared with the coseismic slip for the m8 mainshock and the m7 4 aftershock afterslip between those two earthquakes is inferred at the southwestern adjacent region of the mainshock between two epicentral regions which possibly triggered the aftershock in the southwest subsequently deeper slip occurs the afterslip loci are distinct from the rupture regions the non uniform propagation of afterslip may reflect the depth dependence of the effective normal stress and the distance between the closest unstable slip patches

aseismic slip transients emerge spontaneously in three dimensional rate and state modeling of subduction earthquake sequences 1 to investigate the possible physical mechanisms of recently observed aseismic slip events in the cascadia japan and mexico subduction zones we apply a dieterich ruina rate and state friction law to a three dimensional model of a shallow subduction fault that is loaded by imposed steady plate slip rate far downdip along the thrust interface friction properties are temperature and hence depth dependent such that sliding is stable at depths below about 30 km the system is perturbed into a significantly nonuniform slip mode along strike by introducing small along strike variations in the constitutive parameters a and a b in addition to large heterogeneous earthquake slip at seismogenic depths and associated postseismic transients we found that slip events which have clearly aseismic slip rates emerge spontaneously around the downdip end of the seismogenic zone both transients which start well after a seismic event and those which are triggered by other transients are observed from the simulations the slip velocity depth range and sometimes along strike migration speed of simulated transients are similar to the observations from natural subduction zones unstable stable transitional friction properties near the downdip end of the seismogenic zone are suggested to be an ingredient allowing such transients simulated transients can weaken the locking intensity of the updip seismogenic zone while enhancing that of the transition zone spatial temporal correlation of aseismic transients and nearby seismicity in the guerrero mexico area suggests that transients may signal a period of increased probability for nucleating their high frequency counterparts as damaging subduction thrust events

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

on the rate of aeolian sand transport a simple explicit formula for the transport rate of windblown sand is derived based on physical reasoning the curve relating the dimensionless transport rate to the dimensionless friction speed exhibits the empirically well established peak in fact the theory developed in the paper can explain the peaked shape of this curve three empirically determined coefficients in the formula can be given a physical interpretation the formula is shown to fit transport rates measured in wind tunnel experiments well except for very coarse sand formulae for the wind profile in the saltation layer and for the grain dislodgement rate in dependence on the friction speed are obtained as part of the theory

retracted the influence of sand diameter and wind velocity on sand particle lift off and incident angles in the windblown sand flux the problem of impact entrainment is one of the central issues in understanding the process of saltation in this paper through improving the experimental scheme of particle image velocimetry piv and data processing methods using wind tunnel data the measurement of sand particle lift off and incident angles near the sand bed was achieved based on experimental data we analyze the probability distribution of sand particle lift off and incident angles and the influence of wind velocity and sand diameter on the probability distribution as well as the relation between incident angle and lift off angle the results demonstrate that wind velocity and sand diameter have no obvious influence on the distribution shape of sand particle lift off and incident angles however wind velocity will influence the decay constant and amplitude of the probability distribution c 2013 elsevier b v all rights reserved

3d numerical modeling of forward folding and reverse unfolding of a viscous single layer implications for the formation of folds and fold patterns abstract the main aims of this study are to show i that non cylindrical three dimensional 3d fold shapes and patterns can form during a single unidirectional shortening event and ii that numerical reverse modeling of 3d folding is a feasible method to reconstruct the formation of 3d buckle folds 3d viscous newtonian single layer folding is numerically simulated with the finite element method to investigate the formation of fold shapes during one shortening event an initially flat layer rests on a matrix with smaller viscosity and is shortened in one direction parallel to the layering forward modeling with different initial geometrical perturbations on the flat layer and different lateral boundary conditions generates non cylindrical 3d fold shapes and patterns the simulations show that in reality the initial layer geometry and the boundary conditions strongly control the final fold geometry fold geometries produced from the forward folding models are used as initial setting in numerical reverse folding models with parameters identical to those of forward models these reverse models accurately reconstruct the initial geometry of forward models with also only one extension event parallel to the previous shortening direction the starting geometry of the forward models is inaccurately reconstructed by the reverse models if a significantly different viscosity ratio than in the forward models is used this work demonstrates that reverse modeling has a high potential for reconstructing the deformation history of folded regions and rheological constraints such as viscosity ratio reverse models may be applied to natural 3d fold shapes and patterns in order to determine if they formed i during a single or multiple deformation events and ii as active buckle folds with a viscosity ratio 1 or as passive kinematic folds without buckling this approach may find much application to fold interference patterns in particular

a steady state model of wind blown sand transport a model for steady state eolian saltation is presented in which computation of sand grain trajectories in the wind and of the wind velocity profile modified by saltating grain drag forces is combined with experimental data on grain bed collisions in an iterative simulation scheme which resembles the time development of natural saltation qualitative features of eolian saltation are reproduced in the simulations including a height in the saltating layer at which the wind velocity remains roughly constant with changing free stream friction velocity and an approximate separation of the saltating population into successively hopping grains and reptating or creeping grains the numerical solutions give rise to more general arguments in support of the conclusions that fluid entrainment of grains is unimportant in steady state saltation that the mass flux profile obeys roughly an inverse power law dependence on height and that the vertically integrated mass flux dependence on the free stream friction velocity

spontaneous and triggered aseismic deformation transients in a subduction fault model 1 aseismic deformation transients can emerge as a natural outcome of the rate and state friction processes revealed in laboratory fault sliding experiments when that constitutive formulation is applied to model subduction earthquake sequences transients can arise spontaneously for certain effective stress variations with depth we show that if interstitial fluids are present and pore pressure is near lithostatic around and downdip from the frictional stability transition transients with recurrence intervals of 1 year are predicted on the basis of laboratory friction parameters and their temperature hence depth variations the recurrence interval decreases with and reaches 14 months when is 2 3 mpa dimensional analysis and numerical studies show that the fault response primarily depends on a parameter w h here the high pore pressure zone extends distance w updip from the stability transition and h is the stable patch size for steady sliding evidence that such fluid conditions may actually be present is independently provided by the occurrence of nonvolcanic tremors as apparent responses to extremely small stress changes and by petrological constraints on expected regions of dehydration for the shallow dipping subduction zones where transients are observed transient sequences can also be triggered by a modest one time step like interseismic stress perturbation on the subduction fault due to nearby earthquakes or to pore pressure changes e g during episodes of metamorphic fluid release properties of triggered transients and future thrust earthquakes depend on the interseismic time when the perturbation is introduced its relative location along the subduction fault and its magnitude

nucleation and early seismic propagation of small and large events in a crustal earthquake model 1 earthquake nucleation and early seismic propagation are studied in a two dimensional strike slip fault model with depth variable properties the fault is governed by the dieterich ruina rate and state friction law we use an efficient and rigorous numerical procedure for elastodynamic analysis of earthquake sequences on slowly loaded faults developed by lapusta et al 2000 we find that for decreasing values of the characteristic slip distance of the friction law small events appear at the transition from the locked to creeping behavior toward the bottom of the seismogenic zone small and large events have very similar nucleation phases in our simulations here by nucleation phase we mean gradually accelerating aseismic slip in a small slowly expanding zone before the breakout of the dynamic seismically detectable event moment acceleration to which velocity seismograms are proportional in early stages of seismic propagation exhibits irregular fluctuations in the form of speedups and slowdowns in the moment release rate consistently with observations as reported by ellsworth and beroza 1995 our simulations show that such irregular moment acceleration can at least in part be due to the heterogeneous stress distribution imprinted on the fault by the arrest of previous small events and by stress concentrations at the borders of creeping regions and to partial arrest of the rupture in velocity strengthening fault regions which inhibit seismic slip index terms 7209 seismology earthquake dynamics and mechanics 7260 seismology theory and modeling 3220 mathematical geophysics nonlinear dynamics 7230 seismology seismicity and seismotectonics 3230 mathematical geophysics numerical solutions 8164 tectonophysics stresses crust and lithosphere keywords earthquake nucleation phase event clustering irregular moment release stress concentrations rate and state friction earthquake sequences

forecast model for great earthquakes at the nankai trough subduction zone an earthquake instability model is formulated for recurring great earthquakes at the nankai trough subduction zone in southwest japan the model is quasistatic two dimensional and has a displacement and velocity dependent constitutive law applied at the fault plane a constant rate of fault slip at depth represents forcing due to relative motion of the philippine sea and eurasian plates the model simulates fault slip and stress for all parts of repeated earthquake cycles including post inter pre and coseismic stages calculated ground uplift is in agreement with most of the main features of elevation changes observed before and after the m 8 1 1946 nankaido earthquake in model simulations accelerating fault slip has two time scales the first time scale is several years long and is interpreted as an intermediate term precursor the second time scale is a few days long and is interpreted as a short term precursor accelerating fault slip on both time scales causes anomalous elevation changes of the ground surface over the fault plane of 100 mm or less within 50 km of the fault trace

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

imaging rapid early afterslip of the 2016 pedernales earthquake ecuador abstract high rate hr gps time series following the 2016 mw 7 8 pedernales earthquake suggest significant postseismic deformation occurring in the early postseismic period i e first few hours after the earthquake that is not resolved with daily gps time series to understand the characteristics of early postseismic deformation and its relationship with the mainshock rupture area aftershocks and longer term postseismic deformation we estimate the spatio temporal distribution of early afterslip with hr gps time series that span 2 5 min to 72 hr after the earthquake and compare with afterslip models estimated with daily gps time series spanning a similar postseismic time period and up to 30 days after the earthquake inversion of the hr gps time series enables us to image the initiation of afterslip in the initial hours after the earthquake bringing us closer to the transition between the coseismic and postseismic phases the spatial signature of early afterslip in the region updip of the mainshock rupture area is consistent with longer term afterslip that occurs in the 30 day postseismic period indicating that afterslip initiated updip of and adjacent to peak coseismic slip asperities in two localised areas and subsequently continued to grow in amplitude with time in these specific areas a striking difference however is that inversion of the 72 hour hr gps time series suggests early afterslip within the mainshock rupture area but which may have been short lived finally using the first daily gps position as the origin of the postseismic displacement here at 12 hr after the earthquake biases the postseismic geodetic moment with 60 missing over the first 72 hr that corresponds to 10 over the first 30 days the results of our study demonstrate that imaging the spatio temporal evolution of afterslip using subdaily gps time series is important for evaluating postseismic slip budgets and provides additional insights into the postseismic slip behaviour of faults

geodetic data inversion using a bayesian information criterion for spatial distribution of fault slip summary we developed a new inversion method to reconstruct static images of seismic sources from geodetic data using akaike s bayesian information criterion abic coseismic surface displacements are generally related with a slip distribution on a fault surface by linear integral equations parametric expansion of the fault slip distribution by a finite number of known basis functions yields a set of observation equations expressed in a simple vector form incorporating prior constraints on the smoothness of slip distribution with the observation equations we construct a bayesian model with unknown hyperparameters the optimal values of the hyperparameters which control the structure of the bayesian model are objectively determined from observed data by using abic once the values of hyperparameters are determined we can use the maximum likelihood method to find the optimal distribution of fault slip we examined the validity of this method through a numerical experiment using theoretical data with random noise we analysed geodetic data associated with the 1946 nankaido earthquake ms 8 2 by using this method the result shows that the fault slip distribution of this earthquake has two main peaks of 4 and 6 m located off kii peninsula and muroto promontory these two high slip areas are clearly separated by a low slip zone extending along kii strait such a slip distribution corresponds with the fact that the rupture process of this earthquake in the western part is notably different from that in the eastern part

aeolian transport with collisional suspension this paper considers the aeolian transport of sand by a wind so strong that the concentration of sand near the bed makes collisions between grains inevitable it employs an improved model of such a collisional flow which includes turbulent suspension viscous dissipation and new top boundary conditions that are validated by numerical calculations of collisionless trajectories

interaction of slip on asperities numerical simulation of seismic cycles on a two dimensional planar fault with nonuniform frictional property 1 numerical simulation is conducted to understand the variety of frictional sliding on a plate interface and complex recurrence of earthquakes a planar square fault in an infinite uniform elastic medium is considered and the frictional stress on the fault is assumed to obey a rate and state dependent friction law nonuniformity in a frictional constitutive parameter is introduced on the model fault on the fault plane one or two circular patches with velocity weakening frictional property are surrounded by velocity strengthening areas unstable slip may occur for velocity weakening friction and aseismic sliding occurs for velocity strengthening friction velocity weakening patches correspond to asperities because intense seismic slip may occur there simulation results indicate that episodic aseismic slip events slow earthquakes occur when the velocity weakening patch size is close to the critical size of earthquake nucleation propagation of postseismic sliding on the velocity strengthening region follows an earthquake at a velocity weakening patch when the postseismic sliding reaches another velocity weakening patch an earthquake may be triggered at the patch resulting in a double earthquake the time delay between two events of the double earthquake increases with the distance between the two velocity weakening patches or the degree of velocity strengthening in the region between the patches when the distance between the two velocity weakening patches is long an earthquake at one patch does not directly cause an earthquake at the other patch in these cases complex earthquake recurrence may appear due to the interaction between ruptures at the two patches and the recurrence interval of earthquakes and coseismic slip is not constant at each velocity weakening patch

resolving the kinematics and moment release of early afterslip within the first hours following the 2016 mw 7 1 kumamoto earthquake implications for the shallow slip deficit and frictional behavior of aseismic creep continuous measurements of postseismic surface deformation provide insight into variations of the frictional strength of faults and the rheology of the lower crust and upper mantle as stresses following rupture are dissipated however due to the difficulty of capturing the earliest phase of afterslip most analyses have focused on understanding postseismic processes over timescales of weeks to years here we investigate the kinematics moment release and frictional properties of the earliest phase of afterslip within the first hours following the 2016 m w 7 1 kumamoto earthquake using a network of five minute sampled continuous gps stations using independent component analysis to filter the gps data we find that 1 early afterslip contributes only 1 of total moment release within the first hour and 8 after 24 hours this suggests that the slip model of the mainshock which we estimate using standard geodetic datasets e g insar gps and pixel offsets and which span the first four days of the postseismic period is largely reflective of the dynamic rupture process and we can rule out contamination of moment release by early afterslip 2 early afterslip shows no evidence of a delayed nucleation or acceleration phase where instead fault patches transition to immediate deceleration following rupture that is consistent with frictional relaxation under steady state conditions with dependence only on the sliding velocity 3 there is a close correlation between the near field aftershocks and afterslip within the first hours following rupture suggesting afterslip may still be an important possible triggering mechanism during the earliest postseismic period

real data assimilation for optimization of frictional parameters and prediction of afterslip in the 2003 tokachi oki earthquake inferred from slip velocity by an adjoint method