evaluating the hydraulic conductivity at three different scales within an unconfined sand aquifer at lachenaie quebec this paper presents the evaluation of scale effects for the hydraulic conductivity k of a sand data were obtained using several methods at a site that was densely instrumented with piezometers within an area of about 100 m 100 m the 3 1 3 6 m thick sand deposit rests on a thick nonfissured champlain sea clay deposit at the small scale local k values were obtained from the grain size curves of sand samples and also from ground penetrating radar surveys at the intermediate scale k values were obtained from field variable head tests using piezometers at the large scale k values were obtained from pumping test drawdowns in steady state conditions in this sand aquifer the careful evaluations at three scales gave similar narrow distributions for the hydraulic conductivity and therefore no scale effect is evidenced key words hydraulic conductivity sand scale effect gradation monitoring well pumping

spatial variation of ground motion determined from accelerograms recorded on a highway bridge a set of time synchronized strong motion accelerograms obtained on the san juan bautista 156 101 separation bridge in california during the 6 august 1979 coyote lake earthquake m l 5 9 are used to study the spatial variation of ground motion at the bridge site including traveling wave effects and the influence of multiple support excitation analysis of the ground motion recorded at the base of two of the bridge supports 32 6 m apart revealed the presence of a differential support excitation having a period of 3 sec much longer than any structural periods of the bridge this signal also appeared as a noticeable long period component in the superstructure displacements analysis of the vertical and radial components of the 3 sec ground motion indicated that ground displacements were retrograde for the duration of strong shaking with several cycles exhibiting elliptical particle motions these findings suggest that long period differential support motions were induced by phase delays in a rayleigh wave traveling across the bridge site further support to this premise is given by the location of the bridge site near a maxima of the rayleigh wave radiation pattern for the coyote lake earthquake based on published focal mechanism data traveling wave effects were also detected for compressional body waves by a correlation analysis which indicated a time delay of 7 msec between p wave arrivals at two of the bridge supports

multiscale solute transport upscaling for a three dimensional hierarchical porous medium a laboratory generated hierarchical fully heterogeneous aquifer model fhm provides a reference for developing and testing an upscaling approach that integrates large scale connectivity mapping with flow and transport modeling based on the fhm three hydrostratigraphic models hsms that capture lithological static connectivity at different resolutions are created each corresponding to a sedimentary hierarchy under increasing system lnk variances 0 1 1 0 4 5 flow upscaling is first conducted to calculate equivalent hydraulic conductivity for individual connectivity or unit of the hsms given the computed flow fields an instantaneous conservative tracer test is simulated by all models for the hsms two upscaling formulations are tested based on the advection dispersion equation ade implementing space versus time dependent macrodispersivity comparing flow and transport predictions of the hsms against those of the reference model hsms capturing connectivity at increasing resolutions are more accurate although upscaling errors increase with system variance results suggest 1 by explicitly modeling connectivity an enhanced degree of freedom in representing dispersion can improve the ade based upscaled models by capturing non fickian transport of the fhm 2 when connectivity is sufficiently resolved the type of data conditioning used to model transport becomes less critical data conditioning however is influenced by the prediction goal 3 when aquifer is weakly to moderately heterogeneous the upscaled models adequately capture the transport simulation of the fhm despite the existence of hierarchical heterogeneity at smaller scales when aquifer is strongly heterogeneous the upscaled models become less accurate because lithological connectivity cannot adequately capture preferential flows 4 three dimensional transport connectivities of the hierarchical aquifer differ quantitatively from those analyzed for two dimensional systems

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

viscoelastic postseismic rebound from strike slip earthquakes in regions of oblique plate convergence according to the slip partitioning concept the trench parallel component of relative plate motion in regions of oblique convergence is accommodated by strike slip faulting in the overriding continental lithosphere the pattern of postseismic surface deformation due to viscoelastic flow in the lower crust and asthenosphere following a major earthquake on such a fault is modified from that predicted from the conventional elastic layer over viscoelastic half space model by the presence of the subducting slab the predicted effects such as a partial suppression of the postseismic velocities by 1 cm yr or more immediately following a moderate to great earthquake are potentially detectable using contemporary geodetic techniques

geostatistical analysis of aquifer heterogeneity from the core scale to the basin scale a case study this study examines the spatial variability of conductivity within the sandstone wabiskaw member of the lower cretaceous middle mannville in the alberta basin the wabiskaw is an important regional hydrostratigraphic unit vertical variability within the aquifer is characterized by downhole variograms of log conductivity from core measurements they are found to exhibit pseudoperiodic structures due to alternating sand and shale layers horizontal spatial variability is characterized using variograms of log transmissivity and indicator data these variograms show a steady increase in spatial variability over length scales ranging from 400 m to 100 km characteristic of self similar or fractal behavior they also reveal distinct correlation structures related to both high and low transmissivity depositional features this study also considers the upscaling of conductivity vertically from the core to the well scale and horizontally from the well to the basin scale it is shown that traditional vertical upscaling of conductivities by arithmetic averaging causes an overestimation of transmissivity in two dimensional areal flow models an alternative approach based on power averaging is proposed transmissivities derived by vertical upscaling of core measurements are compared with values derived from drill stem tests in the same well no correlation between these quantities is observed an average transmissivity for the wabiskaw in the study area is determined by geometric spatial averaging however the highly clustered spatial distribution of well locations requires a weighting of sample values using ordinary kriging

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

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

postearthquake relaxation evidence for laterally variable viscoelastic structure and water content in the southern california mantle i reexamine the lower crust and mantle relaxation following two large events in the mojave desert the 1992 m7 3 landers and 1999 m7 1 hector mine california earthquakes time series from continuous gps sites out to 300 km from the ruptures are used to constrain models of postseismic relaxation crustal motions in the mojave desert region are elevated above background for several years following each event to account for broadscale relaxation of the lower crust and mantle the burgers body model is employed involving transient and steady state viscosities joint afterslip postseismic relaxation modeling of the gps time series up to one decade following the hector mine earthquake reveals a significant rheological contrast between a northwest trending southwest domain that envelopes the san andreas fault system and western mojave desert and an adjacent northeast domain that envelopes the landers and hector mine rupture areas in the central mojave desert the steady state viscosity of the northeast domain mantle asthenosphere is inferred to be 4 times greater than that of the southwest domain this pattern is counter to that expected for regional heat flow which is higher in the northeast domain but it is explicable by means of a nonlinear rheology that includes dependence on both strain rate and water concentration i infer that the southwest domain mantle has a relatively low steady state viscosity because of its high strain rate and water content the relatively low mantle water content of the northeast domain is interpreted to result from the continual extraction of water through igneous and volcanic activity over the past 20 myr

evaluation of the importance of model features for cyclic deformation due to dip slip faulting summary finite element techniques are used to investigate models of cyclic deformation on dip slip faults the models are based largely on the conceptual formulations of matsu ura sato 1989 savage 1983 and thatcher rundle 1984 we investigate the interaction of rheology fault geometry mechanical structure non tectonic forces and the earthquake recurrence interval the interaction of gravity and viscoelastic flow is complex for example if the asthenosphere is very weak then regions that rise rapidly after an earthquake may subsequently subside due to isostatic readjustment by contrast if the asthenosphere is more viscous uplifted regions may continue to grow throughout the earthquake cycle the magnitude and width of regions of both uplift and subsidence depend on density viscosity and viscoelastic channel thicknesses the inclusion of plate bending appears to be important in earthquake modelling at subduction zones the steady state convergence of plates may lead to net vertical motion in the subduction zone

modeling earthquake cycles in the shumagin subduction segment alaska with seismic and geodetic constraints deformation associated with the earthquake cycle in the shumagin islands segment of the alaska aleutian subduction zone is analyzed with the use of a two dimensional finite element model the model consists of an oceanic plate dipping under an upper plate both of which respond elastically to stress fluctuations in the earthquake cycle and these are underlain by asthenospheric mantle and mantle wedge regions which respond viscoelastically it is tailored to the geometry of the shumagin islands region by using seismicity to define the position of the interplate interface and partially coupled region along it the model is preconditioned by forcing this interface to undergo periodically repeated slips up to and including the time of the may 31 1917 event ms 7 4 in that region with each chosen to be consistent with the moment and estimated rupture area of that event we investigated the dependence of model results for geodetic signals on the strength of seismic coupling between the plates and viscoelastic relaxation of deviatoric stresses in the mantle including in the mantle wedge close to the plate junction and along the aseismic downdip continuation of the thrust interface in models with significant relaxation in the wedge or downdip thrust zone results show that as the intraseismic stage matures there is a region of diminished compressional strain rates and even of locally extensional rates on the earth s surface above the downdip end of the seismically coupled zone based on the seismic estimates of the location of the coupled zone this region is in the area of the shumagin islands we find that if approximately 20 of the convergence takes place seismically compatible with the previous seismic history and if an extensive region of relaxed deviatoric stress is assumed to be present in the wedge and or along the downdip interface then deformations predicted by the model can be made consistent with the measured strain data from the shumagin islands geodetic network lisowski et al 1988 larson and lisowski 1994 as well as uplift and tilt data savage and plafker 1991 beavan 1992 our model simulations here suggest that the shumagin segment is capable of large earthquakes the hypothesis of totally aseismic subduction is not similarly consistent with all geodetic constraints

deep learning of aftershock patterns following large earthquakes aftershocks are a response to changes in stress generated by large earthquakes and represent the most common observations of the triggering of earthquakes the maximum magnitude of aftershocks and their temporal decay are well described by empirical laws such as bath s law1 and omori s law2 but explaining and forecasting the spatial distribution of aftershocks is more difficult coulomb failure stress change3 is perhaps the most widely used criterion to explain the spatial distributions of aftershocks4 8 but its applicability has been disputed9 11 here we use a deep learning approach to identify a static stress based criterion that forecasts aftershock locations without prior assumptions about fault orientation we show that a neural network trained on more than 131 000 mainshock aftershock pairs can predict the locations of aftershocks in an independent test dataset of more than 30 000 mainshock aftershock pairs more accurately area under curve of 0 849 than can classic coulomb failure stress change area under curve of 0 583 we find that the learned aftershock pattern is physically interpretable the maximum change in shear stress the von mises yield criterion a scaled version of the second invariant of the deviatoric stress change tensor and the sum of the absolute values of the independent components of the stress change tensor each explain more than 98 per cent of the variance in the neural network prediction this machine learning driven insight provides improved forecasts of aftershock locations and identifies physical quantities that may control earthquake triggering during the most active part of the seismic cycle neural networks trained on data from about 130 000 aftershocks from around 100 large earthquakes improve predictions of the spatial distribution of aftershocks and suggest physical quantities that may control earthquake triggering

centroid moment tensor solutions for 35 earthquakes in western north america 1977 1983 abstract seismic records from the gdsn sro asro dwwssn rstn and ida networks were used to obtain long period t 45 sec focal mechanisms for 35 earthquakes in western north america longitude 140 to 110 latitude 30 to 60 employing the centroid moment tensor method of dziewonski et al 1981 and dziewonski and woodhouse 1983 the same algorithm was applied to all events the smallest m 0 6 4 10 23 dyne cm being an aftershock to the 1979 imperial valley california earthquake and the largest m 0 8 5 10 26 dyne cm the 1980 eureka california earthquake all events were analyzed with and without the constraint m r m r 0 on the moment tensor an ad hoc criterion on the relative variance reduction was employed to determine a favored solution our solutions show general agreement with other published results as well as with tectonic structures agreement with results obtained using the abundant local and regional data confirms the adequacy of the method in determining long period source parameters and verifies its applicability in regions where local and regional data are scarce or nonexistent in some cases disagreement between our solution and results from first motion studies appears to be related to source complexities our moment tensor represents the total stress release of the composite event a consistent westward movement of the centroid locations reflects lateral heterogeneities in the crust and mantle

oblique plate convergence slip vectors and forearc deformation slip vectors from thrust earthquakes at subduction zones where convergence is oblique to the trench often point between the directions of relative plate convergence and normal to the trench axis suggesting that oblique convergence is taken up by partial decoupling decoupling means that a component of arc parallel motion of the leading edge of the upper plate results in less oblique thrusting at the trench partial decoupling is modeled by partitioning of oblique convergence into slip on thrust and strike slip faults that are parallel to the trench and to each other and starting with a force equilibrium condition a relationship between the obliquity and the earthquake slip vector orientation is derived assuming that either fault slips when shear stress on it reaches a yield stress oblique slip parallel to the plate vector should occur on the thrust fault when obliquity is smaller than a critical angle for obliquity at or greater than this angle the stress on the strike slip fault is large enough to start it slipping and when both faults are active the arc parallel motion of the forearc deflects the slip vector back toward the trench normal if we assume that continued slip on either fault occurs at constant stress but the two faults can be at different stresses the slip vector will maintain a constant angle relative to the trench normal even when obliquity is larger than the critical angle this limiting angle of the slip vector called max measured relative to the trench normal is simply the arcsine of the ratio of the shear forces resisting slip on the strike slip and thrust faults a consequence is that when the obliquity exceeds max the slip vectors on the thrust fault are sensitive only to the thrust fault orientation and contain no information about the convergence direction between the plates slip vectors at the java trench southwest of sumatra show the relationship clearly with max 20 5 while slip vectors at the aleutian trench show the relationship less clearly with max 25 to 45 the greater angle at the aleutian trench suggests that the upper plate is stronger in the aleutian arc relative to the thrust fault than in the sumatran arc consistent with the sumatran arc being continental and having a well developed strike slip fault while the aleutian arc is oceanic and without a clear transcurrent fault slip vectors at the philippine trench which like sumatra has a large strike slip fault inboard of it tend to stay within 25 of the trench normal when obliquity is as large as 50 if obliquity exceeds max and continues to increase along a subduction zone the rate of motion of the forearc relative to the upper plate will vary with obliquity in which case the forearc sliver should extend or contract parallel to the arc from the geometry of modern island arcs arc parallel extension should be the more common and has been hypothesized for both sumatra and the aleutians on the basis of earthquake slip vectors and for these and other arcs from geological observations from estimates of max and the arc parallel gradients in obliquity arc parallel strain rates are estimated to be 1 to 3 10 8 yr for the sumatran forearc 2 to 6 10 8 yr for the aleutian forearc and 0 3 to 3 10 8 yr for the philippine forearc oblique convergence and subsequent arc parallel extension if accompanied by crustal thinning may provide an important yet little appreciated mechanism for bringing high grade metamorphic rocks to the surface of subduction complexes

three dimensional structure characterisation and transient flow modelling of a variably saturated heterogeneous monolith in this study we investigate the possibility of modelling the transient hydraulic behaviour of an undisturbed monolithic subsoil sample of 0 5 m 3 based on a detailed characterisation of the soil structure at the larger scale the subsoil core structure is defined by the presence of discontinuous clay and a stone layer within a large sandy matrix a second structural level is characterised by the spatial distribution of hydraulic properties in the sandy matrix and described using the vogel similarity concept vogel t cislerova m hopmans j w 1991 porous media with linearly variable hydraulic properties water resources research 27 2735 2741 this exhaustive structural information is subsequently implemented into a 3 d transient and variably saturated flow model simulation results are compared with experimental observations and it is showed that the presence of a discontinuous clay and stone layer is sensitive in predicting effective outflow given the fact that no calibration is performed we consider that the outflow predictions are good the results are however disappointing for the prediction of time series of pressure head moreover the local scale kat had to be scaled based on structural and hydraulic monolith scale observations this study points out that i it would be necessary to characterise the continuity of flow and related parameters such as the hydraulic conductivity at the appropriate scale to adequately simulate variable saturated transient flow at that scale and ii a smaller spacing in the sub sampling would be needed to property predict local scale time series c 2006 elsevier b v all rights reserved

delineating hydrological response units by geographical information system analyses for regional hydrological modelling using prms mms in the drainage basin of the river brol germany a modified concept of hydrological response units hrus for regional modelling of river basins using the prms mms model is presented the hrus are delineated by geographical information system gis analysis from physiographic basin properties such as topography soils geology rainfall and land use using a thorough hydrological systems analysis the hrus once classified by gis analysis preserve the three dimensional heterogeneity of the drainage basin the river brol basin a 216km 2 rheinisches schiefergebirge germany was selected to apply the concept in total 23 hrus were delineated and tested with the prms mms model using a 20 year hydrometeorological daily database the hydrological systems analysis revealed that interflow is the dominant flow process through the basin s slopes and the major contribution to groundwater recharge and river runoff this was accounted for by parameterizing the hrus in the model control file to drain their surplus water not used for satisfying the demand of evapotranspiration to a common conceptual subsurface storage this storage was simulated by interflow drainage to the groundwater aquifer in the valley floor which in turn drained to the channel network the prms mms model simulated the observed daily discharge very well and the fit was described by a daily correlation coefficient of r 0 91 the nasim and hspf models using different means to represent the basin s physiographic heterogeneity were applied to the brol basin as well but did not achieve this correlation the hru concept was found to be a reliable method for regional hydrological basin modelling and allows spatial up and downscaling future research on this concept will focus on incorporating the variable precipitation distribution into the classification of hrus and on the hydrodynamic routing of the modelled discharge additionally satellite imagery must be used for classifying land use in macroscale drainage basins

possible source models for the 1855 wairarapa earthquake new zealand the magnitude 8 wairarapa new zealand earthquake of 1855 was associated with surface rupture along the wairarapa fault and regional uplift of the southwest of the north island forward elastic dislocation modelling shows that movement on a steeply dipping wairarapa fault alone cannot account for the recorded deformation data modelling of movement on the subduction interface that underlies the wellington region as well as the wairarapa fault also fails to produce a satisfactory ill to the data although a complex wairarapa fault model may be able to explain the deformation pattern if its location subsurface geometry and slip distribution could be independently constrained the best effort supported by available data a flexed model incorporating a left side step of 8 km at the surface incorrectly locates the deformation the best fit to the data is obtained from a listric wairarapa fault model involving rupture on 0 to 50 km width of the deeper part of the subduction interface the shallower pan of the subduction interface east of the wairarapa fault apparently did not rupture in 1855 and the uplift mechanism for the overlying aorangi range remains unexplained partitioning of strike slip and dip slip components of the relative plate motions may involve separate earthquakes seismological verification of listric fault rupture mechanisms is required to determine the plausibility of the listric model presented here because its implications arc that the 1855 earthquake did not completely account for the relative plate motion in the region

effects of three dimensional inhomogeneous viscoelastic structures on postseismic surface deformations associated with the great 1946 nankaido earthquake we investigated the effects of various viscoelastic structures on postseismic surface displacement and principal strain fields associated with the great 1946 nankaido earthquake which occurred on the plate boundary between the subducting philippine sea plate and the continental eurasian plate for this purpose we constructed two kinds of three dimensional structural models using the finite element method one is the layered model in which a semi infinite maxwell viscoelastic material is underlying an elastic layer and the other is the more realistic plate model in which the three dimensional configuration of the subducted philippine sea plate is taken into account we also considered two cases with different thicknesses of the elastic layer 50 and 33km for the respective models the difference between the two models in postseismic surface deformations is significant for the case with the thinner elastic layer in this case the horizontal surface displacement and principal strain for the layered model is two to three times larger than those for the plate model downward surface deformation tends to be dominant for the layered model while the change in the pattern for the plate model is less marked the spatial extent of uplift and subsidence for the plate model is broader than that for the layered model postseismic vertical displacements in shikoku were found to be strongly dependent on the viscoelastic structures from these results we suggest that the estimates of the viscosity of the uppermost mantle interplate coupling and the area and the amount of after slip following the 1946 nankaido earthquake which have been estimated based on simple layered viscoelastic models should be re evaluated using realistic three dimensionally heterogeneous viscoelastic structures

asthenospheric viscosity inferred from correlated land sea earthquakes in north east japan the viscosity of the earth s mantle has been estimated from studies of post glacial rebound1 2 post seismic deformations of the ground following large earthquakes3 4 and aftershock sequences5 7 here we derive a value for the viscosity of the asthenosphere from a correlation found in the historical catalogue of subduction induced seismicity between the intraplate land and interplate sea earthquakes in north east japan the correlation persists since the time of reliably reported earthquakes in ad 1600 land events precede sea events by 36 yr with a mean distance between land sea pairs of 200 km because of the visocoelastic coupling of the lithosphere to the asthenosphere a plausible mechanism to explain the correlation is stress migration governed by the viscosity of the asthenosphere large land shocks generate diffuse like stress pulses which sweep past and unlock the thrust fault in the subduction zone thus triggering the sea events the correlation time and distance provide a measure of the speed of diffusion 5 6 km yr 1 and hence an estimate of the viscosity 7 1018 pa s

aftershocks of the coyote lake california earthquake of august 6 1979 a detailed study aftershock hypocenters and focal mechanism solutions for the coyote lake california earthquake reveal a geometrically complex fault structure consisting of multiple slip surfaces the faulting surface principally consists of two right stepping en echelon northwest trending partially overlapping nearly vertical sheets and is similar in geometry to a slip surface inferred for the 1966 parkfield california earthquake the overlap occurs near a prominent bend in the surface trace of the calaveras fault at san felipe lake slip during the main rupture as inferred from the distribution of early aftershocks appears to have been confined to a 14 km portion of the northeastern sheet between 4 and 10 km depth focal mechanisms and the hypocentral distribution of aftershocks suggest that the main rupture surface itself is geometrically complex with left stepping imbricate structure seismic shear displacement on the southwestern slip surface commenced some 5 hours after the mainshock aftershocks in this zone define a single vertical plane 8 km long between 3 and 7 km depth within the overlap zone between the two main slip surfaces the average strike of aftershock nodal planes is significantly rotated clockwise relative to the strike of the fault zone in close agreement with the stress perturbations predicted by crack interaction models aftershock activity in the overlap zone is not associated with a simple dislocation surface space and time clustering within the entire aftershock set suggest an alternation of seismic displacement between the component parts of the fault zone this alternation is consistent with local stress perturbations predicted by crack interaction models we conclude that the fault structure is geometrically complex and that the displacements that occur on its component surfaces during the aftershock process dynamically interact by generating perturbations in the local stress field which in turn control the displacements table 5 is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j82 006 1 00 payment must accompany order

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

time dependent uplift of the kenai peninsula and adjacent regions of south central alaska since the 1964 prince william sound earthquake leveling global positioning system very long baseline interferometry and tide gauge observations indicate that time dependent uplift has occurred on the kenai peninsula and adjacent regions of southern alaska that subsided coseismically in the 1964 prince william sound earthquake these observations have been critically assessed and used along with seismological and geological information as constraints in various aseismic slip and viscoelastic flow models of crustal deformation the postseismic uplift rate in most of the region is significantly greater than the expected interseismic average some but not all of the data indicate that the uplift rate was quite rapid more than several centimeters per year in the years immediately following the earthquake and has slowed to a few centimeters per year or less since then the modeling shows that the uplift can be explained by aseismic slip at depth but not by viscoelastic flow the slip at depth since 1964 must have a transient as well as a steady component since the deduced slip is considerably greater than the roughly 1 5 m expected from north american pacific plate convergence since the 1964 event the minimum amount of slip required to fit the observations comes from an elastic model and is about 2 75 m viscoelastic models require more slip since the dominant effect of viscoelastic flow is to produce subsidence in the region that is uplifted a simple parameterization of the transient component using an amplitude and decay time is adequate to explain the observations while the parameters deduced from the viscoelastic models have some ambiguity the viscosity of models that best fit the observations cannot be much less than several times 1019 pa s when the thickness of the north american plate is taken to be about 90 km

depth of seismic coupling along subduction zones underthrusting at subduction zones can cause large earthquakes at shallow depths but it is always accommodated by aseismic deformation below a certain depth the maximum depth of the seismically coupled zone or seismogenic zone is a transition from unstable to stable sliding along the plate interface we have determined the depth of this stability transition for the circurn pacific subduction zones of honshu kuriles kamchatka aleutians alaska mexico and chile these subduction zones have experienced great interplate earthquakes and the aftershock regions are well located depth estimates of interplate events that are located at the downdip edge of the aftershock regions are used to determine the maximum depth of seismic coupling for an average p wave velocity of 6 7 km s 1 above the plate interface we find that for most subduction zones the stability transition occurs at 40 5 km depth there are however several exceptions at the hokkaido trench junction where the japan trench and the kurile trench intersect seismic coupling is deep and extends down to 52 55 km deep coupling was also found in the coquimbo region in central chile the mexico subduction zone has shallow coupling the transition occurs at 20 30 km depth previous studies of micro earthquakes in honshu hokkaido the aleutians and alaska show that earthquakes within the upper plate extend no deeper than the downdip edge of the coupled zone that we find given our measurements of seismic coupling depth we then explore the mechanism that may determine coupling depth the concept of critical temperature has been used to explain the depth of seismic coupling in other tectonic environments thus we first test whether a critical temperature can explain our results temperatures at the plate interface are dependent on many variables but two that are poorly determined are shear stress and radiogenic heat generation shear stress has been constrained by inversion of heat flow data assuming a crustal radiogenic heat production rate of 3 1 exp z 8 5 wm 3 and a constant coefficient of friction we find two critical temperatures of about 400 c and 550 c the lower critical temperature may be characteristic of regions with a relatively thick continental crust and the higher temperature of regions with a relatively thin continental crust on the other hand one single critical temperature of about 250 c can explain the coupling depths if shear stresses are constant with depth

the rupture mechanism of the coyote lake earthquake of 6 august 1979 inferred from near field data the coyote lake earthquake ml 5 7 occurred within the dense network of seismic instruments of central california and was recorded by numerous accelerograph stations two of these stations located within the fault zone itself provide particularly remarkable records of the rupture process we use these data obtained in the immediate vicinity of the fault and the broadband seismograms recorded at berkeley about 100 km away from the epicenter to infer the velocity of propagation of the rupture the extent of the fractured area the rupture front geometry and other characteristics of the fracture mechanism in order to extract this information from the data we model the earthquake as a propagating dislocation starting at the hypocenter and spreading radially we compute the resulting ground motion at the receiver sites using the discrete wavenumber representation of green s functions bouchon 1981 the results yield a rupture velocity of 2 6 km sec a fault length of about 14 km and a fault slip of 15 to 20 cm they also show that the fault extends to shallower depth than indicated by the aftershocks the most important result is the finding that slip at any given location on the fault takes place in a very short time span and that simple uniform dislocation models give a good description of the rupture process

the 1971 san fernando earthquake a double event evidence is presented which suggest that the 1971 san fernando earthquake may have been a double event that occurred on two separate subparallel thrust faults it is postulated that the initial event took place at depth on the sierra madre fault zone which runs along the base of the san gabriel mountains rupture is postulated to have occurred from a depth of about 15 km to a depth of about 3 km a second event is thought to have initiated about 4 sec later on another steeply dipping thrust fault which is located about 4 km south of the sierra madre fault zone the surface trace of this fault coincides with the san fernando fault zone which was the principal fault associated with surface rupture it is postulated that rupture propagated from a depth of 8 km to the free surface the moments of the first and second events are approximately 0 7 10 26 dyne cm and 1 0 10 26 dyne cm respectively this model is found to explain the combined data sets of strong ground motions teleseismic p and s waveforms and static offsets better than previous models which consist of either a single fault plane or a plane having a dip angle which shallows with decreasing depth nevertheless many features of the observed motions remain unexplained and considerable uncertainty still exists regarding the faulting history of the san fernando earthquake

scale dependency of the hydraulic properties of a variably saturated heterogeneous sandy subsoil the effective hydraulic behaviour of heterogeneous sand was experimentally investigated at two scales under transient flow upper boundary conditions at the monoliths scale one dimensional inverse modelling was performed from a transient infiltration experiment by implementing in the objective function the outflow and pressure head time series at four depths notwithstanding the important heterogeneity of the subsoil principally due to the presence of discontinuous clay and a stone layer we observed that the effective behaviour was surprisingly well reproduced it was also observed that the structural features mainly induced a kind of hysteresis between the saturation and drainage cycles of the outflow time series subsequently 104 kopecky cores 100 cm 3 were sub sampled throughout the monolith mainly in the sandy matrix the variability of local hydraulic parameters was investigated by optimising the local hydraulic parameters from mufti step outflow experiments and measured retention points the comparison between 1 d optimised measured and kopecky averaged retention curves showed relatively similar shape near saturation in contrast to this important discrepancies existed between averaged local scale hydraulic conductivity and effective hydraulic conductivity close to saturation different experimental designs at different scales may explain the observed discrepancies it is further suggested that the monolith scale effective hydraulic functions are more representative for wet soil conditions this case study illustrates the complexity of finding validated scaling relationships for the hydraulic properties of heterogeneous soils at scales larger than the usual small column scale c 2005 elsevier b v all rights reserved

postseismic deformation due to subcrustal viscoelastic relaxation following dip slip earthquakes the deformation of the earth following a dip slip earthquake is calculated by using a three layer rheological model and finite element techniques the three layers are an elastic upper lithosphere a standard linear solid lower lithosphere and a maxwell viscoelastic asthenosphere attention is focused on the magnitude of the postseismic subsidence and the width of the subsidence zone that develops due to the viscoelastic response to coseismic reverse slip detailed analysis for a fault extending from the surface to 15 km with a 45 dip reveals that postseismic subsidence is sensitive to the depth to the asthenosphere but is only weakly dependent on lower lithosphere depth the greatest subsidence occurs when the elastic lithosphere is about 30 km thick and the asthenosphere lies just below this layer asthenosphere depth 2 times the fault depth the extremum in the subsidence pattern occurs at about 5 km from the surface break of the fault and lies over the slip plane at this location the subsidence reaches 60 of the coseismic uplift after about 30 maxwell times unlike the horizontal deformation following a strike slip earthquake significant vertical deformation due to asthenosphere flow persists for many times the maxwell time of the asthenosphere as a consequence the relaxation of the lower lithosphere has only a secondary effect on uplift and subsidence it does however substantially increase horizontal straining the width of the postseismic subsidence zone also depends strongly on the depth to the asthenosphere and shows little sensitivity to the presence of a slowly relaxing lower lithosphere parametric adjustment of the lithosphere thickness and fault dip angle over a considerable range of values in a simple model of an elastic lithosphere and viscoelastic asthenosphere reveals that the postseismic subsidence is greatest when the fault penetrates through about one half the lithosphere previous estimates of the asthenosphere viscosity 1019 pa s and lithosphere thickness 30 40 km for the region of japan affected by the 1896 riku u earthquake are confirmed by model calculations

moving through scales of flow and transport in soil flow and transport in soil is governed by the binary geometry of solid and void this may be described at typical length scales of some millimeters and even less in contrast the problems which are supposed to be solved in soil physics are related to a scale of some meters the typical distance between soil surface and groundwater a quantitative understanding of flow and transport based on measurements of hydraulic properties and transport parameter at a given scale requires the transfer of information in space time and across scales this is the major challenge in heterogeneous soils and this has motivated many concepts for the organization of heterogeneities including macroscopic homogeneity discrete hierarchy and fractal geometry we propose a conceptual approach termed the scaleway to predict flow and transport in structured materials whatever the scale and whatever the specific type of structural organization this is based on the explicit consideration of structure that is assumed to be present at the scale of interest while the microscopic heterogeneities are replaced by averaged effective descriptions the three ingredients needed are a representation of the structure a process model at the scale of interest and corresponding effective material properties we demonstrate the scaleway for one example of solute transport in a soil column and discuss implications for future research

source study of the 1906 san francisco earthquake all quality teleseismic recordings of the great 1906 san francisco earthquake archived in the 1908 carnegie report by the state earthquake investigation commission were scanned and digitized first order results were obtained by comparing complexity and amplitudes of teleseismic waveforms from the 1906 earthquake with well calibrated similarly located more recent earthquakes 1979 coyote lake 1984 morgan hill and 1989 loma prieta earthquakes at nearly co located modern stations peak amplitude ratios for calibration events indicated that a localized moment release of about 1 to 1 5 10 27 dyne cm was responsible for producing the peak the teleseismic body wave arrivals at longer periods 50 to 80 sec we found spectral amplitude ratios of the surface waves require a total moment release between 4 and 6 10 27 dyne cm for the 1906 earthquake comparable to previous geodetic and surface wave estimates thatcher 1975 we then made a more detailed source analysis using morgan hill s body waves as empirical green s functions in a finite fault subevent summation the morgan hill earthquake was deemed most appropriate for this purpose as its mechanism is that of the 1906 earthquake in the central portion of the rupture from forward and inverse empirical summations of morgan hill green s functions we obtained a good fit to the best quality teleseismic waveforms with a relatively simple source model having two regions of localized strong radiation separated spatially by about 110 km assuming the 1906 epicenter determined by bolt 1968 this corresponds with a large asperity on the order of the loma prieta earthquake in the golden gate san francisco region and one about three times larger located northwest along strike between point reyes and fort ross this model implies that much of the 1906 rupture zone may have occurred with relatively little 10 to 20 sec radiation consideration of the amplitude and frequency content of the 1906 teleseismic data allowed us to estimate the scale length of the largest asperity to be less than about 40 km with rough constraints on the largest asperity size and magnitude we produced a suite of estimated synthetic ground velocities assuming a slip distribution similar to that of the loma prieta earthquake but with three times as much slip for purposes of comparison with the recent abundant loma prieta strong motion data set we moved the largest 1906 asperity into loma prieta region peak ground velocity amplitudes are substantially greater than those recorded during the loma prieta earthquake and are comparable to those predicted by the attenuation relationship of joyner and boore 1988 for a magnitude m w 7 7 earthquake

the near source ground motion of the 6 august 1979 coyote lake california earthquake a finite fault striking n24 w and extending to a depth of 10 km is proposed to explain the strong ground motion data for the 6 august 1979 coyote lake california earthquake m l 5 9 our source model suggests that right lateral faulting initiated at a depth of 8 km and ruptured toward the south with a velocity of 2 8 km sec this unilateral rupture can explain the large displacement recorded south of the epicenter however the waveform coherency across an array south and southwest of the epicenter suggests that the rupture length is less than 6 km the maximum dislocation is about 120 cm in a small area near the hypocenter and the total moment is estimated to be 3 5 10 24 dyne cm an abrupt stopping phase which corresponds to a deceleration of right lateral motion can explain the high peak acceleration recorded at array station 6 the stress drop in the hypocentral area is about 140 bars the average stress drop over the entire rupture surface is 30 bars the preferred finite source model can predict the p n1 waveforms and the beginning features in the teleseismic seismograms no clear arrivals can be observed in the near source data for the possible second and third smaller events suggested by nabelek personal communication

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

a comparative review of upscaling methods for solute transport in heterogeneous porous media the classical fickian model for solute transport in porous media cannot correctly predict the spreading the dispersion of contaminant plumes in a heterogeneous subsurface unless its structure is completely characterized although the required precision is outside the reach of current field characterization methods the advection dispersion model remains the most widely used model among practitioners two approaches can be adopted to solve the effect of physical heterogeneity on transport first based on a given characterization of the spatial structure of the subsurface upscaling methods allow the computation of apparent scale dependent parameters especially longitudinal dispersivity to be used in the classical fickian model in the second approach upscaled non fickian transport equations with scale independent parameters are used in this paper efforts are made to classify and review upscaling methods for fickian transport parameters and non fickian upscaled transport equations for solute transport with an emphasis on their mathematical properties and their one dimensional analytical formulations in particular their capacity to mode scale effects in apparent longitudinal dispersion is investigated upscaling methods and upscaled models are illustrated in the case of two three dimensional synthetic aquifers with lognormal hydraulic conductivity distributions characterized by variance values of 2 and 8 c 2008 etsevier b v all rights reserved

slip partitioning of the calaveras fault california and prospects for future earthquakes examination of main shock and microearthquake data from the calaveras fault during the last 20 years reveals that main shock hypocenters occur at depths of 8 9 km near the base of the zone of microearthquakes the spatial pattern of pre main shock microseismicity surrounding the coyote lake and morgan hill hypocenters is similar to the pattern of the post main shock microseismicity microseismicity extends between depths of 4 and 10 km and defines zones of concentrated microseismicity and aseismic zones estimates of the fault regions which slipped during the coyote lake and morgan hill earthquakes as derived from seismic radiation coincide with zones which are otherwise aseismic we propose that these persistent aseismic zones represent stuck patches which slip only during moderate earthquakes from the pattern of microearthquake locations we recognize six aseismic zones where we expect future main shocks will rupture the calaveras fault from an analysis of historic seismic data we establish the main shock rupture history for each aseismic zone and identify two zones that are the most likely sites for the next m 5 earthquakes the first zone is located near gilroy and was last ruptured by a m5 2 earthquake in 1949 the second zone is located south of calaveras reservoir and north of the 1988 m5 1 alum rock earthquake it has not slipped seismically since at least 1903 and the size of the aseismic region is sufficiently large to sustain a m5 5 earthquake

the effect of quaternary alluvium on strong ground motion in the coyote lake california earthquake of 1979 abstract the effect of alluvium on strong ground motion can be seen by comparing two strong motion records of the coyote lake california earthquake of 6 august 1979 m l 5 9 one record at a site on franciscan bedrock had a peak horizontal acceleration of 0 13 g and a peak horizontal velocity of 10 cm sec the other at a site 2 km distant on 180 meters of quaternary alluvium overlying franciscan had values of 0 26 g and 32 cm sec amplifications by factors of 2 and 3 horizontal motions computed at the alluvial site for a linear plane layered model based on measured p and s velocities show reasonably good agreement in shape with the observed motions but the observed peak amplitudes are greater by a factor of about 1 25 in acceleration and 1 8 in velocity about 15 per cent of the discrepancy in acceleration and 20 per cent in velocity can be attributed to the difference in source distance the remainder may represent focusing by refraction at a bedrock surface concave upward there is no clear evidence of nonlinear soil response fourier spectral ratios between motions observed on bedrock and alluvium show good agreement with ratios predicted from the linear model in particular the observed frequency of the fundamental peak in the amplification spectrum agrees with the computed value indicating that no significant nonlinearity occurs in the secant shear modulus computations show that nonlinear models are compatible with the data if values of the coefficient of dynamic shear strength in terms of vertical effective stress are in the range of 0 5 to 1 0 or greater the data illustrate that site amplification may be less a matter of resonance involving reinforcing multiple reflections and more the simple effect of the low near surface velocity application of traditional seismological theory leads to the conclusion that the site amplification for peak horizontal velocity is approximately proportional to the reciprocal of the square root of the product of density and shear wave velocity

large scale natural gradient tracer test in sand and gravel cape cod massachusetts 3 hydraulic conductivity variability and calculated macrodispersivities hydraulic conductivity k variability in a sand and gravel aquifer on cape cod massachusetts was measured and subsequently used in stochastic transport theories to estimate macrodispersivities nearly 1500 k measurements were obtained by borehole flowmeter tests and permeameter analyses of cores the geometric mean for the flowmeter tests 0 11 cm s is similar to that estimated from other field tests the mean for the permeameter tests 0 035 cm s is significantly lower possibly because of compaction of the cores the variance for the flowmeter 0 24 is also greater than that for the permeameter 0 14 geostatistical analyses applying negative exponential models with and without nuggets reveal similar spatial correlation structures for the two data sets estimated correlation scales range from 2 9 to 8 m in the horizontal and from 0 18 to 0 38 m in the vertical estimates of asymptotic longitudinal dispersivity b 35 0 78 m are similar in magnitude to that observed in the natural gradient tracer test 0 96 m previously conducted at this site

aftershock patterns and main shock faulting we have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms well located aftershock hypocenters are projected onto the main shock fault plane and their positions are examined relative to the zones of coseismic displacement indicated by the estimated distributions of main shock slip we also examine the aftershock focal mechanisms when these data are available in an attempt to identify possible patterns of secondary faulting within the aftershock zone our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault aftershocks following the earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip the spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture

three dimensional numerical experiments of strain partitioning at oblique plate boundaries implications for contrasting tectonic styles in the southern coast ranges california and central south island new zealand a three dimensional numerical model is used to investigate the nature and distribution of crustal scale deformation and strain partitioning across obliquely convergent transpressive plate boundaries a uniform elastic plastic crustal layer obeying murrell s extension to three dimensions of the griffith failure criterion was deformed under basal kinematic boundary conditions that correspond to the oblique convergence between two mantle lithospheres one of which detaches and subducts beneath the other the results show deformation concentrated in relatively narrow shear zones the character planar versus curved and dip of these shear zones or crustal scale faults depend on the relative amount of convergence versus transcurrent motion imposed across the plate boundary in models dominated by transcurrent boundary conditions two separate sets of coexisting structures develop 1 a pair of planar relatively shallow dipping thrust zones arranged in a v structure that accommodate convergent motion and 2 a set of curved near vertical strike slip zones arranged in a flower structure that accommodates the transcurrent motion in models dominated by convergence both contractional and transcurrent deformations are accommodated by oblique slip across a single pair of structures that have the same geometry as the thrust shear zones there is a gradational behavior between these end member partitioned and nonpartitioned modes for intermediate boundary conditions in all cases the dip of the shear zones predicted by the numerical model is in good agreement with the dip of ideal faults predicted by mohr s incipient faulting hypothesis the two basic modes are interpreted to underlie the contrasting tectonic styles of the southern coast ranges california and central south island new zealand factors other than obliquity of convergence which play a role in strain partitioning are discussed