a fractal model for crustal deformation abstract we hypothesize that crustal deformation occurs on a scale invariant matrix of faults for simplicity we consider a two dimensional pattern of hexagons on which strike slip faulting occurs the behavior of the system is controlled by a single parameter the fractal dimension deformation occurs on all scales of faults the fractal dimension determines the fraction of the total displacement that occurs on the first order or primary faults the value of the fractal dimension can be obtained from the frequency magnitude relation for earthquakes our results are applied to the san andreas fault system in central california earthquake studies give d 1 90 we associate the main strand of the san andreas fault with the primary faults of our fractal system we predict that the relative velocity across the main strand is 2 93 cm yr the remainder of the relative velocity of 5 5 cm yr between the pacific and north american plates occurs on higher order faults the predicted value is in reasonably good agreement with the value 3 39 0 29 cm yr obtained from geological studies

validation of regional and teleseismic travel time models by relocating ground truth events recently developed 3d global seismic velocity models have demon strated location improvements through independent regional and teleseismic travel time calibration concurrently a large set of high quality ground truth gt events with location accuracies 10 km or better gt0 gt10 has been collected for europe the mediterranean north africa the middle east and western eurasia in this study we demonstrate event location improvements using this new data set by applying the regional and teleseismic model based travel time calibrations independently and jointly besides relocating events using all arrivals a subset of the gt events was also relocated using controlled station geometries generated from a constrained boot strapping technique this approach simulates sparse networks and reduces the effect of correlated errors to ensure valid 90 error ellipse coverage statistics with respect to the gt events we compared event relocations with and without travel time cal ibrations considering statistics of mislocation error ellipse area 90 coverage or igin time bias origin time errors and misfit relocations of over 1200 gt events show that pn and or p calibration reduced mislocation for 60 70 of the events joint regional pn and teleseismic p travel time calibration provided the largest lo cation improvements and achieved approximately gt5 accuracy levels due to cor related errors event locations using large numbers of stations have deficient 90 error ellipse coverage however the coverages derived from the model errors are appropriate for the simulated sparse regional and teleseismic networks our valida tion effort demonstrates that the global model based calibrations of pn and teleseis mic p travel times reduce both location bias and uncertainty over wide areas

post 12 m y rotation of southwest washington paleomagnetic field directions from the basalt of pack sack lookout are compared to those from the pomona member of the saddle mountains basalt of the columbia river basalt group the pomona crops out over a wide region on the columbia plateau east of the cascade range and the basalt of pack sack lookout crops out well to the west of the cascades about 30 to 60 km east of the washington coast our paleomagnetic results support existing geologic and geochemical evidence that both these units are part of a single 12 m y old flow that erupted in western idaho and flowed to the washington coast the magnetic data further indicate that southwest washington has undergone clockwise rotation with respect to the columbia plateau and stable north america the data suggest that both a large scale regional rotation of 16 and locally complex small scale rotations exist the two being present to different degrees in the eastern and western regions of southwest washington the cascade range appears to coincide with the tectonic boundary separating rotated and unrotated regions of washington state rotation of southwest washington appears to have been associated with the rotation of large pieces of western oregon and southern washington possibly as a result of either a ridge push force from the basin and range province or shear along the pacific north america plate boundary

computer synthesis of geomagnetic palaeosecular variations computer models designed to synthesize palaeosecular variations of the geomagnetic field cast doubt on some widely accepted palaeomagnetic dogmas westward or eastward drift cannot be uniquely deduced from the sense of rotation of the geomagnetic vector the use of unit vectors in statistical analyses leads to systematic errors which render investigation of the global symmetry of the palaeofield more difficult than previously supposed at least some geomagnetic excursions may be regarded as large amplitude secular variations

the earthquake deformation cycle at the nankai trough southwest japan geodetic measurements made landward of the nankai trough site of great subduction zone thrust earthquakes in 1854 and 1946 provide a uniquely detailed picture of the strain buildup process supply constraints on the mechanism of strain accumulation and allow for improved estimates of earthquake recurrence provided the two most recent movement cycles are similar the observations dating from about 1890 may be used to reconstruct a single complete deformation cycle coseismic strain release postseismic transients interseismic strain accumulation very complete leveling and tidal gage data indicate that postseismic deformation extends more than 300 km inland from the plate boundary persists for at least 30 years and shows a clear tendency to become longer wavelength with increasing time the transient movements have two timescales the first of about a year or less corresponds to deformation largely uplift concentrated close to the coseismic fault and is most easily explained by aseismic slip or very localized deformation downdip of the earthquake rupture plane the second longer timescale is associated with a diffusion like spread of the deformation further landward an effect qualitatively similar to that first predicted by elsasser to be an expected consequence of faulting in an elastic plate overlying a viscoelastic asthenosphere cumulative uplift since 1890 correlates well with the distribution of uplifted marine terraces although average post 1890 tilt rates exceed late quaternary and holocene averages by at least a factor of three because of the nonlinearity of strain buildup and the significant permanent deformation simple recurrence calculations typically overestimate the true interval between great earthquakes by a factor of 2 to a factor of 3 strict application of the time predictable model assumed correct overcomes these difficulties provided the cumulative transient deformation and the proportion of permanent deformation per cycle can be estimated

epicentre accuracy based on seismic network criteria summary we establish reliable and conservative estimates for epicentre location accuracy using data that are readily available in published seismic bulletins a large variety of seismic studies rely on catalogues of event locations making proper assessment of location uncertainty critical event location and uncertainty parameters in most global regional and national earthquake catalogues are obtained from traditional linearized inversion methods using a 1 d earth model to predict traveltimes reported catalogue uncertainties are based on the assumption that error processes are gaussian zero mean and uncorrelated unfortunately these assumptions are commonly violated leading to the underestimation of true location uncertainty especially at high confidence levels we find that catalogue location accuracy is most reliably estimated by station geometry we make use of two explosions with exactly known epicentres to develop local network location 0 2 5 accuracy criteria using monte carlo simulations of network geometry we find that local network locations are accurate to within 5 km with a 95 per cent confidence level when the network meets the following criteria 1 there are 10 or more stations all within 250 km 2 an azimuthal gap of less than 110 3 a secondary azimuthal gap of less than 160 and 4 at least one station within 30 km to derive location accuracy criteria for near regional 2 5 10 regional 2 5 20 and teleseismic 28 91 networks we use a large data set of exceptionally well located earthquakes and nuclear explosions beyond local distances we find that the secondary azimuthal gap is sufficient to constrain epicentre accuracy and location error increases when the secondary azimuthal gap exceeds 120 when station coverage meets the criterion of a secondary azimuth gap of less than 120 near regional networks provide 20 km accuracy at the 90 per cent confidence level while regional and teleseismic networks provide 25 km accuracy at the 90 per cent confidence level

tidal marsh stratigraphy sea level change and large earthquakes i a 5000 year record in washington u s a abstract many of the estuaries of the pacific northwest of the u s a and canada contain stratigraphic sequences typified by alternating peat mud couplets recent studies in this region interpret such couplets as the product of repeated large magnitude s or 9 earthquakes on the cascadia subduction zone the resultant pattern of land level movements is described by a model the earthquake deformation cycle of coseismic land subsidence followed by land uplift during interseismic strain accumulation however peat mud couplets similar to those recorded in the pacific northwest are found on other less tectonically active temperate latitude coasts such as northwest europe and the atlantic coast of the u s a where they have been interpreted as the product of non seismic coastal processes in this paper we apply the methods and scientific framework common to sea level investigations in northwest europe to a sequence of peat mud couplets recorded in the lower johns river an estuary in southern washington to provide a test of the earthquake deformation cycle stratigraphic investigations of the intertidal sediments along the lower johns river using lithological pollen diatom and foraminiferal data show evidence for eight coastal submergence events during the last 5000 years to evaluate the earthquake deformation cycle we assess the lateral extent of peat mud couplets the synchroneity of submergence the presence of tsunami deposits accompanying submergence and the suddenness and amount of submergence each submergence is shown to be accompanied by changes in coastal sedimentation broadly commensurate with those predicted by the earthquake deformation cycle demonstrating the continued intermittent seismic activity of the cascadia subduction zone throughout the mid and late holocene quantitative analyses of contemporary and fossil biostratigraphic data using twinspan and detrended correspondence analysis enable us to estimate the magnitude of submergence accompanying each peat mud couplet one event was accompanied by submergence of about 1 5 m or more four events by intermediate submergence of about 1 0 5 m and a further three events by submergence of

thermal constraints on the seismogenic portion of the southwestern japan subduction thrust for coastal cities an important factor in earthquake hazard from subduction zone earthquakes is the landward extent of the seismogenic portion of the subduction thrust fault in this study we test the hypothesis that the maximum downdip extent is defined by a critical temperature we have developed a transient thermal model for the nankai subduction zone of southwest japan to allow comparison of the thermally estimated downdip extent of the seismogenic zone with that from 1 seismicity and tsunami data for two great subduction earthquakes 2 the coseismic faulting extent of these events estimated from geodetic deformation data and 3 the interseismic locked zone determined from interseismic geodetic data the nankai margin has extensive heat flow and heat production data to control thermal models and thus crustal temperatures it has earthquake tsunami and geodetic data that constrain the coseismic rupture portion of the subduction thrust fault for past great earthquakes and the portion of the thrust fault that is locked and storing interseismic elastic strain on the nankaido margin off shikoku island the thermal model indicates that a temperature of 350 c taken to be the limit for seismic initiation from laboratory and field data is reached on the subduction thrust fault 150 km from the trench a transition zone into which rupture may extend with decreasing offset taken to be 450 c extends an additional 45 km downdip the thermal model results are in excellent agreement with the maximum downdip extent of coseismic displacement for the 1946 nankaido ms 8 2 earthquake off shikoku island and with the downdip extent of the present locked zone in the region of the 1944 tonankai ms 8 2 earthquake to the northeast the subduction angle is much steeper and the thermal models indicate a narrower downdip seismogenic extent the seismogenic locked zone from earthquake and geodetic data is also narrower thus our analysis of the southwest japan margin indicates that all three constraints on the downdip extent of the seismogenic zone thermal coseismic and interseismic geodetic data are in general agreement the study also supports the hypothesis that the seismogenic portion of subduction thrust faults is limited primarily by temperature the thermal control implies that subduction thrust faults with shallow dip have wider seismogenic zones compared to those with steep dip the subducting plate age and thus heat flow and the thickness of the insulating sediments on the incoming plate are also very important to the thermal regime and thus to the seismogenic width the relation of the maximum seismic rupture area to the interseismic locked zone is particularly important for earthquake hazard estimation on subduction margins such as cascadia where there have been no great historical events

the quantification of geology from abacus to pentium a chronicle of people places and phenomena abstract the geological profession has only recently become numerically literate but highly so in a relatively short time mathematics was applied to geological problems mostly in the fields of hydrology engineering geology and geophysics until the past few decades statistics were used by sedimentologists and paleontologists to describe populations with some univariate bivariate and multivariate statistics used by a few avant garde workers geocomputing really started in the 1960s but the slow start became an avalanche in the 1980s with the introduction of microcomputer personal computer pc the trend towards increasing quantification of the discipline is noticeable and in recent years this trend has been accelerating there is seemingly no limit to the information and communication revolution

current sierra nevada north america motion from very long baseline interferometry implications for the kinematics of the western united states we use geodetic measurements from very long baseline interferometry to estimate the motion of the sierra nevadan microplate which is composed of the sierra nevada and the great valley the motion of the sierra nevadan microplate relative to the north american plate is described by a right handed rotation of 0 61 m y about lat 32 n long 128 w this euler pole lies only 10 southwest of the sierra nevadan microplate and predicts a significant counterclockwise rotation about a local vertical axis it further predicts a velocity of the eastern edge of the sierra nevada at 38 0 n 119 3 w relative to stable north america of 11 1 mm yr toward n36 3 w quoted uncertainties are plus or minus one standard error which accounts for about one fourth of the velocity between the pacific and north american plates and is 25 clockwise of many prior estimates the velocity nearly parallels the boundary between the sierra nevada and the great basin which implies that current motion within the great basin results in a rotational noncoaxial deformation we use this velocity to estimate how motion is distributed across the broad deforming zone taking up pacific north america plate motion we find that the vector sum of strike slip along the san andreas fault and motion of the sierra nevada relative to stable north america taken up by deformation within the great basin differs little from the pacific north america plate velocity the difference can be described at 36 n along the san andreas fault by a vector of 6 mm yr directed toward n20 w this vector resolves into components of 5 mm yr parallel to the fault and 2 mm yr perpendicular to the fault with 95 confidence intervals of 0 to 10 mm yr and 1 to 5 mm yr respectively the component perpendicular to the fault is several times smaller than found in prior studies and places a small upper bound on fault perpendicular shortening we conclude that motion previously inferred to be taken up by deformation other than strike slip along the san andreas fault or deformation within the great basin is much smaller than previously thought

texture representation of deformed dolomite rocks the determination of the orientation distribution function odf from pole figures measurements and from individual crystal measurements is illustrated for trigonal crystal and triclinic specimen symmetry with an example of the rhombohedral carbonate mineral dolomite we emphasize methodology of fabric analysis taking into account some new aspects about the significance of the inversion center in odf calculations the odd coefficients of the harmonic expansion which can not be easily derived from pole figure measurements have been determined with universal stage data of c axes and f twin lamellae their contribution to the odf is 20 30 and therefore necessary in any quantitative representation of textures

regional travel time uncertainty and seismic location improvement using a three dimensional a priori velocity model we demonstrate our ability to improve regional travel time prediction and seismic event location accuracy using an a priori 3d velocity model of western eurasia and north africa wena1 0 travel time residuals are assessed relative to the iasp91 model for approximately 6000 pg pn and p arrivals from seismic events having 2 epicenter accuracy between 1 km and 25 km ground truth 1 gt1 and gt25 respectively recorded at 39 stations throughout the model region ray paths range in length between 0 and 40 local regional and near teleseismic providing depth sounding that spans the crust and upper mantle the dataset also provides representative geographic sampling across eurasia and north africa including aseismic areas the wena1 0 model markedly improves travel time predictions for most stations with an average variance reduction of 29 for all ray paths from the gt25 events when we consider gt5 and better events alone the variance reduction is 49 for location tests we use 196 geographically distributed gt5 and better events in 134 cases 68 of the events locations are improved and average mislocation is reduced from 24 9 km to 17 7 km we develop a travel time uncertainty model that is used to calculate location coverage ellipses the coverage ellipses for wena1 0 are validated to be representative of epicenter error and are smaller than those for iasp91 by 37 we conclude that a priori models are directly applicable where data coverage limits tomographic and empirical approaches and the development of the uncertainty model enables merging of a priori and data driven approaches using bayesian techniques online material correction surfaces and histograms of travel time residuals for 40 stations

geology and mathematics progressing mathematization of geology surveying the history of mathematical geology since the times of lyell it is shown that its characteristic feature is that of interaction between a strongly historically inclined science and rather abstract mathematics statistics it is proven that mathematization of geology and experimental geology stimulate one another and that mathematical geology can be of essential aid in formulating conceptual models and scientific theories to integrate and unify diverse geological phenomena

gps deformation in a region of high crustal seismicity n cascadia forearc we estimate the rate of crustal deformation in the central and northern cascadia forearc based on a combination of existing global positioning system gps velocity data along the cascadia subduction zone gps strain rates and velocities show that the northwestern washington southwestern british columbia region is currently shortening at 3 3 5 mm yr 31 in a n s direction in good agreement with inference from crustal earthquake statistics on the longterm the shortening rate is 5 6 mm yr 31 providing that the subduction related interseismic loading of the margin is purely elastic compared to the velocity of the oregon forearc with respect to north america v 7m m yr 31 this indicates that most of the forearc motion is accommodated in the puget georgia basin area corresponding to the main concentration of crustal seismicity the difference between the current and long term shortening rates may be taken up during subduction megathrust earthquakes thus these events could produce a sudden increase of n s compression in the puget sound region and could trigger major seattle fault type crustal earthquakes published by elsevier science b v

generation of evenly spaced pressure solution seams during late diagenesis a kinetic theory stylolites and pressure solution seams can form during diagenesis of rocks subjected to stress through a feedback involving texture and pore fluid solute concentration this feedback destabilizes the state of uniform texture represented here only by porosity for simplicity a mathematical kinetic model that includes pressure solution diffusion and reprecipitation predicts the spontaneous generation even in initially uniform rocks of regions alternatingly in space more and less soluble a region that becomes more soluble also becomes simultaneously more porous the kinetic theory predicts that stylolites can form at roughly constant spacings this agrees with many field and petrographic observations bedding planes between beds that have initially different texture are shown by the theory to be the focus of a porosity instability that can lead to the formation of a stylolite and to the generation of more stylolites within each bed this prediction agrees with the observation that many stylolites have developed at bedding planes

a revised dislocation model of interseismic deformation of the cascadia subduction zone 1 cas3d 2 a new three dimensional 3 d dislocation model is developed to model interseismic deformation rates at the cascadia subduction zone the model is considered a snapshot description of the deformation field that changes with time the effect of northward secular motion of the central and southern cascadia forearc sliver is subtracted to obtain the effective convergence between the subducting plate and the forearc horizontal deformation data including strain rates and surface velocities from global positioning system gps measurements provide primary geodetic constraints but uplift rate data from tide gauges and leveling also provide important validations for the model a locked zone based on the results of previous thermal models constrained by heat flow observations is located entirely offshore beneath the continental slope similar to previous dislocation models an effective zone of downdip transition from locking to full slip is used but the slip deficit rate is assumed to decrease exponentially with downdip distance the exponential function resolves the problem of overpredicting coastal gps velocities and underpredicting inland velocities by previous models that used a linear downdip transition a wide effective transition zone etz partially accounts for stress relaxation in the mantle wedge that cannot be simulated by the elastic model the pattern of coseismic deformation is expected to be different from that of interseismic deformation at present 300 years after the last great subduction earthquake the downdip transition from full rupture to no slip should take place over a much narrower zone

confidence intervals for motion and deformation of the juan de fuca plate finite rotation parameters for 17 isochrons from anomalies 1 4a for the juan de fuca pacific plate pair are reported comparison of confidence intervals for plate rotations derived by different techniques indicates that a single plate misfit criterion significantly underestimates the confidence region defining the confidence interval by a threshold level of misfit determined by an f statistic gives similar results to the technique of bootstrap resampling for internally consistent data bootstrap resampling offers far greater robustness in the case of inconsistent data precision of about 1 km in the direction normal to isochrons is available for the younger anomalies this precision allows confident recognition of 2 5 km of eastward deformation of the pacific plate 50 100 km south of the active sovanco transform slight deformation of the northern juan de fuca plate adjacent to the nootka fault zone is also apparent east of the northern gorda ridge younger 3 ma anomalies do not show measurable deformation near the blanco fracture zone but older anomalies are up to 30 km east of their position predicted by rigid behavior of the juan de fuca plate reconstruction of the overlap geometry of past propagators shows no evidence that the extent of overlap has ever exceeded 70 km even with offset of 75 km in one case and 140 km in another new techniques for testing for intervals of constant plate motion require at least two changes in instantaneous motion at 99 confidence a clockwise change in motion direction at about 5 ma and an increase in the gradient of spreading rate since 2 ma two other changes in gradient since 5 ma are required at 95 confidence

reply to comment on improving sparse network seismic location with bayesian kriging and teleseismically constrained calibration events by stephen c myers and craig a schultz by a douglas we thank alan douglas douglas 2004 for his thoughtful comments on myers and schultz 2000 in myers and schultz 2000 we improve seismic location accuracy and uncertainty estimates for a sparse regional network by improving travel time predictions and better characterizing residual uncertainties station specific travel time corrections and associated uncertainty estimates are calculated using the bayesian kriging methodology of schultz et al 1998 the bayesian kriging methodology is an empirical approach that exploits the spatial correlation of travel time residuals to interpolate an empirical calibration set of travel time residuals into a minimum variance geographically continuous surface of travel time corrections and an associated uncertainty surface in myers and schultz 2000 we test the bayesian kriging approach by relocating events in the 1991 racha georgia earthquake sequence 42 n 43 e we compare uncalibrated locations based on p wave travel times for the ak135 model kennett et al 1995 and calibrated locations calibrated travel times and uncertainties to benchmark locations that are constrained with a dense local distance network the calibration data set consists of event locations that are constrained by a teleseismic network one goal of the study was to assess the utility of teleseismically constrained events for calibration we find that better travel time prediction for regional paths can be achieved by using the teleseismically constrained calibration events and the improved travel time prediction improves regional network location accuracy a major advantage of bayesian kriging over many other interpolation techniques is the propagation of uncertainty from the calibration data set into a travel time prediction uncertainty surface sources of data set uncertainty include calibration event locations phase observations for calibration events and calibration event spacing we find that coverage ellipses evernden 1969 are representative of observed epicenter accuracy i e confidence level of the coverage ellipse is indicative of the number of occurrences of the benchmark location within the ellipse when the

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

fractal geometry in the san andreas fault system it has been noted that the spatial distribution of earthquakes and the mode of strain release in the san andreas fault system is related to the complexity of fault geometry because of their rough appearance over many length scales faults can be regarded as fractal surfaces direct estimates of fractal dimension d of portions of the san andreas fault system between the northern gabilan range and the salton sea including the postulated extent of the great 1857 fort tejon earthquake are obtained from measured fault lengths analogous to the lengths of coastlines as discussed by mandelbrot regions characterized by complicated fault geometry are associated with larger values of d based on fault traces mapped at a scale of 1 750 000 d is 1 3 for this reach of the fault defined as a 30 km wide band about a main fault trace for that part near parkfield which could be associated with the nucleation of the 1857 earthquake d is 1 1 at this same scale d is 1 4 for the san andreas and related faults near san bernardino where the 1857 rupture stopped compared to 1 2 for the san andreas san juan fault segments near the point of arrest of the 1966 parkfield earthquake at finer map scales 1 24 000 and 1 62 500 critical lengths of 500 m and 1 km are identified which might relate to the extent of off san andreas fault offsets the critical lengths also suggest that fault geometry is not self similar if this fractal geometry persists through the seismic cycle it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault

coseismic slip resolution along a plate boundary megathrust the nankai trough southwest japan geodetic survey measurements are used to estimate the coseismic slip distribution in the 1944 tonankai mw 8 1 and 1946 nankaido mw 8 3 earthquakes and to assess quantitatively the degree to which this slip is resolved on the plate boundary megathrust data used include 798 angle changes from triangulation surveys 328 leveling section differences and 5 coseismic tidal gage offsets many of the nominally coseismic triangulation data span 50 years nearly half the earthquake cycle and correction for interseismic deformation using post 1950 observations is applied microseismicity is used to define the configuration of the plate boundary interface and approximate it with a continuous multisegment fault model because the onshore geodetic data have very limited resolving power for offshore fault segments offshore coseismic slip was constrained by satake s 1993 estimation based on tsunami data the majority of the coseismic slip occurs between 15 and 25 km depth although resolution declines toward the trench axis it is sufficiently good to define two distinct high slip regions one off southeastern shikoku island 11 m maximum and the other offshore of kii peninsula 3 m maximum the slip magnitude off southeastern shikoku coupled with the plate convergence rate would imply an recurrence interval of about 270 years much longer than the average repeat time of 120 years for historical great earthquakes on the nankai trough however the maximum coseismic slip is sensitive to the assumed fault geometry and slippage on trough parallel splay faults could significantly decrease the maximum slip to about 6 m

three dimensional dislocation model for great earthquakes of the cascadia subduction zone there have been no historical cascadia great subduction thrust earthquakes but there is good recent evidence that very large earthquakes have occurred in the past and that strain is building up toward a future great event geodetic measurements in the coastal region from northern california to southern british columbia show vertical and horizontal deformation as expected for the strain accumulation of a locked thrust fault the segment of the subduction thrust that is locked and may rupture in future great events has previously been estimated through two dimensional 2 d elastic dislocation modeling of interseismic deformation geodetic data in this study a general 3 d dislocation model for thrust faults has been developed that accommodates curved fault geometry and nonuniform interseismic locking or coseismic rupture the model is based on die surface deformation due to shear faulting in an elastic half space the 3 d model of the cascadia subduction zone calculates the surface deformation for a locked zone or a rupture zone of variable width along the margin the bend in the margin trend and subducting slab end effects are included there is a downdip transition zone between interseismic completely locked and free slip portions of the fault or between coseismic full rupture and no displacement an initial 3 d model based upon 2 d dislocation models and upon thermal constraints was adjusted to optimize the fit of the predicted interseismic surface deformation to current deformation geodetic data the best fit model has the thrust locked along the whole margin with an average locked zone width of 60 km and a transition zone width of 60 km the two zones lie mainly offshore beneath the continental shelf and slope the locked and transition zone widths vary smoothly along the margin being greater off northern washington where the thrust dip is shallow and narrower off central oregon assuming that the locked plus transition zones approximate the maximum coseismic rupture area these widths permit amw 9 earthquake

a fractal approach to the relationship between ore grade and tonnage it is now recognized that a variety of natural processes exhibit scale invariance over a wide range of scales scale invariant processes often exhibit a fractal behavior there are various ways to define fractal behavior one is to relate the frequency of occurrence to size tonnage and grade relations for economic ore deposits exhibit a fractal behavior if the tonnage of ore with a mean grade is proportional to the mean grade raised to a power we show that such a relation is a good approximation for mercury copper and uranium deposits in the united states the respective fractal dimensions are 2 01 1 16 and 1 48 the renormalization group approach is a quantitative method for studying scale invariant processes if it is assumed that the concentration of elements in ores is statistically scale invariant the renormalization group approach can be used to derive a fractal relationship between tonnage and mean grade

errors in hypocenter location picking model and magnitude dependence abstract the location procedures of seismic events are influenced by two major classes of errors the error in picking individual seismic phases and modeling error due to the departure of the real earth from the reference model used in the location both classes of error influence the estimate of location and it is difficult to separate them the role of picking errors can be assessed by a nonlinear analysis using a monte carlo procedure arrivals times are perturbed with random numbers drawn from a normal distribution and the event is relocated using these perturbed arrival times by repeating the procedure many times a cluster of locations is obtained which can be used to investigate the effects of picking errors on the hypocenter this analysis is insensitive to velocity model errors as these are fixed for a given combination of stations and phases some care must be exercised when analysing multidimensional distributions in two dimensional slices because of a projection effect the modeling error due to the influence of lateral heterogeneity in the earth is examined by comparing the locations of the same event using different combinations of phases and network geometries which reinforces the need to use arrivals other than p for accurate depth resolution the sensitivity of p arrivals to changes in depth are swamped by model errors and inclusion of depth sensitive phases such as pp is highly recommended the effect of picking errors on location is found to be much smaller than the mislocation caused by neglecting lateral heterogeneity when only p arrivals are used consequently the monte carlo analysis which is primarily aimed at picking errors only is most appropriate when multiple phases have been used to more accurately constrain the hypocenter especially for the depth component altering the type of phase data used in the location plays a similar role in changing the network geometry in that both are mechanisms that influence the nature of the constraint on the hypocenter by relocating events with network geometries corresponding to the different magnitudes it is found that the location of the event can be affected significantly by the magnitude and when using robust statistics to describe earthquake residuals the mislocation can occur in a systematic manner the effect is marked in regions with significant lateral variations in seismic velocities for example low magnitude events in the flores sea are found to be dragged toward australia as a result of the fast paths to australian stations relative to the iasp 91 reference velocity model

tidal marsh stratigraphy sea level change and large earthquakes ii submergence events during the last 3500 years at netarts bay oregon usa abstract this is the second investigation where we apply the methods and scientific framework common to sea level investigations in northwest europe to test a model of coseismic land subsidence followed by land uplift during interseismic strain accumulation used to explain alternating peat mud couplets of late holocene age found in many of the estuaries of the pacific northwest of the usa and canada recent studies in this region interpret such couplets as the product of repeated large magnitude 8 or 9 earthquakes on the cascadia subduction zone stratigraphic investigations of the intertidal sediments at netarts bay oregon using lithological pollen and diatom analyses reveal different types of submergence associated with peat mud couplets during the last 3500 yr three peat mud couplets record gradual sedimentation changes within an infilling body of water four other couplets record rapid submergence burial of tidal marshes and their replacement by low marsh environments in three of the events rapid submergence is small 0 0 5 m the most recent marsh submergence event around ad 1700 was 0 4 0 3 m most of the buried peats contain microfossil evidence for a gradual increase in marine influence before the rapid change from organic to minerogenic sedimentation similar gradual changes are common in comparable palaeoenvironments on non seismic coasts and are strong evidence against a simple interseismic strain accumulation coseismic subsidence model one hypothesis is that the gradual increase in marine influence before each submergence represents pre seismic relative sea level rise caused by a reduction in the rate of land uplift the microfossil analyses provide evidence of three stages within an earthquake deformation cycle coseismic subsidence interseismic land uplift and pre seismic reduction in the rate of land uplift at present the microfossil data do not differentiate between rapid post seismic land uplift and rapid sedimentation

improving sparse network seismic location with bayesian kriging and teleseismically constrained calibration events monitoring the comprehensive nuclear test ban treaty will require improved seismic location capability for small magnitude events the international monitoring system ims is well suited to locate events that are large enough to be recorded at teleseismic distances however small events are likely to be recorded on a sparse subset of ims stations at regional to upper mantle distances less than 30 and sparse network locations can be strongly effected by travel time errors that result from path specific velocity model inaccuracies in an effort to improve sparse network location capability we outline a procedure that applies empirical corrections to travel times determined with an appropriate velocity model more specifically bayesian kriging and calibration events constrained with a global network are used to estimate epicenter specific travel time corrections for a test sparse network of stations we calculate travel time residuals for the calibration events relative to the ak135 velocity model travel time residuals are assigned to the respective calibration epicenter forming a set of spatially varying travel time correction points the spatial set of correction points is declustered to reduce the dimension of the observations with minimal reduction in accuracy of the travel time corrections we then use the declustered set of calibration points and bayesian kriging to form continuous travel time correction surfaces for each station of the test network the effectiveness of travel time correction surfaces is evaluated by locating with and without corrections a subset of the 1991 racha earthquake sequence caucasus mountains for which we have accurate locations that were independently determined with a dense local network when no travel time correction is applied the mean horizontal distance between the local and test network locations is 42 km and there is a distinct bias in sparse network locations toward the north northwest the mean difference between local and sparse network locations is cut to 13 km when corrections are applied and the bias in location is significantly reduced when calibration events in the racha vicinity are not used to make the correction surfaces there is still a significant improvement in location with mean mislocations of 15 km when corrections are not applied only one of the locally determined locations lies within the associated 90 coverage ellipse determined with the test sparse network however by using travel time corrections and estimates of model uncertainty determined using kriging representative error ellipses are obtained this study demonstrates that kriging correction surfaces based on global network constrained calibration events can improve the ability to accurately locate lower magnitude events while providing representative coverage ellipses

postglacial rebound at the northern cascadia subduction zone postglacial rebound is the response of the earth to the decay of ice sheets a postglacial rebound model explains crustal tilting and rapid uplift at the northern cascadia subduction zone that occurred during retreat of the cordilleran ice sheet observations explained by the model include the shoreline tilts of two proglacial lakes that formed at 13 5 14 ka 14c yr ago and rapid sea level fall land uplift at 12 12 5 ka modelled mantle viscosity values range from 5 1018 to 5 1019 pa s and are consistent with previous viscosity inferences from observations of crustal deformation following subduction zone earthquakes 1018 1019 pa s no lower limit to subduction zone mantle viscosity is apparent from our model but viscosity values equal to or larger than 1020 pa s are de nitely ruled out our modelled subduction zone viscosity values are smaller than most upper mantle viscosity estimates derived from postglacial rebound studies of tectonically less active regions 1020 1021 pa s the rapid observed uplift at 12 ka requires in addition to a low mantle viscosity rapid unloading from a sudden collapse of remaining coastal portions of the southern cordilleran ice sheet the sudden collapse provides 0 18 m of global eustatic sea level rise approximately 0 7 of the sea level rise associated with melt water pulse ia predictions of a global postglacial rebound model ice 3g with a 1021 pa s upper mantle viscosity were previously applied to geodetic data from this region to isolate signals associated with the earthquake cycle owing to the low viscosity values and resulting rapid recovery of glacial deformation our model predicts present day postglacial rebound uplift rates at least 10 times smaller than ice 3g less than about 0 1 mm yr as the ice 3g adjustments were substantial this indicates the need for re evaluation of the geodetic data 2000 elsevier science ltd all rights reserved

present day vertical deformation of the cascadia margin pacific northwest united states we estimate present day uplift rates along the cascadia subduction zone in california oregon and washington in the pacific northwest united states by utilizing repeated leveling surveys and tide gauge records these two independent data sets give similar profiles for latitudinal variation of contemporary uplift rates along the coast uplift rates are extended inland through east west leveling lines that connect the north south line along the coast to the north south line along the inland valleys just west of the cascades the results are summarized as a contour map of present day uplift rates for the western pacific northwest we find that rates of present day uplift vary latitudinally along the coast and inland valleys as well as longitudinally along transects connecting the coast to the inland valleys long term tidal records of neah bay astoria and crescent city indicate uplift of land relative to sea level of 1 6 0 2 0 0 0 2 and 0 9 0 2 mm yr respectively 1 standard error unlike previous estimates of relative sea level change at astoria we adjust for discharge effects of the columbia river including human management influences after approximating an absolute framework by using 1 8 0 1 mm yr to compensate for global sea level rise results indicate that much of the western pacific northwest is rising at rates between 0 and 5 mm yr the most rapid uplift rates are near the coast particularly near the olympic peninsula the mouth of the columbia river cape blanco and cape mendocino two axes of uplift are identified one trends northeast from the southwest oregon coast and the other trends south southeasterly from the olympic peninsula to the columbia river the puget sound vicinity and a small east west region from the north central oregon coast to the inland willamette valley are subsiding at rates up to 1 mm yr we interpret the overall pattern of rapid present day uplift to be generated by interseismic strain accumulation in the subduction zone this interseismic elastic strain accumulation implies significant seismic hazard

time and size of a giant earthquake in cascadia inferred from japanese tsunami records of january 1700 geological evidence shows that great earthquakes have occurred in the recent prehistoric past in the cascadia subduction zone off the pacific coast of north america the most recent event or series of events is dated at about 300 years ago1 4 but the precise date and magnitude have not been determined geological investigations have not been able to distinguish a single giant earthquake from a series of great earthquakes occurring over a timespan of a decade or two4 although this information is important for the assessment of future hazard5 we have found several tsunami records in japan from ad 1700 with no indication of a local cause historical earthquake records and palaeoseismic evidence indicate the absence of a large earthquake in 1700 in south america alaska or kamchatka leaving cascadia as the most likely source of this tsunami the estimated time of the earthquake is the evening about 21 00 local time of 26 january 1700 the magnitude is estimated as 9 from the tsunami heights in which case the earthquake ruptured the entire length of the cascadia subduction zone2 these estimates are consistent with native american legends that an earthquake occurred on a winter night6

coupling of tectonic loading and earthquake fault slips at subduction zones because of the viscoelastic behaviour of the earth accumulation of elastic strain energy by tectonic loading and release of such energy by earthquake fault slips at subduction zones may take place on different spatial scales if the lithospheric plate is acted upon by distant tectonic forces strain accumulation must occur in a broad region however an earthquake releases strain only in a region comparable to the size of the rupture area a two dimensional finite element model of a subduction zone with viscoelastic rheology has been used to investigate the coupling of tectonic loading and earthquake fault slips a fault lock and unlock technique is employed so that the amount of fault slip in an earthquake is not prescribed but determined by the accumulated stress the amount of earthquake fault slip as a fraction of the total relative plate motion depends on the relative sizes of the earthquake rupture area and the region of tectonic strain accumulation as well as the rheology of the rock material the larger the region of strain accumulation is compared to the earthquake rupture the smaller is the earthquake fault slip the reason for the limited earthquake fault slip is that the elastic shear stress in the asthenosphere induced by the earthquake resists the elastic rebound of the overlying plate since rapid permanent plate shortening is not observed at subduction zones there must be either strain release over a large region or strain accumulation over a small region over earthquake cycles the former can be achieved only by significant aseismic fault slip between large subduction earthquakes the most likely mechanism for the latter is the accumulation of elastic strain around isolated locked asperities of the fault which requires significant aseismic fault slip between asperities

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses