elastic finite difference modeling of the 1971 san fernando california earthquake finite difference seismograms calculated for the 1971 san fernando earthquake show strong effects due to lateral variation in sediment thickness in the san fernando valley and the los angeles basin using basin structure derived mostly from well logs and teleseismically determined source parameters two dimensional sh and p sv finite difference calculations reproduce the amplitude and duration of the strong motion velocities recorded across the los angeles and san fernando basins for the period range of 2 to 10 sec the edges of basins nearest the seismic source show ground motion amplification up to a factor of 3 over the case without the basin and tend to convert direct shear waves into love and rayleigh waves that travel within the basins

sensitivity analysis of nonequilibrium adaptation parameters for modeling mining pit migration the nonequilibrium adaptation parameters of a depth averaged two dimensional hydrodynamic and sediment transport model were examined in the study calculated results were compared to data measured in two sets of published laboratory experiments that investigated mining pit migration under well controlled boundary conditions including steady flow and uniform rectangular cross sections along the flume except in the vicinity of the experimental mining area the two sets of experiments were chosen as representatives of bed load dominated and suspended load dominated cases respectively a sensitivity analysis was conducted to estimate the influence of the nonequilibrium adaptation parameters on mining pit migration simulation calculated results indicate that appropriate selection of the adaptation parameters is critical in order to close the nonequilibrium sediment transport formulas when modeling mining pit migration

an experimental study of flow bedload transport and bed topography under conditions of erosion and deposition and comparison with theoretical models the nature of flow sediment transport and bed texture and topography was studied in a laboratory flume using a mixed size density sediment under equilibrium and non equilibrium aggradational degradational conditions and compared with theoretical models during each experiment water depth bed and water surface elevation flow velocity bed shear stress bedload transport and bed state were continuously monitored equilibrium uniform flow was established with a discharge of about 0 05 m3 s 1 a flow depth of about 0 01 m a flow velocity of about 0 81 0 88 m s 1 a spatially averaged bed shear stress of about 1 7 2 2 pa and a sediment transport rate of about 0 005 0 013 kg m 1 s 1 i e close to the threshold of sediment transport such equilibrium flow conditions were established prior to and at the end of each aggradation or degradation experiment pebble clusters bedload sheets and low lying bars were ubiquitous in the experiments heavy minerals were relatively immobile and occurred locally in high concentrations on the bed surface as lag deposits aggradation was induced by 1 increasing the downstream flow depth flume tilting and 2 sediment overloading tilt induced aggradation resulted in rapid deposition in the downstream half of the flume of a cross stratified deposit with downstream dipping pebbles pseudo imbricated and caused a slight decrease in the equilibrium mean water surface slope and total bedload transport rate these differences between pre and post aggradation equilibrium flow conditions are due to a decrease in the local grain roughness of the bed sediment overloading produced a downstream fining and thinning wedge of sediment with upstream dipping pebbles imbricated whereas the equilibrium flow and sediment transport conditions remained relatively unchanged degradation was induced by 1 decreasing the downstream flow depth flume tilting and 2 cutting off the sediment feed tilt induced degradation produced rapid downstream erosion and upstream deposition due to flow convergence with little change to the equilibrium flow and sediment transport conditions the cessation of sediment feed produced degradation and armour development a reduction in the mean water surface slope and flow velocity an increase in flow depth and an exponential decrease in bedload transport rate as erosion proceeded a bedload transport model predicted total and fractional transport rates extremely well when the coarse grained or bedform trough areas of the bed are used to define the sediment available to be transported a sediment routing model midas also reproduced the equilibrium and non equilibrium flow conditions total and fractional bedload transport rates and changes in bed topography and texture very well

modeling the evolution of incised streams i model formulation and validation of flow and streambed evolution components a robust computational model for simulating the long term evolution of incised and restored or rehabilitated stream corridors is presented the physically based model simulates the three main processes that shape incised streams hydraulics sediment transport and streambed and bank adjustments a generalized implicit preissmann scheme is used for the spatial and temporal discretization of the flow governing equations to accommodate large time steps and cross sections spaced at irregular intervals the solution method introduces several enhancements that increase its robustness specifically to simulate flashy flows transport of cohesive or cohesionless graded bed material is based on a total load concept and suspended and bed load transport modes are accounted for through nonequilibrium effects the model simulates channel width adjustment by hydraulic erosion and gravitational mass failure of heterogeneous bank material the present paper focuses mainly on the treatment of streamflow hydraulics and evolution of graded streambeds and reports simulations of published experiments on degrading and aggrading channels with graded bed material description and validation of the model s stream bank erosion component and the application of the model to incised stream systems are presented elsewhere

modeling of riverbed evolution for bedload sediment mixtures a new computational methodology for fully coupled simulation of unsteady water and sediment movement in mobile bed alluvial rivers has been developed and tested the one dimensional approach treats bedload transport of nonuniform sediment mixtures with sorting and armoring effects considered spatial lag effects in nonequilibrium bedload transport are taken into account through innovative use of the recently developed notion of a loading law the new system of equations for water and sediment movement is solved in a fully coupled implicit manner using the preissmann finite difference scheme implemented to allow for either upstream or downstream induced mobile bed perturbations formal analysis of the coupled system sheds new light on boundary condition requirements for the multiple size class problem the fully coupled implicit solution has proven to be robust and stable and it respects the underlying volumetric conservation laws remarkably well as demonstrated in continuity analyses of computed bed e

influence of vertical resolution and nonequilibrium model on three dimensional calculations of flow and sediment transport this note using a three dimensional model of river flow and sediment transport examines the effect of the vertical resolution and the choice a nonequilibrium adaptation length ls in predicting flow and sediment transport around groins in china s yongding river the results show that a fine vertical grid and nonequilibrium sediment transport model provide good predictions especially on the river bed profile with an obvious main channel and flood plain

fully coupled unsteady mobile boundary flow model a fully coupled one dimensional river model capable of predicting sediment transport and bed level changes under unsteady flow conditions is described the governing equations for mass and momentum balance of sediment water mixture under unsteady flow conditions in natural rivers with irregular geometries are solved simultaneously using the preissmann four point linear implicit scheme with weighting factors for space and time coordinates the resulting system of algebraic equations is solved using a solution procedure that bridges upstream and downstream boundary nodal values by successive substitutions the friction slope is expressed in a consistent form that allows the consideration of the changing alluvial roughness effect the system of governing equations is explicitly coupled by introducing the term representing the rate of change of bed level the fully coupled unsteady mobile boundary flow model fcm is applied to the classical problem of sediment deposition upstream of a dam with an arbitrar

unified structural representation of the southern california crust and upper mantle we present a new 3d description of crust and upper mantle velocity structure in southern california implemented as a unified structural representation usr the usr is comprised of detailed basin velocity descriptions that are based on tens of thousands of direct velocity vp vs measurements and incorporates the locations and displacement of major fault zones that influence basin structure these basin descriptions were used to developed tomographic models of crust and upper mantle velocity and density structure which were subsequently iterated and improved using 3d waveform adjoint tomography a geotechnical layer gtl based on vs30 measurements and consistent with the underlying velocity descriptions was also developed as an optional model component the resulting model provides a detailed description of the structure of the southern california crust and upper mantle that reflects the complex tectonic history of the region the crust thickens eastward as moho depth varies from 10 to 40 km reflecting the transition from oceanic to continental crust deep sedimentary basins and underlying areas of thin crust reflect neogene extensional tectonics overprinted by transpressional deformation and rapid sediment deposition since the late pliocene to illustrate the impact of this complex structure on strong ground motion forecasting we simulate rupture of a proposed m 7 9 earthquake source in the western transverse ranges the results show distinct basin amplification and focusing of energy that reflects crustal structure described by the usr that is not captured by simpler velocity descriptions we anticipate that the usr will be useful for a broad range of simulation and modeling efforts including strong ground motion forecasting dynamic rupture simulations and fault system modeling the usr is available through the southern california earthquake center scec website http www scec org

note on lag in bedload discharge it is postulated that movable sediment beds comprise of two types of grains termed undisturbed and disturbed grains the probability of entrainment by flow of the latter is higher than that of the former the lag in bedload transport is due to the difference in the entrainment probabilities of the two types of grains a model is developed to predict lag in bedload transport the spatial and temporal lag coefficients are functions of both the inner and outer variables the 50 of the equilibrium bedload discharge is attained within about 26 of the total lag distance or lag time the lag model was verified by conducting laboratory experiments and using experimental data of bagnold the proposed model agrees with the experimental data both the lag distance and lag time decrease with increasing equilibrium bedload discharge the findings of the model can be used to improve the einstein formula for the equilibrium bedload discharge

basin structure estimation by waveform modeling forward and inverse methods we introduce a technique for using broadband seismograms recorded from earthquakes at local and regional distances to refine basin structure for the region outside the basin we assume a one dimensional 1d crustal model and analytical techniques grt to propagate the energy from sources to the basin edge where the motions are then interfaced with a 2d finite difference algorithm wen and helmberger 1996 we parameterize the basin section by isovelocity layers with linear dipping segments between control points the control point depths are allowed to vary to improve the modeling of waveform data of stations inside the basin the comparison between data and synthetics is qualified by a fitness function defined by two factors the timing shift required for best alignment and the correlation coefficient the procedure was applied to a strong motion waveform profile across the extended los angeles basin produced by the 1992 landers california earthquake to refine the velocity structure using sensitivity testing and forward modeling only the correlation coefficient and amplitude were used because absolute timing was unknown the procedure was extended to a direct waveform inversion by employing a conjugate gradient approach which uses numerical derivatives numerical tests using the new inversion process with synthetic data demonstrate that it is possible to recover a detailed basin structure if a sufficient amount of high quality data exists

the laptev sea rift abstract in north eastern siberia the active mid ocean gakkel ridge interacts with the continental shelf of the laptev sea extension has affected the shelf since at least the early tertiary and has resulted in the formation of a complex horst and graben system we present new seismic data from the laptev sea including deep seismic soundings the most prominent rift basin is the ust lena rift with a minimum e w width of 300 km at latitude 75 n and a cenozoic infill up to 13 km in thickness the asymmetric shape of the basin and conclusive evidence for a detachment imply a simple shear geometry the suggested rift model combines a ramp and flat geometry for the detachment with ductile stretching beneath the detachment a major west dipping hingeline listric fault separates the ust lena rift from the laptev horst the 100 150 km wide laptev horst is subdivided into three units by narrow rift grabens another prominent rift graben is the anisin basin which is located in the northern shelf area though the laptev sea rift formed in interaction with an active mid oceanic ridge there are indications that the laptev sea rift is of the passive rift type the rift was developed east of a sw ne trending transfer zone which links the gakkel ridge to the laptev sea rift

simulation of gravel sand bed response to flushing flows using a two fraction entrainment approach model development and flume experiment 1 in this work we combine existing ideas on gravel and sand entrainment into a simulation model for flows that flush sand from the surface and subsurface of a gravel riverbed a flume experiment is conducted to provide a test of the flushing model the primary advance represented in this paper is incorporation of a two fraction entrainment approach into a routing model to account for the effect of sand content on the entrainment and transport of bed sediment which is crucial for simulation of the flushing process associated with progressively decreasing sand proportions a combination of the active layer concept and two layer treatment is adopted herein to outline the framework of sediment transport system which allows incorporation of subsurface sand into the surface layer through the mechanisms of upward entrainment and bed degradation sediment routing computations are executed in two steps in the first step the change of bed level is computed with the continuity equation of sediment in the surface layer in the second step the changes of sediment storage in the surface and subsurface layers are calculated with the mass conservations of sediment an important finding of this study is that the flume results could not be adequately simulated without an upward sand flux from the subsurface which confirms the operation of a process that has only been hypothesized the simulation results including the evolutions of bed composition and elevation are in good agreement with the observations implying a potential application of the proposed model in determining flushing flows for environmental benefit

preliminary analysis of long period basin response in the los angeles region from the 1994 northridge earthquake long period 1 10 sec ground motions recorded in the los angeles basin region during the northridge earthquake show complex waveforms extended durations and multiple sets of arrivals which cannot be attributed solely to source processes or wave propagation within a plane layered medium these features suggest a strong interaction between the propagating seismic wave field and the laterally varying subsurface geologic structure of this region recorded motions at a hard rock site in the santa monica mountains scrs are smaller by nearly a factor of three in peak velocity compared to recordings at more distant sites in the adjacent northwest portion of the los angeles basin in addition although the rock site recording has a relatively simple wave shape the basin site recordings are dominated by late arriving large amplitude pulses of energy we interpret these arrivals to be surface waves which are generated by body waves interacting with the thickening margin of the basin a preliminary modeling analysis of these data indicates that a combination of both large scale deep basin and small scale shallow micro basin structures are needed to explain the observed responses

cohesion influences on erosion and bed load transport 1 studies on erosion and transport rates of cohesive sediment mixtures containing gravel are not reported so far in the literature to the best of our knowledge results from laboratory experiments on the process of erosion of cohesive sediment mixtures by open channel flow are presented the sediment used for experimentation consisted of fine gravel mixed with clay in proportions varying from 10 to 50 and fine gravel fine sand in equal proportion by weight mixed with clay proportions again varying from 10 to 50 by weight experimental observations have revealed that the process of detachment of cohesive sediment mixtures containing gravel is significantly different from that of cohesionless sediments also it is different from the detachment process of cohesive sediment mixtures not containing coarser size material experimental data on transport rates of the bed load of the cohesive sediment mixtures are presented on the basis of dimensional considerations a computational procedure is proposed to determine the bed load transport rates generated from erosion of the different size fractions of sediment mixtures clay percentage and unconfined compressive strength of the sediment bed were the main parameters controlling bed load transport rate of such sediments in the absence of cohesion the proposed method reduces to the patel and ranga raju 1996 method for bed load transport rate computation of nonuniform cohesionless sediments

response of high rise and base isolated buildings to a hypothetical mw 7 0 blind thrust earthquake high rise flexible frame buildings are commonly considered to be resistant to shaking from the largest earthquakes in addition base isolation has become increasingly popular for critical buildings that should still function after an earthquake how will these two types of buildings perform if a large earthquake occurs beneath a metropolitan area to answer this question we simulated the near source ground motions of a m w 7 0 thrust earthquake and then mathematically modeled the response of a 20 story steel frame building and a 3 story base isolated building the synthesized ground motions were characterized by large displacement pulses up to 2 meters and large ground velocities these ground motions caused large deformation and possible collapse of the frame building and they required exceptional measures in the design of the base isolated building if it was to remain functional

expected seismic shaking in los angeles reduced by san andreas fault zone plasticity computer simulations of large m 7 8 earthquakes rupturing the southern san andreas fault from se to nw e g shakeout widely used for earthquake drills have predicted strong long period ground motions in the densely populated los angeles basin due to channeling of waves through a series of interconnected sedimentary basins recently the importance of this waveguide amplification effect for seismic shaking in the los angeles basin has also been confirmed from observations of the ambient seismic field by simulating the shakeout earthquake scenario based on a kinematic source description for a medium governed by drucker prager plasticity we show that nonlinear material behavior could reduce the earlier predictions of large long period ground motions in the los angeles basin by up to 70 as compared to viscoelastic solutions these reductions are primarily due to yielding near the fault although yielding may also occur in the shallow low velocity deposits of the los angeles basin if cohesions are close to zero fault zone plasticity remains important even for conservative values of cohesions suggesting that current simulations assuming a linear response of rocks are overpredicting ground motions during future large earthquakes on the southern san andreas fault

mid cenozoic tectonic and paleoenvironmental setting of the central arctic ocean drilling results from the integrated ocean drilling program s arctic coring expedition acex to the lomonosov ridge lr document a 26 million year hiatus that separates freshwater influenced biosilica rich deposits of the middle eocene from fossil poor glaciomarine silty clays of the early miocene detailed micropaleontological and sedimentological data from sediments surrounding this mid cenozoic hiatus describe a shallow water setting for the lr a finding that conflicts with predrilling seismic predictions and an initial postcruise assessment of its subsidence history that assumed smooth thermally controlled subsidence following rifting a review of cenozoic tectonic processes affecting the geodynamic evolution of the central arctic ocean highlights a prolonged phase of basin wide compression that ended in the early miocene the coincidence in timing between the end of compression and the start of rapid early miocene subsidence provides a compelling link between these observations and similarly accounts for the shallow water setting that persisted more than 30 million years after rifting ended however for much of the late paleogene and early neogene tectonic reconstructions of the arctic ocean describe a landlocked basin adding additional uncertainty to reconstructions of paleodepth estimates as the magnitude of regional sea level variations remains unknown

irregular recurrence of large earthquakes along the san andreas fault evidence from trees old trees growing along the san andreas fault near wrightwood california record in their annual ring width patterns the effects of a major earthquake in the fall or winter of 1812 to 1813 paleoseismic data and historical information indicate that this event was the san juan capistrano earthquake of 8 december 1812 with a magnitude of 7 5 the discovery that at least 12 kilometers of the mojave segment of the san andreas fault ruptured in 1812 only 44 years before the great january 1857 rupture demonstrates that intervals between large earthquakes on this part of the fault are highly variable this variability increases the uncertainty of forecasting destructive earthquakes on the basis of past behavior and accentuates the need for a more fundamental knowledge of san andreas fault dynamics

a numerical study of sediment transport and event bed genesis during tropical storm delia some event beds tempestites are thought to be emplaced on shallow marine shelves by the combined action of strong coastal currents and high waves during fairly short lived storms to test this hypothesis a storm sedimentation system has been constructed from six numerical models describing a cyclonic wind field three dimensional coastal circulation wind waves generated over the continental shelf the combined effect of steady and oscillatory currents within the benthic boundary layer suspended and bed load transport of sediment and conservation of the seafloor this model system is used to hindcast winds currents waves and resulting sedimentation during tropical storm delia which passed over the texas louisiana shelf on september 3 4 1973 sensitivity to the initial substrate is investigated in four experiments using uniform silt uniform sand a mud line at the 20 m isobath and a simplified modern sediment distribution modeled coastal currents are vertically uniform and do not reveal the structure predicted by the mid latitude geostrophic storm circulation model because the predicted depth of the wind mixed layer is greater than the water depth over the shelf shelf currents in excess of 2 m s flow predominantly along the coast to the southwest during most of the storm driven by the wind stress and the trapped coastal wave which peaks at 180 cm near galveston significant wave heights reach 8 m on the outer shelf but are less than 4 m over the inner shelf these waves combine with steady currents to produce bed shear velocities which locally exceed 20 cm s the region of highest stresses always lies to the right of the storm track viewed down the path and moves across the shelf with the eye of the storm three general sediment transport paths are evident 1 onshore transport of finer sediment over the outer shelf to the right of the storm track 2 westward directed along shelf transport of predominantly fine sediment between approximately 40 m and 20 m water depths and 3 minor offshore transport of sand from the shoreface to depths less than 30m the resulting event bed has a ragged appearance with a maximum thickness of about 20 cm in region 1 and covers an area of approximately 3 104 km2 to the right of the storm track aside from local transport associated with finer sediments these results are relatively insensitive to initial sediment type comparison of model results to observed data from buccaneer platform shows that the different models performed adequately during the peak of the storm except for a significant underprediction of the significant wave height by the wind sea model the estimated uncertainty in the calculated combined shear stresses u based on errors produced by the individual model components is most dependent on the wave bottom orbital amplitude the total uncertainty in u is estimated to be approximately 7

finite difference modeling of two aftershocks of the 1994 northridge california earthquake recent evidence for nonlinear behavior of strong motions generated by the northridge california earthquake relies explicitly on the analysis of aftershock data thus correcting these observations for propagational and source effects becomes a crucial step in these studies here we demonstrate that the dipping structure near the edges of the san fernando valley can strongly alter the local site responses especially for shallow events we model two aftershocks with similar epicenters but with shallow 4 km and deep 16 km hypocentral depths waveforms from 12 portable instruments deployed across the basin and recording these events were processed and studied in the 0 3 4 hz bandpass for the shallow event distinctive features are a broad direct s phase and large amplitude surface waves at the basin stations and high frequency s phases at stations in the santa monica mountains the deep event is less strongly affected by the basin but displays strong evidence of the source radiation pattern an array analysis indicates 2d propagation for most of the strong arrivals some of these features are explained by a simple 2d basin model containing a strong shallow contrast a factor of 2 jump in seismic velocity at a depth of 1 km within the basin and a moderate deeper gradient

coupled modeling of alluvial flows full recognition of the physical coupling of water and sediment phases of alluvial flows leads to the need for a concurrent solution of the water routing and sediment routing components in mobile bed river modeling in this paper the coupled and uncoupled methods of alluvial stream modeling are compared a newly developed coupled model of one dimensional riverine water and sediment flow called coupflex is briefly introduced several schemes in discretization of the sediment continuity equation often used in uncoupled approaches are mentioned two elaborate flume tests on river degradation are briefly described experimental data is used to compare the performance of coupflex with that of the uncoupled approaches this comparison highlights the advantages of the coupled method over the traditional uncoupled method performing several numerical tests some aspects of numerical modeling of alluvial flows are briefly dealt with these include problems resulting from the use of equilibrium relations in nonequilibrium situations the dominant role of empirical sediment transport and hydraulic resistance formulas in the accuracy of the answers from any alluvial flow model significance of the computational time step violation of the sediment mass conservation law and the use of approximate water routing models

variable slip rupture model of the great 1923 kanto japan earthquake geodetic and body waveform analysis abstract the available geodetic and teleseismic data sets for the 1923 kanto earthquake m s 8 1 have been combined into a joint inversion for both temporal and spatial slip variations we assumed an initial faulting model to be consistent with the geometry determined by kanamori 1971 on the basis of first motion data aftershock area and the amplitude of surface waves at teleseismic distances and also to enclose the slipped area estimated by matsu9ura et al 1980 from the geodetic data employed here we then inverted for a heterogeneous distribution of slip of the fault plane the leveling routes and triangulation stations used consisting of 225 bench marks and 31 triangulation points are from matsu9ura et al 1980 we chose to first determine the overall static slip distribution by inverting the geodetic data alone we then proceeded to gradually increase the importance of the teleseismic data always requiring a good fit to the geodetic leveling and horizontal displacements in this way we could provide a constraint on the overall static slip characteristics from the geodetic data and provide stability for the teleseismic inversion yet determine the degree of slip heterogeneity and time history most suitable for matching the waveform data and for simulating strong ground motions our analysis yields a seismic moment of 7 to 8 10 27 dyne cm m w 7 8 to 7 9 with a maximum slip of approximately 8 m the most concentrated slip is in the shallow central and western portion of the fault the location of the concentrated slip on the fault plane has important consequences for the amplitude duration and frequency content of the resulting ground motions as documented by takeo and kanamori 1993

two case histories demonstrating the effect of past earthquakes on liquefaction resistance of silty sand abstractthe paper compares two liquefaction case histories in california 1 the response of the wildlife site in the imperial valley to the 2010 el mayor cucapah earthquake mw 7 2 amax 0 15 g

three dimensional finite difference modeling of the san andreas fault source parameterization and ground motion levels olsen et al 1995 recently simulated an mw 7 75 earthquake on the san andreas fault predicting long period t 2 5 sec ground velocities of 140 cm sec in the los angeles basin about 60 km from the fault these motions are much larger than estimates derived from empirical relations or other numerical simulations standard area magnitude relations predict that the 170 16 km fault used in the simulations would produce an mw 7 5 earthquake giving a moment of 2 0 1027 dyne cm which is 2 4 times smaller than the moment used by olsen et al 1995 further self similar scaling predicts a rise time of 3 sec for an mw 7 75 event and 2 2 sec for an mw 7 5 event the filtered impulse slip function used by olsen et al 1995 has an effective rise time of 1 6 sec yielding a response that is about 2 times larger than expected for periods less than 5 sec this combination of high seismic moment and short rise time along with the use of a uniform slip distribution leads to the extreme ground motion levels predicted by olsen et al 1995 to quantify the sensitivity of the long period ground motion response to source parameterization we have performed 3d finite difference fd simulations using various combinations of seismic moment source rise time and slip heterogeneity these calculations incorporate the same grid dimensions fault size and bandwidth employed by olsen et al 1995 with a moment of 2 0 1027 dyne cm a rise time of 2 sec and a smoothly heterogeneous slip distribution we simulate peak long period ground velocities of 155 cm sec in the near fault region and 40 cm sec in the los angeles basin these values are much closer to although still higher than empirical predictions a uniform slip distribution produces the largest peak motions both in the near fault region and in the los angeles basin whereas a rough asperity slip distribution noticeably reduces the maximum near fault ground velocities our results indicate that the accurate simulation of long period ground motions requires a realistic source parameterization including appropriate choices of seismic moment and rise time as well as the use of spatial and temporal variations in slip distribution

coupled and decoupled numerical modeling of flow and morphological evolution in alluvial rivers existing numerical river models are mostly built upon asynchronous solution of simplified governing equations the strong coupling between water flow sediment transport and morphological evolution is thus ignored to a certain extent an earlier study led to the development of a fully coupled model and identified the impacts of simplifications in the water sediment mixture and global bed material continuity equations as well as of the asynchronous solution procedure for aggradation processes this paper presents the results of an extended study along this line highlighting the impacts on both aggradation and degradation processes simplifications in the continuity equations for the water sediment mixture and bed material are found to have negligible effects on degradation this is however in contrast to aggradation processes in which the errors purely due to simplified continuity equations can be significant transiently the asynchronous solution procedure is found to entail appreciable inaccuracy for both aggradation and degradation processes further the asynchronous solution procedure can render the physical problem mathematically ill posed by invoking an extra upstream boundary condition in the supercritical flow regime finally the impacts of simplified continuity equations and an asynchronous solution procedure are shown to be comparable with those of largely tuned friction factors indicating their significance in calibrating numerical river models it is concluded that the coupled system of complete governing equations needs to be synchronously solved for refined modeling of alluvial rivers

estimation of strong ground motion from the great 1964 mw 9 2 prince william sound alaska earthquake we are generating physically plausible near field synthetic ground motions for the great 1964 prince william sound alaska earthquake compatible with available seismological data tectonic information and eyewitness accounts the first objective of this study is the simulation of the low frequency i e f 0 03 hz strong ground motions on selected locations and on a dense grid of observation points extending over the shallow dipping causative fault of the 1964 alaska earthquake in order to accomplish this task we are utilizing the slip model proposed by johnson et al 1996 based on a joint inversion of tsunami waveforms and geodetic data the calculations are carried out using the discrete wavenumber representation method bouchon and aki 1977 bouchon 1979 and the generalized transmission and reflection coefficient technique luco and apsel 1983 the second objective of this study is the reconstruction of the strong ground motion time histories and response spectra that the city of anchorage experienced during the 1964 alaska earthquake the low frequency i e f 0 03 hz ground motions are generated using the methodology described previously the intermediate frequency i e 0 03 f 0 50 hz ground motions are simulated by convolving green s functions generated by the discrete wavenumber representation method with far field radiation pulses of circular cracks sato and hirasawa 1973 dong and papageorgiou 2002a the high frequency i e 0 5 f 8 0 hz ground motions are simulated using the stochastic modeling approach the three independently derived ground motion components are then properly combined to generate synthetic broadband ground motion time histories and response spectra for the city of anchorage due to the 1964 prince william sound earthquake the third objective of this study is the validation of the synthetic strong ground motions for the 1964 alaska earthquake against observed tectonic deformation ground motion estimates inferred from descriptions of structural damage and eyewitness accounts in summary the analysis presented in this study contributes to a better understanding of the seismological aspects of the 1964 alaska earthquake and provides synthetic time histories and response spectra for engineering applications compatible with all available information i e seismological tectonic and eyewitness accounts it should be noted however that the generated strong ground motions are not necessarily unique nor do they reflect the entire uncertainty that characterizes the problem under investigation

bed scouring downstream of hydraulic structures under steady flow conditions experimental analysis of space and time scales and implications for mathematical modeling abstract sediment transport and bed deformation in alluvial rivers are space and time dependent the knowledge of the space and time scales can be helpful for the definition of predictive procedures of an alluvial reach response to changing boundary conditions in this work attention is paid to scouring process occurring downstream of the rigid basement of a hydraulic structure the analysis is focused on transient bed profiles which are determined under steady flow conditions by a decrease of the upstream sediment transport rate in particular the paper is aimed at improving understanding of the space and time scales required by the alluvial system to reach the equilibrium conditions for this purpose movable bed runs are carried out in a straight laboratory channel for two values of the water discharge during each run the longitudinal bed profiles are measured at different times based on experimental data spatial scale factors of the bed scouring and of the bed load transport to reach the equilibrium conditions are defined particularly it is found that the scour length varies especially during the first evolution phase and then it oscillates around of a mean value that is about 40 of the channel reach interested by the phenomenon under consideration an expression is found for the adaptation coefficient which allows the estimation of the spatial delay of the bed load transport rate using both the collected data and literature data an expression defining the time scale of scouring is deducted according to this expression the non dimensional time scale is related to shields parameter through an exponential law then by the help of a 1 d numerical model previously developed by the writer the implications for choosing the spatial and temporal resolutions on which numerical results depend significantly are shortly discussed the results show that the time and space scales which represent physical constraints of the spatial and temporal resolutions need to be properly defined in order to simulate the scouring process evolution

three dimensional simulation of a magnitude 7 75 earthquake on the san andreas fault simulation of 2 minutes of long period ground motion in the los angeles area with the use of a three dimensional finite difference method on a parallel supercomputer provides an estimate of the seismic hazard from a magnitude 7 75 earthquake along the 170 kilometer section of the san andreas fault between tejon pass and san bernardino maximum ground velocities are predicted to occur near the fault 2 5 meters per second and in the los angeles basin 1 4 meters per second where large amplitude surface waves prolong shaking for more than 60 seconds simulated spectral amplitudes for some regions within the los angeles basin are up to 10 times larger than those at sites outside the basin at similar distances from the san andreas fault

multiple time scales of fluvial processes with bed load sediment and implications for mathematical modeling fluvial bed load transport is often considered to assume a capacity regime exclusively determined by local flow conditions but its applicability in naturally occurring unsteady flows remains to be theoretically justified in addition mathematical river models are often decoupled being based on simplified conservation equations and ignoring the feedback impacts of bed deformation to a certain extent so far whether the decoupling could have considerable impacts on the fluvial processes with bed load transport remains poorly understood this paper presents a theoretical investigation of both issues the multiple time scales of fluvial processes with bed load sediment are evaluated to examine the applicability of bed load transport capacity and decoupled models numerical case studies involving active bed load transport by highly unsteady flows complement the analysis of the time scales it is found that bed load transport can sufficiently rapidly adapt to capacity in line with local flow because sediment

modelling basin effects on earthquake ground motion in the santiago de chile basin by a spectral element code summary simulations of strong ground motion within the santiago de chile metropolitan area were carried out by means of 3 d deterministic wave propagation tool based on the spectral element method the simulated events take into account the pronounced interface between the low velocity sedimentary basin and the bedrock as well as topography of the area to verify our model we simulated a regional earthquake recorded by a dense network installed in the city of santiago for recording aftershock activity after the 2010 february 27 maule main shock the results proof the alluvial basin amplification effects and show a strong dependence of spectral amplification in the basin on the local site conditions moreover we studied the seismic response due to a hypothetical mw 6 0 event occurring along the active san ramon fault which is crossing the eastern edge of the city the scenario earthquakes exhibit that an unfavourable interaction between fault rupture radiation mechanism and complex geological and topographic conditions in the near field region may give rise to large values of peak ground velocity in the basin finally 3 d numerical predictions of ground motion are compared with the one computed according to ground motion prediction equations selected among the next generation attenuation relationships in terms of ground motion peak values and spectral acceleration the comparison underlines that the 3 d scenario simulations predict a significantly higher level of ground motion in the santiago basin especially over deep alluvial deposits moreover also the location of the rupture nucleation largely influences the observed shaking pattern

1d finite volume model of unsteady flow over mobile bed summary a one dimensional 1d finite volume method fvm model was developed for simulating unsteady flow such as dam break flow and flood routing over mobile alluvium the governing equation is the modified 1d shallow water equation and the exner equation that take both bed load and suspended load transport into account the non equilibrium sediment transport algorithm was adopted in the model and the van rijn method was employed to calculate the bed load transport rate and the concentration of suspended sediment at the reference level flux terms in the governing equations were discretised using the upwind flux scheme harten et al 1983 hll and hllc schemes roe s scheme and the weighted average flux waf schemes with the double minmod and minmod flux limiters the model was tested under a fixed bed condition to evaluate the performance of several different numerical schemes and then applied to an experimental case of dam break flow over a mobile bed and a flood event in the rillito river tucson arizona for dam break flow over movable bed all tested schemes were proved to be capable of reasonably simulating water surface profiles but failed to accurately capture the hydraulic jump the waf schemes produced slight spurious oscillations at the water surface and bed profiles and over estimated the scour depth when applying the model to the rillito river the simulated results generally agreed well with the field measurements of flow discharges and bed elevation changes modeling results of bed elevation changes were sensitive to the suspended load recovery coefficient and the bed load adaptation length which require further theoretical and experimental investigations

source process of the 1995 kobe earthquake determination of spatio temporal slip distribution by bayesian modeling the kobe hyogo ken nanbu earthquake ms 6 8 occurred on 16 january 1995 in western japan bringing about a tremendous disaster we constructed its source model by determining a spatio temporal slip distribution using strong motion seismograms recorded at a number of stations near the hypocenter the source area is expressed using both a rough and a detailed subfault discretization system and a source time function expanded with a finite number of basis functions at each subfault is determined to perform stable inversions with many parameters we construct a bayesian model with unknown hyperparameters incorporating prior constraints on the smoothness of spatio temporal slip distribution in the observation equation using akaike s bayesian information criterion abic the optimal set of hyperparameters are objectively determined from observed data which enables us to uniquely determine a spatio temporal slip distribution after rough analysis in which the actual rupture area is estimated as 45 20 km we carried out a detailed analysis with a finer subfault discretization system 5 5 km in our final source model most of the slip exists beneath awaji island and the rupture below the city of kobe where the damage was most serious is relatively smaller the large slips of about 2 m in the shallowest subfaults located southwest of the hypocenter correspond to the surface offsets observed along the nojima fault the overall focal mechanism of the source is right lateral strike slip with a small thrust component while total seismic moment is 2 0 1019 nm the source time functions at shallow subfaults show a longer duration than those at deeper ones being hypothesized to represent a possible combined effect of low rupture propagation velocity and varying friction behavior in shallow regions of crust

network scale dynamics of grain size sorting implications for downstream fining stream profile concavity and drainage basin morphology we explore the link between channel bed texture and river basin concavity in equilibrium catchments using a numerical landscape evolution model theory from homogeneous sediment transport predicts that river basin concavity directly increases with bed sediment size if the effective grain size on a river bed governs its concavity then natural phenomena such as grain size sorting and channel armouring should be linked to concavity we examine this hypothesis by allowing the bed sediment texture to evolve in a transport limited regime using a two grain size mixture of sand and gravel downstream fining through selective particle erosion is produced in equilibrium as the channel bed texture adjusts downstream so does the local slope our model predicts that it is not the texture of the original sediment mixture that governs basin concavity rather concavity is linked to the texture of the sorted surface layer two different textural regimes are produced in the experiments a transitional regime where the mobility of sand and gravel changes with channel bed texture and a sanddominated region where the mobility of sand and gravel is constant the concavity of these regions varies depending on the median gravel or sand grain size erosion rate and precipitation rate the results highlight the importance of adjustments in both surface texture and slope in natural rivers in response to changes in fluvial and sediment inputs throughout a drainage network this adjustment can only be captured numerically using multiple grain sizes or empirical downstream fining rules copyright 2004 john wiley sons ltd

synthetic hybrid broadband seismograms based on insar coseismic displacements abstract conventional acceleration records do not properly account for the observed coseismic ground displacements thus leading to an inaccurate definition of the seismic demand needed for the design of flexible long period structures large coseismic displacements observed during the 27 february 2010 maule earthquake suggest that this effect should be included in the design of flexible structures by modifying the design ground motions and spectra considered consequently green s functions are used herein to compute synthetic low frequency seismograms that are consistent with the coseismic displacement field obtained from interferometry using synthetic aperture radar sar images in this case the coseismic displacement field was determined by interfering twenty sar images of the advanced land observation satellite alos palsar satellite taken between 12 october 2007 and 28 may 2010 these images cover the region affected by the 2010 m w 8 8 maule earthquake synthetic broadband seismograms are built by superimposing the low pass filtered synthetic low frequency seismograms with high frequency strong motion data the broadband seismograms generated are then consistent with the coseismic displacement field and the high frequency content of the earthquake a sensitivity analysis is performed using three different fault and slip parameters the rupture velocity the corner frequency and the slip rise time results show that the optimal corner frequency of the low pass filter f c 1 t c leads to a trade off between acceleration and displacement accuracy furthermore spectral response for long periods say t 8 s is relatively insensitive to the value of t c whereas shorter periods are strongly dependent on both the slip rise time and t c in general larger displacements consistent with coseismic data are obtained using this technique instead of digitally processing the acceleration ground motion records

estimates of regional and local strong motions during the great 1923 kanto japan earthquake ms 8 2 part 2 forward simulation of seismograms using variable slip rupture models and estimation of near fault long period ground motions abstract this article addresses the forward simulation of regional and local strong motions from the 1923 kanto japan earthquake ms 8 2 using two variable slip rupture models the wald and somerville 1995 slip model ws slip model derived from geodetic and teleseismic data and a resampled version of the takeo and kanamori 1992 slip model tk slip model that was obtained from the forward simulation of the ewing seismoscope record at hongo hng epicentral distance r 60 km green9s functions are calculated using flat layered velocity models for specific source receiver paths which were developed in our first article sato et al 1998 for regional stations sendai r 350 km and gifu r 220 km the ws slip model provides a much better match to the waveform data than the tk slip model for local station hng the first 40 sec of the n77 e imamura seismogram is successfully reproduced by both of the slip models although the arrivals are delayed in the tk slip model the large amplitude long duration long period 13 sec later phases in the southwest component ewing seismogram are not reproduced by either of the slip models our results suggest that the ws slip model gives a better representation of the overall rupture process of the 1923 event than the tk slip model does near fault long period ground motions calculated at several stations using the ws slip model suggest that the motions at hng were not the largest in the tokyo metropolitan area during the 1923 event in addition we estimate that the ground motions near the southern margin of the fault plane were significantly larger than the recorded near fault motions of recent magnitude 7 earthquakes such as northridge and kobe for periods longer than several seconds this suggests that design codes based on the experience of these recent events may not adequately describe the long period response expected during a magnitude 8 earthquake

crustal structure of the lomonosov ridge and the fram and makarov basins near the north pole reversed refraction surveys were conducted along and across the lomonosov ridge as part of the 1979 lomonosov ridge experiment interpretation of the strike profiles indicates a 5 km thick upper crustal layer with a velocity of 4 7 km s overlying a 15 to 20 km thick layer of 6 6 km s material an upper mantle velocity of 8 3 km s is indicated by a few pn arrivals high amplitude reflection events recorded from this boundary can be successfully modeled by a transition zone of rapidly changing velocity over a depth interval of 5 km ray trace modeling of the dip profiles suggests a root structure extending to about 28 km depth flanked by crust thinning to a depth near 13 km beneath the makarov basin and a more gradual thinning to near 16 km beneath the fram basin the similarity between the crust of the lomonosov ridge and that beneath the barents and kara seas supports the suggestion that the ridge is a slice rifted from the baltic shelf

one dimensional numerical modeling of sediment transport and bed deformation in open channels 1 a one dimensional numerical model for simulating unsteady flow and sediment transport in open channels is presented and tested the flow hydrodynamics is represented by the shallow water equations and the bed morphodynamics is represented by the exner equation and an additional equation describing the nonequilibrium sediment transport sediment size distribution is represented by the median grain diameter and the standard deviation instead of the usual modeling with multiple particle size classes various methods for computing bed elevation changes at a cross section due to erosion or deposition of sediment are proposed and tested including an innovative approach that relates the spatial pattern of erosion and deposition rates to boundary shear stress distribution which is calculated by the merged perpendicular method an explicit finite difference scheme is employed for solving the water and sediment governing equations the pertinence of the model is examined for two hypothetical cases the model is then tested on one set of laboratory experiments on bed degradation under steady flow showing excellent model data fit and indicating that incorporating a nonequilibrium sediment transport equation into the model structure is an important element in reproducing the bed degradation process finally the model is applied to simulate the morphological changes taking place in the ha ha river quebec after the failure of the ha ha dyke on july 1996 relevant results can be obtained in terms of changes in longitudinal bed profile and cross sectional geometry as well as water levels although some discrepancies are obtained between the simulated and surveyed cross sectional geometries mainly because bank failure and channel widening are not modeled

the 1923 kanto earthquake reevaluated using a newly augmented geodetic data set 1 this study revisits the mechanism of the 1923 ms 7 9 kanto earthquake in japan we derive a new source model and use it to assess quantitative and qualitative aspects of the accommodation of plate motion in the kanto region we use a new geodetic data set that consists of displacements from leveling and angle changes from triangulation measurements obtained in surveys between 1883 and 1927 two unique aspects of our analysis are the inclusion of a large number of second order triangulation measurements and the application of a correction to remove interseismic deformation the geometry of the fault planes is adopted from a recent seismic reflection study of the kanto region we evaluate the minimum complexity necessary in the model to fit the data optimally our final uniform slip elastic dislocation model consists of two adjacent 20 dipping low angle planes accommodating reverse dextral slip of 6 0 m on the larger eastern plane and 9 5 m on the smaller western plane with azimuths of 163 and 121 respectively the earthquake was located in the sagami trough where the philippine sea plate subducts under honshu compared to the highly oblique angle of plate convergence the coseismic slip on the large fault plane has a more orthogonal orientation to the strike of the plate boundary suggesting that slip partitioning plays a role in accommodation of plate motion what other structure is involved in the partitioning is unclear uplift records of marine coastal terraces in sagami bay document 7500 years of earthquake activity and predict average recurrence intervals of 400 years for events with vertical displacement profiles similar to those of the 1923 earthquake this means that the average slip deficit per recurrence interval is 50 of the relative plate convergence these findings of plate motion partitioning and slip deficit lead us to suggest that instead of a simple recurrence model with characteristic earthquakes additional mechanisms are necessary to describe the accommodation of deformation in the kanto region so far obvious candidates for these alternative mechanisms have not been discovered

numerical simulation of widening and bed deformation of straight sand bed rivers ii model evaluation in this paper the numerical model presented in the companion paper is tested and applied assessment of model accuracy was based on two approaches first predictions of evolution of a 13 5 km reach of the south fork of the forked deer river in west tennessee were compared to observations over a 24 yr period results suggest that although the model was able to qualitatively predict trends of widening and deepening quantitative predictions were not reliable simulated widths and depths were within 15 of the corresponding observed values but observed change in these parameters at the study sites were also close to these values simulated rates of depth adjustment were within 15 of observed rates but observed rates of channel widening at the study sites were approximately three times those simulated by the model in the second approach the model was used to generate relationships between stable channel width and bank full discharge the model was able to successfully replicate the form of empirically

an analysis of simulated and observed blast records in the salt lake basin we have simulated 0 2 to 1 2 hz 3d elastic wave propagation in the salt lake basin from a blast at a nearby open pit mine a fourth order staggered grid finite difference method was used to simulate the blast in a two layer basin model 58 43 9 km consisting of semiconsolidated sediments up to 1 3 km thick surrounded by bedrock data from four blasts in the mine pit recorded by a network of 10 digital three component instruments were compared to the results of the simulation the simulation reproduces the overall pattern of ground motion amplification at basin sites relative to a rock site as measured by ratios of peak particle velocities cumulative kinetic energies and spectral magnitudes considering the simple two layer basin model used in the 3d simulation this finding suggests that the deep 3d basin structure significantly contributes to low frequency ground motion amplification in the salt lake basin 1 1 effects of a near surface layer of low velocity unconsolidated sediments p and s wave velocities of 1 65 and 0 41 km sec respectively that at soil sites along the profile increase the peak particle velocities by up to a factor of 3 and significantly increase the ground motion durations 2 2 attenuation in the sediments which greatly diminishes the ground motion durations on the synthetic seismograms when parameterized by realistic values of the quality factor q 20 for soil sites and 35 for bedrock sites 3 3 2d topographic scattering which increases the peak particle velocities by up to a factor of 2 and increases the signal durations for sites along the profile compared to the records from the simple two layer 3d simulation the records from a 2d p sv wave simulation that includes processes 1 through 3 provide a better match to the blast data especially the observed durations of shaking at five of the six stations along the profile the 2d simulation reproduces the normalized radial and vertical peak particle velocities to within a factor of 2 and the normalized cumulative kinetic energies and spectral amplitudes on these components to within generally a factor of 3 our results suggest that deep basin resonance reverberations in the near surface low velocity layer attenuation and topographic scattering significantly influence site amplification in the salt lake basin future studies of site amplification in the salt lake basin should include the effects of all of these mechanisms

low frequency 3d wave propagation modeling of the 12 may 2008 mw 7 9 wenchuan earthquake the seismic potential of southern china is associated with the collision between the indian and the eurasian plates this is manifested in the western sichuan plateau by several seismically active systems of faults such as the longmen shan the seismicity observed on the longmen shan fault includes recent events with magnitudes of up to 6 5 and the one of 12 may 2008 mw 7 9 wenchuan earth quake herewith as part of an ongoing research program a recently optimized three dimensional 3d seismic wave propagation parallel finite difference code was used to obtain low frequency 0 3 hz 3d synthetic seismograms for the wenchuan earthquake the code was run on kanbalam universidad nacional autonoma de mexico mexico and hector uk national supercomputing service supercompu ters the modeling included the u s geological survey 40 315 km 2 kinematic description of the earthquake s rupture embedded in a 2400 1600 300 km 3 phys ical domain spatially discretized at 1 km in the three directions and a temporal dis cretization of 0 03 s the compression and shear wave velocities and densities of the geologic structure used were obtained from recently published geophysical studies performed in the sichuan region the synthetic seismograms favorably compare with the observed ones for several station sites of the seismological and accelerographic networks of china such as mzq gya and tiy located at about 90 500 and 1200 km respectively from the epicenter of the wenchuan event moreover the com parisons of synthetic displacements with differential radar interferometry dinsar ground deformation imagery as well as of maximum velocity synthetic patterns with mercalli modified intensity isoseist of the 2008 wenchuan earthquake are acceptable 3d visualizations of the propagation of the event were also obtained they show the source rupture directivity effects of the mw 7 9 wenchuan event our results partially explain the extensive damage observed on the infrastructure and towns located in the neighborhood of the wenchuan earthquake rupture zone

three dimensional simulations of ground motions in the san bernardino valley california for hypothetical earthquakes on the san andreas fault three dimensional finite difference simulations of elastic waves in the san bernardino valley were performed for two hypothetical earthquakes on the san andreas fault a point source with moment magnitude m5 and an extended rupture with m6 5 a method is presented for incorporating a source with arbitrary focal mechanism in the grid synthetics from the 3 d simulations are compared with those derived from 2 d vertical cross section and 1 d flat layered models the synthetic seismograms from the 3 d and 2 d simulations exhibit large surface waves produced by conversion of incident s waves at the edge of the basin seismograms from the flat layered model do not contain these converted surface waves and underestimate the duration of shaking the seismograms from the 3 d simulations have larger amplitude coda than do the seismograms from the 2 d case because of the presence of off azimuth surface wave arrivals in the 3 d simulations that are not included in the 2 d simulations snapshots of the wavefield of the 3 d simulation show that these off azimuth arrivals represent surface waves reflected from the edges of the basin the anelastic attenuation of the sediments is a key parameter controlling the overall duration of motion some of the coda energy at rock sites near the basin edges represents leakage of surface wave energy out of the basin for the m6 5 earthquake simulation the largest ground velocities occur where surface waves reflected from the edge of the basin interfere constructively with the trapped waves that follow the direct s wave maps of maximum ground velocity are produced for two directions of rupture propagation the largest velocities occur in localized portions of the basin the location of the largest velocities changes with the rupture propagation direction contours of maximum shaking are also dependent on asperity positions and radiation pattern

a 1 d morphodynamic model of postglacial valley incision chilliwack river is typical of many cordilleran valley river systems that have undergone dramatic holocene degradation of valley fills that built up over the course of pleistocene glaciation downstream controls on base level mainly blockage of valleys by glaciers led to aggradation of significant glaciofluvial and glaciolacustrine valley fills and fan deposits subsequently incised by fluvial action models of such large scale long term degradation present a number of important challenges since the evolution of model parameters such as the rate of bedload transport and grain size characteristics are governed by the nature of the deposit sediment sampling in the chilliwack valley reveals a complex sequence of very coarse to fine textural modes we present a 1 d numerical morphodynamic model for the river floodplain system tailored to conditions in the valley the model is adapted to dynamically adjust channel width to optimize sediment transporting capacity and to integrate relict valley fill material as the channel incises through valley deposits sensitivity to model parameters is studied using four principal criteria profile concavity rate of downstream grain size fining bed surface sand content and the timescale to equilibrium model results indicate that rates of abrasion and coarsening of the grain size distributions exert the strongest controls on all of the interrelated model performance criteria while there are a number of difficulties in satisfying all model criteria simultaneously results indicate that 1 d models of valley bottom sedimentary systems can provide a suitable framework for integrating results from sediment budget studies and chronologies of sediment evacuation established from dating

simulation of long period ground motion near a large earthquake we estimated the possible range of long period ground motion for sites located on a soft sedimentary basin in the immediate vicinity of a large earthquake since many large cities in the world e g los angeles san francisco and tokyo where many large structures have been recently constructed are located in this type of environment a better understanding of long period ground motion is becoming increasingly important our objective is to estimate the possible range of long period ground motion rather than ground motion for a specific fault model we computed ground motion time series and pseudo velocity response spectra pvs for more than 5 000 models for the 1923 kanto japan earthquake m w 7 9 using 180 slip distributions eight rupture geometry and rupture velocities ranging from 1 5 to 3 0 km sec two seismograms recorded in tokyo during the 1923 kanto earthquake are used for comparison the response spectra computed using seismologically reasonable sets of source parameters for the 1923 kanto earthquake vary by more than an order of magnitude at periods of 10 to 13 sec they range from 25 to 170 cm sec in tokyo for some combinations of model parameters the response spectra exhibit peaks in the range of 10 to 13 sec many of the computed response spectra have peaks at periods longer than 10 sec which is considerably longer than the dominant period 6 to 8 sec estimated from studies of small earthquakes and microtremor measurements thus the dominant period of the subsurface structure determined locally may not be representative of the dominant period of ground motion from a nearby large earthquake which is controlled by rupture directivity and source depth we performed a similar simulation for a hypothetical m w 7 5 earthquake located beneath the los angeles basin for a site just above the center of the fault the ground motion spectral amplitude at a period of 10 sec can vary from 50 to 350 cm sec this range though very large is what is expected for a seismologically plausible range of source parameters

morphology and structure of the lomonosov ridge arctic ocean the lomonosov ridge is a band of continental crust that stretches across the arctic ocean and separates the mesozoic amerasian basin from the cenozoic eurasian basin from about 87 n north of greenland across the pole to about 86 n the lomonosov ridge is a single highstanding blocky ridge with minimum depths of 950 1400 m south of 86 n on the siberian side the ridge breaks up into a series of ridges spread over a width of about 200 km in this region a highstanding blocky ridge with minimum depths of 650 1400 m bounds the eurasian basin and continues to the siberian continental margin this ridge is continuous with the single ridge making up the lomonosov ridge toward north america and is the former outermost continental shelf of eurasia bounding the amerasian basin the eurasian basin margin of the lomonosov ridge consists of a series of rotated fault blocks stepping down to the basin that result from nearly orthogonal rifting to form the eurasian basin no rotated fault blocks are observed on the amerasian basin margin of the lomonosov ridge on the amerasian basin side marvin spur a linear ridge separated from lomonosov ridge by a deep basin parallels lomonosov ridge on the north american side of the pole at the bend in the lomonosov ridge near the north pole marvin spur continues along strike across the makarov basin south of 86 n toward siberia a continuous outer ridge makes up the amerasian basin edge of the lomonosov complex with a series of basins and ridges between it and the former eurasian shelf the outer ridge marks an abrupt boundary between the lomonosov ridge complex and the apparently oceanic crust of the makarov basin the outer ridge and marvin spur very closely follow small circles about a pole located on the mackenzie delta the observed structure on the amerasian basin side of the lomonosov ridge is analogous to that observed at well studied shear margins and supports rotational models for the development of the amerasian basin

modeling non uniform sediment fluvial process by characteristics method this paper presents a numerical model based on a multimode characteristics method for fully coupled simulation of water and sediment movement in mobile bed alluvial channels with nonuniform bed materials along with the characteristics the temporal evolutions of flow depth and velocity bed elevation and bed material composition of a well defined river reach with proper boundary conditions can be simultaneously determined from the results of the test runs the proposed model provides useful information about the interactions among disturbance waves of different orders of magnitude and their influence on the formation of flow field bed topography and bed material composition such information cannot be easily obtained from finite difference methods

morphodynamic responses to the deep water harbor development in the caofeidian sea area china s bohai bay vast bay type tidal inlets can be found along the coastal zones of china they are generally suitable for deep water channels and large harbors because of the presence of large water depth and good mooring conditions the deep channel in front of the head of caofeidian island in bohai bay china is a typical bay type tidal inlet system the tidal current a type of reverse flow makes the key contribution to maintain the deep water depth the co action of waves and tidal currents is the main dynamic force for sediment motion waves have significant influence on the sediment concentration based on the characteristics of waves tidal currents sediment and seabed evolution in caofeidian sea area a 2d mathematical model for sediment transport under influence of waves and tidal currents is developed to study the development schemes of the caofeidian harbor the model has been verified for spring and neap tides in winter as well as in summer of 2006 the calculated tidal stages flow velocities flow directions and sediment concentrations at 15 stations are in good agreement with the observations furthermore the calculated data on pattern and magnitude of sedimentation and erosion in the related area agree well with the observations this model has been used to study the effects of the reclamation scheme for caofeidian harbor on the hydrodynamic environment sediment transport and morphological changes attentions are paid to the project inducing changes of flow velocities and morphology in the deep channel at the south side of caofeidian foreland in the laolonggou channel and in various harbor basins the conclusions can provide the important foundation for the protection and use of bay type tidal inlets and the development of harbor industry

physically based model of downstream fining in bedrock streams with lateral input 1 bed load particles in bedrock streams receiving lateral input from hillslopes may or may not show a clear monotonic pattern of size reduction in the downstream direction both abrasion and selective sorting may play important roles in generating downstream fining the objective of this study is to develop a physically based model of downstream fining in bedrock streams with lateral input based on both processes a surface based gravel transport relation for the size mixture is employed to account for the effect of selective sorting differential transport while the model produces silt and sand by abrasion it is also assumed to loosely capture particle fracturing via a lumped abrasion coefficient embodied in sternberg s law the model is here tested against field data from vieux habitants river in guadeloupe island which is located in the caribbean sea the river shows clear downstream fining and this pattern is captured reasonably well by the model the model results indicate that abrasion including fracturing is solely responsible for the downstream fining pattern for most of the study reach of the vieux habitants river sensitivity analysis of the model has also been performed the model results suggest that in general selective sorting by differential transport can play a role in downstream fining only in cases of streams with relatively fine gravel sizes and lower slopes the results also indicate that abrasion including fracturing and selective sorting can be equally important for downstream fining in bedrock rivers the results also suggest that future work should explicitly consider fracturing comminution separately from abrasion wear rather than lumping them in a sternberg type coefficient

grain scale nonequilibrium sediment transport model for unsteady flow abstracta one dimensional 1d finite volume model is developed for simulating nonequilibrium sediment transport in unsteady flow the governing equations are the 1d mass and momentum conservation equations for sediment laden flow and the sediment continuity equation for both bed load and suspended load transport the rouse profile is modified to consider the nonequilibrium transport of suspended sediment the spatial lag between the instantaneous flow properties e g velocity bed shear stress and the rate of bed load transport in unsteady flow is quantified by using an adaptation length which is derived theoretically by applying the momentum principle in the bed load layer this new method for calculating the adaptation length is verified using data from several experiments and yields better results than other empirical formulas for a wide range of shear stress the nonequilibrium model is applied to simulate a series of laboratory dam break flows over erodible beds and the simulated results agree

reinterpretation by ray tracing of a transverse refraction seismic profile through the california sierra nevada part i abstract this study reanalyzes a refraction seismic profile from nts nevada to san francisco transverse to the high sierra nevada three models of the earth9s crust with an asymmetrical mountain root constructed by different authors are tested by the use of ray tracing model cqm carer et al 1970 with a maximum crustal thickness of 35 km centered about 50 km west of the crest of the sierra models a and b pakiser and brune 1980 with a mountain root extending to a depth of 55 km below the sierra in the latter guided and diffracted waves are used to explain seismic p n energy in the shadow zone of the root the preferred model a has a high velocity layer dipping from west to east in the upper crust while model b does not the present study demonstrates how fallacies in interpretation of complicated structures can occur if all ray types are not quantitatively traced the influence of the p wave gradient in the upper mantle on the length of the shadow zone is shown to be important and it is demonstrated that a modified cqm model explains the observed travel times when diffracted waves are included cqm does not however explain why the p n travel times on a separate refraction profile along the sierra nevada from a truckee earthquake are so great model b interprets the p n signals at 200 km as diffracted waves but the computed travel times do not fit the observations the dipping wave guide in model a does not work as expected and perhaps should be ruled out

routing graded sediments in streams formulations a one dimensional numerical model is developed for simulating the movement of well graded sediments through a stream network the model is based on the physical processes governing the mechanics of sediment movement in alluvial channels it incorporates the effect of sediment gradation on the stream s potential transport capacity it also accounts for the effect of particle exchange between the sediment load and the bed while simulating aggradation degradation and armoring of the bed the applicability of the model is restricted to noncohesive materials and relatively stable channel geometries any valid water routing algorithm can be used in simulating the movement of water

a more precise chronology of earthquakes produced by the san andreas fault in southern california improved methods of radiocarbon analysis have enabled us to date more precisely the earthquake ruptures of the san andreas fault that are recorded in the sediments at pallett creek previous dates of these events had 95 confidence errors of 50 100 calendar years new error limits are less than 23 calendar years for all but two of the dated events this greater precision is due to larger sample size longer counting time lower background noise levels more precise conversion of radiocarbon ages to calendric dates and better stratigraphic constraints and statistical techniques the new date ranges with one exception fall within the broader ranges estimated previously but our estimate of the average interval between the latest 10 episodes of faulting is now about 132 years variability about the mean interval is much greater than was suspected previously five of the nine intervals are shorter than a century three of the remaining four intervals are about two to three centuries long despite the wide range of these intervals a pattern in the occurrence of large earthquakes at pallett creek is apparent in the new data the past 10 earthquakes occur in four clusters each of which consists of two or three events earthquakes within the clusters are separated by periods of several decades but the clusters are separated by dormant periods of two to three centuries this pattern may reflect important mechanical aspects of the fault s behavior if this pattern continues into the future the current period of dormancy will probably be greater than two centuries this would mean that the section of the fault represented by the pallett creek site is currently in the middle of one of its longer periods of repose between clusters and sections of the fault farther to the southeast are much more likely to produce the next great earthquake in california the greater precision of dates now available for large earthquakes recorded at the pallett creek site enables speculative correlation of events between paleoseismic sites along the southern half of the san andreas fault a history of great earthquakes with overlapping rupture zones along the mojave section of the fault remains one of the more attractive possibilities

simulation of missouri river bed degradation the future course of bed degradation in the middle missouri river has been predicted using numerical simulation techniques the simulation required development of the new total load transport model tltm which incorporates the interdependence of friction factor and sediment transport through data based empirical relations tltm was implemented in a mathematical simulation model called ialluvial which computes quasi steady water and sediment flow in natural rivers having nonuniform bed sediments ialluvial also incorporates bed sediment sorting and armoring which are processes of fundamental importance to the future course of missouri river degradation ialluvial was first validated through simulation of the 1960 1980 severe degradation in the missouri river between sioux city iowa and omaha nebraska subsequently ialluvial was used to predict 1980 2000 degradation for several river management scenarios the simulations suggest that the worst of the degradation is now over and that it is the channelization rather than upstream regulation which is primarily responsible for the degradation a companion paper describes the details of ialluvial s armoring and sorting simulation procedures

3 d wave propagation in the los angeles basin for the whittier narrows earthquake abstract elastic wave propagation within and around the los angeles basin during the whittier narrows earthquake in 1988 is simulated with a 3 d finite difference method the model consists mainly of a sedimentary layer over the basement but lateral variations inside the sedimentary basin is also included to approximate observed variations in surface shear velocity the minimum shear velocity is 1 km sec on the surface and fairly reliable results are obtained up to 0 75 hz the total simulation lasts 26 sec our simulation can reproduce the general amplification pattern small east of the epicenter and large in the l a basin and the san fernando valley due to thick sediments of low velocity in these areas surface waves are generated by the primary s wave and trapped inside the basins in the southern part of the l a basin a distinct later phase delayed by 5 to 6 sec relative to the primary s wave is produced in our simulation which matches some strong motion records

a faulting model for the 1979 imperial valley earthquake by comparing synthetic particle velocities with the near source strong motion data we have constructed by trial and error a faulting model for the 1979 imperial valley earthquake the calculation of the synthetic seismograms takes into account the vertical inhomogeneity of the elastic parameters in the imperial valley and the spatial variation of the slip rate parameters on the fault plane the independent slip rate parameters are 1 the strike slip rate amplitude 2 the dip slip rate amplitude 3 the duration that slip rate is nonzero the rise time of the slip function and 4 the rupture time which determines when the slip rate is initiated our faulting model has the following principal features 1 faulting occurred on the imperial fault and on the brawley fault rupture on the brawley fault being triggered by rupture on the imperial fault 2 the imperial fault is a plane 35 km long and 13 km wide with a strike of 323 measured clockwise from north and a dip of 80 ne the brawley fault is a 10 km long and 8 km wide plane with a strike of 360 and a dip of 90 3 faulting on the imperial fault is primarily right lateral strike slip with a small component of normal dip slip in the sediments at its northern end the larger strike slip rates are generally confined between depths of 5 and 13 km with maximum values of about 1 0 m s the duration varies on the fault with a maximum of 1 9 s which is considerably shorter than the total time for the rupture to take place 4 the rupture velocity on the imperial fault is highly variable locally it exceeds the shear wave velocity and in one instance the compressional wave velocity the average rupture velocity though is less than the shear wave velocity 5 although the slip on the brawley fault contributes only about 4 of the total moment it greatly affects the ground motion at nearby stations 6 the total seismic moment is 6 7 1018 n m where the imperial fault contributes 6 4 1018 n m and the brawley fault contributes 2 7 1017 n m in the process of trying almost 300 faulting models we found that given the elastic parameters of the medium the synthetic seismograms were most sensitive to the specification of the rupture time although the slip rate amplitudes are linearly related to the data the rupture time and the duration are not the parameterization of the nonlinear variables has a strong effect on the generation of synthetic seismograms from a finite fault

prospects for larger or more frequent earthquakes in the los angeles metropolitan region far too few moderate earthquakes have occurred within the los angeles california metropolitan region during the 200 year long historic period to account for observed strain accumulation indicating that the historic era represents either a lull between clusters of moderate earthquakes or part of a centuries long interseismic period between much larger moment magnitude m w 7 2 to 7 6 events geologic slip rates and relations between moment magnitude average coseismic slip and rupture area show that either of these hypotheses is possible but that the latter is the more plausible of the two the average time between m w 7 2 to 7 6 earthquakes from a combination of six fault systems within the metropolitan area was estimated to be about 140 years

routing of heterogeneous sediments over movable bed model development a one dimensional numerical model of sediment routing is derived to simulate erosion transport and deposition of individual size density fractions in the bed material within a relatively straight nonbifurcating alluvial channel the reach of interest is subdivided into a number of longitudinal elements of varying width averaged properties during each time step flow depths and velocities in each element are determined from the gradually varied flow equation using the standard step method for backwater calculations the bedload transport rate of each size fraction is calculated from a modified bagnold equation implementing a novel approach that takes into consideration the effects of turbulent fluctuations in the bed shear stress critical shear stresses for entrainment of particles from the mixed bed are determined using relationships that treat grain protrusion and hiding the transport of particles in suspension is modeled using a convection diffusion sediment continuity equation either explicitly

three dimensional mathematical model of suspended sediment transport this paper presents the basic equations for a mathematical model of sediment laden flow in a nonorthogonal curvilinear coordinate system the equations were derived using a tensor analysis of two phase flow and incorporate a natural variable density turbulence model with nonequilibrium sediment transport correspondingly a free surface and the bottom sediment concentration are employed to provide the boundary conditions at the river surface and the riverbed the finite analytic method is used to solve the equations of mass and momentum conservation and also the transport equation for suspended sediment to demonstrate the method the sediment deposition for the three gorges project is considered the mathematical model specifies the boundary conditions for the inlet and outlet using data from physical model experiments the results for the mathematical model were tested against laboratory measurements from the physical model experiment good agreement and accuracy were obtained

numerical simulation of downstream fining by selective transport in gravel bed rivers model development and illustration a numerical model has been developed for the routing of gravel sized sediment along a river channel which is free to adjust both its long profile and surface texture hydraulic calculations use a step backwater approach and sediment transport is predicted with the method of parker 1990a which uses a low degree of size selectivity exchange of sediment between the surface and subsurface is described using the modified exner equation of parker and sutherland 1990 the model is applied to an idealized channel based on the highly concave allt dubhaig scotland in which fining by particle wear is minor the rapid downstream fining observed in this river is closely matched by model predictions after a time equivalent to 102 years under the present flow regime of the river the evolution of the fining pattern during the model run and associated changes in sediment transport and bed aggradation are described it is concluded that strong profile concavity can force rapid downstream fining even though bed load transport is only slightly size selective this run of the model serves as a basis for testing of the sensitivity of downstream fining to alternative choices of parameter values and boundary conditions which are summarized here and will be described in a subsequent paper

three dimensional finite difference simulations of long period strong motions in the tokyo metropolitan area during the 1990 odawara earthquake mj 5 1 and the great 1923 kanto earthquake ms 8 2 in japan utilizing a crustal velocity model that includes the complexity of the irregular subsurface structure of the kanto basin we have performed three dimensional 3d finite difference fd simulations of near source long period strong ground motions in the tokyo metropolitan area for the 1990 odawara mj 5 1 and the 1923 kanto ms 8 2 earthquakes constraints on the development of the 3d velocity model come from available geological and geophysical data as well as our previous 1d waveform modeling results sato et al 1998a the simulation of the moderate sized odawara earthquake demonstrates that the 3d velocity model works quite well at reproducing the recorded long period t 3 33 sec strong motions including basin generated surface waves for a number of sites located throughout the kanto basin region using this validated 3d model along with the variable slip rupture model of wald and somerville 1995 we then simulate the long period t 4 sec ground motions in this region for the 1923 kanto earthquake the simulation results for the 1923 event show that the largest ground motions occur east of the epicenter along the central and southern part of the boso peninsula these large motions arise from strong rupture directivity effects and are comprised of relatively simple source controlled pulses with a dominant period of about 10 sec north of the epicentral region in the tokyo area 3d basin generated phases are quite significant and these phases produce large amplitude late arriving pulses in the ground motions at station hongo hng which is the only site having digitized and restored near fault strong motion records for this event our 3d simulations compare quite well with the ground motions of the restored imamura seismogram for the restored ewing record our 3d simulations reproduce the phase and amplitude of the initial pulses of motion however the dominant period of the large amplitude later phases is noticeably shorter in the simulations about 5 to 6 sec than in the observation 13 sec these results suggest that the restored imamura seismogram may be a better representation of the gross features of the actual motion than the restored ewing seismogram although the first clipped and restored part of the imamura seismogram may still underestimate the strength of the actual motion

far source long period displacement response spectra in the po and venetian plains italy from 3d wavefield simulations abstract design elastic displacement spectra for seismic codes and zoning studies of seismic hazard for long period structures are becoming of utmost importance in modern earthquake engineering the increase of displacement based design approaches together with the availability of good quality digital strong motion data allow the creation of reliable spectral shapes for seismic design of up to 10 s nevertheless to characterize the site amplification effects during large levels of shaking additional studies are needed especially in deep sedimentary basins and plains that can be strongly excited by large amplitude long period waves data within deep basins is rare because accelerometric seismic networks are normally deployed on rock or stiff soil and modeling of waveforms is hence necessary for bridging this gap focusing on the numerical modeling of the 3d wavefield in 1d flat layered and 3d structures in the po and venetian plains northern italy and on earthquakes with magnitudes m 6 6 and hypocentral distances greater than 50 km in this study we 1 estimate the displacement response spectra drs from 1 to 10 s in the po and venetian plains 2 compare the drs from numerical simulations using flat layered and heterogeneous 3d models against the currently available uniform hazard drs for italy and 3 evaluate the influence of deep sediments on drs shape and thus on seismic codes finally 1d and 3d simulated drs are compared with drs obtained from recordings in the kanto basin where similar long period displacement is observed

terashake2 spontaneous rupture simulations of mw 7 7 earthquakes on the southern san andreas fault abstract previous numerical simulations terashake1 of large m w 7 7 southern san andreas fault earthquakes predicted localized areas of strong amplification in the los angeles area associated with directivity and wave guide effects from northwestward propagating rupture scenarios the terashake1 source was derived from inversions of the 2002 m w 7 9 denali alaska earthquake that source was relatively smooth in its slip distribution and rupture characteristics owing both to resolution limits of the inversions and simplifications imposed by the kinematic parameterization new simulations terashake2 with a more complex source derived from spontaneous rupture modeling with small scale stress drop heterogeneity predict a similar spatial pattern of peak ground velocity pgv but with the pgv extremes decreased by factors of 2 3 relative to terashake1 the terashake2 source excites a less coherent wave field with reduced along strike directivity accompanied by streaks of elevated ground motion extending away from the fault trace the source complexity entails abrupt changes in the direction and speed of rupture correlated to changes in slip velocity amplitude and waveform features that might prove challenging to capture in a purely kinematic parameterization despite the reduced pgv extremes northwest rupturing terashake2 simulations still predict entrainment by basin structure of a strong directivity pulse with pgvs in los angeles and san gabriel basins that are much higher than predicted by empirical methods significant areas of those basins have predicted pgv above the 2 probability of exceedance poe level relative to current attenuation relationships even when the latter includes a site term to account for local sediment depth and wave guide focusing produces localized areas with pgv at roughly 0 1 0 2 poe about a factor of 4 5 above the median in contrast at rock sites in the 0 100 km distance range the median terashake2 pgvs are in very close agreement with the median empirical prediction and extremes nowhere reach the 2 poe level the rock site agreement lends credibility to some of our source modeling assumptions including overall stress drop level and the manner in which we assigned dynamic parameters to represent the mechanical weakness of near surface material future efforts should focus on validating and refining these findings assessing their probabilities of occurrence relative to alternative rupture scenarios for the southern san andreas fault and incorporating them into seismic hazard estimation for southern california

numerical simulation of contraction scour in an open laboratory channel a finite volume computer code developed at the institute for hydromechanics university of karlsruhe has been used to calculate the flow and sediment transport in a laboratory channel with constriction and movable bed the flow is calculated by solving the fully three dimensional reynolds averaged navier stokes equations with k e turbulence model the bed deformation is obtained from an overall mass balance equation for sediment transport and the bed load transport is simulated with a nonequilibrium model the calculated results for flow and scour development in the laboratory channel are compared with experimental measurements the sensitivity of the simulated results to the nonequilibrian adaptation length parameter in the nonequilibrium bed load transport model is investigated systematically which represents the main contribution of this paper

inversion of long period p waves from great earthquakes along subduction zones abstract long period p waves from subduction zone earthquakes in the moment range from 7 1027to 8 1029dyn cm are analyzed using an iterative deconvolution method in addition to discrete subevents which effectively contribute to the observed seismograms the long period component of the moment rate function is derived with the constraint that the total seismic moment is equal to the moment determined from long period surface waves it is shown that great earthquakes can be described by several subevents with a duration of about 10 s which changes little from earthquake to earthquake in the above moment range the long period component of the moment rate function becomes larger for a greater earthquake the greatest earthquakes of mw 9 additionally involve subevents with another duration scale much longer than 10 s it is also shown that the local stress drop is 1 order of magnitude larger than the stress drop averaged over the entire fault plane the constancy of the local stress drop as well as the average stress drop holds among various magnitudes of earthquakes these observations suggest an essential similarity in the mode of dislocation distribution

a study on the response of a soft basin for incident s p and rayleigh waves with special reference to the long duration observed in mexico city abstract the responses of two types of soft basins for incident sh sv p and rayleigh waves in a 2 d elastic half space are investigated with special reference to the long duration of strong motions observed in mexico city during the michoacan mexico earthquake of 1985 first the difficulty for simple 1 d models to reproduce the later part of the accelerogram observed in mexico city is shown then the effect of a 2 d deep basin structure of a relatively large scale 10 km wide and 1 km deep and a moderate impedance ratio 2 5 is studied the results show that surface waves generated at the edges of the basin are clearly propagating inside the basin back and forth however the increase in duration by these surface waves is 20 sec at most introducing another much softer layer inside the basin we found that the calculated durations and envelop shapes become very similar to the observed ones because of the slowness of surface wave propagation these theoretical studies suggest that the exceptionally long duration observed in mexico city might be caused by a strong constructive interaction of soft surface layers with a deep basin structure beneath the city

process form interactions in unstable sand bed river channels a numerical modeling approach abstract a deterministic numerical model of bed deformation and channel widening which accounts for specific mechanisms of bank erosion and collapse is used to analyze morphological and flow energy parameters in adjusting sand bed channels for a range of simulated fluvial environments the model is based on a set of conservation and process equations solved in conjunction with a set of specific initial and boundary conditions simulated channels with a range of assumed boundary material characteristics were subjected to identical disturbances imposed by reducing the supply of sediment from upstream asymptotic reductions of the rate of energy dissipation energy slope and boundary shear stress were found to be unifying characteristics of channel adjustment in all simulations morphologic responses to an identical disturbance reduction of sediment supply from upstream with identical bed material d 50 1 mm and channel gradient s b 0 001 were diverse the relative magnitude of simulated widening versus simulated bed level change was greatest for sand bank channels and least for clay bank channels stable channel dimensions were attained most rapidly for silt bank channels where simulated adjustments of channel width were similar to simulated vertical adjustments because all components of total mechanical energy flow depth or pressure head bed elevation and channel gradient or datum head and flow velocity or velocity head decrease simultaneously each simulated channel subjected to the baseline disturbance had an initial width to depth ratio f of 13 5 asymptotic values of energy dissipation rate adjusted f values and time taken to reach equilibrium after the disturbance are shown to vary as a function of simulated environmental boundary conditions the importance of channel widening in controlling and reducing the flow depth of a given discharge and average boundary shear stress is highlighted for the silt and sand bank cases channel widening causes a shift from degradation to aggradation during adjustment because of delivery of sand sized sediments from failed bank material to the simulated channel

a review of the discrete wavenumber method we present a review of the discrete wavenumber dwn method the method introduced by bouchon and art 1977 allows the simple and accurate calculation of the complete green s functions for many problems in elastodynamics

numerical model of sediment pulses and sediment supply disturbances in mountain rivers sediment pulses in rivers can result from many mechanisms including landslides entering from side slopes and debris flows entering from tributaries artificial sediment pulses can be caused by the removal of a dam this paper presents a numerical model for the simulation of gravel bedload transport and sediment pulse evolution in mountain rivers a combination of the backwater and quasi normal flow formulations is used to calculate flow parameters gravel bedload transport is calculated with the surface based bedload equation of parker in 1990 the exner equation of sediment continuity is used to express the mass balance at different grain size groups and lithologies as well as the abrasion of gravel the river is assumed to have no geological controls such as bedrock outcrops and immobile boulder pavements the results of nine numerical experiments designed to study various key parameters relevant to the evolution of sediment pulses are reported here results of the numerical runs indicate that the evol

modeling three dimensional site response effects in the marina district basin san francisco california abstract loma prieta aftershock data recorded in the marina district of san francisco clearly show a large amplification in ground motion and a much longer duration of shaking relative to the response recorded at nearby rock sites for frequencies between 1 and 10 hz some of the amplification can be explained by the difference in impedance between the marina sites and the rock sites however 1d models underpredict the amplification in the range 1 to 3 hz and cannot account for the increased durations the available geologic information within the marina district indicates lateral variations in sediment thickness and composition our previous experience with modeling wave propagation in these types of basin environments has shown that these structures can greatly amplify and prolong the duration of the signals observed at sites within the basin in this study the seismic response of the marina basin is modeled with a 3d finite difference wave field simulation technique results from the numerical simulations at the basin sites indicate that the large amplitude arrivals following the direct s wave are surface waves traveling at relatively slow apparent velocities in general the surface waves contain the strongest recorded motions and produce the long duration of shaking observed at these sites in addition spectral ground motions from the 3d basin models do fairly well in reproducing the observed spectral amplification near 1 hz that is characteristic of the basin sites the simulation results suggest that focusing effects due to the geometry of the basin structure itself have a significant impact in determining the resonant periods at these basin sites

late pleistocene stratigraphy and micropaleontology of a part of the eurasian basin fram basin central arctic ocean during the 1979 lomonosov ridge experiment lorex 12 short gravity cores were collected from the fram basin part of the eurasian basin on the eastern flank of the lomonosov ridge sediments of these cores are organized into 11 lithologic units that constitute the first stratigraphy for any part of the deeper eurasian basin foraminifera are the same species that have been described elsewhere in the central arctic ocean but are abundant only in the uppermost part of the cores neogloboquadrina pachyderma is the most abundant species but the presence ofeponides tumidulus horvathi andstetsonia arctica in core ssk 2 provide a general chronologic framework for interpreting the fram basin sediment the stratigraphy a k is unique and is only partially correlated with other sediments of the north polar region including that of the adjacent lomonosov ridge and makarov basin amerasian basin differences in stratigraphies of the lomonosov area are interpreted to be at least in part the result of winnowing by turbidity currents and by currents crossing the ridge from the fram basin toward the makarov basin the sediment consists of silty lutites and sandy lutites as well as laminated lutites interpreted to have been deposited as a result of glacial marine and turbidite sedimentation these short cores document the same sedimentary processes in part of the arctic ocean east of the lomonosov ridge as have been previously reported for the western amerasian basin

a three dimensional simulation of seismic waves in the santa clara valley california from a loma prieta aftershock abstract the finite difference method is used to propagate elastic waves through a 3 d model of the santa clara valley an alluvium filled basin that underlies the city of san jose california the model was based on depth to bedrock information from water wells in the area the simulation corresponded to a region 30 east west by 22 north south by 6 depth km and contained about 4 million grid points synthetic seismograms from the simulation are accurate at frequencies up to 1 hz motions from a magnitude 4 4 aftershock of the loma prieta earthquake were modeled snapshots of ground motion and synthetic seismograms from the simulation are presented the simulation illustrates s to surface wave conversion at the edges of the basin and the large amplitude and long duration of ground motion in the basin compared to the surrounding rock love waves produced at the edge of the basin are the largest arrivals in the transverse synthetics because of the slow group velocity of the love waves sites near the center of the basin have longer durations of significant motions than basin sites near the valley edges sites near the center of the basin also show larger peak amplitudes on the transverse component array analysis of the synthetic seismograms indicates that love waves tend to propagate parallel to the eastern and western edges of the valley rayleigh waves are produced along the southern margin of the basin from incident s waves large radial motions occur where a rayleigh wave impinges on the northeast margin of the valley some rayleigh waves travel westward across the basin after being scattered from the eastern edge of the valley synthetic seismograms from the simulation have similar peak amplitudes as seismograms recorded by the sunnyvale dense array for this aftershock although the duration of the tranverse component is not matched by the synthetic seismogram using this basin model the simulation indicates that the love waves observed on the actual seismograms were produced by conversion of incident s waves at the southern margin of the santa clara valley 2 d simulations show how the s to love wave conversion is affected by the angle of incidence of the s wave and the sharpness of the velocity transition between the alluvium and bedrock as more accurate basin models are developed 3 d simulations should become valuable for predicting ground motions in sedimentary basins for future large earthquakes

one dimensional numerical model for nonuniform sediment transport under unsteady flows in channel networks in this study the proposed one dimensional model simulates the nonequilibrium transport of nonuniform total load under unsteady flow conditions in dendritic channel networks with hydraulic structures the equations of sediment transport bed changes and bed material sorting are solved in a coupling procedure with a direct solution technique while still decoupled from the flow model this coupled model for sediment calculation is more stable and less likely to produce negative values for bed material gradation than the traditional fully decoupled model the sediment transport capacity is calculated by one of four formulas which have taken into consideration the hiding and exposure mechanism of nonuniform sediment transport the fluvial erosion at bank toes and the mass failure of banks are simulated to complement the modeling of bed morphological changes in channels the tests in several cases show that the present model is capable of predicting sediment transport bed changes and bed material sorting in various situations with reasonable accuracy and reliability

gradation effects in sediment transport to determine the effects of grain size and density gradation in oscillatory sheet flow experiments are conducted in an oscillating water tunnel a formal derivation of a schematised transport model shows that the transport rates per sediment fraction can be determined with and without the assumption of an active layer a technique that measures sediment composition from natural occurring radionuclides is used to determine the transport rates without that assumption of an active layer the measurements on total sediment transport rates and suspended sediment concentrations show that effects of gradation are present the effects of size gradation are mainly in the increased transport rates of the coarse fraction with respect to the uniform coarse material and the availability at the bed under similar conditions the experiments on density graded sediments indicate that total mass transport rates are larger than the mass transport rates of quartz material whilst the transport rates of the quartz fraction show that this fraction is not hindered by the availability at the bed

modeling nonuniform suspended sediment transport in alluvial rivers problems and difficulties in modeling sediment transport in alluvial rivers arise when one uses the theory of equilibrium transport of uniform sediment to simulate riverbed variation a two dimensional mathematical model for nonuniform suspended sediment transport is presented to simulate riverbed deformation through dividing sediment mixture into several size groups in which the sediment particles are thought to be uniform the nonuniformity and the exchange between suspended sediment and bed material are considered the change of concentration along the flow direction size redistribution and cross sectional bed variation can then be described reasonably well by the model in simulating the flow field with big dry wet flats moving boundary problems are solved very well by introducing a so called finite slot technique verification with laboratory data shows that the model has a good ability to simulate channel bed variations last the model was applied to a real alluvial river system variables such

a well posed alternative to the hirano active layer model for rivers with mixed size sediment the active layer model hirano 1971 is frequently used for modeling mixed size sediment river morphodynamic processes it assumes that all the dynamics of the bed surface are captured by a homogeneous top layer that interacts with the flow although successful in reproducing a wide range of phenomena it has two problems 1 it may become mathematically ill posed which causes the model to lose its predictive capabilities and 2 it does not capture dispersion of tracer sediment we extend the active layer model by accounting for conservation of the sediment in transport and obtain a new model that overcomes the two problems we analytically assess the model properties and discover an instability mechanism associated with the formation of waves under conditions in which the active layer model is ill posed numerical simulations using the new model show that it is capable of reproducing two laboratory experiments conducted under conditions in which the active layer model is ill posed the new model captures the formation of waves and mixing due to an increase in active layer thickness simulations of tracer dispersion show that the model reproduces reasonably well a laboratory experiment under conditions in which the effect of temporary burial of sediment due to bedforms is negligible simulations of a field experiment illustrate that the model does not capture the effect of temporary burial of sediment by bedforms

constraints on mantle viscosity based upon the inversion of post glacial uplift data from the hudson bay region summary we outline two parametrizations for post glacial relative sea level rsl histories associated with previously glaciated regions the first parametrization is based on a site dependent normalization of the rsl history while the second involves the estimate of a site dependent logarithm of the inverse decay time for the exponential like form which characterizes these histories both parametrizations are shown to yield data sets which are relatively insensitive to the details of the late pleistocene surface load history and therefore inferences of mantle viscosity based upon them will be particularly robust we apply the two parametrizations to consider the rsl record at a number of sites across the hudson bay region in this regard our inferences which are derived from both forward and inverse calculations are based upon the actual rsl age height pairs obtained by survey rather than the highly subjective set of rsl trends adopted in previous studies one of the main goals of the analysis is to assess the validity of a set of previously published and highly contradictory inferences of the radial profile of mantle viscosity based on the hudson bay rsl record forward analyses using models with isoviscous upper and lower mantle regions as adopted in the vast majority of previous analyses indicate that the parametrized versions of the rsl record in hudson bay excluding data from the cape henrietta maria site are best fitted by a lower mantle viscosity near 1021 pa s the same conclusion holds when data from only northern hudson bay are considered the rsl record in southern hudson bay is not self consistent if the error bars adopted herein are reasonable however the parametrized versions of the rsl curves from each site in this region can be reconciled by a model with a lower mantle viscosity somewhere in the rather moderate range 0 5 3 0 1021 pa s the value of 3 1021 pa s represents a lower bound on the lower mantle viscosity required to fit the rsl records at cape henrietta maria this record is characterized by a longer decay time than those associated with other sites in the data base this lower bound is in contrast with previous suggestions that the rsl record at cape henrietta maria requires a lower mantle viscosity of 30 1021 pa s inverse analyses described herein indicate that the rsl record from the entire hudson bay constrains the average viscosity in the radial region extending from the lower reaches of the upper mantle to mid lower mantle depths the inferences listed above are therefore more properly ascribed to this region rather than the entire lower mantle we have found that the data are sensitive to moderately deeper variations in the radial viscosity profile as one considers sites situated further north in hudson bay this provides one means for a spherically symmetric model to yield decay times which vary across the hudson bay however the data do not provide an unambiguous requirement for such a variation

numerical modeling of gravel bed river response to meander straightening the coupling between the evolution of bed pavement and long profile 1 artificial meander straightening rectification was conducted in the early 1960s along the sainte marguerite river canada in order to facilitate highway construction along the valley previous studies talbot and lapointe 2002 confirm that vertical reprofiling coupled with pavement coarsening in the degrading reach were the main responses counteracting the disequilibrium in gravel transport rates triggered at rectification of this system numerical simulations using sedrout2 0 a one dimensional hydraulic and sediment transport model and validated against the observed channel response show the important role played by an advancing wave of pavement coarsening down the rectified reach in modulating the bed degradation response simulations extending into the future reveal an asymptotically slowing approach to equilibrium in the middle of the 21st century with a response half time of the order of 10 years in near threshold gravel bed systems like the sainte marguerite river pavement coarsening after rectification buffers the system against extreme degradation most significantly for watershed management this also appears to severely limit the extent of propagation of degradation upstream of the rectification