the infiltration of fine matrices into coarse grained alluvial sediments and its implications for stratigraphical interpretation traps designed to simulate the framework gravel of natural streams and installed in a coarse grained channel allow the identification and differentiation of the processes governing the infiltration of fines into bed interstices vertical patterns of matrix distribution reflect the relative importance of variables acting at both the surface of the channel bed and within the bed sediments differences in grain size and therefore pore size of the framework exercise a strong controlling influence an armour layer of coarse particles superimposed on comparatively finer sub surface bed material common to many coarse grained rivers is shown to encourage the clogging of near surface pores with matrix fines below the obstruction interstices may be protected from incursion and the gravel framework is often left open this is the reason for patchy concentrations of matrices often reported in the stratigraphical literature in contrast a uniform size grading of the bed sediment or an upwards fining leads to a more uniform packing of the interstices with matrix flood history is shown to be an important determinant of both the size distribution and the spatial distribution of matrices and is useful in providing a dynamic explanation of the variability of matrices observed from place to place in ancient deposits

mechanics of low stress forearcs nankai and cascadia the nankai and cascadia subduction zones have low stress forearcs where the margin normal horizontal compressive stress is similar to or less than the vertical stress except in the accretionary prisms in the absence of active back arc spreading the forearc margin normal stress is controlled mainly by the total shear force along the subduction fault or the plate coupling force and the gravitational force the plate coupling force creates compression and the gravitational force in the presence of margin topography creates lateral tension we give a simple expression that relates the forearc stress to topography and average fault strength with the latter represented by an effective coefficient of friction we also use a finite element model of two converging plates in frictional contact to model the forearc stresses the analyses indicate that a low stress forearc requires not only the subduction fault to be very weak but also the mechanically coupled fault area to be narrow in the downdip direction and shallow in depth for nankai and cascadia where the coupled fault areas are narrow and shallow because of the young and hot subducting plates is about 0 05 or less and in any case less than 0 09 the low fault strength is probably not a unique property of low stress forearcs since the same low values combined with wider and deeper coupled areas can be shown to create large margin normal compression in addition there does not seem to be any relation between subduction earthquake magnitudes and plate coupling forces great earthquakes occur at subduction zones having low stress forearcs such as nankai and cascadia

spatiotemporal distribution of interplate coupling in southwest japan from inversion of geodetic data 1 we determine the spatiotemporal distribution of slip or slip deficit on the subduction interface of the nankai trough over an entire earthquake cycle using geodetic data including leveling triangulation and trilateration sea level and gps surveys obtained during the past 100 years in southwest japan we develop a new inversion method that accounts for long term crustal deformation coseismic earthquake displacements and stress relaxation of the viscoelastic asthenosphere from this analysis we obtain a model that shows postseismic afterslip on the deeper part of the plate interface following the 1946 nankaido earthquake significant afterslip is found beneath central shikoku that totals about 0 8 m the slip deficit rate during the interseismic period is 5 6 cm year in the n50 w n60 w direction which is consistent with the relative plate motion between the philippine and amurian plates a fully locked region is found in the shallower portion 30 km and the slip deficit rate has a maximum at a depth of about 20 km the plate interface deeper than 30 km is slowly slipping the amount of slip deficit reaches about 3 3 m off shikoku and about 2 m off the kii peninsula 50 years after the 1946 earthquake this suggests that fault healing and full interplate coupling has occurred by this time along the nankai trough

sediment supply and relative size distribution effects on fine sediment infiltration into immobile gravels 1 we present results and analyses from flume experiments investigating the infiltration of sand into immobile clean gravel deposits three runs were conducted each successive run with the same total sediment feed volume but a 10 fold increase in sand feed rate the highest sand feed rate produced less sand infiltration into the subsurface deposits than the other two runs which had approximately equivalent amounts of sand infiltration experimental data combined with simple geometric relations and physical principles are used to derive two relations describing the saturated fine sediment fraction in a gravel deposit and the vertical fine sediment fraction profile resulting from fine sediment infiltration the vertical fine sediment fraction profile relation suggests that significant sand infiltration occurs only to a depth equivalent to a few median grain diameters of the bed material

dynamic stress drop of recent earthquakes variations within subduction zones stress drop is a fundamental parameter of earthquakes but it is difficult to obtain reliable stress drop estimates for most earthquakes static stress drop estimates require knowledge of the seismic moment and fault area dynamic stress drop estimates are based entirely upon the observed source time functions based on analytical formulas that i derive for the crack and slip pulse rupture models the amplitude and time of the initial peak in source time functions can be inverted for dynamic stress drop for multiple event earthquakes this method only gives the dynamic stress drop of the first event the michigan stf catalog provides a uniform data base for all large earthquakes that have occurred in the past four years dynamic stress drops are calculated for the nearly 200 events in this catalog and the resultant estimates scatter between 0 1 and 100 mpa there is some coherent tectonic signal within this scatter in the sanriku japan and mexico subduction zones underthrusting earthquakes that occur at the up dip and down dip edges of the seismogenic zone have correspondingly low and high values of stress drop a speculative picture of the stress state of subduction zones emerges from these results a previous study found that the absolute value of shear stress linearly increases down the seismogenic interface to a value of about 50 mpa at the down dip edge in this study the dynamic stress drop of earthquakes at the up dip edge is about 0 2 mpa while large earthquakes at the down dip edge of the seismogenic plate interface have dynamic stress drops of up to 5 mpa these results imply that 1 large earthquakes only reduce the shear stress on the plate interface by a small fraction of the absolute level and thus 2 most of the earthquake energy is partitioned into friction at the plate interface

interseismic stress accumulation at the locked zone of nankai trough seismogenic fault off kii peninsula abstract a primary source of stress variation prior to great subduction zone earthquakes is the tectonic loading due to plate convergence we have calculated the elastic stress around the locked zone accumulated during an interseismic period numerically using a 2d plane strain finite element model in the nankai trough off kii peninsula and examined its dependence on elastic properties and some boundary conditions for the modeling we used the geometry of subducting plate interface determined previously through seismic surveys and the physical properties that were obtained through iodp scientific drilling offshore kii peninsula to construct a physically realistic model a dislocation along the plate interface is calculated from a 5 m displacement imposed on one side of the subducting plate with the locked zone defined at a depth of 10 to 25 km along the plate interface calculated shear stress is maximized at the downdip edge of the locked zone decreases exponentially seaward and is almost zero near the updip edge maximum shear stress is primarily proportional to the young s modulus of the overlying section comparing the maximum shear stress with the average stress drop for subduction earthquakes 3 4 mpa the most appropriate young s modulus and poisson s ratio ranges are 50 70 gpa and 0 3 respectively which are in good agreement with previous estimations from observed vp vs the stress accumulated during one seismic cycle can be reasonably explained by a linear elastic model with an appropriately sized locked region we found that the envelope of simulated horizontal displacement on the surface agrees well with gps velocity data which also supports this inference disturbance near the updip edge is no larger than 0 1 mpa of stress or 0 1 radian of tilt which are difficult to detect with current borehole measurement techniques and likely complex borehole conditions

the effects of flood history on sediment transport in gravel bed rivers abstract the transport of coarse sediment during floods often exhibits hysteresis patterns from changes in flow fields channel geometry bedforms or sediment supply conditions flume experiments that simulate hydrographs tend to confirm that hysteresis is a consequence of the progressive organization of surface sediments in terms of grain protrusion imbrication orientation and roughness hysteretic patterns are also highly dependent on the kind of sediment supply conditions and the type of simulated hydrograph a factor that has not been investigated extensively is the effect of the timing and sequencing of floods on bedload transport depending on its magnitude and duration each flood leaves the channel bed in a different condition which influences the bedload transport of the next event representing the river bed s memory of past floods which can determine future responses to natural disturbances in this study i investigated the effects of different sequences of events i e the flood history on sediment transport through a series of flume experiments that simulated three types of stepped and symmetrical hydrographs ranging from short duration high magnitude to long duration low magnitude events under sediment recirculation conditions hydrographs were simulated as a sequence of the same event and with events in different sequences in order to explore the effects of different antecedent conditions on sediment transport the results show that a previous event decreases the rates of sediment transported by a certain hydrograph by around 40 if a high magnitude event precedes another one and around 70 if a low magnitude event precedes another event of similar magnitude a low magnitude event does not affect the rate of sediment transported by a subsequent high magnitude flood but a high magnitude event reduces the sediment transported by a subsequent long duration low magnitude event

the variability of critical shear stress friction angle and grain protrusion in water worked sediments the erodibility of a grain on a rough bed is controlled by among other factors its relative projection above the mean bed its exposure relative to upstream grains and its friction angle here we report direct measurements of friction angles grain projection and exposure and small scale topographic structure on a variety of water worked mixed grain sediment surfaces using a simple analytical model of the force balance on individual grains we calculate the distribution of critical shear stress for idealized spherical grains on the measured bed topography the friction angle projection and exposure of single grain sizes vary widely from point to point within a given bed surface the variability within a single surface often exceeds the difference between the mean values of disparate surfaces as a result the critical shear stress for a given grain size on a sediment surface is characterized by a probability distribution rather than a single value on a given bed the crtitical shear stress distributions of different grain sizes have similar lower bounds but above their lower tails they diverge rapidly with smaller grains having substantially higher median critical shear stresses large numbers of fines trapp ed within pockets on the bed or shielded by upstream grains are effectively lost to the flow our calculations suggest that critical shear stress as conventionally measured is defined by the most erodible grains entrained during transient shear stress excursions associated with the turbulent flow this implies a physical basis for the indeterminacy of initial motion these observations suggest that transport rate shear stress relationships may be controlled in part by the increasing numbers of grains that become available for entrainment as mean shear stress increases they also suggest that bed textures and grain size distributions may be controlled within the constraints of an imposed shear stress and sediment supply regime by the influence of each size fraction on the erodibility of other grain sizes present on the bed

clogging of fine sediment within gravel substrates dimensional analysis and macroanalysis of experiments in hydraulic flumes abstractan understanding of the clogging of fine sediments within gravel substrates is advanced through use of dimensional analysis and macroanalysis of previously conducted clogging experiments in hydraulic flumes dimensional analysis via the buckingham pi theorem is used to suggest that the dimensionless clogging depth can be potentially collapsed using the original and adjusted bed to grain ratios i e ratio of substrate diameter to fine sediment diameter substrate porosity roughness reynolds number and peclet number macroanalysis and statistical analysis is performed using 10 previously published studies that include a total of 146 different test conditions reporting noncohesive fine sediment clogging or deposition in porous gravel beds with hydraulically rough turbulent open channel flow results suggest that the adjusted bed to grain ratio is a reliable predictor of the initiation of clogging with clogging occurring below 27 for the fine fluvial sediment clogging in a gravel bed substrate f

experimental study of the transport of mixed sand and gravel we measured a wide range of transport rates for five different sand gravel mixtures in a laboratory flume each mixture used the same gravel and sand was added to produce mixtures containing 6 15 21 27 and 34 sand control of other variables allows us to isolate the effect of bed sand content on transport as sand content increases gravel transport rates increase by orders of magnitude even though the proportion of gravel in the bed decreases the increase in gravel transport rate is most rapid over the range of bed sand content between 15 and 27 the increase in transport rate is larger than predicted using standard scaling relations between transport rate and grain size indicating that models of transport and sorting and predictions of stream channel response to sand inputs need to be revised to account for the influence of sand content bed surface grain size was measured at the end of each run surface grain size varied with sand content but showed little or no coarsening with flow strength and transport rate this casts doubt on the idea that armor layers form at small flows and weaken or vanish with increasing flow and transport rate

infiltration of fine sediment into a coarse mobile bed a phenomenological study experiments were undertaken to study the nature of granular interaction in running water by examining the influence of fine grain inputs to a coarser sediment bed with a mobile surface video recordings of grain sorting by both kinetic sieving and spontaneous percolation are used to diagnose the critical processes controlling the overall bed response kinetic sieving takes place in the mobile bed surface with the finer sediment moving to the bottom of the bedload transport layer at the interface with the underlying quasi static coarse bed we show that the behavior at this interface dictates how a channel responds to a fine sediment input if by spontaneous percolation the fine sediment is able to infiltrate into the underlying quasi static bed the total transport increases and the channel degrades however if the fine sediment input rate exceeds the transport capacity or is geometrically unable to infiltrate into the underlying bed it forms a quasi static layer underneath the transport layer that inhibits entrainment from the underlying bed resulting in aggradation and an increase in bed slope this article is protected by copyright all rights reserved

runaway slip to the trench due to rupture of highly pressurized megathrust beneath the middle trench slope the tsunamigenesis of the 2011 tohoku earthquake off the east coast of northern japan abstract the gigantic 2011 march 11 mw 9 tohoku earthquake is examined from the viewpoint of the pre seismic forearc structure the seismic reflection properties of a megathrust around the usual up dip limit of the seismogenic zone the thermal state of a shallow subduction zone and the dehydration of underthrust sediments at the japan trench the pacific plate is subducting westward beneath northeast japan at a dip angle of 4 6 the middle and lower slopes of the landward side dip eastward at angles of 2 5 and 8 0 respectively the forearc prism beneath the middle and lower slopes is inferred to be in extensionally and compressively critical states respectively based on the presence of clear internal deformation features and on the occurrence of aftershock earthquakes the rapid uplift of the forearc that caused the 2011 tohoku tsunami may have been associated with this internal deformation of the prism the critical state of the prism indicates that the effective basal friction b of the plate boundary megathrust is 0 08 for the lower prism the megathrust especially under the middle slope is characterized by a prominent reflector with negative polarity one of multiple possible explanations is that the megathrust hosts highly pressurized fluids underthrust sediments in this part of the japan trench are dominated by pelagic and siliceous vitric diatomaceous silt with clay the dehydration kinetics of opal a to quartz the clay transformation of smectite illite and the thermal structure of the japan trench suggest that maximum dehydration of the sediments would take place at 50 60 km horizontally from the deformation front where the temperature along the megathrust is 100 120 c the zone of maximum dehydration coincides with the prominent seismic reflector that has negative polarity we hypothesize a possible free slip along this portion of the megathrust during the 2011 tohoku earthquake caused by anomalously high fluid pressure resulting from fluid accumulation over centuries

bedload transport of a bimodal sediment bed 1 despite several decades of investigations accounting for the effect of the wide range of grain sizes composing the bed of rivers on bedload transport remains a challenging problem we investigate this problem by studying experimentally the influence of grain size distribution on bedload transport in the simple configuration of a bimodal sediment bed composed of a mixture of 2 populations of quartz grains of sizes d1 0 7 0 1 mm and d2 2 2 0 4 mm respectively the experiments are carried out in a tilted rectangular flume inside which the sediment bed is sheared by a steady and spatially uniform turbulent flow using a high speed video imaging system we focus on the measurement of the average particle velocity and the surface density of moving particles defined as the number of moving particles per unit surface of the bed these two quantities are measured separately for each population of grains as a function of the dimensionless shear stress or shields number and the fraction of the bed surface covered with small grains we show that the average velocity and the surface density of moving particles obey the same equations as those reported by lajeunesse et al 2010 for a bed of homogeneous grain size once in motion the grains follow therefore similar laws whether the bed is made of uniform sediment or of a bimodal mixture this suggests that the erosion deposition model established by lajeunesse et al 2010 for a bed of uniform sediment can be generalized to the case of a bimodal one the only difference evidenced by our experiments concerns the critical shields number for incipient sediment motion above a uniform sediment bed the latter depends on the particle reynolds number through the shields curve in the case of a bimodal bed our experiments show that the critical shields numbers of both populations of grains decrease linearly with the fraction of the bed surface covered with small grains we propose a simple model to account for this observation

grain size and topographical differences between static and mobile armour layers a series of laboratory flume experiments under conditions of sediment starvation zero sediment feeding and recirculation were conducted in order to identify the temporal evolution and surface properties of static and mobile armour layers the experiments were carried out in an 8 m long flume using a bimodal grain size mixture d50 6 2 mm and a range of shear stresses ranging from 4 0 to 8 6 n m 2 the results confirm that a static armour layer is coarser than a mobile one and that the grain size of a mobile armour layer is rather insensitive to changes in the imposed flow strength an analysis of laser scan bed surveys revealed the highly structured and imbricated nature of the static armour layer under these conditions the vertical roughness length scale of the bed diminished and it became topographically less complex at higher forming discharges the topography of mobile armour layers created by rising discharges differed they exhibited a greater roughness length scale and were less organized despite the fact that the grain size of the surface material maintained an approximately constant value during recirculation also the mobile armour tended to create larger cluster structures than static armour layers when formed by higher discharges these differences were mainly due to the transport of the coarser fraction of bed sediments which diminished to zero over the static armour because of being hidden within the bed whereas in the mobile armour the coarser particles protruded into the flow and were actively transported increasing the vertical roughness length scale overall the results show that an examination of the grain size characteristics of armour layers cannot be used to infer sediment mobility and bed roughness detailed elevation models of exposed surfaces of gravel bed rivers are required to provide critical insight on the sediment availability and sedimentation processes copyright 2011 john wiley sons ltd

framework dilation winnowing and matrix particle size the behavior of some sand gravel mixtures in a laboratory flume abstract a series of experiments have been carried out in a laboratory flume to simulate the conditions in a gravel bed river with a supply of finer sand size material under flow conditions where some or all of the material is in motion the experimental program incorporated three sets of experiments 1 where flows were just above the theoretical threshold for entrainment of the sand 2 where flows were at the theoretical threshold for entrainment of the gravel and 3 where flows were well above the threshold for both transport of sand and gravel particle movements were monitored using a new digital photographic and image analysis method that allows detection of motions over periods as small as 0 04 s the results show that where flows are capable of moving only the finer material grain size of the matrix is controlled by a combination of winnowing and particle overpassing under these conditions the grain size of the fine material trapped in the pore spaces of the gravel declines downstream once the gravel becomes entrained the processes are very different just before the surface gravel layer is eroded the framework lifts and dilates causing matrix particles to move down into subsurface pores under these conditions matrix grain size increases downstream because larger matrix particles are more likely to become stuck in pore throats and entrained with the gravel framework the dilation process is hitherto unreported and has many implications for sediment transport it appears that lift not drag is the important force during the early stages of entrainment and as a result fine matrix particles can be less mobile than those of the coarser framework

influence of sand on hydraulics and gravel transport in a braided gravel bed river measurements in a braided reach of the proglacial white river washington are used to compare the bed load capacity and competence of flow over the predominant gravel bed and over a narrow ribbon of mobile sand which extended alongside the talweg analysis of 144 velocity profiles and 222 bed load samples shows that shear stress and roughness height were significantly lower over sand than gravel but maximum bed load diameter and total gravel transport rate significantly higher as were transport rates of given size fractions at similar shear stresses these differences in competence and capacity are explained by relative size effects on the threshold shear stress for entrainment the influence on gravel transport of local variation in bed material size may explain the self sorting of bed load sheets described by other workers however in channels like that described here the continuous longitudinal ribbon of sand allows the flow to develop a lower shear stress over the smoother bed which partly offsets the relative size effects on competence and capacity

predicting plate velocities with mantle circulation models 1 we predict plate motions from a comprehensive inversion of theoretical estimates of tectonic forces in order to evaluate the relative importance of these and the uncertainties of such models plate driving forces from the mantle are calculated using global flow models that are driven by tomography and subduction derived density fields observed and predicted plate velocities agree well for a variety of models leading to varied conclusions about the relative importance of forces the dominance of the subduction related density pattern in the mantle is confirmed it appears that p wave models do not satisfactorily image all of the slab associated anomalies in the upper mantle furthermore lower mantle structure always improves the plate motion fit with respect to models that are based on upper mantle anomalies and lithospheric thickening only we show that the average torques from the lower mantle scale with the radial flow through the 660 km phase transition the amplitude of the lower mantle torques will be significant for a range of models if there is mass flux through 660 km we also evaluate parameterized edge forces and find that the additional inclusion of such torques does not significantly improve the model fit the main reason for the nonuniqueness of the inversions is plate boundary geometry since all plate motions are dominated by the trench ridge system and plates move from ridges to trenches

a low velocity zone with weak reflectivity along the nankai subduction zone three dimensional seismic reflection data reveal the presence of a low seismic velocity zone lvz with weak reflectivity character along the nankai accretionary prism this lvz is intercalated between an upper offscraped layer and a lower underthrusting layer in the outer accretionary wedge wide angle ocean bottom seismograph data also support the presence of the lvz which is estimated to be a maximum of 2 km thick 15 km wide and 120 km long the lvz could be an underthrust package underplated in response to the lateral growth of the nankai accretionary prism underplating of the underthrusting layer beneath the overlying offscraped layer would maintain a critical taper of the accretionary prism so that the offscraped layer can continue to grow seaward the lvz could have elevated fluid pressure leading to rigidity reduction of the entire outer accretionary wedge the rigidity lowered outer wedge containing the lvz may be more easily uplifted and thus eventually foster tsunami generation during a nankai megathrust earthquake if the fluid rich lvz supplies a significant amount of the fluid to the megasplay fault zone at depth it may affect stick slip behavior of the fault

vertical gradational variability of fines deposited in a gravel framework vertical gradational structures develop as sand infiltrates into static gravel beds understanding the vertical distribution of interstitial sand deposits will improve predictions of ecological suitability and hyporheic hydrodynamics a series of flume experiments was performed to investigate fine infiltration processes four sand distributions were introduced into flows over gravel beds after each experiment bed cores were extracted and analysed in vertical layers to examine the gradational trends with depth vertical trends of fine content were highly sensitive to the relative grain size distributions of the gravel bed and the introduced sand for experiments with d15gravel d85sand ratios 15 4 and larger unimpeded static percolation was observed where sand filled the voids relatively uniformly from the bottom of the gravel layer to the top experiments with ratios 10 6 and smaller bridged sand clogged a thin layer of gravel pores near the bed surface precluding subsequent infiltration interstitial sand deposits fined with depth of penetration for all experiments which was the result of three distinct but overlapping processes i granular sorting as particles fell through the substrate smaller material preferentially passed through the voids deeper into the gravel ii bed load sorting size segregation occurs in the wake of the leading bed form as smaller particles saltate further and settle first iii hydraulic sorting smaller sand was transported preferentially as suspended load filling the deep voids of the furthest flume positions downstream finally when the experiments that formed a bridge layer were replicated with higher bed shear stresses less interstitial sand deposition was observed higher shear stresses transported coarse particles downstream more efficiently causing bridge layers to form earlier and allowing less time for suspended load to settle into the deeper substrate pores before the pathways were closed

two decked nature of the ouachita mountains arkansas the ouachita mountains of arkansas and oklahoma are made up of two structural decks the lower deck of tight to isoclinal folds in pre middle mississippian strata records multiple folding and low grade metamorphism the upper deck of open folds in carboniferous rocks shows no evidence of the multiple folding and metamorphism dips of fold limbs in the lower deck are typically more than 60 dips of fold limbs in the upper deck are generally less than 45 fold wavelengths in the lower deck are in the range of 0 5 to 3 5 km fold wavelengths in the upper deck are generally in the range of 12 to 15 km estimates of shortening of the folds in the lower deck are five times greater than those of shortening of the upper deck the change from tight folding to broad folding takes place in the middle part of the mississippian stanley group the difference in fold style has been attributed to disharmonic folding of a stiff upper deck and a ductile lower deck however the boundary between harmonic and disharmonic folds shows no apparent relation to the fold wavelength or the stratigraphic spacing of stiff beds we hypothesize that the difference in structural style reflects the unconformable deposition of younger folded and faulted foreland basin strata the upper deck over the older lower deck strata which were stacked in an accretionary wedge

thermal state under the tohoko arc with consideration of crustal heat generation abstract the thermal structure beneath subduction zones plays a key role in aiding understanding of tectonic activities such as seismicity volcanism arc formation and genesis of back arc basins around subduction zones many simulations have been made to estimate the thermal process in the mantle wedge which causes the surface activities in the tohoku arc many heat flow measurements have been made and the heat flow profile from the trench to the back arc has been constructed in this study the thermal structure in the crust of northeast japan is investigated to account for the surface heat flow data to estimate the contribution of the heat generation in the crust to the surface heat flow the heat production rate was obtained on granitic and metamorphic rocks collected from the hidaka metamorphic zone hokkaido japan where the vertical crustal section of an island arc is understood to be exposed at the surface instrumentation neutron activation analysis and gamma ray spectrometry were adopted to analyze the concentration of heat producing elements the obtained rate of heat generation and its decrease with increasing depth for the upper part of the crust were found to be similar to those estimated for stable continental areas but the heat generation rate was almost constant in the lower part of the crust the vertical distribution of the heat production rate in the crust of the northeastern japan arc was estimated from the present results and previous estimates of heat production rates in various rocks using the crustal structure determined by explosion seismology the total heat generation in the crust thus estimated is about 30 mw m 2 with the surface heat flow data and estimated heat generation distribution in the crust the thermal structure in the crust was simulated numerically modeling calculations were made on a cross section along the line from the japan trench to the japan sea a direction parallel to the direction of convergence of the pacific and eurasian plates the models were two dimensional and included frictional heating at the upper surface of the slab the calculated thermal structure in the crust shows that the temperature at the moho is about 850 c and almost about 250 c lower than previous estimates the magnitude of the interplate stress was derived by considering the rate of frictional heating at the interface between the plates in order to explain the surface heat flow between the trench and aseismic front the interplate stress should be less than 20 mpa at depth in the crust

elevated fluid pressure and extreme mechanical weakness of a plate boundary thrust nankai trough subduction zone pore fluid pressure is a key parameter governing both the shear strength of faults and the conditions for seismic and tsunamigenic slip on subduction zone megathrusts however quantitative constraints on this parameter based on in situ data in these or any faults have proven elusive using seismic interval velocities derived from a three dimensional seismic reflection survey we compute porosity fluid pressure and effective stress at the plate interface in the nankai trough subduction zone offshore southwestern japan to 20 km down the fault dip using well constrained locally calibrated empirical relationships between velocity porosity and effective stress we show that the fault and immediately subjacent footwall are nearly undrained implying that the subduction megathrust slips under a shear stress of

waveform tomography imaging of a megasplay fault system in the seismogenic nankai subduction zone abstract we apply frequency domain waveform tomography to form quantitative high resolution p wave velocity images of a megasplay fault system within the central nankai subduction zone offshore of southwest japan using controlled source ocean bottom seismometer obs data originally acquired in 2004 the waveform tomography method exploits recorded seismic waveforms beyond their first arrivals and thus achieves a much higher resolution of the order of a wavelength than that of conventional traveltime tomography methods frequency domain waveform tomography facilitates a multi scale approach to stabilize the inversion in which initial traveltime tomography results are sequentially improved on by first fitting low frequency components of the seismic records starting at 2 25 hz higher frequency components up to 8 5 hz are then introduced progressively our final waveform tomography image allows velocity anomalies as small as 700 m horizontally and 350 m vertically to be discerned and interpreted as confirmed by checkerboard modeling tests the improved explanatory power of the final images is verified by observing that synthetic waveforms calculated from the final results yield much better fit to the observed waveforms than those estimated from the original traveltime tomography image apparent lithological boundaries from waveform tomography agree well with corresponding reflections on seismic migration images providing further confidence in the validity of the results the megasplay fault is evident on the final waveform tomography image as a sharp velocity discontinuity delineating the upper surface of a velocity reduction of nearly 1 km s with respect to the regional 1d velocity trend the megasplay fault can be traced continuously throughout the entire image from a nearly horizontal section at the landward extent moving seaward through to a steeper angle penetrating the old accretionary prisms with several additional splays appearing to branch in the shallow subsurface the location of the low velocity zones imaged by our waveform tomography method coincides with two previously identified low velocity zones the image reveals a low velocity zone that is continuous from deeper to shallower portions of the subsurface suggesting that pore fluids may be transported from the inner wedge to the transition zone and to the surface through fluid conduits associated with the megasplay fault system

kinematic analysis of the taiwan slate belt the taiwan slate belt can be subdivided into two structural domains based on fold and cleavage geometries and finite and incremental strain histories the two belts correspond generally to two topographic ranges in taiwan the hsuehshan range and the backbone range rocks in the hsuehshan range are characterized by upright symmetric folds and a steeply se dipping axial planar pressure solution cleavage synkinematic fibers in pressure shadows are typically straight parallel to cleavage and plunge downdip indicating that the rocks experienced a coaxial strain history in contrast rocks in the backbone range are characterized by inclined asymmetric folds that verge toward the foreland and display a moderately se dipping axial planar pressure solution cleavage synkinematic fibers are straight and parallel to the downdip stretching lineation in xy sections in xz sections however the fibers typically display a clockwise curvature viewed to the ne indicating a noncoaxial strain history we propose that the different strain histories are due at least in part to differences in the original tectonostratigraphic settings of the strata in the two ranges strata in the hsuehshan range are interpreted to have been deposited in a half graben associated with an east dipping normal fault the strata of the backbone range in contrast are considered to have been deposited on the unfaulted chinese continental margin we suggest that the basement horst on the east side of the half graben functioned as a steep faced rigid backstop that concentrated pure shear deformation throughout most of the hsuehshan range shear strains were apparently limited to zones near the base of the sedimentary sequence and adjacent to the backstop the noncoaxial strains characteristic of the backbone range are interpreted to be the result of a regional scale shear zone that formed as chinese basement and its sedimentary cover were underthrust southeastward beneath the luzon arc

numerical modelling of the three dimensional stress field in southwestern japan abstract it has been inferred from the focal mechanism of earthquakes and their hypocenter distribution shiono 1977 that the stress field in southwestern japan indicates complicated features a nw se compression at shallow depths along the nankai trough an e w or ese wnw compression in the inland crust an extension parallel to the leading edge of the philippine sea plate at subcrustal depths in the region from the southern chubu to northwestern shikoku and a down dip tension beneath the kyushu island in order to investigate possible sources of these complex features of the stress state a three dimensional finite element method is employed to model the configuration of the subducting philippine sea plate taking into consideration the following three possible types of forces 1 1 a negative buoyancy due to the density contrast between the subducting plate and the surrounding mantle 2 2 a northwestward compressive force generated by the movement of the philippine sea plate 3 3 a westward compressive force due to the movement of the pacific plate for various combinations of different magnitudes of these forces and of different elastic moduli the stresses at a number of selected sites are calculated and their directions are compared with those inferred from the focal mechanism and other geophysical information it is found that the observed extensional stresses parallel to the leading edge of the subducting philippine sea plate may be caused mainly by the negative buoyancy the northwestward compressive force may not play an important role in generating the complex stress field in southwestern japan the observed e w compressional stress field prevailing in the inland region appears to result mainly from the westward moving pacific plate the present results suggest that if a thin low velocity transitional layer exists just above the subducting philippine sea plate it could give appreciable effects on the mechanism of low angled thrust faulting off the kii peninsula and the shikoku island the magnitude of the shear stress in the continental crust and in the subducting plate is estimated to be of the order of several hundred bars although the calculated shear stresses are considerably affected by the configuration of the subducting plate and also by the applied forces it is interesting that the stress distribution appears to have some relations to seismicity of subcrustal earthquakes and to the rupture process of large thrust earthquakes along the plate boundary

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

displacement fields due to the 1946 nankaido earthquake in a laterally inhomogeneous structure with the subducting philippine sea plate a three dimensional finite element approach abstract the displacement fields associated with the 1946 nankaido earthquake have been investigated in detail taking into account the configuration of the philippine sea plate subducting beneath southwest japan we used a three dimensional finite element method for the elastic problem to examine the effects of three dimensionally inhomogeneous structure some differences in the displacement patterns between homogeneous and inhomogeneous media have been identified the amounts of displacements are large in low rigidity portions such as in the crust and mantle wedge and are small in a high rigidity portion composed of the subducting plate the inhomogeneity affects horizontal displacements at the earth s surface more than vertical displacements if the rigidity and the poisson ratio given here to southwest japan are appropriate the fault parameters of the earthquake which have been estimated from simple dislocation models in a homogeneous semi infinite medium need to be modified somewhat the present computations indicate that larger dip angles and smaller fault slips are more appropriate fault parameters when structural inhomogeneity is taken into account this suggests that the discrepancy in the obtained total seismic moment between the geodetic and seismic models of the nankaido earthquake could be reduced

a model with rigid rotations and slip deficits for the gps derived velocity field in southwest japan abstract we interpret the gps derived velocity field in southwest japan by a superposition of the elastic deformation caused by fault interactions slips or slip deficits on the rigid motion of tectonic blocks or plates based on the strain rate field and crustal seismicity we apply a model with three blocks inner arc outer arc and the northern ryukyu block and slip deficits along the block boundaries several characteristics of the synthesized contributions are found 1 westward motion of the outer arc relative to the amurian plate and the inner arc 2 southeastward motion of the northern ryukyu block relative to the amurian plate 3 2 4 mm yr deficits of left lateral slip rates along the boundary at 32 n in southern kyushu 4 0 8 mm yr deficits of right lateral slip rates along the median tectonic line and the beppu shimabara graben 5 slip deficit rates on the plate interface smaller than those in the case without any consideration for rigid block motions 6 clockwise deflection of slip deficit rate vector on the plate interface from that estimated when not taking rigid block motions into consideration

bridging process threshold for sediment infiltrating into a coarse substrate sand infiltration into gravel frameworks poses significant engineering and ecological difficulties ten flume experiments were conducted to quantify a sand bridging threshold in a static gravel bed the d15 substrate d85 sand ratio was computed for each of 37 unique sand substrate pairs and the data were plotted with previously published flume data to determine the threshold between bridging and unimpeded static percolation the process threshold boundary between bridging and unimpeded static percolation fell in the range of 12 d15 substrate d85 sand 14 substantially higher than predicted by standard geotechnical filter criteria plotting the results against the critical constriction size of the substrates provided a more definitive process separation along the line dc d85 3

high pore fluid pressure may cause silent slip in the nankai trough silent slip events have been detected at several subduction zones but the cause of these events is unknown using seismic imaging we detected a cause of the tokai silent slip which occurred at a presumed fault zone of a great earthquake the seismic image that we obtained shows a zone of high pore fluid pressure in the subducted oceanic crust located down dip of a subducted ridge we propose that these structures effectively extend a region of conditionally stable slips and consequently generate the silent slip

striations duration migration and tidal response in deep tremor deep tremor in subduction zones is thought to be caused by small repeating shear slip events on the plate interface with significant slow components it occurs at a depth of about 30 kilometres and provides valuable information on deep plate motion and shallow stress accumulation on the fault plane of megathrust earthquakes tremor has been suggested to repeat at a regular interval migrate at various velocities and be modulated by tidal stress here i show that some time invariant interface property controls tremor behaviour using precise location of tremor sources with event duration in western shikoku in the nankai subduction zone japan in areas where tremor duration is short tremor is more strongly affected by tidal stress and migration is inhibited where tremor lasts longer diffusive migration occurs with a constant diffusivity of 10 4 m 2 s 1 the control property may be the ratio of brittle to ductile areas perhaps determined by the influence of mantle wedge serpentinization on the plate interface the spatial variation of the controlling property seems to be characterized by striations in tremor source distribution which follows either the current or previous plate subduction directions this suggests that the striations and corresponding interface properties are formed through the subduction of inhomogeneous structure such as seamounts for periods as long as ten million years

determination of the pore fluid pressure ratio at seismogenic megathrusts in subduction zones implications for strength of asperities and andean type mountain building 1 we construct the differential stress profile across the fore arc in a subduction zone from the force balance between the shear stress at seismogenic megathrust and the lithostatic pressure we assume that is written by 1 n where is the pore fluid pressure ratio is the coefficient of static friction and n is the normal stress given a density structure of the fore arc wedge we determine by comparing calculated fore arc stresses with observed ones as 0 95 0 98 in shikoku miyagi peru north chile and south chile and 0 90 0 93 in south vancouver island and washington the parameter averaged over the seismogenic megathrust is of the order of 10 mpa stress drops of great earthquakes in these zones occupy 14 87 and not a constant fraction of they on the other hand increase linearly with 1 we propose a simple fault model in which the area of asperities as a fraction of the total fault area is proportional to 1 variation of fractional area of asperities thus may explain the observed correlation and the regional variation of assuming that the differential stress at summit of the andean mountains is zero not at the coast as observed at present we determine to be 0 84 in north chile in the mountain building stage such a smaller value of along with 0 9 in subduction zones would suggest that variation of controls the tectonic style of the earth

effects of sand addition on turbulent flow over an immobile gravel bed 1 the factors controlling the complex interaction of a coarse streambed with flow and sediment are difficult to measure however planning for reservoir flushing or dam removal requires knowledge of these interactions in both cases impounded sediments are introduced to channel beds that have had fine sediment particles removed without replacement the channel bed pore space interacts with the flow and provides storage for particles in order to address the need for information on such systems an adjustable slope recirculating laboratory flume was used to study the changes in flow and turbulence caused by sand added to an immobile gravel bed detailed measurements were made using an acoustic doppler velocimeter that collected three velocity components at a rate of 200 hz because of the rough nature of the bed individual velocity profiles varied significantly therefore in order to determine general trends the data were spatially averaged over six 10 20 cm planes parallel to the bed with the lowest plane about 2 cm below the maximum gravel elevation the increasing elevation of sand relative to the gravel layer resulted in decreased bed shear stress decreased reynolds stress increased relative turbulence intensity and a near bed shift toward sweep dominated turbulence

case for very low coupling stress on the cascadia ssubduction fault a fundamental problem in plate tectonics is the shear strength of major plate boundary faults this translates to the question whether the generally observed small earthquake stress drops of 3 10 mpa on major faults release most of the accumulated stress or only a small fraction of it there is strong evidence that the san andreas fault a major transform plate boundary is weak 20 mpa shear resistance it is not yet clear whether subduction thrust faults are also weak we present two types of evidence from the northern cascadia subduction zone that indicate very low coupling shear stress on that plate interface and hence very low strength of the subduction thrust fault comparable to that estimated for the san andreas fault first the well defined surface heat flow and heat generation allow negligible frictional heating on the plate interface the average shear stress on the fault must thus be very low over a time scale of a few million years second focal mechanism solutions for small crustal earthquakes in the southern vancouver island area indicate that the horizontal stress in the direction of plate convergence has a similar magnitude to the vertical stress this inferred stress state requires the present tectonic stress coupled across the subduction thrust fault to be very low one explanation for the weakness of the fault is the presence of near lithostatic pore fluid pressure in the region of the fault zone for which there is independent evidence the conclusion of a weak subduction thrust fault does not conflict with geodetic observations of contemporary surface deformation which indicate that the fault is currently locked accumulating strain energy toward a future great earthquake the surface deformation responds to the small 20 mpa temporal changes of the stress field associated with the subduction earthquake cycle this transient stress is superimposed on the larger background regional stress field in which the maximum compression is parallel to the margin the weakness of the cascadia subduction thrust fault and the unusual stress state of the forearc region have important implications for earthquake hazards for example a subduction earthquake may induce large strike slip earthquakes in the forearc that affect a large area

particle velocity and concentration profiles in bedload experiments on a steep slope depth profiles of particle streamwise velocity concentration and bedload sediment transport rate were measured in a turbulent and supercritical water flow one size 6 mm diameter spherical glass beads were transported at equilibrium in a two dimensional 10 steep channel with a mobile bed flows were filmed from the side by a high speed camera particle tracking algorithms made it possible to determine the position velocity and trajectory of a very large number of particles approximately half of the sediment transport rate was composed by rolling grains and the other half by saltation this revealed a complex structure with several concentration and flux peaks due to rolling and one peak due to saltation with an increase of the sediment transport rate the depth structure remained the same at the water granular interface with peak value increases but with no shift in elevations the saltation region expanded towards higher elevations with an increase of the particle velocity commensurate to the water velocity the proportion of the sediment transport rate in saltation did not vary significantly the particle streamwise velocity profiles exhibited three segments an exponential decay in the bed a linear increase where rolling and saltation co existed and above this a logarithmic like shape due to saltating particles these results are comparable to profiles measured and modelled in dry granular free surface flows and in more intense bedload such as sheet flows copyright 2014 john wiley sons ltd

space geodetic observation of deep basal subduction erosion in northeastern japan abstract observation of tectonic erosion von huene and scholl rev geophys 29 1991 279 316 in a subduction zone has been difficult as it leaves little geological and geophysical evidence three dimensional velocity profiles of crustal movement obtained by global positioning system across ne and sw japan agree well with those predicted by the elastic loading of the subducting slabs however vertical velocities in the ne japan forearc show significant negative deviation relative subsidence this may indicate loss of material at the plate interface that can be attributed to the erosion of the upper plate by the underthrusting slab basal subduction erosion the estimated rate 15 mm yr down to a slab depth of 90 km is somewhat faster than the geological average the erosion speed may be variable being controlled by the surface roughness of subducting slabs

rupture to the trench dynamic rupture simulations of the 11 march 2011 tohoku earthquake there is strong evidence that the 11 march 2011 tohoku earthquake rupture reached the seafloor this is surprising because the shallow portion of the plate interface in subduction zones is thought to be frictionally stable leading to the widely held view that coseismic rupture would stop several tens of kilometers downdip of the seafloor various explanations have been proposed to reconcile this seeming inconsistency including dynamic weakening e g thermal pressurization and extreme stress release around shallow subducted seamounts we offer a simpler explanation supported by 2d dynamic rupture simulations of the tohoku earthquake our models account for depth dependent material properties and the complex geometry of the fault seafloor and material interfaces based on seismic surveys of the japan trench the fault obeys rate and state friction with standard logarithmic dependence of shear strength on slip velocity in steady state in our preferred model the uppermost section of the fault is velocity strengthening rupture nucleates on a deeper velocity weakening section waves released by deep slip reflect off the seafloor transmitting large stress changes to the upper section of the fault driving the rupture through the velocity strengthening region to the trench we validate the model against seafloor deformation and 1 hz global positioning system gps data the seafloor displacements constrain the seismogenic depth and overall amount of slip particularly near the trench our simulations reproduce many features in the gps data thereby providing insight into the rupture process and seismic wave field sensitivity to parameters is explored through an extensive suite of simulations neither static seafloor deformation nor onshore 1 hz gps data can uniquely determine near trench frictional properties due to trade offs with average stress drop while conducted specifically for the japan trench region our simulations suggest that rupture to the trench in megathrust events is quite possible even if velocity strengthening properties extend tens of kilometers landward from the trench online material mp4 movies of particle velocities

seismic slip propagation to the updip end of plate boundary subduction interface faults vitrinite reflectance geothermometry on integrated ocean drilling program nantro seize cores seismic faulting along subduction type plate boundaries plays a fundamental role in tsunami genesis during the integrated ocean drilling program iodp nankai trough seismogenic zone experiment nantro seize stage 1 the updip ends of plate boundary subduction faults were drilled and cored in the nankai trough offshore japan where repeated large earthquakes and tsunamis have occurred including the a d 1944 tonankai mw 8 1 earthquake samples were obtained from the frontal thrust which connects the deep plate boundary to the seafloor at the toe of the accretionary wedge and from a megasplay fault that branches from the plate boundary decollement the toe of the accretionary wedge has classically been considered aseismic but vitrinite reflectance geothermometry reveals that the two examined fault zones underwent localized temperatures of more than 380 c this suggests that frictional heating occurred along these two fault zones and implies that coseismic slip must have propagated at least one time to the updip end of the megasplay fault and to the toe of the accretionary wedge

in situ stress state in the nankai accretionary wedge estimated from borehole wall failures we constrain the orientations and magnitudes of in situ stress tensors using borehole wall failures borehole breakouts and drilling induced tensile fractures detected in four vertical boreholes c0002 c0001 c0004 and c0006 from nw to se drilled in the nankai accretionary wedge the directions of the maximum horizontal principal stress shmax indicated by the azimuths of borehole wall failures are consistent in individual holes but those in c0002 margin parallel shmax are nearly perpendicular to those in all other holes margin normal shmax constrained stress magnitudes in c0001 and c0002 using logged breakout widths combined with empirical rock strength derived from sonic velocity as well as the presence of the drilling induced tensile fractures suggest that the stress state in the shallow portion of the wedge fore arc basin and slope sediment formations is predominantly in favor of normal faulting and that the stress state in the deeper accretionary prism is in favor of probable strike slip faulting or possible reverse faulting thus the stress regime appears to be divided with depth by the major geological boundaries such as unconformities or thrust faults the margin perpendicular tectonic stress components in the two adjacent sites c0001 and c0002 are different suggesting that tectonic force driven by the plate pushing of the philippine sea plate does not uniformly propagate rather the stress field is inferred to be influenced by additional factors such as local deformation caused by gravitation driven extension in the fore arc and thrusting and bending within individual geologic domains

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

slow earthquakes coincident with episodic tremors and slow slip events we report on the very low frequency earthquakes occurring in the transition zone of the subducting plate interface along the nankai subduction zone in southwest japan seismic waves generated by very low frequency earthquakes with seismic moment magnitudes of 3 1 to 3 5 predominantly show a long period of about 20 seconds the seismicity of very low frequency earthquakes accompanies and migrates with the activity of deep low frequency tremors and slow slip events the coincidence of these three phenomena improves the detection and characterization of slow earthquakes which are thought to increase the stress on updip megathrust earthquake rupture zones

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

the effects of kinetic sorting on sediment mobility on steep slopes in poorly mobile static armour sorting is usually considered the result of hiding exposure effects we called this effect static sorting in opposition to very efficient grain to grain mechanisms produced by a mobile mixture called kinetic sorting we hypothesized that kinetic sorting can be an important contributor to the morphodynamics of mountain streams and attempted to demonstrate this with new flume experiments two long runs were produced with natural poorly sorted sediments and with transport stages of the coarse fraction defined by the ratio between the shear stress and the critical shear stress for transport smaller and higher than 1 respectively both runs produced an efficient transfer downstream of the injected material but with a major difference the first run no kinetic sorting produced permanent armour figuring clusters akin to what has already been observed in similar experiments the second run with kinetic sorting also produced bed armouring but this armour was periodically totally destroyed leading to substantial bed erosion this phenomenon was explained by kinetic sorting the effects of which are to produce an efficient downward migration of fine materials and bed surface armouring the consequence is that fine materials are hidden to the flow during aggradation allowing the slope to attain values much steeper than would have been expected at equilibrium for the mixture however whereas the surface armouring tends to stabilize the bed construction of a layer of fine sediments at the subsurface also contributes to making it very unstable these two contradictory effects explain the complex bed behaviours and the existence of very large bedload and slope fluctuations copyright 2014 john wiley sons ltd

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

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

rupture process of the 1944 tonankai earthquake ms 8 1 from the inversion of teleseismic and regional seismograms 1 we digitized teleseismic and regional records of the 1944 tonankai earthquake we used the multiple time window method to invert these records for the spatial and temporal distribution of slip and rake we assume a 220 140 km fault with a spacing of 20 20 km and a maximum rupture velocity of 2 5 km s the inversion resolved an asperity along the accretionary wedge and under the shima and atsumi peninsulas the rupture propagated from southwest to northeast and there was little slip near the hypocenter consistent with the absence of uplift in the overlying submarine forearc basin the peak slip is 2 3 m and the total seismic moment is 2 4 1028 dyn cm mw 8 2 we compared the predicted and observed vertical geodetic displacements and inferred that the limit of rupture is consistent with the change from subsidence to uplift west of the atsumi peninsula this suggested that the earthquake did not rupture the plate interface in the tokai gap we modeled the tsunami using sea bottom displacements generated from this slip model the tide gauge amplitudes and frequency content are consistent with those predicted resolution tests from inverting synthetic seismograms computed using a simplified slip model indicated that the combination of teleseismic and regional data sets best recovers the asperity locations and peak slips given similar station geometry and degrees of freedom an inversion of the synthetic regional data set indicates that slip artifacts can occur early in the rupture process due to many clipped records while the inversion of synthetic teleseismic data set had less resolution and recovered only 50 of the peak slip

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

tsunamigenic potential of the shallow subduction plate boundary inferred from slow seismic slip at subduction zones slip along the shallowest parts of the plate boundary is generally thought to be aseismic observations of very low frequency earthquakes occurring at shallow levels on the plate boundary of the nankai trough subduction zone imply that slow but seismic slip can occur there and could potentially generate tsunamigenic earthquakes

sediment pulses in mountain rivers 1 experiments 1 sediment often enters rivers in discrete pulses associated with landslides and debris flows this is particularly so in the case of mountain streams the topographic disturbance created on the bed of a stream by a single pulse must be gradually eliminated if the river is to maintain its morphological integrity two mechanisms for elimination have been identified translation and dispersion according to the first of these the topographic high translates downstream according to the second of these it gradually diffuses away in any given river both mechanisms may operate this paper is devoted to a description of three controlled experiments on sediment pulses designed to model conditions in mountain streams each of the experiments began from the same mobile bed equilibrium with a set rate and grain size distribution of sediment feed in one experiment the median size of the pulse material was nearly identical to that of the feed sediment in the other two the pulse material differed in grain size distribution from the feed sediment being coarser in one case and finer in the other case in all cases the mode of pulse deformation was found to be predominantly dispersive a result that constitutes the main conclusion of this paper the pulses resulted in a notable but transient elevation of sediment transport rate immediately downstream when the pulse was coarser than the ambient sediment the bed downstream remained armored and a migrating delta formed in the backwater upstream when the pulse was finer than the ambient sediment translation was observed in addition to dispersion the presence of the finer material notably elevated the transport of ambient coarse material on the bed downstream in part 2 cui et al 2003 the experimental results are used to test a numerical model

detailed structural image around splay fault branching in the nankai subduction seismogenic zone results from a high density ocean bottom seismic survey 1 to investigate megathrust earthquake and tsunami generation in a subduction seismogenic zone it is important to know the detailed structure around the plate boundary and active splay fault system the nankai trough southwestern japan is among the best studied subduction zones with splay faults in the world this paper presents a detailed structural image around the splay fault in the coseismic rupture zone of the 1944 tonankai earthquake in the central nankai trough based on results from a wide angle high density ocean bottom seismograph obs survey our seismic image clearly shows for the first time the subduction structure along with the splay fault reflections imaged on a previously obtained seismic reflection profile the correspondence between the splay fault reflections imaged on the seismic reflection profile and our reflectivity image was confirmed by converting the time migrated section to a depth section by using a velocity model estimated from the wide angle obs data in this study the high resolution seismic image obtained by the high density obs survey demonstrates a zone of low velocity gradient just above and along the splay fault we focused specifically on the detailed structure around the splay fault a simple amplitude analysis of the wide angle reflections showed that it is likely that a thin low velocity layer with velocities 0 5 1 5 km s slower than those in the surrounding rock exists above the splay fault the presence of this layer suggests elevated fluid pressure in the fault zone which cut through the relatively homogeneous rock of the accretionary prism and generated past megathrust earthquakes

placer formation in gravel bedded rivers a review the literature on placer formation processes within fluvial systems is widespread and ranges between detailed laboratory studies of the hydrodynamic segregation processes through to the intuitive interpretation of the distribution of minerals within geological sections however there are few if any comprehensive reviews of the literature surprisingly given the economic importance of placers the theoretical framework relating to the hydrodynamics of physical grain sorting is not well developed and there are relatively few detailed laboratory hydraulic investigations to inform theory in this wide ranging review the history of the development of principles of placer formation is explored as far as possible in a non technical fashion a consideration is given to the hydrodynamics of physical grain sorting above lower stage and upper stage bedforms and the typical internal sedimentary structures associated with placer concentrations are detailed finally examples of the depositional environment of diamond tin and gold placers are considered

on why gravel bed streams are paved bedload transport in poorly sorted gravel bed streams downstream of dams is considered bedload and typical bed material subpavement size distributions are observed to be similar it follows that the coarse half of the subpavement moves through a reach at a rate near that of the fine half since coarser grains are intrinsically less mobile than fine grains it follows that some mechanism must act to nearly equalize mobility it is hypothesized that the pavement seen in gravel bed streams at low flow is in fact in place during typical transport events capable of moving all available sizes this pavement can provide the equalizing mechanism by exposing proportionally more coarse grains to the flow field data are used to quantify this concept and to develop a predictive relation for river pavement the model indicates that pavement should be absent in most sand bed streams in agreement with observation

mobilization of coarse surface layers in gravel bedded rivers by finer gravel bed load 1 additions of sand to gravel beds greatly increase the mobility and flux of gravel however it is not known how additions of finer gravel to coarser gravel beds will affect the mobility of bed material here we examine the effect of fine gravel pulses on gravel bed material transport and near bed flow dynamics in a series of flume experiments bed material refers exclusively to sediment in the channel prior to the pulse introduction the observations indicate that fine sediment pulses tend to migrate downstream in low amplitude waves as the waves pass over the gravel bed the interstitial pockets in the bed material surface fill and coarse gravel particles are entrained this increases bed material transport rates and causes a distinct shift from a selective mobility transport regime where particles coarser than the bed material median 8 mm make up 30 of the load to an equal mobility transport regime where bed materials coarser than 8 mm and finer than 8 mm are transported in equal proportions the only possible source for this coarser bed load material is the sediment bed suggesting that portions of the coarse surface layer are being mobilized observations of near bed velocity and turbulence suggest that fine gravel pulses cause fluid acceleration in the near bed region associated with a reduction in the level of turbulence produced at the sediment boundary this accelerated fluid at the bed increases drag exerted on coarse surface layer particles promoting their mobilization our findings suggest that in general finer bed sediment not just sand can mobilize coarser sediment and that expressions for the influence of sand on bed mobility need to be generalized on the basis of grain ratios

high precision slip distribution of the 1944 tonankai earthquake inferred from tsunami waveforms possible slip on a splay fault abstract inversion of tsunami waveforms is a well established technique for estimating the slip distributions of subduction zone earthquakes with some of the most detailed results having been obtained for earthquakes in the nankai trough sw japan the present study although it uses a method and tsunami waveform data set almost identical to previous study aims to improve on previous work by using a more precise specification of initial conditions for the calculation of tsunami green s functions specifically we incorporated four improvements in the present study 1 we used a realistic plate model based only on seismic survey results and assumed it to be the fault plane of the 1944 tonankai earthquake 2 the smallest subfaults consistent with the long wavelength approximation were used in the tsunami inversion analysis 3 we included the effect of horizontal displacement of the ocean bottom on tsunami generation and 4 we performed a checkerboard resolution test as obtained in previous studies a zone of high slip 2 0 m was resolved off the shima peninsula however the more precise calculation of tsunami green s functions has revealed additional detail that was not evident in previous studies which we demonstrate is resolvable and correlates with the position of known faults in the accretionary prism while there was little or no slip near the trench axis in the eastern part of the rupture zone there was up to 1 5 m of slip resolved within 30 km of the trough axis in the western part along the coast of the kii peninsula this troughward slip zone coincides with the position of a large splay fault mapped in multichannel reflection surveys furthermore it is also clear that the upper edge of the enshu fault off shima and atsumi peninsulas is consistent with the up dip limit of slip in the eastern part of our model we tested the possibility that slip occurred on the former splay fault instead of on the plate interface during the 1944 tonankai earthquake and find that slip on this splay fault is also consistent with the data although we cannot distinguish whether slip was dominant on the splay fault or on the plate interface we further suggest that the position of the enshu fault may be determined by the subduction of topographic highs and that such faults may have an important influence on the up dip rupture limit of the 1944 tonankai and potentially other subduction zone earthquakes

seismic structure of western end of the nankai trough seismogenic zone 1 in 1998 a seismic experiment along a 320 km long profile using an air gun array and ocean bottom seismographs obss was collected in the on shore offshore forearc region of the western nankai trough seismogenic zone southwestern japan this area is outside the coseismic rupture area of the 1946 nankaido earthquake ms 8 2 the main objectives of this paper are to clarify the p wave and the poisson s ratio profile around the forearc region of southwestern japan and estimate differences between this area and the nankaido coseismic rupture area the p wave velocity model estimated by two dimensional 2 d ray tracing and travel time inversion indicates three units with distinctive velocity patterns the lens shaped unit has a maximum thickness of 5 km and velocity of 3 4 4 0 km s the underlying unit has velocity of 5 4 5 6 km s and its p wave velocity increases on land vp 6 2 6 4 km s the relative homogeneous unit with p wave velocity of 6 6 6 9 km s exists just beneath secondary unit with p velocity of 5 4 5 6 km s the angle of subduction is 7 we also obtained a poisson s ratio of the crustal structure of the forearc region the poisson s ratio of the southern part of secondary unit is larger than that of the northern part we conclude that these data indicate clay rich metamorphic rocks plus oceanic basaltic rocks rather than high porosity materials comprise the majority of the layer we suggest that the region of high poisson s ratio probably corresponds to underplating and the metamorphism of the clay rich sediments and possibly the oceanic basalt just below the decollement

crustal velocity field of southwest japan subduction and arc arc collision we investigate crustal deformation in southwest japan over a 3 year period revealed by a permanent dense global positioning system gps array southwest japan is a part of the amurian plate a microplate moving about 10 mm yr toward the east with respect to the eurasian plate it overrides the philippine sea plate at the nankai trough and collides with the northeast japan arc in the central part of japan in this paper we first derive gps site velocities relative to the stable part of the amurian plate in order to isolate signals of crustal deformation caused by the subduction and or the collision the velocity field has a conspicuous feature indicating the interseismic elastic loading by the philippine sea plate slab at the nankai trough characterized by the northwestward movements of points throughout the studied area their amplitudes are the largest at the pacific coast and decay toward the japan sea coast with a subtle systematic shift of azimuths a model assuming an elastic half space the convergence rate at the nankai trough based on a refined euler vector and the strength of the coupling inferred from a thermal model could explain the velocity field in the western part of the studied area to a large extent those in the eastern part systematically deviate from them and the residual components there show east west shortening and north south extension this may represent crustal thickening and trenchward extrusion of crustal blocks caused by the collision between southwest and northeast japan this suggests that the collision between southwest and northeast japan gives rise to not only crustal thickening but also trenchward extrusion of crustal block a velocity contrast was found across the median tectonic line the largest inland active fault in japan but the current permanent gps network is not dense enough for us to discuss its coupling depth

theory of fine sediment infiltration into immobile gravel bed a theoretical model is developed to describe the process of fine sediment infiltration into immobile coarse sediment deposits the governing equations are derived from mass conservation and the assumption that the amount of fine sediment deposition per unit vertical travel distance into the deposit is either constant or increases with increasing fine sediment fraction model results demonstrate that fine sediment accumulation decreases rapidly with depth into coarse substrate initially void of fine sediment which is consistent with experimental observations that significant fine sediment infiltration occurs to only a shallow depth comparisons of the theory with flume data indicate that the model adequately reproduced the weighted averaged fine sediment fraction values from experiments an early model developed by sakthivadivel and einstein for fine sediment infiltration is in part based on the generally incorrect assumption that intragravel flow remains constant following fine sediment infiltration applying a correction to the sakthivadivel and einstein model based on alternate hypothesis that introgravel flow is driven by a constant head gives similar results as the proposed model

effect of sediment pulse grain size on sediment transport rates and bed mobility in gravel bed rivers 1 sediment supply to gravel bed river channels often takes the form of episodic sediment pulses and there is considerable interest in introducing sediment pulses in stream restorations to alter bed surface grain size distributions and bed mobility a series of laboratory experiments was conducted in order to examine how sediment pulse grain size and volume affects the mobility of bed material in gravel bed channels pulses used in the experiments were composed of either the fine tail or the median of the subsurface bed material grain size distribution bed material refers to sediment in the channel prior to the pulse introduction exclusively both types of pulse were finer than the bed material surface median two pulse sizes were used which were either equivalent to the volume of sediment required to cover the entire bed one median subsurface bed material grain diameter deep full unit or 1 4 of this volume 1 4 unit the latter was designed to produce a transitory pulse with the exception of the 1 4 unit coarse pulse introduction of the sediment pulses to the channel caused dramatic increases in the bed load flux the coarse sediment pulses fine the bed surface and coarsen the bed load finer pulses also fine the surface but the bed load fines while the bed material load that excludes pulse material coarsens the greatest effects on the fractional transport occurred during the full unit fine pulse where the pulse covered the greatest bed surface and effectively smoothed the bed increasing near bed velocity and mobilizing the coarse particles overall the coarse pulses were not very effective at mobilizing bed material the large fine pulse mobilized 35 of the bed material surface 35 of its input weight and was most effective at mobilizing the surface however the small fine pulse mobilized 50 of its input weight as it passed through the channel making it the most efficient at mobilizing the bed material

broad weak regions of the nankai megathrust and implications for shallow coseismic slip abstract deep within the nankai trough subduction zone the plate boundary thrust slips along a well imaged megasplay fault system during the megathrust earthquakes that regularly strike southwest japan the routing of the active plate boundary thrust along an upward branching splay fault causes deep underthrusting of an unusually thick section of material attached to the subducting ocean crust here we present three dimensional seismic reflection data that shows this unusually thick section is fluid rich sediment that results in broad weakly coupled regions of the megathrust down into the updip end of the seismogenic zone the weakly coupled regions lie above an underthrust low seismic impedance presumed to be low velocity and low density sediment section that is between one and two kilometers thick and covers 3300 km2 at least one eighth of the total rupture area of the 1944 mw 8 1 tonankai earthquake this underthrust sediment section is broader and much deeper than inferred at other margins sediment underthrusting into the normally well coupled seismogenic zone likely releases fluids and elevates fluid pressure which reduces inter plate coupling along portions of the megasplay fault and allows coseismic rupture to propagate to unusually shallow depths and generate large tsunami as inferred for the 1944 tonankai event splay faults may be a common yet transient mechanism for developing weak subduction zone thrusts

the slip distribution of the 1946 nankai earthquake estimated from tsunami inversion using a new plate model abstract a new model for the shape of the philippine sea plate psp subducting beneath southwest japan was constructed by combining marine seismic survey results and seismicity data this resulted in a plate model that is generally 3 5 km shallower than previous estimates and contains new details of plate boundary structure near the nankai trough axis we estimated the slip distribution of the 1946 nankai earthquake by inverting tsunami waveforms using the new plate boundary model and found that the large slip off cape muroto and seismic moment were reduced by about 10 from the previous estimate of tanioka and satake 2001a however we also found reason to suspect the tide gauge closest to the epicenter at shimotsu and this resulted in a much more substantial reduction in the amount of slip in the eastern segment of the rupture area we also find that our new rupture model correlates well with features of the subducting plate boundary such as a large subducting seamount off cape muroto kodaira et al 2000a this suggests that such features have an important effect on either earthquake rupture propagation or the interseismic accumulation of elastic strain energy or both

sediment transport and resulting deposition in spawning gravels north coastal california incubating salmonid eggs in streambeds are often threatened by deposition of fine sediment within the gravel to relate sedimentation of spawning gravel beds to sediment transport infiltration of fine sediment 2 mm in diameter into clean gravel beds bed material size distributions scour fill depths and sediment transport during 10 storm flow events were measured in three streams of north coastal california although suspended sediment comprised most 75 94 of the clastic load during storm flows bed load material 0 25 2 mm accounted for most 70 78 of the fine sediment accumulated in experimental gravel implanted in the streambeds sand trapped in the interstices of the top several centimeters formed a seal that impeded deeper deposition of very fine sand and finer material the seal was responsible at least in part for a decrease in the rate of fine sediment accumulation with increasing cumulative bed load transport areas of the streambeds commonly scoured or filled 0 1 m or more during storm flows and thus scour and fill commonly created a sandy layer at least as thick as the seal formed by sediment infiltration scour could erode eggs laid in the bed and expose deeper levels of the bed to infiltration by fine sediment but at the same time could allow fine sediment to be winnowed away great temporal and spatial variation in sedimentation in these streams suggests that individual storms of moderate size pose a threat to eggs in many but not all areas selected by fish for spawning

effect of sand supply on transport rates in a gravel bed channel in a series of flume experiments using constant discharge flow depth and gravel feed rate sand feed rates were varied from 0 16 to 6 1 times that of gravel the bed slope decreased with increasing sand supply indicating that the gravel could be transported at the same rate along with increasing amounts of sand at smaller shear stresses prediction of river response to an increase in sediment supply requires prediction of mutual changes in bed composition and transport and therefore a transport model defined in terms of the grain size of the bed surface a recent model provides satisfactory prediction of the experimental observations and indicates the general response of gravel beds to increased sand supply an increase in sand supply may increase the sand content of the river bed and the mobility of gravel fractions which can lead to bed degradation and preferential evacuation of these sediments from the river

rapid forearc basin uplift and megasplay fault development from 3d seismic images of nankai margin off kii peninsula japan abstract offshore kii peninsula japan a large thrust within the overriding forearc the megasplay fault appears to move coseismically during great earthquakes 3d seismic images of the kumano forearc basin that overlies the megasplay correlated with iodp drilling data are a potential record of the history of large scale motion along this structure in the early quaternary uplift occurred in the southwest portion of the basin that may be a preliminary phase of motion along the megasplay more extensive landward tilting of the outer basin sediments across the seismic volume occurred over 300 kyr in the middle to late quaternary 1 3 1 ma this tilting event may represent the major period of motion along the megasplay that formed the modern fault geometry extensive normal faulting that cuts the forearc basin sediments clearly formed subsequent to the late quaternary tilting and in many cases offset the modern seafloor these faults may form either due to gravitational response to the uplift or as a by product of sediment underthusting these results suggest that the megasplay is a recently formed and transient structure and support the idea that out of sequence thrusts serving as the dominant structure for convergence driven shortening in a subduction zone may be short lived geologically but dominate a margin during these intervals

detachment levels in the marathon fold and thrust belt west texas surface and subsurface data are integrated to characterize the structural architecture of the marathon fold and thrust belt in west texas multiple detachment levels are present within the thrust belt and result in distinct structural domains in addition to the basal decollement whose stratigraphic position varies along strike we recognize a regionally extensive detachment zone in the late mississippian to early pennsylvanian lower tesnus formation the lower tesnus detachment forms a structural domain boundary that can be observed along strike in the surface data and at depth in the subsurface the stratigraphic intervals above and below this detachment exhibit characteristic patterns of deformation the lower tesnus detachment is folded by imbrication and the formation of duplexes in the early mississippian to ordovician section suggesting that the detachment may have initially formed as a perched decollement in the foreland that was subsequently exploited as a roof thrust in a duplex system as deformation progressed in a break forward sequence and older strata were incorporated into the toe of the allochthonous wedge the structural model presented here for the marathon region may be applicable across much of the ouachita orogenic system

vp vs ratio and shear wave splitting in the nankai trough seismogenic zone insights into effective stress pore pressure and sediment consolidation to estimate variation of stress state and sediment consolidation in the nankai plate subduction zone off southwest japan we measured the p wave to s wave velocity ratio vp vs and s wave splitting along the seismic line extending from the trench to the seismogenic zone for this purpose we used active source seismic data recorded by multicomponent ocean bottom seismometers obs because it is difficult to identify the ps converted reflection waveforms for each of the geological boundaries in this deep offshore region we focused on the more easily identified pps refracted waveforms that register the conversion of the up going p waves to s waves at the igneous crust surface we estimated the average vp vs ratio within the sedimentary section by using the time lag between the p refracted waves and pps converted waves this vp vs ratio changes abruptly at the trough axis i e the deformation front of the accretionary prism arguably because of compaction associated with the accretion process we observ

plate convergence and long term crustal deformation in central japan surveys by continuous global positioning system in and around japan revealed that the amurian plate collides with the north american plate in central japan by 2 cm yr long term crustal deformation seems to be influenced mainly by this collision although subduction of oceanic plates governs short term elastic deformation over the arc here we study the long term deformation field by carefully removing the short term signals inferred from a priori plate convergence vectors and coupling strengths predicted by a thermal model the obtained field shows that the change in velocities occurs along the longitude 135 137 and there exist a relatively rigid block and zones accommodating strains characteristic compressional deformation is found northwest of izu due possibly to the collision of the izu bonin arc with honshu plate convergence rate along the nankai suruga trough is considerably smaller in eastern parts due partly to the transition from the amurian to the north american plate of the landward side and partly to the motion of the izu microplate relative to the philippine sea plate this accounts for longer recurrence intervals of interplate earthquakes in the suruga trough where the tokai earthquake is anticipated to occur

bedload a granular phenomenon bedload the transport of sediment remaining in contact with the stream bed has mainly been studied from the perspective of the correlation between fluid driving forces and the responding sediment flux yet grain grain interactions are important and bedload should also be considered as a granular phenomenon we review progress made recently in the study of granular flows especially on segregation and rheology that better illuminates the nature of bedload granular flows may exhibit gas like or fluid like flow or quasi solid deformation all three conditions might be duplicated in bedload understanding of intense bedload transport occurring continuously in a layer several grains deep typical of sand beds might greatly benefit from results in granular physics as illustrated by grain inspired bedload results however processes restricted to the surface of the bed when particles move intermittently and the bed becomes structured while characteristic in gravel bed channels are not well addressed in granular physics mutual study of these phenomena may benefit both physics and fluvial geomorphology we intend therefore to contribute to an enhanced dialogue between granular physics and bedload science communities copyright 2010 john wiley sons ltd