ground motion modeling of the 1906 san francisco earthquake part ii ground motion estimates for the 1906 earthquake and scenario events abstract we estimate the ground motions produced by the 1906 san francisco earthquake making use of the recently developed song et al 2008 source model that combines the available geodetic and seismic observations and recently constructed 3d geologic and seismic velocity models our estimates of the ground motions for the 1906 earthquake are consistent across five ground motion modeling groups employing different wave propagation codes and simulation domains the simulations successfully reproduce the main features of the boatwright and bundock 2005 shakemap but tend to over predict the intensity of shaking by 0 1 0 5 modified mercalli intensity mmi units velocity waveforms at sites throughout the san francisco bay area exhibit characteristics consistent with rupture directivity local geologic conditions e g sedimentary basins and the large size of the event e g durations of strong shaking lasting tens of seconds we also compute ground motions for seven hypothetical scenarios rupturing the same extent of the northern san andreas fault considering three additional hypocenters and an additional random distribution of slip rupture directivity exerts the strongest influence on the variations in shaking although sedimentary basins do consistently contribute to the response in some locations such as santa rosa livermore and san jose these scenarios suggest that future large earthquakes on the northern san andreas fault may subject the current san francisco bay urban area to stronger shaking than a repeat of the 1906 earthquake ruptures propagating southward towards san francisco appear to expose more of the urban area to a given intensity level than do ruptures propagating northward

monsoon fluctuations in two 20 000 yr b p oxygen isotope pollen records off southwest india abstract two marine pollen diagrams for sediments off the southwest coast of india provide a 20 000 yr history of the nearby continental vegetation determined by the monsoon climate within the framework of the isotopic stratigraphy two important phases of the evolution of the monsoon climate are a very arid period about 22 000 18 000 yr b p and a very humid period culminating at 11 000 yr b p the very arid period corresponds to the lowest pollen representation of mangrove vegetation which is used here as an indirect indicator of monsoonal runoff this aridity is due to a very weak southwest airflow a great reduction of summer monsoonal rainfall and reduced runoff of the western ghats rivers the extension of the monsoon over india after the last glacial maximum has been a gradual process following the northward progression of the intertropical convergene zone the very humid period corresponding to the highest pollen representation of mangrove vegetation and the heaviest summer rainfall is a climatic response to the maximum summer insolation of the northern hemisphere at 11 000 yr b p

finite difference technique for sh waves in 2 d media using irregular grids application to the seismic response problem summary the finite difference method is applied to compute the seismic response of 2 d inhomogeneous structures for sh waves a technique is proposed which uses an irregular grid a rectangular grid with varying grid spacing a geological structure may be composed of blocks of media inside of which velocity and density vary linearly in horizontal and vertical directions the technique allows better adjusted modelling of a medium and in numerical examples presented yields more efficient computations as compared to those with regular grids the technique is tested through comparison with a discrete wavenumber method as an example the seismic response of the sediment filled chusal valley carm region ussr is computed the numerical results are compared with observations

three dimensional dynamic simulation of the 1992 landers earthquake the 1992 landers california earthquake magnitude 7 3 was modeled as the propagation of a spontaneous rupture controlled by a realistic prestress distribution with the use of a three dimensional finite difference method the dynamic rupture reproduces the general slip pattern used to compute the initial stress distribution and generates near fault ground motions at the surface similar to observations the simulated rupture propagates on the fault along a complex path with highly variable speed and rise time changing the magnitude and pattern of the stress significantly the method provides the framework to estimate earthquake rupture parameters from recorded seismic and geodetic data

50 ma initiation of hawaiian emperor bend records major change in pacific plate motion the hawaiian emperor bend has played a prominent yet controversial role in deciphering past pacific plate motions and the tempo of plate motion change new ages for volcanoes of the central and southern emperor chain define large changes in volcanic migration rate with little associated change in the chain s trend which suggests that the bend did not form by slowing of the hawaiian hot spot initiation of the bend near kimmei seamount about 50 million years ago ma was coincident with realignment of pacific spreading centers and early magmatism in western pacific arcs consistent with formation of the bend by changed pacific plate motion

a bump on the upper surface of the philippine sea plate beneath the boso peninsula japan inferred from seismic reflection surveys a possible asperity of the 1703 genroku earthquake abstract to reveal a subsurface structure beneath the southern part of the boso peninsula japan where the philippine sea plate is subducting and great interplate earthquakes associated with the subduction occur repeatedly we conducted a new seismic reflection survey from march to april 2005 boso05 we also reanalyzed old multi channel seismic mcs survey data that had been collected off the boso peninsula in 1978 sk78 we found clear strong reflectors beneath the southern coast of the boso peninsula since common mid points cmps were distributed widely beneath the study area owing to the design of the receiver and shot lines of boso05 we selected appropriate directions of stacking lines to get the best image of the dipping reflectors by optimum azimuth search oas processing we carefully checked the seismic profiles at the intersections of the survey lines to confirm the nne dipping configuration of the strong reflectors these strong reflectors were interpreted as the upper surface of the subducting phs plate from their locations and the estimated velocities beneath the reflectors furthermore these reflectors revealed a topographic high bump beneath the southern coast of the boso peninsula where the source fault of the genroku earthquake of 1703 is thought to be located

constraining earthquake source inversions with gps data 2 a two step approach to combine seismic and geodetic data sets 1 we present a new method to combine static and wavefield data to image earthquake ruptures our combined inversion is a two step procedure following the work of hernandez et al 1999 and takes into account the differences between the resolutions of the two data sets the first step consists of an inversion of the static field which yields a map of slip amplitude this inversion exploits a special irregular grid that takes into account the resolution of the static data the second step is an inversion of the radiated wavefield it results in the determination of the time evolution of slip on the fault in the second step the slip amplitude is constrained to resemble the static slip amplitude map inferred from the gps inversion using this combined inversion we study the source process of the 2004 m6 parkfield california earthquake we conclude that slip occurred in two main regions of the fault each of which displayed distinct rupture behaviors slip initiated at the hypocenter with a very strong bilateral burst of energy here slip was localized in a narrow area approximately 10 km long the rupture velocity was very fast 3 5 km s and slip only lasted a short period of time 1 s then the rupture proceeded to a wider region 12 20 km northwest of the hypocenter here the earthquake developed in a more moderated way the rupture velocity slowed to 3 0 km s and slip lasted longer 1 2 s the maximum slip amplitude was 0 45 m

structure of the crust beneath the southeastern tibetan plateau from teleseismic receiver functions abstract southeastern tibet marks the site of presumed clockwise rotation of the crust due to the india eurasian collision and abutment against the stable sichuan basin and south china block knowing the structure of the crust is a key to better understanding of crustal deformation and seismicity in this region here we analyze recordings of teleseismic earthquakes from 25 temporary broadband seismic stations and one permanent station using the receiver function method we find that the crustal thickness decreases gradually from the tibetan plateau proper to the sichuan basin and yangtze platform but that significant intra crustal heterogeneity exists on shorter lateral scales 0 30 are detected beneath the southeastern margin of tibet but in the sichuan basin and southeastern yangtze platform the values are close to the global average combined with high regional heat flow and independent evidence for mid crustal layers of high electric conductivity the large intra crustal s wave velocity reduction 12 19 and the intermediate to high average crustal poisson s ratios are consistent with partial melt in the crust beneath parts of southeastern tibet these results could be used in support of deformation models involving intra crustal flow with the caveat that significant lateral variation in location and strength of this flow may occur

crustal structure of mainland china from deep seismic sounding data abstract since 1958 about ninety seismic refraction wide angle reflection profiles with a cumulative length of more than sixty thousand kilometers have been completed in mainland china we summarize the results in the form of 1 a new contour map of crustal thickness 2 fourteen representative crustal seismic velocity depth columns for various tectonic units and 3 a pn velocity map we found a north south trending belt with a strong lateral gradient in crustal thickness in central china this belt divides china into an eastern region with a crustal thickness of 30 45 km and a western region with a thickness of 45 75 km the crust in these two regions has experienced different evolutionary processes and currently lies within distinct tectonic stress fields our compilation finds that there is a high velocity 7 1 7 4 km s layer in the lower crust of the stable tarim basin and ordos plateau however in young orogenic belts including parts of eastern china the tianshan and the tibetan plateau this layer is often absent one exception is southern tibet where the presence of a high velocity layer is related to the northward injection of the cold indian plate this high velocity layer is absent in northern tibet in orogenic belts there usually is a low velocity layer lvl in the crust but in stable regions this layer seldom exists the pn velocities in eastern china generally range from 7 9 to 8 1 km s and tend to be isotropic pn velocities in western china are more variable ranging from 7 7 to 8 2 km s and may display azimuthal anisotropy

geometric evolution of a plate interface branch fault system its effects on the tectonic development of the himalayas abstract crustal deformation due to fault slip depends strongly on fault geometry and fault geometry is changed by the deformation of the crust this feedback mechanism causes the geometrical evolution of the fault system we have studied the progress of the geometrical evolution of a plate interface branch fault system through numerical simulation based on elastic viscoelastic dislocation theory if the plate interface is smooth no significant change occurs in fault geometry if the plate interface has a ramp we observe the gradual horizontal motion of the ramp toward the hanging wall side of the interface at half the plate convergence rate the offset of the ramp decreases with time the dip angle of thrust faults branching from the plate interface increases more rapidly as the dip of the fault increases we have applied these results to the plate interface branch fault system at the india eurasia collision boundary and obtained a scenario for the tectonic development of the himalayas for the last 30 myr

late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments the modern indian ocean summer monsoon is driven by differential heating between the asian continent and the indian ocean to the south this differential heating produces a strong pressure gradient which drives southwest monsoon winds during june july and august satellite and meteorological observations aerosol measurements sediment trap studies and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest arabian sea analyses of lithogenic grain size and mass accumulation rate mar records from the owen ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr visual inspection shows that the mar record is positively correlated with global ice volume as indicated by the marine 18o record in contrast the grain size record varies at a much higher frequency showing little correlation to either the mar or the 18o records spectral analyses confirm these relationships indicating that the lithogenic grain size and mar records are coherent only over the precession band whereby the grain size leads the mar by 124 8 kyr we conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and mar with independent eolian records we use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic mar as a paleoclimatic indicator of source area aridity these interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength globigerina bulloides upwelling record and aridity a loess record from central china such comparisons indicate high coherence and zero phase relationships our work supports the findings of previous studies which have documented the link between monsoon strength and the earth s axial precession cycles both the lithogenic mar and the grain size records have high coherency with precessional insolation maximum lithogenic mar source area aridity is in phase with 18o global ice volume and leads maximum precessional insolation by 88 6 kyr we attribute this lead to the influence of glacial conditions on the aridity and therefore the deflation potential of the source areas maximum lithogenic grain size summer monsoon wind strength lags maximum precession by 148 9 kyr we attribute this lag both to the influence of global and or local ice volume and to the availability of latent heat from the southern hemisphere indian ocean the two of which combine to determine the strength of the indian ocean monsoon

sedimentary phosphorus record from the oman margin new evidence of high productivity during glacial periods 1 the northern region of the arabian sea is one of the biologically most fertile regions of the world oceans with present productivity rates varying between 150 and 2500 mgc m2 day madhupratap et al 1996 this is related to the influence of the southwesterly summer monsoon which causes vigorous upwelling along the oman margin upwelling ceases during northeasterly winter monsoon activity productivity rates however remain relatively high about 800 mgc m2 day related to deep water mixing madhupratap et al 1996 the goal of this study is to verify if during the last glacial period a period in which winter monsoon conditions prevailed productivity rates were similarly high with an analysis of phosphorus phases stable nitrogen isotopes organic matter content and bulk mineralogy of the upper 10 m of the cores of odp hole 724c corresponding to the last 140 000 years sample resolution is 5 kyr we provide new evidence of high productivity during this last glacial period marine isotopic stages 2 3 and 4 this was probably related to the combined effect of 1 increased eolian input of iron containing dust due to dryness on the adjacent continent and stronger winter monsoon and 2 regeneration and diffusion of dissolved phosphorus from the sediments to the water column due to variations in the position and intensity of the oxygen minimum zone these findings suggest that there is no one to one relationship between summer monsoon activity and productivity which emerges to be a quasi persistent phenomenon across glacial and interglacial stages

active tectonics of the beichuan and pengguan faults at the eastern margin of the tibetan plateau the steep high relief eastern margin of the tibetan plateau has undergone rapid cenozoic cooling and denudation yet shows little evidence for large magnitude shortening or accommodation generation in the foreland basin we address this paradox by using a variety of geomorphic observations to place constraints on the kinematics and slip rates of several large faults that parallel the plateau margin the beichuan and pengguan faults are active dominantly dextral slip structures that can be traced continuously for up to 200 km along the plateau margin both faults offset fluvial fill terraces that yield inheritance corrected cosmogenic 10be exposure ages of 15 kyr indicating latest pleistocene activity the pengguan fault appears to have been active in the holocene at two sites along strike latest quaternary apparent throw rates on both faults are variable along strike but are typically 1 mm yr 1 rates of strike slip displacement are likely to be several times higher probably 1 10 mm yr 1 but remain poorly constrained late quaternary folding and dextral strike slip has also occurred along the western margin of the sichuan basin particularly associated with the present day mountain front these observations support models for the formation and maintenance of the eastern plateau margin that do not involve major upper crustal shortening they also suggest that activity on the margin parallel faults in eastern tibet may represent a significant seismic hazard to the densely populated sichuan basin

3 d simulation of tectonic evolution of the mariana arc back arc system with a coupled model of plate subduction and back arc spreading abstract we developed a mechanical model for the nonlinear coupled system of plate subduction and back arc spreading on the basis of mathematical formulation for internal deformation due to a moment tensor in an elastic viscoelastic layered half space under gravity in our modeling the plate subduction and the back arc spreading are rationally represented by the increase of tangential displacement discontinuity at the plate interface and normal displacement discontinuity at the spreading center respectively through 3 d numerical simulation with this model we obtained a possible scenario for the tectonic evolution of back arc basins as follows at the first stage steady plate subduction gradually forms tensile stress fields in the back arc region when the accumulated tensile stress reaches a critical level back arc spreading starts at a structurally weak portion of the overriding plate the back arc spreading pushes out the frontal part of the overriding plate toward the plate boundary and leads to the increase of slip rates at the plate interface the local increase of slip rates at the plate interface produces additional tensile stress in the back arc region the incremental tensile stress is canceled out by further back arc spreading such a feedback mechanism is necessary to maintain steady back arc spreading the long duration of slip rate excess due to back arc spreading leads to the gradual protrusion of the plate boundary toward the descending plate trench retreat as the plate boundary moves away from the back arc spreading center the accumulation rate of tensile stress at the spreading center gradually decreases and the slip rate excess at the plate interface due to back arc spreading also decreases then the original back arc spreading center becomes less effective in releasing the tectonic tensile stress and new active back arc spreading will start somewhere closer to the plate boundary such a qualitative scenario accords with the evolution history of back arc basins in the mariana region we obtained the slip rate excess of 7 mm year at the plate interface and the 20 km trench retreat for the last 4 5 myr these simulation results are significantly smaller than observations in the mariana region the discrepancy between simulation results and observations can be ascribed to the effect of the negative buoyancy acting on cold descending slab which advances spontaneous plate subduction and directly increases the slip rate excess and the trench retreat in our model

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

continental crust crustal underplating and low q upper mantle beneath an oceanic island arc a detailed structural model of the crust subducting slab and underlying upper mantle across the northern izu ogasawara bonin island arc system is derived from a marine seismic reflection and ocean bottom seismographic refraction survey and subsequent forward modeling combined with tomographic inversion the model indicates that the crust is thickest beneath the presently active rift zone and a granitic crust may have formed in the mid crust a highly attenuative mantle that is one with low quality q seems to be confined mainly beneath the presently active rift zone in contrast high p wave velocity persists in the lower crust between the forearc and eastern margin of the back arc basin suggesting a large scale magma input responsible for the arc formation

ground motion modeling of the 1906 san francisco earthquake part i validation using the 1989 loma prieta earthquake we compute ground motions for the beroza 1991 and wald et al 1991 source models of the 1989 magnitude 6 9 loma prieta earthquake using four different wave propagation codes and recently developed 3d geologic and seismic velocity models in preparation for modeling the 1906 san francisco earthquake we use this well recorded earthquake to characterize how well our ground motion simulations reproduce the observed shaking intensities and amplitude and durations of recorded motions throughout the san francisco bay area all of the simulations generate ground motions consistent with the large scale spatial variations in shaking associated with rupture directivity and the geologic structure we attribute the small variations among the synthetics to the minimum shear wave speed permitted in the simulations and how they accommodate topography our long period simulations on average under predict shaking intensities by about one half modified mercalli inten sity mmi units 25 35 in peak velocity while our broadband simulations on average under predict the shaking intensities by one fourth mmi units 16 in peak velocity discrepancies with observations arise due to errors in the source models and geologic structure the consistency in the synthetic waveforms across the wave propagation codes for a given source model suggests the uncertainty in the source parameters tends to exceed the uncertainty in the seismic velocity structure in agree ment with earlier studies we find that a source model with slip more evenly distributed northwest and southeast of the hypocenter would be preferable to both the beroza and wald source models although the new 3d seismic velocity model improves upon previous velocity models we identify two areas needing improvement nevertheless we find that the seismic velocity model and the wave propagation codes are suitable for modeling the 1906 earthquake and scenario events in the san francisco bay area online material modified mercalli intensities and velocity waveforms and a movie of simulated wave propagation

seismotectonics beneath the tokyo metropolitan area japan effect of slab slab contact and overlap on seismicity 1 we first determine the configuration of the upper surface of the pacific pac slab beneath kanto japan from the distribution of interplate earthquakes relocated by an appropriate 1 d velocity model then traveltime tomography is carried out to estimate three dimensional seismic velocity structures around kanto using 735 520 p wave and 444 049 s wave arrival times from 6508 local earthquakes the obtained results suggest that the philippine sea phs slab is subducting to depths of 130 140 km without a gap even to the northwest of the izu collision zone we subsequently define the lateral extent of the contact zone between the bottom of the phs slab and the upper surface of the pac slab phs pac interface and reveal that the slab contact zone underlies a wider area beneath kanto in harmony with the kanto plain the downdip limit of interplate thrust type earthquakes on the pac slab is deepened by 30 km locally under the slab contact zone this deepening is probably caused by a lower temperature environment in the pac slab resulting from the overlap with the phs slab subducting above and consequent thermal shielding by the phs slab from the hot mantle wedge we detect an extremely low velocity anomaly in the easternmost portion of the phs slab which is probably attributable to serpentinization of mantle peridotite interplate earthquakes are almost absent along the phs pac interface overlain by the serpentinized mantle in the phs slab suggesting that ductile deformation takes place along the interface because of low viscosity of the serpentine

kinematic inversion of the 2004 m 6 0 parkfield earthquake including an approximation to site effects the 2004 m 6 0 parkfield earthquake yielded one of the largest amounts of near source strong ground motion seismic data ever we invert strong motion seismograms to obtain a model for the space time distribution of coseismic slip on the fault to reduce noise in the inversion we take into account local amplifications that affect each station by using records of the 1983 m 6 5 coalinga earthquake site amplification correlates well with large peak ground velocities registered during the 2004 parkfield mainshock the inversion for a kinematic rupture model yields a nonunique solution we therefore analyze various rupture models that explain the data equally well our preferred rupture model identifies a primary zone of high slip surrounding the hypocenter where the maximum slip is 57 cm a secondary slip area over which contours are not well resolved is located northwest of the hypo center the rupture speed is highly heterogeneous we infer an average rupture ve locity of 2 8 km sec close to the hypocenter and of 3 3 km sec in the secondary region of large slip to the northwest of the hypocenter by correlation of our rupture model with both microseismicity and velocity structure we identify six patches on the fault plane that behave in seismically distinct ways online material kinematic rupture model parameters

evidence for a change in the periodicity of tropical climate cycles at 2 4 myr from whole core magnetic susceptibility measurements the earth s orbit about the sun is influenced by gravitational interactions with the moon and other planets the resulting orbital perturbations give rise to cyclical variations in orbital eccentricity obliquity and precession with periods of 100 41 19 and 23 kyr respectively1 these variations are climatically important because they affect the seasonal and latitudinal distribution of solar radiation magnetic susceptibility measurements in deep sea sediment cores can be used as a sensitive indicator of temporal variations in the concentration of terrigenous material supplied to the sea bed here we use this approach to study the evolution of cycles of terrigenous sedimentation at ocean drilling program sites in the arabian sea and the eastern tropical atlantic we show from spectral analyses of the two susceptibility time series spanning the past 3 2 3 5 myr that the records are driven strongly by orbital forcing before 2 4 myr before present bp both records are strongly influenced by the 23 and 19 kyr periodicities but after 2 4 myr they are both significantly influenced by the 41 kyr periodicity this shift coincides with the beginning of major northern hemisphere glaciation which indicates for the indian ocean site that the supply of terrigenous sediment carried by monsoonal winds has responded to the rapid increase in ice cover at this time we cannot however exclude possible effects of changes in bottom water circulation on the susceptibility record of the atlantic site

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

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

postcollisional exhumation history of the tanzawa tonalite complex inferred from u th he thermochronology and fission track analysis 1 the tanzawa mountains in the south fossa magna region in the middle of the japan arc were formed due to collision of the izu bonin arc against the japan arc during the last several million years the tanzawa tonalite complex is exposed in the tanzawa mountains and is inferred to represent middle crust of the izu bonin arc we performed new thermochronometry consisting of u th he dating fission track dating and fission track length analysis for the complex to investigate the exhumation history of the tanzawa tonalite complex caused by arc arc collision typical u th he ages were 2 0 0 2 ma on apatite 3 3 0 2 ma on zircon and 4 5 to 6 9 ma on zircon using the fission track method the mean fission track length was 9 7 0 6 m 2 se the cooling rate of the tonalite has been calculated to be in the range of 20 60 c ma 1 from 7 to 3 3 ma 80 c ma 1 from 3 3 to 2 0 ma and 30 c ma 1 from 2 0 to 0 ma assuming a surface temperature of 10 c the exhumation rate has been calculated to be 0 5 to 1 5 mm a 1 from 7 to 3 3 ma 2 mm a 1 from 3 3 to 2 0 ma and 0 8 mm a 1 from 2 0 to 0 ma with an assumed geothermal gradient of 40 c km 1 the exhumation rate has not changed significantly despite the simultaneous tectonic changes around the tanzawa mountains after 7 ma

the evolution of saharan dust input on lanzarote canary islands influenced by human activity in the northwest sahara during the early holocene an overall holocene increase of saharan dust input to the canary islands and to the north canary basin is accompanied by a strong coarsening of saharan dust in loess like sediments deposited on lanzarote from 7 8 ka no similar coarsening events are indicated in investigations of the sedimentological record for the last 180 ka a period showing several dramatic climate changes therefore a mobilisation of holocene dust by anthropogenic activity in the northwest sahara east of the canary islands is assumed although scarce archaeological data from the coastal area of that region does not point to strong anthropogenic activity during the early holocene a high density of unexplored archaeological remains is reported from the coastal hinterlands in the western sahara thus the hypothesis of early anthropogenic activity cannot be excluded

3 d modelling of plate interfaces and numerical simulation of long term crustal deformation in and around japan we developed a 3 d simulation model for long term crustal deformation due to steady plate subduction in and around japan by incorporating viscoelastic slip response functions into a realistic 3 d plate interface model constructed on the basis of the topography of ocean floors and hypocenter distributions of earthquakes the lithosphere asthenosphere system is modelled by an elastic surface layer overlying a maxwellian viscoelastic half space kinematic interaction at plate interfaces is rationally represented by the increase of tangential displacement discontinuity fault slip across the interfaces with this model giving the steady slip rates at plate interfaces calculated from nuvel 1a we simulated long term crustal deformation due to steady plate subduction in and around japan the simulated crustal deformation pattern is characterized by steep uplift at island arcs sharp subsidence at ocean trenches and gentle uplift at outer rises the numerical results show the strong dependence of the deformation pattern on the 3 d geometry of plate interfaces

clay mineral accumulation rates in the arabian sea during the late quaternary abstract the regional variations in clay mineral concentrations in 39 turbidite free and undisturbed deep sea sediment cores from the arabian sea are compared with distribution patterns of clay mineral accumulation rates during the holocene and the last glaciation dust plumes from the red sea area arabia mesopotamia iran and pakistan can be traced by accumulation rates of mineral specific dust loads during the late quaternary the major proportions of aeolo marine sediments in the western arabian sea were derived from arabia during the summer season the clay mineral assemblage in these dust plumes consists of illite smectite kaolinite chlorite and palygorskite in decreasing order of abundance the distribution pattern of palygorskite in particular reveals that dust transport from southern arabia occurs mainly with northwesterly to westerly winds in the mid troposphere dust plumes from iran and pakistan which are characterized by high chlorite content are dispersed by northwesterly winds over the northwestern arabian sea dust contributions from the red sea area which are rich in smectite and characterized by the occurrence of amphiboles are transported to the gulf of aden the amount of dust related to northeast monsoon winds during the winter season appears to be negligible when compared to the proportions borne on other dust bearing winds in addition to aeolian contributions we distinguish two fluvial contributions a chlorite illite kaolinite and quartz rich assemblage from oman and pakistan into the gulf of oman and a smectite rich assemblage which is dominant off southern india originating from rivers that drain the indian subcontinent the significant difference between the holocene and glacial accumulation rates of wind transported clay minerals consist in the higher abundance of quartz illite and chlorite in the northwestern arabian sea during the last glaciation this pattern indicates intensified dust contributions by northwesterly winds from the persian gulf area which was dry during glacial times

simulation of tectonic evolution of the kanto basin of japan since 1 ma due to subduction of the pacific and philippine sea plates and the collision of the izu bonin arc abstract the kanto basin the largest lowland in japan developed by flexure as a result of 1 the subduction of the philippine sea phs and the pacific pac plates and 2 the repeated collision of the izu bonin arc fragments with the japanese island arc geomorphological geological and thermochronological data on vertical movements over the last 1 my suggest that subsidence initially affected the entire basin after which the area of subsidence gradually narrowed until finally the basin began to experience uplift in this study we modeled the tectonic evolution of the kanto basin following the method of matsu ura and sato 1989 for a kinematic subduction model with dislocations in order to quantitatively assess the effects of phs and pac subduction we include the steady slip rate deficit permanent locking rate at the plate interface in our model to account for collision process we explore how the latest collision of the izu peninsula block has been affected by a westerly shift in the phs plate motion vector with respect to the eurasian plate thought to have occurred between 1 0 0 5 ma using long term vertical deformation data to constrain extent of the locked zone on the plate interface we evaluated the change in vertical deformation rate for two scenarios 1 a synchronous shift in the orientation of the locked zone as phs plate motion shifts and 2 a delayed shift in the orientation of the locked zone following the shift in plate motion observed changes in the uplift subsidence pattern are better explained by scenario 2 suggesting that recent

a dislocation model for the earthquake cycle at convergent plate boundaries summary a kinematic model for the earthquake cycle at convergent plate boundaries has been constructed on the basis of dislocation theory we model the lithosphere asthenosphere system by a stratified semi infinite medium under gravity consisting of an elastic surface layer an intervening layer with maxwell viscoelasticity and an elastic substratum the steady motion of plate convergence is naturally represented by uniform slip at a constant rate on the upper boundary of the descending oceanic plate the occurrence of interplate earthquakes is regarded as a perturbation of the steady state plate motion and represented by a periodic sequence of step slips on a finite seismic zone of the plate interface based on dislocation theory we can show that the steady slip on the interface deeper than the lithosphereasthenosphere boundary does not contribute to surface deformation in the steady state accordingly the surface deformation associated with the earthquake cycle is given by the superposition of viscoelastic responses to the steady slip on the interface shallower than the lithosphere asthenosphere boundary the steady backslip on the seismic zone and the periodic sequence of seismic slips we have computed cyclic patterns of vertical displacements at the free surface for two representative cases taking account of gravity effects the patterns of vertical displacements differ notably in the latter stage of the cycle depending on whether or not the seismic zone extends through the entire thickness of the lithosphere after the completion of one earthquake cycle our model yields a certain amount of permanent deformation resulting from the steady plate convergence the pattern of the permanent deformation that is characterized by steep uplift on the continental side sharp subsidence at the plate boundary and gentle uplift on the oceanic side is irrespective of the cyclic process of stress accumulation and release repeated on the seismic zone the earthquake cycle model developed here provides a possible explanation for the formation of earthquake origin marine terraces

reactivation of an old plate interface as a strike slip fault in a slip partitioned system median tectonic line sw japan abstract in models for strain partitioning at obliquely convergent plate boundaries trench parallel slip occurs on a vertical fault trench parallel slip at the nankai subduction zone sw japan is mapped along the median tectonic line mtl which dips approximately 40 n to understand its structural context and how the mtl functions in this slip partitioned system we collected a set of three seismic profiles in the kii peninsula south of osaka using a multi scale acquisition strategy that provides increasingly fine resolution to understand its fault kinematics we analyzed microseismic activity in two locations on the fault using source data from japan s hi net monitoring network structural details suggest that the mtl functioned as a megathrust during subduction of the cretaceous sanbagawa hp metamorphic belt its current pattern of microseismicity shows that it behaves as a strike slip fault with no indication of a vertical fault at or around its surface trace thus trench parallel slip at the nankai is now accommodated on an inclined fault plane in an unusual form of partitioning this system appears to have developed out of a two phase tectonic history in which a thrust structure that formed under initial phase compressive stresses has been reactivated as a strike slip fault under subsequent phase shear stresses its unusual kinematics show that shear failure can occur on an existing non vertical fault plane at a regional scale in preference to the rupture of a new ideal vertical fault plane

site effects and peak ground accelerations observed in guadalajara mexico for the 9 october 1995 mw 8 colima jalisco earthquake on 3 june 1932 an m s 8 2 shallow thrust subduction earthquake struck the colima jalisco cj region of mexico at an epicentral distance of 250 km from guadalajara the second largest town in mexico the return period of these cj earthquakes has been estimated from 77 to 126 years which suggests the next is likely to occur between 2009 and 2058 as a step toward estimating the seismic hazard posed by potential m s 8 2 events on guadalajara we present a study consisting of the following 1 the analysis of the strong ground motions recorded at guadalajara on 11 free field accelerographs for the cj 9 october 1995 m w 8 earthquake 2 the analysis of the site effects in guadalajara observed for this earthquake and 3 the estimation of the spatial distribution of peak ground acceleration pga in guadalajara for this event we propose validate and apply a recurrent neural network rnn technique to the recorded pga important site effects were identified using the horizontal to vertical and h hrocksite techniques on guadalajara s sandy soil layers with thicknesses h 20 m to the basaltic rock basement the estimated pgas in guadalajara for the cj 1995 earthquake varied from 2 to 27 cm s2 for soil layers with h 5 m and h 50 m respectively we expect the hybrid technique to obtain broadband synthetics chavez et al 2011 and the proposed rnn methodology can be used to estimate guadalajara s seismic hazard for m w 8 cj scenario earthquakes online material figures of fourier amplitude spectra h v and h h spectral ratios and signal to noise spectral ratios

crustal structure beneath the eastern margin of the tibetan plateau and its tectonic implications 1 two crustal cross sections through the eastern margin of the tibetan plateau are jointly determined from deep seismic sounding the e w trending line aa passes through the western sichuan plateau including the songpan garze terrane and the longmenshan fault belt and ends in the sichuan basin a part of the yangtze craton line bb has a trend of nne and crosses the songpan garze terrane two dimensional crustal structures along the profiles were jointly determined by the additional use of existing deep seismic sounding data our seismic velocity models indicate that the western sichuan plateau and the sichuan basin have crustal thicknesses of 62 and 43 km average crustal p wave velocities of 6 27 and 6 45 km s and lower crustal vp 6 5 km s thicknesses of 27 and 15 km respectively density models constructed from the seismic velocity models are consistent with observed bouguer gravity anomalies we infer that collision between the tibetan plateau and the yangtze craton has caused thickening of the lower crust and uplift of the western sichuan plateau we detect a low velocity layer in the upper crust of the western sichuan plateau but observe no equivalence in the sichuan basin west dipping thrusts may detach into this low velocity layer the seismic phase pmp in the western sichuan plateau has low amplitude suggesting high attenuation in the lower crust qp of 100 300 we suggest that the high attenuation is a consequence of lower crustal flow caused by the large lower crustal thickness beneath the western sichuan plateau

3 d simulation of tectonic loading at convergent plate boundary zones internal stress fields in northeast japan the evidence of east west compression in northeast japan has been reported by many investigators on the basis of geodetic geologic and geomorphic data but its origin still remains far from understood in the present study we have proposed a mechanical model of tectonic loading at convergent plate boundary zones and demonstrated its validity through the numerical simulation of internal stress fields in northeast japan with realistic 3 d geometry of plate interfaces at convergent plate boundary zones in general a part of plate convergence is consumed by steady slip along plate interfaces and the remaining part by inelastic deformation seismic faulting aseismic faulting and active folding of overriding plates such a plate boundary process to be called partial collision can be quantitatively described by introducing a collision rate defined as c 1 steady slip rate at plate interfaces plate convergence rate by this definition we can simply represent the mechanical process of partial collision which includes total subduction c 0 and total collision c 1 as two extreme cases in terms of steady slip rates at plate interfaces on the basis of elastic dislocation theory first we numerically computed the internal stress fields in northeast japan produced by the total subduction of the pacific plate beneath the north american plate however the computed stress pattern was opposite in sense to observations then we computed the internal stress fields by taking c 0 1 on average and succeeded in reproducing the observed east west compression in northeast japan this indicates that the concept of partial collision is essential to understand the mechanism of intraplate tectonic loading

rupture history of the 2008 mw 7 9 wenchuan china earthquake evaluation of separate and joint inversions of geodetic teleseismic and strong motion data an extensive data set of teleseismic and strong motion waveforms and geodetic offsets is used to study the rupture history of the 2008 wenchuan china earthquake a linear multiple time window approach is used to parameterize the rupture because of the complexity of the wenchuan faulting three separate planes are used to represent the rupturing surfaces this earthquake clearly demonstrates the strengths and limitations of geodetic teleseismic and strong motion data sets geodetic data static offsets are valuable for determining the distribution of shallower slip but are insensitive to deeper faulting and reveal nothing about the timing of slip teleseismic data in the distance range 30 90 generally involve no modeling difficulties because of simple ray paths and can distinguish shallow from deep slip teleseismic data however cannot distinguish between different slip scenarios when multiple fault planes are involved because steep takeoff angles lead to ambiguity in timing local strong motion data on the other hand are ideal for determining the direction of rupture from directivity but can easily be over modeled with inaccurate green s functions leading to misinterpretation of the slip distribution we show that all three data sets are required to give an accurate description of the wenchuan rupture the moment is estimated to be approximately graphic 1 with the slip characterized by multiple large patches with slips up to 10 m rupture initiates on the southern end of the pengguan fault and proceeds unilaterally to the northeast upon reaching the cross cutting xiaoyudong fault rupture of the adjacent beichuan fault starts at this juncture and proceeds bilaterally to the northeast and southwest 1 embed inline graphic 1 gif

cenozoic motion of the philippine sea plate palaeomagnetic evidence from eastern indonesia the history of motion of the philippine sea plate is poorly known because it is isolated from the oceanic ridge system interpretation of palaeomagnetic results from the plate has been controversial because declination data have been obtained only from the eastern margin where subduction related tectonic processes may have caused local rather than plate wide rotations new palaeomagnetic data relevant to the problem have been obtained from 34 sites north of the sorong fault and 29 sites within the sorong fault system these sites record south ward movement during the eocene and northward movement during the neogene sites within the sorong fault system record both counterclockwise and clockwise rotations interpreted as the result of neogene block movements at the southern boundary of the philippine sea plate north of the sorong fault all sites record clockwise declinations neogene rocks have small deflections consistent with rotation about the present day eurasia philippine sea plate pole oligocene middle eocene rocks show consistent clockwise declination deflections of 40 o declinations of lower eocene rocks indicate 90 o of clockwise rotation we propose that the entire area north of the sorong fault in east indonesia has always been part of the philippine sea plate and that the whole plate has rotated clockwise in a discontinuous manner by approximately 90 o since the early eocene the new data from north of the sorong fault provide a basis for determining rotation poles which satisfy all the palaeomagnetic data from the philippine sea plate and permit its reconstruction

rupture process of the 2011 tohoku oki earthquake and absolute elastic strain release 1 on 11 march 2011 the tohoku oki earthquake in eastern japan and the devastating tsunami that followed it caused severe damage and numerous deaths to clarify the rupture process of the earthquake we inverted teleseismic p wave data applying a novel formulation that takes into account the uncertainty of green s function which has been a major error source in waveform inversion the estimated seismic moment is 5 7 1022 nm mw 9 1 associated with a fault rupture 440 km long and 180 km wide along the plate interface the source process is characterized by asymmetric bilateral rupture propagation but we also found continuous slips up dip from the hypocenter which led to a large maximum slip 50 m long slip duration 90 s and a large stress drop 20 mpa the long slip duration large stress drop extensional normal faulting aftershocks in a previously compressional stress regime and low angle normal slips at approximately the depth of the plate interface suggest that the earthquake released roughly all of the accumulated elastic strain on the plate interface owing to exceptional weakening of the fault the stress accumulated on the plate interface was about 20 mpa near the trench and 0 10 mpa in the down dip source region

subducting seamounts and deformation of overriding forearc wedges around japan abstract two subducting seamounts under inner trench slopes have been identified around japan on the basis of magnetic anomalies morphology and geological structure the first one is located under the foot of the inner trench slope at the junction between the japan trench and the kuril trench another one occurs beneath the slope slightly seaward of the tosabae the basement high at the trench slope break along the nankai trough off shikoku the magnetic anomalies of seamount origin are accompanied by the characteristic morphology of a forearc wedge i e a swell landward and a depression seaward the seamounts beneath the inner trench slopes have preserved magnetization showing reasonably consistent directions which suggests that the subducting seamounts have kept roughly their original shapes the morphology of the forearc wedge can be explained by a subducting seamount on the oceanic crust pushing the forearc material forward and upward deformation of the forearc wedge by the subducting seamount extends to the forearc basin the seamounts are stronger and less deformable than the inner slope material and are not offscraped onto inner trench slopes two other examples of deformed inner trench slopes around japan which can be explained by subduction of topographic highs are presented one example is a depression on the foot of the inner trench slope northeast of the junction between the kyushu palau ridge and the nankai trough another one is an area of complex morphology of the inner trench slope along the japan trench around the daiichi kashima seamount

impact of productivity events on the benthic foraminiferal fauna in the arabian sea over the last 150 000 years we have studied the sediment geochemistry and benthic foraminiferal fauna in a piston core from the northwest arabian sea covering the last 150 000 years and compared the results with the stable isotopic record from both benthic uvigerina peregrina and planktonic globigerinoides sacculifer foraminifera the 18o record of the planktonic foraminiferal species shows excursions towards heavier 18o values when compared to the benthic record and the specmap stack particularly in stage 3 between approximately 30 and 45 50 kyr we call this the stage 3 event species diversity and relative abundance data on benthic foraminifera reveal that some species e g cibicidoides wuellerstorfi oridorsalis umbonatus pullenia bulloides pyrgo spp and the uvigerinids increased in relative abundance during glacial stages 2 and 4 and during the stage 3 event whereas other e g astrononion novozealandicum cibicidoides bradyi eggerella bradyi gyroidina altiformis hoeglundina elegans pullenia subcarinata and sigmoilina edwardsii decreased using correspondence analysis we determined that approximately 50 of the total sample variation may be accounted for by three first factors which all are interpreted as primarily related to surface water productivity and the quality of the organic matter that reaches the seafloor the relative abundance of some species appears to vary on a precessional cycle perhaps responding to monsoon driven upwelling and associated increased food supply whilst the abundances of other species are related to the 100 kyr ice volume cycle and may be responding to changes in intermediate and deep water chemistry geochemical paleoproductivity tracers such as the ba content of the sediment have a very similar distribution to specific foraminiferal factors in both time and frequency domains certain planktonic foraminifera e g globigerina bulloides also display obvious maxima in the stage 3 event the stage 3 event occurs at a time of reduced rate of amplitude change in both solar radiation and monsoon pressure index we conclude that there was a period 15 to 20 kyr duration during stage 3 with cooler than normal surface waters enhanced productivity and rapid settling of biogenic matter

opening mode of the japan sea inferred from the palaeomagnetism of the japan arc the western edge of the pacific plate is marked by a chain of back arc basins stretching from the aleutians through japan and the philippines to new zealand most of the basins lie behind volcanic island arcs far from continents and are the result of extension of the oceanic lithosphere1 but the japan sea is bounded on one side by continental crust the sikhote alin and korean peninsula of the asian continent and on the other by an active arc with continental fragments it can thus be said to be associated more with continental rifting1 4 than with oceanic processes we report here palaeomagnetic data from the japan arc which indicate that since the early miocene north east japan has rotated counter clockwise through 47 around a vertical axis while south west japan has rotated clockwise through 56 refs 5 8 we attribute this differential rotation which took place concurrently between 21 and 11 myr ago to the back arc opening of the japan sea8 with a double door mode that is there are two fan shaped spreading basins facing each other such a fan shaped opening is probably peculiar to the geological phenomenon of rifting of a continental fragment from thick continental lithosphere

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

the relationship between late cenozoic tectonic events and stress field and basin development in northeast japan the regional tectonic stress field basin development and crustal deformation of the ne japan arc in the interval between 32 ma to the quaternary can be synthesized based on dike vein and fault orientation data as well as on the compilation of the regional geology an extensional stress field became prevalent from 32 ma and major normal faulting started at 25 20 ma which resulted from back arc rifting normal faulting trending nearly parallel to the arc propagated from the present japan sea coast to the forearc side following the trenchward migration of the main volcanic field from 20 to 15 ma normal faults with an oblique trend to the arc developed due to the counterclockwise rotation of ne japan the rapid clockwise rotation of sw japan since 16 ma produced a nw se directed transtensional stress regime in the ne japan arc due to crustal stretching associated with this pull apart movement the back arc side of the ne japan arc subsided rapidly to middle bathyal environments after the termination of the opening of the japan sea at about 14 ma a neutral stress regime prevailed which included phases of both weak extension and compression lithospheric cooling eventually led to thermal subsidence of the back arc region and igneous underplating caused uplift of the axial zone of the volcanic arc the increase in velocity of the westward motion of the pacific plate at around 4 ma produced strong compression across the arc reactivating most of the miocene normal faults and uplifting the volcanic arc the greatest crustal shortening occurred in areas that were stretched the most in the miocene within the volcanic arc which implies tectonic inversion

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

the concentration of particulate aluminum and clay minerals in aerosols from the northern arabian sea abstract aerosol samples have been collected from the northern arabian sea during the northeast monsoon total atmospheric al concentrations ranged between 323 and 20 300 ng m 3 of air these are among the highest found over marine regions and demonstrate that the atmosphere is an important pathway for the transport of crustal material to the northern arabian sea and the gulf of oman the clay mineralogy of the soil sized particulates in the aerosol is similar to that of the surface sediments underlying the collection region but is different from that of the other sediments in the arabian sea the clay mineral data provide evidence supporting previously proposed theories that the relatively high concentrations of chlorite in the sediments of the northern arabian sea and the gulf of man are a consequence of the atmospheric transport of crustal material from the adjacent land masses

a unified interpretation of vertical movement in himalaya and horizontal deformation in tibet on the basis of elastic and viscoelastic dislocation theory abstract the present day convergence rate between the indian and the eurasian plates has been estimated to be about 50 mm year at the collision boundary extending along the himalayas about 40 of the total convergence is consumed by the subduction of the indian plate beneath the eurasian plate the rest of about 60 is consumed by the internal deformation of the eurasian plate the present crustal movement in this region is characterized by rapid uplift along the high himalayas and large scale horizontal deformation in and around tibet the fundamental causes of these two different types of crustal movement are the same interaction between the indian and the eurasian plates in this study we represent the plate interaction by steady increase in tangential displacement discontinuity dislocation across the interface that divides a surface layer overlying a viscoelastic half space into the indian and the eurasian plates first given a steady slip of 20 mm year at the plate interface with a ramp shaped undulation below the high himalayas we computed the profile of surface uplift rates along a line perpendicular to the himalayan arc the result accords with observed free air gravity anomalies and the intermediate and short term uplift rates estimated respectively from the present heights of river terraces and levelling data this means that the rapid uplift of the high himalayas is due to the steady slip along the ramp shaped plate interface below it second given the steady slips of 20 mm year along the 2000 km long collision boundary and 50 mm year along the remaining portions of the india eurasia plate boundary we computed the increase rates of horizontal deformation in and around tibet the result accords with the observed strikes and slip rates of major quaternary active faults this means that the horizontal deformation in and around tibet is due to the slip deficits of 30 mm year at the collision boundary from these two results we can conclude that the present rapid uplift of the high himalayas and large scale horizontal deformation in and around tibet are consistently explained by a single plate interaction model based on elastic and viscoelastic dislocation theory this study sheds new light on the driving mechanism of the crustal deformation in the india eurasia collision zone as follows the plate interaction on single plate interface consists of coexisting two different physical mechanisms 1 slip along the ramp undulation spatial changes in slip direction 2 slip deficit at the collision boundary spatial changes in slip rates as a consequence the two different types of crustal deformation in the india eurasia collision zone are driven by these two different physical mechanisms

tectonic evolution along the northernmost border of the philippine sea plate since about 1 ma abstract recent structural tephrochronologic and magnetostratigraphic studies conducted along the northernmost border of the philippine sea phs plate enable us to reconstruct the precise tectonic evolution along the convergent boundary between the phs plate and the northeast japan nej plate or the north american nam plate since about 1 ma the authors of the present study split the tectonic evolution into five stages and present the characteristics of each stage a plate tectonic interpretation is proposed based upon the tectonic evolution with special reference to the mode of convergent motion in brief our interpretations are as follows the relative motion between the phs and the nej plates was not recognized geologically within the area studied from about 1 0 to 0 9 ma stage 1 suggesting either none or small influence from the coupling between the two plates during that period of time convergence between the phs and the nej plates was possibly in n s direction from 0 9 to 0 5 ma stage ii and probably north northwestward since 0 5 ma stages iii to v the mode of the convergent motion was that of buoyant subduction in stages ii and iii the mode changed gradually from buoyant subduction during stage iv to collision in stage v 0 07 ma to the present

collision of the izu block with central japan during the quaternary and geological evolution of the ashigara area abstract the ashigara area is located in the northern part of the izu collision zone and has been suspected as a possible location of the boundary between the eurasian and the philippine sea plates in order to analyse its evolution during the collision we have determined the age of the ashigara group and studied its depositional environments and its deformation the age of the ashigara group is early to middle pleistocene the lower part was deposited in a 1000 2000 m deep trough which lay between the izu peninsula and central japan at that time the sedimentary facies show subsequent upward coarsening and shallowing the beginning of the collision resulted in the uplift of the tanzawa mountains which are the source of the voluminous conglomerates deposited in this area soon after the deposition of the upper part of the ashigara group this area was over thrust by the tunzawa mountains along the kannawa fault and strongly folded under a nw se compressional stress field then about 0 3 ma ago the direction of compression drastically changed to n s or ne sw when the colliding izu peninsula was finally locked against central japan

slip distribution of the 19 september 1985 michoacan mexico earthquake near source and teleseismic constraints we simultaneously invert the strong motion velocity records and the long and intermediate period teleseismic p waveforms of the 19 september 1985 michoacan mexico earthquake to recover the distribution of slip on the fault using a point by point constrained and stabilized least squares inversion method a fault plane with strike fixed at 300 and dip fixed at 14 is placed in the region of the earthquake hypocenter and divided into 120 subfaults rupture is assumed to propagate at a velocity of 2 6 km sec away from the hypocenter synthetic near source ground motions and teleseismic p waveforms for pure strike slip and dipslip dislocations are calculated for each subfault the observed data are then inverted to obtain the amount of strike slip and dip slip displacement required of each subfault we also invert the data sets using a time window procedure where the subfaults are allowed to slip up to three times this approach relaxes the constraint of fixed subfault rupture time imposed by a constant rupture velocity inversion of the strong motion data alone yields a slip model similar to the solution previously obtained using only teleseismic waveforms this result supports the use of teleseismic waveform data for the derivation of fault dislocation models in the absence of strong motion recordings our simultaneous inversion of both data sets suggests that rupture during the michoacan earthquake was controlled largely by the failure of three major asperities located along the length and down the dip of a 150 km segment of the cocos north america plate boundary the solution contains three major source regions including an 80 km by 55 km source near the hypocenter with a peak slip of 6 5 meters two additional sources are present on the southeast portion of the fault about 70 km away from the hypocenter one of these sources with a peak slip of 5 meters covers a 45 km by 60 km area and extends downdip from a depth of about 10 km to 24 km the third source region is somewhat smaller 30 km by 60 km area 3 1 meters peak slip and extends further downdip at depths between 27 km and 39 km aftershock activity following the earthquake was associated mainly with the two shallow sources these two sources are separated by the aftershock zone of the 1981 playa azul earthquake

3 d simulation of steady plate subduction with tectonic erosion current crustal uplift and free air gravity anomaly in northeast japan free air gravity anomaly in plate subduction zones characterized by island arc high trench low and outer rise gentle high reflects the cumulative effects of long term crustal uplift and subsidence in northeast japan the island arc high of observed free air gravity anomaly takes its maximum about the eastern coastline on the other hand the current vertical crustal motion estimated from geological and geomorphological observations shows a gentle uplift in the land area and steep subsidence in the sea area with the neutral point near the eastern coastline such a discrepancy in spatial patterns between the free air gravity anomaly and current vertical crustal motion can be ascribed to a change in the mode of crustal uplift and subsidence associated with the initiation of tectonic erosion at the north american pacific plate interface we developed a realistic 3 d simulation model of steady plate subduction with tectonic erosion in northeast japan on the basis of elastic viscoelastic dislocation theory through numerical simulations with this model we found that simple steady plate subduction brings about the crustal uplift characterized by island arc high with its maximum about the eastern coastline while steady plate subduction with tectonic erosion which is represented by the landward retreat of the plate interface brings about gentle uplift in the land area and steep subsidence in the sea area with the neutral point near the eastern coastline therefore if we suppose that tectonic erosion started 3 4 million years ago after the long duration of simple steady plate subduction we can consistently explain both patterns of free air gravity anomaly and current crustal uplift in northeast japan

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

pliocene change in pacific plate motion the absolute motion of the pacific plate has been nearly constant during the past 15 myr but epp1 recognized that some change took place between 15 myr and the present and tentatively chose 1 myr for the time of the change cox and engebretson2 found a change in pacific absolute motion based on hotspot tracks and a change in pacific antarctic relative motion the pliocene deformation in california and the juan de fuca rotations led them to postulate a 5 myr age for the change the manner and timing of the change are explored more thoroughly here and we put the time for the change in motion of the pacific plate at between 5 and 3 2 myr basing the younger limit on the correlation of computed hotspot tracks with pacific and nazca hotspot traces the change may explain several observations on the neighbouring continental and oceanic plate boundaries including direct adjustments at the pacific spreading ridges a likely mechanism for the change is a large clockwise torque caused by acceleration of the sinking slab beneath the kurile trench where a fossil spreading ridge is inferred to have been subducted

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

crustal structures in the area of the 2008 sichuan earthquake from seismologic and gravimetric data abstract the 12 may 2008 the sichuan earthquake was one of the worst natural disasters in china here we present a detailed picture of the epicentral area inferred geophysical data based on the analysis of teleseismic data acquired by a dense seismic network we highlight an abrupt 20 km moho offset between the sichuan basin and the tibetan plateau and a horizontal discontinuity at 15 km depth which may connect with the ruptured zone of the 2008 event we obtain low mean crustal velocity ratios which suggest the absence of a thick and extensive zone of partial melt within the crust beneath the eastern part of the songpan garze terrane all our data support the idea that the longmen shan range mark a zone of active strain localization due to the rigid yangtze craton resisting eastward displacement of the tibetan plateau

change in motion of pacific plate at 5 myr bp alignments of volcanoes such as the hawaiian seamount chain record the passage of oceanic plates over mantle plumes or hot spots and changes in the orientation of a seamount chain may indicate changes in the direction of motion of the plate within the hotspot frame of reference1 this hypothesis can be tested for the pacific plate by comparing data from the hawaiian volcanoes with tectonic movements inferred from the geology of adjacent plates we have now found that the motion of the pacific plate changed to a more northerly direction 5 myr ago probably as a result of the detachment of a piece of pacific sea floor which had been subducted beneath the fiji plateau during the tertiary

cenozoic tectonic and depth age evolution of the indonesian gateway and associated back arc basins abstract we reconstruct the tectonic and paleo age and depth history of the indonesian seaway and associated southeast asian back arc basins to create a comprehensive paleogeographic framework for the region during the cenozoic we combine published tectonic models with revised models of the evolution of back arc basins based on available marine magnetic anomaly data and a recently published high resolution 1 min marine gravity anomaly grid which reveals many fine scale tectonic features previously not resolved reconstructions of the now subducted ceno tethys ocean floor are integrated with a revised absolute plate motion reference frame for the indian ocean based on moving hotspots all marginal seas north of australia formed in a back arc setting with the caroline and celebes seas opening north of a northward dipping subduction zone and the solomon sea south of a southward dipping subduction zone north of australia we suggest that the evolution of the two sub basins of the caroline sea from 36 to 25 ma followed different seafloor spreading patterns with the western sub basin being influenced by the manus hotspot our model suggests that collision between the melanesian and the caroline arcs led to cessation of oceanic crustal production in the caroline basin shortly before 25 ma combined geophysical and geological observations suggest that several major tectonic events occurred north of australia at around 45 ma roughly at the time when australia started moving northwards at fast rates similar to the present we suggest that this event is related to a relocation of the subduction zone nw of australia under the philippine sea plate due to a collision and subsequent accretion of old pacific plate material to the northward subducting australian plate our gridded oceanic paleo depth maps capture the history of marginal seas north of australia and the stepwise destruction of the ceno tethys ocean floor in the northern wharton basin and the west pacific providing boundary conditions for both paleoceanograpic and geodynamic models a regional analysis of basement depth anomalies reveals that median negative anomalous depth of several back arc basins is of the order of 650 800 m with a range of 300 1100 m accompanied by negative regional heatflow anomalies suggesting that mantle driven dynamic topography plays a larger role in modulating regional basement depth than previously suggested regional shear wave mantle tomography cross sections highlight that all marginal basins that exhibit large negative dynamic topography are underlain by massive buried slab material in the lower portion of the upper mantle and or below the transition zone supporting the notion that the observed paired negative dynamic topography and heatflow anomalies are due to basin formation above slab burial grounds

a kinematic model for evolution of island arc trench systems summary plate subduction zones are typically characterized by the patterns of surface topography and gravity anomalies consisting of island arc high trench low and outer rise gentle high these patterns are stable on the time scale of 106 107 yr at some subduction zones regardless of its age steady uplift of marine terraces formed by eustatic sea level changes during the last lo5 yr can be also observed the stable patterns of topography and gravity anomalies and the steady uplift of marine terraces seem to contradict each other we constructed a kinematic model which could explain the evolution process of island arc trench systems and demonstrated that this puzzle could be solved by considering the effect of accretion at plate boundaries in our model the lithosphere asthenosphere system is represented by a stratified visco elastic half space under gravity which consists of a high viscosity surface layer and a low viscosity substratum the rheological properties of both layers are assumed to be a maxwell fluid in shear and an elastic solid in bulk interaction between oceanic and continental plates is represented by the steady increase of discontinuity in tangential displacement across the plate boundary the other essential factors considered in our model are accretion of oceanic sediments at plate boundaries erosion on land and sedimentation on inner trench wall we computed the evolution process of island arc trench systems by using the kinematic model and obtained the following results the island arc trench systems grow at nearly constant rates in the early stage of plate subduction therefore at young subduction zones we can generally expect the steady uplift of marine terraces the stable patterns of topography and gravity anomalies are formed within several million years after the initiation of plate subduction when the accretion process continuously proceeds at plate boundaries these stable patterns gradually migrate seaward as a whole in such a case we can expect the steady uplift of marine terraces even at old subduction zones we demonstrate that our model can consistently explain the observed surface topography gravity anomalies and uplift rates of marine terraces at subduction zones

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

evolution and variability of the asian monsoon system state of the art and outstanding issues the asian monsoon is comprised of the indian and east asian subsystems these two components are linked to one another in varying degrees by regions of strong sensible heating indo asian landmass and strong latent heat export the western pacific warm pool and the southern subtropical indian ocean variability within the indian and east asian subsystems interactions among them and the extent to which they interact with other climate phenomena e g enso are current topics of modern and paleoclimate research this work provides an overview of past and current paleomonsoon research on tectonic to interannual time scales with a primary focus on marine sediment records while past and current work has contributed greatly to our understanding of paleomonsoon variability at all time scales additional efforts are required to make further progress in two critical areas 1 additional efforts are needed in terms of proxy development and evaluation requiring concerted efforts at long term sediment trap deployments in key monsoon influenced regions as well as development of adequate and widely available core top databases these are necessary to assess the impact of modern oceanographic and seafloor processes on potential monsoon proxies 2 additional effort is also needed in acquiring a sufficient geographic distribution of downcore records to assess linkages among the subsystems and their role in the context of extratropical climate change these records should have high sedimentation rates including varved sections this requires substantial survey support to identify the most appropriate coring and drilling targets c 2004 elsevier ltd all rights reserved

paleogeographic reconstruction and origin of the philippine sea abstract our reconstruction of the philippine sea suggests that it formed by two distinct episodes of back arc spreading each of which resulted from seaward retreat of the trench in the first episode the protoizu bonin trench retreated northward and the west philippine basin formed behind the northern half of the palau kyushu ridge in the second episode the izu mariana trench retreated eastward and the shikoku and parece vela basins formed behind it during the last 17 ma the philippine sea basin has been moving northwestward with respect to eurasia shifting the ttt triple junction off central japan westward by about 50 km the motion of the philippine sea with respect to eurasia at the triple junction changed from north northwestward to west northwestward 10 5 ma ago for the period before 17 ma ago we construct two models retreating trench model and anchored slab model the izu bonin trench migrated from south to northeast rotating in a clock wise sense since 48 ma ago in the retreating trench model in the anchored slab model the trench has been fixed with respect to eurasian margin since 43 ma ago we prefer the retreating trench model because the deformation of the plate boundary along the eastern margin of eurasia during 30 17 ma ago is much simpler for this model than for the anchored slab model furthermore rotations of the bonin mariana islands are consistent with those predicted from the retreating trench model the 48 ma ages of the northern part of the palau kyushu ridge and of chichi jima of the bonin islands indicate that there was subduction beneath the northern half of the ridge beginning at least 48 ma ago from this and the subparallelism in trend between the northern part of the palau kyushu ridge and the central basin ridge we propose that the major part of the west philippine basin formed by back arc spreading in a n s direction behind the northern part of the palau kyushu ridge the pacific plate was moving northward with respect to hot spots from 48 to 43 ma ago which implies that the pacific plate is not likely to have been subducting beneath the west philippine basin during this time we speculate that another plate existed south of the pacific plate and thai it was subducting beneath both tile west philippine basin and australia the annihilation of this plate might he a cause for the sudden change of the pacific plate motion at 43 ma ago

distributions and origins of clay minerals and quartz in surface sediments of the arabian sea abstract mineral distributions in surface sediments of the arabian sea north of 5 n reflect several sedimentary origins and processes smectite and quartz rich sediments occurring along the indian margin have been derived from the western regions of peninsular india in the northern and western most areas of the arabian sea sediments probably have been derived from several sources indus river iran makran region arabian peninsula and somalia these different sediment sources appear to have characteristically high amounts of quartz illite chlorite or palygorskite in addition smectite becomes a significant component in the sediments off somalia horn of africa the sediments derived from the peninsular india and indus river may have been dispersed by prevailing surface oceanic irculation in the region sediments from other sources probably have been transported by wind the sediments of the distal indus fan appear to be a mixture of sediments derived from the indus river iran makran and arabia somalia regions palygorskite clays from the arid regions of arabia somalia appear to have been transported by winds eastward to as far as the indian continental margin in the southernmost region of study relatively high kaolinite derived from the tropical soils of africa madagascar and southern india characterize the sediments

strong ground motion simulations of the mw 7 9 wenchuan earthquake using the empirical green s function method the m w 7 9 wenchuan earthquake shocked china as well as the world not only because of its great moment magnitude but also due to the terrible casualties the complex nature of this earthquake combined with its damage brings the need for studies that assess the seismological characteristics of the m w 7 9 wenchuan earthquake in this study we present the strong ground motion simulation of the great earthquake using the empirical green s function egf method first we select four m w 4 9 and 5 0 aftershocks the motions of which are used as green s functions the source parameters of the aftershocks including fault size and stress drop are estimated for the simulation then the source model of m w 7 9 with asperities strong motion generation area is derived using forward modeling by trial and error to validate the accuracy of the proposed source model strong ground motions at nine stations are synthesized by the egf method the simulated strong ground motions are compared with the observed records in terms of acceleration waveforms velocity waveforms and pseudoacceleration response spectrum despite some discrepancy the synthesized motions at most stations show good agreement with the observed records in the proposed source model the stress drop of the three asperities on the source fault is about 10 mpa whereas the ratio of combined area to the rupture area is 0 24 which approximates 0 22 from the empirical relationship