has the plate boundary shifted from central hokkaido to the eastern part of the sea of japan abstract a ns trending cenozoic fold and thrust belt has developed in the western part of the hidaka collision zone hcz central hokkaido japan a quantitative estimation of the late cenozoic convergence rate at the front of the hidaka thrust system is important in revealing the plate tectonic framework around northern japan high resolution seismic reflection profiling across the active fault related folds was carried out to ascertain the temporal change in the crustal shortening rate overlapping ramp anticlines and growth folds within thrust sheets were examined using balanced cross sections combined with industry seismic and drilling data the rate of shortening was examined using a 3 5 ma horizon and late quaternary horizons at 115 and 41 ka these horizons show that the convergence rate of the hidaka thrust system has not decreased during the last 3 5 ma this suggests that the plate boundary between the eurasian amurian and north american okhotsk plates has not jumped from the central part of hokkaido to the eastern part of the sea of japan since 3 5 ma and that a significant amount of plate convergence is still being absorbed in the hidaka collision zone

middle to late miocene foredeep basin successions in an arc arc collision zone northern tanzawa mountains central honshu japan abstract middle to late miocene coarse siliciclastic and volcaniclastic deposits are distributed along a narrow longitudinal reverse fault and fold belt between the kanto and tanzawa mountains central honshu japan the coarse clastic piles represent foredeep basin successions characterized by a progressive shallowing sequence from basin plain through submarine volcano submarine fan slope to fan delta systems the siliciclastic deposits are clastic wedges that prograded directly into and down the axis of the foredeep basin during the uplift and progressive unroofing of the orogenic northern highlands of the kanto mountains this was accompanied by syndepositional deformation of the basin fills which is mainly represented by the northward tilting and gave rise to active longitudinal drainage on the southern flank of the kanto mountains interbedded volcaniclastic deposits on the other hand were mainly derived from small submarine volcanoes emplaced on the landward basin slope and may represent near trench magmatism evolution of the foredeep basin successions can be explained by collision of the tanzawa block a paleo volcanic island with central honshu honshu arc since the late miocene following northward subduction of the izu bonin volcanic arc ridge which was emplaced by westward subduction of the pacific plate beneath the philippine sea plate

constraints on the moho in japan and kamchatka abstract this review collects and systematizes in one place a variety of results which offer constraints on the depth and the nature of the moho beneath the kamchatka peninsula and the islands of japan we also include studies of the izu bonin volcanic arc all results have already been published separately in a variety of venues and the primary goal of the present review is to describe them in the same language and in comparable terms for both regions we include studies using artificial and natural seismic sources such as refraction and reflection profiling detection and interpretation of converted mode body waves receiver functions surface wave dispersion studies in kamchatka and tomographic imaging in japan the amount of work done in japan is significantly larger than in kamchatka and resulting constraints on the properties of the crust and the uppermost mantle are more detailed japan and kamchatka display a number of similarities in their crustal structure most notably the average crustal thickness in excess of 30 km typical of continental regions and the generally gradational nature of the crust mantle transition where volcanic arcs are presently active

imprint of the north american plate in siberia revealed by gps 1 gps observations in east siberia combined with global observations collected 1995 2002 place constraints on the geometry and motions of the eurasian north american and pacific plates in east asia by comparing velocities relative to eurasia and to north america we conclude that east siberia to the east of the cherskiy range belongs to the north american plate hypothesized for three decades but not proven because of uncertainties with the plate boundary arising from the ambiguous seismicity smaller plates in east asia such as okhotsk and amurian can neither be resolved nor excluded by the gps velocities

seismological features of island arc crust as inferred from recent seismic expeditions in japan abstract crustal studies within the japanese islands have provided important constraints on the physical properties and deformation styles of the island arc crust the upper crust in the japanese islands has a significant heterogeneity characterized by large velocity variation 5 5 6 1 km s and high seismic attenuation qp 100 400 for 5 15 hz the lateral velocity change sometimes occurs at major tectonic lines in many cases of recent refraction wide angle reflection profiles a middle crust with a velocity of 6 2 6 5 km s is found in a depth range of 5 15 km most shallow microearthquakes are concentrated in the upper middle crust the velocity in the lower crust is estimated to be 6 6 7 0 km s the lower crust often involves a highly reflective zone with less seismicity indicating its ductile rheology the uppermost mantle is characterized by a low pn velocity of 7 5 7 9 km s several observations on pmp phase indicate that the moho is not a sharp boundary with a distinct velocity contrast but forms a transition zone from the upper mantle to the lower crust recent seismic reflection experiments revealed ongoing crustal deformations within the japanese islands a clear image of crustal delamination obtained for an arc arc collision zone in central hokkaido provides an important key for the evolution process from island arc to more felsic continental crust in northern honshu a major fault system with listric geometry which was formed by miocene back arc spreading was successfully mapped down to 12 15 km

moho vs crust mantle boundary evolution of an idea abstract the concept that the mohorovicic discontinuity moho does not necessarily coincide with the base of the continental crust as defined by rock type compositions was introduced in the early 1980s this had an important impact on understanding the nature of the crust mantle boundary using information from seismology and from deep seated samples brought to the surface as xenoliths in magmas or as tectonic terranes the use of empirically constrained p t estimates to plot the locus of temperature vs depth for xenoliths defined a variety of geotherms depending on tectonic environment the xenolith geotherms provided a framework for constructing lithological sections through the deep lithosphere and revealed that the crust mantle boundary in off craton regions commonly is transitional over a depth range of about 5 20 km early seismic reflection data showed common layering near the moho correlating with the petrological observation of multiple episodes of basaltic intrusion around the crust mantle boundary developments in seismology petrophysics and experimental petrology have refined interpretation of lithospheric domains the expansion of in situ geochronology especially zircon u pb ages and hf isotopes os isotopes of mantle sulfides has defined tectonic events that affected whole crust mantle sections and revealed that the crust mantle boundary can change in depth through time however the nature of the crust mantle boundary in cratonic regions remains enigmatic mainly due to lack of key xenoliths or exposed sections the observation that the moho may lie significantly deeper than the crust mantle boundary has important implications for modeling the volume of the crust mapping the crust using seismic techniques alone without consideration of the petrological problems may lead to an overestimation of crustal thickness by 15 30 this will propagate to large uncertainties in the calculation of elemental mass balances relevant to crust formation processes and the composition of the convecting mantle

contrasts of seismic velocity density and strength across the moho abstract we provide an overview of contrast of elastomechanical parameters across the moho basically contrasts in seismic wave velocities density and yield strength these can be regarded as dynamic and quasi static endmembers of elastomechanical parameters of the crust mantle transition with respect to practical applications they are closely related because seismic investigations play the role of exploring the earth structure and physical state forming the boundary conditions for determining density and rheological models we address both average global moho models and petrophysical and structural factors that cause deviations from the global averages such as variations in moho depth temperature and rock composition fabric anisotropy and macro scale heterogeneity besides principle considerations these factors are put in a regional context in order to demonstrate how they are related to past and present tectonic processes seismic velocity and density contrasts are found between 0 and 25 whereas strength or viscosity contrasts may be orders of magnitude higher but may vanish as well or show a discontinuity of higher order only especially oceanic and old cratonic crust and near moho mantle may appear as a rheological unit although they are seismically well distinguishable in terms of seismic velocities the moho may vanish mainly under the influence of serpentinization or eclogitization originally defined as a first order discontinuity in seismic velocity the moho has turned out to be an interface across which other seismic properties such as seismic velocity gradients anisotropy and heterogeneity scale parameters can change strongly too however knowledge of these parameters as well as their relation to the rheology of the crust mantle transition is still restricted to local or regional examples so no global conclusions can be drawn

evolution of clastic piles in an arc arc collision zone late cenozoic depositional history around the tanzawa mountains central honshu japan abstract late cenozoic clastic piles around the tanzawa mountains represent trough trench landward and seaward basin fills developed in an arc arc collision zone in central honshu japan the landward basin fills are clastic wedges prograded from the northern orogenic highlands and are characterized by fan deltaic successions succeeding submarine volcano submarine fan slope successions on basin plain deposits the landward basin fills were generally developed intermittently from north to south since the middle miocene evolution of the landward basin fills depended on the interplay of the northward buoyant subduction and suturing of the izu bonin arc in central honshu honshu arc together with submarine magmatism on the landward basin slope emplaced by the subducting pacific plate beneath the izu bonin arc to the west the seaward basin fills however generally lack terrigenous detritus derived from the northern highlands except for a trough fill which received some detritus shed from the rising highs just to the north and are characterized by pyroclastic flow deposits prograded from the southern submarine volcanoes or a volcanic island on the ocean basin the northward progradation of the pyroclastic flow deposits may have been emplaced by the northward drifting of the ocean basin the tanzawa mountains on the other hand consist mainly of early to middle miocene subaqueous volcaniclastic rocks intercalated with some volcanic conglomerates and shallow marine coquinas and can be interpreted as a miocene volcanic island punctuated initiation and propagation of the late cenozoic basin fills diachronously from the north to the south of the tanzawa mountains can be explained by northward drifting and collision of the tanzawa block a paleo volcanic island with central honshu during middle to late miocene and the consequent jump of the subduction zone to the south of it since late miocene preceding the collision of the izu peninsula izu block with the south of the youngest basin fills developed in the southern front of the tanzawa mountains since the middle pleistocene after collision of the izu block with the southernmost basin fills the late cenozoic clastics in and around the tanzawa mountains were uplifted and deformed into northward imbricated structures by rapid slip on the faults framing this area

crustal structure and tectonics of the hidaka collision zone hokkaido japan revealed by vibroseis seismic reflection and gravity surveys abstract this study is the first integrated geological and geophysical investigation of the hidaka collision zone in southern central hokkaido japan which shows complex collision tectonics with a westward vergence the hidaka collision zone consists of the idon nappu belt ib the poroshiri ophiolite belt pob and the hidaka metamorphic belt hmb with the hidaka belt from west to east the pob metamorphosed ophiolites is overthrust by the hmb steeply eastward dipping palaeo arc crust along the hidaka main thrust hmt and in turn thrusts over the idon nappu belt melanges along the hidaka western thrust hwt seismic reflection and gravity surveys along a 20 km long traverse across the southern hidaka mountains revealed hitherto unknown crustal structures of the collision zone such as listric thrusts back thrusts frontal thrust and fold structures and duplex structures the main findings are as follows 1 the hmt which dips steeply at the surface is a listric fault dipping gently at a depth of 7 km beneath the eastern end of the hmb and cutting across the lithological boundaries and schistosity of the hidaka metamorphic rocks 2 a second reflector is detected 1 km below the hmt reflector the intervening part between these two reflectors is inferred to be the pob which is only little exposed at the surface this inference is supported by the high positive bouguer anomalies along the hidaka mountains 3 the shallow portion of the ib at the front of the collision zone has a number of nne dipping reflectors indicative of imbricated fold and thrust structures 4 subhorizontal reflectors at a depth of 14 km are recognized intermittently at both sides of the seismic profile these reflectors may correspond to the velocity boundary 5 9 6 6 km s previously obtained from seismic refraction profiling in the northern hidaka mountains 5 these crustal structures as well as the back thrust found in the eastern end of the traverse represent characteristics of collisional tectonics resulting from the two collisional events since the early tertiary

magma compensated crustal thinning in continental rift zones continental rifts are elongated depressions in the earth s surface often more than 1 000 km long 20 km wide and 10 km deep filled with sediments and volcanic rocks conventional models of rift zones include three characteristic features surface manifestation as an elongated topographic trough moho shallowing due to crustal thinning and reduced seismic velocity in the uppermost mantle hans thybo and christoffer nielsen present a new seismic profile that demonstrates that the baikal rift zone in siberia displays only one of these characteristic features the elongated surface trough there is a localized zone in the lower crust with exceptionally high seismic velocity and high reflectivity the expected moho uplift appears to have been compensated by magmatic intrusion into the lower crust producing the observed high velocity zone this finding points to a previously unknown role for magmatism in rifting this study presents a seismic profile across southern lake baikal in siberia demonstrating that only a surface manifestation is observed there these findings may point toward a new role for magmatism in the rifting process continental rift zones are long narrow tectonic depressions in the earth s surface where the entire lithosphere has been modified in extension1 rifting can eventually lead to rupture of the continental lithosphere and creation of new oceanic lithosphere or alternatively lead to formation of wide sedimentary basins around failed rift zones conventional models of rift zones include three characteristic features surface manifestation as an elongated topographic trough moho shallowing due to crustal thinning and reduced seismic velocity in the uppermost mantle due to decompression melting or heating from the earth s interior2 3 4 here we demonstrate that only the surface manifestation is observed at the baikal rift zone whereas the crustal and mantle characteristics can be ruled out by a new seismic profile across southern lake baikal in siberia instead we observe a localized zone in the lower crust which has exceptionally high seismic velocity and is highly reflective we suggest that the expected moho uplift was compensated by magmatic intrusion into the lower crust producing the observed high velocity zone this finding demonstrates a previously unknown role for magmatism in rifting processes with significant implications for estimation of stretching factors and modelling of sedimentary basins around failed rift structures

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

origin of the cenozoic mesozoic magnetite series and ilmenite series granitoids in east asia abstract among the phanerozoic granitoids of east asia the most prevailing cenozoic mesozoic rocks are reviewed with respect to gabbro granite ratio bulk composition of granitoids redox state and o and sr isotopic ratios quaternary volcanic rocks ranging from basalt to rhyolite but typically felsic andesite in terms of bulk composition in island arcs are oxidized type possibly due to oxidants from subducting oceanic crust into the source regions miocene plutonic rocks in the back arc of japan could be a root zone for such volcanism but are more felsic in composition cenozoic mesozoic plutonic zones are classified by 1 the redox state magnetite ilmenite series and 2 average bulk composition granodiorite granite the granodioritic magnetite series occur with fairly abundant gabbro and diorite in the back arc of island arcs greentuff belt and intercontinental rapture zones yangtze block these rocks are mostly juvenile in terms of the 87sr 86sri and 18o values the granitic magnetite series with some gabbroids occur in rapture zones along the continental coast gyeongsang basin fujian coast and the back arc of island arc sanin belt they were generated mostly in felsic continental crust with the help of heat and magmas from upper mantle the generated granitic magmas had little interaction with c and s bearing reducing materials due probably to extensional tectonic settings the 18o value gives narrow ranges but the 87sr 86sri ratio varies greatly depending upon the age and composition of the continental crust granitic ilmenite series are characterized by high 18o values implying much contribution of sediments the 87sr 86sri ratios are low in island arcs but very high in continental interior settings amount of mafic magmas from the upper mantle seems a key to control the composition of granitoid series in island arc settings while original composition of the protolith may be the key to control granitoid composition in continental interiors

back arc rifting in the okinawa trough abstract geological and geophysical data reveal that the okinawa trough shows incipient continental rifting and crustal separation started from about 2 ma the early extensional movements in the trough are probably of miocene age in addition to the miocene phase two main periods of extension are recognized a pleistocene phase between 1 9 and 0 5 ma and the present day phase during the stage short central rifts central grabens were formed the opening however may have occurred only in the southern part of the trough basin having an average half spreading rate of 2 cm yr 1 since early pleistocene time producing its present width of several tens of kilometres these activities were well represented by igneous intrusions sedimentary facies and sedimentary structures in and around the okinawa trough the width of the zone affected by back arc extension defined as greater okinawa trough is larger than the present okinawa trough whose width is 200 250 km the present form of the greater okinawa trough started to form at the same time as that of the okinawa trough

volcanic sulfate deposition to greenland and antarctica a modeling sensitivity study reconstructions of the atmospheric sulfate aerosol burdens resulting from past volcanic eruptions are based on ice core derived estimates of volcanic sulfate deposition and the assumption that the two quantities are directly proportional we test this assumption within simulations of tropical volcanic stratospheric sulfur injections with the maecham5 ham aerosol climate model an ensemble of 70 simulations is analyzed with so2 injections ranging from 8 5 to 700 tg with eruptions in january and july modeled sulfate deposition flux to antarctica shows excellent spatial correlation with ice core derived estimates for pinatubo and tambora although the comparison suggests the modeled flux to the ice sheets is 4 5 times too large we find that greenland and antarctic deposition efficiencies the ratio of sulfate flux to each ice sheet to the maximum hemispheric stratospheric sulfate aerosol burden vary as a function of the magnitude and season of stratospheric sulfur injection changes in simulated sulfate deposition for large so2 injections are connected to increases in aerosol particle size which impact aerosol sedimentation velocity and radiative properties the latter leading to strong dynamical changes including strengthening of the winter polar vortices which inhibits the transport of stratospheric aerosols to high latitudes the resulting relationship between antarctic and greenland volcanic sulfate deposition is nonlinear for very large eruptions with significantly less sulfate deposition to antarctica than to greenland these model results suggest that variability of deposition efficiency may be an important consideration in the interpretation of ice core sulfate signals for eruptions of tambora magnitude and larger

frequency magnitude and characteristics of aeolian sediment transport mcmurdo dry valleys antarctica 1 due in part to the challenging environment of earth s high latitude regions available information on cold climate effects on aeolian processes in these areas remains limited data from these areas however provide insight into the physics of sediment transport by wind and the controls on erosive winds in proximity to ice caps and topographic influences this study presents a 2 year record of meteorological saltation activity horizontal saltation flux and particle size distribution data from four sites in the mcmurdo dry valleys of antarctica 2008 to 2010 saltation measurements revealed daily and seasonal patterns with spring and summer sediment transport events occurring between 09 00 and 24 00 hours due to thermally generated winds fall and winter events occur at any time of day with the strongest associated with foehn winds threshold wind speed at 4 2 m in all seasons for all locations was 10 m s 1 saltation occurred in the temperature range 40 c to 5 c westerly winds in the fall winter and easterly winds in spring summer are associated with the majority of transport events the sand in transport is mainly 250 to 500 m in diameter and poorly sorted the integrated saltation flux varies over three orders of magnitude among the sites with the lowest mean flux recorded in the taylor valley 2 9 kg m 1 day 1 and the highest in the eastern victoria valley 2271 kg m 1 day 1 for 24 hours of continuous saltation the percentage of time saltation active at these locations annually is 2 4 and 13 respectively for the victoria taylor and wright valleys

earth s crust model of the south okhotsk basin by wide angle obs data abstract deep seismic studies of the sea of okhotsk region started in late 1950s since that time wide angle reflection and refraction data on more than two dozen profiles were acquired only five of those profiles either crossed or entered the deep water area of the south okhotsk basin also known as the kuril basin or the south okhotsk deep water trough only p waves were used to develop velocity interface models in all the early research thus all seismic and geodynamic models of the okhotsk region were based only on the information on compressional waves nevertheless the use of vp vs ratio in addition to p wave velocity allows discriminating felsic and mafic crustal layers with similar vp values in 2007 the russian seismic service company sevmorgeo acquired multi component data with ocean bottom seismometers obs along the 1700 km long north south 2 dv m profile only p wave information was used previously to develop models for the entire profile in this study a multi wave processing analysis and interpretation of the obs data are presented for the 550 km long southern segment of this profile that crosses the deep water south okhotsk basin within this segment 50 seismometers were deployed with nominal obs station spacing of 10 12 km shot point spacing was 250 m not only primary p waves and s waves but also multiples and p s s p converted waves were analyzed in this study to constrain velocity interface models by means of travel time forward modeling in offshore deep seismic studies thick water layer hinders an estimation of velocities in the sedimentary cover and in the upper consolidated crust primarily this is due to the fact that refracted waves propagating in low velocity solid upper layers interfere with high amplitude direct water wave however in multi component measurements with ocean bottom seismometers it is possible to use converted and multiple waves for velocity estimations in these layers consequently one can obtain p and s waves velocity models of the sedimentary strata and the upper consolidated crust velocity values in the upper consolidated crust beneath the south okhotsk basin vp 5 50 5 80 km s vp vs 1 74 1 76 allow interpretation of this 2 5 3 5 km thick layer to be consistent with a felsic granodioritic crust these results suggest that the earth s crust in this region can be considered continental in nature rather than previously accepted oceanic crust even though the crust is thinned and stretched at this location

relationships between kuroko volcanogenic massive sulfide vms deposits felsic volcanism and island arc development in the northeast honshu arc japan the northeast ne honshu arc was formed by three major volcano tectonic events resulting from late cenozoic orogenic movement continental margin volcanism before 21 ma seafloor basaltic lava flows and subsequent bimodal volcanism accompanied by back arc rifting 21 to 14 ma and felsic volcanism related to island arc uplift 12 to 2 ma eight petrotectonic domains parallel to the ne honshu arc were formed as a result of the eastward migration of volcanic activity with time major kuroko volcanogenic massive sulfide vms deposits are located within the eastern marginal rift zone kuroko rift that formed in the final period of back arc rifting 16 to 14 ma volcanic activity in the ne honshu arc is divided into six volcanic stages the eruption volumes of volcanic rocks have gradually decreased from 4 600 km3 per 1 my for a 200 km long section along the arc of basaltic lava flows in the back arc spreading stage to 1 000 2 000 km3 of bimodal hyaloclastites in the back arc rift stage and about 200 km3 of felsic pumice eruptions in the island arc stage the kuroko vms deposits were formed at the time of abrupt decrease in the eruption volume and change in the mode of occurrence of the volcanic rocks during the final period of back arc rifting in the area of the kuroko rift felsic volcanism changed from aphyric or weakly plagioclase phyric before 14 ma to quartz and plagioclase phyric with minor clinopyroxene 12 to 8 ma to hornblende phyric after 8 ma and hornblende and biotite phyric after 4 ma the kuroko vms deposits are closely related to the aphyric rhyolitic activity before 14 ma the rhyolite was generated at a relatively high temperature from a highly differentiated part of felsic magma seated at a relatively great depth and contains higher nb ce and y contents than the post kuroko felsic volcanism the kuroko vms deposits were formed within a specific tectonic setting at a specific period and associated with a particular volcanism of the arc evolution process therefore detailed study of the evolutional process from rift opening to island arc tectonics is very important for the exploration of kuroko type vms deposits

moho depth and crustal vp vs variation in southern korea from teleseismic receiver functions implication for tectonic affinity between the korean peninsula and china we estimated moho depths and v p v s ratios of the crust under 21 broadband stations in southern korea by using a grid search in the crustal thickness v p v s ratio h domain the moho depth varies from 25 9 km to 32 5 km and the v p v s ratio ranges from 1 71 to 1 82 inland moho depths in the southernmost area of the korean peninsula were estimated shallower than those of the previous results obtained assuming a poisson solid in the joint analysis of receiver functions and surface wave dispersion this southernmost area is roughly in accord with the yeongnam massif where relatively high v p v s ratios of 1 78 1 82 are estimated on the contrary comparatively low v p v s ratio measurements 1 71 1 76 are generally distributed in the gyeonggi massif which is located in the central area of the korean peninsula the major factor for the high v p v s ratios in the yeongnam massif is thought to be the plagioclase rich mafic composition of the lower crust rather than partial melting or crustal fluids because high crustal s wave velocities are reported in the yeongnam massif the mafic composition might have been supplied by the magmatic underplating from the clearly divided feature of v p v s ratios in southern korea and the v p v s ratio similarities between southern korea and china it seems that the yeongnam massif might be related to the sino korea craton whereas the gyeonggi massif is related to the yangtze craton

collision structure in the upper crust beneath the southwestern foot of the hidaka mountains hokkaido japan as derived from explosion seismic observations the p wave velocity structure of the upper crust beneath a profile ranging from niikappu to samani in the southwestern foot of the hidaka mountains hokkaido japan was obtained through analysis of refraction and wide angle reflection data the mountains are characterized by high seismicity and a large gravity anomaly the present profile crosses the source region of the 1982 urakawa oki earthquake ms 6 8 the length of the profile is 66 km striking northwest and southeast along the profile 64 vertical geophones were set up and 5 shot points were chosen for each shot a 400 600 kg charge of dynamite was detonated the studied area is composed of four major geological belts neogene sedimentary rocks the kamuikotan belt the yezo group and the hidaka belt the measurement line crosses these geological trend at an oblique angle the structure obtained is characterized by remarkable velocity variations in the lateral direction and reflects the surface geological characteristics a thin high velocity layer hvl was found between low velocity materials in the central part of the profile beneath the kamuikotan metamorphic belt at a depth ranging from 0 5 to 6 km overthrusting toward the west on the low velocity materials consisting of neogene sedimentary rocks and forming gentle folds outlines of the velocity structure of the hidaka mountains yielded by other studies have shown a large scale overthrust structure associated with the collision of the outer kurile and the outer northern honshu arcs the shallow velocity structure inferred by the present study showed a similar although small scale overthrust structure the obtained structure shows that the composite tectonic force comprising westward movement of the outer kurile arc and northward movement of the outer northern honshu arc plays an important role in the evolution of the tectonic features of the crust and upper mantle in a wide depth range beneath the hidaka mountains

characteristics of aeolian grain transport over a fluvio glacial lacustrine braid delta lake tekapo new zealand this paper presents results from one of the few scientific studies to examine the physical characteristics of aeolian sediment transport in an alpine area where topographically reinforced foehn winds initiate dust storm events the major objective of this study is to improve knowledge of aeolian processes in mid latitude alpine regions experiencing extreme wind speeds of particular interest is the role of surface characteristics in contributing to the unusually deep saltation layer which is seen to form over fluvio glacial deposits in the southern alps of new zealand sediment was collected at several heights 0 5 1 2 and 4 m and locations over a large alpine braided river delta and standard laboratory techniques used to examine grain size characteristics an image processing technique was also used to evaluate grain roundness grains filtered from the airstream at 0 5 m and 1 m above such surfaces were found to display a mean grain size of approximately 300 to 435 m resembling grain size characteristics of saltation clouds previously observed in high latitude cold climate locations in contrast to desert and prairie environments samples collected at 2 and 4 m above the surface were found to consist of 60 to 65 per cent sand sized material with some grains exceeding 1 1 5 mm in diameter grain shape analysis conducted on silt and clay sized grains filtered from the airstream above mixed sand and gravel surfaces showed such grains to display an increase in grain roundness with height this characteristic is thought to reflect the airstream s shape sorting ability and has important implications with respect to the often observed increase in grain roundness in aeolian deposits with increasing distance from source areas namely if more rounded grains are preferentially carried higher into the airstream and therefore into regions of higher wind speed they should theoretically be transported further from the entrainment zone before being deposited the high wind speeds observed often exceeding 30 m s 1 are seen to transport significantly larger sediment than reported in the literature for desert and prairie environments in addition the mixture of grain sizes and especially the pebble and cobble sized clasts that dominate the fluvio glacial deposits associated with the braided rivers in this mountain region also appear to increase significantly the trajectory height of saltating sand grains as a result of these two factors the depth of the saltation cloud often exceeds 1 m observations made in this study therefore highlight the need for field and laboratory aeolian process studies to be extended to examine grain transport over coarse grained beds during much higher wind velocities than typically reported in the literature such studies would provide a valuable insight into aeolian processes in high latitude altitude environments such as loess genesis 1997 by john wiley sons ltd

low velocity oceanic crust at the top of the philippine sea and pacific plates beneath the kanto region central japan imaged by seismic tomography 1 we construct fine scale three dimensional p and s wave velocity structures beneath the kanto region central japan by seismic tomography with a spatial correlation of velocities the philippine sea and pacific plates subduct beneath the eurasian plate in this area and are imaged with high velocities oceanic crust at the uppermost part of these subducting plates is a low velocity layer low velocity oceanic crust of the philippine sea plate subducts to a depth of approximately 80 km there are also two low velocity bodies with relatively high v p v s ratios of 1 80 1 90 in the mantle wedge above the oceanic crust of the philippine sea plate we speculate that the westernmost of these two low velocity bodies consists of 20 partially serpentinized peridotite continuous with gabbro in the oceanic crust of the uppermost philippine sea plate while the eastern body is composed of 30 partially serpentinized peridotite we trace the subducting oceanic crust of the pacific plate to a depth of 120 km the estimated v p v s ratio of this layer is 1 85 1 90 which indicates a low probability of molten rock the gabbroic oceanic crust may have been metamorphosed to garnet granulite

crustal structure of the izu collision zone in central japan from seismic refraction data 1 the izu bonin arc iba has been colliding with the more northerly honshu arc since the middle miocene forming a globally unique active izu arc arc collision zone icz in central japan to determine crustal structure of the icz we constrain p and s wave velocities from active source refraction data the velocity structures reveal that the style of collisions of the misaka tanzawa and izu blocks which were derived from the iba has been controlled by subduction of the iba high velocity rocks vp 6 2 km s observed in the icz continuously extend to deeper crust suggesting that plutonic rocks formed by partial melting of the subducted iba crust intruded into the honshu arc crust and the accreted crustal blocks of the iba the northernmost major fault in the icz dips southeastward which is in clear contrast with other major northwestward dipping faults farther southeast in the northernmost part of the icz the upper 5 km crust of the misaka block was delaminated from its lower part and obducted onto the honshu arc the tanzawa block southeast of the misaka block is bounded by northwestward dipping faults and is characterized by crustal stacking a low velocity sedimentary layer between the tanzawa and izu blocks dips northwestward along the collisional boundary and reaches 5 km depth suggesting that the izu block underthrust beneath the tanzawa block the overall geometry of the collisional boundaries exhibits a doubly vergent system which is characterized by inward dipping thrust faults on both sides

heterogeneity in homogeneous brabantian loess during the late pleniglacial abstract the brabantian loess is often seen as a homogeneous sediment package deposited under cold and dry climatic conditions haesaerts et al 1981 however in 1981 two small tundra gleysols were discovered in the brabantian loess haesaerts et al 1981 to unravel other possible changes in the sedimentary system during deposition a more detailed look at the homogeneous brabantian loess is carried out the loess transporting process is reconstructed based on the combination of both grain size and grain shape parameters these parameters are defined with automated dynamic image analysis and statistically compared with the two dimensional kolmogorov smirnov test as suggested by vandenberghe et al 1998 our gleysols are generally correlated to a period of reduced grain size most likely the more subtle the gleysols the weaker the link between their formation and grain size reduction mazzullo et al 1992 already stated that aeolian transport was very selective regarding grain size and sorting capacities our research points toward an extremely selective aeolian transport regarding the shape of the grains therefore combining both particle size and particle shape can be very useful when reconstructing aeolian transport processes this combination can also discriminate samples with a different transport and sedimentation history

grain size characteristics of sediment transported during dust storms abstract the grain size characteristics of sediment transported by wind in creep saltation and suspension during 15 dust storms in the slims river valley yukon territory were investigated grain size analysis of the transported sediment indicated that the suspended sediment is significantly finer and better sorted than the sediment transported in either surface creep or saltation the data also show that during dust storms the mean particle size of the suspended sediment decreases as a power function of height the grain size distributions of the sediment transported in suspension and surface creep are characterized by strong positive skewness which results from the selective removal of surface particles small enough to be transported by the wind at a given velocity in contrast the grai size distribution of the saltation samples are negatively skewed which is thought to result from the selective removal of the finer particles into suspension from those particles initially lifted from the surface into the air stream thus the proportion of sediment initially entrained into the air stream which returns to the surface in saltation will lack the fine grains removed in suspension and will therefore tend to be less positively or negatively skewed

configuration of subducting philippine sea plate and crustal structure in the central japan region a seismic experiment with six explosive sources and 391 seismic stations was conducted in august 2001 in the central japan region the crustal velocity structure for the central part of japan and configuration of the subducting philippine sea plate were revealed a large lateral variation of the thickness of the sedimentary layer was observed and the p wave velocity values below the sedimentary layer obtained were 5 3 5 8 km s p wave velocity values for the lower part of upper crust and lower crust were estimated to be 6 0 6 4 and 6 6 6 8 km s respectively the reflected wave from the upper boundary of the subducting philippine sea plate was observed on the record sections of several shots the configuration of the subducting philippine sea slab was revealed for depths of 20 35 km the dip angle of the philippine sea plate was estimated to be 268 for a depth range of about 20 26 km below this depth the upper boundary of the subducting philippine sea plate is distorted over a depth range of 26 33 km a large variation of the reflected wave amplitude with depth along the subducting plate was observed at a depth of about 20 26 km the amplitude of the reflected wave is not large and is explained by the reflected wave at the upper boundary of the subducting oceanic crust however the reflected wave from reflection points deeper than 26 km showed a large amplitude that cannot be explained by several reliable velocity models some unique seismic structures have to be considered to explain the observed data such unique structures will provide important information to know the mechanism of inter plate earthquakes d 2004 elsevier b v all rights reserved

the initiation of particle movement by wind when air blows across the surface of dry loose sand a critical shear velocity fluid threshold ut must be achieved to initiate motion however since most natural sediments consist of a range of grain sizes fluid threshold for any sediment cannot be defined by a finite value but should be viewed as a threshold range which is a function of the size shape sorting and packing of the surface sediment in order to investigate the initiation of particle movement by wind a series of wind tunnel tests was carried out on a range of pre screened fluvial sands and commercially available glass beads with differing mean sizes and sorting characteristics a sensitive laser monitoring system was used in conjunction with a high speed counter to detect initial grain motion and to count individual grain movements test results indicate that when velocity is slowly increased over the sediment surface the smaller or more exposed grains are first entrained by the fluid drag and lift forces either in surface creep rolling or in saltation bouncing or hopping downwind as velocity continues to rise larger or less exposed grains may also be moved by fluid drag on striking the surface saltating grains impart momentum to stationary grains this impact may result in the rebound of the original grain as well as the ejection of one or more stationary grains into the air stream at shear velocities lower than that required to entrain a stationary particle by direct fluid pressure as a result there is a cascade effect with a few grains of varying size initially moving over a range of shear velocities the fluid threshold range and setting in motion a rapidly increasing number of grains results of the tests showed that the progression from fluid to dynamic threshold based on grain movement can be characterized by a power function the coefficients of which are directly related to the mean size and sorting characteristics of the sediment

anomalous deepening of a seismic belt in the upper plane of the double seismic zone in the pacific slab beneath the hokkaido corner possible evidence for thermal shielding caused by subducted forearc crust materials abstract hypocenter relocations of earthquakes in the pacific slab have shown an anomalous deepening of a seismic belt in the upper plane of the double seismic zone at depths of 80 120 km beneath the hokkaido corner while it is located at depths of 70 90 km in the surrounding tohoku and eastern hokkaido areas seismic tomographic inversions performed beneath the hokkaido corner have shown that a low velocity zone having seismic velocities of crust materials exists in the mantle wedge just above the pacific slab and makes direct contact with the upper surface of the pacific slab these observations suggest that 1 the low velocity zone just above the pacific slab is part of the subducted kuril forearc sliver 2 the contact with the subducted and so relatively cold sliver materials prevents the mantle wedge from heating the pacific slab and causes a lower temperature condition in the pacific slab crust beneath the hokkaido corner than in the surrounding areas 3 as a result a delay of eclogite forming phase transformations occurs and enhances the local deepening of the seismic belt in the slab crust there

configuration of the moho discontinuity beneath the japanese islands derived from three dimensional seismic tomography abstract the mohorovicic discontinuity moho is defined on the basis of an abrupt increase in seismic velocity in the lithosphere which has been observed using seismic refraction and receiver function analysis methods worldwide moho depth varies regionally and remains a fundamental parameter of crustal structure we present a new method of mapping the moho using a 3d seismic tomography model since the tomographic method cannot locate discontinuities we treat the moho as a zone of high velocity gradient maximum lower crust minimum upper mantle p wave velocities in japan are known to be 7 0 km s and 7 5 km s respectively we map the residual between isovelocity surfaces of 7 0 km s and 7 5 km s to find areas where the residual is small the separation between the surfaces is narrow and the velocity gradient is high the moho is best constrained where the isovelocity surfaces are close together and under much of japan they are 10 km apart we chose an isovelocity surface of 7 2 km s as a representative moho proxy in these areas our resulting moho map under japan compares favorably with existing regional moho models that were obtained from controlled source seismic investigations the moho varies from shallow 25 30 km to deep 30 km and this variability relates to the structural evolution of the japanese islands the opening of the sea of japan back arc ongoing arc arc collisions at the hidaka and izu collision zones ongoing back arc extension in kyushu and a possible failed back arc extensional event of mesozoic age it is apparent that the moho is less well constrained in areas where the crustal structure has been modified by magmatic activity or thickened due to arc arc collision

shape effects in aeolian grain transport wind tunnel experiments are reported the results of which show that grain transport rate is responsive to characteristic grain shape it is relatively less sensitive to changes of sorting unless these involve the fraction smaller than 50 m a cubic relationship between transport rate and velocity gradient appears to be valid only for well worked natural grains having high sphericity

temporal constraints on glacial valley cross profile evolution two thumb range central southern alps new zealand abstract a key problem in understanding valley evolution in alpine landscapes has been the lack of an independent timescale against which to measure morphological change here we outline that by using space as a proxy for time the role of glaciation in producing classic u shaped valleys can be quantified the two thumb range in new zealand s central southern alps is undergoing rapid tectonic transport and uplift as it is advected towards the alpine fault repeated cycles of glacial erosion during the quaternary have fashioned an alpine landscape in the north of the range close to the main divide and alpine fault while valleys in the less glaciated south of the range have rounded divides and convex fluvial cross profiles using known rates of tectonic transport and uplift of the southern alps coupled with an offshore oxygen isotope 18o record from the chatham rise and glacio geological reconstructions time constraints can be applied to the erosional development of valleys it is possible to estimate the duration of glacial occupancy of valleys in the two thumb range and the pattern is one of very limited glaciation of the southern valleys with glacial occupancy increasing northwards the key trend identifiable is that valley cross profiles become u shaped with c 400 600 kyr of glacial occupancy other models have shown a flattening of valley long profiles with increased glaciation implying glaciers erode larger volumes of rock from mountains than rivers from a cross profile perspective the simple change in geometry from v to u shape concurs with these models indeed the transition from v to u shape with increasing relief and glaciation indicates glaciers may erode greater volumes of rock from mountain belts than rivers

split philippine sea plate beneath japan 1 the shape of the philippine sea plate subducting beneath western japan is a crucial factor in understanding earthquakes and volcanic activity we propose that the subducted plate was split along an extinct ridge due to an abrupt change of subduction direction followed by elastic deformation of the plate and an accumulation of stress near the ridge this shape is consistent with receiver function images the distribution of deep tremor sources the seismicity and focal mechanisms of intraplate earthquakes and the distribution of anomalous ratios of helium isotopes in ground water the movement history of the plate can explain active tectonics in western japan in the last 2 4 ma the location history of the volcanic front and the tear control where fluids ascend in the crust and these fluids are responsible for the generation of large earthquakes and volcanoes

quaternary volcanic front at the junction of the south west japan arc and the ryukyu arc abstract the hohi volcanic zone a 70 by 40 km volcanic graben on kyushu island at the junction of the south west japan arc and the ryukyu arc has been formed since 6 ma to the present quaternary volcanism producing centers along a ne sw trending line the volcanic front started at about 1 5 ma this volcanic front crosses the e w alignment that was built by the pliocene volcanoes of the hohi volcanic zone the quaternary volcanic front is parallel to the depth contours of the present deep seismic plane and is perpendicular to the current direction of subduction of the philippine sea plate the age of formation of the volcanic front coincides with the time when several other tectonic events occurred such as the counter clockwise shift from nnw to wnw in relative convergence direction of the philippine sea plate the volcanic rocks erupted after 1 5 ma are more widely distributed with a larger total volume in the denser seismic zone than in the aseismic zone this suggests that the volcanism on the volcanic front is closely related to seismicity at about 120 km depth the active seismic area may have accelerated to generate a partially molten zone beyond the dragged hydrated peridotite layer above the downgoing slab in comparison to the aseismic area

earthquake source fault beneath tokyo devastating earthquakes occur on a megathrust fault that underlies the tokyo metropolitan region we identify this fault with use of deep seismic reflection profiling to be the upper surface of the philippine sea plate the depth to the top of this plate 4 to 26 kilometers is much shallower than previous estimates based on the distribution of seismicity this shallower plate geometry changes the location of maximum finite slip of the 1923 kanto earthquake and will affect estimations of strong ground motion for seismic hazards analysis within the tokyo region

mapping the moho with seismic surface waves a review resolution analysis and recommended inversion strategies abstract the strong sensitivity of seismic surface waves to the moho is evident from a mere visual inspection of their dispersion curves or waveforms rayleigh and love waves have been used to study the earth s crust since the early days of modern seismology yet strong trade offs between the moho depth and crustal and mantle structure in surface wave inversions prompted doubts regarding their capacity to resolve the moho here we review surface wave studies of the moho with a focus on early work and then use model space mapping to establish the waves sensitivity to the moho depth and the resolution of their inversion for it if seismic wavespeeds within the crust and upper mantle are known then moho depth variations of a few kilometres produce large 1 perturbations in phase velocities however in inversions of surface wave data with no a priori information wavespeeds not known strong moho depth shear speed trade offs will mask 90 of the moho depth signal with remaining phase velocity perturbations 0 1 only in order to resolve the moho with surface waves alone errors in the data must thus be small up to 0 2 for resolving continental moho with larger errors moho depth resolution is not warranted and depends on error distribution with period an effective strategy for the inversion of surface wave data alone for the moho depth is to first constrain the crustal and upper mantle structure by inversion in a broad period range and then determine the moho depth in inversion in a narrow period range most sensitive to it with the first step results used as reference prior information on crustal and mantle structure reduces the trade offs and thus enables resolving the moho depth with noisier data such information should be used whenever available joint analysis or inversion of surface wave and other data receiver functions topography gravity can reduce uncertainties further and facilitate moho mapping

testing an approach to osl dating of late devensian glaciofluvial sediments of the british isles in the british and irish isles the understanding of expansion and retreat of the last ice sheet in marine isotope stage mis 2 has been hindered by a lack of chronological control for the timing of its maximum extent and subsequent retreat stages in this research a suite of lithofacies from a former distal ice marginal sandur at orrisdale isle of man were identified and selected for optically stimulated luminescence dating different size fractions of quartz grains were extracted from selected lithofacies types with the aim of identifying which depositional environments and grain size fractions are best suited for optical dating tests have been undertaken to identify the luminescence properties of this quartz including preheat dose recovery and constant wave optically stimulated luminescence osl decay curve fitting equivalent dose distributions for all samples were wide and positively skewed indicative of heterogeneous bleaching a comprehensive statistically based decision making protocol has been defined in order to find the appropriate statistical model for burial dose estimation ages in the range of 17 14 ka have been obtained which agree with the expected geologically constrained chronology the orrisdale formation is contemporaneous with heinrich event 1 and the killard point stadial identified in eastern ireland ca 16 4 ka the suggested approach for osl dating of glaciofluvial sediments has the potential for much wider application to high latitude or temperate areas where there is an abundance of such sediments and where improved chronological control is much needed copyright 2009 john wiley sons ltd

meteorological controls on wind erosion during foehn wind events in the eastern southern alps new zealand foehn winds in the lee of mountain barriers create highly favourable meteorological conditions for wind erosion in alpine areas and over adjacent lowlands this paper presents meteorological observations made during winter and summer foehn wind erosion events as part of a 3 year investigation into the physical nature and incidence of eolian processes in the eastern southern alps new zealand foehn winds were observed to initiate eolian activity including dust storm genesis when mean near surface wind speeds exceeded 7 8 m s 1 over a 20 min period in the absence of precipitation wind speeds of 25 30 m s 1 were frequently recorded during typical foehn events and wind speed maxima of 40 50 m s 1 were monitored during severe foehn windstorms saltation clouds sampled at 0 5 and 1 m above glaciofluvial deposits during foehn wind erosion events were found to display a mean grain size of between 300 and 435 m the entrainment of fine grained surface sediments by the airstream appeared to be enhanced in late autumn may and early spring september by freeze thaw cycles that were observed to result in needle ice growth in exposed glaciofluvial and lacustrine deposits the needle ice fragmented such deposits producing surfaces that were aerodynamically rough and highly susceptible to deflation by the airstream following a thaw observations made by this study are thought to be similar to foehn wind erosion events reported in the lee of other substantial mountain ranges such as the rocky mountains andes hindu kush and karakoram

aeolian dust in east antarctica epica dome c and vostok provenance during glacial ages over the last 800 kyr aeolian mineral dust archived in antarctic ice cores represents a key proxy for quaternary climate evolution the longest and most detailed dust and climate sequences from polar ice are provided today by the vostok and by the epica dome c edc ice cores here we investigate the geographic provenance of dust windborne to east antarctica during early and middle pleistocene glacial ages using strontium and neodymium isotopes as tracers the isotopic signature of antarctic dust points towards a dominant south american origin during marine isotopic stage mis 8 10 12 and back to mis 16 and 20 as deduced from edc core data provide evidence for a persistent overall westerly circulation pattern allowing efficient transfer of dust from south america to the interior of antarctica over the last 800 kyr some small but significant dissimilarity between old and recent glacial ages suggests a slightly reduced patagonian contribution during ancient glaciations

crustal structure of southwest japan revealed by the integrated seismic experiment southwest japan 2002 abstract a multi purpose seismic experiment named the 2002 integrated seismic experiment southwest japan was conducted in 2002 along a more than 240 km long line across southwest japan from the pacific coast to the japan sea coast its profile provides the first crustal scale cross section across the japanese island arc which highlights a number of significant points related to the structural development of the arc major outstanding points are that the japanese island arc is composed of two completely different crusts juxtaposed by the median tectonic line mtl and that the mtl started its activity associated with lower crustal thinning and formation of an upper crustal scale half graben in late cretaceous

holocene tephras highlight complexity of volcanic signals in greenland ice cores 1 acidity peaks in greenland ice cores have been used as critical reference horizons for synchronizing ice core records aiding the construction of a single greenland ice core chronology gicc05 for the holocene guided by gicc05 we examined sub sections of three greenland cores in the search for tephra from specific eruptions that might facilitate the linkage of ice core records the dating of prehistoric tephras and the understanding of the eruptions here we report the identification of 14 horizons with tephra particles including 11 that have not previously been reported from the north atlantic region and that have the potential to be valuable isochrons the positions of tephras whose major element data are consistent with ash from the katmai ad 1912 and oraefajokull ad 1362 eruptions confirm the annually resolved ice core chronology for the last 700 years we provide a more refined date for the so called ad860b tephra a widespread isochron found across nw europe and present new evidence relating to the 17th century bc thera aniakchak debate that shows n american eruptions likely contributed to the acid signals at this time our results emphasize the variable spatial and temporal distributions of volcanic products in greenland ice that call for a more cautious approach in the attribution of acid signals to specific eruptive events

polar research buried treasure air bubbles trapped in the antarctic ice sheet could yield precious information about earth s climate more than a million years ago but to access this record scientists first have to climb one of the coldest peaks on earth nicola jones reports

aeromagnetic evidence for a buried early cretaceous magmatic arc northeast japan positive aeromagnetic anomalies recent drilling and models constructed from these data delineate the plutonic roots of the early cretaceous kitakami magmatic arc in northeast japan buried plutons mostly offshore produce belts of positive magnetic anomalies these anomalies and magnetotelluric data suggest that the plutons form a batholith 70 120 km wide nearly 800 km long and 10 15 km thick the batholith may mark the location of the main kitakami arc most of the exposed kitakami plutons are 2 20 km in diameter some are 3 km thick the small plutons line up along nw trending faults some may have been satellite vents that tapped into the magma supply of the main arc the batholithic roots of the main arc now compose almost half of the modern japan forearc basement steep magnetic gradients offset anomalies and basin stratigraphy portray extensive faulting of the kitakami batholith during oblique subduction in the late cretaceous and rifting in the miocene the eastern boundary of the kitakami batholith lies between 90 and 140 km west of the modern trench much closer than the 300 km distance between the active arc and trench the early cretaceous forearc basin and accretionary prism may underlie the modern forearc basin east of the batholith but clear evidence is lacking much of the early cretaceous margin including most of its forearc therefore is missing how the material was removed is unknown it could have been strike slip faulted eroded by subduction related processes or both

simultaneous high p t measurements of ultrasonic compressional and shear wave velocities in ichino megata mafic xenoliths their bearings on seismic velocity perturbations in lower crust of northeast japan arc 1 simultaneous measurements of ultrasonic compressional vp and shear wave velocities vs were conducted under pressures and temperatures representative of the lower crust on five mafic xenoliths derived from the northeast japan arc crust for comparison with the observed seismic heterogeneity of the lower crust of the northeast japan arc the velocity deviations dvp and dvs of the xenoliths were calculated using the average reference vp 6 61 0 1 km s and vs 3 76 0 1 km s the dvp and dvs values of the xenoliths at 700 c and 0 8 gpa are 0 8 and 1 2 for hornblende gabbro 4 8 and 4 0 for hornblende pyroxene gabbro 0 9 and 1 5 for amphibolite 2 5 and 1 7 for pyroxene amphibolite and 0 9 and 5 6 for hornblendite respectively we compared the velocity perturbations in the lower crust determined by seismic tomography with dvp and dvs of the xenoliths using vp vs vp vs deviation diagrams on the basis of our measurements we suggest that 1 the seismically high vp and vs regions beneath the tobishima basin consist of hornblende pyroxene gabbro 2 hornblende gabbro is a predominant rock type beneath the dewa hills and ou backbone range 3 the low velocity anomalies beneath the active volcano areas may be caused by the existence of partial melts of hornblende gabbro and 4 the low vp and high vs regions beneath the kitakami mountains consist of quartz plagioclase bearing rocks our data demonstrate that the seismic heterogeneity in the lower crust of the northeast japan arc reflects variations in rock composition and temperature that are related to the regional geological history

origin and significance of ice rafted detritus in the atlantic sector of the southern ocean piston core tn057 14 from the eastern atlantic sector of the southern ocean contains several layers rich in volcanic tephra that were deposited during the last glacial period comparison with nearby cores tn057 13pc4 odp site 1094 indicates that these tephra layers are correlative with the south atlantic sa ice rafted detritus ird layers identified by kanfoush et al 2000 2002 we analyzed the tephra for major and trace elements as well as isotopic ratios of strontium neodymium and lead the elemental and isotopic composition of all tephra layers examined indicates the south sandwich island volcanic arc ssi as their dominant source with minor input from bouvet island similar analyses of clear mineral grains mainly feldspars quartz and olivine also point to the ssi as the main source we conclude that tephra erupted from the ssi was first deposited as air fall on sea ice and multiyear ice and then secondarily rafted to the studied sites deposition of the tephra rich ird layers was controlled by changes in sea surface temperature and sea ice conditions in the polar frontal zone of the south atlantic rather than antarctic ice sheet dynamics

aerodynamic entrainment thresholds and dislodgement rates on impervious and permeable beds in the literature it has been suggested that on permeable granular beds both the threshold and rate of aerodynamic entrainment may be affected significantly by seepage flows into and out of the bed induced by fluctuating pressures in the overlying turbulent boundary layer using a range of grain sizes and flow conditions the series of laboratory experiments reported here compares directly the aerodynamic entrainment of loose grains overlying fixed permeable sediment beds with that occuring over fixed impervious beds for a given granular material no significant differences in entrainment dynamics on the two types of bed were observed and in the range of flow conditions examined both the threshold shear velocity u t and the aerodynamic entrainment coefficient k were found to be independent of bed permeability

enigmatic highly active left lateral shear zone in southwest japan explained by aseismic ridge collision global positioning system gps site velocities and earthquake focal mechanisms reveal an active left lateral shear zone cutting across kyushu in southwest japan surprisingly no active faults have been identified in association with this zone of rapid contemporary deformation to explain the existence of this shear zone we propose a model comprising subduction of an aseismic ridge kyushu palau ridge at the southwest end of the nankai trough because of rapid 40 mm yr along strike migration of the ridge we suggest that the ridge subduction point and resulting left lateral shear zone is never in one place long enough to enable the development of a through going fault zone that can be identified at the ground surface reconciling the mismatch between the gps seismological and geological data in this region our conceptual model is supported by numerical modeling results we also suggest that the along strike change in subducting plate buoyancy explains the recent counterclockwise rotation of the kyushu forearc documented in paleomagnetic studies as is found in many other western pacific subduction margins

seismic velocity structure of the crust beneath the japan islands abstract more than 13 000 arrival times of 562 local shallow earthquakes selected from the japan university network earthquake catalog are used to investigate the seismic velocity structure of the crust beneath the japan islands we simultaneously determined the hypocenter parameters p and s wave station corrections and depth distributions of the conrad and moho discontinuities beneath the whole of the japan islands by applying an inversion method the p and s wave station corrections show similar distribution patterns they are negative relatively late arrivals of seismic waves in hokkaido and positive relatively early arrivals of seismic waves in western japan in eastern honshu they are positive along the coast of the pacific ocean and negative in the land area and along the coast of the japan sea the conrad discontinuity is located at a depth range from 12 to 22 km in hokkaido the conrad is shallow in the eastern pan and becomes deep toward the west in ne honshu the conrad is deep beneath the land area and becomes shallow toward the surrounding seas in western japan the conrad is shallow in the northern part and becomes deep toward the south the moho is located in a depth range from 25 to 40 km in hokkaido the moho has the shape of a circular cone with a maximum depth of 36 km in most parts of the japan islands the moho is deep beneath the land area and becomes shallow toward the surrounding seas the moho is deepest up to 40 km beneath the central part of the chubu district

aeolian dust transport and deposition by foehn winds in an alpine environment lake tekapo new zealand abstract observations from an automatic weather station and anemograph network are used in conjunction with recorded dust deposition rates to identify principle sources of wind blown dust within an alpine lake basin meteorological observations made throughout the study indicate that foehn windstorms provide ideal conditions for the initiation of aeolian processes including dust storm genesis a mean wind speed during foehn windstorms of 7 5 m s 1 at 2 65 m above the surface was observed to initiate entrainment of dust particles from geomorphically active areas within the lake basin particularly from the dry braid channels of glacier fed rivers exposed lacustrine deltas and degraded tussock grasslands this threshold entrainment velocity is similar to others presented within the international literature for such surface types a diurnal modulation of meteorological parameters monitored during foehn wind events suggests that aeolian processes such as dust entrainment are most likely to occur from late morning to early evening however where topography enhances wind speeds for example by channelling airflow down river valleys favourable conditions for dust entrainment may prevail throughout the night in the absence of precipitation potential dust roses were determined for two sites within the lake basin the dust roses supported anecdotal and observational evidence of principle dust sources within the study area and appear to be an effective tool for identifying the potential hazard to a particular location from blowing dust once the physical trigger conditions for dust entrainment are known this requires detailed and concurrent monitoring of meterological variables in association with dust transportation and deposition rates especially in complex terrain where many micro climates often exist

extensional structure in northern honshu arc as inferred from seismic refraction wide angle reflection profiling a recent extensive seismic wide angle experiment revealed a new image of crustal and uppermantle structure across northern honshu arc japan the western part of the arc recorded the crustal deformation by the miocene back arc spreading of the sea of japan the crust is composed of highly deformed tertiary sedimentary layers a relatively low velocity 5 75 5 9 km s crystalline basement and a 15 km thick lower crust with a velocity of 6 6 7 0 km s clear westward crustal thinning from 32 to 27 km represents the extensional deformation by the backarc spreading the crust attains the maximum thickness 32 35km east of the backbone range for which the magmatic intrusion underplating since 10 15 ma is a predominant factor the eastern part of the arc has a less deformed upper crust and a reflective middle lower crust probably remaining a stable block since the time of the backarc spreading

structural characteristics off miyagi forearc region the japan trench seismogenic zone deduced from a wide angle reflection and refraction study abstract the japan trench subduction zone located east of ne japan has regional variation in seismicity many large earthquakes occurred in the northern part of japan trench but few in the southern part off miyagi region is in the middle of the japan trench where the large earthquakes m 7 with thrust mechanisms have occurred at an interval of about 40 years in two parts inner trench slope and near land a seismic experiment using 36 ocean bottom seismographs obs and a 12 000 cu in airgun array was conducted to determine a detailed 2d velocity structure in the forearc region off miyagi the depth to the moho is 21 km at 115 km from the trench axis and becomes progressively deeper landward the p wave velocity of the mantle wedge is 7 9 8 1 km s which is typical velocity for uppermost mantle without large serpentinization the dip angle of oceanic crust is increased from 5 6 near the trench axis to 23 150 km landward from the trench axis the p wave velocity of the oceanic uppermost mantle is as small as 7 7 km s this low velocity oceanic mantle seems to be caused by not a lateral anisotropy but some subduction process by comparison with the seismicity off miyagi the subduction zone can be divided into four parts 1 seaward of the trench axis the seismicity is low and normal fault type earthquakes occur associated with the destruction of oceanic lithosphere 2 beneath the deformed zone landward of the trench axis the plate boundary is characterized as a stable sliding fault plain in case of earthquakes this zone may be tsunamigenic 3 below forearc crust where p wave velocity is almost 6 km s and larger this zone is the seismogenic zone below inner trench slope which is a plate boundary between the forearc and oceanic crusts 4 below mantle wedge the rupture zones of thrust large earthquakes near land e g 1978 off miyagi earthquake are located beneath the mantle wedge the depth of the rupture zones is 30 50 km below sea level from the comparison the rupture zones of large earthquakes off miyagi are limited in two parts plate boundary between the forearc and oceanic crusts and below mantle wedge this limitation is a rare case for subduction zone although the seismogenic process beneath the mantle wedge is not fully clarified our observation suggests the two possibilities earthquake generation at the plate boundary overridden by the mantle wedge without serpentinization or that in the subducting slab

luminescence dating of glaciofluvial deposits a review abstract for glacigenic sediments optically stimulated luminescence osl dating offers an opportunity to date the time of deposition of quartz and feldspar minerals that are ubiquitous within the sediment matrix rather than relying upon the chance occurrence of organic material for radiocarbon dating the osl dating signal or charge accumulates in crystal defects of individual quartz and feldspar minerals through exposure to environmental radiation within their depositional setting the osl signal within individual grains can be reset or bleached through exposure to daylight during transportation processes thus osl dating of sediments attempts to determine the time elapsed since burial glacigenic sediments present considerable challenges for osl dating not only in terms of poor bleaching of the osl signal during the transport and deposition cycle but also poor quartz luminescence characteristics which are often related to sediment provenance the nature of the bedrock or source material and the freshly eroded nature of many such deposits this paper reviews luminescence dating techniques as applied to glaciofluvial sediments and explores the challenges that such deposits present to the technique successful application of osl techniques can be judged in a number of ways comparison with the independent chronologies is prevalent in the literature but recently the movement towards measurement of large numbers of small aliquots and single grains allows a more robust assessment of luminescence properties and behaviour for individual samples and ultimately more precise luminescence ages to be determined for glaciofluvial sediments in particular it is important to investigate the depositional sub environment of each sample in relation to the chance of sufficient bleaching during transport and deposition a lithofacies based approach to sampling for optically stimulated luminescence dating of these sediments is suggested whereby hypothetically well bleached deposits are targeted after a detailed investigation into possible environments of deposition this approach together with small aliquot single grain analysis methodologies should further enhance the likelihood of obtaining a sufficiently bleached sample for osl dating

quantified time scale for glacial valley cross profile evolution in alpine mountains space is used as a proxy for time in determining the role of glaciation in shaping valley cross profiles in the two thumb range southern alps new zealand the range is undergoing rapid tectonic transport and uplift as it is advected toward the alpine fault repeated cycles of glacial erosion during the quaternary have fashioned u shaped valleys in the north of the range close to the main divide while valleys in the less glaciated south of the range have rounded divides and convex fluvial cross profiles tectonic transport and uplift rates coupled with an offshore oxygen isotope 18o record and glacial geological reconstructions allow time constraints to be applied to valley development along the range valley width and depth measurements and power law equations were used to quantify the shape of cross profile transects in 37 valleys valleys evolved into a characteristic u shaped cross profile formed over 400 k y of glacial occupancy this regardless of other models of glacial flattening of valley long profiles suggests that alpine glaciation excavates greater volumes of rock indicating that glaciers are a more effective erosional agent than fluvial activity in alpine mountain belts

upper and middle crustal deformation of an arc arc collision across hokkaido japan inferred from seismic refraction wide angle reflection experiments abstract the hidaka collision zone hcz central hokkaido japan is a good target for studies of crustal evolution and deformation processes associated with an arc arc collision the collision of the kuril arc ka with the northeast japan arc nja which started in the middle miocene is considered to be a controlling factor for the formation of the hidaka mountains the westward obduction of middle lower crustal rocks of the ka the hidaka metamorphic belt hmb and the development of the foreland fold and thrust belt on the nja side the hokkaido transect project undertaken from 1998 to 2000 was a multidisciplinary effort intended to reveal structural heterogeneity across this collision zone by integrated geophysical geological research including seismic refraction reflection surveys and earthquake observations an e w trending 227 km long refraction wide angle reflection profile found a complicated structural variation from the ka to the nja across the hcz in the east of the hcz the hinterland region is covered with 4 4 5 km thick highly undulated neogene sedimentary layers beneath which two eastward dipping reflectors were imaged in a depth range of 10 25 km probably representing the layer boundaries of the obducting middle lower crust of the ka the hmb crops out on the westward extension of these reflectors with relatively high vp 6 0 km s and vp vs 1 80 consistent with middle lower crustal rocks beneath these reflectors more flat and westward dipping reflector sequences are situated at the 25 27 km depth forming a wedge like geometry this distribution pattern indicates that the ka crust has been delaminated into more than two segments under our profile in the western part of the transect the structure of the fold and thrust belt is characterized by a very thick 5 8 km sedimentary package with a velocity of 2 5 4 8 km s this package exhibits one or two velocity reversals in paleogene sedimentary layers probably formed by imbrication associated with the collision process from the horizontal distribution of these velocity reversals and other geophysical geological data the rate of crustal shortening in this area is estimated to be greater than 3 4 mm year which corresponds to 40 50 of the total convergence rate between the nja and the eurasian plate this means that the fold and thrust belt west of the hcz is absorbing a large amount of crustal deformation associated with plate interaction across hokkaido island

temperature profile for glacial ice at the south pole implications for life in a nearby subglacial lake airborne radar has detected 100 lakes under the antarctic ice cap the largest of which is lake vostok international planning is underway to search in lake vostok for microbial life that may have evolved in isolation from surface life for millions of years it is thought however that the lakes may be hydraulically interconnected if so unsterile drilling would contaminate not just one but many of them here we report measurements of temperature vs depth down to 2 345 m in ice at the south pole within 10 km from a subglacial lake seen by airborne radar profiling we infer a temperature at the 2 810 m deep base of the south pole ice and at the lake of 9 c which is 7 c below the pressure induced melting temperature of freshwater ice to produce the strong radar signal the frozen lake must consist of a mix of sediment and ice in a flat bed formed before permanent antarctic glaciation it may like siberian and antarctic permafrost be rich in microbial life because of its hydraulic isolation proximity to south pole station infrastructure and analog to a martian polar cap it is an ideal place to test a sterile drill before risking contamination of lake vostok from the semiempirical expression for strain rate vs shear stress we estimate shear vs depth and show that the icecube neutrino observatory will be able to map the three dimensional ice flow field within a larger volume 0 5 km3 and at lower temperatures 20 c to 35 c than has heretofore been possible

the moho depth map of the european plate summary the european plate has a 4 5 gy long and complex tectonic history this is reflected in the present day large scale crustal structures a new digital moho depth map is compiled from more than 250 data sets of individual seismic profiles 3 d models obtained by body and surface waves receiver function results and maps of seismic and or gravity data compilations we have compiled the first digital high resolution map of the moho depth for the whole european plate extending from the mid atlantic ridge in the west to the ural mountains in the east and from the mediterranean sea in the south to the barents sea and spitsbergen in the arctic in the north in general three large domains within the european plate crust are visible the oldest archean and proterozoic crust has a thickness of 40 60 km the continental variscan and alpine crust has a thickness of 20 40 km and the youngest oceanic atlantic crust has a thickness of 10 20 km

high resolution seismic velocity structure beneath the hokkaido corner northern japan arc arc collision and origins of the 1970 m 6 7 hidaka and 1982 m 7 1 urakawa oki earthquakes 1 using travel time data from both a nationwide dense seismic network and a dense temporary seismic network we obtain a high resolution three dimensional seismic velocity structure beneath the hokkaido corner considerable inhomogeneity in the seismic velocity structure is clearly imaged above the subducting pacific slab our results indicate that a broad low velocity zone of p and s waves with velocities consistent for crustal rocks is observed west of the hidaka main thrust at depths of 35 90 km the images also indicate that several smaller scale high velocity zones are located at depths of 0 35 km striking approximately north south and inclined to the east northeastward at 40 60 all of these anomalous high velocity zones are located at the deeper extension of neogene thrust faults the clearest high velocity zone is located beneath the hidaka metamorphic belt and is in contact with the eastern edge of the broad low velocity zone moreover the boundary between the clearest high velocity and the broad low velocity zones corresponds to the fault plane of the 1970 mj magnitude determined by the japan meteorological agency 6 7 hidaka earthquake the western boundary of another small high velocity zone at depths of 20 to 30 km within the broad low velocity zone corresponds to the fault plane of the 1982 mj 7 1 urakawa oki earthquake these observations suggest that these two large and anomalously deep inland earthquakes occurred at sharp material boundaries under a northeast southwest compressional stress field caused by ongoing arc arc collision process

topographic control of regional accumulation rate variability at south pole and implications for ice core interpretation snow accumulation rates are known to be sensitive to local changes in ice sheet surface slope because of the effect of katabatic winds these topographic effects can be preserved in ice cores that are collected at non ice divide locations the trajectory of an ice core site at south pole is reconstructed using measurements of ice sheet motion to show that snow was probably deposited at places of different surface slope during the past 1000 years recent accumulation rates derived from shallow firn cores vary along this trajectory according to surface topography so that on a relatively steep flank mean annual accumulation is 18 smaller than on a nearby topographic depression these modern accumulation rates are used to reinterpret the cause of accumulation rate variability with time in the long ice core record as an ice dynamics effect and not a climate change signal the results highlight the importance of conducting ancillary ice dynamics measurements as part of ice coring programs so that topographic effects can be deconvolved from potential climate signals

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

south pole glacial climate reconstruction from multi borehole laser particulate stratigraphy the icecube neutrino observatory and its prototype amanda were built in south pole ice using powerful hot water drills to cleanly bore 100 holes to depths up to 2500 m the construction of these particle physics detectors provided a unique opportunity to examine the deep ice sheet using a variety of novel techniques we made high resolution particulate profiles with a laser dust logger in eight of the boreholes during detector commissioning between 2004 and 2010 the south pole laser logs are among the most clearly resolved measurements of antarctic dust strata during the last glacial period and can be used to reconstruct paleoclimate records in exceptional detail here we use manual and algorithmic matching to synthesize our south pole measurements with ice core and logging data from dome c east antarctica we derive impurity concentration precision chronology annual layer thickness local spatial variability and identify several widespread volcanic ash depositions useful for dating we also examine the interval around similar to 74 ka recently isolated with radiometric dating to bracket the toba sumatra supereruption

contemporary glacigenic inputs to the dust cycle the importance of glacigenic dust in the earth s system during glacial periods is widely acknowledged under contemporary conditions the world s largest dust sources are in low lying hot arid regions and this is where most aeolian research is focused however the processes of dust production and emissions are still operating in cold climate regions particularly in proglacial areas this paper assesses current understanding of the relationship between glacierised landscapes and dust emissions and inputs to the global dust cycle it focuses on how elements in the glacial and aeolian geomorphic sub systems interact to determine the magnitude frequency and timing of aeolian dust emissions and on feedback mechanisms between the systems where they have been measured dust emission intensity and deposition rates in glacierised catchments are very high in some cases far exceeding those in lower latitudes however few studies span long time scales the impact of future glacier retreat on the balance between sediment supply availability and aeolian transport capacity and implications for glacigenic dust emissions is also considered this balance depends on relative spatial and temporal changes in meltwater suspended sediment concentration and wind strengths which promote dust emissions and patterns and rates of soil development and vegetation succession on recently deglaciated terrain which protect sediments from deflation retreat of the antarctic ice sheet could mean that in future glacigenic contributions to the dust cycle exceed those of non glacigenic sources in the southern hemisphere copyright 2012 john wiley sons ltd

crustal evolution of the southwestern kuril arc hokkaido japan deduced from seismic velocity and geochemical structure abstract the southwestern kuril arc which is not affected by a series of accretion and collision processes is one of the most important experimental sites among the world arc trench systems for investigating the evolution of arc crust published petrological and seismic studies have shown that in south central hokkaido the upper part of the kuril arc crust is thrusting upward toward the west while the lower part is descending downward in the same direction among several hypotheses for formation of continental crust we discuss the role of delamination of the island arc lower crust based on geochemical and seismic velocity structure models seismic velocity structure is obtained from an onshore offshore seismic survey across the southwestern kuril arc trench system the structure in the back arc area shows a thick accretionary complex formed by paleogene accretion and collision based on published seismic results this accretionary complex is considered to continue on land to the cretaceous accretionary complex observed in the hidaka belt the structure of the kuril arc appears characteristic of upper crustal andesitic rocks 6 0 6 2 km s and thick middle to lower crust 6 5 7 3 km s based on published geochemical study we consider a geochemical model of simple crustal evolution explaining the mechanism of generation of andesitic rocks on the kuril arc each volume of andesitic basaltic and mafic layers estimated from the geochemical model is consistent with those obtained from the seismic velocity model crustal composition estimated from the geochemical model and major element chemistry of the volcanic rocks in the kuril arc indicate that mechanical delamination is insufficient to cause the oceanic island arc crust to evolve into continental crust

collision and subduction structure of the izu bonin arc central japan revealed by refraction wide angle reflection analysis abstract since the middle miocene the izu bonin arc iba has been colliding from the south with the honshu arc in central japan associated with subduction of the philippine sea plate psp this process is responsible for forming a complex crustal structure called the izu collision zone icz to obtain direct evidence of the deep structure dominated by collision and subduction an intensive seismic experiment using explosive and vibroseis sources was conducted in the eastern part of the icz cmp reflection and refraction wide angle reflection data were acquired on a 130 km long seismic line crossing the kanto mountains km the tonoki aikawa tectonic line tatl and the tanzawa mountains tm from north to south the tatl is considered to be a collision boundary separating the honshu arc km from the iba tm the structural model constructed by refraction tomography and forward ray tracing shows remarkable lateral velocity variation across the tatl and some clear reflectors in the deep crust a north dipping reflector beneath the km was interpreted to be the deeper extension of the tatl from the geometry of reflectors we interpret the tanzawa block is delaminated from the subducting slab due to the collision to form a wedge like body thrusting between the upper and lower crust of honshu the tm itself shows a velocity structure almost consistent with the upper part of the crust of the izu intraoceanic arc south of our study area the relocated hypocenter distribution using our velocity model shows high seismic activity concentrated around the collision boundary which is in a marked contrast of low seismicity within the tanzawa block these features of seismicity are strongly dominated by the collision of the iba with the honshu arc

moho depth variation beneath southwestern japan revealed from the velocity structure based on receiver function inversion abstract the philippine sea plate is subducting under the eurasian plate beneath the chugoku shikoku region southwestern japan we have constructed depth contours for the continental and oceanic mohos derived from the velocity structure based on receiver function inversion receiver functions were calculated using teleseismic waveforms recorded by the high density seismograph network in southwestern japan in order to determine crustal velocity structure we first improved the linearized time domain receiver function inversion method the continental moho is relatively shallow 30 km at the coastline of the sea of japan and at the seto inland sea and becomes deeper greater than 40 km around 35 n and 133 8 e near the seto inland sea a low velocity layer of thickness 10 km lies under the continental moho this low velocity layer corresponds to the subducting oceanic crust of the philippine sea plate the oceanic moho continues to descend from south to northwest and exhibits complicated ridge and valley features the oceanic moho runs around 25 km beneath the pacific coast and 45 km beneath the seto inland sea and it extends to at least to 34 5 n the depth variation of the moho discontinuities is in good qualitative agreement with the concept of isostasy from the configurations of both the continental and oceanic mohos we demonstrate that the continental lower crust and the subducting oceanic crust overlap beneath the southern and central part of shikoku and that a mantle wedge may exist beneath the western and eastern part of shikoku the southern edge of the overlapping region coincides with the downdip limit of the slip area of a megathrust earthquake

submarine geology and post opening tectonic movements in the southern region of the sea of japan abstract the submarine geologic structure of the southern region of the sea of japan was analyzed on the basis of seismic reflection profile data and bottom samples the seismic reflection patterns depict sedimentary layers with well developed onlap and toplap terminations and truncations by submarine erosion the planes marked by series of onlap toplap and erosional truncations enabled us to define three stratigraphic groups composed of six formations in this region they are the kasumioki group the hamasakaoki group and the tottorioki group in ascending order detailed analysis of the seismic reflection profiles reveals subtle structures of these sedimentary units the oldest kasumioki group is folded and faulted forming submarine ridges the hamasakaoki group mainly occurs in the depressions between these ridges the youngest tottorioki group covers widely both of the older formations with a pronounced marine onlap fossil evidence indicates that the depositional ages of the kasumioki group the hamasakaoki group and the tottorioki group are early miocene to earliest pliocene late early to late pliocene and late pliocene to holocene respectively these observations provide the basis to understand two main structural features in this region 1 e w trending folds and 2 northwestward tilting blocks the former construct a fold zone composed of two to four ranges of anticlines that have steeper southern flanks truncated by reverse faults the latter are shown by slightly inclined floors formed by submarine erosion step like asymmetric basins bounded by ne sw trending reverse faults and onlap toplap sedimentation patterns the lateral change in bed thickness sedimentation patterns and age of submarine sediments indicate that the e w trending folds were formed in the early middle or late miocene to the early pliocene by n s compression whereas the northwestward tilt blocks were formed in the late early to late pliocene by nw se compression the sedimentary records in this region dictate an abrupt change in tectonic setting in the late early pliocene this change is interpreted to show that the sea of japan has been closing since then due to either the reactivation of the amurian plate or the directional change of the philippine sea plate motion

depth of the moho discontinuity beneath the japanese islands estimated by traveltime analysis 1 the crustal structure beneath the japanese islands including depth distributions of the conrad and moho discontinuities was estimated using a tomographic inversion of regional body wave arrival times depth distributions of the bottom of the surface layer the conrad and the moho were modeled with two dimensional b spline functions while velocity distributions in layers were expressed by three dimensional b spline functions the depth of the discontinuities and the velocity in the layers were estimated simultaneously by the least squares method the velocity structure was sequentially estimated from shallower parts to deeper parts to avoid correlation between them this sequential analysis provided improved depth resolution the deepest region of the moho discontinuity was located in central honshu reaching about 40 km the moho discontinuity was generally deep in the central part of the islands whereas it was relatively shallow in the kanto southwestern chubu and chugoku districts in honshu and in northern kyushu some of the shallow moho regions would be related to graben formation due to tensile tectonic stress since the miocene the results were compared with those of seismic refraction surveys and receiver function analyses and it was found that the obtained model was consistent with many of these studies

instantaneous global plate motion model from 12 years of continuous gps observations 1 we estimate a global plate motion model for 17 major and minor tectonic plates solely on the basis of analysis of data from 106 globally distributed continuous gps stations spanning the period from january 1991 to july 2003 site positions estimated from 24 hour segments of data are aligned day by day to the international gps service igs realization of the itrf2000 reference frame using a similarity transformation thereby ensuring that the itrf2000 no net rotation condition is preserved linear velocities of a carefully selected set of stations are estimated from the position time series along with annual and semiannual fluctuations and position offsets due to gps instrument changes a white noise plus flicker noise model is applied to estimate realistic uncertainties for the site velocities which are then propagated into the derived plate motion model parameters we also examine the vertical velocities in the site selection process at the scripps orbit and permanent array center we have implemented a procedure whereby the plate motion model is updated on a regular monthly basis to improve its precision and reliability as new data become available and as a baseline against which anomalous motions can be detected

crystalline texture of the 2083 m ice core at vostok station antarctica crystalline texture and c axis orien tation of the 2083 m ice core at vostok station covering more than 150 kyear reveal the existence of strong anisotropies changes in crystal size with depth are compatible with the growth of grains driven by the free energy of grain boundaries a smaller growth rate appears to be associated with cold periods a gradual increase in the horizontal elongation of grains was observed between 350 and 680 m but the mean value of the coefficient of the linear dimensional orientation of grains does not cha nge below 700 m the e axis orientation of ice grains tends to orientate perpendicular to the direction of the elongation of grains forming a vertical girdle patt ern this charac teristic fabric has been interpreted as resulting from the gradual rotation of grains by basal glide under uniaxial longit udi nal tension the rotation of grains was calcu lated with respect to the total strain simulating the form ation of the girdle fabric pattern the fabric enhance ment factor was calculated at various depths it appears that vostok ice hardens gradua lly