anorthosite genesis the mid ocean ridge analogue the mechanism for generating plagioclase supersaturated basic magma is crucial to the origin and evolution of massif anorthosites a model is proposed to explain their temporal and tectonic association invoking iterative plagioclase accumulation magma mixing and phenocryst resorption to produce plagioclase supersaturated parent liquids by analogy to mid ocean ridge systems the model invokes periodic replenishment of magma reservoirs in an environment of incipient or very slow dilation these conditions are believed to characterize anorogenic anorthosite complexes

tracking slabs beneath northwestern pacific subduction zones article i nfo article history this study uses the amplitudes of bottom side reflected shear waves to constrain the morphology and dynam ics of subducted oceanic lithosphere beneath northwestern pacific subduction zones across honshu arc the 410 and 660 km seismic discontinuities are detected at the respective depths of 395 5 and 685 5 km within the wadati benioff zone their topographies are negatively correlated along slab dip showing the dominant effect of temperature on the olivine phase changes within the upper mantle transition zone the base of the upper mantle shows broad depressions as well as localized zones of shallow average depths be neath korea and northeast china the 15 km peak to peak topography west of the wadati benioff zones suggests that the stagnant part of the subducted pacific plate is not as flat as previously suggested eastward slab pile up is also possible at the base of the upper mantle across southern kuril arc the shear wave reflec tion coefficients of major olivine phase boundaries fall below 5 within the wadati benioff zone the appar ent reflection gaps and the spatial connection between a strong reflector at 900 km depth may imply 1 possible compositional variations at the top and bottom of the transition zone and 2 substantial mass heat flux across the 660 km seismic discontinuity we also identify strong reflectors within the subducted oceanic lithosphere at mid transition zone depths the depths and strengths of these reflectors are highly variable be tween honshu and southern kuril islands

sharpness of upper mantle discontinuities determined from high frequency reflections an understanding of the nature of seismic discontinuities in the earth s upper mantle is important for understanding mantle processes in particular the amplitude and sharpness of these discontinuities are critical for assessing models of upper mantle phase changes and chemical layering so far seismic studies aimed at determining the thickness and lateral variability of upper mantle discontinuities have yielded equivocal results particularly for the discontinuity at 410km depth1 2 here we present short period 0 8 2 0 s recordings of upper mantle precursors to the seismic phase p p pkppkp from two south american earthquakes recorded by the 700 station short period array in california our results show that the 410 and 660 km discontinuities beneath the indian ocean are locally simple and sharp corresponding to transi tion zones of 4 km or less these observations pose problems for mineral physics models3 5 which predict a transitional thickness greater than 6 km for the peridotite to spinel phase transition in contrast to the results of long period studies6 7 we observe no short period arrivals from near 520 km depth

the effect of water on the 410 km discontinuity an experimental study 1 in order to evaluate the effect of h on the pressure and transition interval of the olivine wadsleyite transformation synthesis experiments were carried out in hydrous and anhydrous peridotite compositions at 1400 c under hydrous near saturated conditions the pressure of the transition is 1 0 0 5 gpa lower than under anhydrous conditions in addition the two phase interval appears to broaden from about 0 4 gpa 12 km in the anhydrous system to as much as 1 3 gpa 40 km in the hydrous system under hydrous conditions the spatial distribution of olivine and wadsleyite appears to be controlled by h diffusion extrapolating previously measured diffusion coefficients for h in olivine and in liquids it appears that h diffusion driven by gravitational equilibration may serve to narrow the transition interval between olivine and wadsleyite

seismic evidence for a chemical heterogeneity in the midmantle a strong and slightly dipping seismic reflector beneath the mariana subduction zone 1 a clear later phase 80 s after the direct p wave is observed in most of individual seismograms recorded by a short period seismometer network in japan j array from a cluster of deep earthquakes that occurred at the northern mariana subduction zone this phase 1 shows a p wave particle motion 2 arrives later from earthquakes with shallower focal depths 3 has a steeper incident angle than that of p wave and 4 shows a deviation of a few degrees in the arrival azimuth from that of p wave we interpret it as an s to p converted wave which takes off downward from the source and is reflected at a velocity discontinuity reflector below the earthquakes travel time inversion shows that the seismic reflector dips southwest by 20 at 24 25 n 144 75 e and at a depth of 1115 km with a lateral extension at least 100 100 km the location corresponds to the lower edge of a high velocity anomaly in global tomographic models amplitude and waveform analyses suggest a decrease of s wave velocity by 2 6 and an increase of density by 2 9 within the reflector there is almost no difference in p wave velocity 1 between the reflector and the surrounding mantle the estimated thickness of the reflector is 12 km these observations indicate that the observed seismic structure is more likely to be a chemical reservoir rather than a purely thermal anomaly the seismic reflector might be a piece of subducted oceanic crust as suggested by a previous study it also could be related to the break down of the d phase of dense hydrous magnesium silicates at midmantle pressure condition reported by recent mineral physics studies both scenarios imply that mechanical chemical segregation might occur within the subducted slab at midmantle condition

global mapping of topography on the 660 km discontinuity long period precursors to the ss seismic phase are used to produce global maps of topography for the discontinuity at 660 km depth in the upper mantle these maps indicate discontinuity depth variations of up to 30 km and suggest a correlation between regional depressions in the 660 km discontinuity and subduction zones a result more consistent with models in which the subducting slabs are deflected horizontally at the discontinuity than with models of unhindered slab penetration into the lower mantle

melting experiments on the enstatite diopside join at 70 224 kbar including the melting of diopside melting relations on the enstatite diopside en mg2si2o6 di camgsi2o6 join including the compositions of crystalline phases and melts coexisting along the solidi were experimentally determined in the pressure range 70 224 kbar with a split sphere anvil apparatus ussa 2000 melting is peritectic in enstatite rich compositions at 70 124 kbar 1840 2100 c and eutectic at higher pressures while the diopside rich clinopyroxene melts azeotropically at 70 165 kbar and up to 300 c lower temperatures than the eutectic orthopyroxene is replaced with enstatite rich clinopyroxene at 120 kbar and 2090 c first garnet with 17 mol di forms on the solidus at 158 kbar and 2100 c two garnets coexist on the solidus at 165 183 kbar and 2100 c garnet coexists with casio3 perovskite at 183 224 kbar 2100 2230 c and two coexisting perovskites are stable at higher pressures the melting curve of diopside was determined at 80 170 kbar the slope becomes negative at 140 kbar and 2155 c at 170 kbar and 2100 c diopside with 96 di breaks down to garnet with 89 di and casio3 perovskite the new data were used to calculate an improved temperature pressure phase diagram for the cmas system which can be useful for estimating the mineralogy of the earth s upper mantle

physical conditions producing slab stagnation constraints of the clapeyron slope mantle viscosity trench retreat and dip angles abstract recent seismic tomography has revealed various morphologies in the subducted lithosphere in particular significant flattening and stagnation of slabs around the 660 km boundary are seen in some areas beneath the northwestern pacific subduction zones we examined the cause of slab stagnation in terms of the clapeyron slope of the phase transformation from ringwoodite to perovskite magnesiowustite trench retreat velocity dip angles and high viscosity of the lower mantle based on two dimensional 2 d numerical simulations of thermal convection in particular we examined the conditions necessary for slab stagnation assuming a very small absolute value of the clapeyron slope which were proposed based on recent high pressure high temperature high p t experiments our calculations show that slabs tend to stagnate above the 660 km boundary with an increasing absolute value of the clapeyron slope viscosity jump at the boundary and trench retreat velocity and a decreasing initial dip angle stagnant slabs could be obtained numerically for a realistic range of parameters obtained from high p t experiments and other geophysical observations combining buoyancy high lower mantle viscosity and trench retreat we found that a low dip angle of a descending slab at the bottom of the upper mantle plays an important role in slab stagnation two main regimes underlie slab stagnation buoyancy dominated and viscosity dominated regimes in the viscosity dominated regime it is possible for slabs to stagnate above the 660 km boundary even when the value of the clapeyron slope is 0 mpa k

tectonic controls on initial continental rifting and the evolution of young ocean basins a planetary perspective abstract a review and comparison of planetary tectonic literature and terrestrial interpretations of both oceanic and continental tectonics suggests that the earth in common with other terrestrial planets may have developed a global tectonic grid very early in its history this grid still preserved in ancient continental crustal fragments is maintained by both vertical and lateral fracture propagation it influences both the direction of initial continental rifting and the location and orientation of sea floor fracture zones in a developing young ocean basin sea floor spreading directions must continue to be controlled by the direction of easiest slip along major intercontinental wrench faults the atlantic ocean appears to be still in this stage development of subduction zones around the margin of an ocean basin permits greater freedom in spreading direction at this stage as represented by the pacific ocean ridge jumps and changes in spreading direction may occur as the spreading geometry readjusts to more closely reflect stresses associated with underlying convection cells at subduction zones rejuvenation tectonics still operate thick cold oceanic crust may impose its tectonic grain on the relatively thin over riding edge of the continental plate but young thin and hot oceanic crust is forced to conform to the tectonic grain of thick cold continental crust examples of both effects can be seen along the eastern margin of the pacific it is concluded that the structure and evolution of young ocean basins is strongly influenced by ancient fracture patterns in the adjacent continental blocks although greater freedom for readjustment develops as an ocean basin matures the continued need to move or interact with major blocks of continental lithosphere continues to impose severe limitations on directions and rates of spreading until subduction zones decouple oceanic and continental lithosphere both oceanic and continental tectonics can best be understood in terms of mutual interactions between plate tectonics rejuvenation tectonics and continental remnants of an original ancient global scale tectonic grid

the horizontally lying slab an unusual earthquake mb 6 2 occurred in the izu bonin island region in july 1982 the event occurring at a depth of 545 km was clearly separated from the main inclined seismic zone by a distance of about 200 km to diagnose the situation we have considered two possibilities 1 the event might be an unusual event in the sense that its location is unrelated to the position of the subducted slab and that there is probably no slab around it or 2 the slab at this depth might be lying horizontally on top of the 650 km discontinuity and the unusual event occurred in this horizontal part both possibilities have been modeled structurally we have computed the p wave travel times for the present event as well as for two other events located unambiguously in the inclined part of the seismic zone by employing a 3 d ray tracing program the computed travel time residuals have been compared with the observations at stations in western japan the observations are found to be consistent with the model of the horizontally lying slab our result thus suggests that the slab might be horizontal at this depth in this part of the izu bonin islands

hot regions and the origin of marginal basins in the western pacific abstract volcanic provinces showing no genetic relationship to plate boundaries may be classified into two categories hot spots which are a few hundred kilometers across and may be nearly fixed in position with respect to deep mantle and hot regions which are a few thousand kilometers across and can migrate more freely the mantle upwellings which presumably give rise to them may originate at different depths by different causes it is observed that the marginal basins older than 15 ma of the western pacific become progressively younger northward with the exception of the south fiji basin this leads to the hypothesis that the spreading of marginal basins was caused by the mantle upwelling associated with a migrating hot region and that a hot region which started from the australia region in the late cretaceous migrated northward successively creating the tasman coral sea caroline south china parece vela shikoku and japan basins through paleocene eocene oligocene and early miocene time this hot region presently underlies northern china mongolia and adjacent areas another hot region is assumed to have caused the spreading of the south fiji basin and all the currently spreading basins in the southwestern pacific spreading of individual marginal basins occurred during the short period when a hot region was passing the pertinent area the main merit of this hypothesis is that it can explain the relationship between the location and age as well as the short duration of spreading of western pacific marginal basins marginal basins are formed commonly though not always in the overriding plates near subduction zones because in such a setting a spreading marginal basin is readily accommodated either by an oceanward movement of the nearby subduction zone or by a continentward movement and subduction of the overriding oceanic plate there are a few marginal basins that were formed in other tectonic settings and accommodated by some other mechanism of compensative subduction presumably the splitting of the supercontinent pangea was also caused mainly by the effect of the mantle upwelling associated with the same hot region that later migrated northward creating marginal basins in the western pacific the main basis for this presumption is the fact that the splitting of pangea was completed in the australia region in middle cretaceous time whereas the spreading of marginal basins in the western pacific began in the same australia region in the late cretaceous immediately following

a detailed receiver function image of the upper mantle discontinuities in the japan subduction zone abstract we have imaged the upper mantle discontinuities in a 30 20 large region at the active continental margin of the japan subduction zone and neighboring areas using p to s converted phases from teleseismic records of permanent broadband stations the 410 km discontinuity is detected within 10 km of its global average position an interesting exception in its observation is a gap near 135 e very close to the slab penetration of the 410 km discontinuity and in an area where we have rather high data density the 660 km discontinuity reaches 700 km depth at two places where it is hit directly by the slab these data generally show good agreement with tomographic results both the 660 km discontinuity depression and the p velocity anomalies suggest about 400 500 k temperature deficit within the slab however no downward bending of the 660 km discontinuity is observed in eastern china where the flat lying slab is imaged by tomography this suggests that the slab does not cool the 660 km discontinuity in this region therefore the positive buoyancy required to keep the slab lying flat cannot have been provided by the negative clapeyron slope of the spinel perovskite phase transition another mechanism is needed which could possibly be metastable olivine in the cold core of the slab we have also imaged the shallower portion of the slab down to about 150 km underneath some seismic stations likely because metastable gabbro is still existing to this depth providing a sufficient velocity contrast a strong negative converted phase is observed at 150 200 km depth underneath a volcanic region in japan if real observed at one station only the zone which produces this conversion and which may begin exactly above the slab would require fluid fed melting

quantitative estimation of intertidal sediment characteristics using remote sensing and gis abstract high spatial resolution satellite data ikonos combined with in situ data was used to quantitatively estimate the spatial distribution of tidal flat characteristics for the hwangdo tidal flat cheonsu bay korea the classification result was accurate in terms of a comparison with the in situ data and the overall accuracy was 90 7 which confirmed the validity of the classification gis analysis based on a probabilistic model was applied to a quantitative estimation of the relationship between each surface sediment facies and the spectral reflectance mud flat facies showed a high positive correlation r 2 0 91 and sand flat facies showed a high negative correlation r 2 1 00 which was a good reflection of the sedimentary characteristics of hwangdo tidal flat relationships between each sediment facies and dem also showed good agreement with the topographic characteristics in the study area the study revealed that intertidal surface sediment classification using high resolution remote sensing imagery and in situ data successfully shows spectral and topographic characteristics of the study area it was noted that spectral reflectance was affected by a combination of environmental factors including grain size topography and remnant surface water it is possible to determine the type of tidal flat through quantitative estimates of the spatial distribution of surface sediments according to their spectral reflectance

recent advances in the study of mantle phase transitions we review recent advances in the study of phase transitions of minerals in the earth s mantle including unsolved problems regarding these processes the phase boundaries of mg fe 2sio4 in the mantle transition zone are modified under the wet conditions by changes in thermodynamic properties of its polymorphs because of differences in the water solubilities of these minerals the shift of phase boundaries has significant implications for the topography of the 410 km and 660 km seismic discontinuities the post perovskite phase with cairo3 structure exists at pressures above 110 gpa and at high temperature the effects of al and fe on phase transition are under debate several post stishovite phases have been reported but equilibrium boundaries and existence in the real lower mantle are also still debatable spin transition occurs in magnesiowustite perovskite and post perovskite phases at high pressures of the lower mantle and core the pressure interval in the spin transition can be large at high temperature and so the transition might not cause a discrete change in physical properties under real earth conditions 2008 elsevier b v all rights reserved

the use of satellite imagery to determine the distribution of intertidal surface sediments of the wash england abstract three methods of processing landsat 5 thematic mapper data were used to map the surface sediment distribution on the intertidal areas of the wash east england one method used a maximum likelihood classification to define each picture element pixel that equated to a 30 m square on the ground as having a muddy or sandy sediment the other methods used multiple regression mr and spectral mixture modelling to quantify the amount of each sediment type within a pixel all methods produced an acceptable description of sediment when compared with the known sediment composition of 192 sample sites muddy sites were more accurately defined than sandy ones by all methods image derived estimates of sediment composition obtained by the mr method proved to be a robust substitute for field derived values in mr models relating macrobenthos density to sediments and other site characteristics

seismic structure and origin of active intraplate volcanoes in northeast asia abstract three dimensional p wave velocity structure beneath the changbai and other intraplate volcanic areas in northeast asia is determined by inverting 1378 high quality p wave arrival times from 186 teleseismic events recorded by 61 broadband seismic stations low velocity low v anomalies are revealed beneath the changbai longgan xianjindao volcanoes high velocity high v anomalies are found in the mantle transition zone where deep focus earthquakes under hunchun occur at depths of 500 600 km the high v anomaly reflects the deep subduction of the pacific slab under ne asia which may have contributed to the formation of the changbai longgang xianjindao and jingpohu intraplate volcanoes a low v anomaly is also revealed in the mantle transition zone which may have a close relationship with the occurrence of deep earthquakes under the hunchun area our results support the big mantle wedge bmw model by zhao et al zhao d lei j tang y 2004 origin of the changbai volcano in northeast china evidence from seismic tomography chin sci bull 49 1401 1408 zhao d maruyama s omori s 2007 mantle dynamics of western pacific and east asia insight from seismic tomography and mineral physics gondwana res 11 120 131 who proposed that the intraplate volcanoes in ne asia are caused by the back arc magmatism associated with the deep dehydration process of the subducting slab and convective circulation process in the bmw above the stagnant pacific slab

destruction of lithosphere within the north china craton inferred from surface wave tomography 1 the north china craton ncc is one of the oldest cratons in the world however the lithosphere of the craton was destructed during phanerozoic tectonism and then became tectonically and seismically active because the lithospheric structure of this complex craton has not been well studied the mechanism behind the thinning transformation and destruction of the lithosphere remains debated using an efficient and scalable 3 d surface wave tomography method we obtain a high resolution regional s wave velocity model that shows the three dimensional lithospheric structure of the ncc in addition we convert the s wave structure to an estimated thermal structure using accepted relationships between s wave velocity and temperature the model images a large upper mantle low velocity body beneath the eastern ncc especially beneath the seismically active zone from tangshan to xingtai this body is interpreted to represent hot material or volatiles escaping from the slab edge in the transition zone between the upper and lower mantle the low velocity body is a key piece of evidence in demonstrating thermochemical bottom up erosion transformation of the overlying cratonic lithosphere thereby leading to destruction of the lithosphere which may have occurred during the cenozoic this erosion mechanism appears to have had less influence in the western ncc ordos block however our results reveal a 130 km thick lithosphere beneath the present cratonic ordos block which is thinner than the 200 km thickness of the ncc lithosphere during the paleozoic as determined from analyses of xenoliths

semi automated procedures for shoreline extraction using single radarsat 1 sar image coastline identification is important for surveying and mapping reasons coastline serves as the basic point of reference and is used on nautical charts for navigation purposes its delineation has become crucial and more important in the wake of the many recent earthquakes and tsunamis resulting in complete change and redraw of some shorelines in a tropical country like malaysia presence of cloud cover hinders the application of optical remote sensing data in this study a semi automated technique and procedures are presented for shoreline delineation from radarsat 1 image a scene of radarsat 1 satellite image was processed using enhanced filtering technique to identify and extract the shoreline coast of kuala terengganu malaysia radsarsat image has many advantages over the optical data because of its ability to penetrate cloud cover and its night sensing capabilities at first speckles were removed from the image by using lee sigma filter which was used to reduce random noise and to enhance the image and discriminate the boundary between land and water the results showed an accurate and improved extraction and delineation of the entire coastline of kuala terrenganu the study demonstrated the reliability of the image averaging filter in reducing random noise over the sea surface especially near the shoreline it enhanced land water boundary differentiation enabling better delineation of the shoreline overall the developed techniques showed the potential of radar imagery for accurate shoreline mapping and will be useful for monitoring shoreline changes during high and low tides as well as shoreline erosion in a tropical country like malaysia

strontium isotopic constraints on the origin of proterozoic anorthosites abstract the proterozoic giles complex central australia contains an almost complete range of anorthosite types from minor or major layers in gabbronorite intrusions to large anorthosite troctolite bodies to small orthopyroxene anorthosite massifs each type has a distinctive sr isotopic signature anorthosite dominated masses have a regular relationship between ferromagnesian mineralogy initial 87 sr 86 sr and anorthite contents in plagioclase anorthosite troctolite bodies have significant olivine relatively low initial 87 sr 86 sr 0 7038 0 7043 and an 50 69 orthopyroxene dominant anorthosites have relatively high 87 sr 86 sr 0 7045 0 7063 and an 45 60 the pattern is found worldwide detailed study of one intrusion demonstrates that contamination by wall rock granulite produces the higher 87 sr 86 sr values anti correlation between 87 sr 86 sr and an and determines olivine orthopyroxene proportions olivine bearing anorthosites form from a primary aluminous tholeiite magma with plagioclase dominating the liquidus progressive contamination of this parent magma produces a gradation to orthopyroxene anorthosites

dynamical mechanisms controlling formation and avalanche of a stagnant slab abstract we performed a numerical study to understand the dynamical mechanism controlling the formation and avalanche of a stagnant slab using two dimensional dynamical models of the integrated plate mantle system with freely movable subducting and overriding plates we examined slab rheology as a mechanism for producing various styles of stagnating or penetrating slabs that interact with the 410 km and 660 km phase transitions the simulated results with the systematically changed rheological parameters are interpreted using a simple stability analysis that includes the forces acting on the stagnant slab slab plasticity that memorizes the shape produced by past deformation generates slab stagnation at various depths around the 660 km phase transition the slab stagnates even beneath the 660 km phase boundary with a gentle clapeyron slope feedbacks between trench backward migration and slab deformation promote each other during the slab stagnation stage slab viscosity also determines the final state of the subducted slab that is it continues stagnation or initiates penetration a low viscosity slab can finally penetrate into the lower mantle because the growth time of the rayleigh taylor instability is shorter after the avalanche the direction of the trench migration changes depending on the lower mantle slab viscosity

reconciling pacific 410 and 660 km discontinuity topography transition zone shear velocity patterns and mantle phase transitions a r t i c l e i n f o article history we observe that the depths of the 410 and 660 km seismic discontinuities are on average slightly positively correlated globally this is due in large part to a modestly depressed 660 km discontinuity and a large depression of the 410 km discontinuity across the paci c the clapeyron slope dp dt the change in pressure depth of a phase transition with a change in temperature can be used to predict the depth of a phase transformation assuming lateral temperature variations the phase change of olivine to spinel is well understood experimentally almost certainly produces the 410 km discontinuity and has a positive clapeyron slope at the base of the transition zone both the olivine component of the mantle spinel and the pyroxene component garnet transform to perovskite and periclase observations of 660 km discontinuity depths are often consistent with the negative clapeyron slope of the spinel to perovskite and periclase transition with an apparent anti correlation with the depth of the 410 km discontinuity however under the paci c the depression of the 410 km discontinuity and slow seismic velocities indicate that the mantle is warmer than average using a negative clapeyron slope for the perovskite forming reaction the 660 km discontinuity is predicted to be shallow in this region however we observe that it is either depressed or has little de ection from its average depth we nd that if the clapeyron slope associated with the 660 km discontinuity changes sign from negative to positive between 1920 and 2020 k we can explain the correlation of discontinuity structure with seismic velocities in the transition zone this shift in sign is in accord with the dominant 660 km transition forming reaction shifting from spinel to garnet near this temperature

detecting the intertidal morphologic change using satellite data abstract the objectives of this study were a to generate an intertidal digital elevation model dem using waterlines extracted from landsat tm and in situ ground levelling data b to quantitatively estimate morphologic change from the generated dems for the years 1991 and 2000 and c to evaluate the chenier migration in the tidal flats of gomso bay korea on extracting the waterlines we considered the tidal flat environments such as tidal conditions remnant surface water suspended sediment and exposure time ground levelling was carried out along one line in 1991 and two lines in 2000 from the extracted waterlines and ground levelling data we succeeded in generating intertidal dems with an accuracy of 10 9 cm r m s overall and 7 3 cm r m s in the lower tidal flats the morphologic changes estimated by subtracting the two dems showed an erosion rate of 9 0 cm over 9 yr that corresponds to an annual mean morphologic change budget of 309 865 m 3 yr overall the gomso tidal flats can be defined as an erosion dominant environment the changes with respect to the sedimentary facies were also evaluated as a the sandy silt flat had a sedimentation rate of 3 4 cm over 9 yr that corresponds to an annual mean budget of 52 552 m 3 yr b the silty sand flat had a sedimentation rate of 14 3 cm over 9 yr that corresponds to a mean erosion of 197 927 m 3 yr and c the sand flat had a sedimentation rate of 11 8 cm over 9 yr that corresponds to a mean change of 58 808 m 3 yr the results comply with the general rules of sedimentology we also investigated the chenier migration which is the most dynamic geomorphologic change in the tidal flats chenier is usually composed by sand and shell as a result of coastal progradation in sand and it is dominantly fed by sediments transported by long shore currents the chenier was found to have migrated about 148 m landward over 6 yr the results demonstrate that satellite remote sensing is an efficient and effective tool for a long term morphologic change estimation in tidal flats

seismic evidence for a 920 km discontinuity in the mantle analysis of hundreds of seismograms from a seismic array in the japanese islands reveals a seismic discontinuity at a depth of about 920 km in the mantle beneath the tonga subduction zone this discontinuity is also evident beneath subduction zones in the japan and flores seas the discontinuity probably represents either a change in mantle chemical composition or the signature of the subducted slab s garnet layer

upper mantle beneath southeast asia from s velocity tomography 1 we present a three dimensional s velocity model of the se asian western pacific upper mantle with 400 km lateral resolution using the novel automated multimode inversion technique we processed 4038 vertical component seismograms and extracted 22 708 linear equations with uncorrelated uncertainties that constrain upper mantle structure we used time frequency windows to select signal with negligible proportion of scattered energy the windows included the fundamental rayleigh mode and s and multiple s waves the observed range of s velocity variations is the widest 17 18 in the upper 150 km of the mantle high velocity continental roots can reach beyond the present extent of the overlying archean proterozoic crust by 500 km beneath some precambrian units the roots are absent which can be attributed to deformation and gradual destruction of the ancient lithosphere at 120 150 km s velocity beneath some cratons reaches 4 8 km s this can be accounted for by thermal and compositional effects beneath the hainan island area a low velocity anomaly is observed from near the surface to the bottom of our model the hot spot type volcanism here may be caused by the deep mantle hainan plume a low velocity mantle domain underlies the south central sea of japan surrounded on the surface by intraplate volcanoes a deep seismicity gap is present near 40 n in the pacific slab subducting below and may result from a plume slab interaction a high velocity anomaly is present in the transition zone beneath the northern boundary of the yangtze craton we propose that the anomaly corresponds to subducted continental lithosphere stagnant atop the 660 km discontinuity

the influence of trench migration on slab penetration into the lower mantle abstract a two dimensional numerical convection model in cartesian geometry is used to study the influence of trench migration on the ability of subducted slabs to penetrate an endothermic phase boundary at 660 km depth the transient subduction history of an oceanic plate is modelled by imposing plate and trench motion at the surface the viscosity depends on temperature and depth a variety of styles of slab behaviour is found depending predominantly on the trench velocity when trench retreat is faster than 2 4 cm a the descending slab flattens above the phase boundary at slower rates it penetrates straight into the lower mantle although flattening in the transition zone may occur later leading to a complex slab morphology the slab can buckle independent of whether it penetrates or not especially when there is a localised increase in viscosity at the phase boundary flattened slabs are only temporarily arrested in the transition zone and sink ultimately into the lower mantle the results offer a framework for understanding the variety in slab geometry revealed by seismic tomography

waterline extraction from landsat tm data in a tidal flat a case study in gomso bay korea waterline extraction is potentially one of the most effective satellite remote sensing tools for studying changes in tidal flat environment and coastlines however its application to the study of tidal flats has not been investigated in detail the waterline in a tidal flat in gomso bay korea is characterized and evaluated using 27 sets of landsat thematic mapper tm and earth observing system terra eos terra advanced spaceborne thermal emission and radiometer aster data ground truth data including grain size soil moisture content ground levelling and waterline tracking have been obtained the choice of spectral bands in terms of tidal conditions turned out to play a key role in locating the waterline while the waterlines extracted from near infrared nir short wavelength infrared swir and thermal infrared tir data are commonly reliable on the flood tide the discrepancies between different bands become large on the ebb tide the bands tir nir and swir are in that order decreasingly effective in extracting the waterline while ebb tides are in progress the effect of turbid water on nir can be reduced by a ratioing of nir and the visible band the location of the waterline is also an important factor to consider the discrepancy is largest on the middle tidal flat selection of the proper band for waterline extraction under various conditions is suggested however no single band can accommodate all aspects of the tidal flat environment a schematic model associated with the spectral reflectance of the tidal flat is proposed in which the remnant water scattered on the surface after exposure is emphasized as an additional factor

rheologic controls on slab dynamics several models have been proposed to relate slab geometry to parameters such as plate velocity or plate age however studies on the observed relationships between slab geometry and a wide range of subduction parameters show that there is not a simple global relationship between slab geometry and any one of these other subduction parameters for all subduction zones numerical and laboratory models of subduction provide a method to explore the relative importance of different physical processes in determining subduction dynamics employing 2 d numerical models with a viscosity structure constrained by laboratory experiments for the deformation of olivine we show that the observed range in slab dip and the observed trends between slab dip and convergence velocity subducting plate age and subduction duration can be reproduced without trench motion i e slab roll back for locations away from slab edges successful models include a stiff slab that is 100 1000 times more viscous than previous estimates from models of plate bending the geoid and global plate motions we find that slab dip in the upper mantle depends primarily on slab strength and plate boundary coupling with a small dependence on subducting plate age once the slab sinks into the lower mantle the primary processes controlling slab evolution are 1 the ability of the stiff slab to transmit stresses up dip 2 resistance to slab descent into the higher viscosity lower mantle and 3 subduction induced flow in the mantle wedge corner

assessment of ground subsidence hazard near an abandoned underground coal mine using gis this study constructs a hazard map for ground subsidence around abandoned underground coal mines aucms at samcheok city in korea using a probability frequency ratio model a statistical logistic regression model and a geographic information system gis to evaluate the factors related to ground subsidence an image database was constructed from a topographical map geological map mining tunnel map global positioning system gps data land use map lineaments digital elevation model dem data and borehole data an attribute database was also constructed from field investigations and reports on the existing ground subsidence areas at the study site nine major factors causing ground subsidence were extracted from the probability analysis of the existing ground subsidence area 1 depth of drift 2 dem and slope gradient 3 groundwater level permeability and rock mass rating rmr 4 lineaments and geology and 5 land use the frequency ratio and logistic regression models were applied to determine each factor s rating and the ratings were overlain for ground subsidence hazard mapping the ground subsidence hazard map was then verified and compared with existing subsidence areas the verification results showed that the logistic regression model accuracy of 95 01 is better in prediction than the frequency ratio model accuracy of 93 29 the verification results showed sufficient agreement between the hazard map and the existing data on ground subsidence area analysis of ground subsidence with the frequency ratio and logistic regression models suggests that quantitative analysis of ground subsidence near aucms is possible

statistical analysis of landslide susceptibility at yongin korea the aim of this study is to evaluate the susceptibility of landslides at yongin korea using a geographic information system gis landslide locations were identified in the yongin area from interpretation of aerial photographs field surveys and maps of the topography soil type timber cover and geology these data were collected and constructed into a spatial database using gis the factors that influence landslide occurrence such as slope aspect and curvature of topography were calculated from the topographic database texture material drainage and effective soil thickness were extracted from the soil database and type age diameter and density of timber were extracted from the forest database lithology was extracted from the geological database and land use was classified from the landsat tm satellite image landslide susceptibility was analyzed using the landslide occurrence factors by probability and logistic regression methods the results of the analysis were verified using the landslide location data the validation results showed satisfactory agreement between the susceptibility map and the existing data on landslide location the gis was used to analyze the vast amount of data efficiently and statistical programs were used to maintain specificity and accuracy the results can be used to reduce associated hazards and to plan land use and construction

structure of the upper mantle and transition zone beneath southeast asia from traveltime tomography 1 tomographic images of the mantle beneath east asia were obtained from the inversion of traveltime data from global and regional seismograph networks and from temporary arrays on and around the tibetan plateau our results are consistent with previous studies but the unprecedented resolution of mantle heterogeneity provides new insight into the large scale tectonic framework of the continental india asia collision in the western part of the study region and subduction of the oceanic lithosphere in the east in the realm of continental collision west of 100 e a relatively slow p wave speed characterizes the upper mantle beneath much of the tibetan plateau but the wave speed is high beneath cratonic india the southern and western part of the tibetan plateau hindu kush and the tian shan in the subduction realm east of 110 e the main structures are i pronounced low wave speed anomalies at a depth of between 100 and 400 km beneath asia s southeastern seaboard and the back arc regions of ongoing subduction ii narrow fast anomalies in the upper mantle beneath major subduction zones and iii widespread fast anomalies at a depth of 500 700 km beneath the sea of japan the northern part of the philippine sea plate and southeastern china if the latter anomalies represent stagnant slabs their fragmented nature and large lateral extent suggest that they are produced by different episodes of subduction beneath western pacific island arcs along the old se margin of asia or during the mesozoic collision of cratonic units in southeast asia attribution to ancient subduction systems implies that slab fragments can reside in the transition zone for at least several tens of millions of years shallow slow anomalies beneath the red river fault region connect to deep anomalies beneath the south china fold belt and south china sea suggesting a causal relationship between the evolution of the continental lithosphere of sw china and deeper mantle processes between the collision and the subduction realms tomography reveals high wave speed continental roots beneath the western part of the north china craton ordos block and the south china or yangtze craton sichuan basin to a depth of 300 km

landslide susceptibility mapping in the damrei romel area cambodia using frequency ratio and logistic regression models this study applied tested and compared a probability model a frequency ratio and statistical model a logistic regression to damre romel area cambodia using a geographic information system for landslide susceptibility mapping landslide locations were identified in the study area from interpretation of aerial photographs and field surveys and a spatial database was constructed from topographic maps geology and land cover the factors that influence landslide occurrence such as slope aspect curvature and distance from drainage were calculated from the topographic database lithology and distance from lineament were extracted and calculated from the geology database land cover was classified from landsat tm satellite imagery the relationship between the factors and the landslides was calculated using frequency ratio and logistic regression models the relationships frequency ratio and logistic regression coefficient were overlaid to make landslide susceptibility map then the landslide susceptibility map was compared with known landslide locations and tested as the result the frequency ratio model 86 97 and the logistic regression 86 37 had high and similar prediction accuracy the landslide susceptibility map can be used to reduce hazards associated with landslides and to land cover planning

mapping intertidal estuarine sediment grain size distributions through airborne remote sensing abstract the intertidal environments of estuaries represent critical exchange environments of sediment and sediment bound contaminants ecological and sedimentological related investigations of these environments require monitoring methods that provide rapid spatially representative data on sediment grain size distribution remote sensing has the potential to provide synoptic information of intertidal environments previous in situ and laboratory based reflectance investigations have demonstrated that for effective quantification of sediment grain size distributions remote sensing platforms must include measurements within the short wave infrared swir in addition the timing of image acquisition in relation to tidal cycles and sediment moisture content is critical in optimising the spectral differences between the coarser sand and finer mud fraction of sediments daedalus 1268 airborne thematic mapper atm has been identified as an appropriate platform and sensor for providing accurate synoptic maps of estuarine sediment distributions this paper presents the results from the application of atm 1 75 m resolution data to the mapping of surface sediment grain size distributions across intertidal areas of ribble estuary lancashire uk atm imagery was acquired after the intertidal area was exposed to strong summer drying conditions pre processing and linear unmixing of the imagery collected of the intertidal zone following a period of drying allowed accurate sub pixel determinations 1 75 m resolution of sediment clay r2 0 79 but less accurate for sand r2 0 60 the results also demonstrate deterioration in the image calibration with increasing sediment moisture content and microphytobenthos cover however recombining the subpixel end member abundances through multivariate regression analysis improved the image calibration significantly for both sediment clay and sand content r2 0 8 for imagery collected in both dryer and wetter conditions these results demonstrate that atm data or similar can be used to gain quantitative information on intertidal sediment distributions and such data has application to a wide variety of estuarine research

high temperature anomalies oceanward of subducting slabs at the 410 km discontinuity abstract our p wave whole mantle tomography revealed a low velocity region oceanward of the northern honshu slab of the pacific plate at depths around the 410 km seismic discontinuity resolution tests and scrutiny of the traveltime residuals for the ray paths passing through the low velocity region indicate that this anomaly is a resolvable feature and not an artifact due to the strong slab anomalies the existence of the slow anomalies is also supported by the analysis of the p wave records from the j array a large aperture seismic array in japan for a bonin earthquake the p arrivals to northern honshu at epicentral distances of 13 20 are strongly triplicated because of the 410 km discontinuity the later arrivals along the retrograde branch where ray paths pass through the low velocity region are anomalously slow comparison of the observed and synthetic waveforms indicates not only slow anomalies but also depression of the 410 km discontinuity this depression represents the direct evidence for the low velocity zone of primarily thermal origin an excess temperature of 200 k and the associated fractional melt of less than 1 can explain both the results of the tomographic and waveform analyses