cross flows in the taiwan strait in winter abstractin winter a branch of the china coastal current can turn in the taiwan strait to join the poleward flowing taiwan coastal current the associated cross strait flows have been inferred from hydrographic and satellite data from observed abundances off northwestern taiwan of cold water copepod species calanus sinicus and in late march of 2012 also from debris found along the northwestern shore of taiwan of a ship that broke two weeks earlier off the coast of china the dynamics related to such cross flows have not been previously explained and are the focus of this study using analytical and numerical models it is shown that the strait s currents can be classified into three regimes depending on the strength of the winter monsoon equatorward poleward for northeasterly winds stronger weaker than an upper lower bound and cross strait flows for relaxing northeasterly winds between the two bounds these regimes are related to the formation of the stationary rossby wave over the changyun ridge

on the vorticity balance over steep slopes kuroshio intrusions northeast of taiwan abstractthe circulation of the kuroshio northeast of taiwan is characterized by a large anticyclonic loop of surface intrusion and strong upwelling at the shelfbreak to study the mechanisms of kur

recent stabilization of active sand dunes on the canadian prairies and relation to recent climate variations the historical activity of sand dunes on the southern canadian prairies was investigated in order to determine the relation with recent climate variations changes in dune activity were determined from historical aerial photographs at seven sites with active parabolic dunes in saskatchewan and manitoba the methodology developed combines digital image processing and geographical information system gis analysis to measure changes in dune activity from the aerial photographs as well as correlation analysis to determine the relation between dune activity and climate variations overall dune activity has been decreasing since the early to mid 1900s as evidenced by greater vegetation colonization than sand dune migration or reactivation the decrease in dune activity is significantly correlated with decadal scale variations in aridity and is coincident with a decrease in annual wind speed evidence suggests that this response is superimposed on a longer trend towards stabilization possibly in place since the late 1700s taken together the effect of this complex response is that dune recovery on the southern canadian prairies is prolonged well after an initial disturbance and therefore gives the impression of anomalous levels of activity for extended periods thereafter for this reason dune mobility indices predicated on short term climate variations years to decades do not fully describe the present level of dune activity on the southern canadian prairies

causes and processes of sandy desertification in guinan county qinghai tibet plateau by means of field investigations interpretation of remote sensing images analysis of a digital elevation model and grain size tests we analyzed the causes and processes responsible for sandy desertification in guinan county on the qinghai tibet plateau the desertified land is mainly distributed on the mugetan region and covered 566 km2 about 96 1 of which distributed on the sandy hills we found that reactivation of the underlying fossil dunes supplied the sand that contributed to modern sandy desertification the surface turf which supports a dense growth of grass and its matted roots covers the underlying cohesive silty sands in the sandy hills and both layers protect the dunes against erosion mechanical destruction of the protective shell leads to exposure of fossil dune sands the exposed loose fossil sands are then carried away by the wind creating scarps followed by lateral recession at the bottom of the scarp leading to its collapse the process then repeats with the expansion of recession caused by wind erosion abundant sands are supplied and aeolian activity intensifies repetition of this process expands the blowouts leading to merger of the blowouts and the evolution of mobile dunes similar processes occur at the top of cliffs above the yellow river and mangla river

a numerical study on the formation of upwelling off northeast taiwan 1 we examined the spatial and temporal variations of upwelling off northeast taiwan using a fine resolution numerical model with realistic bathymetry the zonally running shelf break in the area deflects the kuroshio seaward and produces upwelling on its on shelf edge the upwelling in turn manifests a cold dome or a cyclonic eddy in depths below 150 m or so the upwelling and hence the cyclonic eddy exist year round above this depth the eddy waxes and wanes as the upper portion of the kuroshio migrates seaward and shoreward respectively the eddy event fluctuates in a wide range of timescales seasonally the occurrence heavily favors summer rather than winter because the mean kuroshio axis migrates seaward in summer intraseasonally the fluctuation contains two dominant periods centered at 70 days and 30 days local wind forcing and channeling by two local canyons do not affect the eddy statistics significantly

seasonal exchanges of the kuroshio and shelf waters and their impacts on the shelf currents of the east china sea previous in situ observations and modeling studies have indicated that through mass and momentum exchanges across the shelf edge the kuroshio can significantly influence the shelf currents of the east china sea ecs here instead of localized observations this study uses 25yr of drifter data supported by satellite and other data to identify seasonal cross shelf exchanges along the entire shelf edge the authors show that kuroshiomeandersonshorefromfalltowinterandoffshorefromspringtosummer withthelargestamplitude northeast of taiwan the influence is limited to the shelf edge when the kuroshio meanders offshore in spring and summer by contrast strong onshelf intrusions and cross shelf exchanges occur when the kuroshio meanders onshore in fall and winter drifters intrude onshelf northeast of taiwan and spread as far north as 308n against the strong northeasterly wind the forcing on the shelf is identified as a northward downsloping of the sea level that is steepest north of taiwan at 258 288n but which is 3 times weaker farther north the vorticity budget computed from a numerical model indicates that intrusion during fall andwinter is primarily a result of balancebetweenonshelfadvectionofambientpotentialvorticityandvorticityproductionbythealong isobath pressure gradient acting on the changing mass of water column across the continental slope

temporal and spatial variability in dune reactivation across the nebraska sand hills usa the nebraska sand hills is a stabilized dune field on the great plains of north america although it is well known that this dune field like several others on the great plains last experienced widespread activity during the medieval climatic anomaly mca ad 900 1300 spatial variation in the timing and nature of drought development is poorly constrained to elucidate spatial trends in dune reactivation samples potentially representing mca activity across the sand hills were collected and dated using optically stimulated luminescence osl ages from the older part of the mca were obtained from eolian sediments in the northwestern sand hills while ages from later in the episode were obtained to the southeast suggesting a geographic trend in the timing of revegetation of the dunes near the end of the drought revegetation likely occurred to the northwest initially as a result of renewed moisture availability from a rising water table in the interdunes which serve as refugia for vegetation during times of drought vegetation then gradually spread to the southeastern sand hills an additional spatial trend in ages is apparent in the chronology of linear dune mobilization across the sand hills linear dunes in the northwest are superimposed on megadunes and originated during the last reactivation while linear dunes in the southeast are built around older cores of dunes and formed during several reactivations our geochronology reveals three episodes of eolian transport including the mca in the formation of linear dunes in the southeast

reactivation of supply limited dune fields from blowouts a conceptual framework for state characterization aeolian dune fields mantle the earth in both vegetated stable and unvegetated active states changes in state are poorly understood in particular little is known about reactivation devegetation from a vegetated state available evidence indicates that dune reactivation can be driven by changes in aridity increased wind speed fire biogenic disturbance human disturbance or a combination of the previous how these controls fit together and define the reactivation potential of dune fields is presently unknown here we develop a framework to describe reactivation potential for a specific case presently vegetated supply limited dune fields that develop blowouts under a unidirectional wind we first define a conceptual model of blowout expansion and then split the functions of vegetation in a stable dune field into i maintenance of a protective skin and ii blowout suppression we model reactivation as disturbance breaking through the protective skin which forms a blowout that is either i suppressed by colonizer species or ii capable of advancing downwind and reactivating part of the dune field the capacity for disturbance to break through the protective skin is a function of disturbance magnitude area and resistance of the skin the blowout suppression capacity of a dune field is a function of sediment flux blowout depth related to geomorphology and colonizer species vitality by plotting a given dune field with two variables protective skin breach rate and blowout suppression capacity we define four states i stable ii blowout dominated iii reactivating or iv stable but disturbance susceptible we reinforce the conceptual model with qualitative examples and discussion of experiments on grassland stabilized dunes in canada overall our framework provides a starting point for quantifying the reactivation potential of vegetated dune fields

the pattern and variability of winter kuroshio intrusion northeast of taiwan the variations of the kuroshio path and velocity northeast of taiwan are analyzed based on along track satellite altimeter data as well as high resolution model experiments observations reveal that in winter the kuroshio intrusion into the east china sea ecs at this location is manifested by a secondary maximum current core smcc shoreward of the kuroshio s main path the smcc varies significantly on interannual time scale and its variability is strikingly out of phase with that of the kuroshio entering the ecs meaning that the stronger the kuroshio the weaker the smcc and vice versa model experiments corroborate the observational results and more importantly indicate that the kuroshio intrusion here follows two primary routes a large anticyclonic loop that separates from the kuroshio at the northern end of taiwan and moves forward to form the smcc and a straight northward path onto the shelf when the kuroshio turns sharply eastward along the continental slope of the ecs the intrusion is controlled by both local forcing and remote effect with its pattern and variability depending mostly on the local heat flux and the inertia of the kuroshio current

short term dynamics of wind erosion of three newly cultivated grassland soils in northern china this study examined the dynamic nature of short term wind erosion processes of three grassland soils under simulated cultivation in a laboratory wind tunnel soil loss on a sandy loam a loamy sand and a sand soil was measured in six successive 10 3 and 1 min exposures at the speeds of 10 18 and 26 m s 1 respectively erodible soil particle sizes of each interval were determined through direct dry sieving it was observed that increasing blowing duration generally led to rapid decrease of soil loss decrease of the erodible soil particle size from a definitely restricted area by any definite speed of wind and the non erodible particles remaining on the soil surface increased from the first to the last blowing interval soil loss decreased by 86 4 94 8 at 10 m s 1 in 60 min 90 0 95 4 at 18 m s 1 in 18 min and 71 5 97 8 at 26 m s 1 in 6 min the results indicate that wind erosion on the newly cultivated soils is most intense during the initial blowing the decrease of soil loss with time is presumed due to modification of soil surface by blowing wind i e the concentration of non erodible aggregates with the deflation of the erodible particles on the soil surfaces

numerical study of the ocean circulation on the east china sea shelf and a kuroshio bottom branch northeast of taiwan in summer using the regional ocean model system the ocean circulation on the east china sea ecs shelf was examined by a fine resolution model which was nested in a coarse resolution pacific ocean model the high resolution simulation shows an accurate volume transport of 2 70 sv sv 10 6 m 3 s 1 through the tsushima strait which is more consistent with the previous 5 5 year observation value 2 64 sv than former model results for the taiwan strait it also shows a close volume transport 1 03 sv to a recent estimate 1 20 sv at the same time the model results reproduced almost all of the known circulation structure on the ecs shelf in addition the hindcast of 2009 shows a kuroshio bottom branch current to the northeast of taiwan kbbcnt the kbbcnt is confirmed by the observational bottom high salinity water from 15 august to 2 september 2009 whose distribution is also reproduced by the model results tracer and particle experiments were carried out to elucidate the formation of the high salinity water and the pathway of the kbbcnt in light of the field observation and numerical experiments a new pathway of the kbbcnt is proposed bifurcated from the subsurface water of kuroshio northeast of taiwan it upwells northwestward gradually from 300 to 60 m then turns to northeast in the region around 27 5 degrees n 122 degrees e and finally reaches 31 degrees n off the mouth of the changjiang river along similar to 60 m isobaths forming the bottom saline water off the coast of zhejiang province china

marine geology in the arc continent collision zone off southeastern taiwan implications for late neogene evolution of the coastal range abstract marine geology in the region between taiwan and luzon is characterized by a convergent tectonics in the south and an oblique arc continent collision in the north in the collision zone six geologic provinces are recognized they are the manila trench the accretionary prism of the hengchun ridge the sutural basin of the southern longitudinal trough the subduction melange of the huatung ridge the forearc basins of the taitung and the north luzon troughs and the volcanic arc of the north luzon ridge the oceanic crust of the south china sea is subducting eastward beneath the philippine sea plate along the manila trench south of 20 n further to the north the trench has changed progressively its axis toward the west from the subduction melanges off southeastern taiwan at 3 ma to the hengchun peninsula of southern taiwan at 2 1 ma and then to the present day location off southwestern taiwan because of the continuing collision and the westward shifting of the manila trench sediments deposited in the region are passively incorporated into the accretionary prism and deformed to the hengchun ridge after the collision the southern longitudinal trough consisting of a 2 km thick of orogenic sediments represents a sutural basin superposed on the plate boundary between the accretionary prism of the hengchun ridge asian continent and the subduction melange of the huatung ridge philippine sea plate the huatung ridge is a bathymetric high connected to the southern coastal range and is characteristic of low negative free air gravity and magnetic anomalies the ridge contains deeply weathered sedimentary blocks with abraded deep water late pliocene foraminifera and identical clay mineral compositions as those in the onshore lichi melange this implies that at least a portion of the huatung ridge is composed of melange materials and represents a former subduction zone extending from the lichi melange of the southern coastal range the north luzon trough and the taitung trough are the constructed foreac basins with 2 km of orogenic sediments unconformably overlying the volcanic islands and the subduction melange the taitung trough is southward connected to the north luzon trough through a bathymetric passage which was formed by narrowing the north luzon trough as a consequence of clockwise rotation of the lutao volcanic island during the late pleistocene a detailed study of the four neogene tectonostratigraphic units in the coastal range shows that the overall history of the formation of the range can be related to the present day geologic provinces and the on going collision processes in the region off southeastern taiwan the range had evolved from a southward accretion of the shuilien loho remnant forearc basin and the chimei volcanic pair at 2 ma followed by the chengkung taiyuan remnant forearc basin and the chengkuangao volcanic island pair at 1 ma and the taitung trough and the lutao volcanic island pair presently in process by analogy the northern part of the north luzon trough and the lanhsu volcanic island will be accreted to the coastal range in the next million years the paired forearc basin volcanic island accretion model proposed in this study may thus have implications for mountain ranges that evolved from similar tectonics of oblique arc continent collision

chronologies for late quaternary barchan dune reactivation in the southeastern arabian peninsula abstract the liwa region of the united arab emirates contains some of the largest and most areally extensive megabarchanoid sand dunes on a global scale here we present optical dating results on samples of aeolian sediment from deep drill cores extracted from the largest dune field of the liwa area optical dating of these core sediments using the single aliquot regeneration protocol indicates mid late holocene phases of rapid dune deposition the most recent period of reactivation began at ca 2 8 ka this event was preceded by a period of deposition at ca 5 ka these results suggest that the dune systems of the southeastern arabian peninsula are closely linked to changes in late quaternary global climate particularly linked to the intensity and spatial extent of palaeomonsoon rainfall since the last precessional maxima at ca 9 ka at which time a peak in monsoonal rainfall has been recognised a significant environmental transition to widespread desert conditions occurred in an apparently abrupt fashion during the initial period of aridification large quantities of sand were transported and deposited in the form of large and very large up to 160 m high scale aeolian bedforms following the initial phase of aeolian accumulation the system appears to have remained in stasis

topographic coupling of the atlantic overturning and gyre circulations abstractthe vorticity dynamics associated with the mean and time varying gyre and overturning circulations of the atlantic ocean are examined in a realistic ocean model hindcast simulation of the late twentieth century abyssal flow interaction with sloping bottom bathymetry gives rise to the bottom pressure torque bpt term of the vertically integrated vorticity equation the dominance of this term in the closure of the barotropic gyre circulation noted in previous studies is corroborated here for both non eddy resolving and eddy resolving versions of the parallel ocean program pop model this study shows that bpt is also a dominant term in the vorticity balance of the atlantic meridional overturning circulation amoc and therefore represents a key dynamical link between the overturning and gyre streamfunctions the interannual variability of the atlantic circulation over the last several decades viewed in terms of time varying integral vorticity balances demonstrates the fundamental role played by

the effect of climate warming and permafrost thaw on desertification in the qinghai tibetan plateau abstract four sets of remote sensing images from 1987 1994 2000 and 2006 50 years of meteorological and soil moisture data corresponding to different desertified lands were combined with populations and livestock data to analyze the process and cause of desertification in a portion of the qinghai tibetan plateau qtp it showed that surface soil temperature in the region has increased at an average rate of 0 6 c per decade between 1980 and 2005 the thawing days on the surface have increased by 60 days from 1983 to 2001 and the depth of the seasonal thawing layer has increased by 54 cm 102 cm and 77 cm in april may and june respectively from 1983 to 2003 as a result the upper soil layer has become drier due to the thickening active layer and soil water infiltration these changes in turn have inhibited the growth of alpine meadow vegetation that has shallow root systems it is concluded that climate warming and permafrost thawing have caused desertification in grazing regions of the qinghai tibetan plateau qtp

modeling upwelling circulation off the oregon coast 1 time dependent three dimensional upwelling circulation on the continental shelf off the oregon coast is studied using a primitive equation numerical model a limited area domain with a high resolution curvilinear grid is utilized the response of the coastal ocean to forcing by observed wind stress and heat flux during the summer 2001 time period of the coastal ocean advances in shelf transport coast field experiment is investigated model results are compared to coast current and hydrographic measurements the shelf velocity and density fields are generally characterized by the presence of a southward alongshore coastal jet with an upwelling density front on the shoreward side of the jet the large variability in shelf topography associated with heceta bank exerts a major influence on the shelf velocity and density fields over the bank the alongshore coastal jet is displaced offshore and colder upwelled water extends farther from the coast northward mean flow and upward motion are found inshore of the jet three dimensional flow structures in response to variable shelf bottom topography are presented and an analysis of time and space dependent alongshore momentum balances is applied to clarify the associated dynamics in general northward pressure gradients set up over the bank during southward upwelling winds accelerate currents on the inshore side of the jet northward when the winds relax analysis of term balances in the depth averaged equation for potential temperature shows that during upwelling across shore advection makes the major contribution to cooling over most of the region except inshore over heceta bank where alongshore advection also plays a significant role

slab breakoff as a mechanism for flipping of subduction polarity in taiwan we propose a model that involves breakoff of the east dipping eurasian slab beneath the taiwan orogen to account for the flipping of subduction polarity in northern taiwan the breakoff was initiated in southern ryukyu in the early pliocene and then propagated southwestward into taiwan like an opening zipper detachment of the eurasian slab has created a mantle window for the north dipping philippine sea plate to move in laterally causing a switch in the subduction polarity slab breakoff not only provides a testable model for the lithospheric structure of taiwan but also accounts for the high heat flow rapid uplift synorogenic extension deep focus earthquakes and north diminishing crustal contraction in the taiwan mountain belt

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

holocene environmental change in subarctic aeolian dune fields the chronology of sand dune re activation events in relation to forest fires palaeosol development and climatic variations in finnish lapland sand dune stratigraphy radiocarbon dated charcoal layers palaeosol development and luminescence dating are used to reconstruct the holocene environmental history of the dune fields in finnish lap

strain and stress field in taiwan oblique convergent system constraints from gps observation and tectonic data abstract this paper focuses on the stress and strain rate field of the taiwan area the strain rate field in the taiwan region is studied qualitatively and quantitatively based on the gps observation in 1990 1995 it reflects the accommodation of the ongoing lithospheric deformation within the seismogenic portion of lithosphere and exhibits zones with contrasting deformation modes and amounts we then compare the obtained strain rate field with the tectonic information provided by studies of borehole breakouts and earthquake focal mechanisms for the present and by fault slip data analyses for the quaternary period in the first approximation the stress and strain rate fields show spatial similarity the orientation of principal shortening is generally consistent with the compressive stress orientation that reflects the oblique indentation of the luzon arc into the eurasian continental margin in more detail significant anomalies in the deformation pattern deserve consideration in that they may reveal ongoing stress accumulation despite the short term variations related to the earthquake cycle some major features of the strain rate field including the distribution of extension and compression highlight the long term tectonic behavior of the mountain belt at the lithospheric scale the time and space variations of strain should be a function of local heterogeneity and be transferred between interseismic and coseismic periods

geomorphic changes leading to natural desertification versus anthropogenic land conservation in an arid environment the negev highlands israel the negev highlands in southern israel are currently under an erosive regime causing degradation of soil and vegetation a process which has often been attributed to land mismanagement and overgrazing caused by the local bedouin population to estimate the anthropogenic role in the erosional processes in the negev highlands two similar drainage basins were selected and studied one undisturbed with almost no human impact and the other with intensive human modification including the establishment of roman to early islamic agriculture field observations and luminescence dating indicate that during the late pleistocene glacial period ois 4 and 3 deposition of fluvio loess sediments with minor erosion cycles occurred in the negev highlands severe erosion started during ois 2 and continued into the holocene as the climate shifted during the termination of the pleistocene to the present interglacial phase higher rain intensity generated the incision of gullies and channels into the fine grained alluvial sediments of the previous phase causing extended soil erosion and reducing the natural biomass and the agricultural potential establishment of runoff harvesting farms in the 3rd century interrupted the holocene natural erosion and gully incision and led to the redeposition of up to 3 5 m of fine alluvial loess sediments originating from late pleistocene loess sections this accumulation is not related to any late holocene pluvial climatic phase and is solely the result of farming we conclude that since the end of the pleistocene a dynamic change in the soil rock ratio related to the long term process of adjustment of the geomorphologic system to the holocene climate has been taking place within the drainage basins in the negev highlands the fluvio loess sediments deposited in the region during ois 4 and 3 have been eroding since the latest pleistocene throughout the holocene this process causes degradation of the biomass and agricultural potential and leads onto natural desertification of the region the historical intervention by establishment of runoff harvesting agriculture which as a by product resulted in the accumulation of redeposited loess sediments counteracted the natural trend of soil erosion this was in fact a land conservation act applied by the ancient farmers in the semi arid regions of the middle east deserts this activity and its geomorphic consequences are in contrast to the well documented land degradation trend generated by recent anthropogenic impact on marginal lands elsewhere in any case the human impact either contributing to land degradation or to soil conservation is super imposed on the natural long term trend leading toward desertification

numerical study on the pattern and origins of kuroshio branches in the bottom water of southern east china sea in summer pattern and origins of kuroshio branches in the bottom water of southern east china sea ecs were carefully examined by numerical simulations based on the regional ocean modeling system roms together with observations model results show that in the bottom water of ecs the intrusion pattern of kuroshio is mainly composed of an offshore kuroshio branch current okbc which bifurcated from the kuroshio northeast of taiwan flows nearly along the isobath of similar to 100 m and a nearshore kuroshio branch current nkbc which originated from the kuroshio northeast of taiwan upwells northwestward gradually from similar to 250 m to similar to 60 m then turns to northeast around 27 5 degrees n 122 e thereafter flows northeastward along the isobath of similar to 60 m and finally reaches at 30 5 degrees n where it turns to east furthermore we found that the nkbc mostly originated in the kuroshio subsurface water 120 250 m east of taiwan whereas the okbc mainly stemmed from the kuroshio water 60 120 m east of taiwan this pattern and origins of okbc and nkbc well addressed the observational phenomena that off the coast of zhejiang province china there were colder less saline and more phosphate rich bottom water near the isobath of similar to 60 m rather than near the isobath of similar to 100 m in august 2009 finally it is proposed that on southern ecs continental shelf kuroshio exhibits its intrusion branches by an anticyclonical stair structure bottom stair nkbc middle stair okbc and top stair kuroshio surface branch kbc

constraints on backstop geometry of the southwest ryukyu subduction based on reflection seismic data abstract based on the analysis of 45 seismic reflection profiles the top of the ryukyu arc basement is mapped in the forearc region east of taiwan the ryukyu arc slope dips 10 trenchward while beneath the forearc basins the arc basement shows a series of morphologic along arc highs and lows one of the basement highs the nanao basement rise has been described as an area uplifted by the subduction of the gagua ridge the other one the hoping basement rise is suggested in this study to be an uplifted feature caused by the subduction or the underplating of some local asperity the nature of this asperity could either be a detached block of the luzon arc an isolated seamount or some material removed from the frontal part southernmost extremity of the ryukyu margin from seismic reflection profiles we infer that the right lateral transcurrent fault system located at the rear of the accretionary wedge defines the surface projection of the southern termination of the ryukyu arc basement two crustal sections across the ryukyu subduction system demonstrate that the backstop terminates in the form of a near vertical wall with its height over 5 km such an unusual geometry could be produced by crustal truncation at the toe of the backstop

temporal and spatial variation of stress field in taiwan from 1991 to 2007 insights from comprehensive first motion focal mechanism catalog article i nfo the total amount of 4 761 focal mechanisms was determined based on p wave first motion polarities from 1991 to 2007 in taiwan region this dataset offers us a good opportunity to examine temporal and spatial variability of the stress field we find that the spatial variations of stress axes are mainly controlled by tectonic structures while the temporal changes are greatly influenced by the chi chi earthquake the orientation of the maximum horizontal compressive stress axes sh shows a general agreement with the direction of plate motion between a depth range of 0 30 km the 20 anticlockwise rotation of sh from the longitudinal valley lv to western taiwan is probably caused by the left lateral motion on the longitudinal valley fault lvf that has consumed part of the oblique motion of plate convergence on the other hand part of the oblique convergence is transferred into the central range and the hsuehshan range judging from counterclockwise rotation of sh from east to west and strike slip faulting in the hsuehshan range most events with a depth greater than 30 km occur offshore eastern taiwan and the azimuth of sh is close to e w directed different from nw se directed at shallow depths this may infer the existence of the transition of lithosphere rheology in offshore eastern taiwan the trends of sh in the depth of 0 10 km are strongly affected by the coseismic stress change of the chi chi earthquake in the northern half of the chi chi rupture area the trends of sh rotate 30 clockwise and the stress ratio increased by a factor of six after the mainshock the orientations of sh still differ by 30 in 2007 comparing to that in the period before the chi chi earthquake the variation of sh trend is more diverse in the southern half of the rupture area showing 20 counterclockwise rotation immediately after the 1999 mainshock followed by a clockwise rotation the trend of sh returns to the pre seismic direction of 110 in 2001 these notable changes of sh before and after the chi chi mainshock suggests that the magnitude of background stress in the rupture area is close to the coseismic stress drop we also recognize a significant 10 counterclockwise rotation of sh in the entire chi chi rupture area between 1991 and 1999 before the earthquake took place however to the south of the chi chi rupture the trends of sh remain little changed before and after the chi chi earthquake

rupture at the flank of the subducted gagua ridge the 18 december 2001 earthquake mw 6 8 offshore eastern taiwan abstract the southern ryukyus represents an area where different tectonic stress regimes result in high seismicity and increased seismic hazard for nearby areas such as taiwan on 18 december 2001 at 04 03 gmt a strong earthquake mw 6 8 occurred in the forearc area of the southern ryukyu subduction zone revised moment tensor solutions published by gcmt and bats groups show a normal faulting mechanism with some strike slip component and also point to a shallow focal depth 12 km we use arrival times picked at both taiwanese and japanese stations along with a 3d geo realistic a priori velocity model in order to obtain accurate absolute locations for the mainshock and 153 of its aftershocks locations are derived by using the maximum intersection maxi algorithm which has been used in many previous seismicity studies in the southern ryukyus these improved locations indicate that the mainshock was caused by the failure of a ne sw oriented fault that extends from the edge of the nanao forearc sedimentary basin to the ryukyu arc basement far field p and sh waveforms of the mainshock recorded at stations surrounding the source and at distances 30 100 were inverted for the purpose of investigating its rupture process a non negative least squares inversion technique utilizing multiple time windows was used to derive the spatio temporal slip distribution the preferred slip distribution model shows that there is one large area of high slip 0 9 m at 5 15 km depth that essentially represents the crystalline rocks of the ryukyu arc basement another smaller area with lower slip 0 4 m extends at 10 15 km depth beneath the nanao basin most aftershocks are located in areas of low slip

okinawa trough backarc basin early tectonic and magmatic evolution the okinawa trough lying between japan and taiwan is a backarc basin formed by extension within the continental lithosphere behind the ryukyu trench arc system stress directions associated with the two last extensional phases in the southwestern okinawa trough have been deduced from a comparison with analog modeling the direction of extension is n 150 o for the pleistocene phase of extension 2 0 1 ma and n 170 o for the late pleistocene holocene phase of extension 0 1 0 ma the present day ryukyu volcanic arc a narrow continuous feature extending from japan to taiwan is located on the eastern side of the okinawa trough 80 100 km above the wadati benioff zone the minimum depth for emplacement of arc magmatism scarce present day backarc volcanism appears in the middle and southern okinawa trough within linear en echelon bathymetric depressions a n045 o oriented seamount volcanic chain cuts across obliquely the southwestern okinawa trough and lies in the direct line of extension of the gagua ridge a n s linear volcanic feature of the philippine sea plate associated with this extension of the gagua ridge a large reentrant located at the base of the ryukyu prism the uplift of part of the nanao forearc basin and the deformation of the sedimentary arc suggest that the voluminous cross backarc volcanism could be tied to the subduction of the gagua ridge located there at a depth of 80 100 km beneath the backarc basin a second area of anomalous volcanism has been identified in the middle okinawa trough in the ene extension of the daito ridge a wnw ese 400 km long volcanic feature of the philippine sea plate we suggest that the gagua and daito ridges initially induced stress at the base of the arc which is still brittle and cracks propagated through the overlying brittle lithosphere allowing magmas with arc affinities to erupt at the seafloor this excessive magmatism reaches the seafloor through conduits which preferentially follow in their shallowest portion the crustal normal faults of the backarc rifts the okinawa trough is consequently still in an early stage of evolving from arc type to backarc activity

topographic control of basin and channel flows the role of bottom pressure torques and friction the topographical control of western boundary currents within a basin and zonal jets in a channel is investigated in terms of the potential vorticity pv and barotropic vorticity bv the curl of the depth integrated velocity budgets using isopycnic adiabatic wind driven experiments along the western boundary the wind driven transport is returned across latitude lines by the bottom pressure torque while friction is only important in altering the pv within an isopycnic layer and in allowing a closed circulation these contrasting balances constrain the geometry of the flow through integral relationships for the bv and pv for both homogenous and stratified basins with sloping sidewalls the northward subtropical jet separates from the western wall and has opposing frictional torques on either side of the jet which cancel in a zonal integral for bv but alter the pv within a layer streamline in a channel with partial topographic barriers the bottom pressure torque is again important in returning wind driven flows along western boundaries and in transferring bv from neighboring wind driven gyres into a zonal jet the depth integrated flow steered by topography controls where the bottom friction alters the pv which can lead to different pv states being attained for separate subbasins along a channel

relationships between desert dunes during the late quaternary in the lake frome region strzelecki desert australia transverse and linear dunes near the ephemeral lake frome in the strzelecki desert of australia provide evidence for a genetic geomorphic relationship between desert dune types transverse dunes overlying palaeoshorelines lie upwind from linear dunes the sedimentology of both dune types is similar suggesting reworking or downwind transport of the same source material over time clay pellets from several horizons within the linear and transverse dunes provide evidence for fluctuating water tables and high evaporation rates during those periods of aeolian activity along with saltinflux associatedwith thedeflation oflakefrome weconclude thatthe nature andinitiation of dune activity is controlled not only by aridity but by local hydrology osl ages from both transverse and linear dunes indicate aeolian activity at 66 57ka and 22 11ka transverse dune building took place around 106 111ka linear dune activity initiated at least 66ka ago with reactivation around 43 28ka followed by pedogenesis in response to humid conditions widespread dune reactivation from around 22ka correlates broadly with the last glacial maximum and late glacial period consistent with evidence of cold arid conditions and dune activity in australia copyright 2007 john wiley sons ltd

why western boundary currents in realistic oceans are inviscid a link between form stress and bottom pressure torques it is shown that wind stress curl is balanced by bottom pressure torque in a zonal integral over any strip wide enough to smooth out the effect of nonlinear terms typically about 3 of latitude the derivation is completely general as long as the zonal wind stress is balanced by form stress at each latitude as is known to be the case in the ocean this implies that viscous torques are not important in western boundary currents their place being taken by bottom pressure torques the prediction is confirmed in the context of a global eddy permitting numerical ocean model this link between form stress and bottom pressure torques makes it easier to consider southern ocean dynamics and subtropical gyre dynamics in the same conceptual framework with topographic interactions being important in both cases

seismicity patterns along the ecuadorian subduction zone new constraints from earthquake location in a 3 d a priori velocity model to improve earthquake location we create a 3 d a priori p wave velocity model 3 dvm that approximates the large velocity variations of the ecuadorian subduction system the 3 dvm is constructed from the integration of geophysical and geological data that depend on the structural geometry and velocity properties of the crust and the upper mantle in addition specific station selection is carried out to compensate for the high station density on the andean chain 3 d synthetic experiments are then designed to evaluate the network capacity to recover the event position using only p arrivals and the maxi technique three synthetic earthquake location experiments are proposed 1 noise free and 2 noisy arrivals used in the 3 dvm and 3 noise free arrivals used in a 1 dvm synthetic results indicate that under the best conditions exact arrival data set and 3 dvm the spatiotemporal configuration of the ecuadorian network can accurately locate 70 per cent of events in the frontal part of the subduction zone average azimuthal gap is 289 44 noisy p arrivals up to 0 3 s can accurately located 50 per cent of earthquakes processing earthquake location within a 1 dvm almost never allows accurate hypocentre position for offshore earthquakes 15 per cent which highlights the role of using a 3 dvm in subduction zone for the application to real data the seismicity distribution from the 3 d maxi catalogue is also compared to the determinations obtained in a 1 d layered vm in addition to good quality location uncertainties the clustering and the depth distribution confirm the 3 d maxi catalogue reliability the pattern of the seismicity distribution a 13 yr record during the inter seismic period of the seismic cycle is compared to the pattern of rupture zone and asperity of the mw 7 9 1942 and the mw 7 7 1958 events the mw 8 8 1906 asperity patch is not defined we observe that the nucleation of 1942 1958 and 1906 events coincides with areas of positive simple bouguer anomalies and areas where marine terraces are still preserved on the coastal morphology from north to south 1 the 1958 rupture zone is almost aseismic and is attributed to a zone of high coupling 2 south of the galera alignment perpendicular to the trench the 1942 rupture zone presents moderate seismicity deeper on the seismogenic interplate zone and abutting on the jama cluster to the south this cluster is facing the cabo pasado cap and positive bouguer anomalies on the overriding margin we suspect that this cluster reflects a zone of local asperity partial coupling south of the jama cluster the spherical aseismic zone in the bahia area is interpreted as having a low seismic coupling steady creep motion or slow slip events we suspect that the site that generated the three m 7 events 1896 1956 and 1998 correspond to a small patch of strong coupling to the south in the manta puerto lopez zone the seismicity is mainly organized in earthquake swarms 1998 2002 2005 although slow slip events have been observed in the area vallee et al submitted we infer from the coastline shape the marine terraces and the high positive bouguer anomalies that the seismicity here might reveal a significant amount of seismic coupling

interpretations of the jebar term abstract in diagnostic calculations of the ocean s circulation the so called jebar joint effect of baroclinicity and relief term may induce a significant depth average current field as has been noted in the oceanographic literature here we present two consistent interpretations of this term in the equation governing the vorticity of the depth averaged current a topographic vortex stretching term proportional to the dot product of depth averaged velocity and the depth gradient arises we show that jebar corrects this term by removing the contribution of the geostrophic flow referenced to the bottom which cannot generate topographic vortex stretching in the evolution equation for the vorticity of the depth integrated flow a bottom torque term is present we show that the jfbar term discussed above enters here as a contribution to the bottom torque emphasizing the role of jebar as a forcing term we also show that when a diagnostic calculation is formulated completely in terms of the transport str

parabolic dune reactivation and migration at napeague ny usa insights from aerial and gpr imagery abstract observations from mapping since the 19th century and aerial imagery since 1930 have been used to study changes in the aeolian geomorphology of coastal parabolic dunes over the last 170 years in the walking dune field napeague ny the five large parabolic dunes of the walking dune field have all migrated across or are presently interacting with a variably forested area that has affected their migration stabilization and morphology this study has concentrated on a dune with a particularly complex history of stabilization reactivation and migration we have correlated that dune s surface evolution as revealed by aerial imagery with its internal structures imaged using 200 mhz and 500 mhz ground penetrating radar gpr surveys both 2d transect and high resolution 3d gpr imagery image downwind dipping bedding planes which can be grouped by apparent dip angle into several discrete packages of beds that reflect distinct decadal scale episodes of dune reactivation and growth from aerial and high resolution gpr imagery we document a unique mode of reactivation and migration linked to upwind dune formation and parabolic dune interactions with forest trees this study documents how dune dune and dune vegetation interactions have influenced a unique mode of blowout deposition that has alternated on a decadal scale between opposite sides of a parabolic dune during reactivation and migration the pattern of recent parabolic dune reactivation and migration in the walking dune field appears to be somewhat more complex and perhaps more sensitive to subtle environmental pressures than an idealized growth model with uniform deposition and purely on axis migration this pattern believed to be prevalent among other parabolic dunes in the walking dune field may occur also in many other places where similar observational constraints are unavailable

crustal and upper mantle structure in the ryukyu island arc deduced from deep seismic sounding summary in 1984 an extensive geophysical investigation was conducted in the northernmost part of the ryukyu island arc south of kyushu island japan the aim of this investigation was to obtain new information on the nature of crust and upper mantle at the continental margin through various geophysical measurements seismic profiling gravity magnetism sea beam and heat flow this paper presents the crust and upper mantle structure deduced from ocean bottom seismographic profiling conducted along two lines one line 190 km long was taken behind the northernmost part of the ryukyu island arc parallel to the major tectonic units i e the okinawa trough ryukyu arc and ryukyu trench the other 295 km long was perpendicular to the tectonic units along these profiles we deployed ocean bottom seismograms spaced 10 20km apart as a controlled source we used both explosives and an airgun array the experiment was successful and provided quite important information on the tectonics of a trenchisland arc back arc system the velocity structure obtained for the profile behind the ryukyu islands has continental properties the sediment thickness is 3 4 km although it shows lateral variations due to basement undulation the velocities of the upper and lower crust are 5 8 6 2 and 6 6 6 8 km s respectively the total crustal thickness decreases southwestward from 27 30 to 23 24 km this is direct evidence for crustal thinning associated with the process of back arc spreading the velocity structure along the profile from the trench to the island arc clearly shows the subduction accretion and deformation at this margin the crust beneath the trench has oceanic properties the sediment thickness is 1 3 3 0 km beneath which the igneous basement shows severe undulation the total crustal thickness is 7 8 km the p velocity is slightly less than 8 0 km s our seismic data revealed a huge sedimentary wedge located 50 150 km landward of the trench the maximum thickness of this wedge exceeds 12 km the origin of this wedge may be oceanic because the p wave velocity in its eastern half is almost comparable to that obtained for the trench area the velocity structure landward of the wedge is continental and similar to that obtained for the profile behind the island arc

kuroshio subsurface water feeds the wintertime taiwan warm current on the inner east china sea shelf the taiwan warm current twc has an overwhelming influence on the heat salt and nutrients balance on one of the broadest shelf in the world the east china sea shelf in winter the twc flows in an unusual upwind direction and reaches the changjiang yangtze river estuary but its origin and pathway are intensely debated here combined evidences from current measurement hydrographic and stable isotopic data all suggest that the wintertime twc intrusion off the changjiang estuary mainly originates from the kuroshio subsurface water northeast of taiwan rather than from the taiwan strait warm water the kuroshio branched water northeast of taiwan can intrude into the inner shelf near the zhe min coast via bottom layer manifesting by a pronounced boundary at 50 m isobath around 28 n and thereby feeds the twc intrusion into the changjiang estuary the intrusion complicates the hydrological process in the estuary and shelf sea and its impact on marine environment deserves more research attentions

a three layer alternating spinning circulation in the south china sea abstractunderstanding of the three dimensional circulation in the south china sea scs is crucial for determining the transports of water masses energy and biogeochemical substances in the regional and adjacent larger oceans the circulation s kinematic and dynamic natures however are largely unclear results from a three dimensional numerical ocean circulation model and geostrophic currents derived from hydrographic data reveal the existence of a unique three layer cyclonic anticyclonic cyclonic cac circulation in the upper 1500 m layers in the scs with differing seasonality an inflow outflow inflow structure in luzon strait largely induces the cac circulation which leads to vortex stretching in the scs basin because of a lateral planetary vorticity flux in each of the respective layers the formation of joint effects of baroclinicity and relief jebar is an intrinsic dynamic response to the cac circulation the jebar arises from the cac flow topog

physical characteristics of subduction interface type seismogenic zones revisited 1 based on global earthquake catalogs the hypocenters nodal planes and seismic moments of worldwide subduction plate interface earthquakes were extracted for the period between 1900 and 2007 assuming that the seismogenic zone coincides with the distribution of 5 5 m 7 earthquakes the subduction interface seismogenic zones were mapped for 80 of the trench systems and characterized with geometrical and mechanical parameters using this database correlations were isolated between significant parameters to identify cause effect relationships empirical laws obtained in previous studies were revisited in light of this more complete accurate and uniform description of the subduction interface seismogenic zone the seismogenic zone was usually found to end in a fore arc mantle rather than at a moho depth the subduction velocity was the first order controlling parameter for variations in the physical characteristics of plate interfaces determining both the geometry and mechanical behavior as such the fast subduction zones and cold slabs were associated with large and steep plate interfaces which in turn had large seismic rates the subduction velocity could not account for the potential earthquake magnitude diversity that was observed along the trenches events with mw 8 5 preferentially occurred in the vicinity of slab edges where the upper plate was continental and the back arc strain was neutral this observation was interpreted in terms of compressive normal stresses along the plate interface large lateral ruptures should be promoted in neutral subduction zones due to moderate compressive stresses along the plate interface that allow the rupture to propagate laterally

mobility of a remobilised parabolic dune in kennemerland the netherlands abstract a parabolic dune in the netherlands was remobilised in december 1998 by removing vegetation and soil the main aim of the experiment was ecological to investigate whether permanent rejuvenation at the landscape scale is possible by restoration of natural processes if processes can be reactivated at coarse scale periodic rejuvenation of the landscape over the long term is possible without the need for managers to interfere further the experiment provides the opportunity to address another important question can large parabolic dunes in the netherlands be mobile in the present climate mobility of the dune is investigated by means of erosion pins aerial photography and measurement of cross sections activity indices are derived from erosion pin recordings and correlated to weather conditions from 1999 to 2001 displacement of the dune ranged from 0 to 12 m in east northeasterly direction activity of the dune is related to wind conditions but the relationship is strongly influenced by precipitation and therefore differs for wet and dry periods periods with extreme wind speeds resulted in much less geomorphic change than expected

indentation of the philippine sea plate by the eurasia plate in taiwan details from recent marine seismological experiments abstract we analyze in this study a new set of marine data including 3d local tomography 1992 2008 relocated earthquakes and two recent multichannel seismic lines to characterize the deformation style in the collision area offshore east taiwan we have mapped in detail the mohos of the converging plates as well as the subduction interface with a resolution never reached before we show that the sharp continental subduction of the eurasia plate beneath the middle part of the central range indents the philippine sea plate psp as attested by intra oceanic slicing and incipient subduction of the psp beneath the east coast of taiwan the westernmost part of the psp slab is probably experiencing a beginning of break off as attested by nw trending en echelon shear zones beneath the southern slope of the southern ryukyu arc sra these en echelon shear zones have a sinistral component favored by the collision free subduction of the psp north of 24 30 n the down faulting of the subduction interface forms ramps along which earthquakes clusterize three m7 subduction earthquakes occurred offshore suao city along these ramps with a recurrence interval of about 40 years 1920 m w 7 7 1963 m w 7 2 and 2002 m w 7 1 events the 1966 m w 6 0 7 5 earthquakes sequence likely outlines a wnw ese left lateral intra slab shear zone the sra upper plate accommodates the complex geometry and deformation of the subducting psp through seismic deformation shallow high velocities fringing the luzon volcanic arc lva beneath the longitudinal valley and north of the southernmost ryukyu forearc basins are interpreted as relics of the lva forearc basement squeezed in the collision zone based on the accommodation of a large part of the convergence through shortening within the psp and the subsequent segmentation of the shallow subduction interface we consider that the nucleation of a m w 8 earthquake along the southernmost ryukyu megathrust is unlikely