seismic microzonation based on large geotechnical database application to lisbon abstract historically portugal has suffered the effects of several strong earthquakes in particular lisbon and the south and southwestern portuguese coast were affected by the largest known european earthquake on november 1st 1755 it is well known that the local ground conditions strongly affect the seismic ground motion modifying the signal s amplitude duration and frequency content which induces large variability in the motion induced to buildings and infrastructures aware of this situation the lisbon municipality promoted the development of a project to elaborate a new seismic microzonation map based on a large geotechnical database and geological data the eurocode 8 ground classification based on the vs30 parameter was adopted as reference however the geotechnical database has a very small number of geophysical logs and is mainly composed of borehole data and spt blows number an expedited methodology was applied to determine the n30 parameter as a proxy of the vs30 parameter non invasive field experiments surface waves seismic profiles and hvsr performed with ambient vibrations and data collected from independent geophysical reports were also used to check and validate the classification based on n30 because the distribution of the classified profiles was not uniformly distributed the final microzonation map was obtained from the combination of the profile classification and the surface geology

the initiation of subduction by crustal extension at a continental margin summary we investigate how subduction may be triggered by continental crust extension at a continental margin the large topography contrast between continental and oceanic domains drives the spreading of continental crust over oceanic basement subduction requires the oceanic plate to get submerged in mantle so that negative buoyancy forces may take over and drive further descent this is promoted by two mechanisms loading by continental crust bends the oceanic plate downwards extension in the continental domain induces crustal thinning which acts to raise mantle above the oceanic plate in this model the width of the continental region undergoing extension is an important control parameter the main physical controls are illustrated by laboratory experiments and simple theory for elastic flexure coupled to viscous crustal spreading three governing dimensionless parameters are identified one involves the poorly constrained oceanic plate buoyancy we find that the oceanic plate can be thrust to depths larger than 40 km even if it is buoyant enabling metamorphic reactions and density increase in the oceanic crust another parameter is the ratio between the width of the continental extension region and the flexural parameter for the oceanic plate initiating subduction is easier if the continent thins over a short lateral distance or if the oceanic plate is strong the third important parameter is the ratio of oceanic plate thickness to initial continental crust thickness such that a weak plate and a thick crust do not favour subduction thus the change from a passive to an active margin depends on the local characteristics of the continental crust and is not determined solely by the age and properties of the oceanic lithosphere it is shown that the spreading of continental crust induces uplift of the margin as the adjacent seafloor subsides evidence for the emplacement of continental crust over oceanic basement at passive margins is reviewed

m2 baroclinic tide variability modulated by the ocean circulation south of japan we analyze a concurrent simulation result of the ocean circulation and tidal currents using a data assimilative ocean general circulation model covering the western north pacific with horizontal resolution of 1 36 to investigate possible interactions between them four sites of active m2 internal tide variability in open ocean hot spots such as tokara strait izu ridge luzon strait and ogasawara ridge are detected from both the satellite observation and the simulation energy cycle analysis of the simulated m2 baroclinic tide indicates two types of the hot spots dissipation tokara strait and izu ridge and radiation luzon strait and ogasawara ridge dominant sites energy conversion from barotropic to baroclinic m2 tides at the hot spots is modulated considerably by the lower frequency changes in the density field modulation at the two spots tokara strait and izu ridge is affected by the kuroshio path variation together with the seasonal variation of the shallow thermocline at the other two sites influence from changes in the relatively deep stratification through the kuroshio intrusion into south china sea luzon strat and mesoscale eddy activity ogasawara ridge is dominant in the modulation

microzonation of zeytinburnu region with respect to soil amplification a case study abstract a microzonation study is performed as a part of the zeytinburnu pilot project within the framework of the earthquake master plan for istanbul to determine the effects of local soil conditions on the earthquake forces that will act on structures for this purpose detailed geological and geotechnical studies are conducted at the site a geological map which demonstrates the local geological features of the site is prepared and the site is classified with respect to the dynamic behaviour based on the data gathered from the soil borings in order to investigate the effects of local soil conditions on the dynamic behaviour site response analyses are performed with the computer code eera by utilizing the findings of field and laboratory investigations the behaviour of the region during a probable earthquake is investigated through one dimensional response analyses and microzonation maps are prepared with respect to ground shaking intensity in accordance with the new microzonation manual ansal a laue j buchheister j erdik m springman s studer j and koksal d 2004 site characterization and site amplification for a seismic microzonation study in turkey 11th int conference on soil dynamics and earthquake engineering and 3rd earthquake geotechnical engineering san francisco studer j and ansal a 2004 belediyeler icin sismik mikrobolgeleme el kitabi arastirma raporu afet isleri genel mudurlugu bayindirlik ve iskan bakanligi afet risk yonetimi dunya enstitusu

generation of a trigger meander for the 2004 kuroshio large meander 1 a generation process of a small meander southeast of kyushu which triggered the subsequent kuroshio large meander in 2004 has been investigated using an ocean data assimilation and prediction system the assimilation result reveals that the small meander is the most developed one since 1993 a cyclonic eddy propagating westward from the kuroshio recirculation kr and a disturbance from the east china sea esc that accompanies a high potential vorticity high pv anomaly play important roles for the generation of the small meander the cyclonic eddy triggers an initial cyclonic anomaly southeast of kyushu when the high pv anomaly passes through the tokara strait a large positive vorticity is generated because the stretching of the water column is enhanced the positive vorticity is brought in the cyclonic anomaly and accumulates there as a result the small meander is generated from two sensitivity experiments an occurrence condition is determined by the cyclonic eddy from the kr by triggering the initial small scale meander and the disturbance from the ecs contributes to the horizontal scale of the small meander tracing back the disturbance further to the upstream region of the kuroshio it is revealed that the disturbance is a frontal wave with a large horizontal scale generated by collision between a strong anticyclonic eddy and the kuroshio east of taiwan the frontal wave propagates along the kuroshio accompanying high pv generated around the continental shelf edge by viscosity thus the large frontal wave could contribute to the generation of the developed trigger meander by transporting a larger amount of high pv anomaly to the tokara strait

birth death and resurrection the life cycle of suprasubduction zone ophiolites 1 suprasubduction zone ssz ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites this sequence includes the following 1 birth which entails the formation of the ophiolite above a nascent or reconfigured subduction zone this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex 2 youth during which is continued melting of refractory asthenosphere depleted during birth occurs in response to fluid flux from the subducting slab with extensional deformation of the older plutonic suite eruption of refractory lavas and the intrusion of wehrlite pyroxenite 3 maturity with the onset of semistable arc volcanism typically calc alkaline as the subduction zone matures and stabilizes and the intrusion of quartz diorite and eruption of silicic lavas and 4 death which is the sudden demise of active spreading and ophiolite related volcanism which in many cases is linked to collision with an active spreading center and the onset of shallow underthrusting of the buoyant spreading axis expressed as dikes and lavas with oceanic basalt compositions that crosscut or overlie rocks of the older suites 5 resurrection with emplacement by obduction onto a passive margin or accretionary uplift with continued subduction the early stages 1 3 may be diachronous and each stage may overlap in both time and space the existence of this consistent progression implies that ophiolite formation is not a stochastic event but is a natural consequence of the ssz tectonic setting

mean antarctic circumpolar current transport measured in drake passage the antarctic circumpolar current is an important component of the global climate system connecting the major ocean basins as it flows eastward around antarctica yet due to the paucity of data it remains unclear how much water is transported by the current between 2007 and 2011 flow through drake passage was continuously monitored with a line of moored instrumentation with unprecedented horizontal and temporal resolution annual mean near bottom currents are remarkably stable from year to year the mean depth independent or barotropic transport determined from the near bottom current meter records was 45 6 sv with an uncertainty of 8 9 sv summing the mean barotropic transport with the mean baroclinic transport relative to zero at the seafloor of 127 7 sv gives a total transport through drake passage of 173 3 sv this new measurement is 30 larger than the canonical value often used as the benchmark for global circulation and climate models

variations of current path velocity and volume transport of the kuroshio in relation with the large meander abstract the variations of the kuroshio current path and their relations with current velocity volume transport and upstream position of the kuroshio are examined using sea level data after the long time non large meander nlm path during 1963 75 the kuroshio takes a large meander lm path during most of 1975 91 1975 80 1981 84 1986 88 and 1989 91 the study of these meanders confirms the description of the path of the kuroshio based on the three typical paths and the transitions between them with an exception being the 1981 84 lm path the formation and decay of the large meander are associated with velocity and position of the kuroshio in the tokara strait south of kyushu a small meander precursor of the large meander seems to be formed southeast of kyushu in relation with a temporary increase of kuroshio velocity and a northward shift of the kuroshio in the tokara strait an eastward propagation of the small meander leading to the lm formation is associated with remaining in the northe

geochemical variability of the oman ophiolite lavas relationship with spatial distribution and paleomagnetic directions 1 the multielemental composition of 31 lavas sampled in the extrusive section of the oman ophiolite was determined by inductively coupled plasma source mass spectrometry icp ms this study allowed us to define clear geochemical criteria to characterize the different lavas types in oman most of the oman ophiolite extrusive sequence is composed of lavas of composition similar to present day morb with the exception of slight nb ta negative anomalies v1 magmatism v1 lavas display ree patterns and zr hf ratios in the range of morb zr hf 33 15 38 7 in contrast the overlaying v2 lavas which outcrop only in the northern part of the ophiolite are ree depleted relative to v1 and display low zr hf ratios 23 6 30 5 v2 lavas may be further classified into two sub groups v2 type i lavas display a continuous decrease from hree to lree the upper v2 type ii lavas are more depleted in hree and mree but they are enriched in lree they are also distinguished by their low nb ta ratios 10 53 11 65 relative to other oman basalts v1 12 5 14 v2 type i 12 35 14 4 as for n morb melting of an upwelling mantle beneath an oceanic spreading centre formed v1 lavas v2 resulted from fluid enhanced melting of previously depleted mantle residual after v1 extraction this process probably occurred at different melt rock ratios thus resulting in the two v2 sub groups and was enhanced in the northern part of the ophiolite v3 lavas overlie the v1 v2 sequence in the salahi area they display incompatible element rich patterns lree mree hree and a high nb ta ratio typical of within plate basalts in the different studied areas the transition from one lava type to the other seems to correlate with the block rotations revealed by paleomagnetic data

coeval blueschist exhumation along thousands of kilometers implications for subduction channel processes we herein focus on understanding what controls the detachment and migration of oceanic crustal slices along subduction zones we provide evidence for the coeval middle to late cretaceous exhumation of oceanic blueschists in the same neotethyan subduction zone across more than 3000 km from depths around 30 40 km over a short time interval similar to 25 ma compared to the duration of subduction 100 ma we stress the importance of such a geodynamic process and suggest that this exhumation was promoted by a regional scale change in the long term interplate mechanical coupling on the basis of geological and geophysical evidence we propose that the upward migration of oceanic fragments in subduction zones is normally inhibited and only occurs discontinuously as the subduction channel opens up in response to a major change in plate geodynamics slab geometry and dynamics mantle wedge and slab hydration or a combination of these

site response of deep alluvial deposits in the northern coast of izmir bay turkey and a microzonation study based on geotechnical aspects izmir the third largest city with fast economically growths in western turkey has experienced various moderate to large historical and recent earthquakes karsiyaka cigli districts and their surrounding areas located in northern coast of izmir bay and one of the major economically and residentially developing districts are subject to strong shakings due to deep sediments and shallow soft liquefiable soils in the area the purpose of this study is to develop a comprehensive microzonation model based on geotechnical aspects and put forth this model for use of residential developments in the area the properties and dynamic behavior of the quaternary alluvial soils in the study area were assessed using geotechnical and geophysical data gathered from 461 boreholes and 205 microtremor recordings one dimensional dynamic site response analyses were performed with equivalent linear earthquake site response analysis eera software by using the simulated earthquake time histories the maximum ground surface acceleration values obtained from the dynamic analyses were also used for liquefaction potential assessment soil classification dynamic soil properties under different earthquake excitations spectral amplification variation of soil predominant period and liquefaction potential of the study area were evaluated and mapped the produced maps showed that highest earthquake hazardous soil conditions are located along the shoreline and in the densely populated section of the southwestern part of the study area

satellite altimeter monitoring the kuroshio transport south of japan in 1993 1995 we carried out observations of the kuroshio south of japan including direct current measurements and repeated hydrographic surveys along a satellite track of the topex poseidon altimeter the velocity field of the kuroshio is determined by geostrophic calculation using the repeated hydrographic survey data referenced to velocities observed at mid and abyssal depths the volume transport of the kuroshio is estimated from this velocity field the estimated transports of the kuroshio have a high correlation with sea surface height differences across the kuroshio having this relationship and using the altimeter data we obtained a time series of the kuroshio transport over seven years at ten day intervals the kuroshio transport excluding contributions by local recirculations is estimated to be 42 106 m sec on average the correlation between sea surface height difference and transport provides a practical method of long term monitoring of the kuroshio transport using satellite altimetry

kuroshio induced wake in the lee of green island off taiwan 1 the wake of green island was investigated in the alongshore flowing kuroshio east of taiwan where current speeds range from 1 to 1 5 ms 1 vertical profiling with shipboard lowered acoustic doppler current profiler and conductivity temperature depth profiler revealed sizable anomalies in flow and water characteristics in the lee of green island two different stages of wake evolution were observed from two shipboard surveys in the first stage a recirculation developed leeward of the island followed by a wavy wave like tail that resembled a weak vortex street in the second stage a cold eddy probably originating from the leeward side of the island showed up 14 km downstream of the island the wake water was colder saltier higher in chlorophyll a concentration and produced isopycnal doming up to 60 m in the recirculation area the relative vorticity either positive or negative was 10 times of planetary vorticity and the horizontal divergence or convergence was o 10 4 s 1 on average flow divergence and convergence in the wake were expected to form upwelling and downwelling zones producing a vertical circulation that vertically displaces isotherms high inverse richardson number produced by strong vertical shear of horizontal currents was associated with intense overturning events in the wake high vertical shear of horizontal currents drove the mixing the dissipation rate of turbulent kinetic energy in the overturn regions is o 10 7 10 5 w kg 1 the corresponding eddy diffusivity is o 10 3 10 1 m2 s 1 the wake water properties are vertically diffused via upwelling and turbulence and can be delivered downstream through eddy shedding or advection the extent of downstream influence remains to be investigated

tectonic development of the samail ophiolite high precision u pb zircon geochronology and sm nd isotopic constraints on crustal growth and emplacement 1 new high precision single grain u pb zircon geochronology and whole rock nd isotopic data provide insight into the magmatic and tectonic development of the samail ophiolite the analyzed rocks can be broadly divided into two groups based on their structural position dates and isotopic composition an older group related to on axis magmatism and a younger group of post ridge dikes sills and stocks on axis gabbros tonalites and trondhjemites yielded th corrected 206pb 238u dates from 96 441 0 062 to 95 478 0 056 ma these dates combined with dates from rioux et al 2012 suggest that most of the ophiolite crust formed at an oceanic spreading center in 1 ma the post ridge intrusions come from all depths in the crust the upper mantle and the metamorphic sole post ridge gabbros tonalites and trondhjemites from the crust and mantle yielded th corrected 206pb 238u dates of 95 405 0 062 to 95 077 0 062 ma a small trondhjemitic pod from the metamorphic sole yielded younger th corrected 206pb 238u dates of 94 90 0 38 to 94 69 0 12 ma isotopic data suggest two distinct sources for the post ridge magmas five of the gabbros and tonalites from the crust have end 96 ma 6 90 0 12 to 7 88 0 16 and two trondhjemites from the upper mantle and metamorphic sole have end 96 ma 7 77 0 08 and 7 01 0 16 the negative end t and u pb dates from the mantle dike require that subduction or thrusting was established below the ophiolite 0 25 0 5 ma after formation of the crust the bimodal isotopic composition of post ridge magmas may reflect coeval decompression and or fluid fluxed melting of the mantle and melting dehydration or assimilation of sediment in the down going plate at this time the new data place temporal constraints on mid ocean ridge and supra subduction zone models for ophiolite formation

interannual variations of kuroshio transport in the east china sea and its relation to the pacific decadal oscillation and mesoscale eddies results of a data assimilative ocean model jcope2 from 1993 to 2012 were used to examine the correlation between the pacific decadal oscillation pdo index and interannual variations of the kuroshio transport in the east china sea ecs and the influences of mesoscale eddies on this correlation in a period from 1993 to 2002 the kuroshio transport estimated from the jcope2 reanalysis has a positive correlation with the pdo index this well known correlation became weak or even disappeared when the analysis period was extended from 1993 2002 to 1993 2012 this occurs because the variation range of the pdo index became small during enhanced mesoscale eddy activity southeast of taiwan in years after 2002 the eddies caused a larger variation in the kuroshio transport in the years after 2002 than before 2002 and therefore changed the correlation between the pdo index and kuroshio transport in the ecs the influence of mesoscale eddies on the kuroshio transport has strong regional dependence the kuroshio transport from the area east of taiwan to the midway along the shelf break in the east china sea depends mainly on eddies arriving from southeast of taiwan while transport from the midway along the shelf break to the tokara strait depends mainly on the eddies arriving from northeast of okinawa island the combination of pdo related signals and eddy related signals determines the interannual variations of the kuroshio transport in the ecs and sufficient attention must be paid to the spatial dependence of the kuroshio transport in the ecs on eddies

kuroshio stream path variation and its associated velocity structures south of shikoku japan during 1993 1995 twelve repeat observations of the kuroshio south of shikoku japan were carried out for obtaining a vertical velocity section of the upper 300m using a towed type acoustic doppler current profiler adcp among the twelve observations the kuroshio took the onshore path 9 times and the offshore path 3 times the cross stream velocity distribution around the kuroshio stream axis is asymmetric steeper on the onshore side than on the offshore side for the onshore path while it is symmetric for the offshore one the core with a maximum velocity is submerged to 100 200m depths for the onshore case and located at the near surface for the offshore case in the combined analysis with the rapid bulletin of ocean conditions the kuroshio mainly took an onshore path with stream axis positions less than 80km from cape ashizuri but the distance was increased over 150km at the frequency once a year

fluctuations of sea level in the western north pacific and inferred flow of the kuroshio abstract monthly sea level elevations at naze and aburatsu sites on either side of the tokara strait through which the kuroshio flows were analyzed for the period 1963 74 the sea level elevations were adjusted to uniform atmospheric pressure using a barometric factor of 1 cm mb 1 the adjusted elevations are presented as 1 long term mean seasonal values and 2 deviations from the long term means differences in the elevations between the two sites were then used as indices of the transport of the kuroshio the seasonal amplitude of the elevation differences across the kuroshio naze minus aburatsu is 13 of the mean surface geopotential anomaly difference of 0 6 dyn m 0 1000 db the phase of this difference signal indicates maximum northward flow in summer zonally integrated wind stress curl at this latitude in the pacific interior however is most anticyclonic during winter instead the seasonal fluctuations of the kuroshio are more nearly in phase with the fluctuations in the latitudinal grad

structure and variability of the kuroshio current in tokara strait four years of mooring array measurements in tokara strait south of kyushu japan from 1992 to 1996 are used to analyze the structure and temporal variability of the kuroshio current the mean kuroshio current in tokara strait shows a nearly permanent subsurface double core structure possibly due to topographic blockage effects the dominant variations of the kuroshio in tokara strait are separated into long term variability typically 100 day period and short term variability 10 days to 1 month according to spectrum and wavelet analysis the long term variability has a large horizontal scale across the strait with a striking twofold banded structure in spatial correlations this is due to the north south kuroshio axis shift that advects the double core structure of the mean current the axis shift can be indexed with the northeastward current velocity at the northernmost station a composite analysis using this index shows well defined northward and southward axis shift structures of the kuroshio current from the composite of the topex poseidon sea level anomaly in terms of this index the kuroshio axis shift and the current structure change are associated with a dipole shape sea level anomaly east of tokara strait on the other hand the short term variability of high kinetic energy only has a small horizontal scale within the northern part of the current which is related to frontal variability there exists a deep southwestward undercurrent below 600 m in the northern part of tokara strait flowing along the isobaths the undercurrent becomes stronger during the northward shift of the kuroshio axis while it almost disappears during the southward shift

how islands stir and fertilize the upper ocean 1 large differences between the upstream and lee side flow characteristics of an isolated island in the kuroshio have been identified from a three dimensional velocity survey and from vertical profiles of fine and micro structure in the island wake the relative vorticity is o 10f the horizontal current divergence indicates upwelling of o 0 01 m s 1 and the rate of dissipation of kinetic energy is o 10 4 w kg 1 isopycnal surfaces shoal by 60 m on the lee side and surface nitrate concentration increases seven fold flow blockage by the island and the izu ogasawara ridge on its flanks induces horizontal and vertical flow separation the associated lateral and vertical shear drive the upwelling and the vertical mixing in the wake and produces a very pronounced island mass effect

tidal currents and kuroshio transport variations in the tokara strait estimated from ferryboat adcp data from 2003 through 2011 current surveys using an acoustic doppler current profiler adcp mounted on the ferry naminoue were conducted across the tokara strait tks 1 234 of the resulting velocity sections were used to estimate major tidal current constituents in the tks the semi diurnal m2 tidal current maximum amplitude 27 cm s 1 was dominant among all the tidal constituents and the diurnal k1 tidal current maximum amplitude 21 cm s 1 was the largest among all the diurnal tidal constituents over the section the ratios relative to m2 of averaged amplitudes of m2 s2 n2 k2 k1 o1 p1 and q1 tidal currents were 1 00 0 44 0 21 0 12 0 56 0 33 0 14 0 10 tidal currents estimated from the ship mounted adcp data were in good agreement with those from the mooring adcp data their root mean square difference for the m2 tidal current amplitude was 2 0 cm s 1 after removing the tidal currents the annual mean of the net volume transport nvt through the tks its standard derivation was 23 03 3 31 sv sv 106 m3 s 1 the maximum minimum monthly mean nvt occurred in july november with 24 60 21 47 sv nvt values from the ship mounted adcp were in good agreement with previous geostrophic volume transports calculated from conductivity temperature depth data but the former showed much finer temporal structure than those from the geostrophic calculation this article is protected by copyright all rights reserved

the kuroshio large meander formation in 2004 analyzed by an eddy resolving ocean forecast system 1 the recent formation of the kuroshio large meander southeast of the kii peninsula during the period from may to july 2004 has been simulated successfully in an eddy resolving ocean forecast system japanese coastal ocean predictability experiment the formation process was examined from the viewpoint of eddy kuroshio interactions using sensitivity experiments that had various initial conditions for eddies in march and may 2004 we confirmed that the large meander does not occur when the trigger meander southeast of the kyushu island has small amplitude and that the cyclonic eddy on the offshore side of the kuroshio contributes to the large meander formation our results show that the large amplitude of the trigger meander southeast of kyushu island in april 2004 was caused by downstream advection of anticyclonic eddies along the kuroshio in the east china sea from east of taiwan the results suggest that the successive westward propagation of strong anticyclonic eddies in the subtropical frontal region from 2003 to 2004 was the origin of the formation of the kuroshio large meander south of japan in summer 2004

evolving force balance during incipient subduction nearly half of all active subduction zones initiated during the cenozoic all subduction zones associated with active back arc extension have initiated since the eocene hinting that back arc extension may be intimately associated with an interval several tens of myr following subduction initiation that such a large proportion of subduction zones are young indicates that subduction initiation is a continuous process in which the net resisting force associated with forming a new subduction zone can be overcome during the normal evolution of plates subduction initiation is known to have occurred in a variety of tectonic settings old fracture zones transform faults and extinct spreading centers and through polarity reversal behind active subduction zones although occurring within different tectonic settings four known subduction initiation events izu bonin mariana ibm along a fracture zone tonga kermadec along an extinct subduction boundary new hebrides within a back arc and puysegur fiordland along a spreading center were typified by rapid uplift within the forearc followed by sudden subsidence other constraints corroborate the compressive nature of ibm and tonga kermadec during initiation using an explicit finite element method within a two dimensional domain we explore the evolving force balance during initiation in which elastic flexure viscous flow plastic failure and heat transport are all considered in order to tie theory with observation known tectonic settings of subduction initiation are used as initial and boundary conditions we systematically explore incipient compression of a homogeneous plate a former spreading center and a fracture zone the force balance is typified by a rapid growth in resisting force as the plate begins bending reaching a maximum value dependent on plate thickness but typically ranging from 2 to 3 1012 n m for cases that become self sustaining this is followed by a drop in stress once a shear zone extends through the plate the formation of a throughgoing fault is associated with rapid uplift on the hanging wall and subsidence on the footwall cumulative convergence not the rate of convergence is the dominant control on the force balance viscous tractions influence the force balance only if the viscosity of the asthenosphere is 1020 pa s and then only after plate failure following plate failure buoyancy of the oceanic crust leads to a linear increase with crustal thickness in the work required to initiate subduction the total work done is also influenced by the rate of lithospheric failure a self sustaining subduction zone does not form from a homogeneous plate a ridge placed under compression localizes subduction initiation but the resisting ridge push force is not nearly as large as the force required to bend the subducting plate the large initial bending resistance can be entirely eliminated in ridge models explaining the propensity for new subduction zones to form through polarity reversals a fracture zone fz placed in compression leads to subduction initiation with rapid extension of the overriding plate a fz must be underthrust by the older plate for 100 150 km before a transition from forced to self sustaining states is reached in fz models the change in force during transition is reflected by a shift from forearc uplift to subsidence subduction initiation is followed by trench retreat and back arc extension moderate resisting forces associated with modeled subduction initiation are consistent with the observed youth of pacific subduction zones the models provide an explanation for the compressive state of western pacific margins before and during subduction initiation including ibm and tonga kermadec in the eocene and the association of active back arcs with young subduction zones on the basis of our dynamic models and the relative poles of rotation between pacific and australia during the eocene we predict that the northern segment of the tonga kermadec convergent margin would have initiated earlier with a progressive southern migration of the transition between forced and self sustaining states

variability of site response in the los angeles urban area this article addresses the variability of site response in the los angeles area and possible structural causes for the observations aftershock records from 231 sites in the san fernando and los angeles basins and the surrounding mountains are used in this study spectral ratios taken with respect to a low amplitude reference site are used to document the variation in site amplification in the frequency range 2 to 6 hz both spatially and with backazimuth to the source at higher frequencies 6 to 10 hz spectral ratios are shown to have greater spatial variability interstation spectral ratios are used to measure the standard deviation among source as a function of station separation an increase in the variation in ground motion is shown to take place at a station separation of 1 km relative site response estimates between nearby stations are used to demonstrate that preferred directions of motion can exist even in areas with no surface topographic effects significant variations in site response exist over short baselines up to a factor of 2 over 200 m that are not explained by differences in surficial geology or shallow shear wave velocity a variety of investigative approaches is used including spectral ratios arrival time variations 1d and 2d waveform modeling and comparison with seismic reflection lines to determine the most likely causes of these observations a correlation is demonstrated between late arrival times of p and s waves and larger site amplification in sherman oaks and northridge this observation in conjunction with waveform modeling and seismic reflection profiles is used to infer that sedimentary structures in the upper 1 to 2 km and topography on the sediment basement interface play an important role in determining site amplification these structures in the form of folds and buried basins focus energy in spatially restricted areas at the surface comparison of displacement waveforms at nearby stations having disparate site amplifications complemented by known shallow shear wave velocities at selected sites is used to support the argument that these structures in some cases can be the dominant factor in the modification of local ground motions

symmetric instability in the gulf stream abstract analyses of wintertime surveys of the gulf stream gs conducted as part of the clivar mode water dynamic experiment climode reveal that water with negative potential vorticity pv is commonly found within the surface boundary layer sbl of the current the lowest values of pv are found within the north wall of the gs on the isopycnal layer occupied by eighteen degree water suggesting that processes within the gs may contribute to the formation of this low pv water mass in spite of large heat loss the generation of negative pv was primarily attributable to cross front advection of dense water over light by ekman flow driven by winds with a down front component beneath a critical depth the sbl was stably stratified yet the pv remained negative due to the strong baroclinicity of the current suggesting that the flow was symmetrically unstable a large eddy simulation configured with forcing and flow parameters based on the observations confirms that the observed structure of the sbl is consistent with the dynamics of symmetric instability si forced by wind and surface cooling the simulation shows that both strong turbulence and vertical gradients in density momentum and tracers coexist in the sbl of symmetrically unstable fronts si is a shear instability that draws its energy from geostrophic flows a parameterization for the rate of kinetic energy ke extraction by si applied to the observations suggests that si could result in a net dissipation of 33 mw m 2 and 1 mw m 2 for surveys with strong and weak fronts respectively the surveys also showed signs of baroclinic instability bci in the sbl namely thermally direct vertical circulations that advect biomass and pv the vertical circulation was inferred using the omega equation and used to estimate the rate of release of available potential energy ape by bci the rate of ape release was found to be comparable in magnitude to the net dissipation associated with si this result points to an energy pathway where the gs s reservoir of ape is drained by bci converted to ke and then dissipated by si and its secondary instabilities similar dynamics are likely to be found at other strong fronts forced by winds and or cooling and could play an important role in the energy balance of the ocean circulation

kuroshio path meander between the continental slope and the tokara strait in the east china sea 1 horizontal patterns and meander motions of the kuroshio paths in the northern okinawa trough between the continental slope and the tokara strait are investigated using surface drifter buoy trajectory data noaa sea surface temperature sst measurements and shipboard acoustic doppler current profiler adcp current observations temporal variations are also examined by spectral analyses of 1 year moored velocity temperature records along the continental slope near 28 8 30 5 n and of the kuroshio position time series in the tokara strait drifter buoy trajectories show that the kuroshio paths in the northern okinawa trough are quasibimodal in character consisting of the northern paths and southern ones which are associated with anticyclonic and cyclonic kuroshio circulations respectively the kuroshio position time series show that the northern paths tend to be persistent and intermittently undergo transition to southern paths at periods of 1 3 months moored current variations in the slope area and the kuroshio path variations in the tokara strait are highly coherent near a period of 34 days due to the meander motions resulting from the transitions between the northern and southern paths successive noaa sst images and shipboard adcp current fields show that the transition from the northern path to the southern one is associated with a spatially growing cyclonic eddy which is initially generated from a downstream propagating frontal meander with wavelength of about 200 km when the cyclonic eddy grows into the scale of the northern okinawa trough about 200 km e w 250 km n s the kuroshio path changes from the northern path to the southern one

tidal and residual currents across the northern ryukyu island chain observed by ferryboat adcp ferryboat acoustic doppler current profiler adcp data from 2003 to 2012 are used to estimate the tidal and residual currents across the northern ryukyu island chain ric between the islands of okinawa and amamioshima in this region the m2 tide current is the strongest tidal component and the k1 tide current is the strongest diurnal tidal component the corresponding maximum amplitudes are 40 and 34 cm s 1 respectively after removal of the tidal currents the mean volume transport 1 5 2 7 sv flows into the east china sea ecs from the western north pacific through four channels in this area in an empirical orthogonal function eof analysis performed to clarify the temporal and spatial variability of currents through the four channels the first two eof modes account for 71 and 18 of the total variance respectively the eof1 mode shows a clear bottom intensified mode through the deep channel which is likely to be formed by the propagation of bottom trapped long topographic rossby wave caused by the impingement of westward propagating mesoscale eddies upon the eastern slope of the northern ric the eof2 mode has significant seasonal variability and may be driven by the wind stress prevailing over the kuroshio flow region around the northern ric in october to november this study provides observational evidence of the water exchanges across the northern ric which is essential for constructing a circulation scheme in the north pacific subtropical western boundary region

the kuroshio structure and transport estimated by the inverse method abstract structure and transport of the kuroshio are examined by the inverse method based on a dataset around the tokara strait subsurface velocities measured by a shipborne acoustic doppler current profiler are used together with ctd sections across the kuroshio to estimate the absolute flow fields the dataset was obtained along a closed line south off the kyushu by the r v chofu maru in september 1987 the kuroshio transport through the tokara strait was 28 109 kg s 1 at the time of observations the transport of warm water eddy south of the kuroshio is estimated at larger than 39 109 kg s 1 but its precise value is difficult to determine because of strong transport dependency on the solution rank the result also suggests a southward flow below the kuroshio off cape toimisaki and in the tokara strait in the section east of amamioshima island a broad northward flow is suggested on the continental slope

obduction why how and where clues from analog models obduction is an odd geodynamic process characterized by the emplacement of dense oceanic ophiolites atop light continental plates in convergent settings we herein present analog models specifically designed to explore the conditions i e sharp increase of plate velocities herein coined as acceleration slab interaction with the 660 km discontinuity ridge subduction under which obduction may develop as a result of subduction initiation the experimental setup comprises an upper mantle modeled as a low viscosity transparent newtonian glucose syrup filling a rigid plexiglas tank and high viscosity silicone plates convergence is simulated by pushing a piston with plate tectonics like velocities 1 10 cm yr onto a model comprising a continental margin a weakness zone with variable resistance and dip w an oceanic plate with or without a spreading ridge a preexisting subduction zone s dipping away from the piston and an upper active continental margin below which the oceanic plate is being subducted at the start of the model as for the neotethyan natural example several configurations were tested over thirty five parametric models with special emphasis on comparing different types of weakness zone and the degree of mechanical coupling across them measurements of displacements and internal deformation allow for a precise and reproducible tracking of deformation models consistently demonstrate that once conditions to initiate subduction are reached obduction may develop further depending on the effective strength of w results 1 constrainthe range of physical conditions required for obduction to develop nucleate and 2 underline the key role of such perturbations for triggering obduction particularly plate acceleration they provide an explanation to the short lived peri arabic obduction which took place along thousands of km almost synchronously within 50 10 myr from turkey to oman while the subduction zone beneath eurasia became temporarily jammed they also demonstrate that the emplacement of dense oceanic material on continental lithosphere is not a mysterious process requiring extraordinary boundary conditions but results from large scale normal oceanic then continental subduction processes

turbulent mixing within the kuroshio in the tokara strait turbulent mixing and background current were observed using a microstructure profiler and acoustic doppler current profilers in the tokara strait where many seamounts and small islands exist within the route of the kuroshio in the east china sea vertical structure and water properties of the kuroshio were greatly modified downstream from shallow seamounts in the lee of a seamount crest at 200 m depth the modification made the flow tend to shear instability and the vertical eddy diffusivity is enhanced by nearly 100 times that of the upstream site to k o 10 3 o 10 2 m2 s 1 a one dimensional diffusion model using the observed eddy diffusivity reproduced the observed downstream evolution of the temperature salinity profile however the estimated diffusion time scale is at least 10 times longer than the observed advection time scale this suggests that the eddy diffusivity reaches to o 10 1 m2 s 1 in the vicinity of the seamount at a site away from the abrupt topography eddy diffusivity was also elevated to o 10 3 m2 s 1 and was associated with shear instability presumably induced by the kuroshio shear and near inertial internal wave shear our study suggests that a better prediction of current water mass properties and nutrients within the kuroshio requires accurate understanding and parameterization of flow topography interaction such as internal hydraulics the associated internal wave processes and turbulent mixing processes

effects of mesoscale eddies on the volume transport and branch pattern of the kuroshio east of taiwan using satellite altimeter data and a long term altimetric transport index for the kuroshio inflow northeast of taiwan the effects of mesoscale eddies on the kuroshio volume transport kvt at the east taiwan channel and the branching pattern of the kuroshio east of taiwan are investigated at scales from those of individual events to interannual timescales both anticyclonic and cyclonic eddies are found to be able either to strengthen or weaken the kvt depending on the relative strength of mass convergence and divergence produced upstream and downstream of the eddies the major factor influencing the intensity of the kuroshio inflow is the meridional location of the eddies for single eddy events the kvt is significantly correlated with the latitude of the eddy s center the correlations being 0 44 and 0 48 for anticyclonic and cyclonic eddies respectively for dipole eddy events when the direction angle falls in the interval 40 150 240 300 the kvt anomaly tends to be positive negative furthermore low kvt events generally correspond to the formation of the ryukyu current branch which is also generated from strong mass divergence produced by the eddies in addition on interannual time scales the variation of kvt is closely related to the relative number of anticyclonic to cyclonic eddies west of 125 e with a correlation of 0 5 this article is protected by copyright all rights reserved

kuroshio meanders in the east china sea abstract an array of seven inverted echo sounders was moored along and across the kuroshio in the east china sea for more than one year the data from this array show evidence of energetic meanders with periods of 7 11 and 16 days the respective phase velocities of these meanders are 28 20 and 17 km day 1 downstream the 7 and 16 day waves are intermittent but the 11 day waves are present throughout the deployment the instability responsible for these waves is investigated with a spectral numerical model applied to a background state representing the kuroshio in this region the fastest growing instability from the model has e folding growth time of 2 days period of 12 days and phase velocity of 18 km day 1 downstream it appears to be a close representation of the 11 day wave seen in the observational data such a model has been previously used to represent meanders in the gulf stream at similar latitudes off the east coast of the united states the kuroshio meanders have approximately half the

time frequency variability of kuroshio meanders in tokara strait 1 the meander of the kuroshio path with periods of 30 90 days dominates tokara strait japan to understand the time frequency variability of this meander two kuroshio indicators were subjected to wavelet analysis for the period 1984 2004 the 30 90 day variance of the position of the kuroshio in tokara strait shows a season fixed nature with larger amplitudes in the period december july the amplitude of the variance in this phenomenon is also modulated by interannual variations with small variance recorded during 1989 1992 large variance during 1993 1998 and a return to small variance from 1999 2003 this interannual variation is positively correlated with that of kuroshio volume transport in tokara strait the largest variance during february april precedes the largest volume transport in april may by about 1 month suggesting that mesoscale menders are the forcing of the volume transport increase not the other way around