on using the effective contact angle and the water drop penetration time for classification of water repellency in dune soils sandy soils are often water repellent when dry in sloping areas this may result in surface runoff and erosion water repellency in soils can be classified with the solid liquid contact angle which is difficult to determine another method is the water drop penetration time this method is not only easier to apply but provides a more useful scale for classifying water repellent soils moreover it is directly related to erosion hazard because runoff depends on the time required for the infiltration of rain drops a close relationship was found between the contact angle and the water drop penetration time in dune soils along the coast of the netherlands

a search for split sks waveforms in the north atlantic summary to test a prediction of the anisotropic properties of the upper mantle beneath the central north atlantic we measure splitting of the waveforms of sks phases recorded at wwssn stations in the azores pda and on bermuda bec because the analysis of individual analogue records does not provide sufficient resolution we have developed a new technique for representing the confidence limits that permits a straightforward estimation of the average splitting beneath a station from a group of events if events from a variety of different azimuths are recorded the average splitting parameters can be tightly constrained we found five records for pda and eight for bec that have good signal to noise ratio and a prominent sks phase only one of the phases at pda shows evidence of splitting the average anisotropy must be small if it exists at all at bec the average anisotropy is significant with a fast direction between nw se and n s and a time delay between the two split components of about 1 s both of these observations are significantly smaller than predicted by a model of the upper mantle anisotropy based on ss s differential traveltimes the absence of systematic anisotropy at pda may be attributable to a complex flow pattern in the upper mantle at this site near the eurasian african plate boundary in the vicinity of an active hotspot at bec the observed direction is consistent with the prediction and both the direction and the magnitude of the average anisotropy are indicative of a sublithospheric source to check the reliability of these results from analogue records we have performed a similar analysis for station kip on oahu where digital records are available for comparison the results from digital and analogue records are similar at kip the splitting is more variable than expected for uniform anisotropy with the fast directions for individual records ranging from about n26 e to about n83 e and with variable time delays similar variability is observed at all three stations the average anisotropy at kip is well constrained however with a time delay of about 0 6 s and fast direction n75 e the fast direction coincides with the fossil sea floor spreading direction beneath the hawaiian islands suggesting that the dominant source of anisotropy beneath kip is lithospheric

variations in shear wave splitting in young pacific seafloor 1 analysis of sks phases recorded by ocean bottom seismometers in the glimpse experiment has expanded the region of in situ measurements of shear wave splitting in young seafloor near the southern east pacific rise average splitting times at individual glimpse sites range from 1 1 to 2 2 s with fast direction azimuths trending approximately in the direction of absolute plate motion and fossil spreading for the pacific plate the glimpse study area at 12 to 14 s is adjacent to the melt experiment the new observations demonstrate that splitting delays are not uniform on the pacific plate and that the contrast between the nazca and pacific plates is not a fundamental consequence of the asymmetric plate motion the variations in degree of splitting could be caused by small scale convection variations in water content or rate of deformation in the asthenospheric return flow to the east pacific rise

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

toroidal mantle flow through the western u s slab window the circular pattern of anisotropic fast axis orientations of split sks arrivals observed in the western u s cannot be attributed reasonably to either preexisting lithospheric fabric or to asthenospheric strain related to global scale plate motion a plume origin for this pattern accounts more successfully for the anisotropy field but little evidence exists for an active plume beneath central nevada we suggest that mantle flow around the edge of the sinking gorda juan de fuca slab is responsible for creating the observed anisotropy seismic images and kinematic reconstructions of gorda juan de fuca plate subduction have the southern edge of this plate extending from the mendocino triple junction to beneath central nevada and flow models of narrow subducted slabs produce a strong toroidal flow field around the edge of the slab consistent with the observed pattern of anisotropy this flow may enhance uplift extension and magmatism of the northern basin and range while inhibiting extension of the southern basin and range

shear wave splitting in the upper mantle wedge above the tonga subduction zone summary intermediate period seismograms of shear waves from deep earthquakes are examined for shear wave splitting diagnostic of seismic velocity anisotropy in the upper mantle wedge between the subducting tonga slab and stations in the fiji islands earthquakes with near vertical incidence angles are selected to minimize complications of converted phases and the free surface horizontal component seismograms for 25 deep earthquakes recorded at station lak on the lau ridge show splitting of up to 0 9 s with an average of 0 45 0 25 s between fast and slow s wave components anisotropy in the upper mantle is the most likely cause of the splitting the ese orientation of the fast velocity direction at station lak corresponds to an axis of symmetry of the anisotropic mantle and is approximately perpendicular to magnetic lineations in the lau basin and the northeastern portion of the south iiji basin the observations are consistent with a model of flow alignment of olivine 100 and orthopyroxene 001 axes parallel to the direction of basin extension seismograms for eight deep earthquakes at station sva on viti levu show up to 1 0 s splitting with an average of 0 65 0 29 s and a weak nne preferred orientation of fast velocity polarizations of shear wave particle motions corrected for anisotropy are within 36 5 26 of polarixations predicted for nine moment tensor solutions the magnitude of shearwave splitting and estimates of the thickness of the lithosphere in the fiji region imply that the anisotropy cannot be contained in the lithosphere alone either the anisotropy is distributed in both the lithosphere and asthenosphere or the asthenosphere alone is anisotropic

seismic anisotropy in the java banda and philippine subduction zones and its implications for the mantle flow system beneath the sunda plate

upper and mid mantle anisotropy beneath the tonga slab measurements of source side splitting in s waves fromevents within the tonga slab reveal anisotropy in the upperand mid mantle beneath the slab we observed splitting forevents originating at both upper mantle and transition zonedepths anisotropic fast directions are trench parallel orsub parallel for both upper mantle and transition zoneevents delaytimes dt decreasewithdepthforuppermantleevents the source of anisotropy for the upper mantle eventsis likely in the sub slab mantle and is likely indicative oftrench parallel flow due to slab rollback the source ofanisotropy for the deeper earthquakes is more difficult toconstrain but the pattern of splitting measurements arguesfor an uppermost lower mantle anisotropic source and slabinduced deformation may be responsible for this anisotropyas well additional constraints from mineral physics studiesare necessary to interpret the mid mantle anisotropy signalin terms of geodynamical processes

shear wave polarization anisotropy and subduction induced flow in the mantle wedge of northeastern japan abstract shear wave polarization anisotropy in the central part of northeastern ne japan was investigated we analyzed s phases of 293 intermediate depth earthquakes recorded at 77 stations and obtained 1286 splitting parameters the obtained results show the systematic variation in splitting parameters across the arc the leading shear wave polarization directions fast direction obtained at stations in the western side of the study area are oriented nearly e w which is sub parallel to the direction of relative plate motion between the pacific plate and the north american okhotsk plate in contrast fast directions obtained at stations in the eastern side of the study area are oriented approximately n s stations in the western side have a larger average delay time compared to those in the eastern side these variations suggest that the nature of anisotropy is quite different between the eastern and the western sides both experimental studies on the deformation of olivine and numerical simulations of plate driven flow predict that the lattice preferred orientation of olivine causes the fast direction sub parallel to the flow direction for the conditions in the mantle wedge of ne japan we thus infer that the lattice preferred orientation of olivine generated by flow induced strain is the most likely candidate for anisotropy that produces splitting with e w fast direction three possible causes of anisotropy in the eastern side are considered deformation of water rich olivine in the mantle wedge trench parallel flow in the mantle wedge due to along strike dip variations in the slab and anisotropy in the crust and the slab we could not however determine which causes are dominant further systematic study is required to reveal the cause of anisotropy in the eastern side

upper mantle flow beneath french polynesia from shear wave splitting summary upper mantle flow beneath the south pacific is investigated by analysing shear wave splitting parameters at eight permanent long period and broad band seismic stations and 10 broad band stations deployed in french polynesia from 2001 to 2005 in the framework of the polynesian lithosphere and upper mantle experiment plume despite the small number of events and the rather poor backazimuthal coverage due to the geographical distribution of the natural seismicity upper mantle seismic anisotropy has been detected at all stations except at tahiti where two permanent stations with 15 yr of data show an apparent isotropy the median value of fast polarization azimuths n67 5 w is parallel to the present pacific absolute plate motion direction in french polynesia apm n67 w this suggests that the observed sks fast polarization directions result mainly from olivine crystal preferred orientations produced by deformation in the sublithospheric mantle due to viscous entrainment by the moving pacific plate and preserved in the lithosphere as the plate cools however analysis of individual measurements highlights variations of splitting parameters with event backazimuth that imply an actual upper mantle structure more complex than a single anisotropic layer with horizontal fast axis a forward approach shows that a two layer structure of anisotropy beneath french polynesia better explains the splitting observations than a single anisotropic layer secondorder variations in the measurements may also indicate the presence of small scale lateral heterogeneities the influence of plumes or fracture zones within the studied area does not appear to dominate the large scale anisotropy pattern but may explain these second order splitting variations across the network

near inertial ocean current response to hurricane frederic abstract hurricane frederic passed with 80 to 130 km of the u s naval oceanographic office current meter arrays in water depths ranging from 100 to 470 m near the desoto canyon region and within 150 km of an ocean thermal energy conversion otec mooring in 1050 m of water excitation of near inertial waves by the moving hurricane was observed throughout the water column along the canyon walls and at the otec site the frequencies of the waves were blue shifted between 1 to 6 above the local inertial frequency the horizontal wavelength of 250 km is consistent with an energetic first baroclinic mode response but is considerably below the linear theory prediction of 550 km the inferred vertical wavelengths of the immediate response exceeded 1000 m along the northern and eastern sides of the canyon since the currents throughout the water column increased within hours of the hurricane passage later the vertical wavelengths were about equal to the water depth the vertical group velocities associated

anisotropy and mantle flow in the chile argentina subduction zone from shear wave splitting analysis 1 we examine shear wave splitting in teleseismic phases to observe seismic anisotropy in the south american subduction zone data is from the charge network which traversed chile and western argentina across two transects between 30 s and 36 s beneath the southern and northwestern parts of the network fast polarization direction j is consistently trench parallel while in the northeast j is trench normal the transition between these two zones is gradual we infer that anisotropy sampled by teleseismic phases is localized within or below the subducting slab we explain our observations with a model in which eastward nazca entrained asthenospheric flow is deflected by retrograde motion of the subducting nazca plate resulting southward flow through this area produces n s j observed in the south and northwest e w j result from interaction of this flow with the local slab geometry producing eastward mantle flow under the actively flattening part of the slab index terms 7203 seismology body wave propagation 7218 seismology lithosphere and upper mantle 8123 tectonophysics dynamics seismotectonics 8150 tectonophysics plate boundary general 3040 9360 information related to geographic region south america citation anderson m l g zandt e triep m fouch and s beck 2004 anisotropy and mantle flow in the chile argentina subduction zone from shear wave splitting analysis geophys res lett 31 l23608 doi 10 1029 2004gl020906

the taiwan ryukyu subduction collision complex folding of a viscoelastic slab and the double seismic zone 1 the termination of the ryukyu trench against eurasia and the oblique subduction of the philippine sea plate create a subduction collision complex offshore taiwan which has not previously been elucidated in detail we combine traveltime data from the seismic networks in taiwan and japan to better illuminate how the subducting ryukyu slab deforms in this subduction collision zone more than 5000 events recorded by both networks were relocated with the double difference method using an optimal regional one dimensional velocity model the offshore seismicity indicates that the double seismic zone with a gap of 15 20 km exists in the subducting slab in the depth range of 40 80 km focal mechanisms suggest that the double seismic zone is caused by east west compression resulting from oblique convergence the improved hypocentral locations for the first time reveal folding of the slab into a horizontal curvature larger in magnitude than and opposite in sign to that of the ryukyu trench in the depth range 50 100 km the anomalous curvature together with the focal mechanisms suggests that the slab folds against the eurasian lithosphere and that this deformation cannot be fully elastic we model this deformation mode as the developing instability of a viscoelastic maxwell layer embedded in a viscous medium the characteristic wavelength of the instability i e 250 km is consistent with folding of a slab whose viscosity is 100 times higher than that of the surrounding mantle for an along strike elastic membrane strain as small as 0 01 or more than 3 orders of magnitude higher if 5 elastic strain is allowed

effect of three dimensional slab geometry on deformation in the mantle wedge implications for shear wave anisotropy shear wave splitting observations from many subduction zones show complex patterns of seismic anisotropy that commonly have trench parallel fast directions three dimensional flow may give rise to trench parallel stretching and provide an explanation for these patterns of seismic anisotropy along strike variations in slab geometry produce trench parallel pressure gradients and are therefore a possible mechanism for three dimensional flow in this study we quantify the effects of variable slab dip curved slabs oblique subduction and slab edges on flow geometry and finite strain in the mantle wedge of subduction zones temperature dynamic pressure velocity and strain are calculated with high resolution three dimensional finite element models these models include temperature and stress dependent rheology and parameterized slab and trench geometry thick layers 20 60 km with strong trench parallel stretching are observed in the mantle wedge when slab geometry involves a transition to slab dip less than 15 or strong curvature in the slab in these cases strong trench parallel stretching develops when flow lines have an oblique to trench normal orientation this suggests that trench parallel seismically fast directions may not indicate trench parallel flow lines in systems with large along strike variations an oblique component of stretching is confined to a 20 30 km layer above the slab in systems with oblique subduction the effects of slab edges include strong toroidal flow and focusing in the mantle near slab edges and trench parallel flow that extends 50 100 km into the core of the mantle wedge

crustal deformation and block kinematics in transition from collision to subduction global positioning system measurements in northern taiwan 1995 2005 1 we present global positioning system gps measurements for the period 1995 2005 at 125 campaign surveyed sites in northern taiwan based on elastic rotating block modeling analyses derived from the gps data we describe the transitional tectonics from arc continent luzon chinese collision to the converging ryukyu trench subduction and back arc opening along the chinese continental margin station velocities relative to station s01r in the chinese stable continental margin were estimated from coordinate time series of each station by using the weighted least squares technique we found two distinct deformation patterns in two geological areas which are basically separated by the surface projection of the nw trending boundary of the subducting philippine sea plate across northern taiwan 1 a waning collision area to the west and 2 a transition zone to the east in the waning collision area the horizontal velocity field shows vectors of 0 3 7 3 mm yr toward the nw in the foothills and the hsuehshan range of northwestern taiwan the tectonic blocks represent a significant nw se internal contraction along with a small block rotation rate 3 0 myr the transition zone can be further divided into an outer range and inner range with distinguishing rotation rates and deformation behaviors in the outer range of the transition zone velocities of 1 0 7 8 mm yr from south to north rotating from 008 to 143 is found in the northernmost foothills and the hsuehshan range the tectonic blocks within the outer range are characterized by a coherent rotation low internal strain rate of 0 10 strain yr with an angular velocity of 5 1 myr where the euler pole is located near its southeastern boundary in the inner range of transition zone a larger clockwise rotation from west to east with horizontal velocities of 9 3 41 2 mm yr from 053 to 146 are found in the northernmost central range the tectonic blocks of the inner range reveal a remarkable nw se internal extension with an ultrarapid clockwise rotation 47 3 myr where the euler pole is near the southern boundary of the range close to the collision comer with the colliding luzon arc the trench roll back together with back arc opening are interpreted to be substantially superposed on the arc continent collision induced rotation in the transition zone with particular regard to the inner range of the northeast taiwan mountain belt

removing infragravity wave induced noise from ocean bottom seismographs obs data deployed offshore of taiwan abstract vertical ocean bottom seismograph obs data at frequencies below 0 05 hz are contaminated by noise induced by infragravity waves we constructed the transfer function between pressure and velocity data from obss deployed in taiwan waters to remove the wave pressure induced noise from seismic recordings data were analyzed from five portable broadband obss deployed each for 10 months at water depths from 1740 to 4600 m and from a cabled shallow buried seismograph eos1 installed on the seafloor at 300 m depth removing long period noise from these obs data improves the identification of teleseismic phases such as p s ss p diff and pkikp that are otherwise ambiguous or unidentifiable for eos1 infragravity wave signals completely mask the p and s waveforms in the 10 50 s period band suitable for centroid moment tensor cmt solutions for most of the local events application of the transfer functions to predict and remove wave deformation yielded clean prominent p and s waveforms at these periods and aided in the cmt determination for small events jointly with land stations the relative amplitudes of the wavenumber normalized transfer function for some of the obss are mostly determined by the thickness of the sediment at the obs site

trench parallel flow beneath the nazca plate from seismic anisotropy shear wave splitting of s and sks phases reveals the anisotropy and strain field of the mantle beneath the subducting nazca plate cocos plate and the caribbean region these observations can be used to test models of mantle flow two dimensional entrained mantle flow beneath the subducting nazca slab is not consistent with the data rather there is evidence for horizontal trench parallel flow in the mantle beneath the nazca plate along much of the andean subduction zone trench parallel flow is attributale utable to retrograde motion of the slab the decoupling of the slab and underlying mantle and a partial barrier to flow at depth resulting in lateral mantle flow beneath the slab such flow facilitates the transfer of material from the shrinking mantle reservoir beneath the pacific basin to the growing mantle reservoir beneath the atlantic basin trenchparallel flow may explain the eastward motions of the caribbean and scotia sea plates the anomalously shallow bathymetry of the eastern nazca plate the long wavelength geoid high over western south america and it may contribute to the high elevation and intense deformation of the central andes

mantle flow entrained by the hindu kush continental subduction inferred from source side seismic anisotropy abstract the intermediate depth seismicity below the hindu kush orogen is thought to mark the indian plate subduction with the bottom half of the slab currently breaking off unique features of this continental subduction are the near vertical slab and the roughly stationary convergence boundary how this subduction affects the mantle flow patterns remains to be understood in this study we measured source side shear wave splitting on the s waves from hindu kush intraslab events to sample the surrounding mantle the observed fast polarization directions exhibit a circular pattern around the slab resembling that predicted for the toroidal flow driven by slab rollback however the rollback scenario is not favored because it hardly sustains in dynamic models without a considerable retreat of convergence boundary we propose that the observed pattern is produced by the sub vertical shear flow entrained by the steep descent of the slab and the ongoing breakoff this scenario requires the existence of a type or ag type olivine fabrics with strong orthorhombic anisotropy in mid to lower upper mantle which is consistent with the global models of azimuthal and radial anisotropy this interpretation circumvents the debate on the cause of trench parallel anisotropy in some oceanic subduction zones where slab entrainment and rollback may coexist and supports the notion that orthorhombic anisotropy of olivine may play an important role in shaping mantle anisotropy

mantle flow at a slab edge seismic anisotropy in the kamchatka region the junction of the aleutian island and the kamchatka peninsula defines a sharp turn in the boundary of the pacific and north american plates terminating the subduction zones of the northwest pacific the regional pattern of shear wave birefringence near the junction indicates that trench parallel strain follows the seismogenic benioff zone but rotates to trench normal beyond the slab edge asthenospheric mantle is inferred to flow around and beneath the disrupted slab edge and may influence the shallowing dip of the benioff zone at the aleutian junction

hf radar comparisons with moored estimates of current speed and direction expected differences and implications the validation of estimates of ocean surface current speed and direction from high frequency hf doppler radars can be obtained through comparisons with measurements from moored near surface current meters acoustic doppler current profilers or drifters expected differences between current meter cm and hf radar estimates of ocean surface vector currents depend on numerous sources of errors and differences such as instrument and sensor limitations sampling characteristics mooring response and geophysical variability we classify these sources of errors and differences as being associated exclusively with the current meter as being associated exclusively with the hf radar or as a result of differing methodologies in which current meters and hf radars sample the spatially and temporally varying ocean surface current vector field in this latter context we consider three geophysical processes namely the stokes drift ekman drift and baroclinicity which contribute to the differences between surface and near surface vector current measurements the performance of the hf radar is evaluated on the basis of these expected differences vector currents were collected during the high resolution remote sensing experiment ii off the coast of cape hatteras north carolina in june 1993 the results of this analysis suggest that 40 60 of the observed differences between near surface cm and hf radar velocity measurements can be explained in terms of contributions from instrument noise collocation and concurrence differences and geophysical processes the rms magnitude difference ranged from 11 to 20 cm s 1 at the four mooring sites the average angular difference ranged between 15 o and 25 o of which about 10 o is attributed to the directional error of the radar current vector estimates due to the alignment of the radial beams

shear wave splitting at the edge of the ryukyu subduction zone abstract intraslab events recorded by ocean bottom seismometers in the okinawa trough provide an extended depiction of shear wave splitting in the southwest section of the ryukyu subduction zone at 100 200 km from the western edge of the subduction system we observed trench normal fast polarization direction in the back arc compatible with 2d slab or rifting driven corner flow towards the edge the fast directions are sub parallel to the trench in the arc back arc region and rotate to trench normal within 50 km of the edge splitting constrained by land stations with paths mostly in the mantle wedge exhibits similar trench normal fast directions in the subduction edge zone further inland the dominant component of fast directions becomes roughly parallel to the taiwan orogenic fabric splitting of p to s phases converted at the moho of the okinawa trough and of s phases from shallow events suggest that crustal anisotropy may affect the measured splitting but the observed pattern reflects predominantly mantle anisotropy the variation in splitting along the okinawa trough cannot be explained by a b type a type olivine fabric transition in the mantle wedge it may indicate the presence of an along arc flow in the mantle wedge towards the edge where it is blocked and deflected by the eurasian lithosphere this scenario bolsters previous studies suggesting a significant impact of eurasian lithosphere on the dynamics of the ryukyu subduction system

toroidal mantle flow around the calabrian slab italy from sks splitting 1 sks wave birefringence is likely caused by ongoing and or fossil mantle flow splitting parameters in the southern tyrrhenian subduction zone define a quite complex pattern of fast directions with large delay times up to 2 7 s fast directions are prevalently trench parallel below the slab and rotate to trench normal at the western edge of the slab depicting a ring around it we interpret these anisotropic patterns also observed in laboratory experiment as toroidal mantle flow induced by rollback subduction

the relation of near inertial motions observed in the mixed layer during the jasin 1978 experiment to the local wind stress and to the quasi geostrophic flow field abstract oscillations with near inertial frequencies were an energetic component of the upper ocean velocity field observed at each of two moorings separated by 44 km during the joint air sea interaction jasin experiment during the late summer of 1978 at each mooring the amplitude of the inertial motion was highest in the mixed layer where it was nearly depth independent previous work pollard and millard 1970 pollard 1980 had found that the amplitude and phase of inertial motion in the mixed layer was related to the local wind stress in this case the loacal winds measured at each mooring were coherent but the time series of mixed layer near inertial motion at one mooring bore little resemblance to that at the other mooring during jasin 1978 the differences in the inertial response at the two moorings coincided with differences in the quasi geostrophic flow field in the vicinity of the two moorings inclusion of the horizontal gradients of the quasi geostrophic flow in model equations prov

joint vp and vs tomography of taiwan implications for subduction collision orogeny abstract the taiwan orogen sitting at the pre rifted eurasian margin and bracketed by two sub orthogonal subduction systems is subject to complicated geotectonics motivating numerous seismic tomographic studies in local and regional scale most of them obtained p wave velocities vp or with vp vs ratio jointly but few were for s wave velocities vs with unprecedented amount of s wave data in this study a new set of well tuned vp vs and vp vs models were determined by an elaborate joint inversion scheme integrating the data of p and s wave travel times s p times and the borehole logging data for near surface correction into one system this allowed us to revisit the subduction collision process in detail by comparing vp vs and vp vs ratio simultaneously with enhanced slab imaging of philippine sea plate psp under northeast taiwan we are able to discriminate the plausible missing luzon forearc basement along the plate boundary and propose a skateboarding edge model in which the westernmost psp rides on the east subducted forearc basement and subducts northward underneath the eurasian lithosphere the underlain forearc basement along with the psp subduction then results in the anomalous shallow double seismic zone observed only near taiwan island meanwhile at around 121 e the north subducting psp seems dipping west to collide with the deep eurasian lithosphere shaping an irregular corner wedge structure in addition we evaluate our model with previous ones by waveform modeling approach and show the current performance of travel time tomography in taiwan region

immediate effects of wildfires on water repellency and aggregate stability in mediterranean calcareous soils alkaline soils are considered much less prone to developing water repellency induced by fire than acidic soils here we report on the persistence of water repellency present in calcareous soils immediately after wildfires in 10 burned areas in se spain its distribution in different aggregate size fractions 2 2 1 1 0 5 0 5 0 25 and 0 25 mm and on results from aggregate stability tests we also distinguished between soil samples taken beneath pine pinus halepensis and beneath understory vegetation burning appears to have increased the frequency of water repellency occurrence with 74 of burned samples being classified as water repellent compared to 33 from unburned terrain in the composite fraction 2 mm the persistence of water repellency after fire was highly variable but nevertheless showed statistical differences at p 0 001 comparing burned vs unburned moreover statistical differences in the persistence of water repellency were found in soil samples taken from beneath pine between burned and unburned and also beneath understory vegetation results showed that soil beneath understory tend to have lower values of water repellency persistence than soil beneath pine burned soils showed higher aggregate stability a positive tendency was observed between aggregate stability and water repellency the observed changes in wr and as could have implications for soil hydrological behaviour

sks skks splitting and taiwan orogeny 1 we determine 58 sets of splitting parameters fast direction and delay time t from broadband sks skks waves recorded at temporary and permanent stations in taiwan these and earlier results from s and scs as well as sks show an island wide pattern of alignment with n nne structural trends in southern and central taiwan and then turn smoothly to ew following the structural bight in northern taiwan remarkable differences in t for eastern and southwestern events are found resulting probably from a more anisotropic upper mantle in the east under the central range with t an average of 1 3 seconds our observations are consistent with the hypothesis that the orogeny involves shear or flow in the upper mantle in central and southern taiwan in northern taiwan near the ends of the collision and subduction zones the extrusion and the hydration of olivine may contribute to the orientation of

mean and near inertial ocean current response to hurricane gilbert abstract the three dimensional hurricane induced ocean response is determined from velocity and temperature profiles acquired in the western gulf of mexico between 14 and 19 september 1988 during the passage of hurricane gilbert the asymmetric wind structure of gilbert indicated a wind stress of 4 2 n m 2 at a radius of maximum winds rmax of 60 km using observed temperature profiles and climatological temperature salinity relationships the background and storm induced geostrophic currents re 750 m were 0 1 m s 1 and 0 2 m s 1 respectively a loop current warm core ring lcwcr was also located to the right of the storm track at 4 5 rmax where anticyclonically rotating near surface and 100 m currents decreased from 0 9 m s 1 to 0 6 m s 1 at depth the relative vorticity in the lcwcr was shifted below the local coriolis parameter by about 6 in a storm based coordinate system alongtrack residual velocity profiles from 0 to 4 rmax were fit to a dynamical model by least squares to isolate the near

shear wave splitting and implications for mantle flow beneath the melt region of the east pacific rise shear wave splitting across the fast spreading east pacific rise has been measured from records of sks and skks phases on the ocean bottom seismometers of the mantle electromagnetic and tomography melt experiment the direction of fast shear wave polarization is aligned parallel to the spreading direction delay times between fast and slow shear waves are asymmetric across the rise and off axis values on the pacific plate are twice those on the nazca plate splitting on the pacific plate may reflect anisotropy associated with spreading induced flow above a depth of about 100 km as well as a deeper contribution from warm asthenospheric return flow from the pacific superswell region

reconciling surface plate motions with rapid three dimensional mantle flow around a slab edge a central axiom of the theory of plate tectonics is that the surface plates are coupled to and carried along by convection in the earth s mantle the situation is rather different at subduction zones however margarete jadamec and magali billen now present calculations that quantify this variance they use three dimensional numerical models of buoyancy driven deformation with realistic slab geometry for the alaska subduction transform system to determine the surrounding mantle flow field they show that near a subduction zone edge mantle flow velocities can have magnitudes of greater than ten times the surface plate motions and that the complex mantle flow field is consistent with observations from seismic anisotropy these results imply local rapid transport of geochemical signatures through subduction zones the direction of tectonic plate motion at the earth s surface and the flow field of the mantle inferred from seismic anisotropy are well correlated globally implying large scale coupling between the mantle and surface plates but the fit is poor at subduction zones here three dimensional numerical models of buoyancy driven deformation for the alaska subduction transform system are used to find the origin of the regional decoupling of flow the results imply local rapid transport of geochemical signatures through subduction zones the direction of tectonic plate motion at the earth s surface and the flow field of the mantle inferred from seismic anisotropy are well correlated globally suggesting large scale coupling between the mantle and the surface plates1 2 the fit is typically poor at subduction zones however where regional observations of seismic anisotropy suggest that the direction of mantle flow is not parallel to3 4 5 6 7 and may be several times faster than6 plate motions here we present three dimensional numerical models of buoyancy driven deformation with realistic slab geometry for the alaska subduction transform system and use them to determine the origin of this regional decoupling of flow we find that near a subduction zone edge mantle flow velocities can have magnitudes of more than ten times the surface plate motions whereas surface plate velocities are consistent with plate motions8 and the complex mantle flow field is consistent with observations from seismic anisotropy5 the seismic anisotropy observations constrain the shape of the eastern slab edge and require non newtonian mantle rheology the incorporation of the non newtonian viscosity9 10 results in mantle viscosities of 1017 to 1018 pa s in regions of high strain rate 10 12 s 1 and this low viscosity enables the mantle flow field to decouple partially from the motion of the surface plates these results imply local rapid transport of geochemical signatures through subduction zones and that the internal deformation of slabs decreases the slab pull force available to drive subducting plates

faulting and hydration of the upper crust of the sw okinawa trough during continental rifting evidence from seafloor compliance inversion the elastic response of seafloor to ocean gravity wave loading or seafloor compliance provides a constraint on the elastic properties of the crust we measured seafloor compliance at three ocean bottom seismometer obs sites around taiwan two in the southwestern sw okinawa trough and one on the ryukyu arc and performed inversion for crustal structures beneath them models best fitting the data demonstrate a decrease in upper crustal shear velocity and an increase in the compressional shear velocity ratio from the arc site to the trough sites with increasing amount of back arc extension this variation suggests that the upper continental crust is highly faulted and hydrated during rifting of the eurasian lithosphere

observations of near inertial surface currents off oregon decorrelation time and length scales 1 high resolution km in space and hourly in time surface currents observed by an array of high frequency radars off oregon are analyzed to quantify the decorrelation time and length scales of their near inertial motions the near inertial surface currents are dominantly clockwise with amplitudes of 9 12 cm s 1 however they appear asymmetric and elliptical as a result of counterclockwise inertial motions with magnitudes in a range of 2 5 cm s 1 the decorrelation time and length scales are computed from the decay slope of the near inertial peak and the spatial coherence in the near inertial frequency band respectively decorrelation time scales of clockwise near inertial motions increase from 2 days nearshore within 30 km from the coast to 6 days offshore and their length scales increase from 30 to 90 km seaward possibly due to coastal inhibition the local spatial coherence has an exponentially decaying structure for both clockwise and counterclockwise rotations and their phases propagate northwestward offshore for clockwise and northeastward onshore for counterclockwise rotations

the contrasted response of ash to wetting abstract after a wildfire the soil is covered by ash ash properties depend on vegetation type amount of fuel and fire intensity the ash layer controls the post fire soil hydrologic response but little is known about the effect of ash thickness and ash type on infiltration which is relevant for post fire runoff and soil losses and for ecosystems rehabilitation and restoration this paper analyses the role of i ash type black or white ii thickness 5 15 and 30 mm thick and iii temporal variation 0 15 and 40 days under three simulated rain events 55 mm for 1 h on soil surface hydrology the rainfall was simulated on 0 25 m2 plots and time to ponding runoff and runoff discharge were measured the infiltration rates the initial infiltration rate f0 the steady state infiltration rate fc and the infiltration decay factor k were calculated and the horton infiltration equation applied the results show that soils covered with white ash doubled the runoff rates of soils covered with black ash in general runoff decreases as the ash thickness increases and the runoff decreases with the number of rainfall events after the fire in plots covered with white ash ponding time and k are positively correlated by the ash thickness and f0 and fc are correlated by the rainfall events in three runs ash type and ash depth are key factors on the soil hydrology after a wildfire

anisotropy in the subducting slab observations from philippine sea plate events in taiwan in the southernmost ryukyu subduction zone slab guiding behavior from intermediate depth earthquakes is well documented with a low frequency 2 hz first p arrival followed by sustained high frequency 3 10 hz wave trains such waves developed by propagating along a long path within the slab are expected to have high sensitivity to anisotropy within the slab we determine shear wave splitting parameters from 178 intraplate events that are deeper than 100 km the possible slab anisotropy associated polarization pattern shows the fast direction at n65 e and delay time of 0 13 0 45 s this is stronger than the previously documented crust effect 0 1 s similar to the mantle wedge effect 0 28 s in average but weaker than the upper mantle effect 1 3 s in average in taiwan the fast axis reflects the fossil spreading direction of philippine sea plate with minor clockwise rotation due to the collision to eurasian plate

effect of water and stress on the lattice preferred orientation of olivine the influence of water and stress on the lattice preferred orientation lpo of olivine aggregates was investigated through large strain shear deformation experiments at high pressures and temperatures p 0 5 2 1 gpa t 1470 1570 k under both waterpoor and water rich conditions the specimens are hot pressed synthetic olivine aggregates or single crystals of olivine water was supplied to the sample by decomposition of a mixture of talc and brucite deformation experiments were conducted up to shear strain 6 using the griggs apparatus where water fugacity was up to 13 gpa at the pressure of 2 gpa the water content in olivine saturated with water increases with increasing pressure and the solubility of water in olivine at p 0 5 2 gpa was 400 1200 ppm h si several new types of lpo in olivine are found depending on water content and stress samples deformed in waterpoor conditions show a conventional lpo of olivine where the olivine 100 axis is subparallel to the shear direction the 010 plane subparallel to the shear plane type a however we identified three new types type b c and e of lpo of olivine depending on the water content and stress the type b lpo of olivine which was found at relatively high stress and or under moderate to high water content conditions is characterized by the olivine 001 axis subparallel to the shear direction the 010 plane subparallel to the shear plane the type c lpo which was found at low stress and under water rich conditions is characterized by the olivine 001 axis subparallel to the shear direction the 100 plane subparallel to the shear plane the type e lpo which was found under low stress and moderate water content is characterized by the olivine 100 axis subparallel to the shear direction the 001 plane subparallel to the shear plane observations by transmission electron microscopy tem and scanning electron microscopy sem show that the dislocations in water poor samples type a are curved and both b 100 and b 001 dislocations have a similar population numerous subgrains are seen in water poor samples in backscattered electron images in contrast water rich samples both type b and type c contain mostly b 001 dislocations and dislocations are straight and sub grain boundaries are rare compared to those in water poor samples these observations suggest that 1 dominant slip systems in olivine change with water fugacity and stress and 2 grain boundary migration is enhanced in the presence of water seismic anisotropy corresponding to the fabrics under water rich condition is significantly different from that under water poor condition consequently the relationship between seismic anisotropy and flow geometry in water rich regions is expected to be

subsurface imaging taiger experiments and tectonic models of taiwan abstract the seismicity deformation rates and associated erosion in the taiwan region clearly demonstrate that plate tectonic and orogenic activities are at a high level major geologic units can be neatly placed in the plate tectonic context albeit critical mapping in specific areas is still needed but the key processes involved in the building of the island remain under discussion of the two plates in the vicinity of taiwan the philippine sea plate psp is oceanic in its origin while the eurasian plate eup is comprised partly of the asian continental lithosphere and partly of the transitional lithosphere of the south china sea basin it is unanimously agreed that the collision of psp and eu is the cause of the taiwan orogeny but several models of the underlying geological processes have been proposed each with its own evolutionary history and implied subsurface tectonics taiger taiwan integrated geodynamics research crustal and mantle imaging experiments recently made possible a new round of testing and elucidation the new seismic tomography resolved structures under and offshore of taiwan to a depth of about 200 km in the upper mantle the steeply east dipping high velocity anomalies from southern to central taiwan are clear but only the extreme southern part is associated with seismicity toward the north the seismicity disappears the crustal root under the central range is strongly asymmetrical using 7 5 km s as a guide the steep west dipping face on the east stands in sharp contrast to a gradual east dipping face on the west a smaller root exists under the coastal range or slightly to the east of it between these two roots lies a well delineated high velocity rise spanning the length from hualien to taitung the 3 d variations in crustal and mantle structures parallel to the trend of the island are closely correlated with the plate tectonic framework of taiwan the crust is thickest in the central taiwan collision zone and although it thins toward the south the crust is over 30 km thick over the subduction in the south in northern taiwan the northward subducting psp collides with taiwan and the crust thins under northern taiwan where the subducting indenter reaches 50 km in depth the low vp vs ratio of around 1 6 at a mid crustal depth of 25 km in the central range indicates that current temperatures could exceed 700 c the remarkable thickening of the crust under the central range its rapid uplift without significant seismicity its deep exhumation and its thermal state contribute to make it the core of orogenic activities on taiwan island the expanded network during the taiger deployment captured broadband seismic data yielding enhanced s splitting results with mainly sks skks data the polarization directions of the fast s waves follow very closely the structural trends of the island supporting the concept of a vertically coherent taiwan orogeny in the outer few hundred kilometers of the earth

the effect of ash and needle cover on surface runoff and erosion in the immediate post fire period abstract hillslopes are thought to be most susceptible to enhanced surface runoff and erosion immediately following wildfire due to removal of protective vegetation and litter cover and in many cases a fire induced reduction in soil wettability this enhanced susceptibility declines as vegetation and litter layer recover for logistical reasons however few studies have been able to examine the responses of burnt terrain immediately following burning and little is therefore known about the effect of the wettable ash layer that often covers the ground until it is redistributed or removed by wind or water erosion here we quantify the effects of ash and needle cast ground cover on surface runoff generation and soil erodibility in the immediate post fire period 2 10 days following a severe wildfire in an aleppo pine forest over calcareous soils in mediterranean eastern spain a homogenous vegetation cover and lack of wind during the fire resulted in 100 ash cover 36 mm mean depth across the study area the ground fire did not consume the tree crowns but its high intensity caused complete tree mortality leading to subsequent needle fall hydrological and erosional responses were measured for fifteen 1 hour rainfall simulations 55 mm h 1 on 0 25 m2 circular plots for each of three terrain types i ash and needle covered ii ash only covered and iii bare furthermore ash and needle cast cover were monitored over an eleven week period on otherwise undisturbed terrain to examine its evolution during the first critical months following burning the soils exhibited no or slight post fire water repellency the overlying wettable ash layer had a porosity of 83 providing a water storage capacity of 30 mm a third of the plots with ground cover did not generate any surface runoff ash needle and ash only plots showed 25 and 18 fold reductions in surface runoff respectively compared to bare terrain mean sediment yield from covered plots was more than two orders of magnitudes lower than from bare plots the ash cover remained unchanged during the first two weeks while overlying needle cast more than doubled heavy rainfall 153 mm over a subsequent six day period removed the ash almost entirely where no needle cast was present whereas on ash and needle covered ground only a limited redistribution and accumulation into litter dams occurred the results quantify the potential importance of ash deposits on the susceptibility of hillslopes to surface runoff and erosion immediately following fire the combination of ash and needle cast appears particularly effective in reducing hillslope responses the outcomes demonstrate clearly that the widely held notion of landscapes being most susceptible to surface runoff and erosion directly after burning is not correct where a fire has resulted in substantial ash deposition instead the susceptibility will be greatest following a storm event of sufficient severity to remove this protective layer and before the onset of vegetation recovery

upper mantle anisotropy beneath japan from shear wave splitting in this study we utilize data from 64 broadband seismic stations of the japanese f net network to investigate the threedimensional pattern of anisotropy in the subduction system beneath japan we have compiled a database of approximately 1900 high quality splitting measurements selected by visual inspection of over 25 000 records of s sks and skks phases at f net stations covering a wide range of incidence angles incoming polarization angles and backazimuths analysis of the variations of measured splitting parameters with these parameters allows us to consider complexities in structure such as multiple anisotropic layers dipping symmetry axes and small scale lateral variations in anisotropic properties here we focus on the presentation of the splitting measurements themselves a detailed interpretation in terms of tectonics and mantle flow is beyond the scope of this paper in the southern part of the f net array along the ryukyu arc we find that fast directions are consistently trench parallel with splitting times of 1 s or more moving northward along the array the measured splitting patterns become more complicated with significant variations in apparent splitting parameters that indicate complex anisotropic structure additionally measured fast directions vary significantly over short length scales and stations separated by less than 100 km often exhibit very different splitting behavior this increase in complexity of anisotropic structure coincides geographically with the complicated slab morphology of the subducting pacific plate at stations on hokkaido to the north and kyushu to the south we see some evidence that the fast direction of anisotropy may rotate from trench parallel close to the trench to subduction parallel further away from the trench which may correspond either to a change in stress conditions and or volatile content or to a change in flow regime 2005 elsevier b v all rights reserved

water repellency and pore clogging at early successional stages of microbiotic crusts on inland dunes brandenburg ne germany abstract biological soil crusts play a key role for hydrological processes in many open landscapes they seal the topsoil and generate surface run off utilization of the mineral substrate at early stages of microbiotic crusts was investigated using scanning electron microscopy sem water repellency indices were measured using the ethanol water microinfiltrometer method and steady state water flow was determined on the dry crusts and after 300 600 1200 and 1800 s of wetting thus allowing to follow pore clogging through swelling of extracellular polymeric substances eps it was found that water repellency increases with initial crust development where filamentous cyanobacteria and filamentous green algae were dominating but decreases as coccal algae bryophytes and fungi associated with bryophytes emerged swelling of eps took place immediately after wetting and its influence on steady state water flow was most pronounced when filamentous cyanobacteria and algae partially filled in the matrix pores and enmeshed sand grains still leaving micropore channels available for free water infiltration but prior to appearance of coccal algae bryophytes and associated fungi which formed a dense cover on the surface it was concluded that a new phase of crust succession was accompanied by easier wettability but slower infiltration transition from hydrophobicity to pore clogging as ruling mechanisms causing water run off may occur during wetting of individual biological crusts but also during crust succession over time

a complex pattern of mantle flow in the lau backarc shear wave splitting analysis of local events recorded on land and on the ocean floor in the tonga arc and lau backarc indicate a complex pattern of azimuthal anisotropy that cannot be explained by mantle flow coupled to the downgoing plate these observations suggest that the direction of mantle flow rotates from convergence parallel in the fiji plateau to north south beneath the lau basin and arc parallel beneath the tonga arc these results correlate with helium isotopes that map mantle flow of the samoan plume into the lau basin through an opening tear in the pacific plate

tidal motions in the florida current abstract a linear relationship exists between sea level and the north component of the depth averaged tidal velocity in the straits of florida this relationship is used as a one dimensional model to predict barotropic tidal currents across the straits near 27 n predictions are independent of the choice of a sea level reference site between key west and patrick air force base the model when compared with three sets of depth averaged velocity obtained from current profilers can account for at least 70 of the variance in the diurnal and semidiurnal tidal bands the predicted diurnal tidal current is dominant and can account for more than 80 of the predicted tidal energy twice a year the one dimensional model yields a maximum amplitude of 12 cm s 1 3 5 cm s 1 rms this corresponds to a tidal transport of 5 1 106 m3 s 1 1 5 106 m3 s 1 5 1 sv

shear wave splitting from local events beneath the ryukyu arc trench parallel anisotropy in the mantle wedge we present shear wave splitting measurements from local slab earthquakes at eight seismic stations of the japanese f net array located in the ryukyu arc we obtained high quality splitting measurements for 70 event station pairs and found that the majority of the measured fast directions were parallel to the strike of the trench and perpendicular to the convergence direction splitting times for individual measurements ranged from 0 25 to 2 s most values were between 0 75 and 1 25 s both the fast directions and the split times were similar to results for teleseismic s k ks and s wave splitting at the same stations which suggests that the anisotropy is located in the mantle wedge above the slab we considered several mantle deformation scenarios that would result in predominantly trench parallel fast directions and concluded that for the ryukyu subduction system the most likely explanation for the observations is corner flow in the mantle wedge combined with b type olivine fabric in this model the flow direction in the wedge is perpendicular to the trench but the fast axes of olivine crystals tend to align perpendicular to the flow direction resulting in trench parallel shear wave splitting

ant mounds as a source of sediment on citrus orchard plantations in eastern spain a three scale rainfall simulation approach abstract ants are widely found in mediterranean soils where they increase water infiltration rates by forming soil macropores during nest construction while higher water infiltration usually results in lower soil erosion rates new soil brought to the surface by ant activity could increase sediments available for erosion this could be especially important in intensively managed citrus orchards where surface mineral soil is exposed due to the lack of vegetation cover as a consequence of herbicide treatments in the summer of 2009 rainfall simulations of low frequency high intensity rainstorms were conducted in an orange orchard in eastern spain on plots that contained ant nests and adjacent paired plots without ant nests since soil erosion is a scale dependent process we used three plot sizes 0 25 m 2 1 m 2 and 12 m 2 to determine the effect of ant burrowing and nesting on soil and water losses ant nests decreased water losses from 22 5 at 0 25 m 2 to 10 6 at 12 m 2 but soil erosion rates were nearly double in areas with ant activity 0 56 to 0 59 mg ha 1 h 1 as compared to soil with no ants 0 31 to 0 36 mg ha 1 h 1 our results indicate that the presence of ants can increase soil erosion when rainfall intensity is greater than the infiltration capacity of the ant macropores

crustal deformation in the central and southern ryukyu arc estimated from gps data abstract deformation of the ryukyu arc in the period 1999 2001 was investigated on the basis of gps data for horizontal velocity the results show that deformation of the ryukyu arc is divided into three tectonic blocks with all counter clockwise rotation rates of between 18 and 195 nrad yr extensional strain along the ryukyu arc is observed in all three blocks being largest in the southwestern ryukyu arc this suggests that southward bending of the arc occurs in the southwest associated with the arc continent collision in taiwan resulting in clockwise block rotation of the taiwan ryukyu junction thus bending of the ryukyu arc appears to be caused by collision of the luzon arc with the eurasian plate and is likely to contribute to rifting of the okinawa trough

trench parallel flow in the southern ryukyu subduction system effects of progressive rifting of the overriding plate 1 the okinawa trough in the ryukyu subduction system is one of a few actively extending back arc basins within the continental lithosphere recent shear wave splitting measurements show variable fast directions along the trough suggesting a complex three dimensional mantle flow field in this study we use numerical subduction models to demonstrate that the thickness variations of the continental lithosphere bounding the edge of a subduction zone can result in complicated mantle circulation and regional dynamics the model results for the southern ryukyu show a combination of two effects along the okinawa trough the increasing thickness of the overriding eurasian plate toward taiwan due to a gradually diminishing rifting induces pressure gradients that drive trench parallel flow to the edge in the shallow portion of the mantle wedge and the thick eurasian lithosphere to the west effectively blocks and diverts this along arc flow and limits the toroidal flow around the slab edge below it the toroidal flow thus enters the mantle wedge at depths of more than about 100 km opposite in direction with and largely below the along arc flow these combined geometry effects of the eurasian lithosphere create an intricate three dimensional flow structure at the southern edge of the ryukyu subduction zone model predictions for lattice preferred orientations of olivine aggregates show rotation patterns that agree with the observed shear wave splitting patterns this three dimensional scenario echoes the geochemical and seismological evidence worldwide that indicates complex depth varying mantle circulations in subduction systems

on the accuracy of hf radar surface current measurements intercomparisons with ship based sensors high frequency hf radar systems can provide periodic two dimensional vector current estimates over an area approaching 1000 km as the use of these hf systems has gained wider acceptance a number of attempts have been made to estimate the accuracy of such systems however comparisons of hf radar current estimates with in situ sensors are difficult to interpret since hf systems measure currents averaged over an area of 1 km 2 and to a depth of only 50 cm while in situ sensors measure currents at a point and somewhat greater depths 1 to 10 m previous studies of the accuracy of hf radar technology have thus attributed the differences observed between hf radar and in situ sensors to an unknown combination of vertical shear horizontal inhomogeneity in situ instrument errors and hf radar system errors this study examines the accuracy of hf radar current measurements using data from the 1993 high resolution remote sensing experiment conducted off cape hatteras north carolina data from four shipborne in situ current meters are compared with data from an ocean surface current radar oscr a commercial current measuring radar we attempt to discern the predominant sources of error in these data by using multiple simultaneous measurements from different sensors and by examining the variation of observed current differences as a function of location the results suggest an upper bound on the accuracy of the oscr derived radial currents of 7 to 8 cm s the measurement of near surface currents in the coastal environ ment is an important problem

anisotropy in the oceanic lithosphere from the study of local intraplate earthquakes on the west flank of the southern east pacific rise shear wave splitting and waveform modeling shear wave splitting is observed on ocean bottom seismometer records from local intraplate microearthquakes on the west flank of the east pacific rise at 18 s split times reach a maximum of about 0 2 s for most of the incoming waves with long mantle paths 20 km the polarization direction of the fast arrival is subparallel to the spreading direction which we attribute to anisotropy caused by the strain induced preferential orientation of olivine in contrast for some records with short paths or shallower sources or propagation along the spreading direction the fast direction is nearly parallel to the ridge axis these polarizations are probably caused by seismic anisotropy from aligned cracks in the uppermost crust in addition for some events the apparent splitting is frequency dependent to explore the pattern of shear wave splitting that would be expected for nonvertical paths in an oceanic lithosphere with two distinct anisotropic layers we generate synthetic seismograms for a variety of source depths and mechanisms we employ a multidomain pseudospectral method to simulate the elastic wave fields from point sources in an inhomogeneous anisotropic medium splitting parameters measured from synthetic s waves demonstrate that the apparent fast direction is not always parallel to the symmetry axes and that in some cases fast directions at higher frequencies will be more characteristic of the shallower crustal anisotropy while fast directions at lower frequencies are dominated by the mantle portion of the path most of the observed characteristics of splitting can be reproduced if there is approximately 8 s wave anisotropy in the mantle and an average of about 6 s wave anisotropy in the upper crustal seismic layer 2

tomography of the westernmost ryukyu subduction zone and the serpentinization of the fore arc mantle 1 three dimensional tomographic images of the subducting philippine sea slab and the fore arc mantle beneath ne taiwan and the westernmost ryukyu were generated in this study more than 5600 events recorded simultaneously by seismic networks in taiwan and japan were relocated for the inversion for variations in vp vs and vp vs analysis of the trade off between the data variance reduction and model variance helps to determine the appropriate strictness for regularization to avoid either overinterpretatioin or underinterpretation of data the regularization parameters were also chosen to ensure suppression of artificial vp vs anomalies the subducting slab is characterized by high vp high vs and intermediate to low vp vs notable in the mantle wedge is the high vp vs anomalies that abut the surface of the subducting slab at depths of 30 80 km the previously identified positive vp vs channel connecting the slab and the arc volcano interpreted to be a melt pathway is not reproduced in this study we convert vs and vp vs to perturbations of temperature and serpentinization of the mantle the slab is cooled by 200 c 400 c relative to the mantle in accord with the estimates from theoretical modeling of subduction the serpentinization reaches 15 or 2 water content at 50 km depth in the fore arc mantle we interpret the peak serpentinization as hydrated by the water released from the basalt eclogite metamorphic reaction in the oceanic crust of the subducting philippine sea plate the spatial limitation of the present seismic networks in this region with respect to subduction zone events hinders a full description of the pattern of melting in much of the mantle wedge resolution tests of the tomographic inversion provide a basis to guide our interpretation to better resolved regions

the fine structure of nearshore tidal and residual circulations revealed by h f radar surface current measurements abstract using the ocean surface current radar oscr developed by the rutherford appleton laboratory uk 30 days of synoptic hourly surface current vectors were obtained for 84 locations within a nearshore region some 18 kms square tidal analyses of these data show that the currents associated with the predominant m2 constituent sweep smoothly and regularly through the area unaffected by the finer topographic features moreover contours of the amplitude of the m2 semi major axis are mutually consistent to a precision of better than 0 5 cm s 1 statistical analyses of these data indicate that the standard error of oscr current measurements is less than 4 cm s 1 by contrast the major higher harmonic constituent m4 shows pronounced but ordered spatial variability relating the observed distributions for m4 and m2 is foreseen as an instructive modeling problem that should advance our knowledge of shallow water tidal interaction processes standard relationships between residual surface currents and

patterns in seismic anisotropy driven by rollback subduction beneath the high lava plains received 24 march 2011 revised 25 may 2011 accepted 31 may 2011 published 8 july 2011 1 we present three dimensional laboratory modeling of the evolution of finite strain and compare these to shear wave splitting observations in the northwest u s under the high lava plains hlp we show that relationships between mantle flow and anisotropy are complicated in subduction zones and factors such as initial orientation of the olivine fast axis style of subduction and time evolving flow are important due to increased horizontal shear systems with a component of rollback subduction have simple trench normal strain alignment within the central region of the backarc mantle wedge while those with more simple longitudinal sinking are often variable and complex in the hlp splitting observations are consistent with rollback driven laboratory results citation druken k a m d long and c kincaid 2011 patterns in seismic anisotropy driven by rollback subduction beneath the high lava plains geophys res lett 38 l13310 doi 10 1029 2011gl047541

seismic anisotropy reveals focused mantle flow around the calabrian slab southern italy 1 sks splitting at the calabrian subduction zone with delay times t up to 3s reveals the presence of a strong anisotropic fabric fast directions are oriented nne ssw in the calabrian arc c a and rotate nnw sse to the north following the arcuate shape of the subducting plate we interpret the trench parallel as local scale mantle flow driven by the retrograde motion of the slab the absence of trench perpendicular below the southern apennines s a excludes the presence of a seismically detectable return flow at its ne edge this may be due to the relative youth and limited width of the s a slab tear a possible return flow is identified farther north at the boundary of the s a and central apennines different and weaker anisotropy is present below the apulian platform a p this implies that the influence of the slab rollback in the sub slab mantle is limited to less then 100 km from the slab

soil hydrophobicity effects on rainsplash simulated rainfall and photographic evidence laboratory rainfall simulation experiments indicate greater splash losses for hydrophobic water repellent than for wettable sandy loam soils at different rainfall intensities durations and soil surface inclinations using synchronized video cameras with different shutter speeds and stroboscopically illuminated 35 mm still photography differences in splash droplets and ejection trajectory characteristics are examined for hydrophobic soil raindrop impact gives rise to fewer larger slower moving daughter ejection droplets which carry more sediment and hence follow shorter range trajectories compared with wettable soil implications for erosion of hydrophobic soils are discussed

effects of low frequency current variability on near inertial submesoscale vortices from september 30 to october 14 1993 and from may 18 to june 13 1994 ocean surface currents along the inshore boundary of the florida current were measured using a land based ocean surface current radar oscr deployed along the florida keys a dual station oscr mapped the current fields at 20 min intervals with a horizontal resolution of 1 2 km over a 30 44 km domain using the high frequency hf 25 4 mhz mode an upward looking narrowband acoustic doppler current profiler adcp was moored in 150 m of water seaward of the shelf break concurrently sampling the three dimensional current vector between 15 and 130 m at 30 min intervals regression analyses between surface and subsurface currents at 15 m depth from the adcp indicated biases of 3 12 cm s 1 and slopes of o 0 8 1 root mean square differences were about 18 cm s 1 because of a 15 m depth separation between the two measurements and bulk current shears were o 10 3 s 1 in the florida current where maximum velocities exceeded 150 cm s 1 between 40 and 70 m surface tidal currents were 2 10 cm s 1 in the diurnal and semidiurnal bands and revealed fine scale variability in the tidal ellipses due to topographical variations differences in the tidal current amplitudes between the surface and 15 m ranged from 1 to 3 cm s 1 in these constituents and explained more of the current variance with depth during the second experiment a submesoscale surface feature was detected along the shelf break and progressed eastward at a rate of about 30 cm s 1 this feature was embedded in the near inertial wave band where the local inertial period was 29 hours that may have been forced by an abrupt change in the wind direction this transient feature was trapped and advected along the inshore edge of the florida current where the anticyclonic vorticity of the subinertial flow shifted the frequency of the nearinertial motions by a few percent of f these energetic near inertial currents of 15 20 cm s 1 had horizontal and vertical wavelengths of 40 km and 50 100 m respectively

two station measurement of rayleigh wave phase velocities for the huatung basin the westernmost philippine sea with obs implications for regional tectonics summary a broad band ocean bottom seismometer obs deployed 180 km east of taiwan provides a first glimpse into the upper mantle beneath the westernmost section of the philippine sea or the huatung basin hb we measured interstation phase velocities of rayleigh waves between the obs and stations on the eastern coast of taiwan the phase velocities show smooth variations from 3 8 to 3 9 km s 1 for periods of 25 40 s in this short period range phase velocities are comparable to those characterizing the 15 30 ma parece vela basin of the philippine sea modelling of the finite frequency effect proves the validity of the measurement for the average hb the shear wave velocity models inverted from the 25 to 40 s dispersion show a velocity at lithospheric depths about 0 1 km s 1 lower than that of the west philippine sea which agrees with the age effect derived from the pacific pure path model inversions incorporating the less reliable data above 40 s yield a shear velocity 4 0 km s 1 below 150 km an unrealistic value even for a hotspot plume environment the seismological evidence together with the correlation in seafloor depth suggests that the hb and the parece vela basin may have a similar age this is at odds with the previous geochronological study suggesting an early cretaceous age for the hb thermal rejuvenation of the lithosphere was examined as a potential solution to reconciling the two age models

the influence of plate motions on three dimensional back arc mantle flow and shear wave splitting both the polarization direction of the fast shear waves and the types of deformation within overriding plates vary between the back arc basins of western pacific subduction zones the goal of this study is to test the possibility that motions of the overriding plates may control the patterns of seismic anisotropy and therefore the observed shear wave splitting we calculated three dimensional models of viscous asthenospheric flow driven by the motions of the subducting slab and overriding plates shear wave splitting was calculated for polymineralic anisotropy within the back arc mantle wedge assuming that the anisotropy was created by flow induced strain predicted splitting may differ substantially depending on whether anisotropy is computed directly using polycrystalline plasticity models or is based on the orientation of finite strain a parameter study shows that both finite strain and textural anisotropy developed within three dimensional plate coupled asthenospheric flow models are very heterogeneous when back arc shearing occurs within the overriding plate therefore predicted shear wave splitting varies strongly as a function of plate motion boundary conditions and with ray path through the back arc asthenosphere flow models incorporating plate motion boundary conditions for the tonga southern kuril and eastern aleutian subduction zones produce splitting parameters consistent with observations from each region trench parallel flow generated by small variations in the dip of the subducting plate may be important in explaining observed fast directions of anisotropy sampled within the innermost corner of the mantle wedge

trench parallel flow and seismic anisotropy in the mariana and andean subduction systems shear wave splitting measurements above the mantle wedge of the mariana1 and southern andean2 3 subduction zones show trench parallel seismically fast directions close to the trench and abrupt rotations to trench perpendicular anisotropy in the back arc these patterns of seismic anisotropy may be caused by three dimensional flow associated with along strike variations in slab geometry1 2 3 4 5 the mariana and andean subduction systems are associated with the largest along strike variations of slab geometry observed on earth6 7 and are ideal for testing the link between slab geometry and solid state creep processes in the mantle here we show with fully three dimensional non newtonian subduction zone models that the strong curvature of the mariana slab and the transition to shallow slab dip in the southern andes give rise to strong trench parallel stretching in the warm arc and warm back arc mantle and to abrupt rotations in stretching directions that are accompanied by strong trench parallel stretching these models show that the patterns of shear wave splitting observed in the mariana and southern andean systems may be caused by significant three dimensional flow induced by along strike variations in slab geometry

shear wave splitting above the subducting juan de fuca plate shear wave splitting observed in three component broadband recordings of local earthquakes near southern vancouver island british columbia provide the first constraints on shear wave anisotropy in the continental crust above the subducting juan de fuca plate waveforms of 22 shallow earthquakes 15 30 km depth and 16 deep earthquakes 40 60 km depth were examined for shear wave splitting the fast polarization direction is well defined at 312 19 for the deep earthquakes and 293 27 for the shallow earthquakes these fast polarization directions are approximately parallel to the continental margin and coincide with the orientation of the pressure axes of small crustal earthquakes in this region interpreting this polarization pattern in terms of the extensive dilatancy anisotropy model indicates a margin parallel compressive stress regime comparing the average time delays between the fast and slow shear waves for the deep earthquakes 0 32 s and the shallow earthquakes 0 20 s suggests that the source of the seismic anisotropy is stronger in the upper 20 km of the continental crust here the average differential shear wave anisotropy is estimated at 2 3 these observations support the theory of weak coupling between the downgoing juan de fuca plate and the overlying north america plate as the principal stress is perpendicular to the direction of subduction and the s wave splitting above the subducting plate is nearly perpendicular to the sks splitting direction in the upper mantle beneath the subducting plate

split s waveforms observed in northern taiwan implications for crustal anisotropy short period stations ent and nsk in northern taiwan have frequently recorded split s waveforms from earthquakes in the underlying subduction zone to determine splitting parameters together with objective straightforward error estimations we employ a waveform cross correlation method the error for each measurement is estimated by translating the lower limit of the 95 confidence interval of the cross correlation coefficient into azimuth and time only measurements with 95 confidence regions excluding zero delay time are accepted as splitting data we also use an energy minimization method to constrain the solutions with minor splitting we interpret the splitting as caused by stress aligned cracks in the upper crust the average delay times are 0 03 0 04 s for ent and 0 07 s for nsk the fast directions at the two stations are predominantly n s which roughly match the stress trajectories predicted by a model simulating the arc continent collision in the taiwan area however at ent there is a subset of data with fast directions oriented in roughly e w the nearly 90 rotation of the inferred crack orientation occurs in a horizontal distance of 10 15 km in the upper crust both the predicted heterogeneous stress regime and the local structural setting in northeastern taiwan favor a lateral variation with a similar length scale

mantle anisotropy beneath northwest pacific subduction zones to assess the location strength and orientation of seismic anisotropy in the southern kuril japan and izu bonin subduction zones we analyzed shear wave splitting in local s phases and teleseismic sks phases fast directions from these phases are roughly parallel to the direction of absolute pacific plate motion wnw in izu bonin roughly parallel to the strike of the trench nne in central honshu and roughly n in the southern kuril back arc in the vicinity of sakhalin island assuming that the orientation and strength of anisotropy does not vary with depth modeling of splitting times from local s and teleseismic phases recorded at sakhalin island requires that the maximum depth of anisotropy lies between 480 km and 950 km in contrast splitting times for local s phases from events in izu bonin rule out anisotropy in the transition zone all the data are consistent with a model in which the lower transition zone 520 660 km and lower mantle are largely isotropic and in which anisotropy occurs intermittently in the upper transition zone 410 520 km possibly due to preferred orientation of spinel assuming that splitting in the upper mantle is produced by preferred orientation of olivine the observed fast directions indicate that the geometry of back arc strain varies systematically between subduction zones the relationship of fast directions and plate motions suggests that the subducting slab exerts significant control on back arc flow but that flow correlated with upper plate deformation must also exist

the southwestern edge of the ryukyu subduction zone a high q mantle wedge abstract the lateral edge of a subduction zone is usually depicted as an opening to the asthenosphere where invigorated dynamics and amplified magmatism take place in this study we present evidence from seismic data suggesting the presence of a cold and dynamically sluggish edge environment at the southwest end of the ryukyu subduction system we measured attenuation or 1 q for p waves from subduction zone events at 100 km depths received by obss in the okinawa trough and land stations in ne taiwan in the okinawa trough 100 200 km from the edge q values are lower than 100 in the vicinity of the edge q values increase from 100 to over 1000 towards taiwan to reconcile arguments from geophysical and geochemical observations we propose that the mantle wedge near the edge has high q values due to low temperatures and probably low water content these may result from coupling of the slab laterally with the thick eurasian lithosphere which inhibits back arc rifting retards subduction and reduces the water supply to the mantle wedge the sw ryukyu subduction system represents a subduction zone edge type distinct from more commonly documented free or warm edges

can terra rossa become water repellent by burning a laboratory approach abstract fire usually induces water repellency wr in soils reduction in infiltration rates increase of runoff and erosion are some of the consequences of wr in fire affected soils most forest soils can develop wr by burning however some previous observations in burned terra rossa soils have shown little changes in wr laboratory controlled experiments have been done with samples of terra rossa from 14 different sites the objectives are to confirm whether the observed is a common behaviour of terra rossa and to explore the factors controlling the wettability of this soil type after burning samples from the upper 2 5 cm of terra rossa were collected from 12 forest sites of the alicante province spain and from 2 sites in the mt carmel haifa israel with similar environmental conditions laboratory burning of samples at 250 c 300 c and 350 c was performed with and without the addition of litter of pinus halepensis the results confirm that all soils have a very low susceptibility to become water repellent by burning without the addition of litter wr was not detected in any soil sample at any temperature of burning with the addition of litter wr was present only in six of the soils after some of the heating treatments although all soils had enough soil organic matter som to develop wr by heating the ratio between som and clay content was considerably lower compared to other types of forest soils of the region in which wr has been found after forest fires this could explain in part the lower susceptibility of terra rossa to become water repellent by burning since as some authors have indicated fine textured soils are less prone to develop soil wr due to their high specific surface area from mineralogical analysis of the clay fraction we found that the dominant clay types in the studied terra rossa were kaolinite and illite with the exception of one soil where ca montmorillonite content is higher than kaolinite and illite ca montmorillonite was present in only three of the soils comparing the soil properties between the group of terra rossa that in no case become water repellent wettables with the group that in some cases developed wr potentially water repellents some differences were found the kaolinite content is higher in the wettables group p vs kaolinite contents the kaolinite content being the main factor contributing to this separation these results are in agreement with those obtained in experiments with clay additions to water repellent soils in order to reduce the wr and also with some studies which found that kaolinite is one of the most effective clay minerals for this purpose

shear wave anisotropy beneath the taiwan orogen abstract shear wave splitting in regional and teleseismic shear waves scs and s has been analyzed for fast polarization directions and delay times at 33 short period and 17 broad band permanent and temporary seismic stations in the taiwan region the orientations of anisotropy for the taiwan stations are generally parallel to the strike of the mountain belt with a clockwise rotation following the trend of regional geologic fabric in north taiwan the delay times on the other hand vary greatly from 0 5 to 2 1 s the largest values are from the southwestern taiwan foothills and an abrupt change in delay times is found in south taiwan the main source of shear wave splitting in taiwan is compatible with an anisotropic region between 25 and 230 km depths the observed splitting parameters are consistent with upper mantle anisotropy resulting from the collisional tectonics that built the taiwan orogen

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