radial upper mantle attenuation structure of inactive back arc basins from differential shear wave measurements we measure differential attenuation between ss s and sscs scs phase pairs to characterize the variation of attenuation with depth in the upper mantle of five inactive back arc basins the kuril basin sea of japan banda sea the celebes and sulu seas and the shikoku basin a spectral ratio technique is used to measure the differential attenuation operator of the transversely polarized waveforms over a frequency band of 10 to 83 mhz two algorithms are employed to compute the vertically averaged attenuation structure a spectral stacking procedure and a least squares inversion in the spectral stacking method the individual spectra are corrected for the elastic structure at the ss or sscs bounce point and the differential attenuation operator is computed by spectral division the attenuation operators are then normalized and stacked by source depth to obtain more stable spectra and an average t for sources within a restricted depth range is obtained from the slope of the log amplitude spectrum a model for the depth dependent q structure is then calculated from the t measurements assuming q is frequency independent alternatively t measurements for individual phase pairs are made using a similar technique and analyzed by ray tracing and a least squares inversion to obtain the q 1 estimates the q results obtained from the stacking and inversion methods are generally in good agreement the q 1 structures for the various back arc regions are similar to each other within the uncertainties of the derived q models in addition to computing q models for each individual region we partitioned the data into three tectonic provinces based upon bounce point locations the resulting average radial q structure for an inactive basin shows a q of 54 in the uppermost mantle 115 at intermediate depths and 173 in the transition zone we also find a low q zone of 36 beneath active island arcs the q values for inactive back arc basins are lower than the global averages derived from normal modes but are generally consistent with previous body and surface wave studies of other young oceanic regions the most striking feature of this study is the observation of very strong attenuation concentrated at shallow depths 160 km in the upper mantle beneath these basins

twin active spreading ridges in the north fiji basin southwest pacific recent work on the north fiji basin axial spreading ridge and on the active propagating ridge located west of the fiji islands has established the existence of two active spreading ridges that have been functioning synchronously in the basin since at least 1 or 1 5 ma this hypothesis is tested and the kinematics of the twin active ridges are refined further on the basis of analysis of bathymetric and magnetic data

seismic tomography a window into deep earth abstract the goal of this paper is to provide an overview of the current state of the art in seismic tomography and trace its origins from pioneering work in the early 1970s to its present status as the pre eminent tool for imaging the earth s interior at a variety of scales due to length limitations we cannot hope to cover every aspect of this diverse topic or include mathematical derivations of the underlying principles rather we will provide a largely descriptive coverage of the methodology that is targeted at readers not intimately familiar with the topic the relative merits of local versus global parameterization ray tracing versus wavefront tracking backprojection versus gradient based inversion and synthetic testing versus model covariance are explored a variety of key application areas are also discussed including body wave traveltime tomography surface wave tomography attenuation tomography and ambient noise tomography established and emerging trends many of which are driven by the ongoing rapid increases in available computing power will also be examined including finite frequency tomography full waveform tomography and joint tomography using multiple datasets several practical applications of seismic tomography including body wave traveltime attenuation and surface waveform are presented in order to reinforce prior discussion of theory

sediment activation depth values for gentle and steep beaches abstract this paper analyzes methods and terminologies used in literature for the determination and characterization of vertical distribution of sediment activation depth which is bottom sediment layer affected by hydrodynamic processes studies on this topic include assessments carried out during short time spans from minutes to few hours or longer periods from a tidal cycle to several days in the first case activation is generally named mixing depth and is calculated by evaluating vertical distribution of fluorescent tracers in the second case it is referred to as disturbance depth and is generally evaluated using plugs of marked sand and rods or rods with a loose fitting washer vertical cross and longshore distribution of mixing and disturbance depth values recorded in different works with different techniques were also analyzed highlighting the conceptual differences between used methods and obtained results in a further step a data set from literature on this topic was gathered to obtain new formulations between disturbance depth and beach and wave characteristics as well as morphodynamic beach state expressed throughout the surf scaling parameter and the surf similarity index good linear regressions were observed between these variables obtaining expressions that can be easily used in a wide range of beach states from dissipative and intermediate to reflective ones

seismic anisotropy beneath the lau back arc basin inferred from sscs scs splitting data we determine upper mantle anisotropy just beneath active basins by comparing scs and sscs waveform splitting we have measured sscs scs shear wave splitting with data from the spanet and gsn seismic networks the observed sscs scs shear wave splitting suggests that there is a large lateral variation of anisotropy beneath the lau back arc basin scs and sscs waves which sample the southern part of the lau basin show small splitting in contrast the northern part of the lau basin which is characterized to be tectonically active is observed to have large seismic anisotropy with a wnw ese direction the cause of anisotropy may be related to the mantle dynamics of the active basin

radial qμ structure of the lower mantle from teleseismic body wave spectra abstract we have measured 150 000 p and 130 000 s wave spectral ratios up to 0 8 hz using recordings of 250 deep focal depth 200 km earthquakes from 890 global and regional network stations we have inverted these data to estimate the attenuation parameters t p and t s for p and s waves and a radial profile of the quality factor q for the lower mantle on average t p increases by about 0 2 s and t s increases by about 0 7 s between epicentral distances of 30 and 97 the relatively strong increase of t s t s 4t p suggests that intrinsic shear attenuation is the cause of the overall trend in our data the increase of t p and t s with distance is smaller than predicted by models prem 12 ql6 11 and qlm9 16 assuming prem values for q in the upper mantle where the data lack resolving power the p and s wave spectra are explained best if q increases from about 360 at prem s 670 km discontinuity to 670 in the lowermost mantle the high values for q can be reconciled with previously determined values by invoking a frequency dependence of q that is proportional to 0 1 data that are separated in pacific and circum pacific subsets have slightly different trends estimates of t p and t s for the pacific data which sample the large low shear velocity province of the pacific are higher than the circum pacific estimates thus it appears that the pacific large low shear velocity province has accompanying low q the difference in q in the lowermost 1000 km of the mantle beneath the pacific and beneath the circum pacific is at most 17 lateral variations of this magnitude are marginally resolvable given the uncertainties of our measurements

propagating rift west of the fiji archipelago north fiji basin sw pacific a sea beam survey of an area located west of the fiji islands in the north fiji basin between 17 10 s and 18 s and 175 40 e and 176 40 e shows a complex structure characterized by two deep grabens bounding a central plateau in previous papers we interpreted this area as an intraoceanic strike slip deformation zone rejecting the possibility of oceanic spreading in the area by comparison with the structures observed in the galapagos 95 5 w area we now reinterpret the area as a southward propagating spreading system the analysis of structural and magnetic data and earthquake focal mechanisms confirms this new interpretation the full spreading rate for the north fiji basin ridge deduced from magnetic lineations varies from 50 to 80 mm yr for the west fiji spreading ridge the magnetic anomaly analysis gives a spreading rate of about 50 mm yr for the northern segment and slightly slower 40 mm yr for the southeastern segment using a 50 mm yr spreading rate the angles between the pseudofaults allow us to calculate the propagation velocity for an angle of 75 north of 17 35 s the propagation velocity is 33 mm yr the tip of the propagator is characterized by a 20 angle between the pseudofaults which implies a recent increase of propagation velocity to 141 mm yr the initiation of this propagation could be related to the emplacement of the north fiji fracture zone 1 to 1 5 m y ago resulting in the formation of the 16 50 s triple junction the main kinematic implication of the existence of a propagating rift west of the fiji islands is that in the north fiji basin the present day accretion is distributed on two parallel active spreading ridges one in the central part of the basin the other one in its southeastern quadrant such a phenomenon unusual on mid oceanic ridges except for microplates such as galapagos easter and juan fernandez may be more common in marginal basins because of their peculiar geodynamic setting

longshore variability of beach states and bar types in a microtidal storm influenced low energy environment beach classification models are widely used in the literature to describe beach states in response to environmental conditions these models were essentially developed for sandy barred to barless beaches in micro to mesotidal environments subject to moderate to high wave energy conditions and have been based on field studies over limited stretches of coast here we further interrogate the performance of the australian beach classification scheme by analysing beach states and corresponding bar types on a regional scale in a storm influenced low wave energy microtidal environment using a large and unique spatial and temporal dataset of supra and subtidal beach morphology and sedimentology the 200 km long coast of the gulf of lions in themediterranean consists of quasi continuous sandy beaches with a well developed double sandbar system all the reported classical beach stateswere observed on this coast from reflective to dissipative alongwith two more unusual states the rock platform constrained beach state which is associated with bedrock outcrops and the non barred dissipative beach statewhich ismore commonly found in large tidal range settings lidar bathymetry shows that the transitions between beach state zones are marked mainly headlands but transitions also occur progressively along stretches of continuous sandy beach the longshore distribution of beach states and associated bar types on a regional scale can be related to the variability of hydrodynamic conditions wave incidence and energy and sediment characteristics particle size however the influence of these parameters on beach state seems to be largely controlled by the geological context such as the presence of a river mouth headland or rock platform finally we assessed the ability of the parameter commonly used to characterise beach states which combines wave characteristics and sediment fall velocity to predict the observed beach states and bar types using a very large set of hydrodynamic and sedimentary data our results based on high frequency spatial sampling show that the fall velocity of the subtidal sediment coupled with wave statistics one month prior the observed beach state strongly improved the predictive power of the parameter

differential shear wave attenuation and its lateral variation in the north atlantic region because the attenuation of seismic waves is sensitive to variations in temperature and to partial melting mapping seismic q in the upper mantle is an important tool for assessing the processes responsible for lateral heterogeneity utilizing a digital data base of over 150 seismograms and a spectral ratio technique we have measured ss s differential attenuation in the north atlantic region differential attenuation is positively correlated with ss s travel time residual and both differential attenuation and travel time residual decrease with increasing seafloor age in an earlier paper we showed that the age dependence of ss s travel time residual can be explaned entirely by the cooling of the oceanic lithosphere i e contributions from the asthenosphere or from a mantle melt fraction are not required the assumption that plate cooling also dominates the variation of differential attenuation with age permits the derivation of an empirical relation between q 1 and temperature for the oceanic thermal lithosphere i e the depth interval 0 125 km however both the absolute values and the depth distribution of q we obtain under this assumption are at variance with the results of surface wave attenuation studies and the variation of q 1 with temperature that we derive is not as strongly dependent on temperature as indicated by some laboratory measurements we therefore develop models for q in which lateral variations include contributions from the asthenospheric low q zone as well as from lithospheric cooling the q models obtained under this alternative assumption are in good agreement with those obtained from surface wave studies and are therefore preferred over those models with lateral variations confined to the upper 125 km systematic long wavelength 1000 7000 km variations in differential attenuation corrected for seafloor age are evident along the axis of the mid atlantic ridge these variations can be qualitatively correlated with long wavelength variations in ss s differential travel time residuals and are attributed to along axis differences in upper mantle temperature

anelastic structure of the upper mantle beneath the northern philippine sea we investigated the upper mantle anelastic structure beneath the northern philippine sea region including the izu bonin subduction zone and the shikoku basin we used regional waveform data from 69 events in the pacific and the philippine sea slabs recorded on f net and j array network broadband stations in western japan using the s p phase pair method we obtained differential attenuation factors t which represent the relative whole path q we conducted a tomographic inversion using 978 t values to invert for a fine scale 50 100 km three dimensional anelastic structure the results shows two high q regions qp 1000 which are consistent with the locations of the pacific and the philippine sea slabs also there is a low q qp 110 area extending to the deeper parts 350 400 km of the model just beneath the old spreading center and the kinan seamount chain in the shikoku basin a small depth dependence of the laterally averaged qp was found with values of 266 0 250 km 301 250 400 km and 413 400 500 km 2003 elsevier b v all rights reserved

divergent response of an intertidal swash bar this paper examines the processes responsible for the morphodynamics of an intertidal swash bar at skallingen denmark during seven successive storms one with a large surge of 3 02 m dnn during this period a subtidal bar migrated landward onto the foreshore and continued to migrate across the intertidal zone as a swash bar the onshore migration of the inner subtidal bar resulted from the erosion of sediment from the upper foreshore and dune ramp during the large storm surge that was transported seaward causing the landward displacement of the bar through accretion on the landward slope the magnitude and direction of suspended sediment transport within the intertidal zone and more specifically at and close to the crest of the swash bar varied with the ratio of both the significant hs and average havg wave heights to the water depth hcr at the swash bar crest the local depth minimum the transition between onshore and offshore suspended sediment transport was associated with the average wave of the incident distribution breaking on the swash bar crest havgh 0 33 while the onshore directed transport was largest at infragravity frequencies sediment resuspension was best explained by the skewed accelerations under the surf bores offshore transport was dominated by the cross shore mean currents undertow that developed when the significant wave of the distribution broke on the swash bar crest hsh 0 33 and weakened as the average wave of the distribution started to break at the crest havgh 0 33 and the surf zone approached saturation in contrast to subtidal bars the swash bar at skallingen exhibited a divergent behaviour with respect to the cross shore position of the breaker zone migrating onshore when the average wave broke seaward of the crest and migrating offshore when the average wave broke landward of the crest copyright 2006 john wiley sons ltd

morpho sedimentary dynamics of a micro tidal mixed sand and gravel beach playa granada southern spain abstract this paper addresses the changes in the morphology and sedimentology of a micro tidal mixed sand and gravel beach playa granada southern spain forced by wave and water level variations and human intervention through nourishment monthly and storm event driven beach surveys consisting of topographical measurements and sediment sampling in two selected areas were carried out over a one year period three prevailing sediment fractions sand fine gravel and coarse gravel and two end member morphological states of the upper beach profile convex with multiple berms and concave with a single storm berm were identified between them several transitional profiles were formed characterized by developing berms that progressively overlapped generating sediment variability both across the beach profile and with depth the results indicate that the total run up including water level reached during an event represents a more accurate threshold for differentiating between erosional and depositional conditions than wave height they also suggest that mixed sand and gravel beaches recover faster from storm erosion than sandy beaches the long term benefit of the artificial nourishment that took place at the end of the survey period was very limited and this is attributed to the too fine sediment used for the nourishment and its placement too high on the beach clearly nourishment interventions must take into account the natural sediment distribution and the profile shape to avoid rapid losses of the nourished sediment

geophysical evidence for post miocene rotation of the island of viti levu fiji and its relationship to the tectonic development of the north fiji basin geophysical studies of the island of viti levu fiji show largeamplitude magnetic anomalies of up to 1500 nt to be located above the tavua volcanic center field sampling of the volcanic rocks from the intrusive and extrusive centers of the volcano show the rock samples to have initial intensities of natural remanent magnetization of up to 380 a m radiometric dating of fifteen oriented samples show an age range of 2 9 to 7 0 m y b p for the suite of rocks collected from the mba basaltic group paleomagnetic analysis of the dated rocksshows declination vectors ranging from 325 9 for an age of 2 9 0 2 m y b p to 290 4 for an age of 7 0 0 4 m y b p as a group the paleomagnetic declination values of the samples systematically decrease with age this decrease is attributed to progressive anticlockwise rotation of viti levu during the process of formation of the north fiji basin a linear least squares analysis of the paleomagnetic data indicates that the island has rotated in an anticlockwise direction through 90 during the past 7 m y at a rate of 13 7 per million years declination values as low as 245 measured for some sites not dated suggest that anticlockwise rotation of viti levu and development of the north fiji basin could have commenced as early as 10 m y b p following the breakup of the ancient solomons new hebrides fiji lau island arc large rotations of microplates may have occurred along other island arcs and marginal basin systems elsewhere in the western pacific and such rotational histories may reflect in detail the evolutionary development of these arcs and basins

qp and qs in the upper mantle beneath the iberian peninsula from recordings of the very deep granada earthquake of april 11 2010 1 granada southern spain is a place of rare and enigmatic very deep focus earthquakes the last one on april 11 2010 with magnitude of 6 3 and depth of 620 km we use regional broadband recordings to estimate qp and qsin the mantle for frequencies between 0 25 and 8 hz computing the spectra of the direct p and s waves with their early p and s coda we use the spectral decay method constraining crustalq to values given in the literature we obtain robust estimates of qp in 6 frequency bands 0 25 0 5 1 2 4 and 8 hz and of qs in 4 bands 0 25 0 5 1 2 hz qp in the mantle ranges from 13 at 0 25 hz to 346 at 8 hz and qs from 59 at 0 25 to 183 at 2 hz the frequency dependence is well fitted by q q0f with equal to 0 6 for qs and 1 0 for qp and q0 equal to 109 for qs and 63 for qp the qp qs ratio is less than 1 these are extreme values within the ranges of mantle q qp qs and values reported in the literature indicating strong scattering attenuation and absence of melt we propose that such values rather than being an exception may approximate the average upper mantle with solid olivine composition and small scale heterogeneity

frequency dependence of q in earth s upper mantle inferred from continuous spectra of body waves q0 f f0 a and applied a grid search to determine the best fit a and q0 the inferred frequency dependence 0 2 a 0 4 in most regions is consistent with laboratory data on solid olivine but not on partially molten olivine rich rocks except those data for deep events close agreement between seismological and laboratory observations on frequency dependence of q suggests that physical mechanisms of seismic wave attenuation are common and therefore laboratory data can be used to infer the physical state of earth s upper mantle from seismic wave attenuation index terms 5144 physical properties of rocks wave attenuation 7218 seismology lithosphere and upper mantle 8162 tectonophysics rheology mantle citation shito a s karato and j park 2004 frequency dependence of q in earth s upper mantle inferred from continuous spectra of body waves geophys res lett 31 l12603

shallow seismicity and tectonics of the central and northern lau basin abstract the lau basin is an active backarc comprising several spreading centers and microplates rapidly evolving in time as such crustal earthquakes within the lau basin derive from intrabasin tectonic volcanic and hydrothermal sources because of high mantle attenuation small earthquakes from the basin are seldom recorded on land seismographs and it has been difficult to study the pattern of crustal seismicity however the 1994 labatts ocean bottom seismograph experiment in the lau basin recorded more than 100 000 local t and body phases allowing for a detailed examination of basin seismotectonics nearly 1000 events are located within the basin proper with another 2000 associated with the forearc and the aseismic front we identify two previously undocumented tectonic features a triple junction in the northwestern basin and a nanoplate in the central lau basin the single most seismically active feature within the lau basin is the lau extensional transform zone letz just north of the central lau spreading center significant seismicity also occurs near the northern extension of the eastern lau spreading center and along a southeast extension of the letz delineating the boundary of a previously unknown nanoplate swarm activity is common in the backarc basin and dominates regions associated with actively reorganizing tectonics we see no evidence of deformation along the southern boundary of the niuafo ou microplate where 4 5 cm yr of strain is predicted it is possible that the plate boundary extends eastward from the fonualei rift fr tip towards the trench creating a niuatoputapu tonga plate division rather than westward implied by the currently accepted niuafo ou tonga plate system but more data are necessary from the fr to test that hypothesis instead we suggest that the niuafo ou tonga pole is 1 5 further north than previously proposed reducing the predicted strain in this region to

seismic constraints on a model of partial melts under ridge axes in a recent global scale seismic study the correlation between s wave velocity under ridge axes and spreading rate was pointed out the correlation is strong for depths to about 70 km but it diminishes below this depth we present the correlation plots at four depths 38 66 90 and 110 km for which correlation is strong at 38 and 66 km but is weak at 90 km and is almost nonexistent at 110 km we present a model to explain this behavior which includes a thermal conduction model for the development of lithosphere and a simple melt percolation thermal effects on s wave velocity are assumed to be accounted for entirely by the plate cooling thermal conduction model we point out that the thermal model under this assumption predicts asymptotically no correlation between s wave velocity and spreading rate specifically for spreading rate larger than about 3 cm yr 1 this contradicts the correlation observed in the data at shallow depths the existence of partial melt is thus required to explain the observed behavior at 38 and 66 km depths we start from four basic equations that govern the distribution of partial melt and derive the relation between the amount of partial melt and the spreading rate we adopt a simple power law relation between permeability k and porosity by k k 0 n where k 0 and n are constants and assume that pores are filled with melt we then set up an integral relation between s wave velocity and spreading rate the final formula indicates that the gradient in the correlation plots is the inverse of the power 1 n in the permeability porosity relation thus enabling us to constrain n as well as k 0 from seismic data the data also have some sensitivity to the depth to solidus we show that 1 the depth to solidus is probably within the range 60 100 km and 2 if the power n is n 2 3 then k 0 10 8 10 10 m 2 these parameters predict that porosity and fluid velocity are 1 2 and about 0 5 m yr 1 respectively the depth to solidus is consistent with previous estimates by petrological data but is perhaps the first and direct seismological evidence of partial melt from surface wave data analytical forms for the dependence on depth and spreading rate of porosity fluid velocity within permeable rocks and ascent times of magma are also obtained

seismic attenuation tomography of the tonga fiji region using phase pair methods the anelastic structure of the region surrounding the tonga slab and lau back arc spreading center in the southwest pacific is studied using data from 12 broadband island stations and 30 ocean bottom seismographs two differential attenuation methods determine t over the frequency band 0 1 to 3 5 hz for earthquakes in the tonga slab the s p method measures the difference in spectral decay between p and s waves arriving at the same station the p p method measures the difference in spectral decay for p waves with different paths through the upper mantle eight hundred sixty phase pairs are used to invert for two dimensional 1 q structure using a nonnegative least squares algorithm a grid search method determines the q q ratio most compatible with both the s p and p p differential measurements the highest attenuation q 90 is found within the upper 100 km beneath the active portions of the lau basin extending westward to the lau ridge these regions probably delineate the source region for the back arc spreading center magmas expected to be within the upper 100 km based on petrological considerations the high attenuation regions also correlate well with zones of low p wave velocity determined by regional velocity tomography somewhat lower attenuation is found beneath the fiji plateau than beneath the lau basin the entire back arc is characterized by a gradual decrease in attenuation to a depth of 300 to 400 km the slab is imaged as a region of low attenuation q 900 material a q q ratio of 1 75 provides the best fit between the s p and p p data sets upon inversion spectral stacking shows no frequency dependence within the frequency band analyzed

q tomography of the upper mantle using three component long period waveforms summary we present a degree 8 3 d q model qrlw8 of the upper mantle derived from three component surface waveform data in the period range 60 400 s the inversion procedure involves two steps in the first step 3 d whole mantle velocity models are derived separately for elastic sh transverse component and sv vertical and longitudinal component velocity models using both surface and body waveforms and the non linear asymptotic coupling theory nact approach in the second step the surface waveforms thus aligned in phase are inverted to obtain a 3 d q model in the depth range 80 670 km various stability tests are performed to assess the quality of the resulting q model and in particular to assess possible contamination from focusing effects we find that the 3 d patterns obtained are stable but the amplitude of the lateral variations in q is not well constrained because large damping is necessary to extract the weak q signal from data the model obtained agrees with previous results in that a strong correlation of q with tectonics is observed in the first 250 km of the upper mantle with high attenuation under oceanic regions and low attenuation under continental shields it is gradually replaced by a simpler pattern at larger depth at the depths below 400 km the q distribution is generally dominated by two strong minima one under the southern pacific and one under africa yielding a strong degree 2 pattern most hotspots are located above regions of low q at this depth ridges are shallow features in both velocity and q models

morphodynamics of a large scale rip current system at muriwai beach new zealand abstract field measurements of rip spacing nearshore morphology water surface elevation and eulerian and lagrangian flows were made in order to investigate the morphodynamics of a large scale rip current system at muriwai beach new zealand muriwai is a high energy meso tidal beach characterised by modal breaker wave heights of 2 5 m and incident wave periods of 10 15 s the monitored rip system was characterised by a 400 m long 75 m wide longshore feeder channel and a 150 m wide rip neck channel oriented obliquely to the shore and extending over a distance of almost 400 m during the experiment the beach evolved from a longshore bar trough and rip state to a transverse bar and rip configuration mean eulerian flow velocities obtained from ducted flowmeters deployed on the margin of the feeder channel and rip neck were on the order of 1 m s 1 and instantaneous flows were commonly in excess of 2 m s 1 mean lagrangian surface flow velocities extending from the base of the feeder through to the rip head were obtained by tracking rip floaters and were on the order of 0 7 m s 1 with maximums in the rip neck region of 1 4 m s 1 a distinct tidal modulation of rip current flow existed with maximum velocities occurring at low tide and minimum velocities at high tide comparison with other rip studies suggests that although the magnitude of the morphodynamic and hydrodynamic processes occurring within large scale rip systems is extreme the behaviour of these rip systems is very similar to low energy rips with much smaller spatial scales there is evidence to suggest that distinct morphodynamic scaling relationships exist between these environments

global lateral variations of shear wave attenuation in the upper mantle we analyze several thousand high quality globally recorded ss s differential waveforms to constrain the lateral variation of shear wave attenuation q in the upper mantle we use a multitaper frequency domain technique to measure attenuation parameterized by a t operator and implement a robust estimation technique to compute t and its variance the differential waveform technique minimizes the effect of factors such as finite source duration and structural complexity near the source and receiver so the differential ss s waveforms are mainly sensitive to the shear attenuation in the upper mantle under the ss bounce point we use seismograms recorded at ranges of 45 to 100 and compute the ss s differential t from the broadening of the ss waveform relative to the hilbert transform of the s waveform a careful choice of fitting windows allows us to reduce the biasing effects of interfering phases which can affect t by up to 0 5 s the t residuals with respect to preliminary reference earth model prem vary by 1 5 s with an average of 0 24 s our study suggests an average q value of 112 most of the lateral variations of q are within 30 of this value in the top 400 km of the mantle slightly lower than the prem value of 128 there is a qualitative correlation of t residual with tectonic region with distinctly higher attenuation observed under young oceans compared to platforms and shields also the lateral variations of the residuals are similar in trend to those observed in studies of the attenuation of scs multiples at long wavelengths the qp map shows a modest correlation with shear wave attenuation maps computed from surface wave analyses and with the patterns of lateral variations of shear velocities at certain upper mantle depths predicted by the model s16b30 the correlation with the velocity model is highest at 300 500 km depth indicating that there may be a contribution to long wavelength attenuation from relatively deep regions formal inversion for an upper mantle q model shows that while lateral resolution is quite good depth resolution is poor as might be expected better depth resolution must await combined body wave and surface wave inversions

use of bed form climb models to analyze geometry and preservation potential of clastic facies and erosional surfaces based on a combination of walther s law of facies and bed form climb theory we propose a model that explains how erosion surfaces and vertical sequences of clastic strata are preserved where deposition occurs in channelized or locally erosional environments including fluvial and submarine channel deposits barred beaches and transgressive coastlines the model considers both lateral and vertical migration of a scour surface and its associated depositional products as in studies of bed form climb we recognize subcritical critical and supercritical climb of scour surfaces relative to adjacent depositional forms for a given erosion surface the amount of underlying material removed is dictated by the climb angle of the erosion surface preservation of sequences also d pends on whether conditions were relatively variable or invariable one important conclusion of this study is the recognition of the bed form climb angle s control on the thickness of a sedimentary facies estimates of paleochannel depth or paleowater depth based on facies thickness can be made only if the climb angle is zero by combining depositional models of fluvial nearshore and offshore facies it is theoretically possible to model depositional systems such as deltas and passive continental margins potential applications are limited by several factors including influence of sea level climatic fluctuations on sedimentation and variable migration of facies or nonideal behavior or sedimentary environments in addition negative climb angles or climb angles less than horizontal can result in the removal of large amounts of material such negative climb angles may be caused by drops in eustatic sea level and lowering of base levels of drainage systems we believe that this heuristic model has considerable potential in helping sedimentologists and stratigraphers predict the consequences of facies mi ration

temporal and spatial scales of beach profile change duck north carolina abstract an 11 year time series of high resolution beach profile surveys made on an atlantic ocean beach was analyzed for spatial and temporal characteristics of beach profile change approximately 300 profile surveys most extending from the dune to 8 m depth were available for the analysis on each of four cross shore lines together with electronically recorded and statistically processed wave time series from a nearshore gage located seaward of the survey site the profile survey data set was analyzed for such quantities as depth change frequency of depth change general seasonal shape of the profile seasonal depth change and change in the profile produced by extreme storms the morphodynamics of an inner and outer longshore bar were also examined including depth to bar crest bar height and length and speed of bar movement onshore and offshore several properties of depth change were related to wave characteristics representative results were average profile elevation change from 4 m to 4 m was symmetric about the mean sea level shoreline the average spring and autumn profile shapes were almost identical and occurred as transitional states between the summer and winter profile shapes the depth of active profile movement within survey accuracy of about 0 025 m was 4 m for the summer and 6 m for the winter and the 10 year frequencies of maximum absolute depth change in depths of 2 4 6 and 8 m were 1 64 1 38 0 22 and 0 12 m respectively a surprising result was that typical large storms transported sand into the nearshore from the seaward end of the profile from a depth of about 6 8 m

a global tomographic model of shear attenuation in the upper mantle we present a global three dimensional model of shear attenuation in the upper mantle based on the measurement of amplitudes of low frequency 100 300s rayleigh waves observed at stations of the geoscope and iris networks attenuation coefficients are measured on r1 and r2 paths using a method which minimizes the effects of focussing due to propagation in a three dimensional elastic earth through a series of tests which in particular involve the computation of synthetic models of attenuation and focussing we demonstrate that long wavelength lateral variations in attenuation in the first 400 500 km of the mantle can indeed be resolved the model is obtained in a two step procedure the first step consists in the computation of maps of rayleigh wave attenuation at different periods using an inversion method without a priori parametrisation which involves the introduction of a correlation length chosen here at 3000 km to optimize the trade off between resolution and variance in the model in the second step after corrections for shallow structure an inversion with depth is performed assuming lateral heterogeneity is confined to depths between 80 and 650 km the resulting model presents lateral variations in qp that are correlated with tectonic features in particular ridges and shields in the first 250 km of the upper mantle below that depth the pattern shifts and becomes correlated with the hotspot distribution particularly so if the buoyancy strength of hotspots is taken into account two major low velocity zones appear to be located in the central pacific and beneath northern africa in the depth range 300 500 km this pattern seems to continue at greater depth but resolution becomes insufficient below 500 km to draw definitive conclusions the smooth lateral variations retrieved are on the order of 50 down to 400 km we propose an interpretation in terms of plume lithosphere ridge interaction in the upper mantle arguing for deflection of the bulk of hot upwelling material from plumes towards ridges which may be occurring between 200 and 300 km depth

resolution versus speckle relative to geologic interpretability of spaceborne radar images a survey of user preference a survey was conducted to evaluate user preference for resolution versus speckle relative to the geologic interpretability of spaceborne radar images thirteen different resolution looks combinations were simulated from seasat synthetic aperture radar sar data of each of three test sites the sar images were distributed with questionnarires for analysis by eighty five earth scientists the relative discriminability of geologic targets at each test site for each simulation of resolution and speckle on the images is determined here from a survey of the evaluations a large majority of the analysts indicate that for most targets a two look image at the highest simulated resolution is best for a constant data rate a higher resolution is more important for target discrimination than a greater number of looks sand dunes require more looks than other geologic targets multiple look images are preferred over the corresponding single look image at all resolutions the number of multiple looks that is optimal for discriminating geologic logic targets is in general inversely related to the simulated resolution

pervasive seismic wave reflectivity and metasomatism of the tonga mantle wedge subduction zones play critical roles in the recycling of oceanic lithosphere and the generation of continental crust seismic imaging can reveal structures associated with key dynamic processes occurring in the upper mantle wedge above the sinking oceanic slab three dimensional images of reflecting interfaces throughout the upper mantle wedge above the subducting tonga slab were obtained by migration of teleseismic recordings of underside p and s wave reflections laterally continuous weak reflectors with tens of kilometers of topography were detected at depths near 90 125 200 250 300 330 390 410 and 450 kilometers p and s wave impedances decreased at the 330 kilometer and 450 kilometer reflectors and s wave impedance decreased near 200 kilometers in the vicinity of the slab and near 390 kilometers just above the global 410 kilometer increase the pervasive seismic reflectivity results from phase transitions and compositional zonation associated with extensive metasomatism involving slab derived fluids rising through the wedge

a new technique for recognition of geological and geomorphological patterns in digital terrain models abstract we have developed a technique that recognizes monoclinal sedimentary strata showing strike ridge geomorphology and fluvial deposits from digital terrain models dtms this technique is efficient and reliable and may be expanded to analysis of other landforms techniques for rapid geomorphic analysis of dtms are becoming increasingly useful since digital stereoscopic spot data will soon be available worldwide our technique recognizes geomorphic elements in two steps first elementary objects including crests thalwegs and various slope types are classified from slope changes along n s e w nw se and ne sw profiles through pixels in the dtm image second grammatical pattern recognition is used to identify and map geomorphic forms from the succession of elementary objects

dynamics of multiple intertidal bars over semi diurnal and lunar tidal cycles north lincolnshire england multiple intertidal bars are common features of wave dominated sandy beaches yet their short term 1 month and small scale 1 km morphology and dynamics remain poorly understood this study describes the morphodynamics of multiple intertidal bars in north lincolnshire england during single and lunar tidal cycles under two contrasting conditions first when significant wave height was 0 5 m and second when significant wave height frequently exceeded 1 m the relative importance of swash surf and shoaling processes in determining morphological change was examined using detailed field observations and a numerical model the beach featured four intertidal bars and both cross shore and longshore bar morphology evolved during the field investigation particularly under medium to high wave energy conditions numerical modelling suggests shoaling processes are most common on the seaward two bars under calm wave conditions hs 0 5 m and that surf zone processes become more common during neap tides and under more energetic hs 0 5 m conditions surf processes dominate the inner two bars though swash influence increases in a landward direction the numerical modelling results combined with low tide survey data and high resolution morphological measurements strongly suggest changes in the intertidal bar morphology are accomplished by surf zone processes rather than by shoaling wave or swash processes this is because shoaling waves do not induce significant sediment transport to have any morphological effect whereas swash action generally does not have enough scope to act as the swash zone is much narrower than the surf zone it was found however that the absolute rate of morphological change under swash action and surfzone processes are of similar magnitudes and that swash action may induce a significant amount of local morphological change when the high tide mark is located on the upper bar making this process important for bar morphodynamics copyright 2007 john wiley sons ltd

morphodynamics of intertidal bars in wave dominated coastal settings a review abstract intertidal bar systems are ubiquitous features on wave dominated beaches in coastal settings with a significant 1 m tidal range depending primarily on the wave conditions and the tidal range and to a lesser extent on the nearshore gradient they can assume a variety of forms slip face bars represent the most pronounced and dynamic intertidal bar morphology and are generally found on their own around the mean high tide level they usually form low on the intertidal beach after storm induced beach erosion and develop into a berm under prolonged calm wave conditions low amplitude ridges and sand waves represent multiple bar morphologies the bars occur across the entire intertidal profile and they remain present throughout the year multiple intertidal bars tend to be rather subdued and relatively static especially sand waves and their origin remains unclear the morphological response of intertidal bars to changing wave conditions is largely forced bars build up and migrate onshore under calm waves and are flattened and may migrate offshore during storms the morphological response is however significantly affected by relaxation time effects and morphological feedback particularly on beaches with multiple intertidal bars despite their morphological differences the intertidal bar types exhibit pronounced similarities in their morphodynamics sediment transport processes and morphological response are principally controlled by the tidal water levels on the beach because these together with the offshore wave energy level and the beach morphology determine the type intensity and duration of the wave processes operating on the cross shore profile it is the dominant importance of tidal water level variations and wave processes in shallow water depths swash and surf zone bores rather than wave height variability and deeper water wave processes breaking and shoaling waves that constitutes the main difference between intertidal and subtidal bar morphodynamics

seasonal changes in beach topography and beach volume in delaware abstract a beach study was conducted along a shore segment of the delaware coast from march 1982 through to april 1983 results indicate that beach topography and beach volume varied with changes in wave climatic regimes the regimes in turn were generally in phase with the winter and summer seasons because both the magnitude and frequency of storm waves were higher during winter than in summer the winter beach shape was concave upward following the winter storms of 1981 1982 swells rebuilt the beach in two stages from march through to august 1982 in the first stage the beach vertically accreted aggraded and in the second it laterally accreted prograded the aggrading stage involved the welding of a swash bar to the foreshore thereafter swash overtopping caused deposition on and landward of the bar in time the swash bar attained a berm and swale topography the prograding stage started when the swash could no longer overtop the berm crest which confined deposition to the foreshore this stage occurred following a minor or moderate storm event that shifted the berm crest upward and landward or during a neap tidal stage that occurred after the construction of a spring tide berm between march and the end of august 1982 60 m 3 of sediments per 1 m of beach were deposited on the shore of this value 67 was attributed to aggradational processes while the remaining 33 was attributed to progradational processes swells as well as storm waves caused vertical accretion storm waves contributed 20 of the total sediment volume deposited on the beach when the shore was at its maximum sediment volume for 1982 the beach topography was convex upward an inverse relationship existed between the mean monthly sediment volume and the mean monthly surge variability the surge level was used as an index of wave conditions high surge levels were associated with large waves while low surge levels were associated with small waves when surge variability was high during the winter sediment volume on the beach was low and conversely when surge variability was low in summer sediment volume was high correlation analysis showed that 80 of the variance of the mean monthly sediment volume was explained by the mean monthly surge variability

the lau havre taupo back arc basin a southward propagating multi stage evolution from rifting to spreading abstract the lau havre taupo lht system is an active 2000 km long back arc basin associated with pacific australian plate convergence in the sw pacific data from the lht back arc system include odp drillhole swath bathymetric and side scan imagery seismic reflection rock geochemistry magnetic anomaly heat flow shallow seismicity gravity and seismic refraction data the lht forms a longitudinal transect from southward propagating true oceanic spreading in the lau basin near tonga similarly southward propagating arc rifting in the havre trough and southward propagating continental rifting in the taupo volcanic zone tvz in northern new zealand four transitional tectonic settings are identified along the lht north to south between the continuum of spreading to rifting and comprise 1 oceanic spreading of the central lau spreading centre clsc propagating into oceanic crust formed by the eastern lau spreading centre elsc 2 oceanic spreading of the elsc propagating into rifted lau havre arc crust 3 rifting within havre arc crust propagating into rifting new zealand continental crust and 4 rifting of continental crust propagating into as yet non rifted but flexurally subsiding continental crust the enhanced spatial and temporal resolution of observed tectonic and magmatic processes along the strike of the lht is used to constrain a model for the evolution of back arc rifting to back arc spreading a sequence of five stages is identified and comprise 1 a combination of incipient simple and pure shear 2 early distributed and spatially heterogeneous half graben rifting with low angle synthetic and antithetic structures associated with rapid graben sediment infilling ephemeral early morb like rift magmatism and the initial trenchward migration of the arc front 3 a latter phase of half graben rifting mostly confined to a contiguous axial zone with continued ephemeral morb like rift magmatism and further trenchward migration of the arc front 4 initial oceanic spreading with evolving steady state morb magmatism along the axial rift graben system and 5 the reconfiguration of ridge geometry in response to changes in opening orientation leading to the development of ridge propagation into newly created oceanic crust rifting stages 2 and 3 can produce at least 120 km wide back arc crust by a balance of crustal extension with an estimated factor of 3 with rift and constructional arc magmatism in the lht system depending on latitude rates of widening during stages 2 and 3 vary between 15 and 45 mm yr 1 whilst stages 4 and 5 have full spreading rates of 90 mm yr 1

the systematic contribution of transporting mechanisms to the cross shore sediment transport in water depths of 3 to 9 m the systematic contributions of short waves infragravity waves and mean flows to the cross shore sediment transport were studied with direct measurements of instantaneous near bed sediment concentrations and velocities as well as with an energetics based sediment transport model using measured time series of near bed cross shore flow as input the study was conducted at four cross shore positions in the multiple bar system of terschelling netherlands during three field campaigns each with a five week duration the data were collected in 3 to 9 m water depth during a wide range of conditions from low energy non breaking conditions to almost fully saturated breakers the height over depth ratio hs h was applied at all four measuring stations as a local conditional parameter all model predictions were grouped into hs h classes with a width of 0 02 to highlight the generality of the data the energetics approach predicted that the suspended load dominated over the bedload at all four stations both the sediment flux measurements as well as the model predictions showed that the largest contributors to the gross suspended sediment transport were made by the short waves and the undertow inducing an onshore and offshore transport respectively their contributions to the gross suspended transport were about 40 to 50 under surf zone conditions bound infragravity waves were observed and predicted to result in an offshore directed transport that was of subordinate magnitude compared to the observed and estimated magnitudes by the short waves and the undertow however as these transports almost cancelled out because of their about equal magnitude but opposite sign the suspended transport by bound infragravity waves may not be ignored and may rather paradoxically have a relatively large influence on the net suspended sediment transport hydrodynamical processes that do not seem to be of importance to the onshore and offshore sediment transport in 3 to 9 m water depth in the long run are mean flows under non breaking conditions and free infragravity motions a direct comparison between measured sediment fluxes and the model predictions suggests that simple energetics models are suitable for predicting cross shore sediment transport in 3 to 9 m water depth

reconciling mantle attenuation temperature relationships from seismology petrology and laboratory measurements seismic attenuation measurements provide a powerful tool for sampling mantle properties laboratory experiments provide calibrations at seismic frequencies and mantle temperatures for dry melt free rocks but require 102 103 extrapolations in grain size to mantle conditions also the effects of water and melt are not well understood at the same time body wave attenuation measured from dense broadband arrays provides reliable estimates of shear wave attenuation qs 1 affording an opportunity for calibration we reanalyze seismic data sets that sample arc and back arc mantle in central america the marianas and the lau basin confirming very high attenuation qs 25 80 at 1 hz and depths of 50 100 km at each of these sites independent petrological studies constrain the temperature and water content where basaltic magmas last equilibrated with the mantle 1300 1450 c the qs measurements correlate inversely with the petrologically inferred temperatures as expected however dry attenuation models predict qs too high by a factor of 1 5 5 modifying models to include effects of h2o and rheology dependent grain size shows that the effects of water enhanced dissipation and water enhanced grain growth nearly cancel so h2o effects are modest therefore high h2o in the arc source region cannot explain the low qs nor in the back arc where lavas show modest water content most likely the high attenuation reflects the presence of melt and some models of melt effects come close to reproducing observations overall body wave qs can be reconciled with petrologic and laboratory inferences of mantle conditions if melt has a strong influence beneath arcs and back arcs

attenuation structure beneath the lau back arc spreading center from teleseismic s phases teleseismic ss and sscs waveforms provide constraints on the attenuation structure above deep seismic rones we estimate the average q along ss and sscs paths beneath the lau back arc by comparison with s and scs waveforms q is determined using both time and frequency domain analyses of transverse long period records assuming q is frequency independent in the frequency domain technique spectra from reflected ss or sscs and direct s or sscs waveforms are analyzed using least squares the time domain method uses a grid search to determine the attenuation operator that when convolved with the direct phase produces the best fit to the reflected phase in both methods the direct phase is convolved with a crustal response function to simulate the crustal interaction of the reflected phase large events subject to source directivity effects and source station combinations involving ray propagation down the subducting slab are not used the resulting attenuation estimates show low q values which increase with focal depth suggesting high attenuation in the upper mantle and a rapid decrease in attenuation below 200 300 km lateral variations are also indicated with very high attenuation q 20 35 in the upper mantle near the active spreading centers and lower attenuation west of the lau ridge q temperature relationships extrapolated from laboratory experiments suggest that the low q regions represent zones of asthenospheric partial melting

estimation of crustal qβ in the ganga basin using teleseismic broad band sh waveforms for the 1988 nepal india border earthquake abstract the average value of the intrinsic shear wave quality factor q has been estimated for the upper 55 km of the earth 47 km of crustal and upper 8 km of the upper mantle thickness in the border region between the ganga basin and himalaya in bihar we have used the teleseismic broad band sh and s sh waveforms of the 1988 nepal india border earthquake 6 4 m b for this purpose the frequency independent average value of q estimated in the range of 0 2 1 5 hz is found to be 1250 158

sea floor spreading in the lau back arc basin abstract we report the first 3 d magnetization inversion of bathymetry and magnetics data for the entire lau basin and confirm a history of southward propagating sea floor spreading during the past 4 myr magnetic lineations seafloor fabric and ridge segmentation patterns indicate that lithospheric accretion on discrete spreading centers in this back arc basin is fundamentally similar to that occurring on mid ocean ridges the brunhes chron spreading rates 65 100 mm yr are

flow regime and bedforms in a ridge and runnel system s e spain abstract during landward migration ridge and runnel systems are subjected to asymmetric oscillatory and or unidirectional flow regimes depending on the stage of development reached by these systems in the early stages of evolution when the ridge is situated in the upper shoreface the whole system is subjected to asymmetric oscillatory flow the runnel is under lower flow regime conditions and the ridge may be under upper or lower flow regime according to water depth and wave energy later when the ridge has migrated to a position on the foreshore the runnel is largely under a unidirectional lower flow regime while the ridge itself is under oscillatory upper flow regime when the ridge welds to berm it is largely emergent and exposed to high tide swash action under upper flow regime conditions the runnel is eventually filled with sand and transformed into a low lying area all these types grade laterally into each other one or more ridge and runnel systems can occur at the same time wave energy tide level and position of the ridge control the variations in the characteristics of the ridge and also the position of the zones of bedforms found at the upper shoreface

evaluating roughness models of radar backscatter a unique set of data collected for a soil moisture experiment has been used to evaluate three radar backscatter roughness models the data were collected by the nasa space shuttle flight 41g sir b synthetic aperture radar sar in an intensively farmed area near fresno california the sir b data swath included a large number of bare dry fields with a large variety of surface roughnesses the small perturbation model gave the best results particularly when fields with a definite periodic row structure were omitted the standard deviation of surface heights appears to be a good measure of relative roughness conditions but the correlation length did not appear to be a good descriptor of the surface nor did it seem to be related in any way to the measured backscatter

imaging fluid related subduction processes beneath central java indonesia using seismic attenuation tomography abstract we use local earthquake data observed by the amphibious temporary seismic meramex array to derive spatial variations of seismic attenuation qp in the crust and upper mantle beneath central java the path averaged attenuation values t of a high quality subset of 84 local earthquakes were calculated by a spectral inversion technique these 1929 t values inverted by a least squares tomographic inversion yield the 3d distribution of the specific attenuation qp analysis of the model resolution matrix and synthetic recovery tests were used to investigate the confidence of the qp model we notice a prominent zone of increased attenuation beneath and north of the modern volcanic arc at depths down to 15 km most of this anomaly seems to be related to the eocene miocene kendeng basin mainly in the eastern part of the study area enhanced attenuation is also found in the upper crust in the direct vicinity of recent volcanoes pointing towards zones of partial melts presence of fluids and increased temperatures in the middle to upper crust the middle and lower crust seems not to be associated with strong heating and the presence of melts throughout the arc enhanced attenuation above the subducting slab beneath the marine forearc seems to be due to the presence of fluids

constraints on upper mantle discontinuities from observations of long period reflected and converted phases stacked images combining over 5 years of long period global digital seismograph network data reveal many phases associated with reflections and conversions from upper mantle discontinuities these images show travel time and amplitude relative to a reference phase which is aligned and normalized on all seismograms prior to stacking results obtained for p s ss and pp reference arrivals resolve numerous phases from discontinuities near 410 and 660 km while some of the stacks also show evidence for a weaker discontinuity near 520 km phases of particular interest include p and sh multiples resulting from topside reflections precursors to ss from underside reflections and p to sv converted phases these phases can be clearly seen both in the waveform stacks and in cross correlation analysis of individual seismograms travel times for these arrivals are converted to discontinuity depths relative to velocities in the preliminary reference earth model and empirical corrections are applied for the effects of lateral velocity variations in the upper mantle average apparent depths to the discontinuities for the different phases agree to within 3 km for the 410 km discontinuity to within 4 km for the 520 km discontinuity and to within 8 km for the 660 km discontinuity the best global averages are obtained from the ss precursor data which indicate discontinuities at 415 519 and 659 km discontinuity depths obtained from the p to sv converted phases at over 35 individual seismic stations exhibit variations of less than 20 km apparent depths to the 660 km discontinuity consistently show greater variability than depths to the 410 km discontinuity supporting recent laboratory results which indicate that the clapeyron slope for the 660 km discontinuity is significantly larger in magnitude than the slope for the 410 km discontinuity precursors to ss seen between 110 and 180 are particularly useful for mapping possible lateral variations in discontinuity depths since each arrival can be associated with a single underside reflection point apparent discontinuity depths computed from ss precursors for different tectonic regions agree to within about 5 km the ss precursors have especially good coverage near the subducting slabs in the northwest pacific analysis of apparent discontinuity depths in this area suggests the presence of a broad 1000 to 1500 km wide region near the slab in which the 660 km discontinuity is depressed by about 20 km measuring absolute amplitudes for these phases is difficult due to the large corrections required to compensate for the effects of incoherent stacking relative amplitude analysis suggests that the p and s wave impedance changes at 410 km are about 0 8 1 1 times the size of the changes at 660 km and that the contrasts at 520 km are between 0 3 and 0 6 of the changes at 410 km

body wave attenuation in the tonga subduction zone attenuation p and s waves of in the tonga subduction zone is estimated from locally recorded data using a spectral ratio method the data consist of three component digital seismograms of 77 earthquakes recorded at two stations in fiji and one in tonga the stations in the fiji islands lie above the deep earthquakes in the subduction zone while the tonga station is close to the top of the subducted slab variations in the high frequency spectral decay rate define four attenuation provinces paths from earthquakes deeper than 350 km to stations on viti levu fiji and the lau ridge traverse mantle with normal attenuation qp 570 qs 200 400 the subducting tonga slab has very low attenuation qp 2000 qs 1800 relative to the surrounding mantle the wedge of mantle above the slab at depths shallower than 350 km and east of the lau ridge is extremely attenuating for p waves qp 240 several paths from main thrust zone events to the station in tonga show intermediate attenuation qp 300 500 in the forearc region the observed spectra do not require q to be frequency dependent in the 1 0 hz to 7 6 hz band in this region

upper mantle q structure beneath the east pacific rise a model of q as a function of depth has been determined for the upper mantle beneath the east pacific rise the model is appropriate for shear waves with periods from roughly 15 to 30 s the amplitudes of multibounce sh phases which propagate within the upper mantle were used to constrain the q structure the multibounce phase amplitudes were measured with respect to the s wave amplitude for each seismogram the data consist of s ss sss and ssss waves for distances from 30 to 80 the sources are earthquakes which occurred on transform faults associated with the east pacific rise and the seismograms were recorded by world wide standard seismograph network and canadian seismic network stations in western north america mantle beneath oceanic crust less than 15 ma and tectonically active continental crust is sampled since the s wave data primarily sample the deep mantle the resulting upper mantle q model depends on the q structure assumed for the lower mantle we assumed a constant q of 312 for the mantle beneath 650 km depth with this assumption the upper mantle phase amplitudes require a q of about 70 in the upper 150 km of the mantle from 150 to 400 km depth q increases to 180 the q in the transition zone from 400 to 650 km depth was found to be 180 significantly lower than the lower mantle q the resulting q model is consistent with several surface wave studies of mantle attenuation beneath the pacific however our results predict a qscs 210 which is significantly higher than many direct measurements of scs attenuation indicate furthermore the large range in measured qscs is inconsistent with lateral q variations being confined to the upper mantle if the region we have studied represents the low q extreme of upper mantle we conclude that large lateral variations in q exist in the lower mantle

radiometric correction of c band imagery for topographic effects in regions of moderate relief the combined effects of topography slope look angle and aspect on c band synthetic aperture radar sar data on the radiometric quality of sar images in a region of moderate relief are examined a correction method was used to attenuate the change of illumination across the swath due to the antenna pattern ground data were integrated into the analysis using a digital terrain model dtm correction functions based on the cosine of the incidence angle were applied to the thematic classes and to the grouped classes in order to reduce the effects related to topography it was found that it is possible to eliminate part of the radiometric variations created by moderate topographic relief after the corrections were applied a reduction was noted of the variance in the radiometric values of the spectral signatures of the cover types which ranged between 3 03 and 9 47 depending on the correction function used

crustal structure of the niuafo ou microplate and fonualei rift and spreading center in the northeastern lau basin southwestern pacific the northeastern lau basin is one of the fastest opening and magmatically most active back arc regions on earth although the current pattern of plate boundaries and motions in this complex mosaic of microplates is reasonably understood the internal structure and evolution of the back arc crust are not we present new geophysical data from a 290 km long east west oriented transect crossing the niuafo ou microplate back arc the fonualei rift and spreading center frsc and the tofua volcanic arc at 17 20 s our p wave tomography model and density modeling suggest that past crustal accretion inside the southern frsc was accommodated by a combination of arc crustal extension and magmatic activity the absence of magnetic reversals inside the frsc supports this and suggests that focused seafloor spreading has until now not contributed to crustal accretion the back arc crust constituting the southern niuafo ou microplate reveals a heterogeneous structure comprising several crustal blocks some regions of the back arc show a crustal structure similar to typical oceanic crust suggesting they originate from seafloor spreading other crustal blocks resemble a structure that is similar to volcanic arc crust or a hydrous type of oceanic crust that has been created at a spreading center influenced by slab derived water at distances 50 km to the arc throughout the back arc region we observe a high velocity vp 7 2 7 5 km s 1 lower crust which is an indication for magmatic underplating which is likely sustained by elevated upper mantle temperatures in this region

upper mantle q structure beneath old seafloor in the western pacific the pacific lithosphere anisotropy and thickness experiment ocean bottom seismometer array south of the shatsky rise allows imaging the attenuation structure of the upper mantle in the oldest parts of the pacific ocean the array consisted of eight seismometers with a lateral extent of 200 km by 600 km intermediate and deep focus earthquake sources in the mariana and izu bonin subduction zones provide paths that probe different depths beneath the seafloor acceleration spectra from the vertical component of p waves are inverted for the attenuation operator and corner frequency pn propagation indicates very high qp values in the lithosphere of order 1000 while path average qp values in the upper mantle are on the order of 400 the variety of source epicentral distances and depths enables us to deduce the vertical qp 1 structure of the upper mantle using the amplitude spectra directly in a weighted least squares problem that accounts for the effects of triplications in the traveltime curves we invert for qp 1 as a function of depth we demonstrate that qp is frequency dependent and adopt a power law dependence with coefficient 0 27 we resolve three distinct layers using a reference frequency of 1 hz with qp on the order of 145 at depths 100 250 km qp on the order of 350 at depths 250 410 km and very high qp with attenuation indistinguishable from zero for depths below 410 km the p waves have a component of scattering and thus qp 1 represents the maximum intrinsic attenuation beneath normal undisturbed oceanic lithosphere

computer aided recognition of relief patterns on radar images using a syntax analysis abstract we present computerized recognition of relief patterns on an airborne sar image band x 3 2 cm using a syntax analysis the test site is the montagne sainte victoire provence france the pixel size is 2m 2m severe filtering to eliminate the speckle has reduced ground resolution but geologic and geomorphologic objects to extract thalwegs structural escarpments lithologic boundaries and landslides have large dimensions tens of meters far range correction was necessary to compensate weakening of radar signal with aircraft distance significant retrodiffusion values are for horizontal surfaces projected shadows surfaces whose normal is subperpendicular to radar beam steep radiometric gradients elements of the topographic profiles have been correlated with the elementary signals of radar image permitting a codification for syntactic analysis the radar image has been transformed into an image of elementary topographic symbols from which crests and thalwegs can be directly extracted recognition of structural escarpments and landslides involves search for typical sequences of symbols in different profile orientations and determination of a specific grammar syntax assessment of the results was made by comparison with similar syntactic methods of pattern recognition applied to a digital elevation model of the same area and field knowledge the radar image classifications have produced results close to reality imperfections are mainly due to the filtering process radar distance correction and difficulty in measuring significant retrodiffusion values for example retrodiffusion of horizontal surfaces artifacts inherent to radar acquisition also introduced confusions

onshore sandbar migration at tairua beach new zealand numerical simulations and field measurements abstract we observed the onshore migration 3 5 m day of a nearshore sandbar at tairua beach new zealand during 4 days of low energy wave conditions the morphological observations together with concurrent measurements of waves and suspended sediment concentrations were used to test a coupled wave averaged cross shore model because of the coarse bed material and the relatively low energy conditions the contribution of the suspended transport to the total transport was predicted and observed to be negligible the model predicted the bar to move onshore because of the feedback between near bed wave skewness bedload and the sandbar under weakly to non breaking conditions at high tide the predicted bathymetric evolution contrasts however with the observations that the bar migrated onshore predominantly at low tide also the model flattened the bar while in the observations the sandbar retained its steep landward facing flank a comparison between available observations and numerical simulations suggests that onshore propagating surf zone bores in very shallow water

p wave attenuation structure of the lau back arc basin and implications for mantle wedge processes abstract we image 3 d seismic p wave attenuation structure of the tonga subduction zone and the lau back arc basin using local earthquake waveforms recorded by land and ocean bottom seismographs of the 2009 2010 lau spreading center imaging project the amplitude spectra of p waves from local earthquakes are inverted for the path average attenuation operator t with a variety of frequency dependence exponent values analysis shows that the data are best fit by the assumption of a weak frequency dependence 0 3 consistent with laboratory results modeled as the effects of grain boundary sliding the t measurements are inverted for a 3 d tomographic q p 1 model the results show high p wave attenuation within the upper 100 km of the back arc mantle with a sharp boundary at the tofua arc between high attenuation sub arc mantle and the low attenuation fore arc perhaps the highest p wave attenuation q p 1 0 036 or q p 28 known in the mantle occurs at 20 60 km depth beneath the back arc spreading centers high attenuation anomalies form an inclined zone dipping from the spreading centers to the west away from the slab indicating abnormally high temperature and the existence of hydrous partial melt these observations suggest that hot materials supplied from the australian mantle upwell along with the mantle wedge flow pattern triggering extensive decompression melting near the back arc spreading centers the along strike variation of p wave attenuation is different from that of sv velocity possibly implying the different effects of partial melt on seismic attenuation and velocity

multiple scs probing of the ontong java plateau abstract we use multiple scs phases recorded at pohnpei from a 1996 deep earthquake under the solomon islands to investigate the shear velocity and attenuation characteristics of the upper mantle under the ontong java plateau in the western equatorial pacific cross correlation results indicate a vertical one way travel time under the plateau 3 s slow with respect to prem in agreement with previously obtained tomographic results which revealed the existence of an anomalously slow root under the plateau additionally the study of stacked spectral ratios suggests an unusually high qscs 366 with a lower limit of qscs 253 this value is considerably higher than elsewhere in the pacific suggesting the absence of an asthenospheric layer under the edifice the combination of slow shear wave speed and lower than average shear attenuation rules out a temperature anomaly as the source of the ontong java plateau ojp root which must then be related to a chemical or mineralogical heterogeneity

mapping of p wave slab anomalies beneath the tonga kermadec and new hebrides arcs abstract p wave velocity anomalies of several per cent fast relative to the jeffreys bullen jb model are seen around subduction zones under the tonga kermadec and new hebrides trenches from inversion of international seismological centre isc travel time residuals from intermediate and deep focus earthquakes mantle heterogeneities outside the model are corrected using previous velocity models ray paths inside the model region are traced allowing two dimensional velocity variations the rays of similar source and receiver locations are combined into summary rays and the hypocenters are relocated as part of the inversion iterations the resulting images are interpreted in conjunction with resolution and error estimations the slab like anomalies are generally continuous in places of high seismicity and decrease in amplitude with depth most coherent slab anomalies are surrounded by large slow patches between the surface and 350 km depth the fast slab beneath the tonga arc appears to end at 550 km depth before the seismicity ends but there is a fast band at 750 1000 km depths below the deepest tongan earthquakes the fast slab like anomaly beneath the kermadec arc tends to flatten to subhorizontal near the bottom of upper mantle and it occurs aseismically near new zealand down to 500 550 km depth interpretations in the lower mantle in many places such as kermadec and new hebrides arcs however are hampered by poor resolution

statistical analysis of coastal morphological data sets over seasonal to decadal time scales statistical analysis of long term morphological data on coastal sedimentary features provides important information on the processes governing these features and their evolution in space and time in this paper seasonal yearly and decadal i e long term behavior of coastal morphological features is derived from field data by using both simple and advanced statistical techniques the sedimentary features which we are especially focusing on are a nearshore bars and b large scale shoreline undulations for example longshore sand waves and nesses high quality bathymetric field data of regularly sampled cross shore profiles and shorelines were the basis of the available data sets at noordwijk beach the netherlands duck north carolina usa sylt germany lubiatowo poland and winterton uk additional data sets from argus video images see holman r a stanley j 2007 the history capabilities and future of argus coastal engineering special issue of the coastview project doi 10 1016 j coastaleng 2007 01 003 and aerial photographs were used to increase the temporal and spatial resolution of the data sets where possible the statistical methods applied include some linear and non linear techniques described by larson et al larson m capobianco m jansen h rozyfiski g southgate h n stive m wijnberg k m hulscher s 2003 analysis and modeling of field data on coastal morphological evolution over yearly and decadal time scales part 1 background and linear techniques journal of coastal research 19 4 760 775 and southgate et al southgate h n wijnberg k m larson m capobianco m jansen h 2003 analysis of field data of coastal morphological evolution over yearly to decadal timescales part 2 non linear techniques journal of coastal research 19 4 776 789 the methods proved to be useful for extracting characteristics of the coastal sedimentary features concerning length scales e g spacing and rhythmicity and temporal scales e g migration rates and evolutionary patterns however the success of the statistical analysis strongly depends on the total size of the data set characterized by the specific spatial coverage spatial resolution temporal resolution and overall length in time recent data sets from remote sensing video systems like argus often meet these requirements and are of major importance for the formulation of conceptual behavior models c 2007 elsevier b v all rights reserved less

morphodynamic zone variability on a microtidal barred beach abstract this paper builds on the work of masselink masselink g 1993 simulating the effects of tides on beach morphodynamics j coast res si 15 180 197 on the use of the residence times of shoaling waves breaking waves and swash backwash motions across a cross shore profile to qualitatively understand temporal beach behaviour we use a data set of in situ measurements of wave parameters height and period and water depth and time exposure video images overlooking our single barred intertidal measurement array at egmond aan zee netherlands to derive boundaries between the shoaling zone the surf zone and the swash zone we find that the boundaries are functional dependencies of the local relative wave height on the local wave steepness this contrasts with the use of constant relative wave heights or water levels in earlier work we use the obtained boundaries and a standard cross shore wave transformation model coupled to an inner surf zone bore model to show that large 5 relative tide ranges rtr defined as the ratio tide range wave height indicate shoaling wave processes across almost the entire intertidal profile with surf processes dominating on the beach face when the rtr is between 2 and 5 surf processes dominate over the intertidal bar and the lower part of the beach face while swash has the largest residence times on the upper beach face such conditions associated with surf zone bores propagating across the bar around low tide were observed to cause the intertidal bar to migrate onshore slowly and the upper beach face to steepen for rtr values less than about 2 surf zone processes dominate across the intertidal bar while the dominance of swash processes now extends across most of the beach face the surf zone processes were now observed to lead to offshore bar migration while the swash eroded the upper beach face

morphodynamics of a bar trough surf zone abstract a field study was made of the distinguishing morphodynamic processes operating in a surf zone which perennially exhibits accentuated bar trough topography the longshore bar trough and rhytmic bar and beach states as described by wright and short 1984 characteristic features of the morphology include a shallow bar with a steep shoreward face a deep trough and a steep beach face this morphology which is favored by moderate breaker heights and small tidal ranges strongly controls the coupled suite of hydrodynamic processes in contrast to fully dissipative surf zones the bar trough surf zone is not at all saturated and oscillations at incident wave frequency remain dominant from the break point to the subaerial beach the degree of incident wave groupiness does not change appreciably across the surf zone infragravity standing waves which in dissipative surf zones dominate the inshore energy remain energetically secondary and occur at higher frequencies in the bar trough surf zone analyses of the field data combined with numerical simulations of leaky mode and edge wave nodal antinodal positions over observed surf zone profiles indicate that the frequencies which prevail are favored by the resonant condition of antinodes over the bar and nodes in the trough standing waves which would have nodes over the bar are suppressed sediment resuspension in the surf zone appears to be largely attributable to the incident waves which are the main source of bed shear stress in addition the extra near bottom eddy viscosity provided by the reformed non breaking waves traversing the trough significantly affects the vertical velocity profile of the longshore current whereas the bar is highly mobile in terms of onshore offshore migration rates the beach face and inner regions of the trough are remarkably stable over time

tonga ridge and lau basin crustal structure from seismic refraction data 1 the crustal structure across the tonga lau arc back arc system from the lau ridge to the pacific plate 178 170 w 18 19 s is modeled using data from an 840 km long air gun refraction line over 19 ocean bottom seismometers and one land station the data reveal that the pacific plate crust is 5 5 km thick with a velocity structure similar to that found at the present day east pacific rise epr beneath tonga ridge an intermediate velocity layer 6 7 km s is up to 7 5 km thick and has a velocity depth distribution similar to andesitic rocks found in continental crust the crust is abnormally thin 4 km at the boundary between the tonga ridge and the lau basin at the east end of lau basin the crust is 5 5 6 5 km thick and resembles crust formed at the epr except for a thicker sheeted dike section 2 3 km and thinner lower crust 2 km the lau basin crust thickens to 7 8 km near the central lau spreading center clsc mostly through thickening of the lower crust the crust thickens again to 8 5 9 5 km at 50 km west of the clsc mostly through thickening of the midcrust in the thick westernmost section the crustal structure is uniform even though one part of this section formed through extension of arc type crust while the rest was created at an oceanic spreading center the relative homogeneity of these rocks suggests that their petrology may be dominated by postemplacement magmatic infilling from a mantle source west of the spreading center

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

tomographic study of upper mantle atttenuation in the pacific ocean the quality factor q has been measured in the pacific ocean along many paths using long period seismograms of the geoscope and ida networks the love and rayleigh phase velocity and qr 1 have been regionalised in the period range 60s to 200s and then simultaneously inverted at depth to obtain 3d images of s wave velocity and attenuation q 1 in the depth range 60 300km up to 100s three very attenuating zones appear one under the east pacific rise e p r another one around hawaii a third one east of kermadec by inversion those three anomalies are found stable down to 160km below 200km lateral variations are less intense and differently distributed the maximum attenuation seems to concentrate along a northeast trend in the north central pacific

upper mantle structure of the tonga lau fiji region from rayleigh wave tomography we investigate the upper mantle seismic structure in the tonga lau fiji region by jointly fitting the phase velocities of rayleigh waves from ambient noise and two plane wave tomography the results suggest a wide low velocity zone beneath the lau basin with a minimum sv velocity of about 3 7 0 1 km s indicating upwelling hot asthenosphere with extensive partial melting the variations of velocity anomalies along the central and eastern lau spreading centers suggest varying mantle porosity filled with melt in the north where the spreading centers are distant from the tonga slab the inferred melting commences at about 70 km depth and forms an inclined zone in the mantle dipping to the west away from the arc this pattern suggests a passive decompression melting process supplied by the australian plate mantle from the west in the south as the supply from the australian mantle is impeded by the lau ridge lithosphere flux melting controlled by water from the nearby slab dominates in the back arc this source change results in the rapid transition in geochemistry and axial morphology along the spreading centers the remnant lau ridge and the fiji plateau are characterized by 60 80 km thick lithosphere underlain by a low velocity asthenosphere our results suggest the removal of the lithosphere of the northeastern fiji plateau lau ridge beneath the active taveuni volcano azimuthal anisotropy shows that the mantle flow direction rotates from trench perpendicular beneath fiji to spreading perpendicular beneath the lau basin which provides evidence for the southward flow of the mantle wedge and the samoan plume this article is protected by copyright all rights reserved

topographic mapping from interferometric synthetic aperture radar observations interferometric synthetic aperture radar observations provide a means for obtaining high resolution topographic terrain maps from data acquired simultaneously at two slightly displaced antennas calculation of the three dimensional coordinates of all the points in a radar image can be made from the combination of along track slant range and interferometer fringe measurements thus the result compensates for the layover exhibited by conventional radar maps and removes the false targets generated by multiple signal paths to a given object in the scene we have derived a topographic map of a portion of the san francisco bay area utilizing data that were recorded by a radar system mounted on a nasa cv990 aircraft and processed by a general purpose digital computer this map displays the height above sea level of a region approximately 11 km by 10 km in size sampled on an 11 m pixel grid uncertainties in the estimated height result from imprecise knowledge of the observational geometry radar bandwidth limitations and finite signal to noise ratios for our system each factor contributed approximately 3 4 m to a relative rms error of about 6 m additional global errors of the order of 10 m can result from inaccurate monitoring of aircraft attitude the statistical variation of the height measurements from the ocean portion of the map which we can presume to be quite flat is 2 10 m rms which is consistent with the theoretical estimate comparison of our results with u s geological survey contour maps indicates a high degree of correlation between the two sets of altitude data

qp melting temperature relation in peridotite at high pressure and temperature attenuation mechanism and implications for the mechanical properties of the upper mantle the anelastic properties of compressional waves in a peridotite have been determined in the laboratory at sufficiently high temperatures to 1280 c and pressures to 0 73 gpa to warrant comparison with seismic measurements of the earth a substantial decrease of qp is observed at temperatures well below the onset of partial melting qp systematically increases with increasing pressure over the entire temperature range of major significance is the finding that qp is dependent on the ratio of the temperatures to the melting solidus temperature i e qp depends on the homologous temperature the pressure dependence of qp appears through the pressure dependence of the solidus of the peridotite within the uncertainties of measurement of both qp and the phase diagram it appears that melting and high temperature anelastic properties have a common origin in peridotite the homologous temperature dependence of qp suggests that we may estimate the temperature and pressure dependence of qp for peridotites of different compositions and possibly even for hydrous peridotites if solidus temperatures are known as a function of pressure a far easier measurement than elastic and anelastic properties the activation volume of qp is greatly reduced at high pressure since the slope of solidus versus pressure rapidly decreases with increasing pressure pressure dependence of seismic velocity and melt fraction in peridotite also appears to be related to the homologous temperature the qp homologous temperature relation suggests a connection between qp and the properties of the grain boundaries that is the major loss of seismic energy occurs at the grain boundaries grain boundary relaxation or high temperature background attenuation is a possible mechanism for the grain boundary damping no frequency dependence of qp is resolved 0 0 2 in qp f over the pressure temperature and frequency ranges of the measurement the present results and the model of grain boundary relaxation suggest that an appropriate choice of grain size may give an ultrasonic q that is applicable to the earth experimentally determined anelastic properties of a peridotite are critical for modeling mechanical properties of the upper mantle implications of the results are as follows 1 seismic data commonly interpreted as indicating a partially molten asthenosphere may instead reflect a hot solid asthenosphere at 90 100 of the solidus temperature 2 partial melting may not produce any abrupt change of seismic velocity and q rather elastic and anelastic properties of the upper mantle will change gradually at the boundary where the geotherm crosses the solidus 3 there may be no sharp mechanical boundary between the lithosphere and the asthenosphere

equilibrium slopes and cross shore velocity asymmetries in a storm dominated barred nearshore system abstract the near bed 0 10 m elevation horizontal velocities were measured across a two barred lacustrine shoreface during a storm and reveal a spatially coherent but temporally variable pattern in the low order moments of the velocity field large cross shore velocity asymmetries indicated 1 1 spatially extensive and temporally persistent offshore mean flows up to 0 18 m s 1 across the landward slope of the linear outer bar reflecting an undertow driven by a wave induced setup 2 2 an onshore directed skewness opposing the mean flow of wind wave origin and persistent under propagating bores in the inner bar system long after this asymmetry had disappeared from the outer bar extensive sediment reactivation with near zero net sediment flux over the whole of the upper shoreface indicated a sediment prism in a steady state volumetrically over the storm cycle uniform depths of sediment reactivation with zero bed elevation change over the storm cycle revealed local slopes in a steady state in the outer linear bar however time integration of the near bed velocity field at this location indicated an offshore net flux of water while sedimentary structures indicated bedform migration and thus at least bedload almost uniformly onshore when ripples and megaripples were present the sediment transport giving rise to the local equilibrium cannot be explained therefore on the basis of the mean properties of the near bed velocity vector but requires knowledge of the time varying instantaneous sediment transport vector onshore migration of the inner bar correlated well with the large and persistent onshore skewness of the velocity distribution in the inner surf zone associated with translatory surf bores throughout the storm decay period low frequency oscillations were only significant close to the shoreline but may have influenced the development of a sinuous three dimensional inner bar form as it migrated onshore

sandbar dynamics in microtidal environments migration patterns in unprotected and bounded beaches abstract novel observations of bar features and migration patterns at three italian sandy beaches in senigallia central adriatic sea and terracina central tyrrhenian sea are presented while two of these beaches are unprotected one is artificially embayed through the presence of a concrete jetty bar locations and motions are analysed with video imagery data sets from coastal monitoring stations wave climate from the copernicus oceanographic model is used to correlate hydrodynamics and beach morphology clear net offshore migration nom patterns are identified at all beaches although exhibiting different response scales at the low slope beach of senigallia mean surf zone slope of 0 009 bars are more sensitive to seasonal changes in wave climate with offshore shifts in winter and inactivity in summer mean annual migration rates of up to 0 26 m day and 0 09 m day are observed for outer and inner bars respectively no significant response to single storms is observed except during a single nne storm no distinct erosive or accretive trend for the shoreline is evidenced at the steep beach of terracina mean surf zone slope of 0 018 conversely bars are strongly responsive to single storm events with displacements of up to 25 50 m across a single storm the mean inter annual migration rate is 0 08 m day for the single outer bar whereas a slight onshore trend 0 02 m day for the newborn inner bar is established the presence of an artificial jetty at the misa river mouth in senigallia finally leaves the bar system typically oscillating around an equilibrium position susceptible to larger seasonal oscillations and strong offshore migration due to two ese storm events numerical simulations of nearshore circulation for two storms from different directions predict the birth of longshore currents higher ratios of significant wave height to water depth and stronger bottom orbital velocities over bars in case of the ese storm suggesting a greater tendency for offshore directed sediment transport

formation and evolution of multiple intertidal bars on macrotidal beaches application of a morphodynamic model a numerical model is presented to simulate the formation and evolution of intertidal bar morphology dridges and runnelst cross shore sediment transport is modeled using a sediment transport shape function which is a mathematical formulation that expresses the volumetric sediment transport rate as a function of cross shore location for energetic wave conditions the shape function predicts offshore sediment transport in the surf zone and onshore transport outside the surf zone for calm conditions the shape function predicts onshore transport in the surf zone and zero transport outside the surf zone the model is forced by measured wave tide conditions and the time integrated cross shore sediment transport rate is obtained by advecting the shape function up and down the beach with changing tide levels morphodynamic feedback is included in the model specifically the occurrence of relatively flat beach sections troughs leads to the subdivision of the beach profile into distinct cross shore sediment transport cells each forced by its own wave breaking conditions surf zone sediment transport in the troughs is considered zero and the troughs thus effectively serve as sediment transport barriers according to the model and in agreement with field observations intertidal bars form and migrate onshore under the influence of low wave conditions while offshore bar migration and flattening of the morphology occurs under high wave conditions the model supports the contention that ridge and runnel topography has a surf zone origin but the ridges are not breakpoint bars in sensu stricto d 2004 elsevier b v all rights reserved

seismic attenuation structure in central mexico image of a focused high attenuation zone in the mantle wedge velocity spectra from moderate sized earthquakes were used to investigate the p wave attenuation structure in central mexico in particular we included regional events with magnitudes in the range of 4 5 to 6 1 recorded from 2005 to 2007 on the middle american subduction experiment mase array which consists of 100 broadband sensors across central mexico from acapulco to tempoal near the gulf of mexico by assuming a brune type source a frequency independent t value was obtained for each seismogram in the frequency band 1 to 30 hz these measurements were then inverted for two dimensional spatial variations in q p in the cross section along the mase array perpendicular to the trench the model has uniform 20 km vertical grid spacing down to a depth of 200 km and 50 km or 100 km horizontal grid spacing depending on ray coverage the inversion results show low attenuation in the subducting slab and high attenuation in the mantle wedge and the crust below and to the north of the volcanic belt the focused high attenuation zone q p 200 in the mantle wedge lies away from the top of the slab between depths of 80 km and 120 km beneath the volcanic belt and is likely to be related to relatively high temperature fluids and partial melts produced in subduction process the high attenuation region in the lower crust correlates with the low resistivity and low velocity region and could be caused by partial melts and fluids from dehydration and magmatic processes

absorption of p and s waves above subduction zones we investigate local variations of absorption above the subduction zones of the northwest pacific teleseismic broad band bb recordings at german arrays from 59 earthquakes in this area allow the determination of the quality factor qp and qs the method to determine q is the phase pair method here for the first time p wave bb recordings at dense arrays are used extending the frequency range studied and increasing the reliability of the qp determination for the northwest pacific 1 d earth models have typical qp values of 200 to 800 qs 100 to 400 in the upper 200 km qp under the kuriles the kurile basin and japan is about 100 i e significantly lower than average qs under japan is also only about 1 3 of the value of 1 d models no frequency dependence of qp and qs could be detected for the broad frequency range studied 0 05 to 1 hz

short term morphodynamics of an intertidal bar on megatidal ebb delta the morphodynamics of an intertidal bar located on an ebb delta of a megatidal inlet system in normandy france was examined during four short experiments under low to high energy wave conditions and spring or neap tide contexts although there have been numerous studies on ebb tidal bar morphology and on the processes affecting such bars these concern only microtidal or mesotidal settings and are mainly based on observations no detailed work involving hydrodynamic conditions embracing the whole tidal cycle has been carried out so far on the mechanisms of onshore migration of these coastal accumulation features especially along macro and megatidal coasts in this study the morphological response of the bar was coupled with the residence times and intensities of each hydrodynamic process swash surf shoaling waves over a representative bar cross shore profile and sediment transport patterns deduced from fluorescent tracer the results show that the bar migrated exclusively shoreward during moderate to storm conditions hs 0 7 m at the bottom of the bar seaward slope during low energy wave conditions no bar movement was observed swash action was not the dominant process mainly due to its duration which did not exceed 8 min in the course of a semi diurnal tidal cycle the movement of sediments and the bar morphology is induced mainly by surf processes and their associated currents the increase in the significant wave height disturbed the general mean current behaviour which was parallel to the bar crest during low energy conditions under surf conditions mean flows are directed onshore with an absence of bed return flow this allows sediment to be transported towards the bar crest causing a landward bar migration an offshore directed cross shore current not favourable for bar migration is recorded with larger water depths and no breaking waves shoaling conditions this study also highlights the influence of the tidal water level fluctuations in such a large tidal range setting which induce a rapid shift in processes such as bed shear and sediment re working across the shore normal profile these conditions explain the relative low rate of migration of the bar over the delta platform about 33 m year this rate is much less than those reported from micro mesotidal environments calculations of bed shear stress also show that the mean currents alone are not responsible for onshore bar movement notwithstanding the megatidal character of the field site

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

seismic and electrical signatures of the lithosphere asthenosphere system of the normal oceanic mantle although plate tectonics started as a theory of the ocean basins nearly 50 years ago the mechanical details of how it works are still poorly known our understanding of these details has been hampered partly by our inability to characterize the physical nature of the lithosphere asthenosphere system las beneath the ocean we review the existing observational constraints on the seismic and electrical properties of the las particularly for normal oceanic regions away from mid oceanic ridges hot spots and subduction zones where plate tectonics is expected to present its simplest form whereas a growing volume of seismic data on land has provided remarkable advances in large scale pictures seafloor observations have been shedding new light on essential details by combing through these observational constraints researchers are unveiling the nature of the enigmatic las future directions for large scale seafloor observations are also discussed

high frequency shear wave propagation across the hellenic subduction zone abstract this study investigates shear wave propagation across the hellenic subduction zone using high quality waveforms of 71 intermediate depth events 40 160 km depth the data have been recorded by a permanent seismic network consisting of 22 broadband three component stations that cover most parts of greece shear waves can be efficiently transmitted with low attenuation q s 1100 through the descending slab which extends laterally over much of the forearc area with a northwest southeast strike the slab also appears to be continuous downdip in the depth range 60 160 km even though it was found that a gap smaller than 10 km would not affect shear wave efficiency significantly two highly attenuating areas have been detected one in the central southeast aegean corresponding to the mantle wedge and the other in the northern aegean probably caused by elevated upper mantle temperatures owing to the ongoing extension in that area these results provide additional constraints for the geometry of the hellenic subduction zone and the geodynamic setting of the aegean region

high temperature experiments on the elastic and anelastic behaviour of magmatic rocks measurements of the complex shear modulus have been performed on various ultrabasic and basic rocks dunite peridotite gabbro and basalts and a synthetic forsterite at temperatures between 600 and 1500 c depending on the sample material and in the frequency range from 0 003 to 30 hz under forced torsional oscillations the maximum shear stress was 0 3 mpa and the strains were of the order 5 10 6 to 5 10 5 measurements of the electrical resistivity as a function of temperature have been carried out together with the mechanical experiments to indicate the beginning of partial melting the absolute values of the shear modulus below tm are comparable with the results of other authors the onset of melting shows up in a rapid decrease of both shear modulus and electrical resistivity at high temperatures t 0 8 tm the absorption factor q 1 follows a power law q 1 exp a rt with 0 15 0 30 and a between 100 and 200 kj mol 1 towards lower temperatures this high temperature background is superimposed by a flat absorption peak which shifts from high to low frequencies with falling temperature this peak can often be described by a lognormal distribution of simple relaxation processes with a standard deviation of about three and a mean relaxation time exp a rt with a 400 600 kj mol 1 above tm a third contribution to q 1 is observed that can be regarded as independent of frequency between 1 and 30 hz this last component which contributes 50 to the total absorption is attributed to the melt phase in the samples an explanation for the high temperature background and the peak is proposed which is based on the relaxation of pinned dislocation lines by some coupling mechanism via the reorganisation of the stress field with increasing deformation this process may be responsible for both features at very high temperatures and low frequencies a small influence of steady state flow on q 1 is observed and below t 0 6 tm thermal cracking or thermoelastic losses may contribute to q 1 the influence of lithostatic pressure on q 1 is estimated and the extrapolation of the experimental data to the p t conditions of the uppermost mantle are in good agreement with published earth models an attempt is made to establish a general q t relationship from the experimental data

landward migration of inner bars abstract a field investigation was carried out to collect data of inner bar migration profiles were measured once or twice a week for a two year period at naka beach ibaraki prefecture japan it was found that the onshore migration of inner bars could be described by two dimensionless quantities as 5d h b max h b max gt 2 max 20d h b max where h b max is the maximum value of daily average breaker height during one interval between surveys t max is the average wave period of the day giving h b max d is the mean size of the beach sediment and g is the acceleration due to gravity analyses based on surfzone sediment dynamics yields v wd b 2 10 11 h b d 3 where v is the average speed of onshore bar migration b is the bar height h b is the average breaker height and w is the fall velocity of the beach sediment nomographs for the speed of landward migrating bars are also presented

geotherms in the pacific ocean from laboratory and seismic attenuation studies seismic methods have been used extensively to measure attenuation coefficients in various regions of the earth attenuation is inversely related to the quality factor q which may be measured directly a low velocity and high attenuation zone in the upper mantle is commonly reported1 3 until now there has been no direct means to derive thermal structures from such seismic investigations recently q values have been determined in the laboratory for a dry peridotite an upper mantle rock for pressures and temperatures of up to 0 73 gpa and 1 280 c respectively4 the results indicate a quantifiable relation between q and temperature here we use these results to derive geotherms from q measurements for a region beneath the pacific ocean the geotherms are consistent with temperatures obtained from heat flow observations5 6 and imply that the oceanic upper mantle is rather dry in asthenos phere older than 40 myr geotherms for this region are sub solidus and no partial melt is expected

prediction of average mixing depth of sediment in the surf zone abstract a predictive model for the average depth of mixing of sediment in the surf zone is formulated on the basis of the wave induced shear stress on the bottom the model is calibrated using field data obtained through tracer experiments performed on pacific beaches of japan the result gives z d 81 4 b c where z is the average depth of sediment mixing in the surf zone d is the grain size of the sediment b is the shields parameter at the wave breaking point and c is the critical shields number for oscillatory flow the predicted mixing depth is found to increase in an approximately linear fashion with the breaking wave height for significant breaking wave heights up to about 1 5 m for greater breaking wave heights the rate of increase in the mixing depth decreases with increasing wave height the mixing depth is also a strong function of the wave period in the larger wave height region finally the predicted mixing depth is found to be a weakly increasing function of the sediment grain size

depth extent of the lau back arc spreading center and its relation to subduction processes seismic tomography and wave form inversion revealed that very slow velocity anomalies 5 to 7 percent beneath the active lau spreading center extend to 100 kilometer depth and are connected to moderately slow anomalies 2 to 4 percent in the mantle wedge to 400 kilometer depth these results indicate that geodynamic systems associated with back arc spreading are related to deep processes such as the convective circulation in the mantle wedge and deep dehydration reactions in the subducting slab the slow regions associated with the tonga arc and the lau back arc are separated at shallow levels but merge at depths greater than 100 kilometers suggesting that slab components of back arc magmas occur through mixing at these depths

short term morphological change and sediment dynamics in the intertidal zone of a macrotidal beach abstract this paper describes the morphological and sedimentological evolution of amacrotidal beach over a 20 day period under varying hydrodynamicconditions signi cant breaker heights of 0ae3 2 m and tidal ranges of 2 5 m during the eld campaign an intertidal bar developed around the mid tidelevel migrated onshore welded to the upper beach and was then attenedunder energetic wave conditions the bar had a wave breakpoint origin and itsformation was triggered by a reduction in tidal range causing more stationarywater level conditions rather than an increase in wave height most of theonshore bar migration took place while the bar was positioned in the inner tomid surf zone position such that the bar moved away from the breakpoint andexhibited divergent behaviour the depth of disturbance over individual tidalcycles was 10 20 of the breaker height such values are more typical of steepre ective beaches than gently sloping dissipative beaches and are consideredto re ect the maximum height of wave generated ripples the grain sizedistribution of sur cial sediments did not vary consistently across the beachpro le and temporal changes in the sedimentology were mostly unrelated tothe morphological response the lack of clear links between beach morphologyand sedimentology may be in part due to shortcomings in the samplingmethodology which ignored the vertical variability in the sediment sizecharacteristics across the active layer keywords beach sediment depth of disturbance intertidal bar macrotidalbeach morphology introductionbeaches respond rapidly to changing wave andtide conditions through the redistribution of theirsediments by oscillatory and quasi steady cur rents resulting in spatial patterns of erosion sediment divergence and accretion sedimentconvergence given suf cient time these bed level changes modify the beach shape by theformation modi cation destruction and ormigration of secondary morphological features such as berms beach cusps swash bars ripchannels and nearshore bars the dynamics ofthese secondary morphological features and theirrole in affecting beach stability has been a majorfocus of beach research over the last few decades e g komar 1998 short 1999 most short term days to weeks eld investi gations addressing the morphological response ofsandy beaches to wave and tide forcing have beenconducted in microtidal or mesotidal settings beaches in macrotidal settings have on the otherhand only received limited attention despitetheir common occurrence short 1991 a mainreason for this imbalance is that macrotidalbeaches are often planar and lack pronouncedsecondary morphological features indeed theonly type of macrotidal beach that does featureprominently in the coastal literature is the ridgeand runnel beach which is characterized bysedimentology 2007 54 39 53

mantle dynamics of western pacific and east asia insight from seismic tomography and mineral physics abstract recent results of high resolution seismic tomography and mineral physics experiments are used to study mantle dynamics of western pacific and east asia the most important processes in subduction zones are the shallow and deep slab dehydration and the convective circulation corner flow processes in the mantle wedge the combination of the two processes may have caused the back arc spreading in the lau basin affected the morphology of the subducting philippine sea slab and its seismicity under southwest japan and contributed to the formation of the continental rift system and intraplate volcanism in northeast asia which are clearly visible in our tomographic images slow anomalies are also found in the mantle under the subducting pacific slab which may represent a small mantle plumes b upwellings associated with the slab collapsing down to the lower mantle or c sub slab dehydration associated with deep earthquakes caused by the reactivation of large faults preserved in the slab combining tomographic images and earthquake hypocenters with phase diagrams in the systems of peridotite water we proposed a petrologic model for arc volcanism arc magmas are caused by the dehydration reactions of hydrated slab peridotite that supply water rich fluids to the mantle wedge and cause partial melting of the convecting mantle wedge a large amount of fluids can be released from hydrated morb at depths shallower than 55 km which move upwards to hydrate the wedge corner under the fore arc and never drag down to the deeper mantle along the slab surface slab dehydration reactions at 120 km depth are the antigorite related 5 reactions which supply water rich fluids for forming the volcanic front phase a and mg surssasite breakdown reactions at 200 and 300 km depths below 700 c cause the second and third arcs respectively moreover the dehydration reactions of super hydrous phase b phases d and e at 500 660 km depths cause the fluid transportation to the mantle boundary layer mbl 410 660 km depth the stagnant slabs extend from japan to beijing china for over 1000 km long indicating that the arc trench system covers the entire region from the japan trench to east asia we propose a big mantle wedge bmw model herein where hydrous plumes originating from 410 km depth cause a series of intra continental hot regions fluids derived from mbl accumulated by the double sided subduction zones rather than the india asia collision and the subsequent indentation into asia are the major cause for the active tectonics and mantle dynamics in this broad region

validating tomographic model with broad band waveform modelling an example from the la ristra transect in the southwestern united states summary traveltime tomographic models of the la ristra transect produce excellent waveform fits if we amplify the damped images we observe systematic waveform distortions across the western edge of the great plains from south american events starting about 300 km east of the centre of the rio grande rift the amplitude decreases by more than 50 per cent within array stations spanning less than 200 km while the pulse width increases by more than a factor of 2 this feature is not observed for the data arriving from the northwest while the s wave tomographic image shows a fast slab like feature dipping to the southeast beneath the western edge of the great plains synthetics generated from this model do not reproduce the waveform characteristics however once we modify the tomographic image by amplifying the velocity contrast between the slab and adjoining mantle by a factor of 2 3 the synthetics produce observed amplitude decay and pulse broadening in addition to the traveltime delay amplitude variation due to wave phenomena such as slab diffraction focusing and defocusing provide much tighter constraints on the geometry of the fast anomaly and its amplitude and sharpness as demonstrated by a forward sensitivity test and snapshots of the seismic wavefield our preferred model locates the slab 200 km east of the rio grande rift dipping 70 75 to the southeast extending to a depth near 600 km with a thickness of 120 km and a velocity of about 4 per cent fast in short adding waveform and amplitude components to regional tomographic studies can help validate and establish structural geometry sharpness and velocity contrast