infragravity wave dynamics in a barred coastal region a numerical study this paper presents a comprehensive numerical study into the infragravity wave dynamics at a field site characterized by a gently sloping barred beach the nonhydrostatic wave flow model swash was used to simulate the local wavefield for a range of wave conditions including mild and storm conditions the extensive spatial coverage of the model allowed us to analyze the infragravity wave dynamics at spatial scales not often covered before overall the model predicted a wavefield that was representative of the natural conditions supporting the model application to analyze the wave dynamics the infragravity wave field was typically dominated by leaky waves except near the outer bar where bar trapped edge waves were observed relative contributions of bar trapped waves peaked during mild conditions when they explained up to 50 of the infragravity variance near the outer bar the infragravity wave growth was partly explained by nonlinear energy transfers from short waves this growth was strongest for mild conditions and decreased for more energetic conditions when short waves were breaking at the outer bar further shoreward infragravity waves lost most of their energy due to a combination of nonlinear transfers bottom friction and infragravity wave breaking nonlinear transfers were only effective near the inner bar whereas near the shoreline where losses were strongest the dissipation was caused by the combined effect of bottom friction and breaking this study demonstrated the model s potential to study wave dynamics at field scales not easily covered by in situ observations

lithosphere asthenosphere p wave reflectivity across australia abstract a direct image of p wave reflectivity in the lithosphere and asthenosphere beneath seismic stations is extracted from stacked autocorrelograms of continuous component records the autocorrelograms emphasise near vertically travelling waves so that multiples are more muted than in receiver function studies and it is possible to work at higher frequencies than for receiver functions across a wide range of geological environments in australia in the 0 5 4 0 hz frequency band distinct reflections are seen in the crust underlain by weaker reflectivity in the lithosphere and asthenosphere the base of crustal reflectivity fits well with moho estimates from other classes of information few mantle reflectors have been seen in conventional reflection profiling at frequencies above 10 hz the presence of reflections in the 0 5 4 0 hz band suggests variations on vertical scales of a few hundred metres with amplitudes of the order of 1 there are slight indications of a change of reflection character in the lower part of the lithosphere in the transition to the asthenosphere at a few stations there is a very clear lamination at asthenospheric depth as well as reflections from the base of the s wave low velocity zone reflection bands often occur at depths where discontinuities have been inferred from s wave receiver function work at the same station but would not by themselves be distinctive of a mid lithosphere discontinuity

auto correlation analysis of coda waves from local earthquakes for detecting temporal changes in shallow subsurface structures the 2011 tohoku oki japan earthquake for monitoring temporal changes in subsurface structures i propose to use auto correlation functions of coda waves from local earthquakes recorded at surface receivers which probably contain more body waves than surface waves use of coda waves requires earthquakes resulting in decreased time resolution for monitoring nonetheless it may be possible to monitor subsurface structures in sufficient time resolutions in regions with high seismicity in studying the 2011 tohoku oki japan earthquake mw 9 0 for which velocity changes have been previously reported i try to validate the method kik net stations in northern honshu are used in this analysis for each moderate earthquake normalized auto correlation functions of surface records are stacked with respect to time windows in the s wave coda aligning the stacked normalized auto correlation functions with time i search for changes in phases arrival times the phases at lag times of 1 s are studied because changes at shallow depths are focused temporal variations in the arrival times are measured at the stations based on the stretching method clear phase delays are found to be associated with the mainshock and to gradually recover with time the amounts of the phase delays are 10 on average with the maximum of about 50 at some stations the deconvolution analysis using surface and subsurface records at the same stations is conducted for validation the results show the phase delays from the deconvolution analysis are slightly smaller than those from the auto correlation analysis which implies that the phases on the auto correlations are caused by larger velocity changes at shallower depths the auto correlation analysis seems to have an accuracy of about several percent which is much larger than methods using earthquake doublets and borehole array data so this analysis might be applicable in detecting larger changes in spite of these disadvantages this analysis is still attractive because it can be applied to many records on the surface in regions where no boreholes are available

crustal imaging across the north anatolian fault zone from the autocorrelation of ambient seismic noise seismic images of active fault zones can be used to examine the structure of faults throughout the crust and upper mantle and give clues as to whether the associated deformation occurs within a narrow shear zone or is broadly distributed through the lower crust limitations on seismic resolution within the crust and difficulties imaging shallow structures such as the crust mantle boundary moho place constraints on the interpretation of seismic images in this study we retrieve body wave reflections from autocorrelations of ambient seismic noise the instantaneous phase coherence autocorrelations allow unprecedented ambient noise images of the north anatolian fault zone nafz our reflection profiles show a moho reflected p wave and additional structure within the crust and upper mantle we image a distinct vertical offset of the moho associated with the northern branch of the nafz indicating that deformation related to the fault remains narrow in the upper mantle

antarctic ice sheet structures retrieved from p wave coda autocorrelation method and comparisons with two other single station passive seismic methods passive seismology is becoming increasingly popular for glacier ice sheet structure investigations in polar regions single station passive seismic methods including p wave receiver functions prfs horizontal to vertical spectral ratio hvsr and a recently proposed autocorrelation method have been used to retrieve glacier ice sheet structures despite their successful applications analysis regarding their detection abilities in different glaciological environments has not been reported in this study we compare ice thicknesses and v p v s ratios obtained from the three methods using data collected at gamseis and polenet anet seismic arrays in antarctica ice thickness estimates derived from the three methods are found to be consistent comparisons conducted under various model setups including those involving tiled layers and sedimentary layers show that the effectiveness of the autocorrelation method is not superior to the prf method for retrieving ice sheet structures the autocorrelation method however can complement other methods as it only requires a single component seismic record

expected seismicity and the seismic noise environment of europa seismic data will be a vital geophysical constraint on internal structure of europa if we land instruments on the surface quantifying expected seismic activity on europa both in terms of large recognizable signals and ambient background noise is important for understanding dynamics of the moon as well as interpretation of potential future data seismic energy sources will likely include cracking in the ice shell and turbulent motion in the oceans we define a range of models of seismic activity in europa s ice shell by assuming each model follows a gutenberg richter relationship with varying parameters a range of cumulative seismic moment release between 10 16 and 10 18 nm yr is defined by scaling tidal dissipation energy to tectonic events on the earth s moon random catalogs are generated and used to create synthetic continuous noise records through numerical wave propagation in thermodynamically self consistent models of the interior structure of europa spectral characteristics of the noise are calculated by determining probabilistic power spectral densities of the synthetic records while the range of seismicity models predicts noise levels that vary by 80 db we show that most noise estimates are below the self noise floor of high frequency geophones but may be recorded by more sensitive instruments the largest expected signals exceed background noise by 50 db noise records may allow for constraints on interior structure through autocorrelation models of seismic noise generated by pressure variations at the base of the ice shell due to turbulent motions in the subsurface ocean may also generate observable seismic noise

unearthing the buried palu koro fault and the pattern of damage caused by the 2018 sulawesi earthquake using hvsr inversion

sensitivity and inversion of borehole flexural dispersions for formation parameters propagation characteristics of borehole flexural waves are functions of five borehole fluid and formation parameters uncertainties in any of these model parameters may introduce errors in the estimate of formation shear wave speed other sources of error in the estimate may be caused by deviations from the assumed circular borehole cross section or heterogeneity in the material properties of formation in the vicinity of a borehole from the usually assumed homogeneous properties the influence of uncertainties in model parameters on borehole flexural dispersion has been calculated from a general perturbation model based on hamilton s principle a sensitivity analysis of the flexural dispersion to small variations in the model parameters shows that the formation shear speed has by far the most dominant influence in a slow formation in contrast the flexural dispersion in a fast formation is significantly influenced by three of the five model parameters the formation shear speed the borehole fluid compressional speed and the borehole diameter the frequency dependence of these sensitivity functions indicates that the inversion of flexural dispersion for formation shear speed is optimal in the range 2 4 khz for a borehole of diameter 25 4 cm the range of validity of the perturbation model has been estimated by comparing results of concentric annuli of different thicknesses and shear wave speeds different from that of the formation with those from exact numerical solutions from a modal search program generally the perturbation results for altered annuli of thicknesses up to 15 cm are accurate to within 1 per cent for a shear wave speed 10 per cent lower than that of the formation this difference between the perturbation and exact results increases to approximately 1 to 3 per cent for a shear wave speed 20 per cent lower than that of the formation

modeled alongshore circulation and force balances onshore of a submarine canyon alongshore force balances including the role of nonlinear advection in the shoaling and surf zones onshore of a submarine canyon are investigated using a numerical modeling system delft3d swan the model is calibrated with waves and alongshore flows recorded over a period of 1 5 months at 26 sites along the 1 0 2 5 and 5 0 m depth contours spanning about 2 km of coast field observation based estimates of the alongshore pressure and radiation stress gradients are reproduced well by the model model simulations suggest that the alongshore momentum balance is between the sum of the pressure and radiation stress gradients and the sum of the nonlinear advective terms and bottom stress with the remaining terms e g wind stress and turbulent mixing being negligible the simulations also indicate that unexplained residuals in previous field based estimates of the momentum balance may be owing to the neglect of the nonlinear advective terms which are similar in magnitude to the sum of the forcing pressure and radiations stress gradients and to the bottom stress

swash an operational public domain code for simulating wave fields and rapidly varied flows in coastal waters abstract a computational procedure has been developed for simulating non hydrostatic free surface rotational flows in one and two horizontal dimensions its implementation in the publicly available swash an acronym of simulating waves till shore is intended to be used for predicting transformation of surface waves and rapidly varied shallow water flows in coastal waters this open source code http swash sourceforge net has been developed based on the work of stelling and zijlema 2003 stelling and duinmeijer 2003 zijlema and stelling 2005 zijlema and stelling 2008 the governing equations are the nonlinear shallow water equations including non hydrostatic pressure and provide a general basis for describing complex changes to rapidly varied flows typically found in coastal flooding resulting from e g dike breaks and tsunamis and wave transformation in both surf and swash zones due to nonlinear wave wave interactions interaction of waves with currents and wave breaking as well as runup at the shoreline the present paper provides a complete description of the numerical algorithms currently used in the code the code is benchmarked using some analytical problems moreover the numerical results are validated with various cases of laboratory data with the principal aim to convey the capabilities of the swash code in particular emphasis is put on an analysis of model performance and associated physical implications serial and parallel performance scalings are also presented

numerical simulation of interactions between water waves and inclined moored submerged floating breakwaters abstract this paper studies the interactions of water waves with submerged floating breakwaters moored by inclined tension legs using a numerical wave tank model proposed by lee and mizutani 2009 and based on the navier stokes solver this model combines a direct forcing immersed boundary ib method volume of fluid vof method and the mechanics model of the floating breakwater the floating breakwaters are free on three degrees of freedoms namely surge heave and pitch two floating breakwater shapes rectangular and circular are used in the experimental and numerical investigations to validate that the model is capable of treating solid boundaries with complex shapes the non breaking and breaking waves are carefully chosen to study the nonlinear interactions between water waves and the submerged floating breakwaters comparisons of the computed and measured results reveal a favorable agreement in terms of the free water surface tension force acting on the mooring line and dynamics of the floating body a slight phase discrepancy is found between the offshore and onshore mooring forces in the case of a circular floating breakwater whereas this phenomenon is not observed in the rectangular case in addition fully nonlinear phenomena and viscous process in the flow field such as wave breaking the boundary layer separation on the interface vortex formation and motion can be reproduced and captured accurately using the numerical model

mapping the basement of the ebro basin in spain with seismic ambient noise autocorrelations this work is funded by the spanish project misterios cgl2013 48601 c2 1 r we also acknowledge support and discussion through tides cost action es1401

shoreline response to a single shore parallel submerged breakwater submerged breakwaters sbws are becoming a popular option for coastal protection mainly due to their low aesthetic impact on the natural environment however sbws have rarely been employed for coastal protection in the past and therefore their efficacy remains largely unknown the main objective of the present study was to investigate the structural and environmental conditions that govern the mode of shoreline response i e shoreline erosion vs shoreline accretion to sbws the relative importance of the key structural and environmental parameters governing the response mode to a single shore parallel sbw is investigated through a combination of theoretical analysis and numerical modelling using physical considerations a theoretical response function model is derived under several simplifying assumptions including parallel depth contours linear wave theory shore normal waves and no wave current interaction numerical modelling is undertaken with the mike21 model suite to simulate the depth averaged velocity fields without morphological updating due to waves acting on a single shore parallel sbw located on a schematised beach with parallel depth contours in total 92 coupled wave current simulations were undertaken the results indicate that the mode of shoreline response to the sbw can be expressed in terms of the two non dimensional parameters h b h 0 and s b h b 3 2 l b h b 2 a 3 h b 1 2 variables defined in the text c 2010 elsevier b v all rights reserved less

dipole dispersion crossover and sonic logs in a limestone reservoir analyses of sonic logs in a horizontal well provide new information about mechanical properties of rocks made possible by recent developments in our understanding of acoustic wave propagation in prestressed formations most sections of this horizontal well exhibit azimuthal shear isotropy indicating isotropic stresses in the plane perpendicular to the well trajectory leading to stable wellbore conditions however two sections show dipole dispersion crossovers that confirm the presence of stress induced shear anisotropy caused by a difference between the maximum and minimum stresses in the plane perpendicular to the well trajectory the two dipole dispersions are obtained by processing the recorded waveforms by a modified matrix pencil algorithm the fast shear direction is estimated from alford rotation of the cross dipole waveforms one section of the well exhibits the fast shear direction parallel to the overburden stress as the maximum stress direction whereas the other section has the fast shear direction parallel to the horizontal stress that is larger than the overburden stress the cause of this change in the fast shear direction is believed to be the well s penetration into a 3 ft thick bed with lower porosity and permeability and significantly higher elastic stiffnesses than those in the other part of the homogeneous high permeability reservoir a stiff bed is likely to have greater stresses in its plane than perpendicular to it which would make the horizontal stresses greater than the vertical

efficient computation of surf zone waves using the nonlinear shallow water equations with non hydrostatic pressure abstract a numerical method for non hydrostatic free surface irrotational flow governed by the nonlinear shallow water equations including the effects of vertical acceleration is presented at the aim of studying surf zone phenomena a vertical boundary fitted grid is used with the water depth divided into a number of layers a compact finite difference scheme is employed for accurate computation of frequency dispersion requiring a limited vertical resolution and hence capable of predicting the onset of wave breaking a novel wet dry algorithm is applied for a proper handling of moving shoreline mass and momentum are strictly conserved at discrete level while the method only dissipates energy in the case of wave breaking the numerical results are verified with a number of tests and show that the proposed model using two layers without ad hoc assumptions enables to resolve propagating nonlinear shoaling breaking waves and wave run up within the surf and swash zones in an efficient manner

crustal properties from seismic station autocorrelograms s u m m a r y stations on the australian continent receive a rich mixture of continuous ground motion with ambient seismic noise from the surrounding oceans and numerous small earthquakes in the earthquake belts to the north in indonesia and east in tonga kermadec as well as more distant source zones the ground motion at a seismic station contains information about the structure in the vicinity of the site and this can be exploited by applying an autocorrelation procedure to the continuous records by creating stacked autocorrelograms of the ground motion at a single station information on crust properties can be extracted in the form of a signal that includes the crustal reflection response convolved with the autocorrelation of the combined effect of source excitation and the instrument response after applying suitable high pass filtering the reflection component can be extracted to reveal the most prominent reflectors in the lower crust which often correspond to the reflection at the moho because the reflection signal is stacked from arrivals from a wide range of slownesses the reflection response is somewhat diffuse but still sufficient to provide useful constraints on the local crust beneath a seismic station continuous vertical component records from 223 stations permanent and temporary across the continent have been processed using autocorrelograms of running windows 6 hr long with subsequent stacking a distinctive pulsewith a time offset between 8 and 30 s fromzero is found in the autocorrelation results with frequency content between 1 5 and 4 hz suggestingp wave multiples trapped in the crust synthetic modelling with control of multiple phases shows that a local pmp phase can be recovered with the autocorrelation approach this identification enables us to make out the depth to the most prominent crustal reflector across the continent we obtain results that largely conform to those from previous studies using a combination of data from refraction reflection profiles and receiver functions this approach can be used for crustal property extraction using just vertical component records and effective results can be obtained with temporary deployments of just a few months

reflection imaging of the moon s interior using deep moonquake seismic interferometry the internal structure of the moon has been investigated over many years using a variety of seismic methods such as travel time analysis receiver functions and tomography here we propose to apply body wave seismic interferometry to deep moonquakes in order to retrieve zero offset reflection responses and thus images beneath the apollo stations on the nearside of the moon from virtual sources colocated with the stations this method is called deep moonquake seismic interferometry dmsi our results show a laterally coherent acoustic boundary around 50 km depth beneath all four apollo stations we interpret this boundary as the lunar seismic moho this depth agrees with japan aerospace exploration agency s jaxa selenological and engineering explorer selene result and previous travel time analysis at the apollo 12 14 sites the deeper part of the image we obtain from dmsi shows laterally incoherent structures such lateral inhomogeneity we interpret as representing a zone characterized by strong scattering and constant apparent seismic velocity at our resolution scale 0 2 2 0 hz

shallow crustal imaging using distant high magnitude earthquakes global phases viz seismic phases that travel through the earth s core can be used to locally image the crust by means of seismic interferometry this method is known as global phase seismic interferometry glopsi traditionally glopsi retrieves low frequency information up to 1 hz recent studies however suggest that there is high frequency signal present in the coda of strong distant earthquakes this research quantifies the potential of these high frequency signals by analysing recordings of a multitude of high magnitude earthquakes 6 4 mw and their coda on a selection of permanent usarray stations nearly half of the p pkp and pkikp phases are recorded with a signal to noise ratio of at least 5 db at 3 hz to assess the viability of using the high frequency signal the second half of the paper highlights two case studies first a known sedimentary structure is imaged in malargue argentina secondly the method is used to reveal the structure of the midcontinent rift below the spree array in minnesota usa both studies demonstrate that structural information of the shallow crust 5 km below the arrays can be retrieved in particular the interpreted thickness of the sedimentary layer below the malargue array is in agreement with earlier studies in the same area being able to use global phases and direct p phases with large epicentral distances 80 to recover the earth s sedimentary structure suggests that glopsi can be applied in an industrial context

simulating the wave induced response of a submerged wave energy converter using a non hydrostatic wave flow model abstract with the increasing interest in wave energy and when moving towards commercial scale wave energy projects a detailed understanding of the interactions between single and arrays of wave energy converters wecs with the ambient wave and flow field becomes imperative for both design and operational purposes as well as assessment of their environmental impacts this work presents a new numerical approach to simulate the nonlinear evolution of the waves and their interactions with a submerged wave energy converter at the scale of a realistic coastal region the numerical approach is based on the non hydrostatic framework and implemented in the open source swash model which provides an efficient tool to simulate the nonlinear evolution of waves over realistic coastal bathymetries here we present a numerical extension to the non hydrostatic approach to account for interactions between waves and a submerged point absorber and to capture the response of such a wave energy device model results are compared with an analytical solution based on potential flow theory a cfd simulation and experimental data to validate its capabilities in simulating the wave wec interactions for both linear and nonlinear wave conditions overall the results of this validation demonstrate that the model captures the wave structure interactions and the body response with satisfactory accuracy notably the results also indicate that a coarse vertical resolution was sufficient to capture these dynamics making the model sufficiently computationally efficient to simulate the interaction of waves and wecs over large scales as a consequence this new modelling approach should provide a promising new alternative to simulate the interactions between nonlinear wave fields and submerged point absorbers at the scale of a realistic coastal region

the importance of a small wall deformation in the three dimensional acoustic logging results summary a variety of seismic techniques use fluid filled boreholes to host detectors and seismic sources the complexity of the wavefield generated depends on the position of the receivers and the source frequency excited type of formation and type of source in the present paper the boundary element method is used to study the wavefield elicited by monopole or dipole sources within a fluid filled cylindrical cavity drilled through an unbounded elastic formation this model is used to assess the effects of the existence of a small localized wall deformation on the response such a deformation may occur through the mechanical action of the drill string rock failure adjacent to a drilled borehole plastic deformation and washing out of the borehole in soft or poorly consolidated rocks in addition the effect of a source receiver tool placed in an off centre and or tilted position inside the fluid filled borehole on the propagation of both axisymmetric and non axisymmetric wave modes are studied

simulation and interpretation of sonic waveforms in high angle and horizontal wells abstractwe have developed a new method to process and interpret sonic waveforms acquired in high angle ha and horizontal hz wells in the vicinity of layer boundaries numerical simulations are examined for ha hz fluid filled borehole models in which sonic tools with monopole and dipole sources operate across a horizontal bed boundary in hard and soft formations simulations are performed with a 3d time domain finite difference method assuming a sonic logging tool in which each receiver station consists of eight azimuthal receivers instead of conventional processing for monopole and dipole waveforms which takes the average and difference respectively of waveforms acquired with azimuthal receivers we analyze the waveforms acquired individually by each azimuthal receiver for dipole sources we refer to the dispersive signals recorded by individual receivers as pseudo flexural waves and we first process them with a weighted spectral semblance method to obtain the frequency dispersion curves we t

large runup controls on a gently sloping dissipative beach observations on a mildly sloping beach suggest that the largest runup events are related to bore bore capture bbc a numerical model based on the reynolds averaged navier stokes equation is implemented to evaluate the effects that bbc have on runup from simulations with realistic sea states bbc is found to be a necessary but not sufficient condition for large runup generation the dominant dynamics leading to bbc are amplitude dispersion and interactions with infragravity waves in the outer and inner surf zone respectively when the effects of bbc are isolated it is found that the runup associated with the merging of two bores is at least 50 larger than that associated with the larger of the two waves in a monochromatic wave train the phase difference of the incident waves with the infragravity wave can generate up to 30 variability of the runup maxima the majority of the shoreward directed momentum flux prior to runup initiation is related to the interaction between the bores and the infragravity wave followed by that of the incident infragravity waves alone

passive seismic imaging using microearthquakes we have developed a method of processing seismic signals generated by microearthquakes to image local subsurface structure beneath a recording station this technique uses the autocorrelation of the vertically traveling earthquake signals to generate pseudoreflection seismograms that can be interpreted for subsurface structure processed pseudoreflection data from microearthquakes recorded in the island of hawaii show consistent reflectivity patterns that are interpreted as near surface horizontal features forward modeling of the pseudoreflection data results in a p wave velocity model that shows reasonable agreement with the velocity model derived from a refraction study in the region usable signal to noise ratio is obtained down to 2 s a shear wave velocity model was also generated by applying this technique to horizontal component data

towards simulating floating offshore oscillating water column converters with smoothed particle hydrodynamics abstract the mesh free code dualsphysics is applied to simulate the interaction between sea waves and an oscillating water column device owc in this work capabilities and limitations of dualsphysics are shown in simulating owcs on the one hand the new capabilities of dualsphysics are shown by simulating the effect of mooring systems on a floating offshore owc on the other hand simulations only consider a single phase water so that the full owc behaviour is partially reproduced i e air pressure fluctuations are not modelled the model was first validated with one laboratory test that consists of a fixed owc with an open chamber next water surface oscillations inside the chamber of a real owc located in mutriku spain have been predicted using the prevalent wave conditions observed in the area finally the capabilities of dualsphysics were demonstrated by simulating an offshore owc moored to the seabed

ground motion modeling of hayward fault scenario earthquakes part ii simulation of long period and broadband ground motions abstract we simulate long period t 1 0 2 0 s and broadband t 0 1 s ground motions for 39 scenario earthquakes m w 6 7 7 2 involving the hayward calaveras and rodgers creek faults for rupture on the hayward fault we consider the effects of creep on coseismic slip using two different approaches both of which reduce the ground motions compared with neglecting the influence of creep nevertheless the scenario earthquakes generate strong shaking throughout the san francisco bay area with about 50 of the urban area experiencing modified mercalli intensity vii or greater for the magnitude 7 0 scenario events long period simulations of the 2007 m w 4 18 oakland earthquake and the 2007 m w 5 45 alum rock earthquake show that the u s geological survey s bay area velocity model version 08 3 0 permits simulation of the amplitude and duration of shaking throughout the san francisco bay area for hayward fault earthquakes with the greatest accuracy in the santa clara valley san jose area the ground motions for the suite of scenarios exhibit a strong sensitivity to the rupture length or magnitude hypocenter or rupture directivity and slip distribution the ground motions display a much weaker sensitivity to the rise time and rupture speed peak velocities peak accelerations and spectral accelerations from the synthetic broadband ground motions are on average slightly higher than the next generation attenuation nga ground motion prediction equations we attribute much of this difference to the seismic velocity structure in the san francisco bay area and how the nga models account for basin amplification the nga relations may underpredict amplification in shallow sedimentary basins the simulations also suggest that the spudich and chiou 2008 directivity corrections to the nga relations could be improved by increasing the areal extent of rupture directivity with period

a numerical simulation of the acoustic and elastic wavefields radiated by a source on a fluid filled borehole embedded in a layered medium the authors present a method of calculation to simulation the propagation of acoustic and elastic waves generated by a borehole source embedded in a layered medium the method is formulated as a boundary element technique where the green s functions are calculated by the discrete wavenumber method the restrictive assumptions are that the borehole is cylindrical and that its axis runs normal to the layer interfaces the physics of the method rely on huygens s principle that states that a diffracting boundary the borehole wall in the present case can be represented as a distribution of secondary sources the borehole is discretized into small cylindrical elements and each element is represented by three sources a volume source representing the wavefield diffracted in the fluid and two surface forces that give rise to the elastic wavefield radiated outside the borehole the strength of each source is obtained by solving the linear system of equations that describes the boundary conditions at the borehole wall the method is used to generate synthetic acoustic log s and to investigate the wavefield radiated into the formation the simulations considered display the stoneley wave reflections at the bed boundaries and show the importance of the diffraction that takes place wheremore the borehole wall intersects the layer interfaces less

borehole flexural modes in anisotropic formations a perturbation method of solution is an efficient way of analyzing elastic wave propagation along a borehole in anisotropic formations the perturbation model allows us to calculate changes in the modal dispersion curves caused by the differences in elastic constants between the anisotropic formation of interest and a reference or unperturbed isotropic formation the equivalent isotropic constants in the reference formation are obtained from the appropriate compressional and shear wave velocities for the selected propagation and polarization directions of the flexural mode this choice of the unperturbed solution means that the required perturbation is minimal resulting in enhanced accuracy of the perturbed solution computational results are presented for the dispersion curves of borehole flexural waves in a transversely isotropic ti formation as a function of borehole deviation from the ti symmetry axis in addition radial distributions of displacement and stress fields associated with the flexura

global phase seismic interferometry unveils p wave reflectivity below the himalayas and tibet a number of seismic methods exist to image the lithosphere below a collection of receivers using distant earthquakes in the current practice especially mode conversions in teleseismic phases are utilized we present a new method that takes advantage of the availability of global phases this method is called global phase seismic interferometry glopsi with glopsi zero offset reflections are extracted from reverberations near the array caused by global seismicity we exemplify glopsi with data from the hi climb experiment 2002 2005 and migrate the obtained reflection responses this results in a 800 km long reflectivity profile through the himalayas and a large part of the tibetan plateau

phase weighted stacking applied to low frequency earthquakes abstract we apply phase weighted stacking pws to the analysis of low frequency earthquakes lfes in the parkfield california region and central cascadia the technique uses the coherence of the instantaneous phase among the stacked signals to enhance the signal to noise ratio snr of the stack we find that for picking lfe arrivals for the parkfield california region and for lfe template formation in central cascadia pws is extremely effective for lfes in the parkfield california region pws yields many more usable phases than standard linear stacking and for lfe detection in cascadia pws produces templates with much higher snr than linear stacking

crust mantle boundary reflectors in nevada from ambient seismic noise autocorrelations summary the depth of reflector layers in the earth s crust is usually estimated using controlled sources or earthquake signals ambient seismic noise however can also be used for this purpose we develop and apply a new method based on continuous waveform analysis to estimate the two way p wave reflection component of the green s function beneath each station the green s functions are retrieved from continuous record autocorrelation stacks at broad band sensor locations within the usarray earthscope transportable array in the western great basin and the sierra nevada in a region with complex crustal and upper mantle structure in this paper we show evidence of a reflector at the crust mantle boundary moho discontinuity derived for the first time from ambient noise autocorrelations using short period 1 s data our results compare well with earthquake and controlled source investigations and with tomography findings in the region moho depth is difficult to resolve seismically because of the lack of favourable spatial distribution of source and receiver geometries in contrast our method can be applied at any desired sensor spacing to estimate earth reflector depth beneath surface located sensors providing unprecedented resolution

reply to comment on crustal thickness across the trans european suture zone from ambient noise autocorrelations by g becker and b knapmeyer endrun by g helffrich

bathymetric control on the spatial distribution of wave breaking in the surf zone of a natural beach abstract a non hydrostatic wave model swash that phase resolves the free surface and fluid motions in the water column is applied to investigate wave transformation and the spatial distribution of wave breaking over different morphological features the model is forced using observed directional energy spectra and results are compared to wave observations collected outside the surf zone using acoustic wave sensors and over a 100 m nearshore transect using high frequency measurements of the sea surface from a lidar sensor mounted on the beach dune at the field research facility in duck nc the model is applied to four cases with different wave conditions and bathymetry tested for sensitivity of model parameters to these different natural conditions and used to predict the spatial variability in wave breaking and correlation between energy dissipation and morphologic features model results compare very well with observations of spectral evolution outside the surf zone and generally well with the remotely sensed observations of wave transformation inside the surf zone with r 0 85 0 93 for h s along the cross shore transect in particular the model is able to spatially resolve wave shoaling and dissipation at the shore break at the same location as observed in the lidar data the results indicate that nearshore morphology has a significant effect on the spatial distribution of wave energy dissipation alongshore variability in bathymetry due to bars rip channels and larger morphological features such as the scour depression under the pier causes large alongshore changes in cross shore wave energy flux that influence the location and intensity of wave breaking

turbulent mixing in a strongly forced salt wedge estuary up to about 400 m 3 s 1 above which a majority of the mixing occurs offshore observed buoyancy fluxes were more consistent with the k turbulence closure than the mellor yamada closure and more total mixing occurred in the estuary with k calculated buoyancy fluxes were sensitive to horizontal grid resolution as a lower resolution grid yielded less integrated buoyancy flux in the estuary and exported lower salinity water but likely had greater numerical mixing

modes of noncircular fluid filled boreholes in elastic formations dispersion curves for4 the modes of noncircular fluid filled boreholes in homogeneous elastic formations are calculated with a boundary integral formulation results are displayed for the propagatory modes of several borehole shapes in both fast and slow formations any departure from circularity reduces the tube wave speed agreement with exact analytical results is obtained for elliptical boreholes while a simple approximate relation involving borehole perimeter and area is verified for arbitrary cross sections higher order surface modes such as the flexural and screw modes split into two distinct branches distinguished by their orientation with respect to the principal axes of the borehole cross section modal dispersion characteristics in elliptical boreholes may be approximately by scaled circular borehole results in fast formations the effective scaled radii are related to transverse dimensions of the borehole but in slow formations they are more closely related to local radii of curvature of the borehole for more complex cross sections with a single axis of symmetry dispersion of the flexural mode is well modeled by that in elliptical boreholes of similar dimensions while that of stoneley and screw modes is not in asymmetrical boreholes significant torsional and out of phase motion may occur

stacking autocorrelograms to map moho depth with high spatial resolution in southeastern australia current estimates of moho depth in southeastern australia are based on sparse sampling the results are augmented with 180 new moho estimates constructed from spatial stacks of crustal p wave reflectivity derived from autocorrelograms at over 750 stations the spatial stacks of reflectivity are constructed using a gaussian with half width 0 5 picks of the base of crustal reflectivity are made with the aid of the previous moho model based on the sparser data and knowledge of the variation in the character of the crust mantle boundary across the region good ties can be made to previous results from deep reflection profiling the new information fills in many holes in coverage and provides a moho map with closer ties to geological provinces the procedure exploits the continuous records at the stations and just the vertical components and so can be applied to older data for which receiver function techniques cannot be used

simulating waves and their interactions with a restrained ship using a non hydrostatic wave flow model this paper presents a numerical model to simulate the evolution of waves and their interactions with a restrained ship that is moored in coastal waters the model aims to be applicable at the scale of a harbour or coastal region while accounting for the key physical processes that determine the hydrodynamic loads on the ship its methodology is based on the non hydrostatic wave flow model swash which provides an efficient tool to simulate the nonlinear dynamics that govern the nearshore wave field in this work we propose a new numerical algorithm that accounts for the presence of a non moving floating body to resolve the wave impact on a restrained ship the model is validated through comparisons with an analytic solution a numerical solution and two laboratory campaigns the results of the model data comparison demonstrate that the model captures the scattering of waves by a restrained body furthermore it gives a reasonable prediction of the hydrodynamic loads that act on a restrained container ship for a range of wave conditions importantly the model captures these dynamics efficiently which demonstrates that it retains this favourable property of the non hydrostatic approach when a floating body is included the findings of this study suggest that the model provides a promising new alternative to simulate the nonlinear evolution of waves and their impact on a restrained ship at the scale of a realistic harbour or coastal region

modeling of depth induced wave breaking under finite depth wave growth conditions 1 recent studies have shown that the spectral wind wave model swan simulating waves nearshore underestimates wave heights and periods in situations of finite depth wave growth in this study this inaccuracy is addressed through a rescaling of the battjes and janssen 1978 bore based model for depth induced breaking considering both sloping bed surf zone situations and finite depth wave growth conditions it is found that the variation of the model error with the breaker index bj in this formulation differs significantly between the two types of conditions for surf zones clear optimal values are found for the breaker index by contrast under finite depth wave growth conditions model errors asymptotically decrease with increasing values of the breaker index weaker dissipation under both the surf zone and finite depth wave growth conditions optimal calibration settings of bj were found to correlate with the dimensionless depth kpd where kp is the spectral peak wave number and d is the water depth and the local mean wave steepness subsequently a new breaker index based on the local shallow water nonlinearity expressed in terms of the biphase of the self interactions of the spectral peak is proposed implemented in the bore based breaker model of thornton and guza 1983 this breaker index accurately predicts the large difference in dissipation magnitudes found between surf zone conditions and finite depth growth situations hence the proposed expression yields a significant improvement in model accuracy over the default battjes and janssen 1978 model for finite depth growth situations while retaining good performance for sloping bed surf zones

monitoring seismic velocity change caused by the 2011 tohoku oki earthquake using ambient noise records 1 we estimated the changes in seismic velocity in the southern tohoku district of japan during the six month period centered on the 11 march 2011 tohoku oki earthquake using scattered waves retrieved by autocorrelation of ambient seismic noise the estimated velocity decrease after the earthquake and after two large aftershocks in the study area was as great as 1 5 in the area nearest to the mainshock the velocity changes displayed gradual healing the spatial distribution of the velocity change showed a correlation with both the changes in static strain derived from gps records and the peak particle velocity experienced during the three earthquakes derived from strong motion records therefore our results show that velocity changes possibly contain information from deep in the crust bearing on coseismic stress release in addition to shallower effects due to strong ground motion

comprehensive observation and modeling of earthquake and temperature related seismic velocity changes in northern chile with passive image interferometry we report on earthquake and temperature related velocity changes in high frequency autocorrelations of ambient noise data from seismic stations of the integrated plate boundary observatory chile project in northern chile daily autocorrelation functions are analyzed over a period of 5 years with passive image interferometry a short term velocity drop recovering after several days to weeks is observed for the mw 7 7 tocopilla earthquake at most stations at the two stations pb05 and patcx we observe a long term velocity decrease recovering over the course of around 2 years while station pb05 is located in the rupture area of the tocopilla earthquake this is not the case for station patcx station patcx is situated in an area influenced by salt sediment in the vicinity of salar grande and presents a superior sensitivity to ground acceleration and periodic surface induced changes due to this high sensitivity we observe a velocity response of several regional earthquakes at patcx and we can show for the first time a linear relationship between the amplitude of velocity drops and peak ground acceleration for data from a single station this relationship does not hold true when comparing different stations due to the different sensitivity of the station environments furthermore we observe periodic annual velocity changes at patcx analyzing data at a temporal resolution below 1 day we are able to identify changes with a period of 24 h too the characteristics of the seismic velocity with annual and daily periods indicate an atmospheric origin of the velocity changes that we confirm with a model based on thermally induced stress this comprehensive model explains the lag time dependence of the temperature related seismic velocity changes involving the distribution of temperature fluctuations the relationship between temperature stress and velocity change plus autocorrelation sensitivity kernels

influence of borehole eccentred tools on wireline and logging while drilling sonic logging measurements we describe a numerical study to quantify the influence of tool eccentricity on wireline wl and logging while drilling lwd sonic logging measurements simulations are performed with a height polynomial adaptive hp fourier finite element method that delivers highly accurate solutions of linear visco elasto acoustic problems in the frequency domain the analysis focuses on wl instruments equipped with monopole or dipole sources and lwd instruments with monopole excitation analysis of the main propagation modes obtained from frequency dispersion curves indicates that the additional high order modes arising as a result of borehole eccentricity interfere with the main modes i e stoneley pseudo rayleigh and flexural this often modifies decreases the estimation of shear and compressional formation velocities which should be corrected increased to account for borehole eccentricity effects undesired interferences between different modes can occur at different frequencies depending upon the properties of the formation and fluid annulus size which may difficult the estimation of the formation velocities

an efficient method to compute the dynamic response of a fluid filled crack summary the vibration of a fluid filled crack is considered to be one of the most plausible source mechanisms for the long period events and volcanic tremors occurring around volcanoes as a tool for the quantitative interpretation of source process of such volcanic seismic signals we propose a method to numerically simulate the dynamic response of a fluid filled crack in this method we formulate the motions of the fluid inside and the elastic solid outside of the crack using boundary integrals in the frequency domain and solve the dynamic interactions between the fluid and the elastic solid using the point collocation method the present method is more efficient compared with the time domain finite difference method which has been used in simulations of a fluid filled crack and enables us to study the dynamics of a fluid filled crack over a wide range of physical parameters the method also allows us direct calculation of the attenuation quality factor of the crack resonance which is an indispensable parameter for estimating the properties of the fluid inside the crack the method is also designed to be flexible to many applications which may be encountered in volcano seismology and thus extensions of the method to more complicated problems are promising

seismic scatterers within subducting slab revealed from ambient noise autocorrelation 1 we reconstructed new migrated images from autocorrelation functions of ambient noise at seismic stations in northeastern japan during the analysis period the autocorrelation functions having a frequency range of 0 5 2 hz showed some coherent signals at large lapse times of 10 50 s as well as at small lapse times of less than 10 s these signals were also coherent in space along cross sections across the japan subduction zone the migrated images show seismic scatterers within the subducting pacific slab at the depth range of 50 150 km the distribution of the scatterers within the subducting slab is comparable to the double seismic zone in the subduction zone in particular the thickness of the distribution of the seismic scatterers is consistent with that of two planes of the double seismic zone this indicates inhomogeneities in the seismic velocity structure around the upper and lower planes of the seismicity the new migrated images suggest that seismic scatterers such as fluid from dehydration reactions of the hydrated metamorphosed mantle exist in the lower as well as upper plane of the seismicity in the double seismic zone this fluid may act as a scatterer within the subducting slab

pseudoreflection profiling method an efficient complement to cdp method1 a method for pseudoreflection profiling prp is presented by using transmission seismograms this method produces time sections similar to those obtained using the common depth point cdp method pseudoreflection profiles are obtained using the following procedure equivalent transmission responses at sites on soft deposits are derived by wiener filter estimation using seismograms acquired on the sites and on the basement rock these responses are substituted into the claerbout kunetz equation to obtain the pseudoreflection profiles a 3d subsurface model is produced when the prp method is applied to explosion seismograms the time sections thus obtained are consistent with those obtained using the cdp method in a neighbouring area the maximum station interval for obtaining coherent profiles with this method is estimated to be one quarter of the wavelength of the transmitted waves this technique should be used in combination with another method such as the cdp method because it has two weak points the velocity structure cannot be obtained directly and undesirable waves cannot be eliminated through processing