a joint monte carlo analysis of seafloor compliance rayleigh wave dispersion and receiver functions at ocean bottom seismic stations offshore new zealand teleseismic body wave imaging techniques such as receiver function analysis can be notoriously difficult to employ on ocean bottom seismic data due largely to multiple reverberations within the water and low velocity sediments in lieu of suppressing this coherently scattered noise in ocean bottom receiver functions these site effects can be modeled in conjunction with shear velocity information from seafloor compliance and surface wave dispersion measurements to discern crustal structure a novel technique to estimate 1 d crustal shear velocity profiles from these data using monte carlo sampling is presented here we find that seafloor compliance inversions and p s conversions observed in the receiver functions provide complimentary constraints on sediment velocity and thickness incoherent noise in receiver functions from the moana ocean bottom seismic experiment limit the accuracy of the practical analysis at crustal scales but synthetic recovery tests and comparison with independent unconstrained nonlinear optimization results affirm the utility of this technique in principle

wave field decomposition of ocean bottom seismograms seismograms recorded on the seafloor are affected by reverberations in the overlying ocean layer we examine the feasibility of removing these reverberations through a 1d wave field decomposition based on a reflection transmission formulation of the problem two decomposition schemes are presented the first scheme involves a simple manipulation of the fundamental matrix relating stress and displacement of plane harmonic waves to upgoing and downgoing wavevector coefficients and requires measurement of both ocean bottom displacement and pressure the second approach involves only displacement recordings and knowledge of the water column depth this latter quantity will generally be known a priori from deployment logs or alternatively it may be estimated using vertical displacement and pressure seismograms in a preprocessing step both approaches require prior information on seabed properties in the case of p wave incidence the decomposition depends primarily on the seabed s velocity this quantity can be determined by examining trial decompositions over a range of s and selecting the value that minimizes the energy of the upgoing s wave component at the arrival time of the incident wave we apply this approach to synthetic seismograms for a simple earth structure and to recordings of two large events from the central oregon locked zone array colza on the continental margin of oregon the real data indicate that the wave field decompositions are largely successful at lower frequencies 0 1 hz but that 3d scattering likely originating near the sediment basement contact is manifested at higher frequencies

lithospheric structure across oblique continental collision in new zealand from wide angle p wave modeling 1 oblique convergence between the australian and pacific plates in south island new zealand has resulted in crustal thickening and distributed deformation within both plates we measure this thickening and image the deformation with seismic wide angle data along a 600 km long transect that spans the plate boundary p wave arrival times from 34 000 rays are used to construct a two dimensional model for seismic velocity with depth crustal velocities average 6 1 and 6 2 0 23 km s for the australian and pacific sides of the boundary respectively upper mantle velocities average 8 1 0 25 km s distributed deformation is indicated by the following observations a reduction in upper crustal and midcrustal velocities by 4 west of the plate boundary ascribed to flexural bending stresses a velocity reduction of 8 immediately east of the alpine fault linked to high pore fluid pressures 17 km of crustal thickening to form a 44 1 4 km deep crustal root that is offset 10 20 km se of the highest mountains a velocity reversal below the midcrust in the eastern part of the crustal root caused either by heating or an artifact from seismic anisotropy strong thickening of a 7 0 0 4 km s fast lower crust within the crustal root and a low velocity zone in the australian upper mantle due to sampling the slow orientation of upper mantle anisotropy

pressure fluctuations on the open ocean floor off the gulf of california tides earthquakes tsunamis abstract this paper supplements an initial article on sea floor pressure observations conducted with a sensitive though not perfectly stable transducer a variety of examples are used to demonstrate that a wide range of research subjects in the fields of physical oceanography and submarine geophysics can be studied with measurements from bourdon tube pressure sensors combined with inherently linear and friction free electro optical feedback results from a three month experiment in the pacific ocean off the entrance of the gulf of california are presented the background sea level variations in the subtidal and intertidal bands are found to be more energetic than those observed 300 km east of hawaii that is at a great distance offshore the difference between the spectra from the hawaii and the gulf of california measurements has a maximum at 0 025 cph of nearly two decades baroclinic wave trapping along the coast of north america may play a role at the lower frequencies while meteorological noise

surface wave tomography of the western united states from ambient seismic noise rayleigh and love wave phase velocity maps summary we present the results of rayleigh wave and love wave phase velocity tomography in the western united states using ambient seismic noise observed at over 250 broad band stations from the earthscope usarray transportable array and regional networks all available threecomponent time series for the 12 month span between 2005 november 1 and 2006 october 31 have been cross correlated to yield estimated empirical rayleigh and love wave green s functions the love wave signals were observed with higher average signal to noise ratio snr than rayleigh wave signals and hence cannot be fully explained by the scattering of rayleigh waves phase velocity dispersion curves for both rayleigh and love waves between 5 and 40 speriod were measured for each interstation path by applying frequency time analysis the average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station triplets we find that empirical green s functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross correlation without explicit knowledge of the source distribution the average traveltime uncertainty is less than 1 s at periods shorter than 24 s we present rayleigh and love wave phase speed maps at periods of 8 12 16 and 20 s the maps show clear correlations with major geological structures and qualitative agreement with previous results based on rayleigh wave group speeds

wavefield decomposition for passive ocean bottom seismological data summary seismic data from ocean bottom stations show strong water layer multiples on the hydrophone and seismometer channels depending on the water depth and the seafloor impedance contrast these multiples can be attenuated by means of a wavefield decomposition wdc into up and downgoing wavefields we apply an elastic decomposition scheme to earthquake recordings in the tyrrhenian sea to demonstrate the potentials for different passive seismological studies a three step decomposition approach has been developed giving optimal results for our earthquake data relative amplification factors between hydrophone and seismometer can be constrained during decomposition in our case factors in between 0 25 and 0 4 have been found we show that water layer multiples on recordings of local deep earthquakes are significantly reduced so that structural phases in the coda of the p phase can be studied the seafloor p wave impedance contrast at two nearby stations is estimated to the orders of 1 3 and 1 5 indicating that the uppermost layer was very muddy and unconsolidated we demonstrate with synthetic data that teleseismic receiver functions are strongly distorted by means of water layer multiples the wdc significantly improves the signal to noise ratio of structural phases in receiver functions a single station application to real data confirms the theoretical predictions we predict the biasing effect of traveltime residuals as estimated by cross correlation of teleseismic recordings from different stations in the order of up to 8 s at waves with a dominant period of 50 s waveform decomposition removes this apparent traveltime residual and enables unbiased estimates the theoretical predictions are verified with real data from two teleseismic earthquakes based on our results we strongly recommend applying an elastic wdc to passive seismological recordings on broad band stations

shallow sedimentary structure of the brahmaputra valley constraint from receiver functions analysis in this study receiver functions from ten broadband seismograph stations on cenozoic sediment formations of brahmaputra valley and its neighboring region in northeastern part of india are determined receiver function traces from this region show delay in peak by 1 2 5 s and associated minor peaks with the direct p phase peak based on such observation we try to image sedimentary structure of the brahmaputra valley plain adjacent shillong plateau and himalayan foredeep region an adapted hybrid global waveform inversion technique has been applied to extract sedimentary basin structure beneath each site the sedimentary cover of the basin is about 0 5 6 5 km thick across the valley 0 5 1 0 km on shillong plateau and 2 0 5 0 km in nearby foredeep region we have found that sedimentary thickness increases from sw to ne along the brahmaputra valley and towards the eastern himalayan syntaxes the estimated sediment thickness and s wave velocity structure agree well with the results of previous active source gravity and deep borehole studies carried out in this region the thick crustal low velocity sediment cover in brahmaputra valley is expected to amplify ground motions during earthquakes and therefore important for seismic hazard assessment of the region

upper mantle seismic anisotropy at a strike slip boundary south island new zealand new shear wave splitting measurements made from stations onshore and offshore the south island of new zealand show a zone of anisotropy 100 200 km wide measurements in central south island and up to approximately 100 km offshore from the west coast yield orientations of the fast quasi shear wave nearly parallel to relative plate motion with increased obliquity to this orientation observed farther from shore on the eastern side of the island fast orientations rotate counterclockwise to become nearly perpendicular to the orientation of relative plate motion approximately 200 km off the east coast uniform delay times between the fast and slow quasi shear waves of nearly 2 0 s onshore continue to stations approximately 100 km off the west coast after which they decrease to 1 s at 200 km stations more than 300 km from the west coast show little to no splitting east coast stations have delay times around 1 s simple strain fields calculated from a thin viscous sheet model representing distributed lithospheric deformation with strain rates decreasing exponentially to both the northwest and southeast with e folding dimensions of 25 35 km approximately 75 of the deformation within a zone 100 140 km wide match orientations and amounts of observed splitting a model of deformation localized in the lithosphere and then spreading out in the asthenosphere also yields predictions consistent with observed splitting if at depths of 100 130 km below the lithosphere typical grain sizes are 6 7 mm

wave field continuation and decomposition for passive seismic imaging under deep unconsolidated sediments abstract the coastal plains of the central and eastern united states contain deep sections of unconsolidated to poorly consolidated sediments these sediments mask deeper crustal and upper mantle converted phases in teleseismic receiver functions through large amplitude near surface reverberations thick sediments also amplify ambient noise levels to generally reduce data signal to noise ratios removing shallow sediment wave propagation effects is critical for imaging deep lithospheric structures a propagator matrix formalism is used to downward continue the wave field for teleseismic p waves into the midcrust and then to separate the upgoing s wave field from the total teleseismic response of the p wave to expose deep sp conversions this method requires that the earth model from the surface to the reference depth be known teleseismic p wave data for the memphis tennessee station mph are analyzed using a reference station deconvolution technique to produce vertical and radial p wave transfer functions these transfer functions are modeled using a simple model parameterization for sediment structure through grid inversion the inverted earth model is incorporated into the wave field continuation and decomposition technique to estimate the upgoing s wave field at 10 km depth in the crust moho and possible deeper ps conversions are identified with this process

shear velocities in cascadia from seafloor compliance measurements compliance is defined as the transfer function between the vertical displacement of the seafloor and the corresponding pressure expressed as a function of frequency it is sensitive to the elastic parameters of the underlying sediments particularly the shear modulus we have measured normalized compliance from 0 001 to 0 049 hz using ocean surface gravity waves as a source at sites in cascadia near the ocean drilling program odp hole 889b a differential pressure gauge datalogger and self levelling gravimeter were lowered to the seafloor and each site was occupied for eight hours the compliance estimates are reproducible and are consistent with other available data and simple models of sediment physical properties shear strength is increased from a normal profile in the uppermost few hundred meters possibly an effect of the presence of a known hydrate layer and is decreased between 1 2 and 2 km below the seafloor suggesting the presence of a low velocity zone

pn anisotropy beneath the south island of new zealand and implications for distributed deformation in continental lithosphere pn travel times from regional earthquakes recorded both by stations on new zealand and by ocean bottom seismographs deployed offshore indicate anisotropy in the uppermost mantle beneath the region the largest anisotropy of 8 2 1 lies beneath the deforming part of the south island to just off its west coast a zone roughly 100 200 km wide the fastest propagation is aligned n60 e 3 essentially parallel to the largely strike slip relative plate motion since 20 ma also n60 e the magnitude of anisotropy decreases abruptly northwest and southeast of this zone and on the southeast side of the island the orientation of fastest propagation is between n32 w and n s the n60 e orientation of fast propagation is consistent with finite strain within the uppermost part of the mantle lithosphere if the measured 850 km of displacement of the pacific plate past the australia plate is spread over a region with a width of 100 200 km the agreement of this orientation of fast propagation with the orientation or relative plate motion suggests the possibility of but does not require some dynamic recrystallization in rock as cold as 500 800 c where peierls creep seems to be the likely deformation mechanism such a strain distribution matches deformation of a thin viscous sheet that obeys a constitutive relationship of the form e n where e is the average strain rate and is the operative deviatoric stress with an average value of n 3 10 presumably the nw se fast propagation in the region southeast of the island results from strain that precedes the cenozoic deformation that has shaped the island

crustal and uppermost mantle shear velocity structure adjacent to the juan de fuca ridge from ambient seismic noise 1 based on 6 months of obs data from the cascadia initiative experiment near the juan de fuca ridge we obtain rayleigh wave group and phase speed curves from 6 s to about 20 s period from ambient noise cross correlations among all station pairs we confirm the hypothesis that the dispersion data can be fit by a simple age dependent formula which we invert using a bayesian monte carlo formalism for an age dependent shear wave speed model of the crust and uppermost mantle between crustal ages of 0 5 and 3 5 ma igneous crustal structure is age invariant with a thickness of 7 km water depth varies in a prescribed way and sedimentary thickness and mantle shear wave speeds are found to increase systematically with crustal age the mantle model possesses a shallow low shear velocity zone lvz with a velocity minimum at about 20 km depth at 0 5 ma with lithosphere thickening monotonically with age minimum mantle shear velocities at young ages are lower than predicted from a half space conductively cooling model hscm and the lithosphere thickens with age faster than the hscm providing evidence for nonconductive cooling in the young lithosphere the shallow lvz is consistent with expectations for a largely dehydrated depleted harzburgite mantle with a small retained near ridge partial melt fraction probably less than 1 with melt extending to a lithospheric age of approximately 1 ma i e 30 km from the ridge

comment on nature of the seismic lithosphere asthenosphere boundary within normal oceanic mantle from high resolution receiver functions by olugboji et al broadband obs data comments on olugboji et al 2016 nature of the seismic lithosphere asthenosphere boundary within normal oceanic mantle from high resolution receiver functions hitoshi kawakatsu and yuki abe earthquake research institute the university of tokyo 1 1 1 yayoi bunkyo ku tokyo 113 0032 japan hitosi eri u tokyo ac jp now at hot springs research institute of kanagawa prefectural government 586 iriuda odawara kanagawa 250 0031 japan abeyuki eri u tokyo ac jp april 28 2016

continental crust under compression a seismic refraction study of south island geophysical transect i south island new zealand 1 the 1996 south island geophysical transect sight active source seismic survey was designed to show the style of lithospheric thickening due to late cenozoic oblique convergence across the australian pacific plate boundary in new zealand as part of this study two seismic refraction lines were shot across central south island and offshore extensions of the continental crust in the tasman sea and pacific ocean we present the data and a 603 km long seismic velocity profile of the crust and uppermost mantle along one of these seismic transects a tomographic inversion of 62 563 travel times from crustal and upper mantle refractions and wide angle reflections resulted in a model with a two layer crust upper crustal velocities were between 5 9 and 6 3 km s and lower crustal velocities were between 6 5 and 7 0 km s continental compression has locally reduced the seismic velocities in the pacific plate crust by 0 2 0 3 km s a possible effect of high strain and fluids in the crust the thickening of the crust from 28 km at the east coast of south island to 37 km beneath the southern alps can account for about 25 of the 80 110 km shortening of pacific plate crust while the rest must be accounted for by rapid erosion of mesozoic sedimentary rocks on the west side of the orogen in our model the lower crust forms a continuous 2 6 km thick layer beneath central south island the asymmetric topography of the southern alps is reflected in the crustal root which has a steeper flank at the west coast this observation is consistent with westward underthrusting of pacific lower lithosphere beneath south island that has been suggested in earlier studies

catchment scale tracer testing from karstic features in a porous limestone tracer testing was undertaken from sinking streams feeding the chalk a porous limestone aquifer characterised by frequent small scale surface karst features the objective was to investigate the nature and extent of sub surface karstic development in the aquifer previous tracer testing has demonstrated rapid flow combined with low attenuation of tracer in this study at two sites rapid groundwater flow was combined with very high attenuation and at two other sites no tracer was detected at springs within the likely catchment area of the stream sinks tested suggesting that tracer was totally attenuated along the flowpath it is proposed that the networks beneath stream sinks in the chalk and other mildly karstic aquifers distribute recharge into multiple enlarged fractures that divide and become smaller at each division whereas the networks around springs have a predominantly tributary topology that concentrates flow into a few relatively large cavities a morphology with similarities to that of the early stages of karstification tracer attenuation is controlled by the degree to which the two networks are directly connected in the first state there is no direct linkage and flow between the two networks is via primary fractures in which tracer attenuation is extreme the second state is at a percolation threshold in which a single direct link joins the two networks a very small proportion of tracer reaches the spring rapidly but overall attenuation is very high in the third state the recharge and discharge networks are integrated therefore a large fraction of tracer reaches the spring and peak concentrations are relatively high despite the large number of stream sinks that recharge the chalk aquifer these results suggest that sub surface conduit development may not always be continuous with flow down smaller fissures and fractures causing high attenuation of solutes and particulates providing a degree of protection to groundwater outlets that is not seen in more highly karstic aquifers bacteriophage tracers that can be detected at very large dilutions 1015 are recommended for investigating groundwater pathways where attenuation may be high

shallow structure effects on broadband teleseismic p waveforms the first 5 sec of source equalized p wave receiver functions from an array of broadband portable instruments located about 50 km from the coast in western washington are strongly influenced by very shallow structure depths less than 3 km these data display behavior associated with a dipping high velocity contrast interface at shallow depths the direct p wave and the p to s converted phase vary strongly with backazimuth producing an apparent delay in first arriving energy at western backazimuths these patterns are attributed to a shallow contact between low velocity sandstones at the surface and an underlying high velocity volcanic unit this shallow structure influences even the original unprocessed teleseismic p waves suggesting that such shallow structure could affect other studies such as seismic source analysis utilizing broadband data

worldwide correlations for subaerial aqueous flows with exponential longitudinal profiles it is shown that very strong worldwide correlations exist between the bed concavity coefficients of a wide range of subaerial aqueous flows with exponential longitudinal profiles and both the corresponding stream segment lengths and exponential bed particle size diminution coefficients the former correlation is complementary to an existing similar correlation for the exponential size diminution coefficients while the latter is consistent with earlier theoretical correlations based on very limited data the data supporting the correlations extend over virtually the whole range of stream lengths solids concentrations and bed sediment particle sizes found on earth this universality strongly suggests that there are underlying mechanisms common to all kinds of mobile bed subaerial aqueous flows however the scatter of the data for the correlations is significant and is mostly attributable to variations in hydraulic conditions and sediment properties rather than measurement errors some of the conditions and properties have been identified but others remain obscure copyright c 1999 john wiley sons ltd

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

p and s wave delays beneath intraplate volcanic ridges and gravity lineations near the east pacific rise the gravity lineations intraplate melting petrology and seismic expedition glimpse explored the origin of two intraplate non hot spot ridge systems associated with gravity lineations in the south central pacific using the 11 month ocean bottom seismometer obs deployment of the glimpse experiment we determined the average p and s station delays for the region across the array station delays varied by 1 22 s for p waves and 2 13 s for s waves the presence of ultraslow shear velocity

the effective elastic thickness of the india plate from receiver function imaging gravity anomalies and thermomechanical modelling summary the range and the meaning of the effective elastic thickness eet in continental areas have been subject to controversy over the last two decades here we take advantage of the new data set from the hi climb seismological experiment to re estimate the eet of the india plate along a south north profile extending from the ganges basin to central tibet receiver functions give a high resolution image of the base of the foreland basin at 5 km depth and constrain the crustal thickness which increases northwards from 35 km beneath the indo gangetic plain to 70 km in southern tibet together with available data sets including seismic profiles seismological images from both indepth and himnt experiments deep well measurements and bouguer anomaly profiles we interpret this new image with 2 d thermomechanical modelling solutions using different type of crustal and mantle rheologies we find that 1 the eet of the india plate decreases northwards from 60 80 to 20 30 km as it is flexed down beneath himalaya and tibet due to thermal and flexural weakening 2 the only resistant layer of the india plate beneath southern tibet is the upper mantle which serves as a support for the topographic load and 3 the most abrupt drop in the eet located around 200 km south of the mft is associated with a gradual decoupling between the crust and the mantle we show that our geometrical constraints do not allow to determine if the upper and lower crust are coupled or not our results clearly reveal that a rheology with a weak mantle is unable to explain the geometry of the lithosphere in this region and they are in favour of a rheology in which the mantle is strong

ambient noise rayleigh wave tomography of new zealand summary we present the first new zealand wide study of surface wave dispersion using ambient noise observed at 42 broad band stations in the national seismic network geonet and the global seismic network gsn year long vertical component time series recorded between 2005 april 1 and 2006 march 31 have been correlated with one another to yield estimated fundamental mode rayleigh wave green s functions we filter these green s functions to compute rayleigh wave group dispersion curves at periods of 5 50 s using a phase matched filter frequency time analysis technique the uncertainties of the measurements are estimated based on the temporal variation of the dispersion curves revealed by 12 overlapping 3 month stacks after selecting the highest quality dispersion curve measurements we compute group velocity maps from 7 to 25 s period these maps and 1 d shear wave velocity models at four selected locations exhibit clear correlations with major geological structures including the taranaki and canterbury basins the hikurangi accretionary prism and previously reported basement terrane boundaries

quantitative tectonic reconstructions of zealandia based on crustal thickness estimates zealandia is a key piece in the plate reconstruction of gondwana the positions of its submarine plateaus are major constraints on the best fit and breakup involving new zealand australia antarctica and associated microplates as the submarine plateaus surrounding new zealand consist of extended and highly extended continental crust classic plate tectonic reconstructions assuming rigid plates and narrow plate boundaries fail to reconstruct these areas correctly however if the early breakup history shall be reconstructed it is crucial to consider crustal stretching in a plate tectonic reconstruction we present a reconstruction of the basins around new zealand great south basin bounty trough and new caledonia basin based on crustal balancing an approach that takes into account the rifting and thinning processes affecting continental crust in a first step we computed a crustal thickness map of zealandia using seismic seismological and gravity data the crustal thickness map shows the submarine plateaus to have a uniform crustal thickness of 20 24 km and the basins to have a thickness of 12 16 km we assumed that a reconstruction of zealandia should close the basins and lead to a most uniform crustal thickness we used the standard deviation of the reconstructed crustal thickness as a measure of uniformity the reconstruction of the campbell plateau area shows that the amount of extension in the bounty trough and the great south basin is far smaller than previously thought our results indicate that the extension of the bounty trough and great south basin occurred simultaneously