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 liquefaction a pore water pressure gradient viewpoint liquefaction of fully saturated sediments subjected to earthquake motion is often defined by the condition when effective stress reaches zero on the other hand the gradient of excess pore water pressure represents the net local surface force which plays a crucial mechanical role for liquefaction herein we consider two definitions of liquefaction which yield different liquefaction initiation times and depths two hypothetical cases of liquefaction earthquake induced and tsunami induced are given to highlight the differences in the definitions of liquefaction the results from the hypothetical cases show that the effective stress definition of liquefaction is a special case of the pore water pressure gradient definition of liquefaction

the role of attenuation in 2d full waveform inversion of shallow seismic body and rayleigh waves abstractfull waveform inversion fwi of rayleigh waves is attractive for shallow geotechnical investigations due to the high sensitivity of rayleigh waves to the s wave velocity structure of the subsurface in shallow seismic field data the effects of anelastic damping are significant dissipation results in a low pass effect as well as frequency dependent decay with offset we found this by comparing recorded waveforms with elastic and viscoelastic wave simulation the effects of anelastic damping must be considered in fwi of shallow seismic rayleigh waves fwi using elastic simulation of wave propagation failed in synthetic inversion tests in which we tried to reconstruct the s wave velocity in a viscoelastic model to overcome this q values can be estimated from the recordings to quantify viscoelasticity waveform simulation in the fwi then uses these a priori values when inferring seismic velocities and density a source wavelet correction which is inevitable in fwi of field data can compensate a

algebraic reconstruction of a two dimensional velocity inhomogeneity in the high hazles seam of thoresby colliery a high proportion of faces started in mechanized coal mines run into underground faults the faults take many forms from the splitting of a seam through a hidden stress pattern caused by subsidence or folding to a washout or a vertical throw all faults reduce face output a throw of only 1 5 m can lead to a face being abandoned faults of this order cannot be mapped reliably from the surface they may be mapped in an underground seismic survey roadways of a mine may give access to fast refracting horizons above and below a coal seam waveguiding in the plane of the seam if it occurs simplifies migration of wave trains reflected from discrete faults the reduction problem involved in a fault mapping is only two dimensional given guiding whether leaky or not it is possible to map distributed faults of low reflectivity by shooting in transmission across a panel of coal algebraic reconstruction techniques are used here to reduce first break times of flight through a 425 x 950 m rectangular block of coal into the profile of a velocity inhomogeneity input data are derived by static correction from hand picked arrival times the reduction itself is effected using an algorithm which accommodates underground site access restrictions in back projecting first break velocities a truncated cosine is used to weight the relative contributions of rays passing at different distances from any given mapping point the reconstructed velocity field suggests that the coal panel is bisected by a ridge of higher velocity the suspicion of a ridge is reinforced by results of an aberration test based on a standard huygens kirchhoff migration the ridge is found to follow the general line of a system of pillars left in place during the mining of a lower horizon it is concluded that channel waves may be used to map subsidence into old workings underground coal seams apparently share with other sedimentary rocks the property of a pressure sensitive seismic velocity

linearized inversion of seismic reflection data this is the first of a series of papers giving the solution of the inverse problem in seismic exploration the acoustic approximation is used together with the assumption that the velocity field has the form the forward problem is then linearized thus neglecting multiple reflected waves and the inverse problem of estimating is set up its rigorous solution can be obtained using an iterative algorithm each step consisting of a classical kirchhoff migration hyperbola summation plus a classical forward modeling step circle summation

triggering of liquefaction flow slides in coastal soil deposits abstract liquefaction flow slides have been observed in coastal soil deposits throughout the world the causes of many of these slides have never been well understood the materials involved in and circumstances surrounding eight reported liquefaction flow slides are reviewed and compared many of these slides have occurred in very similar materials shortly following small to moderate drawdowns of the adjacent water level liquefaction susceptibility of sands may be evaluated by steady state methods recent research indicates that liquefaction of loose sands similar to those typically involved in these slides may be triggered by very small changes in stress conditions if the sand is initially in equilibrium under high shear stresses the triggering of liquefaction may lead to flow sliding if the unbalanced driving stresses exceed the steady state strength of the liquefied soil elasticity methods are used to estimate the initial stress conditions in a gentle infinite slope and the effect of unloading due to drawdown it is shown that liquefaction flow slides in coastal soil deposits may be initiated by small to moderate drawdowns consistent with those observed in actual slides

potential of surface to tunnel seismic tomography to detect vertical faults application to the tournemire underground research laboratory france the tournemire underground research laboratory aveyron france developed by the french institute for radiological protection and nuclear safety is composed of a tunnel excavated in an argillaceous geological layer belonging to a limestone argillite limestone sub horizontal sedimentary sequence sub vertical fault zones are intercepted by drifts and boreholes excavated from the tunnel in the argillaceous layer at a depth of about 250 m these fault zones are characterized by velocities lower than those of the embedding rocks in this study we assess the capacity of first arrival traveltime tomography to detect and characterize such fault zones in a surface to depth transmission configuration with a limited angle aperture the source at the surface is a sledgehammer and turns out to be very repetitive the source trigger is transmitted to the acquisition bay via a vhf transmitter receivers are located at depth in underground works first arrivals are clear and traveltime picking is straightforward before inverting real data we conduct synthetic tests with the real acquisition geometry to assess limits and validity of first arrival traveltime tomography to detect a lower velocity fault zone using different initial configurations and inversion constraints during the inversion we show that introducing a priori information on velocities in the shallow subsurface limestones and argillaceous layers and constraints on maximum velocities greatly helps improving results and subsequent interpretation velocities obtained from the real data display a main lower velocity zone that extends from the galleries in the argillaceous layer right up to the surface in limestones the location and extension of this lower velocity zone are consistent with fault and fracture zones mapped from geological observations

remote monitoring of the steam flood enhanced oil recovery process cross borehole seismic velocity and high frequency electromagnetic em attenuation data were obtained to construct tomographic images of heavy oil sands in a steam flood environment first arrival seismic data were used to construct a tomographic color image of a 10 m by 8 m vertical plane between the two boreholes two high frequency 17 and 15 mhz em transmission tomographs were constructed of a 20 m by 8 m vertical plane the velocity tomograph clearly shows a shale layer with oil sands above it and below it the em tomographs show a more complex geology of oil sands with shale inclusions the deepest em tomograph shows the upper part of an active steam zone and suggests steam chanelling just below the shale layer these results show the detailed structure of the entire plane between boreholes and may provide a better means to understand the process for in situ heavy oil recovery in a steam flood environment

seismic tomography in boreholes summary synthetic seismic tomographic data sets for cross hole and hole to surface arrays are computed and inverted inversion imaging is performed through an iterative projection solution to a matrix equation the orientation as well as the position of an anomaly relative to the source and recorder arrays affects both the rate of convergence of the solution and the resolution obtained data density and distribution determine the physical validity of the image obtained at convergence borehole tomography is apparently a viable method for imaging inter hole structure

small scale structure of the kane oceanic core complex mid atlantic ridge 23 30 n from waveform tomography of multichannel seismic data 1 frequency domain waveform tomography applied to deep sea multichannel seismic data collected across the kane oceanic core complex occ reveals the small scale structure of this section of oceanic lithosphere formed at the mid atlantic ridge 3 3 2 1 myr ago that has been uplifted and exhumed at the seafloor along an oceanic detachment fault geological and geophysical studies indicate that the central eastern area of the kane occ is formed by a large gabbroic intrusion the new high resolution seismic velocity models show that this gabbroic core is 1 000 1 350 m thick and it is underlain by a 300 m thick layer of low velocity material interpreted as serpentinized peridotite the models also reveal the presence of a deeper 200 m thick by 1 700 m long high velocity body interpreted as a small gabbroic sill embedded in serpentinzed peridotite

efficient 3 d frequency domain mono parameter full waveform inversion of ocean bottom cable data application to valhall in the visco acoustic vertical transverse isotropic approximation computationally efficient 3 d frequency domain full waveform inversion fwi is applied to ocean bottom cable data from the valhall oil field in the visco acoustic vertical transverse isotropic vti approximation frequency domain seismic modelling is performed with a parallel sparse direct solver on a limited number of computer nodes a multiscale imaging is performed by successive inversions of single frequencies in the 3 5 10 hz frequency band the vertical wave speed is updated during fwi while density quality factor qp and anisotropic thomsen s parameters and are kept fixed to their initial values the final fwi model shows the resolution improvement that was achieved compared to the initial model that was built by reflection traveltime tomography this fwi model shows a glacial channel system at 175 m depth the footprint of drifting icebergs on the palaeo seafloor at 500 m depth a detailed view of a gas cloud at 1 km depth and the base cretaceous reflector at 3 5 km depth the relevance of the fwi model is assessed by frequency domain and time domain seismic modelling and source wavelet estimation the agreement between the modelled and recorded data in the frequency domain is excellent up to 10 hz although amplitudes of modelled wavefields propagating across the gas cloud are overestimated this might highlight the footprint of attenuation whose absorption effects are underestimated by the homogeneous background qp model qp 200 the match between recorded and modelled time domain seismograms suggests that the inversion was not significantly hampered by cycle skipping however late arrivals in the synthetic seismograms computed without attenuation and with a source wavelet estimated from short offset early arrivals arrive 40 ms earlier than the recorded seismograms this might result from dispersion effects related to attenuation the repeatability of the source wavelets inferred from data that are weighted by a linear gain with offset is dramatically improved when they are estimated in the fwi model rather than in the smooth initial model the two source wavelets estimated in the fwi model from data with and without offset gain show a 40 ms time shift which is consistent with the previous analysis of the time domain seismograms the computational efficiency of our frequency domain approach is assessed against a recent time domain fwi case study performed in a similar geological environment this analysis highlights the efficiency of the frequency domain approach to process a large number of sources and receivers with limited computational resources thanks to the efficiency of the substitution step performed by the direct solver this efficiency can be further improved by using a block low rank version of the multifrontal solver and by exploiting the sparsity of the source vectors during the substitution step future work will aim to update attenuation and density at the same time of the vertical wave speed

sediment response to tsunami loading mechanisms and estimates tsunami effects on soil stability are evaluated by imposing hypothetical but typical tsunami loads on an idealised beach condition of a plane beach with homogeneous sediments under this model tsunami condition the extent of sediment motion in the form of bed load and suspended load on the beach is demonstrated sediment motions are particularly significant in the nearshore area between the initial shoreline and the maximum tsunami drawdown during the drawdown phase pore pressure gradients develop by rapid reduction in water pressure on the bed creating soil instability and triggering momentary liquefaction in some locations such effects of pore pressure gradients are quantitatively evaluated with a proposed modified shields parameter the analysis used for the model tsunami case is further applied to laboratory data and real field data collected in kesen numa japan during the 2011 east japan tsunami

quantitative imaging of the permo mesozoic complex and its basement by frequency domain waveform tomography of wide aperture seismic data from the polish basin in this study we present the workflow and results of 2d frequency domain waveform tomography applied to the global offset seismic data acquired in central poland along a 50 km long profile during the grundy 2003 experiment the waveform tomography method allows full exploitation of the wide aperture content of these data and produces in a semi automatic way both the detailed p wave velocity model and the structural image i e perturbations in respect to the starting model thirteen frequencies ranging from 4 to 16 hz were inverted sequentially gradually introducing higher wavenumbers and more details into the velocity models although the data were characterised by relatively large shot spacings 1 5 km we obtained clear images both of the mesozoic and permian sedimentary cover velocity patterns indicated facies changes within the jurassic and zechstein strata a high velocity layer ca 5500 m s was found near the base of triassic scythian which made the imaging of a deeper layer difficult nevertheless we were able to delineate the base of the permian i e base of the rotliegend which was not possible to derive from conventional common depth point processing as well as some deeper events attributed to the carboniferous the sub permian events formed a syn form which favoured our previous interpretation of a depression filled with upper carboniferous molasse the validity of the waveform tomography derived model was confirmed by well log data forward ray tracing modelling and synthetic seismograms calculations provided another justification for the key structures present in the waveform tomography model

wide angle seismic velocities in heterogeneous crust summary seismic velocities measured by wide angle surveys are commonly used to constrain material composition in the deep crust therefore it is important to understand how these velocities are affected by the presence of multiscale heterogeneities the effects may be characterised by the scale of the heterogeneity relative to the dominant seismic wavelength a what is clear is that heterogeneities of all scales and strengths bias wideangle velocities to some degree waveform modelling was used to investigate the apparent wide angle p wave velocities of different heterogeneous lower crusts a constant composition 50 per cent felsic and 50 per cent ultramafic was formed into a variety of 1 and 2 d heterogeneous arrangements and the resulting wide angle seismic velocity was estimated elastic 1 d models produced the largest velocity shift relative to the true average velocity of the medium which is the velocity of an isotropic mixture of the two components thick width a horizontal layers as a result of fermat s principle provided the largest increase in velocity thin width 2 vertical layers produced the largest decrease in velocity acoustic 2 d algorithms were shown to be inadequate for modelling the kinematics of waves in bodies with multiscale heterogeneities elastic 2 d modelling found velocity shifts both positive and negative that were of a smaller magnitude than those produced by 1 d models the key to the magnitude of the velocity shift appears to be the connectivity of the fast and or slow components thus the models with the highest apparent levels of connectivity between the fast phases the 1 d layers produced the highest magnitude velocity shifts to understand the relationship between measured seismic velocities and petrology in the deep crust it is clear that high resolution structural information which describes such connectivity must be included in any modelling

joint electromagnetic and seismic inversion using structural constraints we have developed a frequency domain joint electromagnetic em and seismic inversion algorithm for reservoir evaluation and exploration applications em and seismic data are jointly inverted using a cross gradient constraint that enforces structural similarity between the conductivity image and the compressional wave p wave velocity image the inversion algorithm is based on a gauss newton optimization approach because of the ill posed nature of the inverse problem regularization is used to constrain the solution the multiplicative regularization technique selects the regularization parameters automatically improving the robustness of the algorithm a multifrequency data weighting scheme prevents the high frequency data from dominating the inversion process when the joint inversion algorithm is applied in integrating marine controlled source electromagnetic data with surface seismic data for subsea reservoir exploration applications and in integrating crosswell em and sonic data for reservoir monitoring and evaluation applications results improve significantly over those obtained from separate em or seismic inversions

waveform tomography imaging of a megasplay fault system in the seismogenic nankai subduction zone abstract we apply frequency domain waveform tomography to form quantitative high resolution p wave velocity images of a megasplay fault system within the central nankai subduction zone offshore of southwest japan using controlled source ocean bottom seismometer obs data originally acquired in 2004 the waveform tomography method exploits recorded seismic waveforms beyond their first arrivals and thus achieves a much higher resolution of the order of a wavelength than that of conventional traveltime tomography methods frequency domain waveform tomography facilitates a multi scale approach to stabilize the inversion in which initial traveltime tomography results are sequentially improved on by first fitting low frequency components of the seismic records starting at 2 25 hz higher frequency components up to 8 5 hz are then introduced progressively our final waveform tomography image allows velocity anomalies as small as 700 m horizontally and 350 m vertically to be discerned and interpreted as confirmed by checkerboard modeling tests the improved explanatory power of the final images is verified by observing that synthetic waveforms calculated from the final results yield much better fit to the observed waveforms than those estimated from the original traveltime tomography image apparent lithological boundaries from waveform tomography agree well with corresponding reflections on seismic migration images providing further confidence in the validity of the results the megasplay fault is evident on the final waveform tomography image as a sharp velocity discontinuity delineating the upper surface of a velocity reduction of nearly 1 km s with respect to the regional 1d velocity trend the megasplay fault can be traced continuously throughout the entire image from a nearly horizontal section at the landward extent moving seaward through to a steeper angle penetrating the old accretionary prisms with several additional splays appearing to branch in the shallow subsurface the location of the low velocity zones imaged by our waveform tomography method coincides with two previously identified low velocity zones the image reveals a low velocity zone that is continuous from deeper to shallower portions of the subsurface suggesting that pore fluids may be transported from the inner wedge to the transition zone and to the surface through fluid conduits associated with the megasplay fault system

linear and nonlinear computations of the 1992 nicaragua earthquake tsunami numerical computations of tsunamis are made for the 1992 nicaragua earthquake using different governing equations bottom frictional values and bathymetry data the results are compared with each other as well as with the observations both tide gauge records and runup heights comparison of the observed and computed tsunami waveforms indicates that the use of detailed bathymetry data with a small grid size is more effective than to include nonlinear terms in tsunami computation linear computation overestimates the amplitude for the later phase than the first arrival particularly when the amplitude becomes large the computed amplitudes along the coast from nonlinear computation are much smaller than the observed tsunami runup heights the average ratio or the amplification factor is estimated to be 3 in the present case when the grid size of 1 minute is used the factor however may depend on the grid size for the computation

toward a robust workflow for deep crustal imaging by fwi of obs data the eastern nankai trough revisited crustal scale imaging by the full waveform inversion fwi of long offset seismic data is inherently difficult because the large number of wavelengths propagating through the crust makes the inversion prone to cycle skipping therefore efficient crustal scale fwi requires an accurate starting model and a stable workflow minimizing the nonlinearity of the inversion here we attempt to reprocess a challenging 2d ocean bottom seismometer obs dataset from the eastern nankai trough the starting model is built by first arrival traveltime tomography fat which is fwi assisted for tracking cycle skipping we iteratively refine the picked traveltimes and then reiterate the fat until the traveltime residuals remain below the cycle skipping limit subsequently we apply laplace fourier fwi in which progressive relaxation of time damping is nested within frequency continuation to hierarchically inject more data into the inversion these two multiscale levels are complemented by a layer stripping approach implemented through offset continuation the reliability of the fwi velocity model is assessed by means of source wavelet estimation synthetic seismogram modeling ray tracing modeling dynamic warping and checkerboard tests although the visco acoustic approximation is used for wave modeling the synthetic seismograms reproduce most of the complexity of the data with a high traveltime accuracy the revised fwi scheme produces a high resolution velocity model of the entire crust that can be jointly interpreted with migrated images derived from multichannel seismic data this study opens a new perspective on the design of obs crustal scale experiments amenable to fwi however a further assessment of the optimal obs spacing is required for reliable fwi

application of waveform tomography to marine seismic reflection data from the queen charlotte basin of western canada to obtain a higher resolution quantitative p wave velocity model 2d waveform tomography was applied to seismic reflection data from the queen charlotte sedimentary basin off the west coast of canada the forward modeling and inversion were implemented in the frequency domain using the visco acoustic wave equation field data preconditioning consisted of f k filtering 2d amplitude scaling shot to shot amplitude balancing and time windowing the field data were inverted between 7 and 13 66 hz with attenuation introduced for frequencies 10 5 hz to improve the final velocity model two different approaches to sampling the frequencies were evaluated the limited maximum offset of the marine data 3770 m and the relatively high starting frequency 7 hz were the main challenges encountered during the inversion an inversion strategy that successively recovered shallow to deep structures was designed to mitigate these issues the inclusion of later arrivals in the waveform tomography resulted in a veloci

application of seismic full waveform inversion to monitor co2 injection modelling and a real data example from the ketzin site germany seismic monitoring of an injected carbon dioxide co2 distribution at depth is an important issue in the geological storage of co2 to help monitor changes in the subsurface during co2 injection a series of 2d seismic surveys were acquired within the framework of the co2sink and co2man projects at ketzin germany at different stages of the injection process here we investigate using seismic full waveform inversion as a qualitative tool for time lapse seismic monitoring given the constraints of the limited maximum offsets of the 2d seismic data prior to applying the inversion to the real data we first made a number of benchmark tests on synthetic data using a similar geometry as in the real data results from the synthetic benchmark tests show that it is difficult to recover the true value of the velocity anomaly due to the injection but that it is possible to qualitatively locate the distribution of the injected co2 after the synthetic studies we applied seismic full waveform inversion on the real time lapse data from the ketzin site along with conventional time lapse processing both methods show a similar qualitative distribution of the injected co2 and agree well with expectations based upon more extensive 3d time lapse monitoring in the area

reverse time migration of offset vertical seismic profiling data using the excitation time imaging condition to apply reverse time migration to prestack finite offset data from variable velocity media the standard time zero imaging condition must be generalized because each point in the image space has a different image time or times this generalization is the excitation time imaging condition in which each point is imaged at the one way traveltime from the source to that point reverse time migration with the excitation time imaging condition consists of three elements 1 computation of the imaging condition 2 extrapolation of the recorder wave field and 3 application of the imaging condition computation of the imaging condition for each point in the image is done by ray tracing from the source point this is equivalent to extrapolation of the source wave field through the medium extrapolation of the recorded wave field is done by an acoustic finite difference algorithm imaging is performed at each step of the finite difference extrapolation by extracting from the propagating wave field the

seismic imaging of the naga thrust using multiscale waveform inversion this case study images the structural features related to the naga thrust fault northeast india using a combination of multiscale waveform inversion and prestack depth migration psdm the waveform model and the psdm image complement each other the former provides a physical property map p wave velocity model and the latter provides a structural image the velocity model encompassing the starting model for waveform inversion is constructed using joint inversion of first and reflected traveltimes the 4 8 hz data are inverted consecutively in 1 hz bandwidths to yield the final waveform model which in turn is used for psdm the psdm image and the waveform model are consistent with the lithological interpretation of an inline exploratory well when interpreted jointly the psdm image and the waveform model reveal the presence of a conjugate fault system in the naga thrust and fold belt

crosshole seismology and seismic imaging in crystalline rocks a borehole to borehole audiofrequency seismic system using piezoelectric transducers as active elements has been developed and used to investigate crystalline rocks in canada high quality seismograms have been recorded for transmitter receiver distances of up to 230 meters it has been found that both travel times and signal amplitudes provide diagnostic information about rock quality two dimensional images of seismic velocity and transparency distributions between two boreholes derived from observed arrival times and amplitudes by simple back projection tomography reflect lithology and geological structure the results indicate the potential usefulness of crosshole seismic imaging as a tool for rock mass characterization

tsunami run up and draw down on a plane beach tsunami run up and draw down motions on a uniformly sloping beach are evaluated based on fully nonlinear shallow water wave theory the nonlinear equations of mass conservation and linear momentum are first transformed to a single linear hyperbolic equation to solve the problem with arbitrary initial conditions we apply the fourier bessel transform and inversion of the transform leads to the green function representation the solutions in the physical time and space domains are then obtained by numerical integration with this semi analytic solution technique several examples of tsunami run up and draw down motions are presented in particular detailed shoreline motion velocity field and inundation depth on the shore are closely examined it was found that the maximum flow velocity occurs at the moving shoreline and the maximum momentum flux occurs in the vicinity of the extreme draw down location the direction of both the maximum flow velocity and the maximum momentum flux depend on the initial waveform it is in the inshore direction when the initial waveform is predominantly depression and in the offshore direction when the initial waves have a dominant elevation characteristic

effects of caldera collapse on magma decompression rate an example from the 1800 14c yr bp eruption of ksudach volcano kamchatka russia abstract caldera collapse changes volcanic eruption behavior and mass flux many models of caldera formation predict that those changes in eruption dynamics result from changes in conduit and vent structure during and after collapse unfortunately no previous studies have quantified or described how conduits change in response to caldera collapse changes in pumice texture coincident with caldera formation during the 1800 14c yr bp ks1 eruption of ksudach volcano kamchatka provide an opportunity to constrain magma decompression rates before and after collapse and thus estimate changes in conduit geometry prior to caldera collapse only white rhyodacite pumice with few microlites and elongate vesicles were erupted following collapse only gray rhyodacite pumice containing abundant microlites and round vesicles were erupted bulk compositions phase assemblages phenocryst compositions and geothermometry of the two pumice types are indistinguishable thus the two pumice types originated from the same magma geothermobarometry and phase equilibria experiments indicate that magma was stored at 100 125 mpa and 895 5 c prior to eruption decompression experiments suggest microlite textures observed in the white pumice require decompression rates of 0 01 mpa s 1 whereas the textures of gray pumice require decompression at 0 0025 mpa s 1 balancing those decompression rates with eruptive mass fluxes requires conduit size to have increased by a factor of 4 during caldera collapse slower ascent through a broader conduit following collapse is also consistent with the change from highly stretched vesicles present in white pumice and to round vesicles in gray pumice numerical modeling suggests that the mass flux and low decompression rates during the gray phase can be accommodated by the post collapse conduit developing a very broad base and narrow upper region

the 2011 japan tsunami current velocity measurements from survivor videos at kesennuma bay using lidar 1 on march 11 2011 a magnitude mw 9 0 earthquake occurred off the coast of japan s tohoku region causing catastrophic damage and loss of life the tsunami flow velocity analysis focused on two survivor videos recorded from building rooftops at kesennuma bay along japan s sanriku coast a terrestrial laser scanner was deployed at the locations of the tsunami eyewitness video recordings the tsunami current velocities through the kesennuma bay are determined in a four step process the lidar point clouds are used to calibrate the camera fields of view in real world coordinates the motion of the camera during recordings was determined the video images were rectified with direct linear transformation finally a cross correlation based particle image velocimetry analysis was applied to the rectified video images to determine instantaneous tsunami flow velocity fields the measured maximum tsunami height of 9 m in the kesennuma bay narrows were followed by maximum tsunami outflow currents of 11 m s less than 10 minutes later

source models for the 1993 hokkaido nansei oki earthquake tsunami a source model for the 1993 hokkaido nansei oki tsunami must satisfy certain conditions such conditions are presented in this paper and two methods are used to determine the best source model for this event a trial and error method selects dcrc 17a as the best among 24 different models this model has three fault planes dipping westward to reproduce well the tide gauge records at two locations an inversion analysis is used to modify the dislocation of dcrc 17a

inverse theory applied to multi source cross hole tomography part 1 acoustic wave equation method1 frequency domain methods are well suited to the imaging of wide aperture cross hole data however although the combination of the frequency domain with the wavenumber domain has facilitated the development of rapid algorithms such as diffraction tomography this has also required linearization with respect to homogeneous reference media this restriction and association restrictions on source receiver geometries are overcome by applying inverse techniques that operate in the frequency space domain in order to incorporate the rigorous modelling technique of finite differences into the inverse procedure a nonlinear approach is used to reduce computational costs the method of finite differences is applied directly to the frequency domain wave equation the use of high speed high capacity vector computers allow the resultant finite difference equations to be factored in place in this way wavefields can be computed for additional source positions at minimal extra cost allowing inversions to be generated using data from a very large number of source positions synthetic studies show that where weak scatter approximations are valid diffraction tomography performs slightly better than a single iteration of non linear inversion however if the background velocities increase systematically with depth diffraction tomography is ineffective whereas non linear inversion yields useful images from one frequency component of the data after a single iteration further synthetic studies indicate the efficacy of the method in the time lapse monitoring of injection fluids in tertiary hydrocarbon recovery projects

experimental study of tsunami induced scour around a monopile foundation abstract this paper presents an experimental study of the tsunami induced scour process around a monopile foundation representative of those commonly used for offshore wind farms the scour process is studied by subjecting the monopile to a time varying current which enables a properly down scaled experiment from the boundary layer and scour perspective it is shown how the scaled experiments corresponds to real life idealized tsunami cases with periods ranging from 10 to 40 min it is then shown that the boundary layers of the model tsunami are well described by recently developed empirical relations for tsunami boundary layers by subjecting the monopile to several successive tsunami waves the scour process is shown to occur in a stepwise cumulative fashion with the final equilibrium scour depth tending to the depth limited steady current limit it is shown that the entire scour development can reasonably be predicted by a recently developed simple engineering model finally the experimental results are compared to a fully coupled hydrodynamic and morphologic cfd model and a good correspondence is obtained

the effect of bathymetry on tsunami characteristics at sisano lagoon papua new guinea the 1998 papua new guinea tsunami was greater than expected from its earthquake magnitude the area of significant impact was small approximately a 30 km stretch near the mouth of sissano lagoon papua new guinea to explain the localized nature of the event a submarine landslide has been conjectured to be responsible our study indicates that offshore bathymetry is critical to predicting tsunami coastal behavior model runs with newly obtained bathymetric data indicate that an earthquake fault source combined with the existing seafloor geometry may also explain the concentrated tsunami although the definitive cause of the papua new guinea tsunami remains uncertain local bathymetry had a notable effect on the wave behavior

wave induced stresses in unsaturated submarine sediments a simple method to solve the problem of pore pres sure and effective stresses induced by harmonic waves in a poroelastic sediment is presented by using biot s equation and a compatibility condition for elasticity the sediment is assumed to obey the effective stress principle in the normal definition for saturated sedi ments although it may contain gas bubbles occluded in the porewater the governing equation is a fourth order partial differential equation in terms of pore pressure or effective mean normal stress the solutions contain skempton s pore pressure coefficient b for unsaturated sediments with b 1 the pore pressure and effective stresses induced by wave action consist of two parts one part depends only on the wavelength and the other part depends on both the sediment and the wave characteristics the second part is out of phase with the wave when the submarine sediment is unsaturated the wave induced negative effective nor mal stresses become greater under the trough of waves a zone

seismic waveform inversion in the frequency domain part 2 fault delineation in sediments using crosshole data a crosshole experiment was carried out in a layered sedimentary environment in which a normal fault is known to cut through the section initial traveltime inversions produced stable but low resolution images from which the fault could be only vaguely inferred to image the fault wavefield inversion was used to produce a velocity model consistent with the detailed phase and amplitude of the data at a number of frequencies our wavefield inversion scheme uses a classical descent type algorithm for decreasing the data misfit by iteratively computing the gradient of this misfit by repeated forward and backward propagations our propagator is a full wave equation frequency domain acoustic finite difference method the use of the frequency space domain yields computational advantages for multisource data and allows an easy incorporation of viscous effects by running wavefield inversion on the field data a quantitative velocity image was produced that yielded a significantly improved image of the fault when compared with the original traveltime inversions because the original field data were noisy and contained a high degree of multiple scattering from the layering of the sediments the transmitted arrivals were selectively windowed to enhance the image the sediments at the site were strongly attenuating we therefore used a viscoacoustic model during the modeling and the inversion that correctly simulated the observed decrease in amplitude with increasing frequency and source receiver offset furthermore since the traveltime inversion indicated a high degree of anisotropy at the site a fixed homogeneous level of anisotropy was used during the inversion tests at varying levels of anisotropy confirmed the improvement in image quality and in data fit when anisotropy was incorporated the final image was verified by examining the distribution of the residuals in the frequency domain by comparing time domain modeled wavefields with the observed data and by direct comparison with borehole logs

two dimensional velocity models from wide angle seismic data by wavefield inversion summary modern wide angle surveys are often multi fold and multi channel with densely sampled source and receiver spacings such closely spaced data are potentially amenable to multi channel techniques involving wavefield propagation methods such as those commonly used in reflection data processing however the wide angle configuration requires techniques capable of handling very general wave types including those not commonly used in reflection seismology this is a situation analogous to that faced in cross borehole seismics where similar wave types are also recorded in a real cross borehole example we compare pre stack migration traveltime tomography and wavefield inversion we find that wavefield inversion produces images that are quantitative in velocity as are the tomograms but are of significantly higher resolution the wavefield inversion results have a resolution comparable to that of the qualitative pre stack migration images we seek to extend this novel development to the larger scale problem of crustal imaging an essential element of the approach we adopt is its formulation entirely within the temporal frequency domain this has three principal advantages 1 we can choose to decimate the data by selecting only a limited number of frequency components to invert thus making inversion of data from large numbers of source positions feasible 2 we can mitigate the notorious non linearity of the seismic inverse problem by progressing from low frequency components in the data to high frequency components and 3 we can include in the model any arbitrary frequency dependence of inelastic attenuation factors q and indeed solve for the spatial distribution of q an initial synthetic test with an anomaly located within the middle crust yields a velocity image with the correct structural features of the anomaly and the correct magnitude of velocity anomaly this is related to the fact that the reconstruction is obtained from forward scattered waves under these conditions the method thus behaves much like tomography a second test with a deeper more extensive anomaly yields an image with the correct velocity polarity and the correct location but with a deficiency in low and high wavenumbers in this case this is because the reconstruction is obtained from backscattered waves under these conditions the method behaves not like tomography but like migration a more extensive test based on a large wide angle survey in south eastern california and western arizona demonstrates a real potential for high resolution imaging of crustal structures although our results are limited by the acoustic approximation and by the relatively low frequencies that we can model today the images are sufficiently encouraging to warrant future research the problem of local minima in the objective function is the most significant practical problem with our method but we propose that appropriate layer stripping methods can handle this problem

application of a new 2d time domain full waveform inversion scheme to crosshole radar data crosshole radar tomography is a useful tool in diverse investigations in geology hydrogeology and engineering conventional tomograms provided by standard ray based techniques have limited resolution primarily because only a fraction of the information contained in the radar data i e thefirst arrivaltimesandmaximumfirst cycleamplitudesis included in the inversion to increase the resolution of radar tomograms wehavedevelopedaversatilefull waveforminversion scheme that is based on a finite difference time domain solution of maxwell s equations this scheme largely accountsforthe3dnatureofradar wavepropagationandincludes an efficient method for extracting the source wavelet from the radar data after demonstrating the potential of the newschemeontworealisticsyntheticdatasets weapplyitto two crosshole field data sets acquired in very different geologic hydrogeologic environments these are the first applications of full waveform tomography to observed crosshole radar data the resolution of all full waveform tomograms is showntobemarkedlysuperiortothatoftheassociatedraytomograms small subsurface features a fraction of the dominant radar wavelength and boundaries between distinct geological hydrological units are sharply imaged in the fullwaveformtomograms

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

the 15 august 2007 peru tsunami runup observations and modeling 1 on 15 august 2007 an earthquake with moment magnitude mw of 8 0 centered off the coast of central peru generated a tsunami with locally focused runup heights of up to10 m a reconnaissance team was deployed two weeks after the event and investigated the tsunami effects at 51 sites three tsunami fatalities were reported south of the paracas peninsula in a sparsely populated desert area where the largest tsunami runup heights were measured numerical modeling of the earthquake source and tsunami suggest that a region of high slip near the coastline was primarily responsible for the extreme runup heights the town of pisco was spared by the paracas peninsula which blocked tsunami waves from propagating northward from the high slip region the coast of peru has experienced numerous deadly and destructive tsunamis throughout history which highlights the importance of ongoing tsunami awareness and education efforts to ensure successful self evacuation

a study of methods for tomographic velocity estimation in the presence of low velocity zones this paper deals with the problem of seismic velocity estimation from first arrival traveltimes in a two dimensional 2 d cross hole geometry where explosions are detonated in one borehole while recordings are made in another borehole and on the surface standard tomographic procedures are based on decomposition of the cross hole area into a number of cells and a simplifying assumption of straight raypaths in the presence of significant low velocity zones the resulting images may be contaminated different ways of performing tomographic inversion are tested on a number of synthetic examples images obtained by direct unrestricted least squares inversion are often seriously distorted however methods using more cells and some kind of damping often give more satisfactory results because the risk of distorted images is always present in inversion procedures comparison with synthetic data forward modeling is a valuable tool in the interpretation process with a reasonably good initial solution impro

the 2010 mw 7 8 mentawai earthquake very shallow source of a rare tsunami earthquake determined from tsunami field survey and near field gps data 1 the mw 7 8 october 2010mentawai indonesia earthquake was a tsunami earthquake a rare type of earthquake that generates a tsunami much larger than expected based on the seismicmagnitude itproducedalocallydevastatingtsunami withrunupcommonlyinexcess of 6 m we examine this event using a combination of high rate gps data from instruments located on the nearby islands and a tsunami field survey the gps displacement time series are deficient in high frequency energy and show small coseismic displacements 16 m our modeling results show that the combination of the small gps displacements and large tsunami can only be explained by high fault slip at very shallow depths far from the islands and close to the oceanic trench inelastic uplift of trench sediments likely contributed to the size of the tsunami recent results for the 2011 mw 9 0 tohoko oki earthquake have also shown shallow fault slip but the results from our study which involves a smaller earthquake provide much stronger constraints on how shallow the rupture can be with the majority of slip for the mentawai earthquake occurring at depths of 6 km this result challenges the conventional wisdom that the shallow tips of subduction megathrusts are aseismic and therefore raises important questions both about the mechanical properties of the shallow fault zone and the potential seismic and tsunami hazard of this shallow region

sph modeling of dynamic impact of tsunami bore on bridge piers abstract the smoothed particle hydrodynamics sph method is applied to investigate the impact of a tsunami bore on simplified bridge piers in this study this work was motivated by observations of bridge damage during several recent tsunami events and its aim is to further the understanding of the dynamic interaction between a tsunami bore and a bridge pier this study is carried out by simulating a well conducted physical experiment on a tsunami bore impingement on vertical columns with an sph model gpusph the influences of bridge pier shape and orientation on free surface evolution and hydrodynamic loading are carefully examined furthermore the unsteady flow field that is around and in the wake of the bridge pier is analyzed finally gpusph is applied to explore the hydrodynamic force caused by the bridge pier blockage the wave impact on structures and the bed shear stress around a bridge pier due to a strong tsunami bore

diffraction tomography and multisource holography applied to seismic imaging seismic tomography is emerging as an imaging method for determining subsurface structure when the view angle coverage is limited and the scale of the medium inhomogeneities is comparable with the wavelength as is often true in geophysical applications the performance of ordinary ray tomography becomes poor other tomographic methods are needed to improve the imaging process here we study diffraction tomography and multisource holography and evaluate their performances for surface reflection profiling srp vertical seismic profiling vsp and cross hole measurements theoretical formulations are derived for two dimensional geometry in terms of line sources along a source line and line receivers along a receiver line the theory for diffraction tomography is based on the born or rytov approximation the performances of diffraction tomography and multisource holography are evaluated by examining the information coverage in the spatial frequency domain and by numerical examples multisource holography

genetic waveform modeling for the crustal structure in northeast japan we propose a genetic algorithm ga search procedure for waveform modeling of local crustal earthquakes for optimal one dimensional 1 d crustal velocity model both waveforms and travel time data are used for the structure determination the use of travel times in model evaluation improves the waveform modeling performance in the sense of computation speed and accuracy we applied this method to broadband waveforms of a local crustal earthquake m 4 2 in northeast japan p wave velocities of the crustal model are found to be 4 95 0 30 5 9 0 02 and 6 51 0 20 km s for a surface layer upper crust and lower crust respectively the surface layer thickness and the conrad and moho depths are found to be 3 01 0 8 17 77 0 4 and 34 59 1 0 km respectively for epicentral distances 200 km our synthetic waveforms match the observed ones generally well early arrivals are mainly observed at stations near the pacific coast in the forearc area having a thinner crust in contrast delayed arrivals appear at stations near the volcanic front and back arc areas where low velocity anomalies exist due to the effect of the pacific slab dehydration and the hot upwelling flows in the mantle wedge in general our results agree well with the main tectonic setting of the study area which confirms the reliability of the proposed approach despite a 1 d velocity model is too simple to represent the complex crustal structure it is still required for the conventional routine analysis of seismology such as earthquake location and source parameter studies the current approach is considered as a step toward the genetic full waveform modeling for the 3 d velocity model estimation

crosshole seismic waveform tomography i strategy for real data application summary the frequency domain version of waveform tomography enables the use of distinct frequency components to adequately reconstruct the subsurface velocity field and thereby dramatically reduces the input data quantity required for the inversion process it makes waveform tomography a computationally tractable problem for production uses but its applicability to real seismic data particularly in the petroleum exploration and development scale needs to be examined as real data are often band limited with missing low frequencies a good starting model is necessary for waveform tomography to fill in the gap of low frequencies before the inversion of available frequencies in the inversion stage a group of frequencies should be used simultaneously at each iteration to suppress the effect of data noise in the frequency domain meanwhile a smoothness constraint on the model must be used in the inversion to cope the effect of data noise the effect of non linearity of the problem and the effect of strong sensitivities of short wavelength model variations in this paper we use frequency domain waveform tomography to provide quantitative velocity images of a crosshole target between boreholes 300 m apart due to the complexity of the local geology the velocity variations were extreme between 3000 and 5500 m s 1 making the inversion problem highly non linear nevertheless the waveform tomography results correlate well with borehole logs and provide realistic geological information that can be tracked between the boreholes with confidence

reflection seismic waveform tomography 1 in seismic waveform tomography if using reflection data with limited source receiver offsets it is difficult to reconstruct the deep part of the subsurface velocity model we present two approaches to tackle this problem layer stripping and weighted updating in a layer stripping procedure we replace the top portion of seismic data with synthetics generated from the previous layer inversion and make the current inversion focus on the minimization of the data misfit corresponding to the deep part of the model to improve efficiency we use only sparsely sampled frequency data in the deeper layer inversions unlike the first layer inversion where we use densely sampled frequency data as usual the sparsely sampled frequencies together have the full wave number coverage for effective imaging combined use of dense and sparse sampling in frequency is a compromise between resolution and efficiency as it reduces the number of iterations needed in layer stripping inversion while still producing a good image in the second scheme we apply depth dependent weights to model updates in order to improve the convergence in an iterative solution the weighting is inversely proportional to the ray density variation along the depth and is mathematically equivalent to the application of an inverse hessian matrix which sharpens the gradient vector for model updating for real seismic data we transfer point source shot records to line source records by partial amplitude compensation and phase adjusting before inputting it to the waveform tomography we perform traveltime inversion to generate a reliable layered velocity model and then waveform tomography to produce a high resolution image of the subsurface model through frequency domain iteration