passive seismic imaging in the presence of white noise sources passive seismic imaging is based on the relation between the reflection and the transmission responses of the subsurface let one have the transmission responses measured at surface points a and b of a 3d inhomogeneous medium in the presence of white noise sources in the subsurface when these transmission responses are cross correlated one obtains the reflection response of the same medium as if measured at point a in the presence of an impulsive source at point b the quality of the simulated reflection response strongly depends on the whiteness and the distribution of the noise sources reflectors present below the sources cause the appearance of some ghost events random distribution of the noise sources will however weaken these ghost events

extracting time domain green s function estimates from ambient seismic noise 1 it has been demonstrated experimentally and theoretically that an estimate of the green s function between two seismic stations can be obtained from the time derivative of the long time average cross correlation of ambient noise between these two stations this tdgf estimate from just the noise field includes all tensor components of the green s function and these green s function estimates can be used to infer earth structure we have computed cross correlations using 1 to 30 continuous days of ambient noise recorded by over 150 broadband seismic stations located in southern california the data processing yielded thousands of cross correlation pairs for receiver separations from 4 500 km which clearly exhibit coherent broadband propagating dispersive wavetrains across frequency band 0 1 2 hz

3d wave equation interferometric migration of vsp free surface multiples interferometric migration of free surface multiples in vertical seismic profile vsp data has two significant advantages over standard vsp imaging 1 a significantly larger imaging area compared to migrating vsp primaries and 2 less sensitivity to velocity estimation and static errors than other methods for migration of multiples in this paper we present a 3d wave equation interferometric migration method that efficiently images vsp free surface multiples synthetic and field data results confirm that a reflectivity image volume comparable in size to a 3d surface seismic survey around the well can be computed economically the reflectivity image volume has less fold density and lower signal to noise ratio than that obtained by a conventional 3d surface seismic survey because of the relatively weak energy of multiples and the limited number of geophones in the well however the efficiency of this method for migrating vsp multiples suggests that it might sometimes be a useful tool for 4d seismic monitoring where reflectivity images can be computed quickly for each time lapse survey

transmission to reflection transformation of teleseismic wavefields 1 in this paper we review the transformation of p and sv transmission green s functions into the corresponding reflection quantities for one dimensional elastic media at precritical slownesses to obtain estimates of the transmission green s functions from observed data we apply a recently developed approach that exploits the minimum phase nature of the direct waves and employs autospectra and cross spectra of raw component seismograms representing multiple sources recorded at a single station to accomplish transformation to reflection green s functions we outline a practical recipe that involves amplitude balancing energy normalization cross correlation and removal of free surface effects we assess its performance through application to both synthetic seismograms and data from station hyderabad in all cases we are able to identify the first order scattering contributions from the continental moho the transmission to reflection transformation has potential applications for imaging hitherto elusive shallow mantle discontinuities since interfering forward and back scattering contributions are effectively separated by component in the resulting reflection green s functions

tutorial on seismic interferometry part 1 basic principles and applications seismic interferometry involves the crosscorrelation of responses at different receivers to obtain the green s function between these receivers for the simple situation of an impulsive plane wave propagating along the x axis the crosscorrelation of the responses at two receivers along the x axis gives the green s function of the direct wave between these receivers when the source function of the plane wave is a transientas in exploration seismology or a noise signalas in passive seismology then the crosscorrelation gives the green s function convolved with the autocorrelation of the source function direct wave interferometry also holds for 2d and 3d situations assuming the receivers are surrounded by a uniform distribution of sources in this case the main contributions to the retrieved direct wave between the receivers come from sources in fresnel zones around stationary points the main application of direct wave interferometry is the retrieval of seismic surface wave responses from ambient noise and the subsequent tomographic determination of the surfacewave velocity distribution of the subsurface seismic interferometry is not restricted to retrieving direct waves between receivers in a classic paper claerbout shows that the autocorrelation of the transmission response of a layered medium gives the plane wave reflection response of that medium this is essentially 1d reflected wave interferometry similarly the crosscorrelation of the transmission responses observed at two receivers of an arbitrary inhomogeneous medium gives the 3d reflection response of that medium one of the main applications of reflected wave interferometry is retrieving the seismic reflection response from ambient noise and imaging of the reflectors in the subsurface a common aspect of direct and reflected wave interferometry is that virtual sources are created at positions where there are only receivers without requiring knowledge of the subsurface medium parameters or of the positions of the actual sources

multiparameter two dimensional inversion of scattered teleseismic body waves 3 application to the cascadia 1993 data set this is the third paper in a three part series that examines formal inversion of the teleseismic p wave coda for discontinuous two dimensional 2 d variations in elastic properties beneath dense arrays of three component broadband seismometers in this paper the method is applied to data from the incorporated research institutions for seismology program for array seismic studies of the continental lithosphere iris passcal cascadia 1993 experiment undertaken across central oregon two major features are imaged in the resulting model the continental moho becomes evident 150 km from the coast beneath the western cascades and extends through the eastern end of the profile at 35 40 km depth in the western portion of the model oceanic crust of the subducting juan de fuca plate dips shallowly 12 at the coast and more steeply 27 below the willamette valley and is evident to depths of 100 km beneath the high cascades the abrupt increase in plate dip at 40 km depth coincides with an apparent thickening of the oceanic crust followed by a diminution in its signature building on previous work we argue that these results are consistent with the consequences of prograde metamorphic reactions occurring within the oceanic crust progressive dehydration at lower grade facies conditions culminates in the transformation to eclogite producing a pronounced increase in the seismic velocity density and dip of the subducting plate and structural complexity in the overlying wedge

evaluation of surface wind fields for prediction of directional ocean wave spectra during hurricane sandy abstract hurricane sandy was the largest storm on historical record in the atlantic ocean basin with extensive coastal damage caused by large waves and high storm surge in this study three different spatially varying surface wind and atmospheric pressure fields that are used for forecasting or hindcasting hurricane waves on the continental shelf are investigated these wind fields include two 2d parametric wind models holland model h80 generalized asymmetric holland model gahm and a 3d atmospheric model with data assimilation weatherflow regional atmospheric modelling system wrams these wind fields are used to drive wave hindcasts using coupled delft3d swan hydrodynamic and ocean wave models on a regional grid and the bulk wave statistics and the directional wave spectra are compared to observations at offshore wave buoys to investigate the impact of differences between the complex wind fields on predictions of the sea surface evolution the spatial and temporal distribution of bulk wave parameters are different for each wind field the wrams wind field produces wave model predictions in the best agreement with significant wave height observations followed by the gahm and h80 wind fields with mean correlation coefficients of 0 91 0 82 and 0 75 respectively averaged over 9 sites the directional wave spectra for hurricane sandy was bi modal predominantly in the two left quadrants of the hurricane in agreement with buoy observations the results indicate that a regional atmospheric wind model that has the best description of the wind field is the most appropriate forcing for hindcasting hurricane waves when detailed observations are available however a parametric vortex model that incorporates wind at multiple isotachs results in very good agreement with wave observations when used in the wave model and is a useful too for forecasting hurricane sea surface conditions the results of this study are relevant for other tropical cyclones that undergo extratropical transition or are influenced by other atmospheric disturbances at mid latitudes resulting in storms with large spatial size and high asymmetry

multiparameter two dimensional inversion of scattered teleseismic body waves 2 numerical examples in this paper we investigate the formal inversion of synthetic teleseismic p coda waves for subsurface elastic properties using a ray theoretic approach which assumes single scattering bostock et al this issue we consider a model comprising an idealized lithospheric suture zone whose geometrical configuration is drawn from previous deep crustal seismic studies two dimensional pseudospectral synthetic seismograms representing plane waves propagating through this model are preprocessed to extract an estimate of the scattered wave field generated by short wavelength structure these data are employed in a series of numerical simulations which examine the dependence of multiparameter inversion results on a range of input parameters in particular we demonstrate 1 the contrasting sensitivity which forward and backscattered waves display to structural recovery 2 the diminution of the problem null space accompanied by increased source coverage 3 improvements in model reconstruction achieved through simultaneous treatment of multiple scattering modes and 4 the robustness of the method for data sets with noise levels and receiver geometries that approach those of field experiments

teleseismic shot profile migration the shot profile migration approach of wave equation migration generates subsurface images using the interferometric principle of crosscorrelating two passive wavefields these wavefields are typically a source wavefield containing energy from an excited source and a receiver wavefield comprised of scattered source wavefield energy by the discontinuous earth structure shot profile migration can be recast as a novel way of imaging the earth s lithosphere using teleseismic wavefield data where the source wavefield is the directly arriving wavefront and the receiver wavefield is the following wavefield coda we demonstrate that the shot profile technique can be tailored to suit teleseismic acquisition geometry and wavefields assuming an acoustic framework and 2 5d experimental geometry we develop procedures that enable kinematic and structural imaging migration using both transmission and free surface reflected passive wavefields experiments with synthetic data demonstrate the method s applicability a

interferometric imaging of a salt flank using walkaway vsp data vsp has long been a tool for investigating the location of salt flanks traditionally a salt proximity survey has been used to estimate the location of salt boundaries relative to a wellbore however this technique depends on accurate knowledge of the shape of the salt and the local sediment velocities in addition this method does not work well with complicated 3d salt structure beyond the traditional salt proximity survey many researchers have developed various methods and strategies for improving the locating and or imaging of salt flanks o brien et al 2002 brandsberg dahl et al 2003 zhao et al 2006 with these methods the quality of the resultant image depends on a prior knowledge of the possibly anisotropic overburden velocity field for very long offsets and also is concerned with multi pathing through salt invalidating a 2d assumption in looking for a simpler approach to this problem a single well imaging concept may be attractive using downhole sources and receivers it is possi

characterization of shallow geology by high frequency seismic noise tomography summary to study the applicability of the passive seismic interferometry technique to near surface geological studies seismic noise recordings from a small scale 2 d array of seismic stations were performed in the test site of nauen germany rayleigh wave green s functions were estimated for different frequencies a tomographic inversion of the traveltimes estimated for each frequency from the green s functions is then performed allowing the laterally varying 3 d surface wave velocity structure below the array to be retrieved at engineering geotechnical scales furthermore a 2 d s wave velocity cross section is obtained by combining 1 d velocity structures derived from the inversion of the dispersion curves extracted at several points along a profile where other geophysical analyses were performed it is shown that the cross section from passive seismic interferometry provides a clear image of the local structural heterogeneities that are in excellent agreement with georadar and geoelectrical results such findings indicate that the interferometry analysis of seismic noise is potentially of great interest for deriving the shallow 3 d velocity structure in urban areas

convergence of the two point correlation function toward the green s function in the context of a seismic prospecting data set when considering direct waves in the correlation process the green s function is reconstructed when using an even distribution of seismic sources or when the source distribution is restricted to the direction close to the alignment of the sensors on the other hand when considering records of coda waves the convergence is achieved for any source distribution as expected theoretically we extract the expected amplitude decay along a seismic profile from the correlation functions when an even distribution of sources is considered or when the time window includes scattered waves

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

surface wave tomography from ambient seismic noise of accelerograph networks in southern korea 1 an efficient and robust cross correlation technique for estimation of surface wave green s function between two locations is applied to a set of ambient noise data recorded by accelerograph networks in the southern korea we have estimated 1843 group velocities of rayleigh waves in the period band of 2 4 seconds from correlation pairs of 91 accelerograph stations relatively dense and uniform coverage of the pairs provides us with high resolution tomographic image of surface wave group velocities in the region the resulting group velocity distribution correlates well with the characteristic features of geological map of the region displaying low velocities for the sedimentary basins and regions of volcanic and metasedimentary rocks and high velocities for the regions where granitoid basement rocks outcrop the short period information from the accelerograph network can enhance resolution of the subsurface structures at depths within a few kilometers which may be predominantly responsible for simulation results of strong ground motions

broadband ambient noise surface wave tomography across the united states 1 this study presents surface wave dispersion maps across the contiguous united states determined using seismic ambient noise two years of ambient noise data are used from march 2003 through february 2005 observed at 203 broadband seismic stations in the us southern canada and northern mexico cross correlations are computed between all station pairs to produce empirical green functions at most azimuths across the us coherent rayleigh wave signals exist in the empirical green functions implying that ambient noise in the frequency band of this study 5 100 s period is sufficiently isotropically distributed in azimuth to yield largely unbiased dispersion measurements rayleigh and love wave group and phase velocity curves are measured together with associated uncertainties determined from the temporal variability of the measurements a sufficient number of measurements 2000 is obtained between 8 and 25 s period for love waves and 8 and 70 s period for rayleigh waves to produce tomographic dispersion maps both phase and group velocity maps are presented in these period bands resolution is estimated to be better than 100 km across much of the us from 8 40 s period for rayleigh waves and 8 20 s period for love waves which is unprecedented in a study at this spatial scale at longer and shorter periods resolution degrades as the number of coherent signals diminishes the dispersion maps agree well with each other and with known geological and tectonic features and in addition provide new information about structures in the crust and uppermost mantle beneath much of the us

reflection images from ambient seismic noise one application of seismic interferometry is to retrieve the impulse response green s function from crosscorrelation of ambient seismic noise various researchers show results for retrieving the surface wave part of the green s function however reflection retrieval has proven more challenging we crosscorrelate ambient seismic noise recorded along eight parallel lines in the sirte basin east of ajdabeya libya to obtain shot gathers that contain reflections we take advantage of geophone groups to suppress part of the undesired surface wave noise and apply frequency wavenumber filtering before crosscorrelation to suppress surface waves further after comparing the retrieved results with data from an active seismic exploration survey along the same lines we use the retrieved reflection data to obtain a migrated reflection image of the subsurface

seismic interferometry with a tbm source of transmitted and reflected waves we discuss the use of autocorrelogram interferometry by using noise from the tunnel boring machine tbm the tbm provides seismic signals waves while drilling in a tunnel tswd the tunnel geometry unlike a reverse vertical seismic profile rvsp using a drill bit makes it possible to record the waves reflected from the region between the tunnel face and the projected tunnel exit and those transmitted ahead of the tunnel face we processed the waves recorded at back positions with respect to the tbm in a manner similar to a rvsp data set obtained by conventional reference correlation techniques we processed the waves transmitted ahead of the tbm using autocorrelogram interferometry techniques using these wavefields offers advantages over conventional borehole drill bit vertical seismic profiles vsps the most important advantage is getting reflections from the transmitted front wavefield by utilizing kunetz s equation and reversed time traces the approach also improves the analysis of the trans

surface wave tomography from microseisms in southern california received 5 april 2005 revised 23 may 2005 accepted 9 june 2005 published 26 july 2005 1 since it has already been demonstrated that point topoint seismic propagation green functions can be extracted from seismic noise it should be possible to image earth structure using the ambient noise field seismic noise data from 148 broadband seismic stations in southern california were used to extract the surface wave arrival times between all station pairs in the network the seismic data were then used in a simple but densely sampled tomographic procedure to estimate the surface wave velocity structure within the frequency range of 0 1 0 2 hz for a region in southern california the result compares favorably with previous estimates obtained using more conventional and elaborate inversion procedures this demonstrates that coherent noise field between station pairs can be used for seismic imaging purposes citation sabra k g p gerstoft p roux w a kuperman and m c fehler 2005 surface wave tomography from microseisms in southern california geophys res lett 32 l14311 doi 10 1029 2005gl023155

ambient noise rayleigh wave tomography in western sichuan and eastern tibet abstract we perform rayleigh wave tomography in western sichuan and eastern tibet by applying the ambient noise method to broadband data recorded at 49 stations from the sichuan digital seismic network cross correlations of vertical component ambient noise data are computed in one hour segments and stacked over 7 months from june to december 2007 then rayleigh wave group dispersion curves from 6 to 48 s were measured using the multiple filter analysis method group velocity maps at periods from 8 to 44 s were inverted the resulting group velocity maps generally show good correlations with tectonic features the sichuan basin is clearly resolved with lower group velocities at the short periods 8 to 20 s due to thick sedimentary layers and a prominent low velocity zone exhibits in the middle crust beneath the eastern margin of the tibetan plateau the longmen shan thrust belt marks not only the rapid lateral velocity variation between the topographically high tibetan plateau and low elevation sichuan basin but also the transition from the thick crust beneath the tibetan plateau to the normal continental crust beneath the sichuan basin

lunar subsurface investigated from correlation of seismic noise by correlating seismic noise recorded by four sensors placed on the moon during the apollo 17 mission we have retrieved a well defined dispersed rayleigh wave pulse inversion of its group velocity provides new constraints on the lunar subsurface structure the estimated signal to noise ratio snr of the retrieved rayleigh wavetrain is strongly dependent on solar illumination effectively making solar heating a source of seismic noise on the moon this result suggests that in future planetary missions it is feasible to extract information on the internal structure of extraterrestrial objects by correlating seismic noise even when natural quakes are absent

green s functions extraction and surface wave tomography from microseisms in southern california we use crosscorrelations of seismic noise data from 151 stations in southern california to extract the group velocities of surface waves between the station pairs for the purpose of determining the surface wave velocity structure we developed an automated procedure for estimating the green s functions and subsequent tomographic inversion from the 11 325 station pairs based on the characteristics of the noise field we eliminate specific events by a procedure that does not introduce any spurious spectral distortion in the band of interest 0 05 0 2 hz further we only used the emerging arrival structure above a threshold signal to noise ratio the result is that mostly station pairs with their axes oriented toward the sea are used consistent with the noise having a microseism origin finally it is the time derivative of the correlation function that is actually related to the green s function the emergence of the time domain green s function is proportional to the square root of the recording time and inversely proportional to the square root of the distance between stations the tomographic inversion yields a surface wave velocity map that compares favorably with more conventional and elaborate experimental procedures

redatuming through a salt canopy and target oriented salt flank imaging we describe a new shortcut strategy for imaging the sediments and salt edge around a salt flank through an overburden salt canopy we tested its performance and capabilities on 2d synthetic acoustic seismic data from a gulf of mexico style model we first redatumed surface shots using seismic interferometry from a walkaway vertical seismic profile survey as if the source and receiver pairs had been located in the borehole at the positions of the receivers this process creates effective downhole shot gathers by completely moving surface shots through the salt canopy without any knowledge of overburden velocity structure after redatuming we can apply multiple passes of prestack migration from the reference datum of the bore hole in our example first pass migration using only a simple vertical velocity gradient model reveals the outline of the salt edge a second pass of reverse time prestack depth migration using full two way wave equation was performed with an updated velocity model that consisted of the velocity gradient and salt dome the second pass migration brings out dipping sediments abutting the salt flank because these reflectors were illuminated by energy that bounced off the salt flank forming prismatic reflections in this target oriented strategy the computationally fast redatuming process eliminates the need for the traditional complex process of velocity estimation model building and iterative depth migration to remove effects of the salt canopy and surrounding overburden this might allow this strategy to be used in the field in near real time

migration methods for imaging different order multiples multiples contain valuable information about the subsurface and if properly migrated can provide a wider illumination of the subsurface compared to imaging with vsp primary reflections in this paper we review three different methods for migrating multiples the first method is model based and it is more sensitive to velocity errors than primary migration the second method uses a semi natural green s function for migrating multiples where part of the traveltimes are computed from the velocity model and part of the traveltimes i e natural traveltimes are picked from the data to construct the imaging condition for multiples the third method uses cross correlation of traces the last two methods are preferred in the sense that they are significantly less sensitive to velocity errors and statics because they use natural data to construct part of the migration imaging conditions compared with the interferometric i e crosscorrelation imaging method the semi natural green s function method is more computationally efficient and is sometimes less prone to migration artifacts numerical tests with 2 d and 3 d vsp data show that a wider subsurface coverage higher fold and more balanced illumination of the subsurface can be achieved with multiple migration compared with migration of primary reflections only however there can be strong interference from multiples with different orders or primaries when multiples of high order are migrated one possible solution is to filter primaries and different orders of multiples before migration and another possible solution is least squares migration of all events a limitation of multiple migration is encountered for subsalt imaging here the multiples must pass through the salt body more than twice which amplifies the distortion of the image