Waveform tomography at a groundwater contamination site: VSP-surface data set

Application of 2D frequency-domain waveform tomography to a data set from a high-resolution vertical seismic profiling (VSP) experiment at a groundwater contamination site in Hill Air Force Base (HAFB), Utah, reveals a surprisingly complicated shallow substructure with a resolution of approximately 1.5 m. Variance in the waveform misfit function is reduced 69.4% by using an initial velocity model from first-arrival traveltime tomography. The waveform tomography model suggests (1) a low-velocity layer at 1 to 4 m depth, (2) a high-vertical-velocity gradient of 80 m/s/m on average, and (3) severe lateral variations — velocity contrasts as large as about 200 m/s occur in a distance as short as 1.5 m. The model is well correlated with lithologic logs and is interpreted geologically. A Q-value of 20 is estimated for the target area. The extreme lateral and vertical variations of the subsurface compromise many standard seismic processing methods.

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Waveform tomography at a groundwater contamination site: Surface reflection data

Geophysics ◽

10.1190/1.2752744 ◽

2007 ◽

Vol 72 (5) ◽

pp. G45-G55 ◽

Cited By ~ 44

Author(s):

Fuchun Gao ◽

Alan Levander ◽

R. Gerhard Pratt ◽

Colin A. Zelt ◽

Gian-Luigi Fradelizio

Keyword(s):

Groundwater Contamination ◽

Nonaqueous Phase Liquids ◽

Seismic Profiles ◽

Lateral Velocity ◽

Data Set ◽

Surface Reflection ◽

Traveltime Tomography ◽

Velocity Models ◽

Reflection Data ◽

Waveform Tomography

We have applied acoustic-waveform tomography to 45 2D seismic profiles to image the 3D geometry of a buried paleochannel at a groundwater-contamination site at Hill Air Force Base in Utah. The paleochannel, which is incised into an alluvium-covered clay aquitard, acts as a trap for dense nonaqueous-phase liquids (DNAPLs) that contaminate the shallowest groundwater system in the study area. The 2D profiles were extracted from a 3D surface reflection data set. First-arrival traveltime tomography provided initial velocity models for the waveform tomography. We inverted for six frequency components in the band [Formula: see text] of the direct and refracted waves to produce 45 2D velocity models. The flanks and bottom of a channel with a maximum depth of about [Formula: see text] were well modeled in most of the 45 parallel 2D slices, which allowed us to construct a 3D image of the channel by combining and interpolating between the 45 image slices. The 3D model of the channel will be useful for siting extraction wells within the site remediation program. The alluvium that fills the channel showed marked vertical and lateral velocity heterogeneity. Traveltime tomography and waveform tomography can be complementary approaches. Used together, they can provide high-resolution images of complicated shallow structures.

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Imaging the Active Faults of the Central New Madrid Seismic Zone Using Panda Array Data

Seismological Research Letters ◽

10.1785/gssrl.63.3.375 ◽

1992 ◽

Vol 63 (3) ◽

pp. 375-393 ◽

Cited By ~ 62

Author(s):

J.M. Chiu ◽

A.C. Johnston ◽

Y.T. Yang

Keyword(s):

Hanging Wall ◽

Active Faults ◽

Velocity Model ◽

New Madrid Seismic Zone ◽

Seismic Zone ◽

Thrust Faults ◽

Secondary Phases ◽

Low Velocity ◽

Data Set ◽

New Madrid

Abstract More than 700 earthquakes have been located in the central New Madrid seismic zone during a two-year deployment of the PANDA array. Magnitudes range from < 0.0 to the mblg 4.6 Risco, Missouri earthquake of 4 May 1991. The entire data set is digital, three-component and on-scale. These data were inverted to obtain a new shallow crustal velocity model of the upper Mississippi embayment for both P- and S-waves. Initially, inversion convergence was hindered by extreme velocity contrasts between the soft, low-velocity surficial alluvial sediments and the underlying Paleozoic carbonate and clastic high-velocity rock. However, constraints from extensive well log data for the embayment, secondary phases (Sp and Ps), and abundant, high-quality shear-wave data have yielded a relatively robust inversion. This in turn has led to a hypocentral data set of unprecedented quality for the central New Madrid seismic zone. Contrary to previous studies that utilized more restricted data, the PANDA data clearly delineate planar concentrations of hypocenters that compel an interpretation as active faults. Our results corroborate the vertical (strike-slip) faulting of the the southwest (axial), north-northeast, and western arms and define two new dipping planes in the central segment. The seismicity of the left-step zone between the NE-trending vertical segments is concentrated about a plane that dips at ∼31°SW; a separate zone to the SE of the axial zone defines a plane that dips at ∼48°SW. The reason for this difference in dip, possibly defining segmentation of an active fault, is not dear. When these planes are projected up dip, they intersect the surface along the eastern boundary of the Lake County uplift (LCU) and the western portion of Reelfoot Lake. If these SW-dipping planes are thrust faults, then the LCU would be on the upthrown hanging wall and Reelfoot Lake on the downthrown footwall. If in turn these inferred thrust faults were involved in the 1811–12 and/or pre-1811 large earthquakes, they provide an internally consistent explanation for (1) the existence and location of the LCU, (2) the wide-to-the-north, narrow-to-the-south shape of the LCU, and (3) the subsidence and/or impoundment of Reelfoot Lake.

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Nonuniqueness in traveltime tomography: Ensemble inference and cluster analysis

Geophysics ◽

10.1190/1.1444040 ◽

1996 ◽

Vol 61 (4) ◽

pp. 1209-1227 ◽

Cited By ~ 30

Author(s):

Don W. Vasco ◽

John E. Peterson ◽

Ernest L. Majer

Keyword(s):

Cluster Analysis ◽

Conjugate Gradient ◽

Seismic Inversion ◽

Low Velocity ◽

Data Set ◽

Traveltime Tomography ◽

All Solutions ◽

And Cluster Analysis ◽

Starting Model ◽

Norm Penalty

We examine the nonlinear aspects of seismic traveltime tomography. This is accomplished by completing an extensive set of conjugate gradient inversions on a parallel virtual machine, with each initiated by a different starting model. The goal is an exploratory analysis of a set of conjugate gradient solutions to the traveltime tomography problem. We find that distinct local minima are generated when prior constraints are imposed on traveltime tomographic inverse problems. Methods from cluster analysis determine the number and location of the isolated solutions to the traveltime tomography problem. We apply the cluster analysis techniques to a cross‐borehole traveltime data set gathered at the Gypsy Pilot Site in Pawnee County, Oklahoma. We find that the 1075 final models, satisfying the traveltime data and a model norm penalty, form up to 61 separate solutions. All solutions appear to contain a central low velocity zone bounded above and below by higher velocity layers. Such a structure agrees with well‐logs, hydrological well tests, and a previous seismic inversion.

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Application of waveform tomography to marine seismic reflection data from the Queen Charlotte Basin of western Canada

Geophysics ◽

10.1190/1.3553478 ◽

2011 ◽

Vol 76 (2) ◽

pp. B55-B70 ◽

Cited By ~ 17

Author(s):

E. M. Takam Takougang ◽

A. J. Calvert

Keyword(s):

Seismic Reflection ◽

Field Data ◽

Velocity Model ◽

P Wave ◽

Low Velocity ◽

Seismic Line ◽

Seismic Reflection Data ◽

Reflection Data ◽

Sonic Log ◽

Waveform Tomography

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 velocity model that extends to a depth of approximately 1200 m, twice the maximum depth of ray coverage in the ray-based tomography. Overall, there is a good agreement between the velocity model and a sonic log from a well on the seismic line, as well as between modeled shot gathers and field data. Anomalous zones of low velocity in the model correspond to previously identified faults or their upward continuation into the shallow Pliocene section where they are not readily identifiable in the conventional migration.

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Using 2D long-streamer seismic data waveform tomography to decipher sedimentary record of fault activity

10.5194/egusphere-egu2020-9073 ◽

2020 ◽

Author(s):

Amin Kahrizi ◽

Matthias Delescluse ◽

Mathieu Rodriguez ◽

Pierre-Henri Roche ◽

Anne Becel ◽

...

Keyword(s):

Mass Transport ◽

Seismic Data ◽

Velocity Model ◽

P Wave ◽

Fault System ◽

Fault Activity ◽

Traveltime Tomography ◽

P Wave Velocity ◽

Waveform Tomography ◽

Mass Transport Deposits

<p>Acoustic full-waveform inversion (FWI), or waveform tomography, involves use of both phase and amplitude of the recorded compressional waves to obtain a high-resolution P-wave velocity model of the propagation medium. Recent theoretical and computing advances now allow the application of this highly non-linear technique to field data. This led to common use of the FWI for industrial purposes related to reservoir imaging, physical properties of rocks, and fluid flow. Application of FWI in the academic domain has, so far, been limited, mostly because of the lack of adequate seismic data. While refraction seismic datasets include large source-receiver offsets that are useful to find a suitable starting velocity model through traveltime tomography, these acquisitions rarely reach the high density of receivers necessary for waveform tomography. On the other hand, multichannel seismic (MCS) reflection data acquisition has a dense receiver spacing but only modern long-streamer data have offsets that, in some cases, enable constraining subsurface velocities at a significant enough depth to be useful for structural or tectonic purposes.</p><p>In this study, we show how FWI can help decipher the record of a fault activity through time at the Shumagin Gap in Alaska. The MCS data were acquired on RV Marcus G. Langseth during the ALEUT cruise in the summer of 2011 using two 8-km-long seismic streamers and a 6600 cu. in. tuned airgun array. One of the most noticeable reflection features imaged on two profiles is a large, landward-dipping normal fault in the overriding plate; a structural configuration making the area prone to generating both transoceanic and local tsunamis, including from landslides. This fault dips ~40&#176;- 45&#176;, cuts the entire crust and connects to the plate boundary fault at ~35 km depth, near the intersection of the megathrust with the forearc mantle wedge. The fault system reaches the surface at the shelf edge 75 km from the trench, forming the Sanak basin where the record of the recent activity of the fault is not clear. Indeed, contouritic currents tend to be trapped by the topography created by faults, even after they are no longer active.&#160; Erosion surfaces and onlaps from contouritic processes as well as gravity collapses and mass transport deposits results in complex structures that make it challenging to evaluate the fault activity. The long streamers used facilitated recording of refraction arrivals in the target continental slope area, which permitted running streamer traveltime tomography followed by FWI to produce coincident detailed velocity profiles to complement the reflection sections. FWI imaging of the Sanak basin reveals low velocities of mass transport deposits and velocity inversions indicate mechanically weak layers linking some faults to gravity sliding on a d&#233;collement. These details question previous interpretation of a present-day active fault. Our goal is to further analyze the behavior of the fault system using the P-wave velocity models from FWI to quantitatively detect fluids and constrain sediment properties.</p>

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Anisotropic 3D full-waveform inversion

Geophysics ◽

10.1190/geo2012-0338.1 ◽

2013 ◽

Vol 78 (2) ◽

pp. R59-R80 ◽

Cited By ~ 233

Author(s):

Michael Warner ◽

Andrew Ratcliffe ◽

Tenice Nangoo ◽

Joanna Morgan ◽

Adrian Umpleby ◽

...

Keyword(s):

High Velocity ◽

Field Data ◽

Waveform Inversion ◽

Velocity Model ◽

Full Waveform Inversion ◽

Low Velocity ◽

Data Set ◽

Reflection Data ◽

Full Waveform ◽

Gas Cloud

We have developed and implemented a robust and practical scheme for anisotropic 3D acoustic full-waveform inversion (FWI). We demonstrate this scheme on a field data set, applying it to a 4C ocean-bottom survey over the Tommeliten Alpha field in the North Sea. This shallow-water data set provides good azimuthal coverage to offsets of 7 km, with reduced coverage to a maximum offset of about 11 km. The reservoir lies at the crest of a high-velocity antiformal chalk section, overlain by about 3000 m of clastics within which a low-velocity gas cloud produces a seismic obscured area. We inverted only the hydrophone data, and we retained free-surface multiples and ghosts within the field data. We invert in six narrow frequency bands, in the range 3 to 6.5 Hz. At each iteration, we selected only a subset of sources, using a different subset at each iteration; this strategy is more efficient than inverting all the data every iteration. Our starting velocity model was obtained using standard PSDM model building including anisotropic reflection tomography, and contained epsilon values as high as 20%. The final FWI velocity model shows a network of shallow high-velocity channels that match similar features in the reflection data. Deeper in the section, the FWI velocity model reveals a sharper and more-intense low-velocity region associated with the gas cloud in which low-velocity fingers match the location of gas-filled faults visible in the reflection data. The resulting velocity model provides a better match to well logs, and better flattens common-image gathers, than does the starting model. Reverse-time migration, using the FWI velocity model, provides significant uplift to the migrated image, simplifying the planform of the reservoir section at depth. The workflows, inversion strategy, and algorithms that we have used have broad application to invert a wide-range of analogous data sets.

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Early arrival waveform tomography on near-surface refraction data

Geophysics ◽

10.1190/1.2210969 ◽

2006 ◽

Vol 71 (4) ◽

pp. U47-U57 ◽

Cited By ~ 116

Author(s):

Jianming Sheng ◽

Alan Leeds ◽

Maike Buddensiek ◽

Gerard T. Schuster

Keyword(s):

Ground Truth ◽

Velocity Model ◽

Frequency Method ◽

Near Surface ◽

Good Convergence ◽

Traveltime Tomography ◽

Early Arrival ◽

Synthetic Test ◽

Waveform Tomography ◽

Tomography Method

We develop a waveform-tomography method for estimating the velocity distribution that minimizes the waveform misfit between the predicted and observed early arrivals in space-time seismograms. By fitting the waveforms of early arrivals, early arrival waveform tomography (EWT) naturally takes into account more general wave-propagation effects compared to the high-frequency method of traveltime tomography, meaning that EWT can estimate a wider range of slowness wavenumbers. Another benefit of EWT is more reliable convergence compared to full-waveform tomography, because an early-arrival misfit function contains fewer local minima. Synthetic test results verify that the waveform tomogram is much more accurate than the traveltime tomogram and that this algorithm has good convergence properties. For marine data from the Gulf of Mexico, the statics problem caused by shallow, gassy muds was attacked by using EWT to obtain a more accurate velocity model. Using the waveform tomogram to correct for statics, the stacked section was significantly improved compared to using the normal move-out (NMO) velocity, and moderately improved compared to using the traveltime tomogram. Inverting high-resolution land data from Mapleton, Utah, showed an EWT velocity tomogram that was more consistent with the ground truth (trench log) than the traveltime tomogram. Our results suggest that EWT can provide supplemental, shorter-wavelength information compared to the traveltime tomogram for both shallow and moderately deep seismic data.

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3D seismic refraction traveltime tomography at a groundwater contamination site

Geophysics ◽

10.1190/1.2258094 ◽

2006 ◽

Vol 71 (5) ◽

pp. H67-H78 ◽

Cited By ~ 54

Author(s):

Colin A. Zelt ◽

Aron Azaria ◽

Alan Levander

Keyword(s):

Groundwater Contamination ◽

Velocity Structure ◽

Seismic Refraction ◽

Vertical Direction ◽

Velocity Model ◽

3D Seismic ◽

Traveltime Tomography ◽

3D Velocity Model ◽

First Arrival ◽

Tomographic Approach

We have applied traveltime tomography to 3D seismic refraction data collected at Hill Air Force Base, Utah, in an approximately [Formula: see text] area over a shallow [Formula: see text] groundwater contamination site. The purpose of this study is to test the ability of 3D first-arrival-time data to characterize the shallow environment and aid remediation efforts. The aquifer is bounded below by a clay aquiclude, into which a paleochannel has been incised and acts as a trap for dense nonaqueous phase liquid (DNAPL) contaminants. A regularized nonlinear tomographic approach was applied to [Formula: see text] first-arrival traveltimes to obtain the smoothest minimum-structure 3D velocity model. The resulting velocity model contains a velocity increase from less than [Formula: see text] in the upper [Formula: see text]. The model also contains a north-south-trending low-velocity feature interpreted to be the paleochannel, based on more than 100 wells in the area. Checkerboard tests show [Formula: see text] lateral resolution throughout most of the model. The preferred final model was chosen after a systematic test of the free parameters involved in the tomographic approach, including the starting model. The final velocity model compares favorably with a 3D poststack depth migration and 2D waveform inversion of coincident reflection data. While the long-wavelength features of the model reveal the primary target of the survey, the paleochannel, the velocity model is likely a very smooth characterization of the true velocity structure, particularly in the vertical direction, given the size of the first Fresnel zone for these data.

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Depth image focusing in traveltime map‐based wide‐angle migration

Geophysics ◽

10.1190/1.1527090 ◽

2002 ◽

Vol 67 (6) ◽

pp. 1903-1912 ◽

Cited By ~ 12

Author(s):

Igor B. Morozov ◽

Alan Levander

Keyword(s):

Velocity Model ◽

Depth Image ◽

Velocity Spectrum ◽

Prestack Depth Migration ◽

Data Set ◽

Arrival Times ◽

Depth Migration ◽

Traveltime Tomography ◽

Interactive Analysis ◽

The Common

Wide‐aperture, prestack depth migration requires application of challenging and time‐consuming velocity analysis and depth focusing, collectively referred to here as depth focusing. We present an approach to depth focusing using (1) a detailed starting velocity model obtained by a 1‐D transformation of the first‐arrival times, followed iteratively by (2) interactive analysis of the common‐image gathers, (3) computation of coherency attributes of the wavefield in the depth domain, and (4) 2‐D traveltime tomography to update the background velocity model. We employ two interactive method of migration velocities refinement. In the first method (similar to the common‐midpoint velocity spectrum approach), residual velocity updates are picked directly from the common‐image gathers. In another method (analogous to the common velocity stacks), we pick the velocity updates from the areas of maximum coherency in depth sections that are migrated using rescaled traveltime maps. Both types of migration velocity picks, optionally combined with the first arrivals, are inputs for a 2‐D traveltime inversion scheme that uses either the infinite‐frequency or a finite‐bandwidth approximation. This flexible and versatile depth focusing approach is implemented for several prestack depth migration algorithms and illustrated on an application to a real, ultrashallow seismic data set. The technique resolves overburden velocity variations and facilitates reliable high‐resolution reflection imaging of a paleochannel that was the target of the study.

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Q-model building using one-way wave-equation migration Q analysis — Part 2: 3D field-data test

Geophysics ◽

10.1190/geo2017-0032.1 ◽

2018 ◽

Vol 83 (2) ◽

pp. S111-S126 ◽

Cited By ~ 6

Author(s):

Yi Shen ◽

Biondo Biondi ◽

Robert Clapp

Keyword(s):

Wave Equation ◽

Model Building ◽

Velocity Model ◽

Seismic Attenuation ◽

Low Velocity ◽

Data Set ◽

The North ◽

Q Model ◽

Text Model ◽

Interval Velocities

We previously evaluated an inversion-based method, wave-equation migration [Formula: see text] analysis (WEMQA), to estimate the quality factor [Formula: see text] model for seismic attenuation. To demonstrate the feasibility of this method, we applied this method to a 3D seismic data set acquired in the North Sea. Attenuation problems caused by a shallow gas and a shallow channel are observed in this field. We aim to characterize these attenuation anomalies. These attenuation anomalies are correlated with low interval velocities. The provided velocity model does not accurately reflect the low-velocity anomalies. Therefore, we first applied wave-equation migration velocity analysis to update the provided velocity model. The updated velocity shows low-velocity regions around the gas and channel features. The subsurface angle gathers migrated using the updated velocity model are flatter, and the events in the migrated images after velocity updating are more coherent. Then, we applied WEMQA [Formula: see text] to invert for the [Formula: see text] model. The inverted [Formula: see text] model detects the shape and location of the gas and channel. Consequently, the migration with the estimated [Formula: see text] anomalies enhances the damped amplitudes and the frequency content of the migrated events corrects the distorted phase of the migrated events and makes them more coherent.

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