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  • 1
    Publication Date: 2022-05-25
    Description: Author Posting. © Acoustical Society of America, 2018. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 143 (2018): EL405-EL411, doi: 10.1121/1.5039769.
    Description: This paper presents single receiver geoacoustic inversion of a combustive sound source signal, recorded during the 2017 Seabed Characterization Experiment on the New England Mud Patch, in an area where water depth is around 70 m. There are two important features in this study. First, it is shown that high-order modes can be resolved and estimated using warping (up to mode number 18 over the frequency band 20–440 Hz). However, it is not possible to determine mode numbers from the data, so that classical inversion methods that require mode identification cannot be applied. To solve this issue, an inversion algorithm that jointly estimates geoacoustic properties and identifies mode number is proposed. It is successfully applied on a range-dependent track, and provides a reliable range-average estimation of geoacoustic properties of the mud layer, an important feature of the seabed on the experimental area.
    Description: This research was supported by the Office of Naval Research and the Office of Naval Research Global.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
    Publication Date: 2022-05-26
    Description: © The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bonnel, J., Dosso, S. E., Eleftherakis, D., & Chapman, N. R. Trans-dimensional inversion of modal dispersion data on the New England Mud Patch. IEEE Journal of Oceanic Engineering, 45(1), (2020): 116-130, doi:10.1109/JOE.2019.2896389.
    Description: This paper presents single receiver geoacoustic inversion of two independent data sets recorded during the 2017 seabed characterization experiment on the New England Mud Patch. In the experimental area, the water depth is around 70 m, and the seabed is characterized by an upper layer of fine grained sediments with clay (i.e., mud). The first data set considered in this paper is a combustive sound source signal, and the second is a chirp emitted by a J15 source. These two data sets provide differing information on the geoacoustic properties of the seabed, as a result of their differing frequency content, and the dispersion properties of the environment. For both data sets, source/receiver range is about 7 km, and modal time-frequency dispersion curves are estimated using warping. Estimated dispersion curves are then used as input data for a Bayesian trans-dimensional inversion algorithm. Subbottom layering and geoacoustic parameters (sound speed and density) are thus inferred from the data. This paper highlights important properties of the mud, consistent with independent in situ measurements. It also demonstrates how information content differs for two data sets collected on reciprocal tracks, but with different acoustic sources and modal content.
    Description: 10.13039/100000006-Office of Naval Research 10.13039/100007297-Office of Naval Research Global
    Keywords: Dispersion ; Cascading style sheets ; Sea measurements ; Receivers ; Chirp ; Sediments ; Uncertainty
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    Society of Exploration Geophysicists
    In:  Geophysics, 68 (5). pp. 1485-1496.
    Publication Date: 2015-11-25
    Description: This paper uses a Bayesian approach for inverting seismic amplitude versus offset (AVO) data to provide estimates and uncertainties of the viscoelastic physical parameters at an interface. The inversion is based on Gibbs' sampling approach to determine properties of the posterior probability distribution (PPD), such as the posterior mean, maximum a posteriori (MAP) estimate, marginal probability distributions, and covariances. The Bayesian formulation represents a fully nonlinear inversion; the results are compared to those of standard linearized inversion. The nonlinear and linearized approaches are applied to synthetic test cases which consider AVO inversion for shallow marine environments with both unconsolidated and consolidated seabeds. The result of neglecting attenuation in the seabed is investigated, and the effects of data factors such as independent and systematic errors and the range of incident angles are considered. The Bayesian approach is also applied to estimate the physical parameters and uncertainties from AVO data collected at two sites along a seismic line in the Baltic Sea with differing sediment types; it clearly identifies the distinct seabed compositions. Data uncertainties (independent and systematic) required for this analysis are estimated using a maximum-likelihood approach.
    Type: Article , PeerReviewed
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  • 4
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    Society of Exploration Geophysicists
    In:  Geophysics, 72 (2). C31-C43.
    Publication Date: 2020-07-30
    Description: We examine the usefulness of amplitude versus offset (AVO) analysis of bottom-simulating reflections (BSRs) for estimating associated marine gas hydrate and free-gas concentrations. A nonlinear Bayesian inversion is applied to estimate marginal probability distributions (MPDs) of physical parameters at a BSR interface, which are related to overlying gas hydrate and underlying free-gas concentrations via rock physics modeling. The problem is constrained further by prior information and re-parameterization of inversion results. Inversion of BSR AVO data from offshore Vancouver Island, Canada, shows that gas hydrate and free-gas concentrations are, respectively, 0%-23% and 0%-2% of the pore volume, at a 90% credibility level. This result indicates that the data do not provide sufficient information to independently resolve gas hydrate and free-gas concentrations to useful accuracy. The Study is directed primarily at AVO for gas-hydrate-related BSRs, but may have important applicability in testing the degree of constraint of formation characteristics in other AVO studies. The inversion method is applied also to synthetic AVO data generated from Ostrander's gas-sand model. In this case, MPDs sufficiently constrain the relationship between P- and S-wave velocities in the sandstone unit to determine if it is gas-charged. The variable degree of model constraint obtained in this AVO study highlights the need to include rigorous quantitative uncertainty analysis in all AVO studies.
    Type: Article , PeerReviewed
    Format: text
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  • 5
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    Society of Exploration Geophysicists
    In:  In: Geophysical Characterization of Gas Hydrates. , ed. by Riedel, M. SEG Geophysical Developments Series, 14 . Society of Exploration Geophysicists, Tulsa, Okla., pp. 73-93.
    Publication Date: 2016-01-14
    Description: This paper examines the usefulness of amplitude versus offset (AVO) analysis for marine and permafrost gas hydrate settings. In marine environments, AVO analyses have traditionally focused on bottom-simulating reflections (BSRs) for estimating associated marine gas hydrate and free gas concentrations. A nonlinear Bayesian inversion is applied to estimate marginal probability distributions (MPDs) of physical parameters at a BSR interface, which are related to overlying gas hydrate and underlying free-gas concentrations via rock physics modeling. The problem is further constrained by prior information and re-parameterization of inversion results. Inversion of BSR AVO data from offshore Vancouver Island, Canada, shows that gas hydrate and free-gas concentrations are, respectively, 0-23% and 0-2% of the pore volume, at a 90% credibility level. However, it should be noted that these two parameters are not independent in the analysis, but instead inversely related. Thus, 0% in gas hydrate concentrations requires some percent of free gas within the range stated (and vice versa). This result indicates that the data do not provide sufficient information to independently resolve gas hydrate and free-gas concentrations to useful accuracy. The same Bayesian inversion method is applied to synthetic AVO data generated from well-log data obtained at the Mallik 5L-38 well in the Mckenzie Delta, NWT. The model cases representing typical permafrost gas hydrate occurrences are investigated and include shale over gas hydrate-bearing sand, gas hydrate-bearing sand over shale, and gas hydrate-bearing sand over water-saturated sand scenarios. The AVO inversion sufficiently constrains the shear-wave velocity for reliable quantitative analysis, only if the gas hydrate concentration exceeds ~40%. The variable degree of model constraint obtained in this AVO study highlights the need to include rigorous quantitative uncertainty analysis in all AVO studies.
    Type: Book chapter , NonPeerReviewed
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  • 6
    Publication Date: 2012-04-01
    Description: This paper applies double-difference earthquake relocation techniques to investigate sources of seismicity in southwest British Columbia, Canada, and the San Juan Islands, Washington. The study area is a complex region of deformation and has the potential for large earthquakes in the North Americancrust. Double-difference earthquake relocation techniques are applied to identify otherwise-hidden active structures that may pose a hazard to nearby population and infrastructure. We present evidence for previously unrecognized active structures using precise relative earthquake relocations obtained using both catalog and waveform cross-correlation data. Results have significantly reduced errors over routine catalog locations and show lineations in areas of clustered seismicity. In southwest British Columbia, these lineations or streaks appear to be hidden structures that do not disrupt near-surface sediments; however, in the San Juan Islands the identified lineation could be related to recently mapped surface expressions of faults identified from seismic reflection and multibeam bathymetric surveys. We use a variety of velocity models for the relocations and find that inappropriate models lead to artifacts at layer boundaries and increased vertical errors.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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