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  • Data for: Improved Characterization of Ultralow-velocity Zones through Advances in Bayesian Inversion of ScP Waveforms

    Description:
    Ultralow-velocity zones (ULVZs) have been studied using a variety of seismic phases; however, their physical origin is still poorly understood. Short period ScP (S wave converted to, and reflected as, P wave from the core-mantle boundary) waveforms are extensively used to infer ULVZ properties because they may be sensitive to all ULVZ elastic moduli. However, ScP waveforms are additionally complicated by the effects of path attenuation, coherent noise, and source-time function (STF) complexity. To address these complications, we developed a hierarchical Bayesian inversion method that allows us to invert ScP waveforms from multiple events simultaneously and accounts for path attenuation and correlated noise. The inversion method is tested with synthetic predictions which show that the inclusion of attenuation is imperative to recover ULVZ parameters and that the ULVZ thickness and S-wave velocity decrease (δVS) are most reliably recovered. Utilizing multiple events reduces the effects of coherent noise and STF complexity, which in turns allows for the inclusion of more data to be used in the analyses. We next applied the method to ScP data recorded in Australia for 291 events that sample the CMB beneath the Coral Sea. Our results indicate that S-wave velocity across the region is ~-14% in average, but there is a greater variability in the south than that in the north. P-wave velocity reductions and density perturbations are mostly below 10%. These ScP data show more than one ScP post-cursor in some areas which may indicate complex 3-D ULVZ structures. Seismic data are provided for 291 earthquakes in Northern Territory, Australia.
    Keyword:
    seismology, mantel phases, ULVZ, and short period ScP waveforms
    Subject:
    Geology, Seismology, and Geophysics
    Creator:
    Pachhai, Surya and Thorne, Michael S.
    Owner:
    Surya Pachhai
    Based Near Label Tesim:
    Northern Territory, Northern Territory, Australia
    Language:
    English
    Date Uploaded:
    12/10/2022
    Date Modified:
    06/03/2024
    Date Created:
    2005-01-01 to 2021-12-30.
    License:
    Public Domain – This data is free of copyright restrictions (e.g. government sponsored data).
    Resource Type:
    Dataset
    Identifier:
    https://doi.org/10.7278/S50d-a67s-y717

  • Data for: A Compositional Component to the Samoa Ultralow-velocity Zone Revealed through 2- and 3-D Waveform Modeling of SKS and SKKS Differential Travel-times and Amplitudes

    Description:
    We analyzed 4,754 broadband seismic recordings of the SKS, SKKS, and SPdKS wavefield from 13 high quality events sampling the Samoa ultralow-velocity zone (ULVZ). We measured differential travel-times and amplitudes between the SKKS and SKS arrivals, which are highly sensitive to the emergence of the SPdKS seismic phase, which is in turn highly sensitive to lowermost mantle velocity perturbations such as generated by ULVZs. We modeled these data using a 2-D axi-symmetric waveform modeling approach and are able to explain these data with a single ULVZ. In order to predict both travel-time and amplitude perturbations we found that a large ULVZ length in the great circle arc direction on the order of 10° or larger is required. The large ULVZ length limits acceptable ULVZ elastic parameters. Here we find that δVS and δVP reductions from 20% to 22% and 15% to 17% respectively gives us the best fit, with a thickness of 26 km. Initial 3-D modeling efforts do not recover the extremes in the differential measurements, demonstrating that 3-D effects are important and must be considered in the future. However, the 3-D modeling is generally consistent with the velocity reductions recovered with the 2-D modeling. These velocity reductions are compatible with a compositional component to the ULVZ. Furthermore, geodynamic predictions for a compositional ULVZ that is moving predict a long linear shape similar to the shape of the Samoa ULVZ we confirm in this study. and This collection includes radial component displacement seismograms in the time window including the SKS, SKKS and SPdKS seismic arrivals. These data all interact with the Samoa ultra-low velocity zone at the core-mantle boundary. All data used in the study of Krier et al., 2021 (JGR) is included in this collection.
    Keyword:
    seismology, Samoa hot spot, geodynamic predictions model, 3-D model, ULVZ, and ultra-low velocity zone
    Subject:
    Geology, seismology, and Geophysics
    Creator:
    Thorne, Michael S. , Nissen-Meyer, Tarje , Krier, Justin D. , and Leng, Kuangdai
    Owner:
    Michael Thorne
    Based Near Label Tesim:
    Tonga Trench, , Tonga
    Language:
    English
    Date Uploaded:
    02/17/2021
    Date Modified:
    10/25/2024
    Date Created:
    2019-01-01 to 2020-01-31
    License:
    Public Domain – This data is free of copyright restrictions (e.g. government sponsored data).
    Resource Type:
    Dataset
    Identifier:
    https://doi.org/10.7278/S50DT3X22GGB