Shear-wave velocity (Vs) to over 2 km depth as characterized through the krSPAC microtremor array method: Case study from the Seattle basin, Washington

William J. Stephenson, Michael W. Asten, Jack Odum

Research output: Contribution to conferenceAbstract

Abstract

We acquired microtremor array data at 11 sites in the Seattle basin, Washington State, and applied the wavenumber-normalized SPAC method (krSPAC) to obtain Vs to over 2000 m depth. In the krSPAC approach, we transform observed coherency-versus-frequency spectra to coherency-versus-kr (where k and r are wavenumber and station separation, respectively) prior to Vs modeling. Through this transformation, the requirement for array symmetry is eased. We deployed seven-sensor nested irregular triangular arrays, with nominal interstation separations that varied from ~300 m to 2000 m. Comparison of krSPAC Vs results to a previous interpretation from ambient noise tomography suggests a broadly comparable Vs structure in the 250 to 1000 m depth range and improved resolution at shallower depth. At each site, we interpret a high-velocity Quaternary boundary where Vs increases above 900 m/s. Using this boundary as the reference horizon, we calculate ground motion amplification of a factor of up to 2 from the overlying Quaternary sediments between 0.3 and 7 Hz.

Original languageEnglish
Pages4703-4707
Number of pages5
DOIs
Publication statusPublished - 1 Jan 2019
EventSociety of Exploration Geophysicists International Exposition and Annual Meeting, 2018 - Anaheim, United States of America
Duration: 14 Oct 201819 Oct 2018
Conference number: 88th
https://seg.org/Events/Events-Calendar/ModuleID/3784/ItemID/1318/mctl/EventDetails

Conference

ConferenceSociety of Exploration Geophysicists International Exposition and Annual Meeting, 2018
Abbreviated titleSEG 2018
CountryUnited States of America
CityAnaheim
Period14/10/1819/10/18
Internet address

Cite this

Stephenson, W. J., Asten, M. W., & Odum, J. (2019). Shear-wave velocity (Vs) to over 2 km depth as characterized through the krSPAC microtremor array method: Case study from the Seattle basin, Washington. 4703-4707. Abstract from Society of Exploration Geophysicists International Exposition and Annual Meeting, 2018, Anaheim, United States of America. https://doi.org/10.1190/segam2018-2985851.1