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Near-Surface Structure Constrained Using Body-Wave Polarization

Sunyoung Park, Victor C. Tsai, & Miaki Ishii

Published August 7, 2019, SCEC Contribution #9360, 2019 SCEC Annual Meeting Poster #047

Body-wave polarization is sensitive to properties immediately beneath a seismic instrument, and has been demonstrated to be effective at estimating the near-surface P- and S-wave speeds (Park & Ishii, 2018*). In this presentation, we discuss the frequency dependent depth sensitivity of body-wave polarization. We find that the depth sensitivity of P-wave polarization peaks at the surface and decreases abruptly over a depth range shorter than its wavelength, with a strong dependence on frequency content. This allows constraints on local 1-D structure, where frequencies between 0.1 and 10 Hz illuminate structure at depths of ten meters to several kilometers.

We apply the frequency-dependent analysis to explore near-surface and upper-crustal structure of the continental United States, including southern California. Our preliminary results show correlation with geological features and prominent basins, with depth-dependent features that suggest complex subsurface processes at some sites. This versatile technique requires minimal computational resources and can be applied to any single three-component seismograph. It opens a new path to a reliable, non-invasive, and inexpensive way of performing hazard assessment even for sites where drilling or field experiments using vibro-trucks or explosives are not practical options, and improves our knowledge of near-surface seismic structure beyond Vs30.

*Park, S., & Ishii, M. (2018). Near-surface compressional and shear wave speeds constrained by body-wave polarization analysis. Geophysical Journal International, 213, 1559-1571, doi:10.1093/gji/ggy072.

Park, S., Tsai, V. C., & Ishii, M. (2019, 08). Near-Surface Structure Constrained Using Body-Wave Polarization. Poster Presentation at 2019 SCEC Annual Meeting.

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