A New Approach to Constrain Near-Surface Seismic Wave Speed Based Upon Body-Wave Polarization

Sunyoung Park

Harvard University

Date & Time
Building 3, Rambo Auditorium
Ruth Harris

Near-surface structure is important in understanding earthquake and volcano hazards. It is directly related to the level of ground shaking, and its temporal change can track magma migration. We introduce a novel technique to constrain near-surface seismic wave speed based upon the polarization measurements of teleseismic body-wave arrivals.

Polarization analysis of three-component seismic data has been widely used until about two decades ago for detection and identification of different types of seismic arrivals (e.g., compressional, shear, and surface waves). Today, we have good understanding of the expected polarization for any given seismic phase arrival based upon a reference seismic model such as IASP91, and deviations from the predicted polarization provide constraints on the near-surface wave speeds.

This approach is applied to the High-Sensitivity Seismograph Network (Hi-net) in Japan, where the results are benchmarked against the in-situ measurements of the P and S wave speeds that are available at most stations. The polarization-based estimates and the well measurements show good agreement, confirming the efficacy of the new method. This technique provides reliable, non-invasive, and inexpensive estimates of near-surface elastic properties at various locations, and can be expanded in the depth dimension by examining the frequency dependence and in the time dimension by analyzing earthquakes from different time periods.

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