Effects of Shallow-Velocity Reductions on 3D Propagation of Seismic Waves

Alan Juarez, & Yehuda Ben-Zion

Published August 10, 2020, SCEC Contribution #10344, 2020 SCEC Annual Meeting Poster #227 (PDF)

We perform 3D simulations of seismic wavefields to clarify the effects of strong reductions of shallow velocities on long-period seismic waves. The simulations use a reference Community Velocity Model of southern California and a modified version with strong velocity reductions in the top 500 m of the Los Angeles basin. Differences between wavefields generated by 10 earthquakes in the reference and perturbed models are analyzed. Velocity changes are estimated by measuring relative time shifts between reference and perturbed seismograms using wavelet cross-correlation spectra. The results indicate that strong localized temporal velocity drops near the surface, such as those observed during strong ground motions, may generate regional perturbations of wavefields at periods up to 20 s. These perturbations may be misinterpreted as generated by temporal changes at seismogenic depths. The results also have important implications for waveform tomography studies.

Key Words
3D simulations, velocity reductions, CVM S4.26

Citation
Juarez, A., & Ben-Zion, Y. (2020, 08). Effects of Shallow-Velocity Reductions on 3D Propagation of Seismic Waves . Poster Presentation at 2020 SCEC Annual Meeting.

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