Daily and seasonal variations of shallow seismic velocities in southern California from analysis of H/V ratios and autocorrelations of seismic waveforms

Guoliang Li, & Yehuda Ben-Zion

Submitted September 11, 2022, SCEC Contribution #11953, 2022 SCEC Annual Meeting Poster #006

Various studies observed changes of seismic velocities related to earthquakes, volcanic processes and other loadings, focusing primarily on short term changes. Establishing a baseline of ongoing secular velocity changes from atmospheric temperature and precipitation can improve the accuracy of detecting and interpreting short term changes, and advance the understanding of nonlinear behavior of subsurface materials. Toward these goals, we develop and apply a deconvolved autocorrelation (DA) method to estimate daily and seasonal changes of seismic velocities in southern California. The DA method combines advantages of traditional autocorrelation and Horizontal-to-Vertical Spectral Ratio, and is used to analyze over 10 yr of data recorded by 50 stations. The analysis allows us to obtain regional maps of subsurface daily and seasonal velocity variations in southern California. The results indicate widespread daily and seasonal changes, which can be up to 10% and 4%, respectively, and likely reflect a combination of thermal and humidity/fluids effects in the top tens of meters. The regional shallow velocity changes have important implications for nonlinear site effects, and provide a broad context for studying velocity changes generated by various sources. The developed DA method can improve the accuracy and robustness of estimated changes of seismic velocities.

Key Words
subsurface velocity variations

Citation
Li, G., & Ben-Zion, Y. (2022, 09). Daily and seasonal variations of shallow seismic velocities in southern California from analysis of H/V ratios and autocorrelations of seismic waveforms. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology