Monitoring seasonal shear wave velocity changes at Garner Valley in Southern California using earthquake data and a cross-hole experiment

Lei Qin, Jamison H. Steidl, Hongrui Qiu, Nori Nakata, & Yehuda Ben-Zion

Published September 11, 2022, SCEC Contribution #12519, 2022 SCEC Annual Meeting Poster #060

We monitor seasonal variations of near-surface shear-wave velocity (VS) using impulse response functions of earthquake (2005-2018) and cross-hole experiment (2015-2018) data from borehole instruments at Garner valley, CA. The shear-wave travel time variation (dt/t) ranges from -10% to 15% in the top 6 m and from -4% to 6% at 2-5 m in depth. The analysis suggests dt/t varies between 0% and 5% below the water table and between -15% and 15% above it. This implies that VS changes more significantly at low saturation level when a small change of moisture affects the cohesion between soil particles. The VS variations also correlate with temperature changes, which affect the moisture content and produce thermoelastic strain. The derived significant variations demonstrate the complicated response of near-surface properties to fluid content and surface temperature loadings. The changes of shallow seismic properties may affect interpretation of processes in deeper crustal sections.

Key Words
near-surface moisture; seasonal variation

Citation
Qin, L., Steidl, J. H., Qiu, H., Nakata, N., & Ben-Zion, Y. (2022, 09). Monitoring seasonal shear wave velocity changes at Garner Valley in Southern California using earthquake data and a cross-hole experiment. Poster Presentation at 2022 SCEC Annual Meeting.

Related Projects & Working Groups
Seismology