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When Water, Temperature, and Earthquakes impact shallow seismic velocities: Decadal records in California and Mexico City

Marine A. Denolle, Tim Clements, & Laura Lermert

Published August 16, 2021, SCEC Contribution #11604, 2021 SCEC Annual Meeting Poster #239

The Earth’s near-surface is the buffer zone between the atmosphere and the solid Earth. It is greatly affected by atmospheric conditions (e.g., temperature, pressure, precipitation), shallow hydrology, and the transient effects of seismic activity. We use the relatively high-frequency content of ambient seismic field single-station cross-correlations to sample the upper ~ 350 m of the near-surface. In this presentation, we present 20+ year records of seismic velocity changes in the state of California and in the Mexico City sedimentary basin. We then analyze each day-stacked correlations to extract changes in the arrival time of phases in the coda and generate time series of perturbation in seismic velocity. In California, we find a highly diverse behavior across the state. We interpret the rainfall impact by fitting several hydrological models and find that sites may experience anywhere between fully drained and undrained poroelastic responses. Sites close to lakes exhibit a more substantial influence from lake levels, including the long-term drying of the Salton Sea. We also find heterogeneity in the contribution between hydrological strains and thermo-elastic strains. Removing these effects allow us to characterize tectonic effects better, and we find that some sites are still recovering from the 1999 Hector Mine Earthquake. In Mexico City, we find a linear increase in seismic velocities that corresponds well to the linear subsidence. The measurements are likely sensitive to the depth of the main groundwater aquifer that supplies Mexico City. Our data processing involves cloud-based workflows, unsupervised learning, and efficient scripting for memory and I/O management.

Key Words
ambient noise, monitoring, site effects

Denolle, M. A., Clements, T., & Lermert, L. (2021, 08). When Water, Temperature, and Earthquakes impact shallow seismic velocities: Decadal records in California and Mexico City . Poster Presentation at 2021 SCEC Annual Meeting.

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