Kuan-Fu Feng , Marine Denolle, Fan-Chi Lin, Tonie van Dam

Ongoing climate change leads to an increase in prolonged drought and severe weather events in the United States, particularly pronounced in semi-arid regions such as the western United States. It could have lasting social and environmental impacts. Continuous monitoring of near-surface hydrological processes and groundwater resources will provide helpful information for effective water resource management. The seismological signature of groundwater fluctuations is clear in the temporal variations in seismic velocities, dv/v. To this end, developing a proxy for groundwater level using dv/v is an opportunity but requires further understanding of the relation between dv/v and subsurface hydrology. In this study, we apply single-station cross-component correlation analysis to 28 broadband seismic stations in Utah between January 2006 and March 2023 and analyze the dv/v in the 2-4 Hz frequency band. To explain dv/v, we linearly superimpose thermoelastic stresses, soil moisture estimated from remote sensing data products, and a long-term deep water table pore pressure. We find that the relative contributions of each depend on the location, but adding a long-term water table decline, which is not systematically observed in soil moisture, better fits our data. We conclude that soil moisture alone does not explain the variations in total water storage when subsurface moisture is decoupled from the deep water table. We also conclude that dv/v can be used as a proxy for water storage.