Ambient Noise Based Ellipticity Observations in Southern California and Their Relation to Ground Water Changes and Seismic Velocity

Session: Advances in Seismic Interferometry: Theory, Computation and Applications [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The increased extraction of ground water resources and frequent drought conditions in the western United States has led to a greater need to monitor water content within the subsurface. Using remote sensing technologies, we can reduce cost and simplify implementation. This work focuses on the capabilities of seismic methods to monitor subsurface water content, specifically horizontal-to-vertical (H/V) amplitude ratios of Rayleigh waves. Short period (2-15 second) H/V measurements, obtained from ambient noise, show promise for monitoring the changing conditions within the shallow subsurface due to their sensitivity to near-sensor earth structure.

We selected Southern California because it is well-studied and heavily-instrumented, allowing for validation and benchmarking. The H/V ratios, measured from stations within the Caltech regional seismic network between 2006 and 2018, show strong seasonal changes. Some long-term variations may correspond to groundwater signals and possible variations in subsurface seismic velocity.

The long-term goal of our research is to infer the aquifer conditions using seismic measurements in addition to other geophysical signals such as gravity and ground deformation. We first need to establish a relationship between water content, density and elastic modulus. We will use simple aquifer models and assumptions such as storage coefficient and confinement state of the aquifer and possibly poro-elastic modeling to help establish these relationships. We will then perform seismic inversion by testing both a Markov Chain Monte-Carlo and a 3D full waveform inversion code to determine seismic velocity changes. Using independent observations, we will calibrate the relationship between velocity changes and water content.

Presenting Author: Jonas Kintner

Authors