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Generating Green's Functions for Use in Seismic Monitoring of Debris Flows Using the Ambient Seismic Field

Description: 

Efforts to utilize seismic monitoring networks to study mass flows that generate seismoacoustic waves, such as debris flows, face challenges such as poorly known near-surface velocity structures, complicating efforts to separate path and site effects from the waves produced by mass flows. Ambient noise cross-correlation techniques have been successfully used to determine empirical surface-wave Green’s functions and resolve velocity structures for remote regions that experience earthquakes. In this study, we use the same approach to retrieve Green’s functions for the purpose of seismic monitoring of debris flows. We installed three-component nodal seismometers for month-long deployments in the summers of 2020-2022 along part of the Tahoma Creek drainage on the southwest side of Mt. Rainier, USA. We used ambient noise cross-correlation techniques to create impulse response functions between the nodal seismometers. While no debris flows occurred during 2020-2022 in the drainage, our impulse response functions may help interpret seismic waves from future debris flows. Additionally, we generated impulse response functions with a force hammer for a roughly 90 m section of the drainage to compare an alternative technique for creating impulse response functions. Our results show that the force hammer generated seismic waves with relatively high-frequency content compared to the ambient noise cross-correlations, with energy concentrated between 20-60 Hz and 5-50 Hz, respectively. We filtered the impulse response functions from both techniques between 25-50 Hz and found that the surface waves have similar arrival times and structure. However, the amplitudes for the waveforms were significantly different. As relative amplitudes for impulse response functions are not preserved during the ambient noise cross-correlation, we are exploring techniques such as modeling surface wave amplitudes and mathematically computing Green’s functions to constrain the amplitudes.

Session: Detecting, Locating, Characterizing and Monitoring Non-earthquake Seismoacoustic Sources

Type: Oral

Date: 4/19/2023

Presentation Time: 08:15 AM (local time)

Presenting Author: Avery E. Conner

Student Presenter: Yes

Invited Presentation: 

Authors