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Quantifying Seismic Properties of a River Channel at Mount Rainier for Use in Debris-Flow Monitoring and Analysis

Description: 

One of several challenges in interpreting properties of surface processes, such as debris flows, from seismic waves is developing accurate Green’s functions for the environments through which the waves propagate. The waves generated from these processes are primarily recorded at local sensors, and the heterogeneous quality of the surface environment greatly affects the waves over relatively short distances. In particular, the high-frequency energy that is primarily generated by many surface processes is highly attenuated by near surface materials. Our research focuses on understanding some common seismic properties of channel material in the Tahoma Creek drainage at Mount Rainier, USA, to accurately analyze the seismic waves from seasonal debris flows in the drainage, the most recent of which occurred on 15 August 2023. To investigate the seismic properties of the channel material, we deployed 9 nodal seismometers on 9 August 2022 in a ~70 m linear array perpendicular to Tahoma Creek. We used a hammer to create seismic impulses adjacent to the active channel to calculate surface wave velocities and Q, the quality factor for attenuation, for 10 Hz frequency bands between 20 Hz and 55 Hz. The 20 Hz to 55 Hz band encompasses both the majority of energy generated by our hammer blows and contained in our empirical Green’s functions for the channel. The 2023 debris flow waveforms that were recorded on additional, nearby temporary stations also primarily contained energy between ~20 Hz and 40 Hz. As the channel is mostly composed of loose gravel, sand, and silt, we find that the surface wave velocities and values for Q are very low and typically decrease with increasing frequency. The surface wave velocities are less than 200 m/s and the values for Q are less than 40 for all frequency bands. We will use the results to correct the amplitudes of the empirical Green’s functions that we created for the region and extend the Green’s functions to the active channel. These results will be crucial for interpreting the seismic signals from debris flows at near-field stations and for modeling debris flows in the drainage.

Session: Detecting, Characterizing and Monitoring Mass Movements [Poster Session]

Type: Poster

Date: 5/2/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Avery

Student Presenter: Yes

Invited Presentation: 

Authors