Seismic and Infrasonic Signals from Debris Flows

Debris flows are known to generate both seismic waves and infrasound, but the mechanisms linking the two are not fully understood. A study of a debris-flow event in the Gadria catchment, BZ, Italy, provides new insights into their interaction.

Key Findings:

1. Seismo-Acoustic Link:

   • Despite different generation processes, the seismic and infrasonic signals show similar spectral content and strong cross-correlation.

   • A significant portion of the recorded infrasound is produced by seismic waves transmitting into the air near the sensor.

2. Flow Threshold Effects:

   • Infrasound is effectively generated only when the flow discharge exceeds a certain threshold, especially at topographic steps.

3. Velocity Estimation:

   • The debris-flow velocity can be accurately estimated using infrasound data alone, matching hydraulically derived velocities.

4. Seismic Radiation Dependence:

   • Seismic amplitude varies with solid-particle transport rate, flow depth, and basal forces, indicating that seismic radiation is sensitive to debris-flow dynamics.

Conclusion:
The study provides new constraints on the source mechanisms of both infrasound and seismic signals in debris flows and demonstrates the potential of infrasound monitoring for estimating flow characteristics.