Frequency Range of Ground Vibrations Produced by Debris Flow Caused by an Artificial Dam Breach

Abstract:

Seismometer and geophone have been often used to detect the ground vibrations generated by debris flows. Based on the monitoring data obtained using geophone it has been shown that the frequency of ground vibrations produced by debris flow ranges between 10 and 100 Hz (Huang et al., 2007).

In this study, we used both geophone and Raspberry Shake, a seismic sensor, to reveal the characteristics of ground vibrations generated by an artificial debris flow induced by the dam breach at Landao Creek, Huisun Forest, Nantou County, Taiwan. Both sensors were deployed along the riverbank to measure the velocity of the ground vibrations. The main differences of these two sensors are in the measuring frequency range. Geophone has the measuring frequency range from 10 to 500 Hz, for the Raspberry Shake the range is from 0.5 to 50 Hz. Because ground vibration signals of higher frequencies decay spatially more quickly than those of lower frequencies. As a result, the debris flows were first detected using geophone, when they are very close to the sensor.

The spectrogram analysis of our field experimental data shows that Raspberry Shake outperformed geophone with its low-frequency signals detection capability. Raspberry Shake observed clearly low-frequency signals (< 5 Hz) after dam-breach. Because low-frequency signals decay spatially slower than high-frequency signals, the low-frequency detection capability of the Raspberry Shake will allow us to identify the debris flow earlier then using the geophone. Furthermore, a local landslide signal has also been observed during the experiment period, demonstrating that Raspberry Shake is a promising ground vibration sensor for detecting slope hazards, such as debris flow, landslide, and rockfall.