Alarm system of Debris flows by monitoring Ground tremor

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Debris flows were observed by using a new system of ground tremor sensor in the Nojiri River of Mt. Sakurajima, Volcano, Japan. In general, going away from valley, ground tremor by debris flow will become small and this phenomenon seems to be different from volcanic activity. To examine the phenomenon of debris flow, we carried out the outdoor experiments in the campus, and replicated the surging out of debris in an active volcano. The spectrum of ground tremor observed in the outdoor experiments is very similar to the spectrum observed in debris flows in the active volcano. We confirmed that the magnitude of discharge has a tendency to be in proportion to the size of ground tremor.We could find that observed frequency of ground tremor distinguishes between debris flow from clear water flow. The value of frequency is from 50 Hz to 100 Hz for debris flow and less than 50 Hz for clear flow. Out trigger system of detecting the volcanic debris flow is available to detect the occurrence of land-slide, snow avalanche and so on.