Field observation of the ground vibration generated by debris flow using the transportable vibration sensor

Shiki YOSHINAGA, Takeshi SHIMIZU, Naoki FUJIMURA, Tadanori ISHIZUKA and Nagazumi TAKEZAWA

This study presents the results of the observation of the ground vibrations generated by debris flows using a transportable vibration sensor. The transportable vibration sensor used for the observation is similar to the one designed by the Earthquake Research Institute, University of Tokyo. The authors installed the transportable vibration sensor into the Arimura River in Sakurajima, Japan, and observed ground vibrations. The data which is collected from March 2013 to May 2014 illuminated the conditions of eight debris flow events. The data revealed the following:1) The fluctuation of the hydrograph and the vibration waveform obtained by the transportable vibration sensor are similar, 2) Maximal discharge is proportional to the two�]third power of the maximal acceleration, 3) The time periods of increasing and decreasing of the acceleration obtained the transportable and buried type vibration sensors are similar, and 4) During the downward peak discharge of debris flow, the vibration obtained by the sensor indicated predominant frequencies ranging from 20 to 30 Hz. Thus, the estimation of the occurrence and discharge of debris flow using a transportable vibration sensor is considered possible.