To grasp vibration due to falling rocks, pebbles or the like as large as possible in a region to be monitored, to eliminate the need for supplying electric power to the side of a site and to easily and precisely detect the kind of a vibration due to an external cause so as to be reported.
A decision computing and processing part 10 (a computer; a CPU) which is provided is provided with a detection-data extraction and processing part 6 in which, whenever data hi obtained by sampling vibration signal as a change in the interference of an optical fiber cable 2 in every definite time is collected in a memory 5, the maximum value of the data hi is read out and in which the data hi is extracted as detection data ki when the maximum value is at a previously stored reference threshold value Vo or more. The computing and processing part 10 is provided with a decision processing part 7 in which the level (voltage) of the detection data ki extracted by the extraction and processing part 6 is compared with various thresholds Vi (the threshold Vi of the pebbles, the threshold V2 of a stone, the threshold V3 of a flood and the like) in a memory 8 (ROM) used to store them in advance and in which the kind of the vibration (a collapse) due to the external cause is judged, so as to be reported.
NIIMI SHINICHI
TAKASHIMA TORU
UNAMI YOSHIHARU
TSUKEN KK