PROBLEM TO BE SOLVED: To generate an alarm at several seconds before swing becomes large when an earthquake occurs for securing safety and at the same time securely performing an action for disaster-prevention treatment by allowing a spring incorporated in a limit switch to absorbed energy being accumulated in an inertia object and the spring by the earthquake and generating a signal. ;SOLUTION: A cantilever-type spring 8 where one end is fixed and an inertia object 7 is mounted at the other end is arranged on a trestle 6, the mass of the inertial object 7 and the spring constant of the spring 8 are matched to the longitudinal natural frequency of the installation ground for installation for swinging in a vertical direction. The vibration of an earthquake is sensed by the inertia object 7, and an electrical circuit is operated and a voice is generated from a speaker 11 of a voice-generating device 10 when a limit switch 9 being arranged adjacent to the inertia object 7 is pressed. Then, when the earthquake occurs, a fast longitudinal wave arrives a ground observation point and a slow traverse wave with a large amplitude arrives at the observation point. The longitudinal wave at the stage of a slight earthquake that arrives first due to the earthquake is sensed by the inertial object 7 for vibrating, and a voice alarm is generated by the voice-generating device 10.;COPYRIGHT: (C)2000,JPO
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