An earthquake detection system configured with a combination configuration of a free field sensor, a structural sensor, a deep well seismograph and a remote signal source applied to an earthquake detection system, comprising:
- a main sensor disposed on a free field as a free field sensor;
- a first backup sensor disposed on a structure;
- a second backup sensor disposed below a ground surface at a depth of at least 20 meters;
- and
- a third backup sensor disposed at a remote end relative to the main sensor, and outputting a remote signal through a network, wherein sensing signals output by the main sensor, the first backup sensor and the second backup sensor, and the remote signal all arrive at the same receiving device.