Seismic sensor

A seismic sensor that switches an operation mode related to earthquake detection or measurement of an earthquake acceleration according to a measured acceleration, the seismic sensor comprising:

• a simple earthquake detection mode in which measured acceleration data is not saved, the simple earthquake detection mode being continued in a case in which the measured acceleration is equal to or less than a predetermined first threshold value;
• an earthquake detection mode in which the measured acceleration data is saved, the earthquake detection mode being continued in a case in which the acceleration measured in the simple earthquake detection mode is greater than the first threshold value and equal to or less than a second threshold value that is greater than the first threshold value;
• and
• an earthquake measurement mode in which the acceleration data and a spectrum intensity (SI) value are measured and saved, the earthquake measurement mode being continued in a case in which the acceleration measured in the earthquake detection mode is greater than the second threshold value.