Seismic sensor and threshold adjusting method

A seismic sensor operated in a power-saving mode and a measuring mode in which power consumption is larger than that of the power-saving mode, the seismic sensor comprising:

• a processor configured with a program to perform operations comprising:
• operation as a measuring part configured to measure an acceleration with low-speed sampling in the power-saving mode and with high-speed sampling in the power-saving mode and in the measuring mode in response to the acceleration being larger than a reference threshold;
• operation as an index calculator configured to transition from the power-saving mode to the measuring mode to calculate an index value indicating a size of an earthquake in response to the acceleration measured with the measuring part in the measuring mode continuously exceeding a first threshold in a plurality of samples measured with the high-speed sampling in a predetermined period;
• and
• operation as a threshold adjuster configured to change the first threshold so as to increase the first threshold relative to a predetermined reference value in response to a predetermined condition in which the acceleration measured with the measuring part in the measuring mode is determined to be caused by other than the earthquake unless the acceleration measured continuously exceeds the first threshold in the plurality of samples measured in the predetermined period.