Earth's surface layers are composed of a small number of moving plates. Their relative motion generates sudden fault motion from time to time. EQs can be classified into two major groups. There are four plates in the region of Japanese Islands.
EQs occur almost everywhere in the Japanese region.
Deep EQs in NE Japan arc reach even under Siberia, whereas those in Izu-Bonin arc are limited within a narrow zone. The seiamisity map around Japan.