Japan is situated in the collision zone of at least four lithospheric plates: the Eurasian/Chinese Plate, the North American Plate, the Philippine Plate and the Pacific Plate. The continuous movements of these plates generate a lot of energy released from time to time in earthquakes and tsunamis of varying magnitude and effects ( Geologist Callan Bentley discusses in great detail the geological setting of the Japanese Islands ). Written records of strong earthquakes date back at least 1.600 years.
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A short History of Earthquakes in Japan