Distribution of Hypocenters Around the Japanese Islands

Please look at the ceiling. You are now looking up at Japan about 1000 km below ground level. You can see the location of earthquakes with magnitudes of six or more over a 50-year period between 1926 and 1976. There are two types of earthquakes. One occurs near areas where a plate subducts below another plate. This type of earthquake occurs mostly near the shallow part of the Pacific Ocean in the Tohoku region, and they become deeper as they move toward the western side of Japan. The other type has a shallow source and it is caused by the movement of active faults on the ground. The red lamps show the earthquakes that caused serious damage. The hypocenters of these earthquakes were relatively shallow.