(1)The Kanto Earthquake (September 1, 1923, M 7.9)
The Kanto earthquake, also known as the Great Kanto Earthquake, was an interplate earthquake. Its focal region extended over a wide area along the Sagami Trough, including Sagami Bay, all parts of Kanagawa Prefecture, and the southern part of the Boso Peninsula. Other idea is that the focal region extended to Cape Manazuru and the Hatsushima Island off the east coast of the Izu Peninsula, due to an earthquake-caused uplift in the land in these areas. Strong ground motion occurred over a wide area centered on the southern Kanto region, and seismic intensity 6 was observed throughout this area (Fig.5-10). Seismic intensity scale, at that time, extended only to 6, but judging from the collapse of houses and other factors, it is estimated that the ground motion corresponded to the contemporary seismic intensity 7 in JMA scale in the area along the coast of Sagami Bay and the southern tip of the Boso Peninsula. In addition to the collapsed houses, avalanche, and landslides throughout the region, a tsunami struck the coastal area. The tsunami height reached 12 m at Atami in Shizuoka (Sizuoka) Prefecture and 9.3 m at Aihama on the Boso Peninsula. This tsunami struck Atami, located close to the focal region, about 5 minutes after the earthquake occurred. The tsunami was also observed along the Pacific Ocean coast from the Tohoku to the Kyushu regions. The fires that broke out immediately after the earthquake caused extensive damage. There were a total of about 142,000 dead and missing in the area of Tokyo Metropolitan District, Kanagawa Prefecture, and others. The damage caused by this earthquake is collectively referred to as the "Great Kanto Earthquake Disaster" (Table5-1, Fig.5-11, Fig.5-12 and Fig.5-13). Uplift (upheaval of the earth) occurred with this earthquake from near Odawara to the tip of the Boso Peninsula. This upheaval reached about 2 m at the highest point, and movement by about 2 or 3 m to the southeast was also observed. The earth's surface subsided by few tens of centimeters in the interior from southwest Tokyo to northern Kanagawa Prefecture (Fig.5-14).
There were many aftershocks over a wide area in southern Kanto that continued from immediately after the main shock until the next year (Fig.5-15). The largest of these (M 7.3) occurred the following day, on September 2, off Katsuura (Katuura) on the Boso Peninsula. It caused damage in Katsuura and other locations. Another large aftershock (M 7.3) occurred four months after the main shock on January 15, 1924 in the Tanzawa mountainous area. Known as the Tanzawa Earthquake, it caused extensive damage in southern Kanagawa Prefecture.
The Kanto earthquake spurred the creation of the Earthquake Research Institute in 1925 at the University of Tokyo (at that time Tokyo Imperial University) as a research institution to replace the existing Imperial Earthquake Investigation Committee.