(1)The Earthquake off the Coast of Tokachi (March 4, 1952, M 8.2)
This was an interplate earthquake whose source region was in the large area off the coast of Tokachi. There was intense ground motion in the coastal area between the Tokachi branch administrative office and the Hidaka branch administrative office in particular. Seismic intensity reached 6 in JMA scale in six towns, including Ikeda and Urahoro, and seismic intensity 5 in JMA scale in two cities and five towns, including Urakawa, Akkeshi, and Hiroo (Fig.3-6). The damage caused by seismic ground motion was pronounced in the low marshy areas in the downstream section of the Tokachi River (Fig.3-7). Extensive damage was caused by a tsunami from Konbumori in Kushiro to the eastern coast (Fig.3-8). The height of the tsunami was 6.5 m at Akkeshi in Akkeshi Town , and about 3 m in Kiritappu. The damage from the tsunami was intensified because many chunks of floe carried by the tsunami destroyed houses located close to the shore. The damage was greatest along the Pacific Ocean coast of Hokkaido, with a total of 33 dead and missing. Basic infrastructure was extensively damaged, including roads, railroads, and other transportation facilities, as well as power and telephone service. The aftershocks gradually decreased, with few perceptible aftershocks occurring by the end of March (Fig.3-9). The largest aftershock of M 6.8 occurred on March 10, causing small amounts of destruction in the area devastated by the main shock.