(2)The 1993 Earthquake off the Coast of Kushiro (January 15, 1993, M 7.8)
This earthquake occurred at a depth of about 100 km off Kushiro, and resulted from the nearly lateral rupture (fault movement) of the subducting Pacific Plate. It was a severe earthquake despite its occurrence at a rather deep location. Therefore, a seismic intensity of 6 (in JMA scale) was observed in Kushiro, and 5 in Urakawa, Obihiro, and Hachinohe (Hatinohe) (Fig.3-10). The earthquake caused great destruction, with two fatalities and 966 wounded, mostly in Kushiro. The damage caused by this earthquake was characterized by ground liquefaction in harbors, low marshy areas, and other reclaimed land, as well as ground subsidence that accompanied liquefaction. Damage also occurred due to slope failure surfaces in embarkment areas, such as development of housing areas land, roads, and railroads (Fig.3-11). No tsunami accompanied this earthquake, because it occurred in a rather deep location. The frequency of aftershocks gradually decreased (Fig.3-12). The largest aftershock (M 4.9) occurred on February 4th of that year, but they were generally much smaller than the main shock. This is a common tendency observed for earthquakes occurring in deep locations.
Results of the leveling survey along the Pacific coast after the earthquake show that the ground had subsided about 6 cm at a location close to the focal region.