As with the Ansei Nankai Earthquake, the 1946 Nankai Earthquake was an interplate earthquake with a source region in an area along the Nankai Trough that included the coastal areas from a location off Shikoku to a location off the Kii Peninsula. Seismic intensity 5 in JMA scale was observed at Cape Shionomisaki, Owase City, Tokushima City, Kochi City, Tsu City, and Hikone City (Fig.7-9). The damage extended from the Chubu region to the Kyushu region. There were a total of 1,443 dead or missing, 3,842 injured, and 9,000 houses completely collapsed. Many other houses were either carried away by the tsunami or burned completely. The damage was particularly heavy at Nakamura in Kochi Prefecture, where there were 273 fatalities and more than 2,000 houses completely collapsed (Fig.8-9). The damage from the seismic ground motion extended as far as the shore of the Seto Inland Sea and the Izumo area. The damage caused by the tsunami was greater than that caused by the earthquake (Fig.8-10). It struck the coastal area from the Boso Peninsula to Kyushu, and reached its greatest height from 4 to 6 m on the coasts of Tokushima and Kochi Prefectures (Fig.8-11).
There were a total of 40 aftershocks of M 5 or larger accompanying this earthquake that lasted until April of the next year. Of these, five aftershocks were of M 6 or larger. The largest two of them were M 6.3 events occurred on December 21 and February 22 of the next year (Refer to Fig.7-12). The largest aftershock (M 7.0) occurred on April 18, 1948 during a series of activity.
Crustal deformation were observed from the 1946 Nankai Earthquake. Uplift of the land occurred at Cape Muroto, Cape Shionomisaki, and Cape Ashizuri, while there was land subsidence as great as 1 meter near Kochi City. Damage was sustained in the lowlands near Kochi City into which sea water rushed. The land also subsided by as much as 30 cm in the coastal areas of the Seto Inland Sea over several years after the earthquake. Damage was also caused here from flooding by seawater.