The 1944 Tonankai Earthquake had strong seismic ground motion that occurred in a wide area centering on the eastern Kii Peninsula. Seismic intensity 6 in JMA scale was observed in Tsu in Mie Prefecture and other locations (Fig.7-7). A tsunami also struck the Pacific Ocean coast from the Izu Peninsula (Izu Hanto) to the Kii Peninsula. The tsunami height was from 6 m to 9 m at the Kumano Sea coast, and reached a maximum of 9 m at Owase (Fig.7-8). The damage caused by the tsunami was centered on Mie and Wakayama Prefectures. Including the damage from seismic ground motion, the damage in the Kinki region was particularly severe in Mie Prefecture. The surrounding areas of Osaka and Shiga, Nara, Wakayama, and Hyogo Prefectures also suffered damage. The overall damage from the Chubu region to the Shikoku region was reported as 1,251 fatalities, 2,971 injured, and 16,455 houses totally collapsed. The numbers vary greatly depending on the report, however. Damage also occurred in areas farther from the source region. For example, there was significant damage in Nagoya in areas with soft ground, such as areas with alluvial ground or reclaimed land. There were four aftershocks of M 6 or larger in the five-day period until December 12. The largest was M 6.4 on the 12th (Fig.6-14), but no aftershocks larger than M 6 were observed thereafter. Observations of the crustal deformation showed that the eastern coast of the Kii Peninsula subsided from 30 cm - 40 cm with the earthquake. Also, a tsunami crossed the Pacific Ocean, and was observed in Hawaii and California.

The 1946 Nankai Earthquake had strong seismic ground motion that occurred in a wide area centering on the southern Kii Peninsula (Fig.7-9). A tsunami also struck the Pacific Ocean coast from Shizuoka Prefecture to Kyushu. The tsunami height reached from 4 m to 6 m along the coast of Mie and Wakayama Prefectures (Fig.7-10). In the Kinki region, damage was particularly severe in Wakayama Prefecture, and damage also occurred in the surrounding prefectures (Fig.7-11). The total damage from the Chubu region to the Kyushu region was reported to be 1,443 dead and missing, 3,842 injured, and 11,591 houses completely collapsed, but the figures differ depending on the report. Five aftershocks of M 6 or larger occurred over the next two months, until February of the following year. Fig.7-12 shows the trends in the aftershock frequency for slightly more than one month after the main shock. The largest aftershock (M 7.0) occurred on April 18, 1948, 16 months after the main shock. Observations of crustal deformation showed an uplifting at the Kii Peninsula and Cape Muroto in Shikoku. The extent of the uplift was about 50 cm near Cape Shionomisaki.

These two earthquakes during the Showa era are the most recent of the great earthquakes that have occurred along the Nankai Trough. They occurred during the wartime confusion and in the immediate postwar period, thus observation data is lacking in both quality and quantity. Observations of the leveling, however, detail the crustal deformation before and after the earthquake, and are valuable data for earthquake research. It is also believed that these earthquakes were somewhat smaller than those that occurred in the past, so knowledge of other earthquakes larger than the Showa earthquakes, such as the Ansei Earthquake, is necessary to evaluate earthquakes in this area. (Refer to 6-2 (1) for information on the Ansei Tokai Earthquake, and 8-2 (1) for information on the Ansei Nankai Earthquake.)