(5)The Niigata Earthquake (June 16, 1964, M 7.5)
Niigata Earthquake occurred in the eastern margin of the Sea of Japan, and its focal region was off the north coast of Niigata Prefecture. Seismic intensity 5 in JMA scale was observed for the earthquake in Niigata City, Aikawa in Sadogashima Island, Sakata, and Sendai (Fig.6-25). The damage spread over a total of nine prefectures, including Niigata and Yamagata Prefectures, and claimed 26 lives. A total of 1,960 houses totally collapsed, and another 290 were completely destroyed by fire. In Niigata Prefecture, extensive damage occurred in Niigata City (Fig.6-27). Fire broke out in nine locations, and one fire ignited an oil tank. There was extensive damage due to liquefaction in sand deposit areas. In one instance, a four-story steel-reinforced apartment building toppled over (Fig.6-28). Substantial damage in a modern city as a result of liquefaction was characteristic of the damage caused by this earthquake. A tsunami hit the shoreline of the Japan Sea about 15 minutes after the main shock (Fig.6-26). It was from 3 m to 5 m high at its highest point near the source region. It was also roughly 3 m high near Ryotsu Bay in Sadogashima Island (Sado-ga-Sima) and 1 m to 2 m high on the coast near the Noto Peninsula. In distant Shimane Prefecture, rice paddies were submerged on Oki Islands (Oki Syoto).
This earthquake caused Awashima Island to rise by 1 meter as a whole. The eastern part of the island seemed to incline upward, however, rising 1.3 m, while the western side rose 0.9 m. On land, at least, there was no offset visible from faulting.
As shown in Fig.6-29, the number of perceptible and imperceptible aftershocks decayed. The two largest aftershocks (M 6.1) occurred about 16 minutes and 3 hours after the main shock.