1964 June 16 04:01 UTC
Aerial view of leaning apartment houses in Niigata produced by soil liquefaction and the behavior of poor foundations. Most of the damage was caused by cracking and unequal settlement of the ground such as is shown here. About 1/3 of the city subsided by as much as 2 meters as a result of sand compaction.
Photo Credit: National Geophysical Data Center
The Showa bridge had only recently been opened to traffic. The bridge had seven spans across the river, each supported by piers consisting of structural steel girders carrying a reinforced concrete deck. Two of the piers collapsed. The corresponding spans of the bridge collapsed and dropped into the river. The successive spans toward the west bank also dropped while one end of each span remained connected at the top of successive piers. The construction was such that one end of the girders was locked and the other end was free to slide longitudinally off the pier after about 30 cm of movement.
Photo credit: National Geophysical Data Center
The earthquake is called the Niigata earthquake because of the extensive damage caused by the shock in this town in spite of it being situated about 50 km south of the epicenter; it was one of the two great destructive earthquakes of 1964. Although the number of victims was fortunately small (36 dead or missing, 385 injured), the material damage was great: 3,534 houses destroyed, 11,000 houses damaged. Our Japanese colleagues immediately investigated the phenomenon in detail (Aki, 1966; Falconer, 1964; IISEE earthquake report, 1965; Japan Nat. Comm. on Earthquake Engineering, 1964; Kawasumi, 1965). The earthquake occurred at a depth of 57 km below the Sea of Japan near the island of Awa-shima, in the deepest of the old formations in the tectonic zone called "internal arc of Honshu." A tsunami generated by the earthquake ravaged the west coast of Honshu, and more particularly the town of Niigata, where the wave reached a height of 1.8 meters; the tsunami was more than 4 meters high at Iwafune on the coast near the epicenter, and 3 meters on the coasts of Sado Island. A detailed study of the effects of the tsunami has been published (Aida et al., 1964; Hatori, 1964).
Investigation of damage in the town of Niigata showed the adverse influence of a poor subsoil. Generally speaking, damage was due far more to perturbation of the subsoil than to direct effect of ground vibration on the buildings. The lower part of the town was built on a thick layer of sand - of recent sedimentation - and the tremor affected the dynamic properties of the sand; "creep" occurred, and modern multistory buildings were suddenly left without support; they tilted over, all in one piece and one block of flats fell over completely, torn out of the ground, complete with its foundations. Several bridges on the River Shinano were destroyed by splaying of the piers; alterations to the subsoil (subsidence, liquefaction of sand) caused spectacular deformations of railway lines.
Extensive topographical changes were observed: the east coast of Awa-shima rose by about 150 cm while the west coast of Honshu, facing the epicenter zone, subsided by 45 cm at Hayakawa. Oceanographic observations revealed the formation of a new fault in the sea bottom between Awa-shima and the coast of Honshu (IISEE earthquake report, 1985; Murai, 1965; Yamaguti, 1965).Abridged from Rothé, J.P., 1969, The seismicity of the earth, 1953-1965: Paris, United Nations Educational, Scientific and Cultural Organization, 336 p.