CAUSES OF SHOWA BRIDGE COLLAPSE IN THE 1964 NIIGATA EARTHQUAKE BASED ON EYEWITNESS TESTIMONY

Testimony from eyewitnesses of the Showa Bridge collapse was collected with the objective of pinning down the cause of the collapse. On the basis of this testimony, a chronology of events was established. The bridge collapsed about 70 seconds from the beginning of the earthquake, i.e., long after the strong shock. The liquefaction-induced flow occurred after the collapse of the bridge. By studying these times of occurrence, as well as observed earthquake records, the cause of the Showa Bridge collapse was deduced. The possibility of inertia force in the superstructure and liquefaction-induced flow is low as the main cause of the collapse of the Showa Bridge. There is a high possibility that it was due to increased displacement of the ground in circumstances where pile deformation occurred more easily due to liquefaction.