A Mechanism of Damage to the Toshibetsugawa Bridge due to the 1993 Kushiro-Oki Earthquake
Makoto NASU
The Toshibetsugawa bridge on the JR Nemuro line has been damaged
by the 1993 Kushiro-oki earthquake. The damaging mechanism has been
attributed to seismic reaction of the "upside-down" ground in which
soft clayey layers underlie sandy and/or gravelly layers. The end
piers before and after damaged girders happened to be just at the
site of a sudden thickness change in the soft clayey layer.
It is estimated that large differential ground displacements occurred
under the earthquake and this hypothesis is confirmed by seismic
response analyses and microtremor measurements.