Damage to structures in Chiba Prefecture during the 2011 Tohoku-Pacific Ocean Earthquake

Abstract

The 2011 Tohoku-Pacific Ocean earthquake caused severe liquefaction in three lowlands in Chiba Prefecture. In artificially reclaimed lands along Tokyo Bay, liquefaction occurred in a very wide area. Total liquefied area was about 39 km². More than 10,000 timber houses, many lifelines and roads were seriously damaged. Especially the damage in Urayasu City was very severe. Though recorded maximum surface accelerations were not high as about 160 to 230 cm/s², severe liquefaction occurred. Main reason must be due to very long duration of shaking and a big aftershock which occurred 29 minutes after the main shock. Moreover much eruption of sands and large ground subsidence occurred in the liquefied zones because liquefied soils were very fine sand or silt. In the lowland along Tone River, liquefaction occurred at many old river channels. Especially the damage in Katori City was severe. About 2,600 timber houses were damaged. In Kujyukuri lowland plain along Pacific Ocean, liquefaction occurred at the replaced sites where the grounds had been excavated to take iron sands.