Effect of Long Duration of the Main Shock and a Big Aftershock on Liquefaction-Induced Damage During the 2011 Great East Japan Earthquake

Abstract

The duration of shaking during the 2011 Great East Japan Earthquake was extremely long, and the main shock was soon followed by big aftershocks because the earthquake was a “megathrust earthquake” with extremely large magnitude; Mw = 9.0. The unique ground shaking caused the following unusual events: (1) serious liquefaction occurred in a wide area of reclaimed land along Tokyo Bay though seismic intensities in the liquefied zones were not high; (2) some inhabitants testified that boiling did not occur during the main shock but occurred during a big aftershock. The occurrence of liquefaction, the settlement and the inclination of houses must have been affected by the aftershock; (3) shaking continued for a long time after the occurrence of liquefaction. Due to the shaking of the liquefied ground, large horizontal displacement, which is a kind of sloshing of liquefied ground, was induced and caused roads to thrust; (4) the large horizontal displacement of liquefied ground had to have caused the severance of pipe joints and the shear failure of manholes, allowing an influx of muddy water into the pipes and manholes.