Seismic Performance of Levees in the Kanto Plains North of Tokyo during the 2011 Tohoku Earthquake

摘要

In the Kanto plains north of Tokyo, Japan, the Magnitude 9.0 (M_w) Tohoku earthquake caused widespread liquefaction, lateral spreading, seismically induced settlement, slope instabilities and, importantly, resulted in 920 river levee failures. Along the Tone, Nakagawa, Fuji Rivers and its tributaries, failures affected more than 40 miles (65 km) of levees. Since the damaged levees were located at an epicentral distance of over 200 miles (320 km), failures of such magnitude surprised many engineers. In April 2011, the authors conducted post-earthquake engineering field reconnaissance as part of an ASCE-sponsored investigation of the Tohoku earthquake. A major portion of the observed levee damage was associated with liquefaction and associated lateral spreading. Importantly, our investigation revealed that much of the liquefaction was associated with anthropogenic (man-made) changes and in particular with fluvial transportation improvements implemented between the 16th and 20th centuries. These findings have important implications for river levees in seismically active areas, such as the Sacramento and American Rivers in California and the Mississipi River near the New Madrid seismic zone.