The 2011 Tohoku-Pacific Ocean earthquake

 The 2011 Tohoku-Pacific Ocean earthquake

with a magnitude of Mw=9.0 occurred in the Pacific Ocean about 130 km off the northeast coast of Japan’s main island on March 11, 2011. Liquefaction occurred in a wide area of reclaimed land along Tokyo Bay, though the epicentral distance was very large, about 380 to 400 km. Much land has been reclaimed in the Tokyo Bay area since the seventeenth century. Liquefaction has been induced during past earthquakes, such as 1923 Kanto Earthquake and 1987 Chibaken-toho-oki Earthquake. However, the Tohoku-Pacific Ocean earthquake is the first on record to cause liquefaction in such a wide area and to severely damage houses, lifelines and roads. The effect of the very long duration of the main shock and of the aftershock, which hit 29 min later, on the occurrence of liquefaction and the associated damage to houses, is discussed. Remarkable phenomena, such as the buckling of sidewalks and damage to sewage facilities, due to a kind of sloshing around of the liquefied ground, are cited, and the effectiveness of soil improvement in the prevention of liquefaction is discussed.