Abstract
A simplified method for evaluating liquefaction potential under ocean trench type long period earthquakes. Since there is no experience on damage or liquefaction under this type of earthquake, effective stress analyses are made on more than 200 sites that are used in the past investigation on liquefaction damage. Accuracy or effectiveness of existing simplified methods is investigated, and is found that they are applicable to near field earthquake, but they result in dangerous evaluation under ocean trench type earthquakes such as artificial earthquake for coming Tonankai earthquake and recorded accelerogram during the Tokachi-oki earthquake of 2003. The reason is found to be effective number of loading cycles; it is about 10 times larger than that considered in the existing simplified procedure. Then a correction factor for liquefaction strength is proposed in order to evaluate liquefaction potential under this type of earthquakes. The factor is a half of the factor in the existing method; liquefaction strength is to be half of the conventional value when comparing maximum shear stress to evaluate FL value. This method works so that dangerous ratio (ratio of number of layers where onset of liquefaction is identified under effective stress analysis but is not identified under existing simplified procedure to the total number of layers) becomes small to be the same order under near field earthquake.
