Case Studies on Preshaking and Reliquefaction Potential for Different Earthquakes in Japan

The paper examines the effect of liquefaction potential of the site due to normal earthquake and sequential earthquakes occurred in Japan. Two earthquakes have been considered (a) 2016 Kumamoto sequential earthquakes with mainshock (M_w = 7.3) and a couple of foreshock in the previous days (M_w = 6.2 and M_w = 6.5); and (b) 2005 Fukuoka-ken Seiho-oki earthquake (M_w = 7.0), the earthquake has only mainshock. With the help of available literatures, damages associated with the liquefaction was examined with reference to effect of preshaking, liquefaction history and earthquake pattern. It is evident that, liquefaction effects of the 2005 earthquake are larger than those associated with Kumamoto sequential earthquakes. It is inferred that liquefaction resistance and reliquefaction potential of the site was highly influenced by the seismic preshaking, liquefaction history and earthquake pattern. This is the most probable explanation for the higher liquefaction resistance exhibited by the Kumamoto earthquake. Preshaking effect is highly associated with earlier earthquake history or significant foreshocks as in the 2016 Kumamoto earthquakes. The occurrence of sequential earthquakes induces reliquefaction phenomenon in the site. It is concluded that, liquefaction history and preshaking effect of the site contributed to the enhanced liquefaction resistance of the site.