Evaluation of Liquefaction Potential for Two Sites Due to the 2016 Kumamoto Earthquake Sequence

Following the 2016 Kumamoto earthquake sequence, which struck the island of Kyushu in Japan, a reconnaissance mission was conducted in the affected region by the seismic events by the UK-based Earthquake Engineering Field Investigation Team (EEFIT). The sequence caused widespread liquefaction in the coastal areas of Kumamoto Prefecture, arguably due to the presence of saturated loose sand deposits. Liquefaction-induced failure was observed in several places including Akitsu River and Kamiezu Lake. Generally, signs of ejected sand, extensive ground settlement and localised ground lateral spreading were noted, which were apparently due to liquefaction. One purpose of this study is to present liquefaction-induced failure during the Kumamoto earthquake for the aforementioned visited regions. An assessment of liquefaction vulnerability for all investigated sites was also conducted using different approaches, namely Eurocode8 and Idriss and Boulanger. The computed factors of safety were compared to results from numerical analyses performed in the object-oriented software OpenSees. The results show that different methods yield similar factors of safety, which are consistent with the numerical results and field observations.