Development of Fragility Curves for Japanese Buildings Based on Integrated Damage Data from the 2016 Kumamoto Earthquake

A series of earthquakes hit Kumamoto Prefecture on Kyushu Island, Japan on April 14 and 16, 2016. Soon after the 2016 Kumamoto earthquake, municipal governments carried out building damage surveys to issue disaster-victim certificates. The building damage caused by the 2016 Kumamoto earthquake was serious in Mashiki Town, which is located close to the source region, but Uki City, next to that area, was also heavily damaged. The present authors have already developed several fragility curves using damage survey data from the Mashiki Town and Uki City governments. Some of the fragility curves for Mashiki Town rise sharply at low PGV levels because of the lack of damage data in the low PGV range. Compared with the fragility curves for Mashiki Town, the fragility curves for Uki City show a lower damage ratio for the same PGV. The fragility curves for Uki City were obtained using the damage data in the PGV range lower than those for Mashiki Town. In this study, we integrated the damage survey data of the Mashiki Town government and the Uki City government due to the 2016 Kumamoto earthquake, and constructed building fragility curves with respect to the structural material and construction period in combination with the estimated seismic motion distribution. The correlation coefficient showed a strong positive correlation of approximately 0.9 in all classifications of the building fragility curves covering a wide range of seismic ground motions. The validity of the proposed fragility curves was demonstrated and compared with existing fragility curves developed using damage survey data from local governments in other earthquakes.