Abstract
During the 2016 Kumamoto earthquake, the extensive surface fault ruptures appeared along the active faults with a length of about 34 km and a maximum slip of about 2 m, resulting in various types of damage to buildings due to the strong ground motion and the fault displacement. The authors conducted a total of 6 field surveys in 2 years regarding building damage around the area within about 100 m from the fault ruptures, and investigated also the subsequent removal status. The appearance locations of the surface fault ruptures are generally consistent with those of the existing active fault map, but they deviate usually on the building scale of several meters. Except for the South Aso area, even though the fault displacement immediately above the fault rupture caused serious building damage, there was little major damage due to strong ground motion, and thus, the JMA Intensity scale was estimated to be 6 or less. On the other hand, the JMA intensity was estimated to be 7 in the South Aso area, because of the severe damage caused by strong ground motion; more than 70% of the collapsed and inclined buildings correspond to the direction perpendicular to the fault strike, suggesting the possibility of the forward directivity pulses. In all areas, severe damage was concentrated on old buildings with poor seismic resistance, whereas new buildings, especially those after the 2000 seismic building code were slight damage or undamaged, even right above the fault ruptures. In the subsequent follow-up survey, we confirmed that the more severe the damage grade was, the higher the rate of demolition was. However, we also confirmed that many buildings had been demolished with less than the moderate structural damage. Part of the reason seems to be due to the government policy that favors demolition over repair in the events of disastrous earthquake damage.
