2018 Volume 2018 Issue 48 Pages 13-34
The 2016 Kumamoto earthquake occurred due to reactivation of active faults, causing severe damage along the faults. Earthquake faults clearly appeared on the ground surface not only along well-known Futagawa-Hinagu active fault, but also in the urbanized area of Mashiki town where no active fault was previously identified. It is essential for earthquake disaster prevention to clarify the details of this unknown earthquake fault and to consider the relationship with the damage. This paper clarifies the distribution of earthquake faults in Mashiki town, discusses the relationship between earthquake faults and tectonic landforms, and then compares the distribution of earthquake faults with the data of previous studies on building damage to examine the relationship between surface faulting and building damage. We concluded that (1) earthquake faults are clearly continuous for about 5 km from the main trace of Futagawa fault to the urbanized area, (2) the fault diverges from the east to the west, and displacement amount of about 70 cm is maintained even at the western end, (3) the earthquake faults are located along the tectonic landforms which were newly identified in the urbanized area of Mashiki, (4) the lateral average slip rate of the active faults in the town is possibly estimated more than 1.8 mm/year, (5) the recurrence interval could be calculated less than a thousand year if the 2016 activity is characteristic for the fault, (6) building damage tends to be severe near the fault where displacement amount exceeds 10 cm.
