Re-examination on the 1891 M8.0 Nobi Earthquake, Japan: Collspse rate distributions in cities, towns and villages

Wednesday, 17 December 2014
Fumiaki Kimata, ADEP, Mizunami, Japan and Nobunao Matta, Okayama University, Okayama, Okayama, Japan
The 1891 M8.0 Nobi Earthquake is the greatest inland earthquakes in Japan. The Neodani Fault was slipped for 80 km length at the earthquake. Over 7000 peoples was perished around Gifu prefecture, central Japan by the earthquake. 
It was passed 20 years to be established a constitutional monarchy in Japan, and Meiji government modernized oneself after the West. The cities, towns and villages were decreasing to 15,859 from 71,314 by the community integration in 1888-1889. And yet, there were 61 towns and villages in Motosu county located in the hypocenter of the Nobi earthquake at the time, and there were 33,000 people. The 61 towns and villages were consisting with populations of 114 -3506, and households of 14-3508. 
Gifu prefecture published a disaster report on the numbers of collapsed house and casualties by the earthquake, including the populations and households on all cities, towns in a week after the earthquake. Already Muramatsu (1983) and Iida (1985) discussed the Gifu prefecture disaster report, and they calculated the collapse rate and estimated the seismic intensities in the towns and villages. However, they never discuss precisely the disaster in each city, town and village. 
Firstly, we make a distribution map of the completely-collapse rates of the cities, towns and villages in Gifu and Aichi prefectures using GIS software. As Muramatsu already pointed out that there are two regions over 90% of collapse rates precisely. One is located along the Neodani fault, and it is a very narrow area. The other is located wide area in north Nobi Plain.
Some research groups suggest another fault named Gifu-Ichinomiya line, because the region of seismic intensity 7 is estimated from Gifu to south Nagoya. However high collapse rate over 90% is not distributed as zones. It is suggested that collapsed houses are increased by shallow ground structures such as alluvium. 
Surely, alluvium is distributed with thick with 50 m maximally in the region. However, more local distribution of gravel layers and natural levee should affect the collapse distributions. 
Additionally, there were remarkable house collapses in the high collapse rate region of at the 1944 M8.0 Tonankai earthquake, one of the mega-thrust earthquakes in Nankai trough. It is very important data at the Nobi earthquake to discuss the regional disaster in next earthquake.