Examination of source fault model for the Gifu-Ichinomiya fault based on seismic intensity data

Abstract

To investigate possible source fault models for the Gifu-Ichinomiya fault, we construct multiple source fault models of the 1891 Nobi earthquake, taking into account several different types of geometry for the Gifu-Ichinomiya fault, and conduct strong ground motion simulations. We choose the most plausible source model by comparing the distribution of simulated seismic intensities with the spatial distribution of a questionnaire-based intensity of 7, and with that of the damage ratio of wooden houses in the near-source region. Our results imply that the length of the source fault of the Gifu-Ichinomiya fault is relatively short and the dip angle is 75 degrees to the east. Because a seismic intensity of 7 is considered to arise from site amplification and the short distance from a source fault, we classified the points with a seismic intensity of 7 based on the H/V spectral ratio of microtremors by considering the contributing factors to the generation of a seismic intensity of 7. A linear distribution of the points, which might have relatively lower site amplification factors, in the northeastern part of the Nobi Plain implies that a part of the source fault of the 1891 Nobi earthquake existed in this area, as indicated through strong ground motion simulations.