The authors used a three-dimensional finite element method (3D-FEM) to examine a series of fault rupture simulations for the 2014 Northern Nagano Earthquake and simultaneously estimate the displacement and strong motions. The computational results confirmed that the maximum responses of ground motions and displacement could be simultaneously evaluated using the appropriate constitutive parameters and fine FEM mesh. However, the duration of the acceleration response and shape of the surface displacement waves were not well simulated. In this study, we examined the influence of the fault bend at a shallow depth and P- and S-wave velocity structure models based on a geological survey. As a result, by taking account of bending of the fault plane and the elastic velocity structure at a shallow depth, it was possible to perform a seismic behaviour analysis using the 3D-FEM approach.
Fault rupture simulations have been performed mainly for the reproduction and prediction of strong motions. After the 1999 Chi-Chi and Kocaeli earthquakes damaged many important structures as a result of surface rupture, the displacement and inclination of the ground surface caused by fault rupture have become significant issues in engineering. Many prediction methods for strong motion, displacement and inclination of the surface ground have been suggested. However, most analytical methods do not evaluate displacement and strong motions at the same time. Furthermore, the parameters adopted in these methods (fault length, slip on fault, stress drop, etc.) are empirically determined and the dynamic destruction process is not taken into account. Therefore, it is difficult to evaluate strong motions of magnitude nine, the seismic response around the epicentre and surface rupture with few observed data.
The authors have examined a series of fault rupture simulations to simultaneously estimate the displacement and strong motions at the ground surface using a three-dimensional finite element method (3D-FEM) considering the dynamic destruction process of the fault plane. This analytical method and modelling of faults was proposed by Toki & Sawada (1988) and Mizumoto et al. (2005). The fault plane was assumed to be discontinuities of bedrock and was modelled by joint elements, and shear failure occurred at the hypocentre and spread to the surrounding areas with increasing shear stress. Iwata et al. (2018) conducted a fault rupture simulation for the 2014 Northern Nagano Earthquake, which was induced by the Kamishiro Fault (Mw6.3). The computational results confirmed that the maximum responses of the ground motion and displacement could be evaluated using the appropriate constitutive parameters and a fine FEM mesh with a size less than 150 m. However, the duration of the acceleration response and shape of the surface displacement response were not well simulated, partly because the fault plane was assumed to be a straight planar feature and the bedrock was assumed to be homogeneous.