Establishment of Evaluation Formulae for Probabilistic Fault Displacement Hazard Analysis (PFDHA) in Japan

A probabilistic fault displacement hazard analysis (PFDHA), which was proposed by Youngs et al. (2003), is a methodology that assesses the annual rate/probability of exceedance that an amount of displacement of a surface earthquake fault exceeds a certain quantity. In this paper, we proposed evaluation formulae in terms of both principal and distributed faults based on data from surface earthquake faults generated by reverse and strike-slip faults in Japan. For principal faults, an abundance of data is accumulated by making use of the past surface earthquake faults in Japan, while for distributed faults, the data are not necessarily sufficient in reality. Therefore, model experiments and numerical analyses based on the discrete element method (DEM) were applied to compensate for the lack of data regarding distributed faults. Although a past study shows that the occurrence probability of a distributed fault depends on the grid size employed in the analysis, no study using Japanese domestic data for distributed faults has been reported. Taking this into account, we tried to improve the reliability of evaluation formulae by analyzing the dependency of the grid size. Furthermore, we adopted a logic tree methodology that can consider epistemic uncertainties and demonstrated an example of its application. As a result of model case analyses, the proposed evaluation formulae gave the prospect of applicability of PFDHA in Japan and we described future tasks to be addressed. (author)