Relationship between Vs30 and fault displacement attenuation relation of PFDHA

An estimation of fault displacements is difficult due to the complex process of fault rupture propagations from a source fault to the surface. A PFDHA (Probabilistic Fault Displacement Hazard Analysis) is one of probabilistic approaches to evaluate on- and off-fault displacement hazards. Attenuation relations of on- or off-fault displacement, and occurrences of surface ruptures are statistically modeled based on the data set of past earthquakes in PFDHA. The variation of the displacement amount of the attenuation relation in the PFDHA is large because there are numerous factors for rupture propagations. A property of surface materials is one of these factors. Moss et al. (2013) suggested the Vs30 (the time-averaged shear-wave velocity to 30 m depth) effects to the occurrence of surface ruptures in reverse-slip earthquakes. In this study, we examined the relationship between Vs30 and fault displacement attenuation relations along the principal faults in our database (Inoue et al., 2018). The attenuation curves of lower Vs30 strike-slip earthquake data rapidly decrease near the ends of the faults. This trend is similar to the global data set of strike-slip earthquake published by Petersen et al. (2011). In contrast, the attenuation curves with higher vs30 strike-slip earthquake data gradually decrease near the ends of the faults. These results indicate one of the possibilities of the Vs30 as PFDHA components of attenuation relations, although this result is a preliminary and rough estimation based on our limited data set and more investigation is required based on more new data and analogue and numerical simulations.

ACKNOWLEDGMENT: This research was part of the 2015-2016 research project 'Development of evaluating method for fault displacement' by the Secretariat of Nuclear Regulation Authority (NRA), Japan.