This study improves the fragility curves for wooden buildings used in probabilistic seismic risk assessment. Specifically, we resolved two issues identified in previous studies. First, the lower limit of seismic intensity at which damage begins to occur was specified. Second, consistency was ensured between the severity of damage and the damage ratio. As a first step in improving the fragility curves, building damage data were added from areas surrounding observation sites where relatively weak ground motion with a seismic intensity of 5.5 or less was recorded. Next, damage functions showing the relationship between the building strength and seismic intensity at which damage occurs were created using regression analysis with constraints set to satisfy the above two conditions. Finally, the validity of the fragility curves was verified by comparing the damage estimates for past earthquakes with the actual damage.
Tokizane et al. (Mon,) studied this question.