Conversion of Seismic Fragility and Vulnerability Models to Alternative Intensity Measures for Regional Risk Analysis

Fragility and vulnerability models are key components of regional seismic risk analysis. They relate ground shaking intensity, expressed through an intensity measure (IM) such as spectral acceleration or peak ground velocity, to a probability of damage or loss. When performing a risk analysis for an entire portfolio of structures, these fragility models are often developed based on different IM types for each taxonomy, creating a problematic mismatch in IMs when looking to comparatively evaluate and collectively apply them regionally. Previous research has proposed various approaches for converting fragility functions to a common IM, including methods based on uniform hazard equivalence, total probability, and the use of proxy structures. Another uniform risk equivalence procedure is trialled here along with a more refined consideration of hazard. These methods are systematically compared via 2,260 conversion cases, assessing their ability to convert fragility functions defined with both traditional and next‐generation IMs, such as average spectral acceleration, which have yet to be explored. The conversion strategy is also extended and tested for vulnerability model conversion, which is still lacking in the literature. Results show that methods based on uniform hazard and risk equivalence are not consistently reliable, while total probability‐based approaches perform better but require detailed hazard information. A key finding is that conversions from suboptimal IMs, such as peak ground acceleration, do not yield improved predictive performance even when mapped to more optimal IMs. Practical guidance and accompanying tools are provided to support analysts in applying and testing these conversion methods for their own fragility and vulnerability models.