SSHAC Revisited: Adapting Site‐Specific Seismic Hazard Analyses for Modern Applications

During three decades of experience in successfully implementing the SSHAC guidelines for seismic hazard analyses, numerous refinements have been made to the procedures, especially to clarify the process for the lower study levels and simultaneously enhance the relevance of Level 1, 2, and 3 SSHAC studies. Lessons recently learned from practical applications, which have yet to be incorporated into formal guidelines, are discussed, particularly with regard to the selection of project participants and to the structuring of their interactions during the course of the PSHA project. The most important insights, however, are related to technical issues, through which ever more efficient and transparent procedures for representing the center, body, and range of model inputs have evolved. The extensive experience and technical achievements gained from conducting many SSHAC Level 3 studies provide the foundational footing for the improvements to the SSHAC process and advancements in underlying PSHA data, models, and methods proposed in the paper. These technical advances and practical experience gained have resulted in mature and widely accepted frameworks for seismic source characterization, ground‐motion modeling, and site response analysis, enabling recent studies to focus on project‐specific data, interpretations, and uncertainty characterization rather than on developing new methodological approaches. This paper summarizes the technical frameworks that have emerged from recent SSHAC studies and presents additional procedural recommendations that will allow future studies to focus their resources on site‐specific data gathering and characterization rather than on redevelopment of the underlying hazard methodologies. These proposed recommendations are intended to initiate discussions with a view to inform potential future improvements to regulatory guidance for siting critical facilities that will be needed in order to fully realize the benefits of the lessons learned from past SSHAC studies, especially as they can be adapted to applications for siting of the next generation of advanced reactors.