Probabilistic Seismic Hazard Analysis Code Verification

Over the past decade, the use of Probabilistic Seismic Hazard Analysis (PSHA) to assess seismic hazards has expanded, leading to the creation of a number of new PSHA computer codes throughout the industry. Additionally, recent seismic source and ground-motion characterization studies have led to more complex source and ground-motion models, which necessitate implementation in PSHA codes. This project was undertaken to update previous PSHA computer code verification efforts by running an expanded set of verification tests on codes currently in use for PSHA calculations. Following an announcement to the community, fifteen owners of PSHA codes from private consulting companies, academic institutions, risk analysis firms, and government agencies participated in the verification project by running verification tests on their own codes. The project included three sets of tests that increased in complexity from the first test in Set 1 to the last test in Set 3. Over the course of the project the group held ten meetings to discuss and finalize the results. Tests were often re-run several times before the results for all codes were finalized. This report documents the specifications and benchmark answers for the verification tests. Common issues and programming errors are also summarized, along with standard modeling approaches and key discussion points from the meetings. Where differences in modeling approaches lead to differences in reported hazard, those different modeling approaches are described. Through participation in the project, code owners verified the primary functions of their codes as benchmark answers were reached. The PSHA codes developed in the future can be verified by running the tests and comparing the results to the benchmark answers documented in this report. Note: the scope of this project is PSHA computer code verification. This project does not make recommendations on how to model earthquake scenarios from the specified source-characterization or ground-motion characterization inputs.