A Comparison of Return Periods of Design Ground Motions for Dams from Different Agencies and Organizations

The purpose of this paper is to review and compare the criteria of seismic design ground motions and approaches in seismic hazard analysis set forth by various agencies and organizations. A total of 13 agencies and organizations were reviewed including three for non-dam structures. It was found the both the deterministic and probabilistic seismic hazard analysis approaches have been used. Many have combined the two approaches to complement each other. High-consequence dams are designed for a long ground motion return period of approximately 10,000 years, which lies between the design return periods of bridges and nuclear power plants. In contrast to other agencies and organizations, U.S. Bureau of Reclamation dams are not subjected to specific design return periods; they are designed based on risk-informed decisions, which consider the failure probability in relation to the public protection guideline values. In addition, criteria from the Reclamation Design Standards are to be followed in any dam modifications. Based on the findings of this paper, it was deemed that the current Reclamation dam safety decisions and practices are in general agreement with other dam agencies and organizations that also adopt the risk-informed decision process.