Seismic Hazard and Seismic Risk

Abstract:

There are many sources of uncertainty involved in seismic safety evaluation of an embankment or earth dam. Even when conservative assumptions and selections of parameters are made, there will always be a probability that performance of the dam during its lifetime may not be as predicted. To evaluate seismic risk of damage or failure of earth dams, a seismic risk analysis procedure is presented. The future occurrence of earthquakes is probabilistically described in terms of both intensity and number of cycles of ground motion (seismic hazard analysis.) Furthermore, a probabilistic procedure for the calculation of permanent deformation of earth dams (seismic performance analysis) is presented, characterizing the seismic event in terms of acceleration, number of cycles and predominant period of motion. The results of seismic hazard and seismic performance analysis are combined to yield the risk of seismic damage or failure of a dam (seismic risk analysis). An example case study is presented, illustrating the application of the procedures. A risk-based seismic safety evaluation of an embankment or an earth dam can provide estimates of relative risks that are useful in design and decision analysis and can avoid compounding of conservatism.

The research described in this report was sponsored by the National Science Foundation through Grant No. DFR-84-12124 for research on integrated seismic risk analysis for earth dams. The writers gratefully acknowledge this support.

Relevant Publications:

• Yegian, M.K., Kadakal, U. and Catan, M. (1999). “Geosynthetic for Earthquake Hazard Mitigation”. Geosynthetics ’99 Boston, Mass. April.
• Ghahraman, V.G. and Yegian, M.K. (1996). “Risk Analysis for Earthquake-Induced Permanent Deformations of Earth Dams” 11th World Conference on Earthquake Engineering, Mexico, June.
• Yegian, M.K. and Ghahraman, V.G. (1993) “Risk-Based Methodology for Seismic Rehabilitation of Earth Dams”. Proceedings of the ASCE Conference on Geotechnical Practice in Dam Rehabilitation, North Carolina, April.
• Ghahraman, V.G. and Yegian, M.K. (1991). “Seismic Deformation Analysis of Earth Dams.” Proc. 1st Int. Conf. Seismology & Earthq. Engrg., vol. 3, May.
• Yegian, M. K. and Marciano, E.A. and Ghahraman., V.G. (1991). “Seismic Risk Analysis For Earth Dams.” Journal of the Geotechnical Engineering Division, ASCE, January.
• Yegian, M.K. (1987). “Methodology for Seismic Safety Evaluation for Earth Dams.” Proceedings of the International Seminar on Seismic Zonation, Guangzhou, China, December.
• Yegian, M.K. (1986). “Geologic Considerations in Seismic Hazard and Risk Assessment.” Proceedings of the International Symposium on Engineering Geology Problems in Seismic Areas, Bari, Italy.
• Yegian, M.K., Holt, R.J. and Murphy, V.J. (1984). “Methodology for Seismic Safety Evaluation of Fossil Power Plants.” Proceedings of Energy 1984 American Society of Civil Engineers Conference, Pasadena, California, August.
• Yegian, M.K. (1984). “Probabilistic Seismic Hazard Analysis for Pore Pressure Build-up in Sands.” Proceedings of the Eighth World Conference on Earthquake Engineering, San Francisco, California.
• Yegian, M.K. (1979). “State-of-the-Art For Assessing Earthquake Hazard in the United States: Probabilistic Seismic Hazard Analysis,” Report No. 13, The U.S. Army Engineers, Waterways Experimental Station, Vicksburg, Mississippi, July.
• Yegian, M.K. and Whitman, R.V. (1977) “Risk Analysis for Ground Failure by Liquefaction”, Journal of the Geotechnical Engineering Division, ASCE, July.