Active Faults in Dam Foundations: An Update

This paper updates the 1974 Geotechnique paper on the same subject by Sherard, Cluff, and Allen. Geologists and seismologists are now able to recognize the presence of, and assess the degree of activity of, faults in dam foundations far more effectively than only a few years ago, thanks to a variety of new neotectonic tools. Similarly, engineers are increasingly able to accept possible foundation displacements with a variety of innovative measures in dam design. Brief case studies of faults beneath dams are presented, and some mitigative measures are described, for Auburn Dam site (USA), Clyde Dam (New Zealand), Eastside Reservoir USA), Lauro Dam (USA), Matahina Dam (New Zealand), Ridgway Dam (USA), Seven Oaks Dam (USA), Steno Dam site (Greece), and Tarbela Dam (Pakistan)

Active Faults in Dam Foundations: An Update

This paper updates the 1974 Geotechnique paper on the same subject by Sherard, Cluff, and Allen. Geologists and seismologists are now able to recognize the presence of, and assess the degree of activity of, faults in dam foundations far more effectively than only a few years ago, thanks to a variety of new neotectonic tools. Similarly, engineers are increasingly able to accept possible foundation displacements with a variety of innovative measures in dam design. Brief case studies of faults beneath dams are presented, and some mitigative measures are described, for Auburn Dam site (USA), Clyde Dam (New Zealand), Eastside Reservoir USA), Lauro Dam (USA), Matahina Dam (New Zealand), Ridgway Dam (USA), Seven Oaks Dam (USA), Steno Dam site (Greece), and Tarbela Dam (Pakistan)

Evidence for Unusually Strong Near-field Ground Motion on the Hanging Wall of the San Fernando Fault during the 1971 Earthquake

Reports of unusually intense ground motions in the very near fields of faults that have ruptured during earthquakes are becoming more common, particularly with the markedly increased worldwide strong-motion instrumentation in recent years (e.g., Heaton and Wald, 1994). The reported ground motions are sufficiently strong to have significant potential engineering impact (Hall et al., 1995). In addition to fault proximity, two other factors that have contributed to unusually high strong motions are rupture directivity (e.g., Somerville et al., 1997) and locations on the hanging walls of thrust faults (e.g., Nason, 1973; Abrahamson and Somerville, 1996; Brune, 1996a; Brune, 1996b). Perhaps nowhere has the sharp distinction between damage on the hanging wall and footwall of a thrust fault been more dramatically documented than during the 1945 Mikawa earthquake, Japan (Iida, 1985)

Probabilities of Large Earthquakes in the San Francisco Bay Region, California

In 1987 a Working Group on California Earthquake Probabilities was organized by the U.S. Geological Survey at the recommendation of the National Earthquake Prediction Evaluation Council (NEPEC). The membership included representatives from private industry, academia, and the U.S. Geological Survey. The Working Group computed long-term probabilities of earthquakes along the major faults of the San Andreas fault system on the basis of consensus interpretations of information then available. Faults considered by the Working Group included the San Andreas fault proper, the San Jacinto and Imperial-faults of southern California, and the Hayward fault of northern California. The Working Group issued a final report of its findings in 1988 (Working Group, 1988) that was reviewed and endorsed by NEPEC. As a consequence of the magnitude 7.1 Loma Prieta, California, earthquake of October 17, 1989, a second Working Group on California Earthquake Probabilities was organized under the auspices of NEPEC. Its charge was to review and, as necessary, revise the findings of the 1988 report on the probability of large earthquakes in the San Francisco Bay region. In particular, the Working Group was requested to examine the probabilities of large earthquakes in the context of new interpretations or physical changes resulting from the Loma Prieta earthquake. In addition, it was to consider new information pertaining to the San Andreas and other faults in the region obtained subsequent to the release of the 1988 report. Insofar as modified techniques and improved data have been used in this study, the same approach might also, of course, modify the probabilities for southern California. This reevaluation has, however, been specifically limited to the San Francisco Bay region. This report is intended to summarize the collective knowledge and judgments of a diverse group of earthquake scientists to assist in formulation of rational earthquake policies. A considerable body of information about active faults in the San Francisco Bay region leads to the conclusion that major earthquakes are likely within the next tens of years. Several techniques can be used to compute probabilities of future earthquakes, although there are uncertainties about the validity of specific assumptions or models that must be made when applying these techniques. The body of this report describes the data and detailed assumptions that lead to specific probabilities for different fault segments. Additional data and future advances in our understanding of earthquake physics may alter the way that these probabilities are estimated. Even though this uncertainty must be acknowledged, we emphasize that the findings of this report are supported by other lines of argument and are consistent with our best understanding of the likelihood for the occurrence of earthquakes in the San Francisco Bay region

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