Geologic and seismic setting pertinent to dam safety. Review of Duncan Dam

Duncan Dam was constructed on the Duncan River in southeastern British Columbia between 1965 and 1967. The dam was founded on a complex sequence of more than 380 m of glacial drift and glaciofluvial sediments, some of which are pervious and compressible. Some sandy units are potentially liquefiable, in particular a sand layer (Unit 3c) up to 23 m thick. Current BC Hydro seismic guidelines require that Duncan Dam should be able to withstand the Maximum Credible Earthquake (MCE) without catastrophic release of the reservoir. This paper describes the geologic and seismic setting of the region around the dam and the selection of seismic ground motion parameters. Probabilistic methods were applied to develop MCE ground motions, which were estimated to consist of a peak horizontal acceleration of 0.12g, which could be caused by a M6.5 earthquake at a distance of about 50 km.