Duncan Dam is a B.C. Hydro facility constructed on the Duncan River in
southeastern British Columbia, Canada, 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 compressi
ble. Some sandy units are potentially liquefiable, in particular a san
d layer (unit 3c) up to 23 m thick. Current B.C. Hydro seismic guideli
nes for dams require that Duncan Dam should be able to withstand the M
aximum Credible Earthquake (MCE) without catastrophic release of the r
eservoir. This paper describes the geologic and seismic setting of the
region around the dam and the selection of seismic ground motion para
meters. Probabilistic methods were applied to develop MCE ground motio
ns, which were estimated to consist of a firm ground peak horizontal a
cceleration of 0.12 g, which could be caused by a M 6.5 earthquake at
a distance of about 50 km. Several time histories with characteristics
similar to this design earthquake were selected for dynamic soil anal
yses.