In seismically active areas, bedrock sites have usually been sought for nuclear power stations because of the presumed stability of the site, and information on the strong ground motion which can occur during an earthquake. Difficulties both in locating suitable sites of this value and in assessing the activity or capability of adjacent faults have led to an examination of alternate sites. A study has been made of the possibility of locating nuclear reactors in areas underlain by deep alluvial deposits. Among the preliminary results of the study, including information on ground motions from recent earthquakes, are indications that the strong ground motions caused by an earthquake at such a site are less intense than was formerly supposed, if the soil is sufficiently stiff. In an alluvial layer of great enough depth, the displacement occurring along a bedrock fault will not propagate to the surface.