Laserfiche WebLink
J. H. KLEINFELDER & ASSOCIATES <br />r� <br />File No. S-1008-35 <br />May 17, 1985 <br />Page 6 <br />greater. In the past, the Foothills fault system has been considered inactive, with no <br />known creep or displacement of geologic features since Late Tertiary time. On August 1, <br />1975, an earthquake of magnitude 5.7 occurred approximately 6 miles southeast of Oroville . <br />As a result of this event and subsequent aftershocks, a reevaluation of the potential activity <br />of the Foothills fault system took place. It has been proposed that a 6.5 magnitude <br />earthquake may occur almost anywhere in the Foothills fault system. <br />The reevaluation of the Foothills fault system consisted, in pert, of trenching across <br />known lineaments of the Bear Mountains and Melones faults. Trenches excavated in the <br />vicinity of Rawhide Flat, near Sonora, California, indicate offset within the older soil <br />horizons. Additional trenching in areas to the north indicate possible offset of the <br />Mio-Pliocene Mehrten Formation by the Bear Mountains fault. <br />Using methods derived by H. Bolton Seed and I. M. Idriss , Table I, below, was <br />compiled for bedrock accelerations to be expected in the site area. <br />