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- 12 - <br />major earthquake located in the Intermountain Seismic Belt should not <br />cause peak ground accelerations at the site in excess of 0.049. • <br />Numerous small earthquakes have occurred in the Rangely Oil <br />Field arr3 have been attributed to fluid injections for secondary oil <br />recovery, Gibbs (1973). These earthquakes have been attributed to <br />decreases in stress on a small normal fault located in the oil field. <br />Epicenters for ten of the larger earthquakes in this area are shown on <br />Fig. 4. The largest earthquake associated with the Rangely Oil Field <br />occurred on February 15, 1967 and had a magnitude of 4.5. Its <br />epicenter was located about 19 miles from the Deserado Mine site. <br />Using magnitude and peak acceleration attenuation correlations <br />prepared by Donovan and Bernstein (1978), it is estimated that the <br />peak horizontal ground acceleration at the site caused by this <br />earthquake would have been about 0.038. In our opinion, it is likely • <br />that future earthquakes will occur in the Rangely Oil Field as long as <br />secondary oil recovery operatio-:a are under way; however, ~.e do not ~~ <br />feel that earthquakes muds strc.•noer than those which have occurred in <br />the past will occur in the future. <br />Algermissen and PErkins (1976) have prepared probabilistic <br />estimates of maximum peak ground acceleration for the United States <br />based on historic seismic activity. Their study indicates that <br />maximum horizontal ground acceleration with a recurrence interval of <br />475 years for the Rangely area would be 0.049. <br />Potentially Capable Faults: Studies done by the Colorado Geological <br />Survey indicate that the faults adjacent to the Uinta Arch to the <br />north of the site may be potentially capable; however, more detailed <br /> <br />