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<br />related to the waste disposal well at the Rocky Mountain Arsenal <br />discussed above. Several historical events located by intensity data <br />occurred at the southem end of the source in the vicinity of two poten- <br />tially active faults, the Fowler and Cheraw faults (Kirkham and <br />Rogers, 1981), that are neazly coincident with the southern basin <br />boundary. <br />The maximum earthquake magnitude for the Denver Basin source is a <br />function of whether or not the 1882 earthquake is assumed to have <br />occurred within the Denver Basin. For the purposes of this study, we <br />conclude that the 1882 earthquake did not occur in the Denver Basin <br />source but instead occurred in the Eastern Rocky Mountains (Source <br />II) discussed below. Accordingly, we assign a maximum earthquake <br />magnitude of 6.0 and recurrence relation as shown on Figure 3. This <br />maximum earthquake magnitude accounts for historical seismicity and <br />the appazent absence of significant Quaternary faults within the source <br />area. The Denver Basin source specifically excludes the Rocky <br />Mountain Arsenal source zone discussed above. <br />Eastern Rocky Mountains -Source 2 <br />The boundaries of the Eastem Rocky Mountains Source (Figure 1) are <br />defined on the basis of topographic and tectonic characteristics and <br />generally conform to the Eastern Mountain Province of Kirkham and <br />Rogers (1981). The western boundary is drawn along, but does not <br />include, structures associated with the Rio Grande rift. To the north, <br />where the rift is poorly defined, the boundary coincides with the range <br />front of the Medicine Bow Mountains and includes the Middle and <br />South Pazk basins. The eastern boundary includes the eastern range <br />front of the Rocky Mountains. The southeastern mazgin coincides <br />with the Sangre De Cristo Range and includes the Wet Mountains. <br />Seismic activity in this source is low and earthquake epicenters do not <br />appear to be associated spatially with mapped faults. The absence of <br />significant late Quaternary surface rupture indicates that earthquakes in <br />this source zone occur at or below the threshold of surface rupture. <br />This observation coupled with the assumption that the 1882 earthquake <br />occurred within this source indicates a maximum magnitude of 6.5. <br />The recurrence relation for this source zone is illustrated on Figure 4. <br />31 <br />