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<br />listed more than once due to the multiple sources of information used <br />in generation of the data base. The computerized earthquake listing <br />was supplemented by historic reports from the Earthquake History of <br />the United States (Coffman and Von Hake, 1977). <br />6.1.1 Southern Rocky Mountains <br />Seismicity of the Southem Rocky Mountain province is generally not <br />related to surface geologic structure and apparent post-Miocene fault- <br />ing. One of the most significant and controversial earthquakes to have <br />occurred in the Southem Rocky Mountains is the November 7, 1882, <br />event. This earthquake, a MM intensity VII event (estimated M~=6.2), <br />was felt over a broad azea from Kansas on the east to Salt Lake City on <br />the west. Hadsell (1968) concluded, based on felt reports, that the <br />event was similar in magnitude and location to subsequent earthquakes <br />near the Rocky Mountain Arsenal. Dames and Moore (1981), as part <br />of their studies for the Rocky Flats Plant, reanalyzed felt reports from a <br />three state area and concluded the 1882 event may have been as large <br />as Richter magnitude M,,=6.5 and was located in the Piceance Creek <br />Basin of western Colorado rather than near Denver as postulated by <br />Hadsell (1968). This interpretation has met with some justified skepti- <br />cism, however. Kirkham and Rogers (1986) estimate the earthquake to <br />have been M~ = 6.2 f 0.3 and infer the earthquake probably occurred <br />in north-central Colorado, either in the Front Range or in the Southem <br />Laramie Mountains. Risk Engineering (1994) generally agreed with <br />Kirkham and Rogers' assessment of epicentral location but assigned a <br />moment magnitude range of MW = 5.0 t 0.4 to 6.0 f 0.2 with a best <br />estimate of 6.4 f 0.3. <br />Excluding the 1882 event, little significant historic earthquake activity <br />has occurred in the Southem Rocky Mountains. Kirkham and Rogers <br />(1981) suggest that a few non-damaging, instrumentally-recorded <br />events may be associated with potentially active faults in the Front <br />Range area. For example, the January 6, 1979, magnitude 2.9 event <br />near Divide may have been related to the Oil Creek fault. This associa- <br />tion, as well as others, however, may be more apparent than real. Any <br />conclusive statement relating instrumentally recorded earthquakes to <br />specific tectonic structures awaits further work. In general, the pattern <br />of seismicity in the Southem Rockies can be characterized as diffuse <br />17 <br />