OFR 97–464: Page [6]
Ms: mb*=1.0*Ms+1.1 for Ms<=2.9; =0.6*Ms+2.3 for 2.9<Ms<=7.5;
=6.8 for Ms>7.5 (4.0,5.0,8.3,8.5)
downweight for Ms<5.0 (s/n) and Ms>8.3 (saturation)
ML: mb*=ML (-,-,6.8,7.0)
downweight for ML>6.8 (saturation)
Mn: mb*=Mn (-,-,6.8,7.0)
doubleweight all Mn (arbitrary decision); downweight for Mn>6.8 (saturation)
Mw: mb*=1.5*Mw-1.5 for Mw<=3.0; =Mw for 3.0<Mw<=6.8; =6.8 for Mw>6.8
MD: same as ML, but don't downweight
FeltArea or MaxIntensity: same as mb, but don't downweight
These conversion rules were generalized from ideas presented by Boore and Joyner (1982), Chung and Bernreuter (1981), Veneziano and Van Dyke (1985), and G. Reagor (personal communication, 1995).
The weighting function is described above under the WUS magnitude conversion rules. For the same reasons as WUS, we decided to remove any DNAG record found in the aftershock window of an earthquake from a higher-preference catalog, regardless of magnitude. We moved the 05/26/1909 magnitude-5.0 Illinois earthquake north from the NCEER location to a location that is more consistent with felt reports (Stover and Coffman, 1993). We moved the 02/21/1916 magnitude-5.2 Skyland earthquake west from the NCEER location (M. Chapman, personal communication, 1996). Finally, we removed man-made seismic events in the following areas: Rocky Mountain Arsenal near Denver since 1962 (Hsieh and Bredehoeft, 1981); Rangely oil field in western Colorado since 1957 (Raleigh et al, 1976); several coal-mining districts in central Utah since 1900 (Wong et al, 1989; W. Arabasz and J. Pechmann, personal communication, 1996); and Cogdell oil field in west Texas since 1974 (Davis and Pennington, 1989).
The final CEUS catalog contained 2750 earthquakes with magnitude >= 3.0; the algorithm eliminated approximately 170 "foreshocks" and 600 aftershocks (Appendix 2). Figure 6 shows the entire CEUS catalog (file emb.cc). Figures 7a, 7b, 7c, 7d, 7e, and 7f, compare the contributions from each original catalog during 1964-1985, a period when all the catalogs were active.
We counted earthquakes on a 0.1o-by-0.1o grid, and normalized by the counting window duration to get a seismicity rate in each grid cell in CEUS. East of -105o longitude we counted earthquakes with magnitude >= 3 since 1924, magnitude >= 4 since 1860, and magnitude >= 5 since 1700. Considering the poorer catalog completeness in CEUS west of -105o, we used 1976, 1963, and 1860 for these magnitude ranges, respectively. This scheme is shown in Figure 8....>>NEXT
Last Update: Thursday, February 16, 2006 9:58
