SEISMICITY PATTERNS AND THE CHARACTERISTIC EARTHQUAKE IN THE CENTRAL MISSISSIPPI VALLEY, USA

The magnitude-frequency distribution of the Armbruster-Seeber (1992) c atalog of the Central Mississippi valley earthquakes from 1811 to 1985 can be well described as a linear combination of three earthquakes po pulations each of which fits a normal distribution with respect to mag nitude. The mean magnitudes of the lower magnitude populations are con sistent with previous work based on a 1974-1991 catalog of the same ar ea. The presence of the high magnitude population, mean M=7.2, account s for the development of a characteristic earthquake pattern. This pat tern is very dependent on the assumed activity of the 7.2 population. The operating basis earthquake (144 years) of interest to structural e ngineers occurs in the region of greatest sensitivity to those assumpt ions about activity, thus complicating matters for design. (C) 1998 El sevier Science B.V. All rights reserved.