Microearthquakes in Kansas and Nebraska 1977--1989

The Kansas Geological Survey operated a microearthquake network from August 1977 to August 1989 with station located in eastern Kansas and Nebraska. Locatable microearthquakes with duration magnitudes less than 3.2 occur at the rate of roughly 20 per year in the two-state area, with most of the magnitudes ranging from 1.4 to 2.5. The microearthquake pattern observed during the 12 years of recording is consistent with the pattern of historical earthquakes reported since 1867. Much of the activity occurs along the Precambrian Nemaha Ridge, which has been the site of several earthquakes of MM Intensity VII over the past 125 years. Some seismicity is observed along the northwest flank of the Midcontinent Geophysical Anomaly in Kansas, but little is observed in the Nebraska or Iowa portions of this Precambrian feature. The Central Kansas Uplift, a buried anticline similar in age to the Nemaha Ridge, has been the site of several felt earthquakes since 1982. Another trend of earthquakes extends northeastward across central Nebraska and is not associated with any prominent geologic structure. All the seismicity in central and eastern Kansas can be roughly correlated to known geologic structures. 32 refs., 4 figs