Kansas Geological Survey, Open-file Report 1990-10
by Don W. Steeples
Brett C. Bennett
Richard D. Miller
Ralph W. Knapp
Kansas Geological Survey
KGS Open-file Report 1990-10
The Kansas Geological Survey operated a microearthquake seismograph network from August 1977 to August 1989. The network originally consisted of nine stations and was expanded to fifteen stations in 1982. All stations were located in the eastern half of 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 events ranging from 1.4 to 2.5 in local magnitude. 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 Nemaha Ridge, a buried Precambrian uplift that runs from roughly Omaha, Nebraska, southward across Kansas to near Oklahoma City. This geological structure 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, which is a buried anticline similar in age to the Nemaha Ridge, has been the site of several felt earthquakes since 1982. A trend of earthquakes extending northeastward across central Nebraska is not associated with any prominent known geologic structure. All the seismicity in central and eastern Kansas can be roughly correlated to known geologic structures.
This report also includes previously unpublished felt reports from two earthquakes that were not listed in DuBois and Wilson (1978) and for which no information was previously available. These data were kindly supplied to us by John M. Peterson of Lawrence, Kansas, who conducted the library search at his own expense. One earthquake occurred near Stockton, Kansas, on April 27, 1879, with Modified Mercalli intensities of at least VI and possibly VII. This new information and the relatively high degree of seismicity noted along the central Kansas uplift in comparison to the Nemaha ridge/Humboldt fault zone leads us to conclude that the earthquake risk associated with the central Kansas uplift has been underestimated.
The other newly discovered earthquake occurred on January 19, 1871 near Lawrence, Kansas, with MM Intensity III or possibly IV. The felt reports for these events are listed in Appendix I.
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Kansas Geological Survey, Geophysics
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