Microearthquakes in Kansas and Nebraska 1977–87

Abstract

The Kansas Geological Survey has operated a microearthquake seismograph network since mid-1977. The network now consists of fifteen stations 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 over the past ten years 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.

Source Spectral Properties of Small to Moderate Earthquakes in Southern Kansas

“…Seismicity rates in southern Kansas began to sharply increase in 2013 compared to historical norms (Buchanan, ; Choy et al, ; Hildebrand et al, ), with this increase attributed in part to the proliferation of wastewater injection related to oil and gas production within the Mississippian limestone play that underlies southern Kansas and northern Oklahoma (Buchanan et al, ; Ellsworth, ; Ellsworth et al, ; Weingarten et al, ). The Precambrian basement formation begins at a depth of 1.7 to 2.0 km and is crosscut by numerous in situ fault systems, the most notable of which is the northeast striking Nemaha fault (Baars & Watney, ; McBee, ; Niemi, ; Steeples et al, ).…”

Spatial and Temporal Analysis of Central Great Plains Seismicity

“…The Humboldt Fault Zone has been identified as tectonically active (Crone and Wheeler, 2000) and poses a seismic risk as identified by Figure 1. Some earthquakes of this cluster are associated with faults associated with or bounding the Nemaha Ridge (Hildebrand et al, 1988). The small cluster to the west that branches from this cluster on Figure 8 and 8b is thought to be caused by faults bounding the MGA, as it is 100 km west of the Nemaha Ridge (Hildebrand et al 1988).…”

“…Some earthquakes of this cluster are associated with faults associated with or bounding the Nemaha Ridge (Hildebrand et al, 1988). The small cluster to the west that branches from this cluster on Figure 8 and 8b is thought to be caused by faults bounding the MGA, as it is 100 km west of the Nemaha Ridge (Hildebrand et al 1988). The weighted kernel density map of earthquakes can skew clusters towards higher magnitude earthquakes which can cause a potential risk area to be less obvious.…”

“…Cluster NE2 is anomalous in that there is no named geologic structure associated with it. Hildebrand et al (1988) mention a pair of normal faults on the USGS/AAPG tectonic map that are coincident with the cluster's trend of northeast-southwest. Korth (2013) conducted an anisotropy analysis on this cluster and also obtained a northeast-southwest trend at 60°.…”

“…Korth (2013) conducted an anisotropy analysis on this cluster and also obtained a northeast-southwest trend at 60°. Hildebrand et al (1988) comments on the almost right angle this trend creates where it intersects the Central Kansas Uplift and notes a concentration of seismicity at this location, which is cluster NE1, near the Sleepy Hollow oil field, on the kernel density maps. Cluster NE2 is blanketed by a PGA of 4-6 %g (Figure 1).…”