Paper No. 74
Presentation Time: 3:15 AM
SPATIAL ANALYSIS OF SEISMIC ACTIVITY IN THE CENTRAL GREAT PLAINS
Midcontinent seismic activity is not well understood and is understudied in the Central Great Plains. The main purpose of the project was to analyze seismic activity spatially to determine whether it is clustered or if another component of random seismic activity is present. Whether seismicity is related to underlying tectonic structures, regional stresses or oil production is also of interest to this project. Earthquake data were collected from multiple sources including the IRIS database and records in the literature of historic earthquakes found in Kansas, Nebraska and South Dakota (Steeples et. al 1988; Steeples et al 1990; Chadima 1992; Burchett 1979). A total of 655 earthquakes was assembled and plotted using ArcGIS to assess if this seismic activity is random or clustered. The Point Density function was used in ArcGIS; which simply calculates the density of how many points fall around any other given point in a given radius (about 1 ft). Clusters are seen with the naked eye, and the densest clusters seen in SW Nebraska and Northern Kansas are likely associated with water injection used in oil production. Some other clusters are seen in the data and are likely associated with underlying structures. Examples include Central Nebraska, NE Kansas, SE Nebraska and Toadstool Geological Park, NE. While about 70% of the seismicity was associated with a cluster, the other 30% of the seismicity was not.
An anisotropy analysis was also done with the data to determine possible orientations of active faults. Six center-points that were picked and used for localized anisotropy analysis were located in the following localities: Sleepy Hollow Oil Field in SW Nebraska, Central Nebraska, SE Nebraska, Toadstool Geological Park, NE, Central South Dakota, and NE Kansas. The size of the area covered for each anisotropy analysis was a 1 km radius around each center point. Common orientations of 10° and 70° were observed in all locations where the anisotropy analysis was done, except in the area of Toadstool Geological Park in NW Nebraska. The preferred orientations of other locations (SE, SW, and Central Nebraska and northern Kansas) are consistent with regional stresses and/or underlying structural features.