MIDCONTINENT RIFT STRUCTURES IN SE NEBRASKA

During the Mesoproterozoic, about 1.1 billion years ago, the North American continent began to break apart along a zone that runs from Oklahoma to northern Michigan and back down to Alabama. This Midcontinent Rift (MCR) failed leaving behind a 2000 km long swath of volcanic rocks. Although these volcanic rocks have been covered by younger sedimentary strata along the southern portion of the rift, the high density and magnetism of the igneous rocks produces a distinct gravity and magnetic signature that allows us to trace the rift zone in areas where it is not visible at the surface. Due to the nature of the MCR, many ancient faults exist in the subsurface. In our study area, the MCR’s trend is northeast to southwest, passing through the major metropolitan areas of Omaha and Lincoln, NE. Reactivation of these faults can lead to increased seismic hazards in these regions; however, the location of many of these faults is not well understood.

The goal of this project is to map the subsurface structures in southeast Nebraska. We use existing gravity and magnetic maps along with limited core, seismic and earthquake data to better constrain the locations and orientations of existing structures and map unknown faults. 2D subsurface models across the MCR, built using Geosoft’s Oasis Montaj program, can further validate our interpretation. Such results have implications for understanding seismic hazard and risk in intracratonic regions that remain subject to potentially damaging earthquake activity.