9-9 Finding Faults in the Midcontinent? Pairing Legacy Data with Modern Topographic Analysis to Locate and Describe the Eureka-House Springs and Cap au Gres Structures

Session: Advances in Geologic Mapping, Databases, and Dissemination: Student Posters

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Abstract:

The Midcontinent region of the United States is part of North America's relatively stable cratonic platform. While the region has not undergone orogeny for over a billion years, it has been subjected to Phanerozoic tectonic and epeirogenic activity. This has resulted in discrete fault-and-fold zones in the shallow crust as well as the formation domes and basins. Recent seismic interpretations indicate that some structures throughout the Midcontinent, most notably the Ste. Genevieve Fault Zone (SGFZ) of Missouri, are much more seismically active than previously interpreted. Previous literature and recently located earthquakes indicate that there are more structures to the north of the SGFZ. Due to the proximity of the recently discovered earthquakes to St. Louis, a city not typically concerned with seismicity, it paramount to locate and understand the orientation and kinematics of the surrounding structures. Unfortunately, there is little exposure and significant ground cover, making it difficult to pinpoint the existence, location, and offset along these structures. However, recent research has shown that some topographic features correlate with previously mapped faults in the region, demonstrating the validity of using topographic analysis for fault mapping. Here we focus on two relatively understudied locations, the Eureka-House Springs Structure (EHSS) to the southwest of St. Louis, and the Cap au Gres Structure (CGS) to the northwest. We couple topographic data with new subsurface maps (created from well logs) to refine the location of previously mapped structures and examine whether this technique can help locate unmapped structures. Our preliminary results emphasize that: (1) there are seismically active structures to the north of the SGFZ in close proximity to St. Louis; (2) the location of some of the structures to the north of the SGFZ, most notably the EHSS, coincides with topographic features; (3) sub-surface maps can help locate unmapped faults and understanding the kinematics of some structures; and (4) the faults in the region likely have a long-lived and complicated history, with some faults showing transpressional and transtensional components of movement. These structures (and associated topographic features) are also (sub)parallel and close in proximity to the SGFZ implying their formation is likely coincident.

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