Strength and Stability of Oklahoma Basement Rock: Preliminary Observations from Experiments at In-situ Conditions
Abstract
The recent M5+ earthquakes occurring in Oklahoma, including the September 3rd, 2016, M5.8 Pawnee earthquake, nucleated at depths well within the igneous basement. These earthquakes have highlighted the fact that the reactivation of basement faults in North-central Oklahoma poses the main source of seismic hazard, even though most wastewater injection, which has been attributed as the cause of the recent activity, occurs in sedimentary sequences. Despite the importance of these igneous basement lithologies, their seismic stability and mechanical properties are essentially unknown. We present preliminary results from rock mechanics tests designed to characterize the seismic potential of Oklahoma basement, including the frictional properties that enhance or suppress seismicity in basement-hosted fault zones. Tested samples were collected from borehole cores, including hydrothermally altered and unaltered cores from wells in Pawnee and Osage counties, as well as outcrop samples from southern Oklahoma. We performed triaxial shear experiments on these samples at temperatures and confining stresses representing a depth range of 1.5 to 7.0 km, the range of most current earthquakes. Our results provide the first characterization of the strength and seismic potential of Oklahoma basement rock and how these properties vary with depth. Our results concerning the velocity dependence of friction and frictional restrengthening allow for the interpretation of coseismic and postseismic slip patterns. Overall, these results provide the mechanical basis for understanding the local seismicity, including depth extent, complexity of slip patterns before and after the main shock, and the post-seismic relaxation of the crust surrounding the M5.8 Pawnee event.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.S44C..06C
- Keywords:
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- 7215 Earthquake source observations;
- SEISMOLOGYDE: 7230 Seismicity and tectonics;
- SEISMOLOGY