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Fault Reactivation Potential in Intraplate North America, From Major Seismic Zones to 3D Gravity Imaging of the Sparta, Nc Epicentral Zone

Description: 

The crustal stress field varies across eastern North America, controlling which of the many orientations of inherited faults may reactivate in future damaging earthquakes. Aftershocks, too, preferentially occur on pre-stressed faults, such that comparatively small coseismic and post-seismic perturbations trigger slip. This study introduces new maps of fault slip potential across much of the eastern United States. Stress inversions are used to map geomechanically favorable fault orientations and disambiguate focal plane orientations at several scales. For instance, oblique extension in the Eastern Tennessee Seismic Zone is accommodated mainly by faults striking between N20E and N85E (and diametric), perhaps without slip on planes in the NW or SE quadrants. In the New Madrid Seismic Zone, significant differences in stress favor strike-slip in the vicinity of the Axial/Cottonwood Grove Fault and reverse motion around the Reelfoot Thrust, independent of the existence of those specific structures. Differences between the southern and northern halves of the Reelfoot Thrust may influence multi-segment rupture propagation onto the adjacent Axial, Risco, and New Madrid North Faults. Finally, the 2020 Mw5.1 Sparta, NC earthquake provided an unprecedented opportunity to examine the reactivation of multiple generations and orientations of inherited faults. Regional gravity data illuminate the structural controls on the exceptionally shallow (~ 1 km) mainshock/aftershock zone. Results will be presented from a microGal-precision, locally decameter-resolution terrestrial gravity survey and associated 3D modeling of the mainshock/aftershock fault network. These findings will add to the growing dataset of reactivated fault orientations that both demonstrate that the stress field across the eastern United States is not uniform, and that there is enough information now available to begin prospectively mapping potentially active fabrics.

Session: Tectonics and Seismicity of Stable Continental Interiors

Type: Oral

Date: 4/19/2023

Presentation Time: 02:15 PM (local time)

Presenting Author: Will Levandowski

Student Presenter: No

Invited Presentation: 

Authors