SUBSURFACE MODELING IN THE VICINITY OF THE EASTERN TENNESSEE SEISMIC ZONE USING AEROMAGNETIC, GRAVITY AND SEISMIC DATA

A seismotectonic model for the active eastern Tennessee seismic zone (ETSZ) is developed using a combination of aeromagnetic, gravity and seismic data. Possible extension of the model to the northeast is explored using potential field data alone. The ETSZ trends NE-SW for about 300 km and displays remarkable correlation with the prominent New York – Alabama (NY-AL) aeromagnetic lineament. Velocity models for the crust derived from a local ETSZ earthquake tomography study reveal the presence of basement structure that correlates with the NY-AL aeromagnetic lineament and associated Bouguer gravity lows. Specifically, a narrow, NE-SW trending, steeply dipping zone of low velocities that extends to a depth of at least 24 km is associated with the vertical projection of the NY-AL aeromagnetic lineament. The low velocity zone is interpreted as a major basement fault that that accommodated left-lateral, transpressive motion of the Amazon craton during the Grenville orogeny. This interpretation is in agreement with recent isotopic geochemical studies and paleomagnetic reconstructions for Rodinia. Relocated ETSZ hypocenters align in near-vertical segments suggesting reactivation of a distributed zone of deformation associated with a major strike-slip fault. This interpretation is supported by an expanded set of focal mechanism solutions and shear wave splitting results. The recent Mw 4.2 Perry County eastern Kentucky earthquake occurred north of the ETSZ but has a focal depth and mechanism that are similar to those for ETSZ earthquakes. We investigate the possibility that the proposed ancient shear zone extends into eastern Kentucky using Bouguer and aeromagnetic maps.