Fault Orientation in the Eastern Tennessee Seismic Zone: A Study Using the Double-Difference Earthquake Location Algorithm

Abstract

We use the double-difference earthquake location algorithm to relocate approximately 1,000 earthquakes in the eastern Tennessee seismic zone (ETSZ). We examine the earthquake hypocenter relocations in an effort to resolve fault orientations and thereby gain insights into the tectonics of the seismic zone. The analysis involves visual comparison of three-dimensional perspective plots of the hypocenter relocations oriented accord ing to focal mechanism nodal planes derived from events within several clusters of earthquakes. Relocations in the central, most seismically active, portion of the ETSZ indicate a diffuse west-striking, north-dipping zone of hypocenters. The orientation of this zone of hypocen ters is consistent with structure imaged by a previous seismic reflection profile that shows a reflective mid-to-upper crust with apparent dips of approximately 35° to the north. Relocation of a smaller cluster of earthquakes near the Tennessee-North Carolina border suggests a steeply dipping northwest trending fault in that area.