A statistical analysis of earthquake focal mechanisms and epicenter locations in the eastern Tennessee seismic zone

Abstract

Abstract The location and orientation of possible seismogenic basement faults in the eastern Tennessee seismic zone is studied using information provided by focal mechanisms and the location of earthquake epicenters. Twenty-six well-constrained focal mechanism solutions are derived using a new velocity model and relocated hypocenters. The results suggest that strike-slip motion on steeply dipping planes is the dominant mode of faulting throughout the 300-km-long seismic zone. Most of the mechanisms can be grouped into two populations. The larger population is characterized by steeply dipping N-S- and E-W-striking nodal planes with right-lateral and left-lateral slip, respectively. The second population differs from the first by an approximate 45° eastward rotation about the B axis. An analysis of the distribution of azimuths between epicenters was conducted. The frequency distribution of interevent azimuths shows significant clustering in the northeasterly and easterly directions, for interevent epicentral distances less than 30 km. Those directions represent the most often observed nodal plane orientations and are interpreted as the dominant strike directions of seismogenic basement faults. The locations of potential faults are inferred on the basis of statistically significant alignments of juxtaposed epicenters and correlation with focal mechanisms. The results suggest a series of northeast-trending, en-echelon basement faults, intersected by several east-trending faults. Most of the larger magnitude, instrumentally located, earthquakes in the seismic zone occurred in proximity to the statistically identified potential faults.