THE MW 4.2 PERRY COUNTY EARTHQUAKE OF 10 NOVEMBER 2012: EVIDENCE OF THE EASTERN TENNESSEE SEISMIC ZONE IN SOUTHEASTERN KENTUCKY

The 10 November 2012 M_w 4.2 Perry County, Kentucky, earthquake provides evidence that the active Eastern Tennessee Seismic Zone (ETSZ) continues farther north than previously recognized. This earthquake was well recorded by regional networks and the Transportable Array component of the EarthScope project, which permitted precise determination of the source parameters and the detection of aftershocks. We found that the mainshock’s focal depth and mechanism – both in terms of the style of faulting and in the strike of the steeply-dipping nodal planes – are consistent with seismicity to the southwest, more central to the ETSZ. In addition, we observed a continuation in the distribution of hypocenters from northeastern Tennessee into the vicinity of the Perry County earthquake. These observations suggest that the same causal geologic structures extant in the more-active ETSZ to the southwest continue into southeastern Kentucky.

There is a well-documented spatial correlation between the ETSZ seismicity and the New York-Alabama Magnetic Lineament (NYAL): the majority of seismicity occurs to the southeast and proximal to the lineament. Guided by patterns of hypocenter locations and the location of the NYAL, we subdivided ETSZ seismicity into four subzones. In contrast to seismicity in subzones to the southwest, in the northeastern-most subzone (northeastern Tennessee and southeastern Kentucky), earthquakes are more diffuse and tend to occur to the northwest of the NYAL, including the Perry County event and all other light-class (magnitude 3.9 and greater) earthquakes. Though diffuse, seismicity in this and the adjacent subzone to the southwest (where most seismicity occurs), is largely bounded to the west by a crustal body evidenced by a high-seismic-velocity anomaly in northern Tennessee and prominent potential-fields anomalies, commonly associated with the East-Continent Gravity High.