Group velocity tomography of the upper crust in the eastern Tennessee seismic zone from ambient noise data

Abstract

The eastern Tennessee seismic zone (ETSZ) is the second most seismically active area in the central and eastern United States after the New Madrid seismic zone, but the relatively weak seismicity and the absence of correlation between the seismicity distribution and the surface geology make its seismogenic potential controversial. In this work we investigate the structure of the upper crust in the ETSZ by means of group velocity tomography maps from seismic noise data. Results show that the seismic activity is associated with a relatively low velocity anomaly mainly located in one or more basement blocks. These blocks, bounded to the NW by the NY–AL lineament and to the SE by the Clingman lineaments, are buried beneath low velocity strata consistent with the presence of a relatively thick sedimentary cover. The imaged low velocity anomaly migrates towards the SE at increasing periods, suggesting a possible SE dipping weak structure where most of the seismic activity takes place.The correlation between the NY–AL magnetic signature and the position of the seismic velocity anomalies supports the interpretation of the low velocity zone as a major basement fault projected to the surface as the NY–AL magnetic lineaments. The fault juxtaposes Granite–Rhyolite basement to the NW with Grenville southern Appalachian basement to the SE.