TYING THE EASTERN TENNESSEE SEIMIC ZONE INTO A REGIONAL TECTONIC SETTING USING AMBIENT NOISE TOMOGRAPHY AND RECEIVER FUNCTIONS

Rayleigh wave group velocity maps over the period range of 5 - 30s for Eastern North America are determined using ambient noise tomography. Seismic ambient noise is dominated by microseismic surface waves created on the continental shelf of North America. These Rayleigh waves can be extracted by cross correlating and stacking long duration time windows of seismic data. Resulting two-station path values are combined using a generalized inverse tomography to produce a map of group velocity variation across the central and eastern US. Tomographic results for shorter periods, less than 15 seconds, show strong spatial correlation with many known geological features. The Mississippi Embayment, the coastal plains and the Appalachian Basin all have relatively low group velocities while features such as the Nashville Dome, Ozark Uplift and areas of Central Virginia show high group velocities. The eastern Tennessee seismic zone (ETSZ) is located in a transition zone separating high and low velocities for not only the shorter group velocity maps, but also the longer period group velocities. We also calculate receiver functions for Transportable Array stations in and around the ETSZ and show a thick crust under the Valley and Ridge Providence of 47 - 52 km. Thickness decreases to 30 - 35 km moving to the SE under the Blue Ridge and Piedmont Providences. These observations support the notion that the ETSZ lies along a major crustal boundary in crust that was not thinned appreciably by Iapetan rifting.