The upper crust of the Eastern Tennessee Seismic Zone: Insights from potential fields inversion

Abstract

The study investigates the crustal structure of the eastern Tennessee seismic zone (ETSZ) by means of potential field inversion through the located Euler deconvolution method. Inversion of magnetic field data shows that the top of the magnetic basement ranges between 6 and 12 km depth in the Valley and Ridge physiographic province while it is shallower (less than 2 km depth) and locally outcropping in the Blue Ridge and Cumberland Plateau provinces. The estimated depth to the top of the magnetic basement is in general agreement with existing sedimentary cover maps of the broad study area. The inversion of gravity data is much more ambiguous, pointing to a generally deeper source, than magnetic data inversion. The findings support the interpretation of ETSZ seismicity as originating in basement structures not related to Appalachian orogeny and likely dating to Grenville age.

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

“…We thus link this low velocity to the sedimentary cover of the Valley and Ridge province. Higher velocities (3-3.2 km/s) are found to the east, across the Blue Ridge, where outcrops of crystalline rocks are well documented [Schedl et al, 1997] and sedimentary rock thickness obtained from magnetic data inversion is less than 2 km [Brandmayr and Vlahovic, 2016]. A localized high velocity anomaly (3-3.2 km/s; Fig.…”

“…The rocks compose of the strongly folded sedimentary cover beneath the Valley and Ridge province and beneath the ETSZ in particular. Thickness of the sediments overlaying the basement has been recently estimated by means of magnetic data inversion and ranges from 4 to 12 km, [Brandmayr and Vlahovic, 2016] thus locally thicker than previous results [Laske and Masters, 1997;Mooney and Kaban, 2010].…”

“…Seismicity in the ETSZ is mainly clustered along the NE-SW trending NY-AL magnetic lineament, a prominent magnetic anomaly which source lies in the bedrock beneath average 7-8 km thick sediments (Fig. S2), in the Valley and Ridge province [Brandmayr and Vlahovic, 2016]. Most of the hypocenters range from 8 to 15 km [Vlahovic et al, 1998], thus they are located in the upper part of the crystalline crust that is sampled by the longest periods presented in this study.…”

“…We tend to exclude that it represents the sedimentary cover (Fig. S2), which is < 2 km in this area [Brandmayr and Vlahovic, 2016]. This area of complex geologic features likely hosts terrains accreted during the Iapetus subduction and rich in metasedimentary rocks [Graw et al, 2015].…”

“…The Cumberland Plateau, which lies west of the Valley and Ridge, is widely agreed to represent the boundary between the stable North American craton and the continental margin, roughly marking the western Grenville deformation front [Thomas, 1982;Tesauro et al, 2015]. The location of the Grenville front to the east and the westward extension of the Appalachians terrains at depth still remains uncertain but basement rocks beneath the ETSZ are presumed to be of Grenville age [Powell et al, 2014 and references therein;Brandmayr and Vlahovic, 2016].…”