New assessment of the Eastern Tennessee seismic zone

Abstract

A new interpretation of why the Eastern Tennessee seismic zone exists is presented based on updated three-dimensional P- and S-wave velocity models and hypocenter relocations. The expanded dataset covers the years 1984 through 2021 and contains 1657 earthquakes and 29,914 arrival times recorded by 119 stations. The new velocity models extend farther west and south than models determined in a previous tomographic study using a smaller dataset. The new inversion provides better resolution of major anomalous features, including a low-velocity zone that parallels the New York–Alabama (NY-AL) magnetic lineament. The low-velocity zone was interpreted in previous studies as part of a major continental transform fault active during the Grenville orogeny. Most Eastern Tennessee seismic zone earthquakes occur in a wedge-shaped area characterized by low magnetic anomalies. The wedge may have formed due to the presence of a releasing bend in the major continental transform fault. We suggest that metasediments are a major constituent of the wedge and facilitate the occurrence of small earthquakes along numerous faults and layer boundaries. Most of the earthquake activity is scattered according to a cluster analysis, but two linear bands of activity are found that may be indicative of more coherent fault planes. The bands trend roughly east-west and northwest-southeast. The tomographic results and distribution of seismicity with depth suggest that seismicity southeast of the NY-AL lineament in Tennessee is driven by near-lithostatic pore pressures in rocks in the releasing bend basin.

Publication Title

Laurentian Tectonics: A Celebration of the Life and Career of William A. Thomas

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