Lithologic Controls on Focused Erosion and Intraplate Earthquakes in the Eastern Tennessee Seismic Zone

• Published in: Geophysical research letters Vol. 45; no. 18; pp. 9569 - 9578
• Main Authors: Gallen, Sean F., Thigpen, J. Ryan
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.09.2018
• Subjects: Appalachians; Drainage basins; Earthquakes; erodibility; Erosion; Erosion control; Evolution; Fault lines; Geological hazards; Geomorphology; Hazard assessment; intraplate earthquake; landscape evolution; Miocene; Modelling; Paleozoic; Plate boundaries; Regional analysis; Rocks; Seismic activity; Seismic hazard; Seismic zones; Seismicity; stress; Stresses; United States > US; Tennessee
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2018GL079157

We present a new geomorphic model for the intraplate eastern Tennessee seismic zone (ETSZ). Previous studies document that the Upper Tennessee drainage basin is in a transient state of adjustment to ~150 m of base level fall that occurred in the Late Miocene. Using quantitative geomorphology, we demonstrate that base level fall resulted in the erosion of ~3,500 km3 of highly erodibility rock in an ~70 km wide by ~350‐km‐long corridor in the Paleozoic fold‐thrust belt above the ETSZ. Models of modern incision rates show a NE‐SW trending swath of elevated erosion ~30 km southeast of the center of the ETSZ. Stress modeling shows that lithologically focused erosion has affected fault clamping stress on preexisting, favorably oriented faults. We argue that the lithologically controlled transient erosional response to base level fall in the Upper Tennessee basin has given rise to and is sustaining earthquake activity in the ETSZ. Plain Language Summary There is currently no adequate theory to explain earthquakes that occur far from plate boundaries, known as intraplate earthquakes, yet they represent a relevant seismic hazard to heavily populated regions like the central and eastern United States. Intraplate earthquakes are often observed in discrete zones defined by low levels of background seismicity and sometimes large, destructive, historical earthquakes. Deriving new models and methodologies for understanding the mechanisms driving intraplate seismicity will improve regional earthquake hazard assessments. Here we present a new model for the eastern Tennessee seismic zone (ETSZ), the second most seismically active region in the central and eastern United States. We model the history of landscape evolution above the ETSZ and show that a zone of weak rocks allowed for focused erosion above the seismic zone. Using stress models, we demonstrate that this erosion was sufficient to unclamp preexisting faults, allowing them to reactivate in the regional stress field. This new model for the ETSZ and the methodology described can be applied to better understand intraplate earthquakes in the central and eastern United States as well as other intraplate settings globally. Key Points Approximately ~3,500 km3 of rock has been eroded from an ~70 by 350‐km corridor of erodible rock units in the Upper Tennessee River basin The zone of preferential erosion lies directly above the intraplate eastern Tennessee seismic zone Modeling indicates focused erosion perturbed local crustal stress allowing pre existing structures to slip in the regional stress field