EAST TENNESSEE GEOLOGICAL SOCIETY
SEPTEMBER 2012


Monday, September 10, 2012
6:00 - 7:30 pm

Pellissippi State Technical Community College
10915 Hardin Valley Road, Knoxville
J.L Goins Administration Building
New Location--- Faculty/Staff Dining Room Room (Beside Cafeteria)

SEPTEMBER PRESENTATION

New Data Providing Additional Paleoseismic Evidence for
Large, Prehistoric Earthquakes in the
East Tennessee Seismic Zone

Presented and Authored By
Robert D. Hatcher, Jr
.
UT Distinguished Scientist and Professor
Tectonics and Structural Geology
Department of Earth and Planetary Sciences
and Science Alliance Center of Excellence
Knoxville, Tennessee

Co-Authors
James Vaughn, MO Geological Survey, Retired
Randel Cox, University of Memphis
Stephen Obermeier, USGS Emeritus
Ron Counts, KY Geological Survey
Kathleen Warrell, UT Graduate Student

Abstract

The East Tennessee seismic zone (ETSZ) is the second most active in the central and eastern US, but it has no recorded history of M > 4.8 earthquakes. Faults producing these earthquakes are sourced in the autochthonous basement and are thought to have no direct surface expression. Paleoseismic features have been mapped and trenched at multiple sites in the ETSZ. Additional sites of possible paleoseismic features, some of which reside beneath reservoirs today, have been identified in 1930s- to 1950s-vintage aerial photographs. Work to date has found evidence for several M>6.5 earthquakes in the French Broad River valley ~50 km E of Knoxville. Several thrust and strike-slip faults cut Quaternary alluvium with 25 cm to ~1 m of displacement have been identified along Douglas Lake near Dandridge, TN. A 30 cm-wide Quaternary sediment-filled fissure in Ordovician Sevier Shale has been traced for over 2 km. It is offset ~1 m by a fault that thrust Ordovician shale over Quaternary river terrace sediments on the N shore of Douglas Lake. Areas of shale chips in similar river terrace sediment have also been identified; these chips may have boiled up from underlying weathered Ordovician Sevier Shale during paleoseismic events. X-ray diffraction (XRD) analyses matched the mineralogy of the shale chips and underlying Ordovician shale. Vintage aerial photos of flood plains along the Tennessee River in E TN and NE AL, and along the Chattooga River in NW GA, reveal circular to elliptical features in river terrace sediment that may be related to liquefaction. Reconnaissance along a segment of the Chattooga River has discovered possible seismogenic sand dikes. Grain-size analyses of sand dikes, source bed, and host bed sediments confirm that the sediments fall in the size range of liquefiable sediments, and that the host is finer grained than the sand dikes or source bed. XRD analyses reveal that the sand dikes and source bed have nearly identical mineralogy, but the host contains more clays. These analyses indicate the source bed is the parent material of the sand dikes. Together, these data support the capability of the ETSZ to produce M > 6.5 earthquakes, which increases the earthquake hazard potential in the southeastern U.S.


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