Science Alliance Annual Report
2008–2009
UT-ORNL Distinguished Scientists
UTK earth and planetary sciences
Robert Hatcher
Structural geology and tectonics of continental crust
Continental crust forms when new material is added to older pieces of crust through buildup of oceanic and continental volcanic arcs, such as the Aleutians and the Andes, and when colliding continents separate and leave fragments behind. Both processes produce mountain chains, which then erode as the new continental crust evolves into part of the stable continental land mass. Confirmation of this process resides in the ancient interiors of continents—“shields”—made up of the roots of ancient mountain chains that have been added to the continents over billions of years.
This process is reasonably well understood, as are those that produce earthquakes and volcanic activity at crustal boundaries where plates are destroyed (as off the coast of Washington and Oregon) or formed (as along the Mid-Atlantic Ridge). Bob Hatcher, a structural and tectonics geologist who studies the processes that generate and change the Earth’s continental crust, has long been fascinated by one of the great unsolved mysteries in crustal tectonics: Why do major earthquakes occur in the “stable” interiors of continents?
Historically, large earthquakes have occurred in the southeastern United States—in the Mississippi Valley (1811–1812; New Madrid seismic zone: magnitude 3; 7½ to 8 quakes in 3 months) and near Charleston, South Carolina (1886; magnitude 7). Neotechtonic studies have shown that major earthquakes recur about every 400 to 600 years in the New Madrid and about every 600 years in Charleston. Understanding this phenomenon has a direct bearing on the stability of the infrastructure of our civilization.
The East Tennessee seismic zone (ETSZ), which extends from just north of Knoxville southward into northwestern Georgia and northeastern Alabama, is the second most active in the eastern U.S. behind the New Madrid seismic zone. The U.S. Geological Survey has estimated the ETSZ is capable of producing a magnitude 7.5 earthquake. But because no earthquakes of a magnitude greater than 5 have been recorded, little incentive has existed to conduct prehistoric studies that detail maximum magnitude or frequency.
In 2009, Hatcher and others received funds from the Nuclear Regulatory Commission to conduct a neotectonics study of the ETSZ.
Primarily a field study, the team is especially interested in finding layers of sandy material overlain by nearly impermeable clay; where the sand could be saturated with water and, during an earthquake, rupture through the clay layer, spreading light-colored “sand blows” onto the surface. Many similar features have been recognized in west Tennessee and in the Charleston area.