© Susan Hough, USGSA model predicted the tsunami wave height from a Jan. 8, 1817, earthquake offshore South Carolina. The earthquake's magnitude was estimated at 7.4 from newspaper accounts.
The study links the tsunami to a known Jan. 8, 1817, earthquake. The temblor shook the East Coast from Virginia south to Georgia, where the seismic waves made the State House bell ring several times.
Based on archival accounts of the 1817 shaking, geologists had gauged the quake's size at magnitude 4.8 to magnitude 6. Now, with new geologic detective work and computer modeling of the tsunami, researchers have considerably revised the earthquake's size. A magnitude-7.4 quake releases almost 8,000 times more energy than a magnitude-4.8 earthquake.
The size and location, or epicenter, of the 1817 earthquake has never been pinned down so closely before. U.S. Geological Survey research geophysicist Susan Hough and her colleagues zeroed in on the source from newly uncovered archival records, looking at where the shaking was strongest.
But they weren't sure about the tsunami link: The 11 a.m. arrival time seemed too late for a 4:30 a.m. earthquake. So they created a computer model of the tsunami, testing different locations and magnitudes. The best fit to force a foot-high (30 centimeters) wave up the mouth of Delaware Bay by about 11 a.m. was a magnitude-7.4 earthquake offshore of South Carolina.
"That was the eureka moment," Hough told LiveScience's OurAmazingPlanet. "Darned if that wave doesn't hit the Delaware River and slow way down."
