BOB HIRSHON (host):
The ghosts of earthquakes past…I’m Bob Hirshon and this is Science Update.
The Midwest is better known for tornadoes than for earthquakes. But between 1811 and 1812, huge earthquakes struck there, along the New Madrid fault. And now scientists have found that aftershocks from those quakes are still rumbling today. This according to Northwestern University seismologist Seth Stein.
SETH STEIN (Northwestern University):
We thought, that’s strange, because in places like the San Andreas fault, aftershocks go on for 10 years, so why should these go on for 200 years?
He says the answer probably lies in the physical differences between the two fault lines. California’s famous San Andreas rests atop a fast-moving boundary between two tectonic plates, whereas the New Madrid fault is located on the slow moving interior of a plate. He says this difference results in aftershocks that last much longer in the Midwest. I’m Bob Hirshon, for AAAS, the science society.