Ancient Earthquakes Leave Tracks From Kentucky To New York

Professor Carlton Brett, graduate students Patrick McLaughlin and Sean Cornell, and undergraduate Alan Turner will present their findings Tuesday, Nov. 14 during the annual meeting of the Geological Society of America in Reno.

While a faculty member at the University of Rochester, Brett spent many years studying rock beds of same age (about 450 million years old) in the Mohawk Valley of New York, include highly deformed sediments. After joining the UC faculty, he and his students began examining the Ordovician deposits of southwest Ohio and northern Kentucky. The patterns of deformation were surprisingly similar.

"One of the interesting things is the widespread distribution of these deformed beds," said Brett. "We see the same kinds of folding and fracturing from Frankfort to Lexington and northeastward to Augusta and Maysville" in Kentucky. The formations can also be found across the Ohio River near Moscow and New Richmond, Ohio.

"We're seeing these patterns in an area that covers at least 50,000 square miles," remarked Brett. "That's an enormous area, and evidence that these were very large earthquakes, probably with a magnitude from 7 to 9 on the Richter Scale."

Meanwhile, similar large quakes were shaking the ground from eastern Virginia through upstate New York. Brett believes the quakes stemmed from the same tectonic forces that created the Taconic mountains in the northeastern United States. The process of mountain-building known as "orogeny" may have activated old faults according to Brett, who emphasized those faults pose virtually no risk today.

"It's intriguing that you see similar effects 700 miles away," said Brett. The common cause? The collision of North America with a volcanic island chain. "Huge blocks of ocean floor sediment were being thrust upon the eastern edge of North America, forming the rising Taconic mountains."

In other aspects of his research, Brett works to understand how large- scale events have impacted life on Earth. Surprisingly, many large regional crises such as the huge earthquakes or widespread volcanic ash burial don't appear to lead to catastrophic extinctions. "Organisms appear to be very resilient to these kinds of events," said Brett.

Brett has found evidence for long periods of stability or near equilibrium in the history of life. He believes it takes a combination of much larger catastrophic events (usually combinations of sea level, climate change and other major crises) to push life out of what he calls "coordinated stasis" into a period of rapid extinction and evolution.

"The common theme seems to be some kind of accelerated change after long periods of little change. And an increased frequency of disturbances may increase the risk that change will occur."