Geology professors in high demand after earthquake

seismogram

The most popular people on campus last week had to be the geologists.

After the Feb. 10 earthquake that startled thousands of people awake across the region, just about everyone – including the media – wanted the expert opinions of the NIU professors who study quakes and man the seismic center in Davis Hall.

Geology professors Paul Stoddard and Philip Carpenter fielded calls from such media as the Chicago Tribune, the Daily Herald, the Christian Science Monitor and Chicago Public Radio.

The earthquake, with a magnitude of 3.8 on the Richter Scale, was centered about 8 miles east of Sycamore, near Lily Lake. Because the epicenter was so close to NIU, many faculty, staff and students not only felt the quake but also heard an accompanying boom.

“An earthquake generates sound waves in rock that are released when they reach the surface,” Stoddard explains.

He also says we can probably blame the glaciers that once covered northern Illinois for our recent earth-moving experience.

Paul Stoddard
“In this area, earthquakes are most likely due to glacial rebound,” Stoddard says. “The surface of earth was depressed by the presence of glaciers. When they retreated, the surface began to rebound to its original position. That’s still occurring today. As this happens, there are occasional adjustments in the rock.”

Both Stoddard and his colleague Carpenter used the quake as teaching moments in their classrooms during the days that followed.

The night before the earthquake struck, Carpenter had actually been writing an Undergraduate Research Apprenticeship Program proposal to study natural ground vibrations to identify the locations of active northern Illinois geologic faults, which are largely a mystery.

Of course, he received a jolt of inspiration the following morning.

“I heard a booming sound followed by shaking, like you’d feel from an explosion, that lasted 10 seconds or so,” Carpenter says.

Scientists now know there must be a fault at the epicenter site near Lily Lake. NIU is submitting its data to the U.S. Geological Survey to help constrain the epicenter location.
Phil Carpenter

“No one knew there was a fault there,” Carpenter says, adding that he’s revising his URAP proposal to study the Feb. 10 event.

Carpenter says there have been two other mild quakes centered in northern Illinois in the last two decades, but they were in other locations. One was centered near Amboy and the other in LaSalle County.

“No faults have been mapped for the three earthquakes in the last 20 years,” he says. “We want to pinpoint the locations.”

In addition to studying natural ground vibrations, scientists also could use portable seismometers that can detect tremors that can’t be felt by people, Carpenter says.

He adds that there are two major identified faults in northern Illinois – the Sandwich fault and the Plum River fault – but both have been inactive for the last 150 years.

The Sandwich fault runs through Sandwich and extends to Oregon, and the Plum River fault runs from the Savanna area toward Byron. Scientists have visibly identified fracture zones for those faults in outcrops, quarries and wells, Carpenter says.

by Tom Parisi

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