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July 11, 2002

Purdue scientists seek aftershocks of June 18 earthquake

WEST LAFAYETTE, Ind. – The earthquake that shook much of Indiana on June 18 did little damage, but Purdue scientists are looking for aftershocks to find out if a bigger quake might be on its way.

Jennifer Haase and Robert Nowack, both researchers in Purdue’s Earth and Atmospheric Sciences department, have laid out a network of seismometers across southern Indiana, in collaboration with Indiana University in Bloomington. Local residents have donated space in their own backyards and electricity for the instruments, which could help the scientists learn about the largely unexplored fault structures north of the Ohio River valley. A better picture of these faults – fractures in the earth’s crust – could improve scientists’ ability to predict future quakes.

"Earthquakes usually happen along fault lines, but we don’t know much about the faults in southern Indiana," Haase said. "In California, many faults are in plain view, so it’s easier to predict where quakes might happen. Around here, faults are covered by sediment, and they don’t rupture often enough to change the landscape signficantly, which makes them tougher to study."

Indiana is not as well known for earthquakes as California, but there were three quakes in 1811-12 in New Madrid, Mo., each estimated to have been between 7.0 to 7.4 on the Richter Scale. They were widely felt in Indiana as well as a large region of the Midwest. Moderate quakes, such as the 5.0-magnitude temblor Indiana experienced last month, are not typically damaging. However, knowing the location of the faults that caused it will help Indiana prepare for a stronger quake in the future.

"The seismometers will help us pinpoint the epicenters of any aftershocks that might occur and measure how strong the shaking is," Haase said. "The data will be used to predict how much shaking different regions might feel if a larger quake were to occur. For example, more damage typically occurs in loose, sandy soils than on harder rock."

Haase said the monitoring efforts would continue for about a month after the initial quake because the probability for aftershocks dies off rapidly for moderate magnitude earthquakes. But she said the data they collect could be of great potential value.

"We are very grateful for the enthusiastic support we have received from the five households that have granted access to their property for this research," Haase said. "In the event of an aftershock, we should be able to triangulate its position and determine its effect on different soils thanks to their help."

The seismographs will provide data that has never been available before in this part of the country and should shed light on earthquake hazard levels that were previously unknown.

Writer: Chad Boutin, (765) 494-2081; cboutin@purdue.edu

Sources: Jennifer Haase, (765) 494-1643, jhaase@purdue.edu

Robert Nowack, (765) 494-5978, nowack@purdue.edu

Purdue News Service: (765) 494-2096; purduenews@purdue.edu


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