A thin mechanical pen, heat-sensitive paper and a small box detecting the earth’s slightest tremors make up the NIU seismograph, on public display in the lobby of Davis Hall.

Associate geology professor Phillip Carpenter has studied the instrument daily since he brought it with him to NIU 15 years ago.

“I like to think of it as the monitor of the earth’s heartbeat,” Carpenter said.

A seismograph expert, Carpenter has kept the machine, which he maintains himself, constantly running since 1986. He uses it to illustrate earth activity to his classes.

“When I show seismographic records to my students, it gives them an idea of the variations in the earth’s regular movements,” Carpenter said. “The earth shakes a little every day from various building repairs and trains passing by, and although these are not natural fault zone movements, the seismograph still records it.”

On display with the seismograph are previous records illustrating what was felt at NIU during earthquakes all over the world. For accuracy and a complete record of the earth’s movements, the seismograph is backed up by a machine that records second-to-second changes on cassette.

“The back-up digital recorder has been very important when the machine broke down or had any complications,” Carpenter said. “This record is important because it will eventually help predict the earth’s future movements.”

Carpenter brought NIU’s seismograph from his previous studies in Los Alamos, N.M., where he used seismology to determine if the Soviet Union was

conducting underground nuclear weapons testing.

“Previous to 1960, seismology stations received very little funding,” he said. “But after it was discovered that it could be used to act as a spy on other

countries, it grew considerably.”

The most recent earthquake recorded on the seismograph was a Feb. 13 quake in El Salvador that reached 6.6 on the Richter scale exactly one month after a Jan. 13 quake. Combined, the two killed more than 1,200 people.

“Those were very powerful,” Carpenter said. “And although we did not pick up the first one in January, it only took less than six minutes to record the

February quake.”

The stronger the quake, the more distortion is displayed in the normal pattern of the Earth’s movement, Carpenter said.

Earthquake activity in northern Illinois is relatively small, usually ranging from zero to 3.0 on the Richter scale, and can’t be felt, Carpenter said. That’s why there’s only one seismograph station in the state —- the one at NIU.

Carpenter said NIU’s machine was especially useful in September 1999, when it recorded northern Illinois’ 16th earthquake, with a magnitude of 3.5.

“We picked up the 1999 earthquake and it was completely unexpected because the exact reason and source of the quake is unknown,” Carpenter said. “We generally do not expect earthquakes to occur in our state, but we should be cautious, especially residents of southern Illinois.”

According to a 1995 Department of Natural Resources brochure, Illinois’ last damaging earthquake was on June 10, 1987, near Olney in southeast Illinois, and it measured 5.0. It was felt in 16 states and caused damage in Richland and Lawrence counties.

The likelihood for the central United States to see an earthquake with a magnitude of 6.3 or greater in the next 15 years is 40 to 63 percent and 86 to 97 percent within the next 50 years.

That size earthquake would damage mostly older structures and school buildings, and could cause deaths.

“If predictions of future serious earthquakes are true, then the most highly populated areas in the southern Midwest area, like St. Louis, are at the highest risk,” Carpenter said. “I have studied those frequent earthquakes that occur in the southern portion of our state, and the interesting thing is that we do not know exactly where they come from.”

Northern Illinois looks earthquake-free for the near future, but could see activity down the line, Carpenter said.

“Active faults lurk beneath the rolling plains of northern Illinois,” he said. “They have stirred at least 15 times in the past 100 years and now are quietly storing up stress which could soon trigger new earthquakes.”