June 17, 1993
Morris Tribune

Likely epicenter near Collis

Collis, an unincorporated village in Tara Township of Traverse County, about 25 miles northwest of Morris, is probably close to the epicenter of the June 4 earthquake.

Val Chandler of the Minnesota Geological Survey said in a news conference Tuessday morning in Graceville, that estimates of the epicenter are now in the area four miles north of Graceville, and one mile east of Collis.

He explained that the epicenter of an earthquake is the spot on the surface of the earth directly above the rupture, or slippage along the fault. There probably is no surface expression of the quake's epicenter, he said.

The first estimates after the earthquake had put the epicenter about five miles east of Dumont. Then, Chandler said, the estimate was revised to a mile north of Graceville.

Chandler said a team of the University of Minnesota students are in the Graceville area to interview people about what they observed during the quake. He said they hope to be able to locate the epicenter through those interviews, and also relate what they find out to what is already known about the geology along the fault zone.

A similar project could be coming out of UMM. Peter Whelan, assistant professor of geology at UMM, said he is seeking funding to start a research program that would look at and compare the 1975 and 1993 earthquakes, a supplement to the work Chandler is doing. While Chandler's teams are concentrating their efforts in the Collis and Graceville areas, Whelan said he would begin in Morris and then expand into other areas. His study could be part of a geology in Minnesota class at UMM.

How quakes are measured

Chandler said Tuesday, that the nearest seismograph to record the quake was in Rapid City, SD. He said there were none in Minnesota; the Nuclear Regulatory Authority had funded one for awhile, but those funds had run out in 1982 -- this isn't a high earthquake area.

The June 4 earthquake had been recorded at 15 seismographic stations in the US and Canada at 4.1 on the Richter scale.

Another of the tasks that Chandler and his team will be working on is developing a "Mercalli scale" estimate of the quake's intensity. The Richter scale measures the magnitude or severity of an earthquake, how much the ground moved, based on a logarithmic scale -- each increase of one number is 10 times higher in magnitude and, Chandler said, 20 to 30 times more energy. This earthquake at 4.1 on the Richter scale was 1000 times less severe than the magnitude 7 Loma Prieta (San Francisco). earthquake of 1989.

It's a process, Chandler said, that would be similar to coming up with one number to capture the essence of a baseball player's stats. He said the Mercalli scale, expressed in Roman numbers, range from II to XII -- XII would be complete destruction.

The strongest Mercalli scale earthquakes in Minnesota have measured VII. Observations at that level include items like masonry in old structures starts to crack and chimneys fall. The Mercalli VII has been associated with two Minnesota quakes -- 1917 in Staples and 1975 in Morris.

Chandler said none of his team of students has found anything over Mercalli V observed with the June 4 earthquake. Nothing had crashed to the floor, but things had moved or rocked on shelves. He said they hoped to find a "cell" of higher intensity that might indicate they were right over the epicenter.

The teams of students were working along county roads in Traverse County to interview people and plot the information on a map.