Seismologists to study psychology of quakes Proximity to D.C. cited for publicity

April 06, 1993|By James M. Coram | James M. Coram,Staff Writer

New York seismologists studying Howard County's recent spate of small earthquakes also are seeking to analyze the psychology of why the quakes are receiving so much attention.

Sunday afternoon's twin tremors near Route 32 and U.S. 29 -- the 10th and 11th earthquakes to occur in the county since March 10 -- registered only 1.5 on the Richter scale yet were reported in the New York Times. Philadelphia papers have also carried stories on the earthquakes.

"It's partly because they are occurring so near Washington, and there is so much media," said seismologist John G. Armbruster, a research scientist from Columbia University's Lamont Doherty Geological Observatory in Palisades, N.Y. Mr. Armbruster was answering his own question about the amount of interest in the earthquakes.

"If they were over, people would forget it. There must have been a thousand people [in Columbia, Sunday] who realized they were feeling an earthquake."

Sunday's tremors occurred two minutes apart, beginning at 1:31 p.m., said Dr. Kelvin Ramsey, an associate scientist at the Delaware Geological Survey.

Mr. Armbruster and fellow Lamont Doherty seismologist Leonardo Seeber returned to New York 10 days ago after setting up monitoring equipment at four Columbia residences. They plan to return with "fancier" equipment in about a week, he said.

The computerized equipment they left behind has a finite storage capacity. The equipment they plan to bring in has 100 times more capacity and can receive time signals, he said.

Since the equipment they have now records everything from foot-steps to earthquakes, the data bank could fill up and an earthquake could go unreported, he said. Unless several more earthquakes occur between now and next week, the present equipment should last until replaced, he said.

In addition to researching newspapers and magazines to understand the psychology surrounding the earthquakes, Mr. Armbruster also is proceeding with his geological analysis.

The Columbia earthquakes are "quite shallow, about 500 meters deep," he said. "In California, you probably wouldn't find any that shallow. One reason people feel them is that they're so shallow."

Mr. Armbruster said "an honest conclusion" is that the Columbia earthquakes would not have to be as big as California earthquakes to cause chimney damage, cracks in plaster and the loosening of tiles.

However, "It would take a hell of a lot of shaking to bring down a wood-frame house," he said.

Residents living near the epicenter of the earthquakes had expressed concerns about the safety of their houses during his stay here, he said. Most of the houses are new and are wood frame, he said, which should lessen the worry.

Mr. Armbruster said he is reviewing earthquake records to see how large an earthquake must become before it does chimney, plaster or tile damage. He said he knows of an intensity 6 earthquake in southern Illinois that registered 3.5 on the Richter scale. Intensity 6, he said, will knock objects off shelves but will not do chimney, tile or plaster damage.

A 3.5 magnitude earthquake at 500 meters -- 1,640 feet -- "would give a pretty good jolt," he said. Such an earthquake would be 10 times greater than the biggest one that so far has struck Howard County.

Howard's biggest quake registered 2.7 on the Richter scale. It was recorded at 11:29 p.m. March 14.

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