Quake likelihood assessed Risk in area called 'very low'

March 17, 1993|By James M. Coram | James M. Coram,Staff Writer Staff writer Jackie Powder contributed to this article.

The Baltimore area may not be safe from large earthquakes after all, a New York seismologist said yesterday.

"The probability of a large earthquake exists, but it is very low," said Leonardo Seeber, a Columbia University research associate at the Lamont Doherty Geological Observatory in Palisades, N.Y.

Large quakes often are preceded by small ones, but "we don't have enough data to generalize," Mr. Seeber said at a news conference in the Hickory Ridge section of Columbia.

Columbia has experienced four small earthquakes in the past six days, the latest registering between 1.0 and 2.0 on the Richter scale about 3 a.m. yesterday.

"We could have already seen the largest" earthquake in the area, Mr. Seeber said. If so, it would have been a tremor that occurred 11:29 p.m. Sunday night at the intersection of Routes 32 and U.S. 29 that registered 2.7 on the Richter scale.

"If there's an earthquake, there's a fault," Mr. Seeber said. "The question is what fault and how big? If it's a large one, we can infer that a large earthquake can occur."

Mr. Seeber's theory is that the recent Columbia quakes are related to a diabase dike -- an intrusion of molten rock into the earth's upper crust 170 million years ago. The dike is located about a half-mile west of U.S. 29 and stretches from Scaggsville to Lancaster, Pa.

Because of the potential weakness of the dike, it is possible that with increased stress, it could become a fault, Mr. Seeber said. "The inference is that the fault may be large and that if ruptured, it could [create] a large earthquake, he said.

"Twenty years ago, the concept of a large earthquake occurring in the East was not accepted," he said, "but the East Coast has seen large quakes in the past. Charleston, S.C., for example, was hit with a magnitude 7 earthquake in 1886 after a week of small quakes similar to those that


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struck Columbia, Mr. Seeber said.

That does not mean a similar pattern will occur here, he said. More likely is a series of small earthquakes similar to those that rattled Lancaster County near the top of the dike beginning on Easter Sunday in 1984. After a week of small earthquakes, nothing more happened.

Mr. Seeber and seismologist John G. Armbruster plan to monitor seismometers at seven Columbia residences over the next five days. Depending upon the amount of seismic activity they discover, they could be here as long as a month, Mr. Seeber said.

Until now, there have been no working seismometers in Maryland to evaluate seismic activity here. The state has a reputation as one of the least geologically active places on the Eastern Seaboard.

"Our plan is to deploy a number of instruments to get an accurate reading so that long-range we can relate to some structural feature," Mr. Seeber said.

If the area does receive further jolts, the quakes probably will not exceed 3 on the Richter scale, said

Jerry A. Carter, director of research at the Center for Seismic Studies in Rosyln, Va. One of the seismometers was placed at Mr. Carter's home on Columbia Road.

"I wouldn't want to predict anything," Mr. Carter said. "Too many people have put their reputations on the line."

"Our response should be long-term," Mr. Seeber said. "We shouldn't be alarmist, but we have had a blip in probability. Long-term, the eastern United States has to realize that the probability of a large earthquake has to be faced. It is not something to panic on, but to take cognizance of. It's good for the psychological health to know what's going on under your feet."

Among the long-term issues, he said, are making sure that the foundations of buildings are firm enough to withstand a major earthquake and that the potential for fires resulting from furnace explosions be minimized.

Although the area is behind the West Coast in terms of earthquake preparedness, "the one saving thing on the East Coast is that you do have a hurricane hazard," Mr. Seeber said. Buildings are built to withstand

hurricane force winds "and that saves you a bit."

Although the chances of a major quake here may be slim to nil, the county government's press office is putting together a pamphlet on earthquake preparedness. The pamphlet should be ready for distribution by the end of the week.

In addition, Rep. Benjamin L. Cardin, D-3, has arranged an earthquake information forum for residents on March 24 at the Howard County Board of Education offices.

The 7:30 p.m forum will feature Robert Wesson, chief of the U.S. Geological Survey Office of Earthquakes, Volcanoes and Engineering, and James Reger, chief of environmental geology at the Maryland Department of Natural Resources.

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