Earth mover

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Jim Reger knew something unusual was happening last week when residents around Dundalk, Md., who said they felt a rumbling under their feet started telephoning to ask whether there had been an earthquake.

Minutes later, a radio signal from a seismograph station near Owings Mills showed up as jerky lines on the computer screen at the Maryland Geological Survey, where Mr. Reger is a principal geologist.

The epicenter of the earthquake six miles under Dundalk registered a magnitude of 2.0, small by California standards but large by Maryland standards.

The biggest known earthquake in Maryland was an estimated 3.5 tremor in 1758, which is enough to cause only minor damage.

Mr. Reger estimates Maryland has about 100 fault lines. The exact number is difficult to determine because many of them will be discovered only after they cause earthquake tremors, he said.

Another unusual characteristic of the Feb. 23 earthquake was the 3- to 5-second duration.

Among Maryland earthquakes, "Most of the time it's a kaboom, and that's it," Mr. Reger said.

Although earthquakes might be the most spectacular part of his job, more often sinkholes, geologic map-making and rock formations take up his daily work schedule.

At the moment, Mr. Reger and the nearly dozen geologists on staff at the Maryland Geological Survey office in downtown Baltimore are mapping sinkholes in the Hagerstown area, where limestone in the bedrock has eroded from subsurface water flow.

"What's above it is just a bridge of soil," Mr. Reger said. "After awhile, these bridges can't support their own weight."