More than a dozen residents of the Allview section of Columbia called Howard County police about 1:30 p.m. yesterday to report an earthquake. The reports could not be confirmed yesterday.
In the past month, seismometers have been placed at several Howard County homes to measure earthquake activity. But the digital instruments can be read only by people trained to use them, said Jerry A. Carter, director of research at the Center for Seismic Studies in Roslyn, Va., and a Columbia resident.
Willis Jacobs, a geophysicist with the National Earthquake Information Center in Colorado, could not confirm the earthquake either because some of the center's equipment in the eastern United States wasn't working yesterday.
Calls began pouring in to police at 1:30 p.m. and trailed off by 1:45 p.m., said Officer Ann Daley of the Howard County police. She said there were no injuries or damage.
Callers described two little rumbles. Most remained calm, but several expressed concern, she said.
"One woman called and asked where she should stand in her house to stay safe," Officer Daley said. Another woman "wanted to know if she could go to a bomb shelter." At least nine minor earthquakes have struck Howard County since March 10, unnerving some residents, fascinating geologists and sparking sales of earthquake insurance. The largest of the tremors measured 2.7 on the Richter scale.
No one is sure what is causing the earthquakes. Several geologists believe they are linked to a crack in the earth's upper crust about a half-mile west of U.S. 29 and stretching from Scaggsville to Lancaster, Pa.
The crack filled with molten rock about 170 million years ago, leaving the earth relatively weak in that area. Shifting sediment from the Appalachians to the Atlantic Ocean may have put pressure on the area, and subsequent release of pressure may have caused the earthquakes, seismologists say.