In Howard County, geology class has never been so popular. As many as 200 people turned out in Columbia last night for a public forum on the earthquakes that have rumbled through the county in the past two weeks.
The forum, organized by 3rd District Rep. Benjamin L. Cardin, a Democrat, provided no revelations. Instead, two geologists did their best to explain the Earth's recent peculiar behavior and answer people's questions.
"I stand before you with torn emotions," said Emery T. Cleaves, director of the Maryland Geological Survey. As "a scientist, I'm very intrigued by what's going on. But as a public official and a concerned citizen, frankly, I hope these things stop."
Using slides, maps, charts and a little gallows humor, the scientists gave a folksy presentation on tectonics that could have been titled "Moving Rocks and You."
Those in attendance seemed more like curious students than frightened residents. Several sat in the front row with their heads bowed, scribbling notes and raising their hands to ask questions.
"I'll try not to have an exam afterward," said James Devine, assistant director of engineering and geology for the U.S. Geological Survey.
Mr. Cleaves captured the audience's imagination with a brief history and theory of seismic activity in the area: The disturbances can be traced to a fissure in the Earth's crust that runs from Lancaster County, Pa., through Howard County. Molten rock filled the fissure millions of years ago, leaving the Earth relatively weak in that area.
The geological phenomenon is called a dike. You can see it in an outcropping along Falls Road in Baltimore County, Mr. Cleaves said.
Since a 1906 tremor in Catonsville, towns along the dike have been hit by earthquakes. They have included one in 1939 in Phoenix, Baltimore County, that might have registered as high as magnitude 4.5 on the Richter scale. Another smaller earthquake struck Randallstown in 1990.
By comparison, the nine quakes that have struck Howard County since March 10 have measured no higher than magnitude 2.7. There have been no reports of injuries and only minor damage.
The reason for all this rumbling isn't clear. As sediment has shifted from the Appalachian Mountains to the Atlantic Ocean, pressure may have built up and occasionally been released through movement along the dike.
But, Mr. Cleaves warned, "This is just a hypothesis. Nothing is set in concrete."
The audience laughed nervously at the geologist's unintentional humor, and the evening moved on to questions and answers.
How big an earthquake would it take to break the Brighton Dam? asked Gary Orr, who lives near the dam along the Howard-Montgomery County border.
A lot bigger than we've been getting, said Mr. Devine. It would take at least a 4 or 4.5 to have any impact.
"Dams have failed in California, so we know what it takes," he said.
"How safe are our homes?" asked Ed Cannell, who lives in the Village of Kings Contrivance. "I'm serious. I have cracks that are visible that I know weren't there before."
XTC No one offered any guarantees.
County Executive Charles I. Ecker said that homes in Columbia had been designed to withstand wind speeds of up to 75 mph. Columbia University seismologist John G. Armbruster also noted that newer homes, like many in Howard County, stand a better chance than older ones that are not as well maintained.