Last week, many residents of Columbia's Kings Contrivance and Hickory Ridge villages were startled by a loud boom -- one that turns out to have been an earthquake registering magnitude 2.0.
The earthquake was the biggest one in the county since the spring of 1993 when Howard was shaken by 16 small quakes, one of which registered magnitude 2.7.
Dozens of concerned Howard residents called 911 in the early hours of Dec. 22, many claiming to have heard the tell-tale thunderclap of an earthquake. But some were befuddled by the sound.
"It sounds like a car crashing into your house, and it feels like it too," said Deborah Spotten, who lives on Walnut Grove near Atholton Middle School and felt two tremors. "I don't know what the deal is with the boom."
No injuries were reported from the quake, said Sgt. Robert Wiseman, emergency management officer from Howard County Department of Fire and Rescue.
Most of the callers were able to identify the booming sound of an earthquake because they were familiar with the loud bang and shaking ground from the 1993 quakes, he said.
John Minsch, a geologist with the U.S. Geological Survey's National Earthquake Information Center in Golden, Colo., said the earthquake's tremors were picked up by his agency's seismographs, but it was not strong enough for regional equipment in Delaware to record.
Minsch could not pinpoint the earthquake's epicenter, but most of the reports from residents came both sides of U.S. 29 between its intersections with Broken Land Parkway and with Route 32.
"Even though it was very minor, it seems it was, indeed, a genuine earthquake," Minsch said.
An earthquake registering a magnitude of 2.0 sometimes is not even felt by nearby residents, according to experts.
But Bane Kelley, a resident of Amherst Drive in Allview Estates, said the early morning tremors drove him right out of bed.
"It really shook the house pretty good," Kelley said. "We woke up and checked the house.
"The sound and effects are not like the ones in California," he said. "They are like explosions and sort of rattle everything about."
Kelley said that after he felt Howard's last round of tremors he bought earthquake insurance.
He hasn't had to use it, he said, but he has noticed cracks in the cement of his carport since the Dec. 22 temblor. He said also has noticed cracks in an overhang that extends over the carport.
Columbia was hit by a wave of earthquakes over four weeks in March and early April of 1993.
The strongest occurred between March 10 and March 14 of that year, and measured magnitudes 2.0 and 2.7, each prompting hundreds of calls to the county's communications center.
Earthquake magnitudes, which range up to 8.0, are calculated from ground motion recorded on seismographs; an earthquake of magnitude 3.0 is 10 times stronger than one of magnitude 2.0.
Columbia's last confirmed earthquake was in late October 1993.
Since then, there have been seven reports of tremors in the county, but no confirmed earthquakes until last week.
Just two weeks ago, Wiseman said, seismologists from Columbia University set up instruments to measure and study earthquakes at the Johns Hopkins Applied Physics Laboratory in Laurel.
However, the equipment was not working the morning of Dec. 22, he said.
Many geologists have theorized that Columbia is on a crack in the earth's upper crust -- known as a "diabase dike" -- which is about a half-mile west of U.S. 29 and stretches from Scaggsville to Lancaster, Pa.
About 170 million years ago, the crack filled with molten rock and left the ground weak in that area.
Seismologists say shifting pediment from the Atlantic Ocean to the Appalachians may have put pressure on the area and a resulting release of pressure may be the cause of the quakes.
An earthquake registering 4.5 hit Phoenix in Baltimore County in 1939, a series of tremors rattled the north end of the "diabase dike" in Lancaster and some parts of the Baltimore area in 1984, and a small earthquake hit Randallstown in 1990.
But big earthquakes stem from big fault lines in the Earth, geologists say, and all of Columbia's tremors of the last few years still would add up only to one minor quake.
Lou Ella Ellis of Allview Estates said she and her husband were having lunch a week before the earthquake when they felt a mild tremor.
However, they dismissed it, thinking it might be nearby construction.
But when the quake hit early on Dec. 22, "We said, 'That has to be an earthquake, because they aren't blasting at this time of night.' "
Still, she said, she is not concerned by the earthquakes -- and even finds them a bit exciting.
"None of us worry about it," Ellis said. "They've all been that mild."
Pub Date: 12/31/96