The earthquake trembled in a five-county area around Charlottesville, Va., at 3:05 p.m. last Feb. 27, rattling windows, dishes and doors. Some people, hearing rumbling, and feeling movement, thought objects have struck their houses.
It was Virginia's 143rd earthquake strong enough to be counted since the first quake recorded in the state shook the Petersburg area and damaged some buildings on Feb. 21, 1774. It was the seventh quake of similar effect to occur in Virginia in the last three years.
There will be more, seismologists say, and there is no guarantee they will be small. Although Virginia and the rest of the eastern part of the United States is not in an earthquake belt, there have been quakes of note in the area in what must be considered the very recent past on the scale of history.
Virginia's largest earthquake came on May 31, 1897, and centered at Pearisburg in Giles County. It was felt from Georgia and Pennsylvania and as far west as Indiana and Kentucky. Brick houses and chimneys cracked. There were fissures in the ground; small landslides occured. Large rocks rolled down mountainsides.
The region's worst recorded quake occured at Charleston, S.C., on Aug. 31, 1886. Buildings collapsed; the ground heaved. About 60 people were killed. The quake was felt in Iowa.
Seismologists termed last month's quake "about average" for Virginia.
The U.S Geological Survey, which had compiled earthquake statistics, says scientists don't know why major quakes sometimes occur outside the well known belts.
None of the Virginia quakes are significant when compared to the earthquakes that killed perhaps as many as 655,000 persons throughout the world in 1976 (according to the Geological Survey), but they are part of the constantly changing physiognomy of the earth that scientists feel they can trace back about 180 million years.
What Mrs. B. G. Largent of a rural area outside Charlottesvill described as "the sound of three trucks rumbling up our driveway," was the earth adjusting itself. Mary Jane Haynes of Charlottesville said she was standing at her kitchen sink and "heard a roar and felt a gentle shake."
They were among 200 persons who wrote letters to the Virginia Division of Mineral Resources to describe their experiences in the quake. The letters have been forwarded to the National Earthquake Center in Denver.
Efforts to gather information about earthquakes, particularly in Virginia, have intensified in recent years because of the construction of nuclear power plants and the possibility that radiation could be released in lethal quantities by earthquake damage.
The planned four-unit nuclear plant being built at North Anna in Louisa County by he Virginia Electric and POwer Co. is located astride a geologic fault that was caused by an earthquake that scientists believed occurred muillions of years ago.
The concensus of scientific opinion about North Anna, is that nuclear plants shouldn't be built on faults deliberately. But according to the best evidence they can muster, the likelihood of another quake occurring at North Anna during the 40-year or so life of the plant is infinitesimal.
Should one occur, however, Vepco and the Nuclear Regulatory Commission say they are confident the plant's strong design will withstand any anticipated shock.
Geologists ans seismologists admit, however, that theirs is among the least, precise of sciences. It is difficult to be positive about anything.
The North Anna Environmental coalition had not given up its four year fight to prevent the plant from receiving an operating license, and the presence of the geologic fault is one of their main points against the plant.
The generally accepted theories about geologic evidence are that the Western Hemisphere originally was jammed together with Africa and Europe. The land mass was split up and the pieces pushed apart through the eons by constant earthquakes of varying magnitudes and intensities.
North America now is steadily moving westward at the rate of an inch or so each year because of earthquakes in the bottom of the Atlantic Ocean, seismologists say. The scientists believe the Appalachian Mountains, which run southwest through Virginia, and mountains in Scotland, Greenland and Norway were part of the same chain when the great schism began.
As the land separate into continents, earthquake zones developed. A quake line extends along the West Coast of the United States and up through Canada to Alaska and extends on around the Aleutian Islands in the Orient. Another goes up and down the Atlantic. Why quakes occur outside the well estabblished patterns, at generally unpreditable times and intensities is unknown.
But records go back only about 200 years and quakes goes back millions of years.
Most geologists appear to be satisfied that the land mass schism occurred as described because the continents seems to fit together when examined on a map of the world and the goelogy is similar along the coastlines that would have been adjacent to one another before the split.
Carl Stepp, a seirmologist at the NRC, likened the East Coast area to "an ice cube floating in a glass of water - although the movement of the cube occurs over millions of years."
Stepp said perhaps the most comforting deterrent against major quakes in the eastern region is that quakes seem to occur along boundaries between solid parts of the earth and "floating" - or "plate" - areas.
The eastern United States is in the middle of a "plate." The point is that the shock of a major quake on a "floating" areas of the world has less effect than it has on solid areas.
Therefore, the chances of major earthquakes here are small, geologists believe, but you never know.