The earth moved last December. It knocked political guru
Larry Sabato’s glassware from shelves and political
mementos from walls at his home on the Lawn at the University
of Virginia in Charlottesville. The quake happened the
day Gore decided to endorse Dean. “I knew Gore’s
endorsement of Dean was important, but I had no idea it
was going to cause an earthquake,” Sabato quipped
to the Hampton Roads Virginian-Pilot.
The quake, at 3:59 p.m. on December 9, registered 4.5
on the Richter scale and was centered about 38 miles west
of Richmond in Powhatan County. A trembler of that magnitude
is considered moderate with little or no damage. However,
it emptied Richmond office buildings, as well as the state
Capitol, wrote Virginian-Pilot reporter Matthew
Roy. In Goochland County, the sheriff cleared the jail
and prisoners stood outside in shackles.
At first, people weren’t aware of what had happened.
Some thought there had been an explosion underground,
a terrorist attack. It was definitely a rare, once-in-a-lifetime
event for many.
Actually, the Old Dominion has an illustrious history
of earthquakes. Since the first recorded tremors in 1774,
there have been more than 300 quakes within or close to
the Commonwealth, reports the Virginia
Department of Mines, Minerals and Energy.
The largest shock ever recorded was the 1897 Giles County
quake, estimated at 5.8 on the Richter scale. Eleven years
earlier, the region’s largest earthquake, centered
in Charleston, S.C., was felt from Canada to Cuba and
across the Commonwealth from Abingdon to Norfolk. Its
estimated magnitude was 6.6 to 6.9. Chimney damage seemed
to be the most frequent result, but in Richmond people
felt nauseous due to the vibrations. Residents milled
in the streets and militia and police were called out
to restore order. In Norfolk, there was panic at the Opera
House, and in Patrick County, bricks from the courthouse
went flying.
None of this, of course, equals the devastation of the
famed 1906 San Francisco earthquake or even the 1989 Loma
Prieta “World Series” quake in California
in 1989. To date, Virginia’s shocks have been less
damaging due to vastly different conditions on each coast.
According to plate tectonics theory, the Earth’s
crust is comprised of large plates that continually bump
into each other. Quakes occur to release the strain along
weak points – called faults – as a result
of this slow movement. Earthquake-prone areas on the West
Coast are located on the San Andreas fault, which falls
between the Pacific plate on the west and the North American
plate on the east.
Virginia is located in the middle of the North American
plate, rather than along the edges of two plates, so there
is much less quake activity. In California, quakes occur
on fault lines closer to the surface. In Virginia, quakes
occur along faults at depths of three to 15 miles. The
December 9 quake occurred at the three-mile depth.
The Commonwealth began measuring its quake activity more
accurately in 1963 when seismographs were set up in Blacksburg
and at Georgetown University in Washington, D.C. In 1977,
additional seismographs were installed and operated by
Virginia Tech and the Virginia Department of Mines, Minerals
and Energy.
Seismographs measure seismic waves, which travel through
the earth the same way sonar waves travel through water.
The single magnitude of an earthquake is calculated by
measuring the amplitude readings on several seismographs
based on the distance from each seismograph to the earthquake.
The first scale used to measure magnitude was developed
by Charles Richter in the 1930s.
Another measure used for earthquakes is the Modified Mercalli
Intensity Scale which measures effects, rather than size.
Roman numerals ranging from I to XII measure the quake’s
effects, with I meaning it was felt by few to XII, which
represents total destruction. For example, the 1897 Giles
County quake measures VIII on this scale. For historical
quakes, scientists use newspaper accounts and diaries
to assess damage.
Since 1977, Virginia’s seismographs have measured
more than 160 earthquakes. Over 27 were felt, including
last December’s tremor. Each year only one or two
are strong enough to be felt.
Since modern Virginia earthquakes have caused little more
than shaken psyches, it’s easy to become complacent.
But James Martin, a professor of civil and environmental
engineering at Virginia Tech, warns there may be more
to be worried about. In a Tech press release published
soon after the December quake, he warned, “Recent
seismological studies suggest that the southern Appalachian
highlands have the potential for even larger earthquakes
than have occurred in the past. ... We are under a significant
threat of large, damaging earthquakes.”
Unlike California, which has constant tremor activity,
the earthquake region in the Southeast experiences large
earthquakes separated by long dormant periods. If a quake
of the magnitude of the 1897 Charleston event hit today,
it would equal the size of the 1999 quake in Turkey that
killed 17,000 people, Martin says. And you thought the
budget impasse was something to worry about!
June 07, 2004
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