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All
Shook
Up --
Virginia
Rumbles
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!
NEXT
UP: She’s
Got a Ticket to Ride, or: The Stock Car Ballet &
Other Curious Virginia Art.
--
June 07, 2004
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