- Spawned by the South Asian earthquake, seismic waves
rolling deep within the Earth made Virginia well water rise and fall by
3 feet, the U.S. Geological Survey reported.
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- Strong oscillations at a 450-foot-deep well near the
Round Meadow Country Club in Christiansburg in western Virginia started
about an hour after the magnitude 9 quake struck some 9,600 miles away.
Seismic waves travel through the Earth at about 7,400 mph.
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- "It took another five hours for that sloshing to
settle out," USGS groundwater specialist David Nelms said yesterday.
"That water's going up and down, up and down, up and down in that
well."
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- The height of the oscillation came about 77 minutes after
the earthquake struck near Sumatra. The water level rose about 2 feet,
according to Nelms. Data indicate that water came at least within 4 inches
of the surface, perhaps even spilling out.
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- "We saw it here. That's what amazes me, we saw it
here," Nelms said. "In about an hour, we were seeing something
from that earthquake here."
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- The well is one of 280 whose groundwater levels are monitored
by the USGS and the Virginia Department of Environmental Quality and one
of about a dozen with satellite equipment that provide daily readings.
The 2002 drought revealed the value of such timely information as residents
across the state wanted to know why their wells ran dry, Nelms said.
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- The equipment at Christiansburg records groundwater readings
once every 15 minutes, so the oscillation may have been even greater, Nelms
said.
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- Data is transmitted from the well to the satellite and
eventually to the USGS in Richmond, allowing DEQ and USGS personnel to
check readings by computer.
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- The earthquake data is considered a "bonus"
to the wells' usual job monitoring groundwater. The Dec. 26 quake is the
first time the DEQ-USGS well project recorded the effect of an earthquake
and had it online in near real-time, Nelms said.
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- Nelms was on vacation when he heard news reports about
the underwater earthquake that sent tsunamis throughout the Indian Ocean.
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- "I wondered if we saw it. I went on the Internet
from home and saw it," Nelms said of the spike recorded at the Christiansburg
well. "As soon as that pops up on the screen, you go, 'I know what
that is.'"
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- The Christiansburg well is known to respond to earthquakes
around the world. When the 1985 Mexico City earthquake struck, with a magnitude
of 8, the well recorded a 7-foot oscillation, according to Eugene Powell
of the DEQ office in Charlottesville.
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- Nelms said he was surprised that the earthquake's effects
were recorded so clearly, because of the 15-minute recording intervals.
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- "We were kind of afraid that maybe [the equipment]
would miss it if it all happened so quick, but the duration of this tremor
was such that we got some good readings," Powell said.
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- Officials at the Richmond USGS office are now discussing
whether the equipment on wells should be altered to record more frequently
when oscillations are greater than expected.
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- The Christiansburg well, taken over by the DEQ in 1969,
is finished in limestone. Water enters the well through fractures or cracks
in the rock. Like fireplace bellows, seismic waves compress and expand
the fractures, drawing water in and expelling it.
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- "We mainly see this, the earthquake effects, in
wells west of [Interstate] 95 in rock country," Nelms said. Those
wells are measured in real time. Monitoring of Virginia's more numerous
coastal wells focuses on the water table, which typically doesn't show
earthquake-related changes.
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- The well just west of Christiansburg is the only one
in Virginia known to have rocked with the South Asian earthquake, although
a Roanoke well dropped a bit around the time of the earthquake, Nelms said.
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- A well in Augusta County reputed to respond to earthquakes
lacks real-time satellite equipment and is not scheduled to be checked
manually until February, Powell said.
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