How could Virginia quake be felt in Canada and crack the Washington Monument?
Rocks of the East Coast conduct earthquakes much better than rocks in the West. It means a moderate quake in rural Virginia can travel far and damage the Washington Monument.
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“We have fewer earthquakes here, but when we do have them, they affect larger areas,” he says.Skip to next paragraph
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All these differences mean “lessons learned” from the seismically active West must be modified for implementation in the East, he adds.
“It is very difficult to do any meaningful statistics on them,” because scientists just don't have the leverage of large numbers, he says via e-mail. “Forget calculating recurrence intervals or anything like that except in the most active zones in the East, like the New Madrid seismic zone.”
This also means that processes like weathering, erosion, and soil formation have a longer period in between quakes to "erase the evidence." Moreover, in the wetter, more humid East, these processes act more quickly.
Eastern quakes are like the old-school college professor who erases with his left hand as he writes with his right,” Professor McGrew adds.
Geologists cannot even locate the faults that are responsible for the seismicity; they remain hidden from view in the underlying "basement" rocks, he says. “Such is the case for the Virginia earthquake, where no surface fault has previously been mapped despite the fact that it is a known seismic zone. “
Relatively moderate earthquakes, such as Tuesday’s event, provide a reminder of the potential for truly damaging earthquakes, he says, which makes the much less frequent quakes in the East all the more important to study carefully and prepare for.
“Much of what is done to understand the hazards from earthquakes is based on the occurrence of past events. These recent earthquakes provide important data for those studies,” he says.
Large earthquakes have occurred in the Midwest and along the East Coast during the past 200 years, inclding the New Madrid earthquakes of 1811 and 1812 and the Charleston earthquake of 1886, which were magnitude 7 or larger, he says.
“Similar events today would certainly result in loss of life, extensive damage, and widespread disruption of commerce," he says. "While these events are extremely rare, it is important to be aware that they can and probably will occur again some time in the future.”