Blacksburg, Va. -- At 3:59 p.m. on Dec. 9, central Virginia experienced an earthquake that registered at 4.5 on the Richter scale. This moderate earthquake was the strongest seismic event to shake the area in 30 years, said Martin Chapman, director of the Virginia Tech Seismological Observatory.
"The event occurred in an area where we would expect earthquakes--in the central Virginia seismic zone," Chapman noted. The U.S. Geological Survey reports that the epicenter of the earthquake was about 30 miles southwest of Richmond at a depth of 3 miles. Details about the event are posted on the observatory website at http://www.geol.vt.edu/outreach/vtso.
Although little or no structural damage occurred during the event, the U.S. Geological Survey reported that the trembles were felt in parts of North Carolina and Maryland.
Virginia and other southeastern states are vulnerable to earthquakes, even though the seismic history and nature of the region is different from that of the West Coast.
In 1897, an earthquake with an estimated magnitude of 6.0 rocked Virginia Tech in the southwestern area of the state, Chapman said. The shock was centered in neighboring Giles County and was felt from Pennsylvania to Georgia. And although we tend to think of Alaska and California as the typical sites of seismic activity in the United States, eastern Tennessee is one of the most active areas in the nation in terms of the number of earthquakes recorded.
The most damaging seismic event in the U.S. prior to the 1906 earthquake and fire that destroyed San Francisco occurred in coastal South Carolina in 1886, Chapman said. The "Charleston earthquake," which caused structural damage as far away as Richmond and Atlanta, reached an estimated magnitude of 7.3 on the Richter scale -- essentially the same magnitude as the shock that killed more than 17,000 people in northwestern Turkey in August 1999.
In addition to the severity of those two earthquakes, another ominous similarity exists. "In terms of seismic vulnerability, many buildings in the southeastern U.S. today are similar to those in Turkey," said James Martin, an associate professor of civil and environmental engineering at Virginia Tech who visited Turkey to study the effects of that earthquake. "In neither place is there adequate structural protection of buildings. If another 7.3 magnitude earthquake hit Charleston today, the city would suffer much the same damage as cities in Turkey."
Despite the Southeast's potential for major earthquakes in the future, few engineering studies or emergency response plans have been devised in our region, Martin noted. That's why he and Chapman founded the Earthquake Engineering Center for the Southeastern United States (http://ecsus.ce.vt.edu/Main1.htm) in 2000.
"Recent seismological studies suggest that the southern Appalachian highlands have the potential for even larger earthquakes than have occurred in the past," Martin said. "But now those events would take place in much more highly populated areas. Felt earthquakes don't occur as often in the Southeast as in California, because the tectonic strain rates are different. Our region tends to experience large earthquakes isolated by long periods of quiet."
"However," Martin warned, "we are under a significant threat of large, damaging earthquakes."
There's another difference between California and the Southeast as seismic zones. "The earth's crust is stronger here," Chapman explained. "So shock waves moving from the epicenter of an earthquake don't lose as much energy as during quakes in California. When a magnitude 7.0 earthquake occurs in the Southeast, the waves affect a larger area and can cause more damage at a greater distance than when a similar shock hits California."
The above story is based on materials provided by Virginia Tech. Note: Materials may be edited for content and length.
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