Virginia Tech Earthquake Engineering Center
Aims to Prepare Southeast for Likely Seismic Events
 
Although we tend to think of Alaska and California as the typical sites of seismic activity in the U.S., eastern Tennessee is one of the most active areas in the nation in terms of the number of earthquakes recorded.

Topics within this article:

Southeast Potential

East-West Differences

What the Center Will Do


Links within the university:

Earthquake Engineering Center for the Southeastern United States

Virginia Tech Seismological Observatory

Civil and Environmental Engineering

James Martin


Martin Chapman

 

 

 

The most damaging seismic event in the United States prior to the 1906 earthquake and fire that destroyed San Francisco occurred in coastal South Carolina in 1886. 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 these two earthquakes, another ominous similarity exists. "In terms of seismic vulnerability, many buildings in the southeastern United States today are similar to those in Turkey," says James Martin, an associate professor of civil and environmental engineering (CEE) at Virginia Tech who went to 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."

The South Carolina coast is not the Southeast's only earthquake vulnerable area. In 1897, an earthquake with an estimated magnitude of 6.0 rocked Virginia Tech -- the shock was centered in neighboring Giles County and was felt from Pennsylvania to Georgia. Although we tend to think of Alaska and California as the typical sites of seismic activity in the U.S., eastern Tennessee is one of the most active areas in the nation in terms of the number of earthquakes recorded. 

Southeast Potential

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 notes. That's why he and Martin Chapman, director of the Virginia Tech Seismological Observatory, have founded the Earthquake Engineering Center for the Southeastern U.S. (ECSUS). 

"Recent seismological studies suggest that the southern Appalachian highlands have the potential for even larger earthquakes than have occurred in the past," Martin says. "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," he says. "We tend to experience large earthquakes isolated by long periods of quiet."

"However," Martin warns, "we are under a significant threat of large, damaging earthquakes." 

East-West Differences

The Southeast is in the middle of the North American plate, while the large faults in California, such as the San Andreas fault, are on the boundary between the North American and Pacific plates, Chapman says. A plate is a vast, mobile block of the earth's crust, and plates move against one another, causing the tectonic strains (forces that affect the earth's crust) that result in earthquakes. The Southeast has less frequent major earthquakes because of its location in the middle of a plate. 

When a magnitude 7 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.

Nevertheless, Charleston, Richmond and parts of the Tennessee Valley have the potential to experience major shocks, Chapman notes. "We can't make forecasts for future quakes in the Southeast," he says, "but geological history shows that during the past 4,000 to 5,000 years the region has experienced about six earthquakes large enough to liquefy the ground." Liquefaction occurs in sandy soils with high water tables, he explains. During a major earthquake, the water pressure in the soil may increase to a level at which the soil actually becomes liquid, and buildings in the area often topple or sink into the ground. This phenomenon was common during the 1886 Charleston quake.

There's another difference between California and the Southeast as seismic zones. "The earth's crust is stronger here," Chapman explains. "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 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." 

What the Center Will Do

Martin, Chapman and other ECSUS researchers intend to lessen the vulnerability of the Southeast to severe earthquake damage by developing and disseminating critical seismic data and technology. 

Funding for the ECSUS already has been provided by the U.S. Geological Survey and more is expected from Virginia Tech, the South Carolina Department of Transportation, and other government agencies and private companies. 

Updating seismic hazard maps and earthquake detection and mitigation technology is a major goal for the ECSUS.

"Very little research on seismic hazard mapping has been conducted specific to the Southeast," Martin says. Most of the latest maps for the region have been developed from Virginia Tech's catalog of historical and seismic instrumentation data, and the university's monitoring network is key to future ECSUS work. However, he notes, there is an urgent need for regional hazard mapping, especially in urban areas. 

Currently, Chapman says, hazard maps available in the Southeast are national maps last updated by the USGS in 1996. These maps offer a good national perspective, but don't provide detailed data for specific sites.

The ECSUS will develop localized hazard maps and teach the region's engineers to use them. Charleston will be the subject of the first series of maps, developed with the latest Geographical Information System (GIS) technology. GIS seismic hazard maps -- computer-based maps showing site-specific potentials for earthquakes -- can help engineers and architects determine if a structure is being designed in an earthquake-prone area, and can help local planners develop protective building codes. 

GIS technology also will be crucial after an earthquake occurs. "When an earthquake triggers seismic monitors," Martin explains, "the information is fed to a GIS network. Within minutes, a local emergency response team can see where the worst damage likely occurred so that teams can be dispatched immediately to the areas most in need of help."

The ECSUS will manage the transfer of such data and technology to the Southeast. For example, Martin says, engineers who are building a bridge in an earthquake-prone area of South Carolina need to use the latest seismic engineering technology and building code criteria, developed primarily in the western U.S., and ECSUS will aid in that information exchange and help adapt the technology to the Southeast.

Building codes are another priority for ECSUS. Codes in the eastern U.S. have been updated to reflect information from 1996 earthquake hazard maps and recent findings on soil response to strong motion. However, there is no organized effort to inform the engineering community in the Southeast about important new design procedures. 

"We want the ECSUS to serve as a regional voice," Martin remarks. "The Southeast needs experts who can address methods of updating building codes and structural designs specific to the needs of the region. We also want to promote the continued evolution of building codes."

"The ECSUS will provide a service that engineers, architects, emergency response teams, and the public in the Southeast need -- a central clearinghouse for critical earthquake information," Chapman says. "It's important that people not become alarmed at the prospect of earthquakes in our region, but we need to learn how to be prepared." 
 

-Written by Liz Crumbley, 
College of Engineering

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