A seismic expert at Virginia Tech said residents in the New River Valley are learning earthquakes can happen here, case in point earlier this month with one that was centered just over the West Virginia state line near Pearisburg. The question is whether there will be one that can do some major structural damage.
Martin Chapman, the director of the Virginia Tech Seismological Observatory, said yes, the region can expect one at a higher magnitude but would not pinpoint any specific time-period.
“Damaging earthquakes of magnitude 5.0 and larger appear to happen at a rate such that the average time between them is about 150 years,” he said.
Historically over the past 50 years, earthquakes have occurred in Giles, Pulaski, Montgomery and Bland counties in Virginia, and in Monroe, Mercer and Summers counties in West Virginia.
The largest historical earthquake in the Giles County seismic zone was magnitude 5.0-5.5, and occurred on May 31, 1897.
The latest was recorded on Sept. 13 and produced little or no damage. A Virginia Tech seismograph showed the epicenter just over the state line in West Virginia. The magnitude was between 3.7 and 4.0. The quake is the area’s largest since 1968. Witnesses said it was loud and dramatically shook the earth with reports as far as Radford and Pulaski.
A major quake with a magnitude of 7.1 did considerable damage last week in Axochiapan, Morelos, Mexico. The death toll in that disaster was 320 people.
In 2011, Louisa County, reported a quake with a magnitude of 6.3 centered near Mineral that was the largest and most damaging earthquake in the eastern United States since 1886. Significant damage was reported in structures within a 100-mile radius including Washington, D.C. with estimated 876 aftershocks.
Reports were similar in the 1897 Pearisburg quake. Tremors were felt in Lynchburg and Bristol, Tennessee. Walls of brick homes were cracked and many chimneys were thrown to the ground. Three weeks prior, a smaller quake was centered near Radford with a magnitude of 4.3.
Typically, people think of earthquakes happening in California and Alaska but eastern Tennessee and southwest Virginia is one of the most active areas in the nation in terms of the number of earthquakes recorded.
James Martin, an associate professor of civil and environmental engineering at Virginia Tech, along with Chapman has founded the Earthquake Engineering Center for the Southeastern United States.
In national reports, Martin said recent seismological studies that the southern Appalachian Highlands have the potential for even larger earthquakes than have occurred in the past. He said “felt” quakes don’t occur often as compared to the west coast.
The San Andreas Fault in California is the best-known problem area in the country with frequent tremors. Much smaller quakes can be felt on the east coast in a larger circle. For example, one at a 4.0 magnitude can be felt as far away as 60 miles from where it occurred.
Virginia has had over 160 earthquakes since 1977, and experts say that equates to an average of one occurring every month with two felt each year.
Seismic activity has been known for several decades to be strongest in and around Giles County with the Giles County seismic zone extending for almost 50 miles along the West Virginia border.
This zone is laced with known faults and many smaller and deeper ones that remain undetected.
Chapman said the recent earthquake was ultimately caused by stress building up in the rocks of the crust due to tectonic forces associated with the motions of the lithospheric plates.
“Over the past 150 years, an earthquake the size of the shock that occurred on September 13, 2017 (mblg 3.7) happens about every 20 years,” he said.
According to Chapman, there is no reason to expect them to stop in the foreseeable future.
Most of eastern Tennessee, northwestern Georgia and northeastern Alabama have earthquakes as rates comparable to the Giles county seismic zone. That area is known as the Eastern Tennessee seismic zone. Central Virginia is also an area of very frequency moderate earthquakes and is known as the Central Virginia Seismic zone.