Magnitude 5.8 Earthquake Strikes Virginia and Rattles the Eastern United States

Virginia Earthquake 2011According to catastrophe modeling firm AIR Worldwide, the largest earthquake to strike Virginia in more than a century rattled buildings in downtown Richmond and caused evacuations across the east coast today.

A strong earthquake struck at 17:51 UTC (1:51 p.m. local time) near Mineral, Virginia, a town with a population of about 500. The epicenter was about 40 miles northwest of the state capital, Richmond, and about 83 miles southwest of Washington, DC. The USGS issued a preliminary magnitude estimate of 5.8, revised it upward to 5.9, and subsequently downward again to 5.8. Focal depth has been estimated at 3.7 miles.

Ground shaking was felt up and down the East Coast, and as far north as Toronto and as far south as North Carolina. According to AIR, the dense rock of the central and eastern United States can propagate seismic energy more efficiently and therefore over a much larger area than in the plate boundary region of the western United States.

At this level of ground motion, there should be minimal structural damage to buildings, according to AIR. Nonstructural damage in the form of superficial cracks in the concrete and stucco walls of engineered structures is possible. However, there could be more significant damage to the historical unreinforced masonry buildings in Virginia, which are characterized by their limited ability to resist earthquake lateral loads without cracking.

According to AIR, the eastern United States has been the site of strong intraplate earthquakes. They are rare compared to the west coast; most earthquakes in the region have small magnitudes and are not widely felt. However, seismic activity is persistent. This is the largest event to strike the area since 1897, when a magnitude 5.9 temblor hit Giles County and was felt in 12 states.

AIR is analyzing the currently available seismological information for this event and will provide further information if warranted

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