August 23, 2011 | 2
A magnitude 5.8 earthquake that shook buildings and sent people in New York, Philadelphia, Washington, D.C., and surrounding areas streaming outside into the summer weather on August 23 might seem like small shakes for residents of more quake-prone regions of the nation. California averages at least one earthquake larger than magnitude 5 per year, and quakes as big as magnitude 6.6 struck the fault-heavy Midwest in the 19th century. But the East Coast’s recent geologic record has hardly been tremor-free.
How does Tuesday’s quake, epicentered near Mineral, Va., measure up to other East Coast temblors on record? It was tied for third-largest (with one near Massena, N.Y.) in the past 228 years. Here are the region’s top 10 big ones on record, according to the U.S. Geological Survey (USGS):
September 1, 1886: Charleston, S.C.: 7.3 (60 fatalities)
May 31, 1897: Giles County, Va.: 5.9
August 23, 2011: Mineral, Va.: 5.8
September 5, 1944: Massena, N.Y.: 5.8
August 10, 1884: New York City, N.Y.: 5.5
November 30, 1783: N.J.: 5.3
October 7, 1983: Blue Mountain Lake, N.Y.: 5.3
September 25, 1998: Meadville, Penn.: 5.2
February 21, 1916: Waynesville, N.C.: 5.2
April 20, 2002: Au Sable Forks, N.Y.: 5.1
Large earthquakes without known magnitudes were also reported by the USGS for these two events: an 1871 quake along the New Jersey-Delaware border (in which “chimneys toppled and windows broke in northern Delaware”); and a 1791 quake near Moodus in Middlesex County, Conn. (during which, on May 16, “stone walls were shaken down, tops of chimneys were knocked off, and latched doors were thrown open”).
The largest quake on record in the lower 48? A historic 1857 rumbler in Fort Tejon, Calif., which is estimated to have been a magnitude 7.9. A powerful shake, given that the earthquake magnitude scale is logarithmic. So that 7.9 is is about 100 times stronger than a magnitude 6.9 quake.*
Editor’s note (08/23/11): This paragraph has been updated to correct the description of the scale and the strength comparison.