The 2011 Virginia Earthquake: What Are Scientists Learning?
event.
Key information on the quake came from the U.S. Geological Survey’s website, “Did you feel it?,” which lets people report when and where they felt an earthquake and describe its intensity. About 148,000 people, from more than 3,400 zip codes, logged on in response to the August 2011 quake – a record for the site since it went online in 2000. USGS scientists Wright Horton and Robert Williams report on this and other quake-related findings in this week’s issue of Eos, the American Geophysical Union’s member newspaper.
Fig. 1. (a) The M = 5.8 earthquake in the Central Virginia seismic zone has a moment tensor solution (http://earthquake.usgs.gov) indicating reverse motion on an east-southeast-dipping
plane consistent with aftershocks. (b) Damage to buildings such as the Washington National Cathedral in Washington, D. C., 135 kilometers northeast of the central Virginia epicenter, is a reminder that engineered structures in eastern North American cities are vulnerable under moderate shaking (photo by J. Scott Applewhite, Associated Press). (c) U.S. Geological Survey “Did You Feel It?” data from the M = 5.8 Virginia earthquake (green) and from one of similar magnitude and depth in California (red) illustrate how earthquakes are felt over much larger areas in the eastern United States than those west of the Rocky Mountains. (d) Virginia aftershocks define an east-southeast-dipping fault rupture plane.
“‘Did you feel it?’ creates an almost real-time compilation and portrayal of earthquake effects] so you can record your shaking experience and see how your dot on the map fits in with all the rest,” said Horton, a research geologist at the USGS National Center in Reston, Virginia.
From this data, scientists were able to determine that the earthquake was felt as far west as the Mississippi River, as far south as northern Florida and as far north as southeastern Canada. The scientists also suggest that this earthquake was probably felt by more residents than any other in U.S. history.
Because of the geologic properties east of the Rocky Mountains, seismic waves from earthquakes in the eastern U.S. propagate more strongly to greater distances from the epicenter than seismic waves in the western part of the country, the scientists write.
The Virginia earthquake shook the metropolitan areas of several cities including Baltimore, Philadelphia, New York City, and Washington D.C. Tens of millions of city-dwellers likely felt the quake, the scientists estimate, and overall, the earthquake was felt by approximately 100 million people – nearly a third of the U.S. population.
Within days of the quake, USGS scientists and researchers from other institutions dispatched seismographs and other monitoring equipment near the Virginia source. About 35 seismographs ran until early 2012, collecting data on the aftershocks.
“All together, these efforts yielded the best recorded aftershock sequence in the eastern United States,” Horton said. “Scientists are working to better understand the event and improve earthquake hazard assessment along the eastern seaboard.”
Researchers continue to investigate the Mineral, Va. earthquake, Horton said, using not only fieldwork at the site but airborne lidar, and magnetic, gravity and radiometric surveys to image the Earth from the surface to the earthquake source miles underground. With more studies, they hope to better understand the earthquake risk for the eastern seaboard.
2012-08-14 15:57:20
Source: http://nanopatentsandinnovations.blogspot.com/2012/08/the-2011-virginia-earthquake-what-are.html
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