Tuesday, August 23, 2011

Reports on shaking from Virginia quake

My fellow State Geologists in the East are sharing reports from today's magnitude 5.9 earthquake in Virginia, that was felt across much of the Eastern U.S. [right, location map from USGS]

  • The RI State House (structure with very large dome) evacuated when shaking felt. It is situated on an uplifted glacial lake delta underlain by lakefloor varves.
  • Businesses and schools closed early in Baltimore and roads were clogged with people heading home (possibly over concerns that a bigger quake was coming)
  • In New Hampshire, one person said she was on third floor of state office building and lights swayed and desks shook for 30 second. That entire building is build on 150+ feet of unconsolidated glacial sand, and near the terminus of the former delta.
  • Many reports [of ground shaking] from southern and coastal Maine, mostly in areas underlain with glacial-marine mud.
  • New York State Museum in Albany built on lake clays experienced moderate shaking.
  • Most areas in Maine reporting shaking from this event are underlain with thick sequences of glacial-marine mud that amplify seismic shaking. Thus, firm knowledge of the distribution of such units is essential to risk analysis. The reduced attenuation of seismic energy in our older, colder crust means much larger areas can be affected by moderate seismic events.
  • Phones ringing off the hook in State Geological Surveys in Massachusetts, New York, Ohio, Virginia, Maryland, etc.

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