Interior US Earthquakes

Today was a pretty interesting day at the conference. I learned plenty about earthquakes, earthquake prediction, and more.

One topic discussed by many of the scientists here is the seemingly abnormal number of noticeable earthquakes recently in odd U.S. locations – from the pair of August 23 earthquakes in Mineral, Va. (magnitude 5.8) and Trinidad, Co. (magnitude 5.3), to the November 6, magnitude 5.6 temblor near Shawnee, Ok. Several presentations at the American Geophysical Union meeting yesterday and today discussed these and other intraplate earthquakes – those occurring away from major fault areas --also including several much larger earthquakes from the last 200 years that also occurred in less likely areas, including the massive New Madrid earthquakes (the largest is estimated at magnitude 7.7) from 1811-12 in the Mississippi River valley. The following interesting tidbits came up in academic presentations:

• That the Va. earthquake might be a reactivation of a 200+ million-year-old fault.
• The U.S. Geological Survey plans to greatly improve the maps and data for Va.
• Many of the best records of the New Madrid earthquakes came from river boatmen. But at least one came from a conspicuous source, a letter from President James Madison to Thomas Jefferson, meaning that the earthquake (which occurred in Missouri) was felt in Washington, D.C.
• Many of the intraplate earthquakes seem to reactivate faults from the opening and closing of basins of previous oceans throughout the tectonic history of the Earth.
• The low end of estimates for the length of aftershock sequences for these types of earthquakes was on the order of decades.

Scientists presenting interesting research on these topics included:

• Susan Hough from the US Geological Survey (USGS)
• Emily Wolin from Northwestern University
• Robert Williams from USGS
• William Thomas from the Geological Survey of Alabama
• Beatrice Magnani from the University of Memphis
• Daniel McNamara from USGS
• William Ellsworth from USGS