Seismologists have been working around the clock at the United States Geological Survey tracking the effects of the 7.2 earthquake in Mexico. Dr. David Wald describes the activity of the earth's crust... more 
Seismologists have been working around the clock at the United States Geological Survey tracking the effects of the 7.2 earthquake in Mexico. Dr. David Wald describes the activity of the earth's crust and how it was felt throughout the southwestern U.S. less 
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Wed, Sep 12, 2012 11:35 PM EDT