The 4.7 earthquake that hit the Anza area Monday proved to be a big test for Cal Tech scientists developing an early earthquake alert system. Initial reports cited the quake was much bigger than it actually was, because of a foreshock that confused the computer system. The USGS early warning system, however, worked without a hitch, giving seismologists a 30-second warning ahead of the temblor. Patrick Healy reports from Pasadena for the NBC4 News at 5 p.m. on March 11, 2013.
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Foreshock Befuddles Early Warning System
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