Ground Shaking from East versus West Coast Earthquakes

Map showing where ground shaking was felt from the magnitude 5.8 earthquake August 23, 2011, near Mineral, Virginia, compared to the similar sized magnitude 6 earthquake September 28, 2004, near Napa, California. Stars show earthquake epicenters, and the blue and red dots show ground shaking reported from the public to the USGS "Did You Feel It?" website. These examples show that an earthquake of similar size in the eastern U.S. is felt more widely than one in the western U.S. because seismic waves travel farther in the colder, denser crust of the eastern U.S.