This map of the world shows seismic stations that detected more than twice the normal number of small, nearby earthquakes after the passage of what are known as "surface waves" from major quakes that were centered hundreds to thousands of miles away and occurred from 1992 through 2006. A new study co-authored by University of Utah seismologist Kris Pankow found that at least 12 of the 15 major earthquakes (greater than magnitude-7) during 1992-2006 triggered small quakes in distant parts of the world. Scientists once believed big quakes could not trigger distant tremors. (Credit: Aaron Velasco, University of Texas at El Paso)