Oceanic earthquakes are not felt, but they are measured. Beth Tyler 06.01.01 Earthquakes occur when the earth beneath us moves. Beneath the earth’s surface, the crust of the earth is divided into many large plates that sometimes need to readjust and move. When they move suddenly and quickly, an earthquake occurs. While earthquakes are often something people can feel on the surface of the earth, sometimes they occur so far beneath the earth’s surface that people cannot feel them. However, scientists can still know they happened using Global Positioning System (GPS) instruments set up at many locations on the ground. The GPS instruments use satellites in outer space to get the exact location of a spot on the earth’s surface. Because the instruments constantly take measurements, scientists can use the GPS information to know how far and how quickly surfaces on the earth move. Using GPS data from seven locations, scientists recently discovered a major earthquake that occurred in the ocean off the coast of the northwest United States. Who knows if the fish felt it. Dragert, Herb, Kelin wang, and Thomas S. James. A silent slip event on the deeper cascadia subduction interface. Science 292: 1525- 1528. ©2001 The Aurora Collection, Inc. All Rights Reserved. Site Development by: Interactive Multimedia. Inc.