National Aeronautics and Space Administration Archives — LIRNEasia

“Scientists have long believed tsunamis form from vertical deformation of seafloor during undersea earthquakes. However, seismograph and GPS data show such deformation from the 2004 Sumatra earthquake was too small to generate the powerful tsunami that ensued. Song’s team found horizontal forces were responsible for two-thirds of the tsunami’s height, as observed by three satellites (NASA’s Jason, the U.S. Navy’s Geosat Follow-on and the European Space Agency’s Environmental Satellite), and generated five times more energy than the earthquake’s vertical displacements.