Earthquake-powered shifts along the seafloor that push water forward, not just up, could help supersize tsunamis.
By combining laboratory experiments, computer simulations and real-world observations, researchers discovered that the horizontal movement of sloped seafloor during an underwater earthquake can give tsunamis a critical boost. Scientists previously assumed that vertical movement alone contributed most of a tsunami’s energy.
More than half of the energy for the unexpectedly large tsunami that devastated Japan in 2011 (SN Online: 6/16/11) originated from the horizontal movement of the seafloor, the researchers estimate. Accounting for this lateral motion could explain why some earthquakes generate large tsunamis while others don’t, the researchers report in a paper to be published in the Journal of Geophysical Research: Oceans.
“For the last 30 years, we’ve been moving in the wrong direction to do a good job predicting tsunamis,” says study coauthor Tony Song, an oceanographer at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “This new theory will lead to a better predictive approach than we have now.”
The largest tsunamis form following earthquakes that occur along tectonic boundaries where an oceanic plate sinks below a continental plate. That movement isn’t always smooth; sections of the two plates can stick together. As the bottom oceanic plate sinks, it bends the top continental plate downward like a weighed-down diving board. Eventually, the pent-up stress becomes too much and the plates abruptly unstick, causing the overlying plate to snap upward and triggering an earthquake. That upward…