The open ocean energy decay of three recent trans‐Pacific tsunamis

Abstract

The 2009 Samoa (Mw 8.1), 2010 Chile (8.8), and 2011 Tohoku (9.0) earthquakes generated destructive tsunamis recorded by a large number of DART stations in the Pacific Ocean. High‐resolution (15 s) DART records yield mean energy decay times for these events of 17.3, 24.7, and 24.6 h, respectively. We attribute these differences to the frequency content of the tsunamis. Specifically, the Samoa tsunami was a “high‐frequency” event with periods of 2–30 min whereas the Chile and Tohoku tsunamis were “broad‐band” events with periods of 2–180 min. Differences in frequency content are linked to differences in the source parameters: Samoa was a relatively small deep‐water earthquake while Chile and Tohoku were extensive shallow‐water earthquakes. Frequency‐dependent analysis of the Chile and Tohoku tsunamis indicates that shorter period waves attenuate much faster than longer‐period waves (decay times range from 15 h for 2–6 min waves to 29 h for 60–180 min waves).