Satellite Observations Defying the Long-Held Tsunami Genesis Theory

Using seismographs and GPS displacement measurements, we have fully estimated the seafloor deformation history of the December 2004 Sumatra-Andaman earthquake and the March 2005 Nias Island earthquake by separating their deformation period into intervals of 800-sec, 1-hour, and 6-months. Their corresponding gravity changes (induced by the seafloor deformation) are 11.3, 12.5, and 14.9 microgalileo, respectively, consistent with the Gravity Recovery and Climate Experiment (GRACE) satellites measurements of 15 microgalileo for the same period of six months. However, the vertical component of the accumulated seafloor deformation during the tsunami formation period could only generate a potential energy of 1.2E+15 Joules and account for only one third of the actual tsunami height measured by altimeters. The evidence is overwhelmingly contrary to the long-held theory that the vertical deformation of seafloor is the primary source of tsunamis. Surprisingly, we also found that a pioneering wave-maker experiment, which conceived the vertically-forced tsunami genesis theory in 1980s, used an exaggerated experimental ratio of the horizontal slip distance to the water depth, the key non-dimensional parameter that allows comparing the experiment with reality on an apple-to-apple basis, about 200 times of realistic earthquake parameters. The experiment is problematic in conceiving the vertically-forced tsunami theory. We conclude that the tsunami source has been poorly understood and the tsunami formation mechanism is not as simple as previously thought. Our study suggests a new method of using gravity measurement from space to constrain the under-sea earthquake source for tsunami modeling and to gain insight into the tsunami genesis theory. Seafloor deformation, corresponding gravity changes, and GRACE measurements of the December 26 Sumatra-Andaman earthquake and the March 2005 Nias Island earthquake.