Remote Sensing of the Changing Oceans pp 327-342
Satellite Observations Defying the Long-Held Tsunami Genesis Theory
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Using seismographs and GPS displacement measurements, we have estimated the seafloor deformation history of the December 2004 Sumatra-Andaman earthquake and the March 2005 Nias earthquake by separating their deformation period into intervals of 800-s, 1-h, and 6-months. We have then calculated their corresponding gravity changes (induced by the seafloor deformation), which are 11.3, 12.5, and 14.9 microgalileo, respectively. We show that the seismographs and GPS-derived values are consistent with the known postseismic to coseismic moment ratio of 30% and the Gravity Recovery and Climate Experiment (GRACE) satellites measurements of 15 microgalileo for the same period of 6 months. However, the vertical component of the accumulated seafloor deformation during the tsunami formation period (~30 min) could only generate a potential energy of 1.2 × 1015 Joules and account for only one third of the actual tsunami height. The evidence is overwhelmingly contrary to the long-held theory that the vertical deformation of seafloor is the primary source of tsunamis.
Furthermore, we have carefully examined the pioneering wave-maker experiment that initially conceived the ubiquitous tsunami genesis theory. Surprisingly, we found that the experimental ratio of the horizontal slip distance to the water depth – the non-dimensional parameter that allows comparing the experiment with reality on an apple-to-apple basis – was 200 times of realistic earthquake parameters. The experimental conclusion is problematic in conceiving the tsunami theory. By including the horizontal momentum energy transferred by the faulting continental slope in a three-dimensional tsunami model, we have re-examined the December 2004 tsunami using both seismographs and GPS measurements. Our results show that the new theory is more consistent with altimetry and tide data than the conventional theory of using the vertical force alone, suggesting that the tsunami formation mechanism is not as simple as previously thought.
KeywordsTsunami genesis theory GRACE Vertical uplift Horizontal displacement Seismograph GPS data
- Chlieh M et al. (2007) Coseismic slip and afterslip of the great Mw 9.15 Sumatra-Andaman earthquake of 2004. Bull Seismol Soc Am 97. doi:10.1785/0120050631Google Scholar
- Hirata K et al. (2006) The 2004 Indian Ocean tsunami: tsunami source model from satellite altimetry. Earth Planets Space 58:195–201Google Scholar
- Hjorleifsdottir V (2007) Earthquake source characterization using 3D numerical modeling. PhD Thesis, Caltech. http://etd.caltech.edu/etd/available/etd-03212007-170259/
- Iwasaki S (1982) Experimental study of a tsunami generated by a horizontal motion of a sloping bottom. Bull Earthq Res Inst Univ Tokyo 57:239–262Google Scholar
- Merrifield MA et al. (2005) Tide gauge observations of the Indian ocean tsunami, December 26, 2004. Geophy Res Lett 32:L09603. doi:10.1029/2005GL022610Google Scholar
- Okada Y (1985) Surface deformation due to shear and tensile faults in a half-space. Bull Scismol Soc Am 75:1135–1154Google Scholar
- Song YT (2007) Detecting tsunami genesis and scales directly from coastal GPS stations. Geophy Res Lett 34. doi:10.1029/2007GL031681Google Scholar
- Song YT et al. (2005) The 26 December 2004 tsunami source estimated from satellite radar altimetry and seismic waves. Geophys Res Lett 23. doi:10.1029/2005GL023683Google Scholar
- Song YT et al. (2008) The role of horizontal impulses of the faulting continental slope in generating the 26 December 2004 tsunami. Ocean Modell. doi:10.1016/j.ocemod.2007.10.007Google Scholar
- Vennard JK, Street RL (1982) Elementary fluid mechanics, 6th edn. John Willey & Sons, New York, p 689Google Scholar