The magnitude 9.1 Great SumatraAndaman Earthquake of December 26, 2004, spawned the deadliest tsunami in history, killing more than 230,000 people in 14 countries around the Indian Ocean. More than half of those killed had lived in Acheh Province, Sumatra, where the tsunami rose as high as 30 m (100 ft.) and traveled more than 4 km (2.5 mi.) inland in this lowlying region.

This earthquake began at its epicenter near northern Sumatra and moved the earth's crust an average of 15 m (50 ft.) as it ruptured northward for at least 1200 km (750 mi.), almost to the coast of Myanmar (Burma), over an 8minute period. This distance is at least 200 km (125 mi.) longer than the length of fault that moved during the largest earthquake ever recorded, the magnitude 9.5 Great Chile Earthquake of 1960.

This animation shows why this southtonorth rupture is important for understanding the behavior of this tsunami, and why such "progressive" rupture needs to be considered for future tsunami forecasting. If the earthquake had moved the fault along its entire length allatonce it would have sent the largest tsunami waves perpendicular to the fault and so they would have passed south of Sri Lanka. The earthquake motion, however, started in the south and moved northward along the fault so the tsunami began radiating from near Sumatra before it could be generated near Myanmar, thus causing the largest tsunami waves to move in a different direction such that they strike Sri Lanka and Somalia directly, consistent with the tsunami waves actually observed in those countries.

PTWC created this animation using the progressive rupture described by Chlieh et al. (2007) as input for their experimental forecast model, RIFT (Wang et al., 2012). For the first 30 minutes of simulated time the animation is centered over the northern Indian Ocean and moves at 30x normal speed to show the details of the tsunami as generated by this progressive rupture. The animation then speeds up to 1800x normal speed (1 sec. = 30 minutes simulated time) to carry the simulation forward a full 24 hours while it also zooms out and rotates the virtual globe to show the entire Indian Ocean. The waves then fade to an "energy map" showing the maximum calculated tsunami heights on the open ocean, then fade again to a map of the maximum calculated tsunami heights on the impacted coastlines.


References:

Chlieh, M., Avouac, J., Hjorleifsdottir, V., Song, T.A., Ji, C., Sieh, K., Sladen, A., Hebert, H., Prawirodirdjo, L., Bock., Y., & Galetzka, J. (2007) "Coseismic Slip and Afterslip of the Great Mw 9.15 SumatraAndaman Earthquake of 2004." Bulletin of the Seismological Society of America, 97 (1A), S152S173, DOI: 10.1785/0120050631

Wang, D., N.C. Becker, D. Walsh, G.J. Fryer, S.A. Weinstein, C.S. McCreery, V. Sardiña, V. Hsu, B.F. Hirshorn, G.P. Hayes, Z. Duputel, L. Rivera, H. Kanamori, K.K. Koyanagi, and B. Shiro (2012) "Realtime Forecasting of the April 11, 2012 Sumatra Tsunami" Geophysical Research Letters, 39, 6 pp., DOI: 10.1029/2012GL053081