1 The Sumatra Earthquake and Indian Ocean Tsunami

At 16:09:36 UTC on March 28, 2005 a strong earthquake struck at southwest of Banda Aceh in northern Sumatra. The epicenter was located at (1.64oN, 96.98oE), which is about 200km in the southeast direction of the epicenter of the December 26, 2004 mega earthquake (3.30°N, 95.78°E). Both earthquakes occurred near the junction of the Indian, Australian and Burma plates. It is known that the Indian plate has been subducting below the Burma microplate (at roughly 60 mm/year) along a fault line stretching from Indonesia in the south to the Andaman Islands in the north. The December 26, 2004 earthquake and aftershocks ruptured approximately 1,200 km of this fault line, along the northern Sunda Trench. It has been estimated that the March 28, 2005 earthquake only ruptured about 400 km fault line filling in the gap between 1861 earthquake and 2004 mega earthquake. The initial estimate of the earthquake magnitude was Mw = 8.6, based on the Harvard University’s Centroid Moment Tensor (CMT) solution. The seismic moment released on the fault plane (strike = 329o and dip =7o) was estimated as 1.1x1029 dyne-cm, which is about one order of magnitude smaller than that of the December 26, 2004 earthquake. In Figure 1, the vertical and horizontal seafloor displacements resulting from the earthquake have been reported by Ji, C. (2005). The maximum positive seafloor displacement is slightly greater than 3m and the maximum negative seafloor displacement is roughly 1m. We remark here that the December 26, 2004 earthquake generated about 7m positive seafloor displacement and 3.5m negative seafloor displacement