An International Tsunami Survey Team ITST conducted field surveys of tsunami effects on the west coast of northern and central Sumatra and offshore islands 3–4 months after the 26 December 2004 tsunami. The study sites spanned 800 km of coastline from Breuh Island north of Banda Aceh to the Batu Islands, and included 22 sites in Aceh province in Sumatra and on Simeulue Island, Nias Island, the Banyak Islands, and the Batu Islands. Tsunami runup, elevation, flow depth, inundation distance, sedimentary characteristics of deposits, near-shore bathymetry, and vertical land movement subsidence and uplift were studied. The maximum tsunami elevations were greater than 16 m, and the maximum tsunami flow depths were greater than 13 m at all sites studied along 135 km of coastline in northwestern Sumatra. Tsunami flow depths were as much as 10 m at 1,500 m inland. Extensive tsunami deposits, primarily composed of sand and typically 5–20 cm thick, were observed in northwestern Sumatra. DOI: 10.1193/1.220772

[1] The structure and variability of the Halmahera and Mindanao Eddies (HE and ME), which are thought to be quasi-stationary eddies, are described based on onboard and timeseries observations in the gateway region of the Indonesian Throughflow (ITF). The HE was found to have a clear anticyclonic eddy structure during all cruises. It tilted northward and/ or westward with increasing depth. The HE mixes waters from the northern and southern hemispheres and transfers this mixed water to the eastern route of the ITF. The HE shifted northwestward in the boreal summer and the cold phase of ENSO (El Niño and Southern Oscillation) and southeastward in the boreal winter and the warm phase of ENSO. In contrast, the ME, with its cyclonic eddy structure, was observed only once and seems not to be a quasi-stationary eddy. It appears in the mean field and is confined above the thermocline. The stationary northward undercurrent, the Mindanao Undercurrent, was also not found at 7 N east of Mindanao, but the northern tip of the HE was found at this latitude.

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On the evening of March 28, 2005 at 11:09 p.m. local time (16:09 UTC), a large earthquake occurred offshore of West Sumatra, Indonesia. With a moment magnitude (M w ) of 8.6, the event caused substantial shaking damage and land level changes between Simeulue Island in the north and the Batu Islands in the south. The earthquake also generated a tsunami, which was observed throughout the source region as well as on distant tide gauges. While the tsunami was not as extreme as the tsunami of December 26th, 2004, it did cause significant flooding and damage at some locations. The spatial and temporal proximity of the two events led to a unique set of observational data from the earthquake and tsunami as well as insights relevant to tsunami hazard planning and education efforts.

For the purpose of developing a practical method for estimating directional wave spectrum from HF radar sea-echo Doppler spectrum, a Bayesian method proposed by Hashimoto and Tokuda (1998) is modified and improved. In the method, a formulation of directional spectrum is characterized by an exponential function having the power expressed by a Fourier series over the directional range, while being assumed to be a piecewise-constant function over the frequency range. The method is examined using numerical simulation, with its validity being discussed. The result shows that the method has advantage in that it requires less memory and shorter computation time in practical applications.