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The Great 2004 Sumatra Earthquake: Evidence from hydroacoustic signals

Analysis of acoustic signals recorded at small-scale horizontal hydroacoustic arrays

Hydroacoustic signals, called T-waves, generated by the megathrust earthquake of 26 Dec, 2004 were recorded by a network of 5 small hydroacoustic arrays located in the Indian Ocean, at distances of 2800 to 7000 km from the epicenter. Analysis of a series of short time windows within the T-wave coda shows that the receiver to source azimuth varies with time, indicating that the apparent T-wave source is not stationary. The apparent T-wave source moves northward along the Sunda trench at an average velocity of 2km/s, closely tracking event rupture. The hydroacoustic data suggest that the rupture proceeded in two phases; initially it progressed northwest along the Sunda trench with a velocity of approximately 2.4 km/s. At 600km from the epicenter the rupture slowed to approximately 1.5 km/s, as it continued to propagate to the northwest

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