Observations of the 2004 and 2006 Indian Ocean tsunamis from a pressure gauge array in Indonesia

[1] Five shallow pressure gauges located in straits in the southern Indonesian islands were used to evaluate tsunami signals triggered by the earthquakes off the northwest coast of Sumatra in December 2004 and the south coast of Java in July 2006. Tsunami waves reached the pressure gauges around 5 to 6 hours after the 2004 earthquake; the largest waves arrived 10 to 23 hours later, with amplitudes ranging from 9 to 25 cm. After the 2006 earthquake, tsunami arrivals were only evident at the Ashmore and Roti pressure gauges in Timor Passage. At these two gauges, the first waves arrived around 2.25 hours after the earthquake, and the largest waves arrived 2 to 3 hours later, with amplitudes of 6 and 18 cm. Spectral analysis shows an increase of energy in the 40to 80-min-period band during the 2004 tsunami, and at periods of 10 to 20 min in 2006. A simple ray tracing model of both the 2004 and 2006 events, which approximates the tsunami as a shallow water wave, was used to evaluate the effect of topography on tsunami propagation in order to provide a physical explanation for the features observed in the pressure gauge data.