Earth Planets Space, Vol. 58 (No. 2), pp. 217-221, 2006
Niigata Junior College, Nippon Dental University, Hamauracho 1-8, Niigata 951-8580, Japan
(Received July 5, 2005; Revised February 14, 2006; Accepted February 14, 2006; Online published February 17, 2006)
Dominant periods determined from tide gauge records of the 2004 Sumatra tsunami were used to estimate the size of the tsunami source. A period of 40 minutes dominates the initial motions and spectra are consistent with a fault width of 110 km for a sea depth of 1000 m. Another dominant period of 140 minutes in the spectra observed at the direction of fault azimuth can be explained using a fault length of 1200 km. These values taken together are consistent with source formation on the continental slope with width of 110 km and length of 1200 km along Nicobar and Andaman Islands.
Key words: Dominant period, Sumatra tsunami, tide gauge records.