Earth Planets Space, Vol. 56 (No. 3), pp. 367-372, 2004LETTER
Kenji Hirata1, Yuichiro Tanioka2, Kenji Satake3, Shigeru Yamaki4, and Eric. L. Geist5
1Deep Sea Research Department, Japan Marine Science and Technology Center, 2-15 Natsuhima-cho, Yokosuka 237-0061, Japan
2Institute of Seismology and Volcanology, Hokkaido University, N10W8 Kita-ku, Sapporo 060-0810, Japan
3Active Fault Research Center, National Institute of Advanced Industrial Science and Technology, Site C7 1-1-1 Higashi, Tsukuba 305-8567, Japan
4Seamus Ltd., 2235 Kizaki, Toyosaka 950-3304, Japan
5U.S. Geological Survey, 345 Middlefield Road, Menlo Park, 94025, CA, USA
(Received November 16, 2003; Revised February 26, 2004; Accepted Feburary 26, 2004)
We estimate the tsunami source area of the 2003 Tokachi-oki earthquake (Mw 8.0) from observed tsunami travel times at 17 Japanese tide gauge stations. The estimated tsunami source area (~1.4 104 km2) coincides with the western-half of the ocean-bottom deformation area (~2.52 104 km2) of the 1952 Tokachi-oki earthquake (Mw 8.1), previously inferred from tsunami waveform inversion. This suggests that the 2003 event ruptured only the western-half of the 1952 rupture extent. Geographical distribution of the maximum tsunami heights in 2003 differs significantly from that of the 1952 tsunami, supporting this hypothesis. Analysis of first-peak tsunami travel times indicates that a major uplift of the ocean-bottom occurred approximately 30 km to the NNW of the mainshock epicenter, just above a major asperity inferred from seismic waveform inversion.
Key words: The 2003 Tokachi-oki earthquake, tsunami, tide gauge records, the 1952 Tokachi-oki earthquake.