Earth Planets Space, Vol. 56 (No. 3), pp. 341-345, 2004LETTER
Nobuo Hamada1 and Yasunori Suzuki2
1Meteorological Research Institute, 1-1, Nagamine, Tsukuba 305-0052, Japan
2Association for the Development of Earthquake Prediction, 1-5-18 Sarugaku-cho, Chiyoda-ku, Tokyo 101-0064, Japan
(Received November 26, 2003; Revised February 3, 2004; Accepted February 25, 2004)
We relocated hypocenters of the March 4, 1952 Tokachi-oki (Mj8.2) earthquake and its aftershocks by reassessing data of the Central Meteorological Station network at the time and found that the distribution of relocated aftershocks is clearly bounded on its eastern extension by the Kushiro canyon, which extends south-east from the coast of Hokkaido near Kushiro to the Kuril trench. The reevaluated aftershock pattern is quite similar to the pattern of the September 26, 2003 Tokachi-oki earthquake (Mj8.0). Detailed seismic intensity maps based on the report of human perceptions in 1952 and the seismic intensity meter network in 2003 also show resemblance. Similar aftershock pattern and seismic intensity distribution imply that both earthquakes are a pair of characteristic earthquakes of the same size sharing the same source area and the same focal process.
Key words: Tokachi-oki, seismic gap, asperity, characteristic earthquake, aftershock, characteristic earthquake, seismic Intensity, seismic gap.