Re-examination of aftershocks of the 1952 Tokachi-oki earthquake and a comparison with those of the 2003 Tokachi-oki earthquake

摘要

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.