Abstract
The Tottorii-ken Seibu earthquake (114JMA7.3) occurred on 6th October 2000 on the border between Tottori and Shimane prefectures, western Japan, an area that contains no significant active faults according to active fault catalogues. No distinct surface rupture became evident as a result of this earthquake, even though it is generally assumed that earthquakes of magnitude 7.0 or larger are almost associated with surface rupture along associated geomorphologically mapped active faults. This means that, despite its large magnitude, the Tottorii-ken Seibu earthquake was not a major intraplate earthquake that took place on geomorphologically mapped active faults, but one related to significant background seismicity. This might explain the minimal damage that it caused, as compared to damage from the Kobe earthquake(MJMA7.2) by the Rokko and Nojima faults. If an occurrence probability of an M7.3 earthquake taking place in this region in 50 years had been calculated using the seismicity catalogue and the Gutenberg-Richter magnitude-frequency law, it would have been 7-12%, because several moderate size earthquakes took place in the previous decade. However, using the seismicity catalogue and the G-R law to evaluate maximum earthquake magnitude and earthquake probability clearly remains problematic for background earthquakes.
