鳥取県西部地震(2000年10月)と山陰地方の地震活動-その特異性の検討

抄録

The West-Tottori Earthquake (Tottoriken-seibu Earthquake) of October 6,2000, JMA Magnitude (Mj) 7.3, accompanied no distinct surface fault and occurred in the active fault-free area. This was a peculiar example in the Japanese on-land earthquakes, considering that all the recent on-land earthquakes greater than Mj 7.2 produced distinct surface faults and occurred along the detectable active fault in the epicentral region.
The moment magnitude for the West-Tottori Earthquake is estimated at Mw 6.6 or Mw 6.7. In the Japanese on-land earthquakes of about Mw 6.6 or 6.7, three in five cases were associated with no distinct surface faults and did not occur along the distinct active fault. This indicates that the West-Tottori Earthquake was not a peculiar_ one in relation to the earthquake size against surface faulting. As for the absence of the known active fault in the epicentral region of the Earthquake it is explained by very low slip-rate of the seismogenic fault which must be about 0.01mm/yr or smaller.
The abnormally high seismicity of the 1900's in the San-in region is indicated by the succesive occurrence of four large earthquakes greater than Mj 6.8, and by comparison of Quaternary moment release rate of the region and possibly by historical records. This implies that there exists rise and fall in seismicity with the return period of 100 years or longer and the existence of triggering among areas several or several tens kilometers apart in the region in 1900's.