open access

https://doi.org/10.14943/gbhu.69.23

https://hdl.handle.net/2115/21495

地震活動静穏化域と1973年根室半島沖地震震源域との間で発生した2004年11月29日釧路沖地震（M7.1)

英語

2006-03-15

北海道大学大学院理学研究科地球惑星科学専攻（地球物理学）

Geophysical bulletin of Hokkaido University

69

23-39

We have investigated the source process and the aftershock distribution of a large earthquake with M=7.1 occurred on 29 November 2004 off the coast of Kushiro (or Shiranuka) in the eastern Hokkaido,Japan. The source parameters are summarized as follows:the total seismic moment M_0=3.4×10^{19}Nm,thatis,M_w=7.0;(strike,dip,ship)=(238°,33°,117°);depth of the initial break point=48 km;and source duration time =10sec. The aftershocks were relocated using the three-dimensional velocity structures of P-and S-waves,and we found that the aftershocks concentrated on a plane with the area of 30×15㎞＾｛2｝dipping 22°toward the landside whose orientation agrees closely with that of the northwest-dipping nodal plane of the focal mechanism. The stress drop was estimated to be 89 bars. The aftershock area does not overlap with the asperity ruptured by the main shock,but outlined the asperity. These observations strongly suggest that the main shock itself is a very usual interplate event at depth of around 50 km in the Japan subduction zone. However,taking the tectonic circumstance into account,thisi is an outstanding event since the focal area was located between the five-years-lasting seismic quiescence area and the asperity ruptured by the 1973 Nemuro- Oki earthquake.

紀要論文

Version of Record

0439-3503

AN0008976X