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调查了日本3个内陆大地震余震的深度分布状态。这3个地震分别是:2000年鸟取县西部7·3级地震、2003年宫城县北部6·4级地震和2004年新潟县中越6·8级地震。对这3个地震,发现在主震发生后,孕震层都向更深和更浅的区域扩展。深层和浅层地震比中间层的地震活动衰减更快。当应力增加很快时,脆性断裂可能发生在一个应力延展衰减过程中。研究结果显示,断层活动可能延展到从地震活动背景估计的孕震区的外部。这应该在地震危险性评价中予以考虑。
The depth distribution of the aftershocks of three inland major earthquakes in Japan was investigated. The three earthquakes are: the T7.3 earthquake in western Tottori Prefecture in 2000, the MS6.4 earthquake in northern Miyagi Prefecture in 2003 and the Sino-Vietnamese earthquake of magnitude 6.0 in 2004 in Niigata Prefecture. For these 3 earthquakes, it is found that after the mainshock occurs, the seismogenic layers expand to deeper and shallower areas. Deep and shallow earthquakes decay more rapidly than the middle earthquakes. When the stress increases rapidly, brittle fracture may occur in a process of stress relaxation attenuation. The results show that the fault activity may extend to the outside of the seismogenic zone estimated from the seismic activity background. This should be considered in the seismic hazard assessment.