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基于同震库仑应力变化的汶川地震余震频次研究
贾若1, 蒋海昆2
1.中国地震局地震预测研究所,北京市复兴路63 号100036;2.中国地震台网中心,北京100045
摘要:
在计算同震静态库仑应力变化的基础上,基于速率-状态摩擦定律及与同震静态库仑应力变化相关的余震频次估计方法,研究了汶川地震余震区及附近不同区域内与汶川地震同震静态库仑应力触发相关的“直接”余震频次。结果显示,主震破裂带尤其是主震破裂带南段的“直接”余震频次明显低于实际情况,其原因在于同震库仑应力变化导致的主震破裂面上应力水平的降低。研究结果还显示,汶川地震同震库仑应力变化对余震活动持续时间的影响与震级下限有关。对ML4. 0 以上余震,持续时间约为震后15 ~ 16 个月; 对ML3. 5 以上余震,接近60 个月。在上述时段内,与同震库仑应力变化相关的“直接”余震占全部余震的比例为44. 7% ~48. 6% 。这表明,即使在同震库仑应力变化的“有效”作用时段内,主震破裂面上也大约有50%的余震活动不是缘于同震库仑应力变化的影响,这可能与震后余滑及粘弹松弛等时间相关因素的影响有关。
关键词:  汶川地震  静态库仑应力变化  “直接”余震频次  余震空间分布  震后余滑
DOI:
分类号:
基金项目:国家“十二·五”科技支撑计划项目专题( 2012BAK19B02-05-02) 资助
Aftershock sequence frequency research on the Wenchuan aftershock sequence based on the coseismic coulomb stress changes
Jia Ruo1, Jiang Haikun2
1.Institute of Earthquake Science,China Earthquake Administration,Beijing 100036,China;2.China Earthquake Networks Center,Beijing 100045,China
Abstract:
On the basis of the aftershock frequency estimation method,the coseismic static coulomb stress changes calculation and rate- and state-dependent fault constitutive law, we calculate the Wenchuan “direct”aftershocks frequency and the coseismic static coulomb stress changes of its aftershock zone in the different areas nearby. We find that the forecast result is lower than the actual significantly in the main fracture zone,especially in the south of the fracture,because of the decrease of the calculated coseismic coulomb stress change. It also shows that the effect time of the coulomb stress changes on aftershock activity is associated with the lower magnitude,which is about 15 ~ 16 months for the aftershocks above ML4. 0,and close to 60 months for that above ML3. 5. In this period,the ratio of the “direct”aftershocks caused by coseismic coulomb stress changes lies between 44. 7% to 48. 6% ,which suggests that,even in the“effective”period of coseismic coulomb stress changes,there is about half of the aftershocks independent of the coseismic coulomb stress changes in the fracture zone of the mainshock. It is pointed out that those aftershocks may be related to the afterslip or the viscoelastic relaxation process,which are time dependent cases.
Key words:  Wenchuan earthquake  Static Coulomb Failure Stress Changes  “Direct” aftershocks frequency  Aftershock spatial distribution  Afterslip