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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:
Research on Frequency of the Aftershock Sequence of the Wenchuan Earthquake Based on Coseismic Coulomb Stress Change
Jia Ruo,Jiang Haikun
Abstract:
By the aftershock frequency estimation method based on the calculation of coseismic static Coulomb stress changes and rate-and state-dependent fault constitutive law,we calculate the frequency of “direct”aftershocks of the Wenchuan earthquake related to coseismic static Coulomb stress changes in its aftershock zone and the areas nearby. It shows that the frequency is significantly lower than the truth in the main rupture zone,especially in the southern rupture zone,due to the decrease of stress level on the rupture plane of the main shock resulting from coseismic Coulomb stress change. The study also shows that the effect of the Coulomb stress change on the duration of aftershock activity is associated with the lower limit magnitude. The duration is about 15 -16 months for aftershocks above ML 4. 0,and close to 60 months for aftershocks above ML3. 5. In this period,the ratio of the “direct”aftershocks caused by coseismic Coulomb stress change ranges between 44. 7% to 48. 6%,which suggests that,even in the“effective”period of coseismic Coulomb stress changes,about half of the aftershocks on the main shock rupture plane are independent of coseismic Coulomb stress changes. It is pointed out that those aftershocks may be related to the afterslip or the viscoelastic relaxation,which are time dependent cases.
Key words:  Wenchuan earthquake  Static Coulomb failure stress change  “Direct” aftershock  Aftershock spatial distribution  Afterslip