日本Mw9.0级地震的库仑应力变化及对余震的触发

采用已公布的1个前震和3个主震震源可变滑动模型,计算了日本Mw7.3级前震、M_w9.0级主震产生的同震库仑应力变化,并采用哈佛Global CMT和日本F-net余震目录,在不同有效摩擦系数取值下计算了主震对余震的触发效应,分析了应力空间分布与余震活动空间分布的相关性。研究表明,日本地震前震对主震有触发作用,前震在主震处产生的正应力变化为0.404 bar,剪应力变化0.282 bar,同震库仑应力变化为0.517 bar,应力变化超过了应力触发阈值0.1 bar,达5倍之多,属于典型的地震应力触发,而非诱发事件。主震对后续余震有触发效应,最小触发率为57%,最大达到75%。余震多分布在主震产生的同震库仑应力红色加载区。同时,分析了可变滑动模型、有效摩擦系数、余震目录、震级及节面选取等对计算结果的影响。可变滑动模型、有效摩擦系数变化对计算结果影响不大,余震目录、震级及节面选取对结果有一定影响,尤其是当余震目录足够多、震级足够大时,计算结果更加可靠。为了深入讨论节面选取对计算结果的影响,对余震两个节面上库仑应力、剪切应力及正应力变化差值进行了频次统计。分析显示节面选取对正应力有一定影响,而对库仑应力及剪应力影响不大。

The Coulomb stress changes of the 2011 Mw9.0 Japan earthquake and its triggered effects on subsequent aftershock

Based on four seismic source variable slipping models published, we calculate coseismic Coulomb stress changes produced by both Mw7.3 foreshock and Mw 9.0 mainshock. Using both Harvard Global CMT and Japan F-net catalogs with coeffective friction factor give variable value, the stress triggering and effect on aftershocks imposed by mainshock are carried out and researched. Meanwhile, the spatial interrelationship between Coulomb stress change and aftershock distribution is preliminarily analyzed. The study illustrates that foreshock trigger subsequent mainshock, on which produce 0.404 bar of normal stress, 0.282 bar of shear stress and as much as 0.517 bar of coseimic Coulomb stress change.Especially, Coulomb stress change reaches more than five times of trigger threshold value of ~0.1 bar, belonging to typical seismic stress triggering not inducing case. The mainshock has a obviously triggering on subsequent aftershocks which numerously fall into certain red region of stress loaded. Furthermore, the influence of model, friction factor, magnitude and nodal plane selection of aftershock on stress calculation results has been analyzed. The preliminary study suggests that model, friction factor affect little to Coulomb stress which mainly depend on magnitude and nodal plane of aftershocks, and specially strong dependence if using enough aftershocks numbers and even bigger magnitude. In order to further discuss the influence of nodal plane section on results, we make histograms of Coulomb stress, shear stress and normal stress changes on two nodal planes, respectively. The conclusion that the nodal plane selection has certain influence on normal stress and weak influence on Coulomb stress and shear stress can be drawn.