基于速率状态摩擦定律研究隆宝湖对甘孜-玉树断裂带玉树段发震能力的影响

A number of large scale strike-slip fault zones are situated in Chinese mainland. To effectively determine the seismogenic potential of strike-slip fault zone from physical perspective is a very important and basic scientific issue in earthquake prevention and disaster relief. Step-overs are the basic geometry structures causing the discontinuity of strike-slip faults, and play an important role in the controlling of energy accumulation and cascading rupture. This project takes Yushu segment of Ganzi-Yushu fault zone as the object of study, which is the causative fault of the 2010 Yushu MS7.1 earthquake. Based on the geological survey, inversion of fault slip distribution and crustal deformation observation from GPS, the numerical model of causative fault including the tensile step-over of Longbao Lake and asperities is established. Based on the rate-and state-dependent friction law, the recurrence interval of Yushu MS7.1 is analyzed by the interaction of the asperities and evolution of fault movement. Earthquake catalogue is extracted from the numerical result, and the effect of the friction parameter and characteristic of asperities on the earthquake number, maximum magnitude and distribution of seismic source in a seismic active period is studied. The interval between two active periods also will be investigated. The possibility for the cascading rupture between the two asperities of the MS7.1 mainshock and the MS6.3 aftershock is explored. The seismogenic potential about the Yushu segment of Ganzi-Yushu fault zone is analyzed synthetically.

对于发育了多条大型走滑活动断层的中国大陆地区，基于数值模拟研究走滑断裂带的发震能力是防震减灾工作中非常重要的基础科学问题。阶区是构成走滑断层不连续性的基本几何结构，对断层能量积累和地震的级联破裂起重要的控制作用。本项目拟以甘孜-玉树断裂带玉树段为例，以2010年玉树MS7.1地震为研究对象，基于已有的地质调查、震源过程研究及GPS观测等资料，建立包含隆宝湖拉张阶区几何结构的玉树地震发震断层的凹凸体数值模型。基于速率状态摩擦定律，模拟凹凸体相互作用和断层运动演化，得到玉树MS7.1的复发周期。把模拟结果虚拟为地震序列，分析摩擦参数和凹凸体特征与地震活跃期内地震数目、最大震级及震源分布的关系，以及对相邻活跃期时间间隔的影响。探索MS7.1主震和MS6.3余震对应的凹凸体发生级联破裂的条件，综合分析甘孜-玉树断裂带玉树段强震发生能力。

甘孜-玉树断裂带玉树段于2010年发生了MS7.1强震，震后1.5h于隆宝湖盆地南侧发生MS6.3强余震，分析隆宝湖对破裂传播的控制作用，以及甘孜-玉树断裂带玉树段发生级联破裂的条件，对理解2010年玉树地震的发震过程以及目标断层的孕震能力有重要意义，研究得到的认识可有助于理解类似的走滑断层系统的孕震机理。我们基于已有的地质调查、震源过程研究及GPS观测等资料，建立了包含玉树地震主震和强余震凹凸体的发震断层模型，令隆宝湖盆地作为阻止破裂传播的障碍体。断层面滑动服从速率状态摩擦定律，通过模拟多周期的地震破裂过程，分析凹凸体性质、断层应力状态的演化，我们发现，凹凸体尺寸、强度、摩擦性质等，都会对玉树地震的发生以及断层发震能力造成影响。探索了目标断层发生级联破裂的条件，发现断层面应力的非均匀分布起到关键作用。进一步分析了断层强度非均匀性对地震孕育和破裂传播的影响。以上研究，有助于我们提高对地震发生机理的认识以及地震危险性的评估。