2008年和2014年于田地震对周边断层发震概率的影响

大震后区域静态库仑应力变化直接影响地震活动性速率的变化、主震断层外余震和即将失稳断层的发震概率的变化.利用滑移速率和状态相依赖的摩擦定律,结合2008年3月21日于田地震前后的地震活动性水平,定量计算了2008年于田地震后该地区周边断层发震概率的变化,着重解释了2014年于田地震发震的可能根源.此外,本文还对库仑应力明显变化的周边三条断层进行了发震概率的定量计算.贡嘎错断裂中段、贡嘎错断裂西南段和康西瓦断裂中段分别经历了发震概率先降后升、先升后升和先降后降两个阶段,充分显示了库仑应力的细微变化造成的周边断层的危险性的变化.这三条断裂发生7.0级以上地震的发震概率超越95%均需要500年左右;贡嘎错断裂西南段发生中强地震的可能性较大,而康西瓦断裂中段活跃度较低.

Effects of the 2008 and 2014 Yutian earthquake on seismic probabilities of adjacent faults

Static stress changes are used to explain variations of seismicity rates, off-fault aftershocks and probability changes for the occurrence of impending earthquakes. Based on the rate- and state- dependent frictional law, combined with the seismicity analysis before and after the 2008 Yutian earthquake, we quantitatively calculate the probability of earthquake occurrences near the main fault, and explain the probable causes for the 2014 Yutian earthquake.#br#The rate- and state- dependent frictional law characterizes variety of materials over a wide range of sliding conditions. This formulation gives a unified representation of diverse sliding phenomena. Earthquake clustering arises from sensitivity of nucleation times to the stress changes. The model provides the characteristic aftershock decay law and interpretation to aftershock parameters. We use this seismicity formulation to predict large changes of earthquake probabilities based on the stress changes. Firstly, we calculate the aftershock duration and seismicity rate after the main shock. Secondly, to illustrate the corresponding sensitivity in the probability of earthquakes to stress history, we use a Poisson model of earthquake occurrence for the probability of one or more earthquakes in a time interval.#br#We have computed the earthquake probabilities of southwest and central segments of the Gonggacuo fault, and the central segments of Kengxiwar fault, where the Coulomb stress also changed after the 2008 Yutian earthquake. The earthquake probabilities of the central segments of Gonggacuo and Kengxiwar faults decreased after the 2008 Yutian earthquake, while that of southwest segments of Gonggacuo fault increased. After the 2014 Yutian earthquake, the earthquake probabilities of the southwest and central segments of the Gonggacuo fault increased, but the central segments of Kengxiwar fault decreased. This result indicates that slight variations in Coulomb stress changes can cause the seismic risk to change on the faults. It needs about 500 years that the probabilities of occurrence an M7.0 earthquake exceed to 95% of the three faults mentioned above. The destructive earthquakes are likely to occur in the southwest segments of the Gonggacuo fault, while the seismic risk of the central segments of the Kengxiwar fault is low.