阿克陶MW6.6地震的发震构造及滑动特征

Seismogenic Structure and Slip Property of the Aketao M W6.6 Earthquake

2016年11月25日新疆阿克陶发生了MW6.6地震。通常震中所处断层的破裂特性与周围区域应力场的动力学特征具有紧密的联系。通过对发震构造断层的精确刻画以及区域地壳中应力释放细节的深入探究,可以加深对发震构造周围地震动力学特征的认识,同时也对判定当地未来一段时间内的地震活动趋势提供了重要参考。首先搜集整理了震源附近的26条余震震源机制,利用网格搜索法反演得到震中附近的应力场,发现该地区主压应力方向为157.36°,倾伏角为1.15°,主张应力方向为66.56°,倾伏角为34.98°,与该地所处的帕米尔高原陆内俯冲形成近东西向断裂的右旋走滑兼有逆冲的背景相一致;然后利用389条余震精定位数据,结合高斯-牛顿算法和模拟退火算法拟合得到发震断层面的走向为103.64°、倾角为65.65°,这与木吉右旋走滑断裂的几何特征基本重合;将所求应力场投影到断层上,得到滑动角为152.77°,该地震表现为右旋走滑断层;最后利用本研究获得的区域应力张量模拟得到的该状态下的各种形状断层面的相对应力分布,发现该地震发生的断层面的相对剪应力接近1,破裂方向与震源区的最优剪切力方向相同,表明该地震是在应力场作用下沿着最有利于背景应力释放的方向上发生的。研究结论对深入理解震源区及周围的构造演化过程和应力状态具有积极的意义。

On November 25,2016,the M W 6.6 earthquake occurred in Aketao,Xinjiang.It is shown that the rupture characteristics of the fault at the epicenter are closely related to the dynamics of the surrounding regional stress field.The precise characterization of the fault of the epicenter and the details of stress release in the regional crust can deepen understanding of the seismic dynamics around the epicenter,and also provide an important reference for determining the trend of local seismic activity in the future.Firstly,26 after shock focal mechanisms near the epicenter were collected,and the stress field near the epicenter was obtained by using the grid search method.The results show that the principal compressive stress direction is 157.36°with a dip angle of 1.15°and the principal extensional stress direction is 66.56°with a dip angle of 34.98°in the area.This conclusion is consistent with the background that an dextral strike and thrust slip occurred on E-W azimuth fault by the intra-land subduction near the Pamir Plateau.Then by using 389 precisely located aftershocks and combination method of Gauss-Newton algorithm and simulated annealing algorithm,the seismogenic fault plane with a strike of 103.64°and dip of 65.65°is estimated,which basically overlap with the geometry of the right-lateral Muji fault.Then by projecting the estimated stress field onto the fault and the sliding angle of 152.77°is obtained,which showing the dextral strike slip property of this earthquake.Finally,the relative stress distributions of variously shaped fault planes is retrieved by using the estimated regional stress tensor in this study.The results show that the relative shear stress on the fault plane of the earthquake is nearly 1,and the rupture direction is nearly the same with the maximum shear stress direction in source region,which indicating that this earthquake occurred under the action of the stress field along the direction most favorable to release of the background stress.The findings of this study is important significance for in-depth understanding of the tectonic evolution and stress state in source region and its adjacent areas.