以形变观测为约束的芦山M_S7.0地震孕震机理数值模拟研究

本文以2013年4月20日芦山MS7.0地震前后在震中附近开展的形变观测研究结果为约束,利用震区天然地震成像、大地电磁测深、人工地震探测剖面、余震精确定位、震源破裂过程、地质考察、GPS观测、构造应力场等结果,建立了芦山地震震中及邻近地区的深浅部构造二维有限元数值模型,探讨了青藏高原向东挤出运动、区域地形特征、地壳内低速带和滑脱面、震区主要断裂带活动等可能因素对芦山地震孕育和破裂的控制作用.模拟结果显示,汶川地震后的青藏高原东部物质相对四川盆地运动速率增大是引发或加快芦山地震发生的主要动力学控制因素,龙门山断裂带西侧上中地壳内部低速带和滑脱面的存在是控制芦山地震震源位置的重要条件,其他因素则是控制龙门山断裂带长时间尺度区域构造活动的动力学因素;同时本文给出了主震破裂为复杂"y"型双破裂面的同震位移,模拟计算的地表垂直位移与观测结果一致,进一步支持了余震精确定位提出的主震为"y"型破裂面的推测.

The numerical simulation on the seismogenic mechanism of the Lushan MS7.0 earthquake constrained by deformation observation

We established a two-dimensional finite element model of the Lushan earthquake and its adjacent region. The model was based on the natural seismic imaging, magnetotelluric sounding, artificial seismic sounding, precise aftershock location, focal rupture inversion, geological survey, GPS observation and tectonic stress field. Using the results of deformation observation of the Lushan M_S7.0 earthquake on April 20, 2013 as constraints, we explored some possible factors, such as eastward extrusion of Qinghai Tibet Plateau, characters of regional topography, lower velocity zone, detachment surface, tectonic faults, and et al, and how these factors impact the rupture character of the Lushan earthquake and its seismogenic process. The numerical results showed that, the movement rate of the material in the eastern part of the Qinghai Tibet Plateau increased after the Wenchuan earthquake, which was the main dynamic factor causing or accelerating the Lushan earthquake; the existence of low velocity zone and detachment surface in the upper middle crust of the Longmen mountain fault zone was an important condition for controlling the location of Lushan epicenter; and the rest of the factors were the dynamic factors controlling the tectonic activity of the Longmen mountain fault zone in the long time scale. Also, this paper gave the simulated result of coseismic displacement caused by the complex "y" type rupture, which further supported the speculation on Lushan mainshock rupture surface as the "y" type.