2008年汶川地震(Ms8.0)非对称同震破碎带的确定：来自WFSD-1随钻流体的证据

Real time drilling mud gas records the asymmetric damaging process associated with the 2008 Ms 8.0 Wenchuan earthquake

地震过程中相当可观的一部分能量消耗于裂隙的活化与形成,来自汶川地震断裂带科学钻探一号孔(WFSD-1)的随钻流体表明,地震新形成的裂隙对应有较强的流体异常,它们为流体的入侵提供了良好的通道。随钻流体呈非对称性分布于主滑移面的两侧,主要的流体异常带集中在主滑移带下方须家河组顶部120 m范围内,该带中气体的含量以及变动的频率明显高于上部相同的宽度范围以及下部沉积岩层,来自地球物理测井的资料同样显示这一带破碎严重并伴随有大量水的侵入,暗示汶川地震形成的裂隙具有非对称性分布的特征。这一特征可能同时受控于断裂上盘彭灌杂岩与下盘须家河组岩层的力学性质差异以及地震破裂过程中形成的非对称性应力分布。

A considerable part of energy released during an earthquake is used to create fractures within the surrounding rocks. The real-time drilling mud gas from WFSD-1 shows that the fractures generated during the Wenchuan Earthquake coincide with large fluid peaks, and hence they are favorable passages for underground fluid migrations. The drilling mud gas distributes asymmetrically around the principal slip zone（PSZ）, with the major anomaly zone emerging 120 m below the PSZ. Gas concentrations are much higher and vary more intensively than the upper 120 m. Additionally, the geophysical logs also prove that this zone is highly fractured and associated with serious water inrush, suggesting that the 2008 Wenchuan earthquake caused more damage to the footwall than to the hanging wall. The difference in rock strength between the volcanic hanging wall of Pengguan complex and the sedimentary footwall of Xujiahe Formation and the asymmetric stress during the rupture propagation might have contributed to the damage process.