Hydraulic properties of a low permeable rupture zone on the Yingxiu- Beichuan Fault activated during the Wenchuan earthquake, China: Implications for fluid conduction, fault sealing, and dynamic weakening mechanisms
Hydraulic properties of a low permeable rupture zone on the Yingxiu- Beichuan Fault activated during the Wenchuan earthquake, China: Implications for fluid conduction, fault sealing, and dynamic weakening mechanisms
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中国汶川地震期间激活的映秀-北川断层上低渗透破裂带的水力特性：对流体传导、断层封闭和动态弱化机制的影响
DOI：
10.1016/j.tecto.2017.10.002
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发表时间：
2017
期刊：
影响因子：
2.9
通讯作者：
Jianye Chen
中科院分区：
文献类型：
--
作者：
Qingbao Duan;Xiaosong Yang;Jianye Chen
断层岩的流体输运性质是影响地震成核和破裂传播的重要参数。在这项研究中，我们研究了断层岩的内部结构，矿物成分和流体输运特性，从两个浅钻孔穿透花岗岩破裂带上的映秀-北川断裂（YBF），在2008年汶川地震期间被激活。使用水作为孔隙流体在范围从10 MPa至165 MPa的有效压力（Pe）下测量流体输送性质。断层岩的渗透率在2.1 × 10− 22 m2到4.6 × 10− 17 m2之间变化很大，这在很大程度上取决于岩石类型和上覆压力。具体来说，在165 MPa的压力下，损伤区样品的渗透率为5.0 × 10 - 21 m2至1.2 × 10 - 17 m2，断层泥为2.1 × 10 - 22 m2至3.1 × 10 - 19 m2。因此，YBF由充当流体屏障的低渗透性断层岩心和充当流体通道的周围高渗透性损害区组成。结合结构和成分的结果和运输数据在一起，我们建议，碎裂和流体-岩石相互作用之间的相互作用控制的水力特性和它们的响应断裂带的演化。值得注意的是，我们测量了极低的渗透率，但高孔隙度和高比存储的断层泥。被推断为相当于汶川地震成核岩石的胶结碎裂岩也具有低渗透率，这表明断裂带是一个潜在的流体储存区，能够在深部产生高孔隙压力。根据我们的实验室数据，我们发现流体增压可能发生在2.7公里以下的深度。我们认为，热增压在汶川地震的动力弱化过程中起了重要作用。
Fluid transport properties of fault rocks are crucial parameters that affect earthquake nucleation and rupture propagation. In this study, we examined the internal structure, mineral composition and fluid transport properties of fault rocks collected from two shallow boreholes penetrating a granitic rupture zone on the Yingxiu-Beichuan Fault (YBF) that was activated during the 2008 Wenchuan earthquake. Fluid transport properties were measured using water as pore fluid at effective pressures (Pe) ranging from 10 MPa to 165 MPa. Permeabilities of fault rocks exhibit a wide variation from 2.1 × 10− 22m2to 4.6 × 10− 17m2, strongly depending on rock types and overburden pressure. Specifically, atPeof 165 MPa, the damage zone samples have permeabilities from 5.0 × 10− 21m2to 1.2 × 10− 17m2, and the fault gouges are between 2.1 × 10− 22m2and 3.1 × 10− 19m2. Thus, the YBF consists of a low-permeability fault core acting as fluid barrier, and surrounding high-permeability damage zones acting as fluid conduits. Combining the structural and compositional results and transport data together, we propose that the interplay between cataclasis and fluid-rock interactions controls the hydraulic properties and their response to the fault zone evolution. It is noteworthy that we measured extremely low permeabilities but high porosities and high specific storages for the gouges. The cemented cataclasites, which are inferred to be equivalent to the rocks in which the Wenchuan earthquake nucleated also have low permeabilities, suggesting the fault zone is a potential area for fluid storage and capable of generating high pore pressure at depths. According to our laboratory data, we found fluid pressurization could occur at depths below 2.7 km. We suggest thermal pressurization has played an important role in causing the dynamic weakening of the Wenchuan earthquake.