地震断层输运特性及愈合作用的实验研究：以汶川地震断裂带为例

Fluid activity in faults affects the fault strength and stability, earthquake nucleation, propagation of ruptures, and earthquake recurrence. The transport properties of faults controls the fluid activity and post-seismic healing. However, the courses of healing will reduce the porosities and permeability, and consequently restrains from the fluid activity. Therefore, it is very important to study the interactions between fault transport properties and healing. This investigation will helps us to be aware of fluid behavior in faults and its effects on fluid migration and compositional responses, on fault stability and earthquake nucleation, on fault weakening and on rupture propagation profoundly. Up to date, the pressure- and stress-dependences of transport properties of fault zone,the fluid behavior in deep faults, fault healing mechanism remains debatable. Furthermore, quite few investigations have been done on the transport properties and healing of Wenchuan earthquake fault zone. There is no data about the relationship between fault healing and transport properties in situ. We are unable to simulate and constrain on fluid migration quantitatively until having these data. In order to study the fluid activity in situ in Wenchuan earthquake faults and its temporal evolution, as well as the influence of them on the petrophysical and mechanic appearances of the fault, we propose doing experiments of transport properties and healing on Wenchuan earthquake fault rocks. The pressure- and stress-dependences of permeability and porosities will be measured in-situ on advanced experiment instruments(ultra-lower permeability instrument, permeability-healing experiment system,100MPa TRI-X Cell). The confining and pore pressures range from 10-200MPa and 5-40MPa for permeability and connected porosity, respectively. The fault healing experiments will be performed on healing-permeability apparatus with confining pressures and temperature ranging from 1-50MPa and 10-100 degree C. On the base of the quantitative experimental data with the composition analysis of outflow from experimental samples, the fluid activity in Wenchuan earthquake fault zone and its effects on the physical appearances of the fault will be modeled. It is expected that the experiments could provide systematic data and essential constraints on ours understanding of the relationship between fluid activity and fault stability, fault weakening, rupture propagation, and earthquake recurrences.

断层带流体活动影响其强度和稳定性、地震成核和扩展过程。断层带的输运特性直接控制了断层带的流体活动和震后愈合作用，而震后愈合进程则抑制断层带的流体渗透性和水岩相互作用。因此将地震断层带的输运特性与愈合作用作为动态的演化系统加以研究有助于人们深刻的理解地震断层带中流体的活动特性及其产生的效应(包括：输运特性的变化、流体迁移、断层带成分变化、断层的稳定性、断层带弱化及地震破裂扩展等)。目前对断层带输运特性对围压和差异应力的依赖性以及断层带愈合方式及过程之研究还很薄弱。而对于影响汶川地震断层带流体活动的因素及其效应之研究几乎空白，缺乏必要的输运参数和愈合作用之实验数据。本申请提出以汶川地震断裂带为样本，开展细致输运特性及愈合作用的实验研究，获取定量可靠的实验数据，为探讨断层带流体活动特性和控制因素，为理解断层带中流体在地震孕育、断层失稳与扩展等过程作用提供约束和启示。

断层带流体活动影响其强度和稳定性、地震成核和扩展过程。断层带的输运特性直接控制了断层带的流体活动和震后愈合作用，而震后愈合进程则抑制断层带的流体渗透性和水岩相互作用。因此将地震断层带的输运特性与愈合作用作为动态的演化系统加以研究有助于人们深刻的理解地震断层带中流体的活动特性及其产生的效应。项目实验研究汶川地震断层岩的流体输运特性和水-岩相互作用导致的断层愈合，探讨了汶川地震断裂带流体活动的基本特征及其响应。研究获得如下主要进展和认识。(A)映秀-北川断层带由极低渗的断层核部, 高渗的破碎带和相对完整且低渗的围岩所组成。横跨断层带, 渗透性整体呈现为“通道/障碍体”体的二元结构. 流体活动主要集中在断层核部与破碎带内。机械破碎和水-岩相互作用共同控制着断层带的流体活动与结构演化。(B)断层岩是由多期次的地震活动及震后长时间的断层蠕动并伴随着持续流体活动的综合产物，物质迁移、溶解-沉淀及压溶作用是断层带体积流失的主要机制。(C)断层岩中的粘土矿物颗粒表面吸附水及粘土矿物吸水膨胀导致有效孔隙尺寸减小是造成断层岩渗透率显著低于绝对渗透率的主要原因. 研究结果显示, 对于富含粘土矿物的断层岩, 经Klinkenberg校正后的气体渗透率与水渗透率并不一致, 因此采用相应的液体作为测量介质才能够更为准确和真实地揭示地下流体的渗流状况。 (D)渗流-愈合作用是断层带愈合的重要机制之一，渗透率(k)随时间(t)的变化遵从k = k0t –λ幂次关系。(E)汶川地震断层主滑动带具备热压作用发生的条件, 同震热压作用可能是映秀-北川断层弱化的重要机制。项目获得的实验数据及结果为探讨断层带流体活动特性和控制因素，理解断层带中流体在地震孕育、断层失稳与扩展等过程中的作用提供约束和启示。