Fault lubrication during earthquake propagation in thermally unstable rocks

在热不稳定岩石（如碳酸盐岩）的滑动过程中，三种热激活机制被认为是特别相关的：1）在高应力摩擦微接触（粗糙体）处的闪热; 2）在滑动区释放和/或捕获的加热流体的热加压;以及3）热诱导化学分解反应（脱碳）产生的纳米颗粒的润滑作用。为了研究碳酸盐岩断层带中的这种化学和物理反应是否会使断层变得非常弱，有利于地震破裂的继续传播，我们在这里提出了一个多学科的研究计划，其中机械，矿物学，显微结构，流体流动特性和建模数据，从现场和实验室研究中获得的集成。将在意大利亚平宁山脉的碳酸盐岩中进行实地研究，以重建天然断层带的几何形状，确定不同的结构域及其相关的断层岩组合。现场观测和显微结构/矿物学分析的整合将提供重要的地质约束的分析和解释的主要变形过程中观察到的实验变形样品。这些结果将被用来产生一个新的分类方案，地震断层岩碳酸盐岩，识别和描述的断层岩和微结构的诊断协会的地震滑动事件的指标。这种分类将有助于识别沿着暴露断层段的化石地震，因此，可用于解释世界其他地区的古地震断层记录，有助于风险/灾害评估。将在固体和粒状碳酸盐岩上进行高速摩擦实验，以类似于大地震中所见的速度（1.3m/s）剪切，以评估从研究区活动断层带收集的断层岩材料的可能动摩擦强度Tf。还将测试通过在炉中热分解碳酸盐获得的合成纳米粉末。实验室摩擦测试结果和实验和自然断层的微观结构研究的整合，应允许识别的主导弱化机制，并限制其在自然环境中的操作条件。颗粒材料的渗透性受颗粒尺寸分布、颗粒形状、固相体积分数和孔隙连通性的控制。所有这些几何参数在断层带上都是变化的。将对沿沿着断面采集的现场样品进行渗透率实验室测量，断面与断层带中的主要滑动面正交和平行。这些数据可以提供有关已知/受控条件（摩擦、位移、流体排放时间）下滑动带渗透率演变的有用“快照”信息，这些信息可用于校准/测试流体流动建模结果。我们将使用一个国家的最先进的数值模型（名称），以确定渗透率张量的几何参数范围内获得定量微观结构分析。这种数值方法将使我们能够探索系统的渗透率变化的方式，不能单独通过实验室实验来实现。将量化滑动过程中碳酸盐热分解产生的流体耗散率，从而确定它们在断层带润滑中的作用。

Three thermally activated mechanisms are considered to be of particular relevance during slip in thermally unstable rocks such as carbonates: 1) flash heating at highly stressed frictional micro-contacts (asperities); 2) thermal pressurization of heated fluids released and/or trapped in the slip zone; and 3) the lubrication effects of nanoparticles produced by thermally-induced chemical decomposition reactions (decarbonation). In order to investigate whether such chemical and physical reactions in carbonate fault zones can make faults extremely weak and favour the continued propagation of earthquake ruptures, we propose here a multidisciplinary research program where mechanical, mineralogical, microstructural, fluid flow properties and modelling data, obtained from both field and laboratory studies are integrated. Fieldwork studies will be carried out in carbonate rocks from the Italian Apennines to reconstruct the natural fault zone geometries, identify the different structural domains and their associated fault rock assemblages. The integration of field observations and microstructural/mineralogical analyses will provide important geological constraints in the analysis and interpretation of the dominant deformation processes observed in experimentally deformed samples. These results will be used to produce a new classification scheme for seismic fault rocks in carbonates, based on the identification and description of diagnostic associations of fault rocks and microstructures which are indicators of earthquake slip events. This classification will aid in the recognition of fossil earthquakes along exposed fault segments and, therefore, can be used to interpret records of palaeo-seismic faulting in other parts of the world, aiding in risk/hazard assessment. High velocity friction experiments will be performed on solid and granular carbonate rocks, sheared at speeds similar to that seen in large earthquakes (1.3m/s), in order to assess the likely dynamic frictional strength Tf of fault rock materials collected from active fault zones in the study areas. Synthetic nano-powders obtained by thermal decomposition of carbonates in a furnace will also be tested. The integration of laboratory friction test results and microstructural studies from both experimental and natural faults should allow the identification of the dominant weakening mechanisms and constrain their operational conditions in natural environments. The permeability of granular materials is controlled by grain size distribution, grain shape, solid volume fraction and pore connectivity. All of these geometric parameters vary across a fault zone. Permeability laboratory measurements will be performed on field samples collected along transects oriented orthogonal and parallel to principal slip surfaces in the fault zones. These data can provide useful 'snapshot' information on the evolution of permeability of slip zones under known/controlled conditions (friction, displacement, timing of fluid emissions), which can be used to calibrate/test fluid flow modelling results. We will use a state-of-the-art numerical model (name) to determine the permeability tensor for the range of geometric parameters obtained from quantitative microstructaral analyses. This numerical approach will allow us to explore systematic permeability variations in a way that cannot be achieved through laboratory experiments alone. The rate of dissipation of the fluids generated by thermal decomposition of the carbonate during slip will be quantified, allowing the role they play in fault zone lubrication to be determined.