断层亚失稳与地震短临前兆物理机制的实验和数值模拟研究

Earthquake prediction, especially short-term to imminent prediction is a valuable scientific problem that needs to be explored persistently. It is suggested that the strong earthquake is the result of sliding instability of pre-existing fault, and the model of meta-instability of fault sliding provides a new way to explore the short-term to imminent prediction of earthquake. Therefore, deepening research on meta-instability of fault and its application in short-term to imminent prediction of earthquake is of theoretical and practical significance. In this project, the spatial-temporal distribution of stress field and related physical parameters and their physical mechanism in the phase of meta-instability of fault will be studied by through experiments of rock friction and analogue model with precise measurements of multi-physical field, combining with numerical simulation constrained by experiments. Effect of friction heterogeneity, medium mechanical property and fault interaction at different depths on meta-instability and their mechanism will be emphasized in the study. On the basis of the experiments and numerical simulation, possible short-term to imminent precursory phenomena and their mechanism will be analyzed, and a physical model for earthquake short-term to imminent precursors based on meta-instability of fault will be proposed. Furthermore, the technical solution for observation and prediction of the short-term to imminent precursors of earthquake will be suggested combined with the present techniques of earthquake monitoring precursory.

地震预测特别是地震短临预测是需要持续探索研究的科学问题。强震的发生是先存断层的滑动失稳所致，而断层滑动亚失稳模型为探索地震短临预测提供了新的思路。因此，深化断层亚失稳行为研究并探索其在地震短临预测中的应用，具有重要的理论和实际意义。本项目拟以断层亚失稳行为现有研究结果为基础，开展岩石摩擦实验、相似材料力学实验以及高分辨的多物理场观测，同时开展以实验结果为约束的数值模拟，研究断层滑动失稳短临阶段应力场及相关物理参量的时空分布特征，重点研究断层摩擦非均匀性、介质力学性质以及不同深度断层相互作用等因素的影响及其物理机制；基于实验和数值模拟结果，分析可能出现的地震短临前兆现象及其机理，建立基于断层亚失稳行为的地震短临前兆物理模型，并结合实际地震观测和前兆观测技术，提出地震短临前兆观测及预测技术方案，为地震预测研究提供理论和技术支撑。

断层滑动亚失稳模型为探索地震短临预测提供了新思路，因此深化断层亚失稳行为研究并探索其在地震短临预测中的应用具有重要的理论和实际意义。本项目针对断层亚失稳研究中需要深入研究的问题，通过开展岩石摩擦实验、相似材料力学实验以及与实验相结合的数值模拟，研究了介质性质、摩擦非均匀、应力扰动、流体作用、断层凹凸体等因素对断层滑动失稳过程特别是亚失稳特征的影响。粘弹性相似材料摩擦实验表明，断层亚失稳滑动亚失稳持续时间随正应力增加和滑动速率降低而增加；岩盐断层带摩擦实验表明，亚失稳持续时间随断层带塑性变形的增强而增加；这意味着亚失稳阶段的持续时间会随地震震级和地震发生深度而增加，从而有利于地震前兆的观测。断层失稳成核出现在亚失稳阶段且符合预滑成核模型，预滑显著部位会出现明显应力下降并伴有两侧断层应力的上升，应力下降区域沿断层扩展直至动态滑动开始；断层泥的存在有利于观测到应力的这种前兆性变化，断层带摩擦非均匀使得应力下降区和上升区更为清晰，而应力扰动则使成核模式从预滑向级联转换；这意味着密度较高且分布合理的形变观测有可能捕捉到地震前兆现象。与应力下降区域的扩展相对应，在扩展区前缘应力集中部位可能出现声发射活动并向外扩展，凹凸体存在的情况下则可能出现声发射从凹凸体向整个断层扩展的现象，声发射活动的发生率和能量释放表现出加速特征，低频事件显著增加而高频事件缺失，这意味着基于高质量的地震观测可能获得有前兆意义的现象。根据实验结果分析了可能观测到的地震短临前兆现象及其物理机制，并初步建立了基于断层亚失稳的地震短临前兆物理模型。研究成果对于地震前兆与预测研究具有重要的理论意义，对于地震预测实践具有实际指导意义。