断层成核与失稳过程热场演化的实验研究

A strong earthquake is thought of the result of abrupt instability of fault. What does a fault experience during the processes from quasi-static to dynamic slide? Whether can these processes be found as early as possible? These problems are of great importance in earthquake research. It is generally accepted that only a small amount of energy is released by seismic wave, and most of the energy is converted to heat (80-90%). The magnitude of heat effect, its evolution, its physical mechanisms and its influencing factors at different stages of faulting may be obtained with the experimental method which conditions can be controlled. Conversely, with the analysis of thermal effects, it is possible to help us identify the fault nucleation and its space-time evolution and the instability of fault. The project is intended to undertake the following tasks:(1) develop the mechanisms of generating heat of faulting; (2) investigate the thermal feature of the initial nucleation and its evolutional processes; (3) identify space-time thermal mark from nucleation to the instability of fault; (4) analyze thermal characteristics during the instability of fault; (5) based on the experimental results, the evolution of the temperature field is numerically simulated, and then to combine with field observations of ground temperature along fault, a comprehensive analysis will be carried out. Eventually, through the implementation of the project, the principle on the thermal field signal from the local pre-slip segment to the instability of fault is obtained, and especially, the thermal marks on nucleation initiation and its conversion into the instability of fault are found. These can provide a physical basis for detecting earthquake thermal precursory and analyzing co-seismic thermal effects.

强烈地震源于断层的突发失稳，断层从准静态到动态滑动经历了怎样的过程，能否尽早发觉是地震学一个倍受关注的问题。通常认为，地震波释放的能量只占小部分，大部分能量转化为热能（80-90%）。通过条件可控的实验手段，弄清断层作用不同阶段生热效应的量级、演化过程和物理机制及其影响因素。反过来，借助热效应的分析，有可能帮助我们识别出断层成核以及失稳阶段的时空演化特征。本项目中，拟以实验为主，开展下列工作:(1)生热机制的参数化与定量化研究;(2)研究断层成核初始、扩展过程热场时空演化特征; (3)探索成核向失稳转换的热场标志;(4)研究断层失稳滑动阶段的热场特征;(5)以实验结果为基础，开展温度场演化数值模拟，结合野外断层地温观测开展综合分析。最终，通过项目的执行，弄清断层局部预滑、扩展及其失稳滑动的热场演化规律，识别出成核起始、扩展及其向失稳转换的热场标志,为地震热前兆与同震热效应分析提供物理依据。

断层从（准）静态变形向动态滑动演化时，断层及其围岩经历了多个力学和热学转变过程，“变形致热”是其重要特色。本项研究，从测温技术、实验研究和野外应用探索三个方面开展工作，并取得了一系列进展。主要进展表现在：(1)在原有温度观测系统的基础上，研发了新一代温度采集系统，采集精度达到0.2mK(=0.0002℃)，相当于可以观测到0.2MPa应力变化引起的温度响应；（2）解决了高精度温度传感器的一致性标定问题：不同传感器的一致性标定可优于1mK；（3）通过岩石单剪断层滑动的温度变化实验，证实：准静态阶段，以围岩降温为主，断层带局部位置升温；准动态阶段，围岩降温幅度减缓，断层带升温加速，在热像增量图上断层位置已经清晰可辨；（4）通过带圆孔岩石样品加载过程的温度变化实验，证实：在充分考虑圆孔几何效应基础上，有可能利用温度观测获知应力变化的大小和方向；（5）以鲜水河断裂带基岩温度观测资料为基础，结合热力学和传热学理论，提出了一套利用基岩温度提取地壳应力状态变化的思路与方法；（6）以2014年11月22日的康定地震的同震温度响应为例，证实：利用温度探测地壳应力变化是可行的。总之，基于实验成果，提出了“热测力学”的概念，同震响应证实了这一思路的可行性。继续下去，有望成为地壳应力动态变化观测的一个新手段，对于地壳动力学研究极具价值。