Fault constitutive properties at high velocities and the earthquake initiating processes

内部故障过程比通常认为的要动态得多。在地震断层运动中，沿断层的滑动速率可达1m/S左右甚至更快，对于大地震，沿断层的总位移可达数米。沿折返断裂偶尔出现的假玄武岩表明，至少在某些地震期间确实发生了摩擦熔融。因此，高速度、大位移下断层的摩擦特性对于理解地震孕育过程具有重要意义，但尚未得到系统的研究。传统的表象在断层位移量上过于有限，不能产生摩擦熔融，也不能模拟热自然的断层内过程。利用1990年安装在东京大学地震研究所的高速旋转摩擦装置进行的实验表明，摩擦加热对断层…的力学性质的影响比滑移率等其他影响大一个数量级以上。本研究项目的主要任务是设计和建造第二台高速装置，用于研究水热条件下的高速摩擦特性，并利用第一台装置进行额外的实验。主要研究成果如下：(1)设计并制造了一种新型的旋转剪切高速摩擦试验台，该试验台的滑移率为3 mm/a~10m/S，环境水压为50 Mpa，温度为500℃。试验取得了成功，不仅为研究水热条件下断层的高速摩擦特性，而且为研究高温腐蚀环境下材料的摩擦磨损特性开辟了新的途径。(2)通过第一台高速试验机的实验，揭示了干燥辉长岩中模拟断层的整体力学性质。(3)在干燥高速实验的基础上，提出了地震孕育过程的两阶段模型，这可能是地震静止的原因。较少

Intrafault processes are far more dynamic than normally considered. The slip rate along a fault during seismic fault motion reaches about 1m/s or even faster and the total displacement along fault amounts to several meters for large earthquakes. Occasional occurrance of pseudotachylytes along exhumed faults indicates that frictional melting indeed occurs at least during some earthquakes. Thus, the frictional properties of faults at high velocities and under large displacements are quite significant to understand the earthquake initiating processes, but they have not been systematically studied. Conventional appearatuses are too limited in the amount of fault displacement to produce frictional melting and are unable to simulate thermally natural intrafault processes. Experiments using a high-velocity rotary friction apparatus, installed to Earthquake Research Insitute, University of Tokyo in 1990, has revealed that the effects of frictional heating on the mechanical properties of faults … More are larger than other effects such as slip rate by more than one order of magnitude. The main task of the present research project has been to design and build the second high velocity apparatus for studying high velocity frictional properties under hydrothermal conditions and to perform additional experiments using the first apparatus. The major results are as follows.(1) A new rotary-shear high velocity friction apparatus was designed and built and this can produce slip rates ranging from 3 mm/yr up to almost 10 m/s, at ambient water pressures to 50 MPa, and at temperatures to 500 degrees Centigrade. Tests were successful and the machine will open ways of studying not only high velocity frictional properties of faults under hydrothermal conditions, but also frictional and wear properties of materials under high-temperature corrosive environments.(2) Overall mechanical properties of simulated faults in dry gabbro have been revealed through experiments using the first high velocity machine.(3) Two-stage model for the earthquake initiating processes has been proposed based on the dry high velocity experiments, and this may account for the origin of seismic quiescence. Less