拐折断层黏滑过程的实验研究

采用位移、应变和声发射等测量手段,研究了预置5°拐折断层的房山花岗岩样品的黏滑过程,分析了不同加载速率下5°拐折断层失稳的黏滑特征及相关物理场的演化过程。实验结果表明: 1)5°拐折断层的黏滑周期与加载速率在数值上呈负对数相关关系; 2)在不同的加载速率下,大多数的5°拐折断层失稳是双震事件, 2次子事件的间隔时间大多在100～200ms之间; 3)采用不同的观测手段,即使采样速率一致,其临震响应也存在差异性,如断层失稳前沿断层的应变测量结果呈现明显的应变弱化,断层位移则未见明显的变化; 4)断层黏滑过程中的声发射事件呈现明显的沿断层迁移的特征。认识强震的发生机理和余震特征需要进一步研究断层失稳过程的动力学信息。

EXPERIMENTAL STUDY ON STICK-SLIP PROCESS OF BENDING FAULTS

The stick-slip process of pre-cut bending faults with a 5°angle at bending point between the two fault segments is investigated by use of fault displacement measurement,strain tensor analysis and acoustic emission(AE)technique in the laboratory.The dynamic process and corresponding properties of physical evolution are discussed.The experimental results from bending faults show that: 1)A negative relationship was revealed between the logarithms of the stick-slip cycle and the logarithms of loading rate; 2)Under different loading rate,most of instabilities of bending faults are earthquake doublets,and the interval time between the two sub-events are primarily from 100ms to 200ms; 3)For different observational approaches,even if with the same sampling rate,the differences of the coseismic response were observed,such as the significant strain weakening stage indicated by strain measurements,but there was no significant change in fault displacement before fault instability; and 4)AE sources obviously migrated along faults during fault sliding.More dynamic information about fault instability process is needed to know the mechanism of strong earthquakes and the features of aftershocks.