地震前兆场物理机制实验研究的新进展

EXTENDED PROGRESS IN EXPERIMENTAL STUDY ON MECHANISM OF EARTHQUAKE PRECURSORS

从“源“和“场”两个角度开展实验研究,以揭示震源体在不同力学状态下变形破坏过程中若干物理响应的时间过程和空间上的分布规律。结果表明:低的轴向刚度会增大断层错动距离,提高失稳以后断层所处的应力水平,缩短地震失稳的重复周期;将不同温度、围压条件下岩体的变形行为(应力-应变曲线)分成5种类型,提出应变响应比与系统失稳(地震)之间的关系可能出现多样性;采用等应变速率和等能量速率加载,以及不同刚度条件等,研究了花岗闪长岩、砂岩和大理岩等的声发射(AE)活动性,认为复杂的变形条件会导致复杂的微震活动性;比较了测量方法对Q值的影响,研究了破裂孕育过程中Q值、波速和振幅的变化;采用大样品对破裂孕育过程中电性特征进行了研究,提出破裂前兆异常具有趋势性异常和突变性异常两类基本形态,异常具有空间分布的差异性和时间分布的阶段性;对含坚固体岩样破裂条件和前兆现象进行了研究,认为坚固体会使应力集中,在一定条件下会先于围岩屈服、软化,直至破裂;给出了含坚固体岩样破裂过程中微破裂(AE)发展的空间图象及波速场变化。

The advanced experimental study on mechanism of earthquake precursors has been performed from two angles of earthquake 'source' and earthquake 'field' to investigate the time process and space distribution of some physical responses during fracturing of source body at different mechanical status. The results indicate that low axial stiffness will increase the faulting distance, enhance the stress level of the system after fracturing, shorten the period of repeat instability. Deformation behaviour (strain-stress curves) of rock body at different temperature and confining pressure are divided into five groups, which are different in relationship between the strain response-ratio and instability of deformation system (earthquake) . The AE (acoustic emission) activity is studied with cm-scale rock samples of granodiorite, sandstone and marble at different testing condition: constant strain rate, constant energy rate, different stiffness, etc. It is concluded that complicated loading processes offer complicated patterns of micro-fracturing ( AE) . Q value measured with different methods is compared, and the changes of Q value, velocity and amplitude of waves during deformation are studied with 20-30 cm-scale rock samples. The changes of electric characteristics are studied with m-scale rock samples. Two types of precursory anomalies are distinguished as: trend anomaly and abrupt one. They behave as discrepancies in locations and episodes in time. The fracture conditions and precursors of rock body with hard inclusions are studied. It is confirmed that hard inclusions will lead stress to be concentrated. The inclusions may be broken before the confining rock yielding at a certain condition. The spatial patterns of micro-fracturing development and changes of wave velocity field are given.