Abstract: A comparative study was performed on the temporal characteristics of b-value and spectrum of acoustic emission during the deformation of samples with different textures, including sample of intact granite, sample of granite with naturally healed joints, and samples with simple, extensional or compressional en-echelon simulated faults. The results indicate that the temporal characteristics of b-value and spectrum of AE events may not only be affected by the sample texture but also differ in the different deformation phases for the same sample. This is closely related to whether the deformation is dominated by fracturing or by frictional sliding. When the deformation is dominated by fracturing, b-value and spectrum of acoustic emission decrease obviously before instability events although fluctuations may occur sometimes. When the deformation is dominated by frictional sliding, b-value and spectrum of acoustic emission show relatively small changes before instability events, and both decreasing and increasing are possible. If the deformation is a process including both fracturing and frictional sliding, b-value and spectrum of acoustic emission may show complex changes. The experimental results imply that b-value and spectrum of acoustic emission as precursors of earthquakes may show different characteristics in different tectonic setting. Using such precursors to predict strong earthquakes may be useful for fracturing type earthquakes, and a little difficult for stick-slip type earthquakes, but very difficult for mixed type earthquakes. Moreover, the preparation of a strong earthquake usually involves quite a big area, in which faults with different geometry may exist. This can cause complexity of b-value and spectrum in statistics and affect their reliability as prediction parameters.It is concluded that fault geometry may be an important factor affecting the heterogeneity in temporal and spatial distribution of short-term precursors.

Key words: Acoustic emission, Temporal scanning of b-value, Temporal scanning of spectrum, Instability mechanism

摘要： 对几种不同结构的岩石标本在变形过程中声发射b值和频谱随时间的变化特征进行了对比研究,其中包括完整花岗岩标本、含有天然愈合节理的花岗岩标本、含有拉张型和挤压型雁列式断层以及平直断层的标本等。研究表明,声发射b值和频谱的特征不仅会受标本结构的影响,而且在同一标本的不同变形阶段也可能表现出不同的特征,其机制与变形方式以破裂为主或以摩擦为主有关。当变形以破裂为主时,声发射b值和频谱在失稳前会出现明显的下降;当变形以摩擦为主时,声发射b值和频谱在失稳前变化相对较小,且上升或下降均可能出现。实验结果意味着b值和频谱特征作为失稳前兆,在不同的构造环境下可能会有不同的特征,而强震孕震区内不同断裂构造的存在会造成前兆时空分布的非均匀性。

关键词: 声发射, b值时间扫描, 频谱时间扫描, 失稳机制