关键词: 声发射, b值时间扫描, 频谱时间扫描, 失稳机制

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