1993年中甸M5.8地震前后区域尾波衰减研究

Study on Regional Coda Wave Attenuation before and after the M5.8 Zhongdian Earthquake in 1993

以Aki,K和Chouet[1] 提出的地方震尾波散射理论为基础 ,利用 1993年 7月 17日中甸MS5 8地震的前震和余震资料 ,研究了该次地震前后的尾波振幅衰减率 β和QC-1值的时空变化。结果表明 ,主震前后区域尾波振幅衰减率 β和QC-1值发生了明显的变化。主震前 ,区域平均 β值为 0 0 12 2s-1,相应的QC 值为 111;主震后 ,区域平均 β值为 0 0 2 3s-1,相应的QC 值为 6 0。主震前后的QC 值变化为 1 85倍 ,表明在以主震为中心 ,半径约 5 0km的小范围内主震前后的介质背景发生了明显变化。用释放的地震应变能ε(t)的空间分布特点分析 ,表明主震前高QC 值地区与高应变能释放地区是相一致的。中甸地震序列的尾波振幅衰减 β和QC 值显示了具有前兆意义时空变化的过程 ,并以力学观点分析解释了产生这种变化的成因。

Based on the scattering theory of coda waves for local earthquakes suggested by Aki,K and Chouet and using the foreshock and aftershock data for the M S5 8 Zhongdian earthquake on July 17,1993,space-time variation in β and Q C -1 values of coda wave amplitude attenuation rates before and after the earthquake is studied.The results show obvious variation in the β and Q C -1 values of regional coda wave amplitude attenuation rates before and after the main earthquake.Before the main earthquake,regional average β value was 0 0122s -1 and Q C value was 111 and after the main earthquake,regional average β value was 0 023s -1 and Q C value was 60,with Q C value variation of 1 85 times,which shows that distinct variation in medium background before and after the main earthquke occurred in small range taking the maim earthquake as center and with radius of about 50 km.It is shown from analysis of space distribution of released seismic strain energy ε( t )that the regions with high Q C value are the regions with high strain release.The β and Q C values of coda amplitude attenuation from the Zhongdian earthquake sequence show space and time variation process with precursor significance and the variation cause is explained from the view point of mechanics.