2001年施甸震群非弹性衰减及震源参数特征研究

Study on Non-elasticity Attenuation and Source Parameters of the Shidian Swarm in 2001

本文根据昆明区域数字台网记录的数字地震波形资料,采用Atkinson方法反演了施甸地震震源区非弹性衰减,运用Moya方法反演了施甸震中200km区域内6个数字地震台的场地响应.首先扣除了地震记录数据中传播路径、场地响应和仪器响应的影响,继而利用遗传算法测定了2001年施甸震群的震源参数.结果表明:①地震矩和近震震级有很好的线性关系,地震矩范围为1×1012～1014N·m,震源破裂半径为157～973m,地震矩与震源半径之间亦呈线性关系.②拐角频率随地震矩的增大而减小.用最小二乘法拟合出拐角频率与地震矩之间的关系式,据此关系式可计算出拐角频率的估计值.拐角频率与其估计值之差的时间进程曲线表明,强余震发生之前会连续出现拐角频率与其估计值的差值呈高值或低值异常.③地震应力降范围为0.07～1.55MPa,应力降与近震震级无明显的依赖关系,强余震发生之前会出现高应力降异常.④余震的震源深度主要分布在5～10km,表明地震能量释放主要集中在这一深度范围内.

Based on horizontal-component digital seismograms recorded on 6 stations of the Kunming Regional Digital Network, we inverse the Non - elasticity attenuation in source region of the Shidian earthquakes using the Atkinson method and site responses of 6 stations 200km around the Shidian epicenter using the Moya method. The observational seismic waveform data are corrected by removing the propagation, instrument and site effects before the source parameters of the Shidian swarm in 2001 are obtained by using genetic algorithms. The results are as follows： （ 1 ） there is a linear relation between seismic moment and local magnitude. The seismic moment is between 1 ×10^12 and 10^14N·m. The rupture radius of seismic focus varies from 157m to 973m. The seismic moment and the rupture radius remain a linear correlation. （2） The comer frequency increases while the seismic moment decreasing. Based on the expression between comer frequency and seismic moment by using least squares fitting, we can obtain the estimated value of comer frequency. The time-varying value of the difference between the calculated comer frequency and estimated comer frequency shows that there are continuous anomalies of high or low before strong aftershocks. （3） The seismic stress drop is in range of 0.07 - 1.55MPa. The stress drop seems independent of the local magnitude. The change of stress drops has feature of high value before occurrence of the strong aftershocks. （4） The depth of aftershocks is mostly in range from 5km to 10km, which means that energy release of aftershocks is mainly concentrated in this range of depth.