安徽“霍山窗”中小地震的地震波衰减特征研究

Study on attenuation characteristics of seismic waves from small-moderate earthquakes in "Huoshan seismic window", Anhui Province

利用安徽合肥台、六安台和豹子崖台记录到的2001—2010年安徽"霍山窗"发生的ML≥2.0地震的波形资料,计算了其振幅衰减系数K值和卓越频率衰减系数a值,分析研究了K值和a值的时空变化特征,并讨论了其与华东地区中强地震的对应关系及与Qc值的相关性.结果表明,3个台站均记录到了明显的变化特征:①"霍山窗"ML4.0地震、江西九江MS5.7地震及河南太康ML5.0地震前6个月左右时间内,K值和a值均呈现持续下降的异常低值状态,平均下降幅度K值为20%—35%,a值为45%—51%,并于上升的过程中发震,震后趋于正常;②K值的平面分布特征显示,K值异常地震主要位于断裂带交汇区附近,并沿断裂带方向分布;③K值、a值与Qc值基本呈负相关.上述特征为进一步了解该区域的地壳介质状态和研究中强震前后Qc的变化特征提供了一定的依据.该研究结果可能对中长期地震预报和震后趋势判断有一定的指示意义.

Based on the waveform data from ML≥2.0 earthquakes during 2001-- 2010 in Anhui ＂Huoshan seismic window＂ recorded by Hefei, Lu＇an and Baoziya stations of Anhui Digital Seismic Network, the amplitude attenuation coefficient K and the predominant frequency attenuation coefficient a were calculated, their temporal and spatial variations were analyzed, and the possible relationship of the variations with moderate-strong earthquake occurrence in eastern China and coda Qc were discussed. The results indicate the following variation characteris- tics. （1） In about six months before the ME4. 0 earthquake in ＂Huoshan seismic window＂, the MsS. 7 Jiangxi Jiujiang earthquake and the ME5. 0 Henan Taikang earthquake, K value and a value decreased continuously to an abnormally low state~ the average rates of decrease for K and a are 20%-35% and 45%- 51%, respectively~ the earthquakes occurred during the rising process of K and a values. （2） By inspecting the plane view of K variation, we found that earth- quakes with abnormal K value are mainly located at or near the fault intersections and distributed along fault zones. 3 K and a values basically showed neg- ative correlation with coda Qc value, providing certain basis for further studying Qc variation before and after moderate-strong earthquakes.