沂沭断裂带重复地震识别及断裂深部活动速率的估算

Identification of Repeating Microearthquakes and Slip Rate Estimation at Depth in the Yishu Fault Zone

利用山东及邻区数字地震台网2001—2012年的地震观测报告及波形资料分析了沂沭断裂带及周缘地区的地震活动并利用识别出的重复地震估算了断层深部滑动速率。重新定位后的地震图像清晰展示了沂沭断裂带南北两段及东西两侧地震活动的显著差异,在研究时段内,60%以上的地震发生在沂沭带东侧的两条断裂上,震源深度分布与研究区的深部构造吻合。根据波形意义上相似地震(cc≥0.8)的定义,识别出了沂沭断裂带及其周缘相似地震共50例,组成相似地震对和多重相似地震对共19组,相似地震对的复发间隔较为随机,从数小时到数百天不等。通过对相似地震对震源位置一致性的强约束后,基于1组重复地震估算出安丘-莒县断裂在地表以下5.9km处的滑动速率估计值为2.19mm/a,与GPS和地质等浅表观测的滑动速率值基本一致。

We analyzed the seismic activity characteristics in and around the Yishu fault zone by the earthquakes observation reports and the seismic waveform data in 2001-2012 recorded by the Shandong Province and adjacent areas digital seismic network. By identif- ying repeating earthquakes, we estimated the slip rates at depth along the Yishu fault zone. The distribution of the relocated earthquake clearly shows that seismic activity dif- fers significantly in the north and south sections, and in the east and west ends of the Yishu fault zone. In the study period, 60~ earthquakes occurred in the east side of the study area, and focal depth distribution is consistent with the fault depth structure. Ac- cording to the definition of repeating earthquakes whose waveform cross-correlation coeffi- cient is not less than 0.8, we identified 50 cases of similar earthquakes, which constitute a total of 19 groups of doublets and multiples, although the time interval of recurrence is random between the similar earthquakes varying from hours to hundreds of days. By strongly constraining the hypocenter location consistency of similar earthquakes, and based on one group of repeating sequence, we obtained the slip rate about 2.19 mm/a at depth 5.9 km of the Anqiu-Juxian fault, which is relatively in agreement with geological and GPS measurements.