沉积盆地台网稀疏地区中等强度浅源地震起始深度测定——以2013年前郭M_(S)5.8和2016年Fairview M_(W)5.1地震序列为例

Hypocentral depth determination for moderate-magnitude shallow earthquakes in sedimentary basins with sparse network——case studies of the 2013 Qainguo M_(S)5.8 and the 2016 Fairview M_(W)5.1 earthquake sequences

沉积盆地中的中等强度浅源地震起始深度不仅是地震成灾研究的重要参数,还是深地下工程开采诱发地震成因研究的关键信息.然而在台网稀疏、沉积层结构复杂的盆地地区,仅利用直达波到时,常常难以获得较为准确的地震起始深度.基于参考事件的Pn/Pg相对定位方法加入Pn震相,可以有效提高震源深度的测定精度.本文针对松辽盆地中2013年前郭M_(S)5.8地震序列以及Oklahoma州2016年Fairview M_(W)5.1地震序列,利用Pn/Pg方法测定了两个地震序列中较大地震的起始破裂深度.结果显示:在2013年前郭地震序列中,两个较大地震起始深度和质心深度均在3~5 km左右,震源机制中含有较大的非双力偶源成分.而2016年Fairview M_(W)5.1地震,主震起始深度约7 km,质心深度约8 km,5个较大的前震则深度分布在5~9 km.根据上述测定结果,推测2013年11月前郭M_(S)5.8地震序列可能与震源附近的注水活动有关,而2016年Fairview M_(W)5.1地震则可能由较远处注水活动触发.

The hypocentral depth of moderate-magnitude shallow earthquakes in sedimentary basins is not only an important parameter in the study of earthquake disaster but also provides important information for the mechanism study of induced-earthquake by deep fluid-injection.However,in sparse network areas with thick sediments,it is difficult to obtain a more accurate hypocentral depth by using only direct waves.Based on reference events,Pn/Pg method combined Pg and Pn phases to improve the accuracy of the hypocentral depth.For the 2013 Qainguo M_(S)5.8 sequence in the Songliao Basin and the 2016 Fairview M_(W)5.1 earthquake sequence in Oklahoma,this study utilizes the Pn/Pg method to determine the hypocentral depth of the larger earthquakes in the two earthquake sequences.The results suggest that for the 2013 QianGuo earthquake sequence,the hypocentral depths and the centroid depths of two larger earthquakes were both around 3~5 km,and the focal mechanism contained a large non-double-couple component.For the 2016 Fairview M_(W)5.1 sequence,the hypocentral depth of the mainshock was about 7 km,the centroid depth was about 8 km,and the five larger foreshocks were distributed at 5~9 km.Based on the results,we inferred that the 2013 Qianguo M_(S)5.8 earthquake sequence may be related to the nearby fluid injection activities.The 2016 Fairview M_(W)5.1 earthquake may be induced by pressure disturbances caused by water injection nearby,which should cause the fault reactivity.