2016—2017年龙门山地区微震活动的演化:基于对微震目录的模糊聚类分析

Evolution of microseismic activity in Longmenshan area from 2016 to 2017:based on fuzzy clustering analysis of microseismic catalogue

地震活动性是区域地壳及其深部的应力及运动状态的地震学表现.本项研究基于2016—2017年发生在龙门山地区及其附近的地震目录,采用模糊C平均聚类分析方法,分时段进行模糊聚类分析,每两个月得到三个分区的隶属度分布及聚类中心,以隶属度的分布以及聚类中心的迁移特征来探讨该区域地壳应力及运动状态的时空演化,并籍此探讨与九寨沟地震的孕育和发生之间的关系.结果表明,沿龙门山断裂分布的三个微震活动区(北段、中段和南段),和2016年相比较.2017年上半年,三个微震活动均有向西南方向移动的迹象,其中龙门山断裂北段的微震活动移至虎牙断裂南端,意味着北段的迁移向虎牙断裂传递了能量.结合其他学者的研究结果,我们认为这是深部物质在四川盆地遇阻后上升、沿龙门山断裂运移的结果,也是九寨沟M_(s)7.0地震孕育和发生的成因之一;龙门山北段的活动对虎牙断裂的作用,可能是九寨沟地震发生的触发因素.

Seismicity is the seismological expression of the stress and motion state of the regional crust and its deep part. Based on the earthquake catalogue in and around Longmenshan area from 2016 to 2017, we used fuzzy c-means clustering analysis method to conduct the analysis by time period, and obtains the membership degree distribution and clustering center of three sections every two months. The evolution of crustal stress and movement state in this area is revealed by the distribution of membership degree and the migration characteristics of clustering center. Based on these and other scholars’ research results, the evolution of crustal stress and movement state is analyzed in this area, the relationship between this and the formation and occurrence of the Jiuzhaigou earthquake M_(s)7.0 is further discussed. The results showed, the three microseismic active sections(North, middle and South sections) along the Longmenshan fault, compared with the results in 2016, in the first half of 2017, the three microseismic sections all showed signs of moving to the southwest. The microseismic activity in the northern segment of Longmenshan fault moved to the southern end of Huya fault, which means that the movement of the northern segment transfers energy to Huya fault. Combined with the research results of other scholars, We think that it was the result of the deep material rising in Sichuan Basin and migrating along Longmenshan fault, and it is also one of the causes of the formation and occurrence of Jiuzhaigou earthquake M_(s)7.0;the action of the northern segment of Longmenshan on Huya fault may be the trigger factor of this earthquake.