新疆南天山西段震群活动特征分析

摘要

The small earthquake swarm activity level in South Tianshan,Xinj iang,was relatively high from March 2008 to December 2013.In this paper,31 small earthquake swarms occurring in this area are systematically studied,the parameter characteristics of earthquake swarms are summarized,the relationship between small earthquake swarms and the occurrence of future moderately strong earthquakes is discussed,and criteria for precursory earthquake swarms are analyzed and tested.Results show that:(1 ) earthquake swarms in South Tianshan are concentrated in several regions,the magnitudes of most are 2.0~3.9,and the largest magnitude of each swarm is mostly about ML3.5.Seven swarms have a total magnitude of ML≥4.0 with a max-imum value of ML4.9 and there are less than 20 earthquakes for most earthquake swarms with a duration of less than seven days.(2 )The activity of earthquake swarms is mainly concentrated near Atushi.75% of the swarms are accompanied with M>5.0 earthquakes two months after their occurrence,and the epicenters of these medium-strong earthquakes are principally located in the intersection of Kashi and Wuqia.The corresponding ratio of the magnitude of earthquake swarmsand future medium-strong earthquakes has no obvious correlation with the magnitude of corresponding earthquakes.There is also no good relationship between the number of earthquakes in an earthquake swarm and the corresponding ratio.(3 )Results using the combined method of U-K and U-ρare preferable for determining the type of earthquake swarm,and the correct rate accounts for about 32% of all results.Results of analysis provide a reference for determining whether an earthquake swarm has precursory characteristics or not.%2008年3月—2013年12月新疆南天山西段小震群活动水平较高,系统整理该地区31次小震群,并对震群活动的参数特征进行分析总结,以探讨小震群活动与中强地震的关系,同时检验前兆震群类型的判断指标.结果表明:(1)新疆南天山西段震群活动集中,强度以ML2.0~3.9地震为主,震群中最大震级多数为ML3.5左右,而震级值ML≥4.0共7次,最大为ML4.9,震群序列总频次多数小于20,持续时间大多为7天以内;震群序列中地震总频次和震群持续时间与震群中最大地震震级之间不成正比.(2)震群活动主要集中在阿图什附近,75%震群发生两个月后对应M5.0以上中强地震,对应范围为0~500 km,未来中强地震震中位置主要集中在喀什—乌恰交汇区,震群强度大小与未来中强地震的对应率高低值和对应的地震强度大小之间没有明显的相关性,震群序列频次与震群的地震对应率之间也不存在相关性.(3)采用U-K和U-ρ组合方法判定震群类型的检验效果相对较好,正确率约占总数的32%.分析结果可以为判断震群活动是否具有前兆特征和震情跟踪提供参考依据.