2003年云南大姚6.2、6.1级地震序列特征分析及地震触发研究

The Characteristic Analysis and Seismic Triggering Study of the Dayao M6.2 and M6.1 Earthquake Sequences in 2003

本文采用双差定位法对2003年7月21日、10月16日云南大姚先后发生的6.2、6.1级地震及其余震序列进行精定位。结果表明,两个主震的震中位置相当接近,余震序列的空间分布呈明显的线性分布,地震序列精定位后的结果同震源机制解吻合很好,两个地震的发震断层均是近乎直立的右旋走滑断层。此次大姚6.2、6.1级双震,和云南地区大多数其它双震有所不同,余震分布并不呈现共轭分布,而近乎一条直线,两者间有部分重叠,表明两者受控于同一发震断层。相对主震而言,余震都呈不均匀分布,近乎一种单侧分布,6.2级地震的余震集中于主震的西北方向,6.1级地震的余震集中于主震的东南方向,并且6.1级地震是6.2级地震在同一断层向东南端延伸的另一次破裂。库仑破裂静应力变化Δσf研究结果表明,7月21日6.2级地震对10月16日6.1级地震有明显的触发作用,两个主震对断层外余震的发生均有不同程度的应力触发作用,并且2000年姚安6.5级地震对大姚两次地震的发生也有触发作用。

The high-resolution hypocenter locations of mainshocks on July 21 （M6.2） and October 16, 2003 （M6.1） and their aftershock sequences are determined in Dayao, Yunnan by using double-difference earthquake location algorithm. The results show that the epicenters of two mainshocks are very close, distribution of the aftershock sequence appear to be very linear, the distribution of earthquake sequence is very consistent with the focal mechanism, and both of the two mainshocks are nearly vertical right-lateral fault. Differently from most other double earthquakes in the Yunnan area, aftershock distribution of the Dayao M6.2 and M6.1 earthquakes does not appear to be conjugated distribution and appears to be in a line, and there are some stacks in two earthquake sequences, which is inferred that they are all controlled by a same fault. The distribution of aftershock is unsymmetrical distribution according to the mainshock location and appears to be unilaterally distribution. The aftershock of M6.2 centralize in the northwest of M6.2 and the aftershock of M6.1 in the southeast of M6.1, moreover, the M6.1 earthquake appears to be another southeastern rupture due to the M6.2 earthquake on the same fault. The results of static Coulomb stress changes △σf show that the earthquake on July 21 （M6.2） trigger apparently the earthquake on October 16 （M6.1）, the two mainshocks have stress triggering to their off-fault aftershocks in different extent, and the M6.5 earthquake occurred in Yao＇an in 2000 also triggered occurrence of the Dayao earthquakes.