摘要
利用双差定位法对2016年3月泸定地震序列进行了重定位,获得了2221个地震的重定位结果,走时均方根残差平均值为0.0131 s,震源位置平均定位误差在E-W、N-S、U-D方向分别为61.1 m、21.8 m、54.4 m.其中泸定地震序列最大地震M_L4.2震中位于29.6234°N、102.0175°E,震源深度为8.257 km.序列震中分布长约21 km,宽约15 km,震源深度的优势分布范围在5~9 km,10 km以下地震较少.震源深度剖面显示断层向NNW向倾斜,浅部倾角和深部倾角比较一致,较陡.利用最大振幅比方法计算了本次泸定序列103个M_L≥2.0地震的震源机制解,结果显示两个节面走向分别在近东西向和近南北向存在优势分布,同样倾角较陡.震源机制类型主要以走滑型和斜滑型为主,占所有解的93.1%.根据重定位和震源机制结果,分别讨论了构造地震和水库诱发地震的可能性,认为本次泸定地震序列存在明确的发震构造——在区域NW-SE向挤压应力作用下产生的SWW向磨子沟断裂.由于本区地震活动与水位高低具有一定的相关性,且蓄水后应力场发生逆时针旋转,所以推测大岗山水库蓄水可能加剧了这组断裂活动.
The Luding earthquake sequence in March 2016 is relocated using the double-difference earthquake location algorithm,and 2221 relocation results are obtained eventually. The mean value of the root-mean-square residual of travel time is 0. 0131 s,and the average error in E-W,N-S and U-D is 61. 1,21. 8,54. 4 m respectively.The M_L4. 2 earthquake,the biggest one among the sequence,is located at 29. 6234° N,102. 0175° E,at a depth of 8. 257 km. The epicenter distribution is 21 km long and 15 km wide,and the hypocenters are located mainly at the depth of 5 ~ 9 km,with fewer events under 10 km. Meanwhile,the depth profiles reveal that the fault plane inclines towards the NNW direction,and the dip angle at shallow depth,which is steep,is consistent with the deep depth.Besides,we calculate 103 focal mechanism solutions of the M_L≥2. 0 earthquakes in Luding sequence using maximum amplitude ratio of P and S wave,and the results indicate that the two nodal planes are almost E-W and N-S strike predominantly. We notice that the focal mechanism solutions also work out planes with steep dip angle.Moreover,the earthquakes of strike-slip type and of oblique-slip type take up a great proportion,accounting for 91. 3% of the tota1 solutions. Based on the results of relocation and focal mechanism,we discuss the possibility of tectonic earthquakes and reservoirinduced earthquakes,respectively. Finally,we come to a conclusion that the Luding sequence has clear seismogenic structure——a SWW trending fault called Mozigou fault,formed by the NW-SE compressive stress of the regional stress field. Nonetheless,the impoundment of Dagangshan reservoir may intensify the seismic activity,considering the obvious relativity between seismic activity and water level,as well as the anticlockwise rotation of the stress field in the study area.
作者
冯静
孔军
康宏
张炜
赵昱
FENG Jing;KONG Jun;KANG Hong;ZHANG Wei;ZHAO Yu(Sichuan Earthquake Agency, Chengdu 610041, China)
出处
《地球物理学进展》
CSCD
北大核心
2018年第2期451-460,共10页
Progress in Geophysics
基金
四川省地震局地震科技专项(LY1604)
四川赛思特科技有限责任公司西部大开发投资项目(D2013007)联合资助
关键词
双差定位
震源机制
构造地震
诱发地震
大岗山水库
double-difference earthquake location algorithm
focal mechanism
tectonic earthquake
reservoir-induced earthquake
Dagangshan reservoir
