2018年9月8日墨江地震及周边地区构造应力场特征分析

2018年9月8日,云南省墨江县发生MS5.9地震并伴随一系列余震,探究该地震周围的应力场对于理解该地震的发生机制和后续地震的发展趋势具有着重要的参考意义.本研究收集了震源及其邻区中前人研究和Global CMT所给出的震源机制资料,对该地区进行了构造应力场反演,并同时利用反演得到的应力张量模拟墨江地区的震源机制解表现.结果表明:(1)在应力轴整体分布上,自西向东σ1轴(压轴)从NNE-SSW向逐渐转向NNW-SSE向,σ3轴(张轴)从WWN-EES向逐渐转向WWS-EEN向,张轴呈弧形分布,压轴呈放射状分布.(2)在应力轴倾伏角上,研究区域内的压应力轴和张应力轴倾伏角都比较小,即两轴均接近水平.(3)R值分布大体是在东南部相较于西北部大,结合当地地质背景分析得到,物质逃逸自西北向东南呈逐渐变缓的趋势.(4)利用反演得到的应力张量和应力状态计算墨江地震震源区的相对剪应力和相对正应力大小.由此推测,墨江地震恰好发生在相对剪切应力值和相对正应力正值最大的节面上.从而可以确定墨江地震的发震节面的基本参数:走向216.32°,倾角86.91°,滑动角0.27°,相对剪应力值0.9,相对正应力值0.3.本研究为此次墨江地震的发震背景和地震动力学研究提供了基础性资料.

Characteristics analysis of tectonic stress field around the Mojiang earthquake and its adjacent areas on September 8, 2018

On September 8, 2018, the M_S5.9 earthquake occurred in Mojiang County, Yunnan Province, accompanied by a series of after-shocks. It is of great significance to know the stress field around the earthquake for understanding the mechanism of earthquake and the developing trend of subsequent earthquakes. We collect the data of focal mechanism from previous studies and Global CMT in the source and its adjacent areas to invert the tectonic stress field, and simulate the focal mechanism solution of the Mojiang earthquake. The results show that:① On the overall distribution of stress axes, from west to east, the σ₁ axis rotates from NNE-SSW to NNW-SSE and the σ₃ axis rotates from WWN-EES to WWS-EEN. Among them, the tensional axis is arc-shaped and the compressional axis is radial-shaped. ② The plunge angles of both the compressive stress axis and tensile stress axis are small in the study area, both the compressive and extensional stress axes are nearly horizontal. ③ The R value is larger in the southeast area than that in the northwest area. According to combining the analysis of the local geological background, the trend of material escape from northwest to southeast is gradually slowing down. ④ In the source area of the Mojiang earthquake, the relative shear stress and normal stress are calculated by using the stress tensor obtained in the inversion. It can be inferred that the Mojiang earthquake occurred on the fault plane where the maximum relative shear stress and positive relative normal stress are. The basic parameters of seismogenic nodal plane in the Mojiang earthquake can be determined:the strike, dip, sliding angle, relative shear stress and relative normal stress are 216.32°, 86.91°, 0.27°, 0.9 and 0.3 respectively. This study provides basic information for the research of seismogenic background and seismic dynamics of the Mojiang earthquake.