2019年6月17日长宁M_(S)6.0地震序列震源区二维构造应力场特征研究

Study on the Characteristics of the Two-dimensional Tectonic Stress Field in the Focal Area of the Changning M_(S)6.0 Earthquake Sequence on June 17,2019

使用近震波形反演方法求解2019年6月17日四川长宁Ms6.0地震序列的震源机制解和震源深度,共得到30个可靠的M>3.0地震震源机制解和震源深度,结合该地区已有的震源机制解,开展震源区构造应力场反演,小尺度探讨震源区的构造应力环境。反演结果显示,震中附近区域主要以逆冲型应力性质为主,局部地区包括少量走滑分量以及混合类型。最大主压应力方向主要以NEE向或NE向为主。在筠连以东地区,不同于北部的逆冲型,应力性质以走滑型兼少量混合类型为主,最大主压应力方向近EW向。构造应力场方向与形成长宁背斜的构造应力存在一定交角,2019年长宁6.0级地震可能是由NE或NEE向近水平应力挤压产生的该地区滑脱面之上背斜核部的逆断层活动造成的。

The focal mechanism solution and focal depth of the Changning M_(S)6.0 earthquake sequence in Sichuan on June 17, 2019 were solved using the near-earthquake waveform inversion method, and a total of 30 reliable focal mechanism solutions and focal depths of the earthquakes with M>3.0 were obtained. Combining with the existing focal mechanism solutions in the area, we carry out the inversion of the tectonic stress field in the focal area, and explore the tectonic stress environment in the focal area on a small scale. The inversion results show that the area near the epicenter is dominated by thrust-type stress, and some areas include a small amount of strike-slip components and mixed types. The direction of the maximum principal compressive stress is mainly in the direction of NEE or NE. In the area to the east of Junlian, unlike the thrust type in the north, the stress properties are mainly strike-slip type with a small amount of mixed type, and the maximum principal compressive stress direction is close to the EW direction. There is a certain angle between the direction of the tectonic stress field and the tectonic stress forming the Changning anticline. The 2019 Changning M6.0 earthquake may be caused by the reverse fault activity at the core of the anticline above the detachment surface of the area caused by the NE or NEE approaching horizontal stress compression.