采用CAP方法得到滇西北地区2013年1月—2022年5月259次3级以上地震震源机制解,采用阻尼参数方法反演应力场,并结合漾濞 M_S6.4 地震震群对滇西北地区震源机制特征进行分析与讨论。结果显示: ①滇西北地区震源机制多为走滑类型,部分为正断型,震源深度较浅,大多为高倾角地震; P轴方向自北向南显示为NNW向、NW和NE向,表现出顺时针偏转趋势,P轴、T轴均有较小的倾伏角,地震震源应力作用以水平为主。②滇西北地区应力场类型以走滑型为主; 研究区北部德钦—中甸断裂附近为拉张型,主压应力轴方向主要为NW向,该区域受到了强烈的拉张作用; 东北部大理—丽江断裂附近有走滑型和拉张型分布,拉张型在西南侧,主压应力轴方向主要为NNW向; 大理地区红河断裂附近为走滑型和过渡型,主压应力轴方向为NNW近NS和NNE向; 区域西南瑞丽—保山腾冲地区应力场为走滑型,主压应力轴方向主要为NE向。整体上,主压应力轴自北向南呈顺时针旋转,在大理地区红河断裂附近顺时针旋转显著转变,由NNW逐渐转变为NNE。③维西—乔后断裂附近多次5级以上地震发震构造存在相同特征,即发震构造均为维西—乔后西侧隐伏断裂或者次生断裂,2022年震源机制变化或许和断裂附近应力变化调整有关,分析认为应进一步研究和重视该区中强地震活动。

In this paper,we utilize the CAP(Cut and Paste) method to determine the focal mechanisms of 259 earthquakes with magnitudes of 3.0 or greater in northwest Yunnan,spanning the period from May 2013 to 2022. We apply the damping parameter method to invert the regional stress field and analyze the seismic source mechanisms in conjunction with the Yangbi M_S6.4 earthquake cluster. The key findings are as follows: ① The focal mechanisms in northwest Yunnan are predominantly strike-slip,with some normal faulting. Earthquakes generally occur at shallow depths and have high dip angles. The P-axis orientation varies from NNW to NW and NE,with a noticeable clockwise deflection from north to south. Both the P-axis and T-axis exhibit small inclination angles,indicating that the stress at the earthquake sources is mainly horizontal. ② The stress field in northwest Yunnan is primarily strike-slip. In the northern part of the study area,near the Deqin-Zhongdian fault,tensile stress dominates,with the principal compressive stress axis oriented NW. In the northeastern region,near the Dali-Lijiang fault,both strike-slip and tensile stress fields are present,with tensile stress concentrated on the southwest side and the principal compressive stress axis oriented NNW. Near the Honghe fault in the Dali area,the principal compressive stress axis shifts from NNW to NNE. In the southwestern region,particularly in the Ruili-Baoshan and Tengchong areas,the stress field is strike-slip,with the principal compressive stress axis oriented NE. Overall,the principal compressive stress axis rotates clockwise from north to south,with a marked shift from NNW to NNE near the Honghe fault in the Dali area. ③ The seismic tectonics of several magnitude 5 or greater earthquakes near the Vexi-Qiaohou fault share common characteristics. These earthquakes are associated with hidden or secondary faults west of the Vexi-Qiaohou fault. The observed changes in seismicity mechanisms in 2022 may be related to the complex stress adjustments near the fault. This area warrants further study and monitoring for potential moderate to strong seismic activity. These findings contribute to a deeper understanding of the complex seismic dynamics in northwest Yunnan and highlight the importance of continued monitoring and research in the region.

P315

中国地震局“三结合”课题(3JH-202401067)、云南省地震局科技人员传帮带(青年骨干人才培养)项目(CQ3-2021005)、云南省重点研发计划(公共安全专项)(202203AC100003)、云南省地震局科技创新团队(CXTD202411)共同资助