地震地质 ›› 2023, Vol. 45 ›› Issue (6): 1370-1384.DOI: 10.3969/j.issn.0253-4967.2023.06.007

• 研究论文 • 上一篇    下一篇

2021—2022年川滇地区4次MS≥6.0地震前井下地电阻率观测的异常变化

解滔(), 韩盈, 于晨   

  1. 中国地震台网中心, 北京 100045
  • 收稿日期:2023-03-02 修回日期:2023-06-01 出版日期:2023-12-20 发布日期:2024-01-16
  • 作者简介:

    解滔, 男, 1986年生, 2017年于中国石油勘探开发研究院获地球探测与信息技术专业博士学位, 副研究员, 主要从事地震电磁监测与预测方法、 地球物理观测与地震孕育过程方面的研究, E-mail:

  • 基金资助:
    国家自然科学基金(42104075); 北京市自然科学基金(8212045)

APPARENT RESISTIVITY ABNORMAL CHANGES OF BOREHOLE MONITORING BEFORE FOUR MS≥6.0 EARTHQUAKES IN SICHUAN-YUNNAN AREA FROM 2021 TO 2022

XIE Tao(), HAN Ying, YU Chen   

  1. China Earthquake Networks Center, CEA, Beijing 100045, China
  • Received:2023-03-02 Revised:2023-06-01 Online:2023-12-20 Published:2024-01-16

摘要:

2021—2022年川滇地区先后发生了云南漾濞 MS6.4、 四川芦山 MS6.1、 马尔康 MS6.0 和泸定 MS6.8 4次MS≥6.0地震。距这些地震震中400km的范围内布设有红格、 冕宁、 甘孜井下地电阻率观测站, 其观测数据在这4次地震前出现了不同程度和形态的中短期异常变化。红格站EW和NS测道自2020年12月开始出现同步下降变化, 2021年漾濞 MS6.4 地震后NS测道的异常恢复, 但EW测道仍然持续下降, 截至2022年9月5日泸定 MS6.8 地震发生, EW测道的异常持续时间约为21个月。甘孜站N10°E测道的下降异常变化始于2022年4月, 6月底开始出现转折回升, 10月异常恢复, 其间先后发生芦山 MS6.1、 马尔康 MS6.0、 泸定 MS6.8 地震。2022年9—11月, 甘孜站 N60°W测道出现年变畸变异常, 2023年1月26日泸定再次发生 MS5.6 地震。冕宁站EW、 NS、 N45°W测道自2022年6月下旬开始出现同步上升变化, 于泸定 MS6.8 地震后异常恢复。依据这些异常变化, 在周、 月会商中对2021年漾濞 MS6.4、 2022年泸定 MS6.8、 2023年泸定 MS5.6 地震做出了短期预测。

关键词: 地电阻率, 井下观测, 川滇地区, 地震, 异常变化

Abstract:

There have been four MS≥6.0 earthquakes, i.e. the Yangbi MS6.4, Lushan MS6.1, Maerkang MS6.0 and Luding MS6.8, occurred in Sichuan-Yunnan area from 2021 to 2022. Three borehole apparent resistivity monitoring stations of Hongge, Mianning and Garzê, normally operated within 400km away from these earthquakes. These stations recorded different types of middle-short abnormal changes before the four earthquakes. The EW and NS arrays at Hongge station began to display synchronous decline change since December 2020. According to the empirical relationship between the duration of the anomaly and the magnitude, it is predicted that there is a possibility of a magnitude 6.0 earthquake in the Sichuan-Yunnan border area. But there had been no short-term abnormal changes that can give a forecast opinion on a time scale. Short-term abnormal changes appeared at Hongge station in March 2021. The maximum decline magnitudes of the NS and EW arrays were 2.1% and 1.4%, respectively. We believed that the risk of a strong earthquake has further increased. The distance from the Yangbi earthquake to Hongge station is 232km. Data of NS array recovered to normal status after the Yangbi MS6.4 earthquake in 2021, but the data of EW array continued to decline. In the fault virtual dislocation(FVD)model, the coseismic slips are loaded in a way of equal in magnitude but opposite in direction, which provides the relative deformation around the epicenter. In a compressive tectonic region, compressive areas from the FVD model can be formed as the areas with compression enhancement. The dilatant areas cannot be distinguished between absolutely dilatant areas and compressive areas. However, they can be regarded as relatively dilatant areas where the original extensive stress is enhanced, or the original compressive stress is released to some extent. It is found that Hongge station is located in the relative expansion region generated by the Yangbi earthquake. Abnormal changes at Hongge station are not only affected by the seismogenic process of the Yangbi earthquake, but also possibly indicating the existence of another strong earthquake. The anomaly duration of the EW array was about 21 months long and the decline magnitude was 2.8%up to September 5, 2023, when the Luding MS6.8 earthquake occurred, which is about 340km far away from Hongge station. The N10°E array of Garzê station began to show abnormal decline change since April 2022 with the maximum decline magnitude of about 0.5%. Apparent resistivity curve changed to rise change since late June, and the anomaly recovered to the normal status in October. Three earthquakes of Lushan MS6.1, Maerkang MS6.0 and Luding MS6.8 occurred during the period of anomaly evolution, with a distance of 306km, 183km and 293km from the Garzê station, respectively. The regional deformation before Lushan and Maerkang earthquakes from the fault virtual dislocation model show that the seismogenic process of these two earthquakes has little influence on the abnormal changes detected from Garzê station. The abnormal changes are probably related to the preparation of another big earthquake. At the earthquake situation consultation meeting on August 26, the Electromagnetism Laboratory predicted that a magnitude 6.0 earthquake would occur in the northwest of Sichuan in the short term. After the Luding MS6.8 earthquake, the observation data of the N10°E array returned to the normal status. The N60°W array showed distortion in annual variation pattern from September to November 2022. Another MS5.6 earthquake occurred in Luding on January 26, 2023. The EW, NS and N45°W arrays of Mianning station showed synchronous rise changes since late June 2022, and anomalies recovered after the Luding MS6.8 earthquake. After the Luding earthquake, the regional deformation characteristics before the earthquake are also analyzed by the fault virtual dislocation model. The Garzê station is located in the area of compression enhancement, while Mianning station is located in the area of relative expansion. Results from petrophysical experiments have demonstrated the decline changes when water-bearing rock and soil samples are under compression, and the rise changes as samples are undergoing stress unloading. Resistivity does not recover to the initial status when the compression stress is completely released, suggesting the existence of irreversible change in the samples. Therefore, the patterns of anomalies recorded at Garzê and Mianning stations are consistent with the area deformation where the stations were located. In summary, according to the abnormal changes of three borehole apparent resistivity observation in Hongge, Mianning and Garzê station from 2020 to 2022, we have made short-term prediction for the Yangbi MS6.4 in 2021, Luding MS6.8 in 2022 and Luding MS5.6 in 2023, at the regular weekly and monthly earthquake situation consultation meetings.

Key words: Apparent resistivity, borehole observation, Sichuan-Yunnan area, earthquake, anomaly