2017年西藏米林MS6.9地震前地磁垂直强度极化异常特征

Anomalous characteristics of geomagnetic vertical strength polarization before the 2017 Milin MS6.9 earthquake in Tibet

  • 摘要: 基于中国大陆65 个地磁台站秒采样观测资料,利用地磁垂直强度极化方法提取了2017年西藏米林MS6.9 地震震中及附近区域超低频电磁异常信号并分析其时空演化特征。结果显示:米林MS6.9 地震前在青藏高原出现了大范围的地磁垂直强度极化高值异常,异常过程共持续9天;高值异常开始于2017 年10 月30 日,高值持续3 天之后出现短时间下降,随即转折上升,再次出现高值异常并持续了4 天,在此过程中各高值台站的时序曲线呈现出单峰或双峰的形态。空间分布图显示高值异常在中国大陆西部区域反复出现,尤其是在青藏高原巴颜喀拉地块与羌塘地块的交界处。异常呈“出现—扩大—收缩—消失—扩大—消失”的演化过程,10月31日异常面积达到最大值。异常过程结束后10天发生了西藏米林MS6.9地震,震中距离10 月31 日异常阈值线5 km。综合分析认为,此次异常与米林地震具有较强的时空相关性,是可靠的地震电磁前兆异常。

     

    Abstract: Based on the second sampling data from 65 geomagnetic stations in Chinese mainland, we extracted the ultra-low frequency electromagnetic anomaly signals from the epicenter of the 2017 Milin MS6.9 earthquake in Tibet and its vicinity using geomagnetic vertical strength polarization method, and analyzed their spatio-temporal evolution characteristics. The results show that a large range of geomagnetic vertical strength polarization high value anomalies appeared in the Qinghai-Xizang (Tibetan) Plateau before the MS6.9 earthquake, and the abnormal process lasted for nine days. The high value anomaly began on October 30, 2017. The high value lasted for three days, followed by a short period of decline, a turning point and an increase. Afterwards the high value anomaly appeared again and lasted for four days. In this process, the time-series curves of each high-value station show single peak or double peak. The spatial distribution map shows that high value anomalies occur repeatedly in the western part of Chinese mainland, especially at the junction of Bayankhara and Qiangtang blocks on the Tibetan Plateau. The anomaly appeared, expanded, contracted, disappeared, expanded and disappeared, and the abnormal area reached its maximum value on October 31. Ten days after the end of the abnormal process, the Milin MS6.9 earthquake occurred, with its epicenter 5 km from the anomaly threshold line of October 31. Comprehensive analysis indicates that this anomaly has strong temporal and spatial correlation with the Millin earthquake and can be regarded as reliable seismic electromagnetic precursor.

     

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