为获取地震发生更全面的电磁异常信息，我国建设了多参量、宽频带信号的极低频地震电磁观测台网。因其数据格式复杂，数据量庞大，之前多年监测数据未能在地震预报工作中得到持续使用。本文以云南省丽江地震台为例，介绍极低频台站观测数据产出及背景变化特征，并利用视电阻率形态法对台站周边中强震进行回溯性分析，有以下几点发现：①由丽江地震台电磁场功率谱随频率的变化可知，5个分量变化形态相似，水平电场在同一数量级发生变化，水平磁场亦是如此，但垂直磁场强度较低；②由丽江台电磁场功率谱随时间的变化可知，5个分量同步显示出“夏高冬低”的一年周期性；③由丽江地震台视电阻率和相位随频率的变化可知，丽江地下介质电性结构复杂，低频（深部）电阻率值偏低，视电阻率和相位在0.1—100 Hz频段较为稳定；④由丽江地震台视电阻率随时间的变化可知，视电阻率呈“夏低冬高”的年变化形态，且随着频率增大，年变特征越明显；⑤在中强震前或发生过程中，丽江地震台视电阻率大多有脉冲式增大、加速下降/上升、年变畸变等异常现象出现，且中高频段异常现象显著。极低频台网的建设实现了对地下介质电性结构和电磁场的动态观测，提高了与地震活动有关的电磁异常识别和捕捉能力。本文针对丽江地震台基础数据的分析和对历史震例的回溯，总结了不同地震事件中视电阻率在不同频段的变化特点，有利于有效识别与地震有关的电磁异常，可为极低频数据在震情跟踪会商中的应用奠定基础。
To obtain more comprehensive anomaly information on earthquakes, China has built a multi-parameter, wide-band signal extremely low frequency (ELF) electromagnetic observation network. However, due to the complex format and huge amount of ELF observation data, the valuable data monitored over the years has not been used effectively in earthquake monitoring and prediction. Taking the Yunnan Lijiang ELF Station as an example, this study introduces the observation data and the background change characteristics and uses the apparent resistivity morphology method to retrospectively analyze M≥5 earthquakes around the station. The following findings were made:①From the change of the electromagnetic field power spectrum with frequency at Lijiang Seismic Station, it is found that the five components have similar change forms. The horizontal electric field changes at the same order of magnitude, and the horizontal magnetic field changes at the same order of magnitude, but the vertical magnetic field intensity is lower.②From the temporal variation of the electromagnetic field power spectrum at Lijiang Seismic Station, it can be seen that the five components synchronously show an annual periodicity of high in summer and low in winter. ③From the changes of resistivity and phase with frequency at Lijiang Seismic Station, it can be seen that Lijiang has complex electrical structure characteristics. The resistivity value at low frequency (deep) is low, and 0.1-100 Hz is a relatively stable frequency band. ④From the temporal variation of the apparent resistivity of Lijiang Seismic Station, we can see that the apparent resistivity presents an annual variation pattern of “low in summer and high in winter”, and the annual variation becomes more obvious as the frequency increases.⑤Before or during strong earthquakes, the apparent resistivity of Lijiang Seismic Station mostly shows abnormal phenomena such as pulsed increase, accelerated decline/rise, and annual distortion, and the abnormal phenomena in the medium and high-frequency bands are the most obvious. The construction of the ELF stations has realized the dynamic observation of electrical structures and electromagnetic fields and improved the ability to identify and capture electromagnetic anomalies related to seismic activities. Based on the analysis of the basic data of Lijiang Seismic Station and the review of historical earthquake cases, this paper summarizes the variation characteristics of apparent resistivity in different frequency bands in different earthquake events, which is conducive to the effective identification of electromagnetic anomalies related to earthquakes and lays the foundation for the application of the ELF data in earthquake tracking and consultation.
2025,46(1): 1-12 收稿日期：2024-11-5
DOI：10.3969/j.issn.1003-3246.2025.01.001
基金项目：2024年震情跟踪定向工作任务（项目编号：2024010401）
作者简介：范晔（1987—），女，高级工程师，主要从事地震电磁数据分析处理工作。E-mail：fanye@seis.ac.cn
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