2020年牙买加M_W7.7地震前蜂群卫星磁场的时变背景场与异常分析  

Time-varying background field and anomaly analysis of Swarm satellite magnetic field data before the 2020 Jamaica MW7.7 earthquake

作　　者：朱凯光[1,2] 贺小丹 樊蒙璇 Dedalo Marchetti 王婷 温佳咪[1,2] 张逸群 Zhu Kaiguang;He Xiaodan;Fan Mengxuan;Dedalo Marchetti;Wang Ting;Wen Jiami;Zhang Yiqun(College of Instrumentation and Electrical Engineering,Jilin University,Changchun 130061,China;Key Laboratory of Geophysical Exploration Equipment,Ministry of Education of China,Changchun 130026,China)

机构地区：[1]吉林大学仪器科学与电气工程学院,中国长春130061 [2]吉林大学地球信息探测仪器教育部重点实验室,中国长春130026

出　　处：《地震学报》2023年第2期315-327,共13页Acta Seismologica Sinica

基　　金：国家自然科学基金(41974084);吉林省自然科学基金(20230101091JC)联合资助。

摘　　要：蜂群卫星磁场数据受地磁活动和地方时的影响,本文先通过变分模态分解去除地磁活动对数据的影响,再建立时变背景场以消除地方时对数据的影响。基于建立的时变背景场,我们利用蜂群卫星磁场数据对2020年牙买加M_W7.7地震进行震前异常分析,计算地震影响区域内轨道数据的能量值,利用时变背景场设置阈值提取异常。结果表明:牙买加地震影响区域内的异常轨道累计数量在震前50天至震前43天出现加速增长的现象。此外,基于时变背景场与昼、夜侧背景场提取异常的结果对比显示:由于昼、夜侧背景场的建立混合了多个当地时间的磁场数据,高值背景场会被低值背景场拉低,导致部分非异常的轨道被错误地识别为异常轨道;而低值背景场会被高值背景场抬高,导致部分异常轨道不能被识别。而时变背景场针对每一个地方时建立了更为准确的背景,其时间分辨率高,能凸显出不同地方时卫星磁场数据的背景值差异,这对异常轨道的准确提取十分重要。进一步对岩石层、大气层和电离层多圈层的参量进行了震前异常分析,并对三个圈层的异常出现时间进行解释,证明了这些异常可能与牙买加地震的孕育有关。The magnetic field data of Swarm satellite are influenced by geomagnetic activity and local time. In this paper,the influence of geomagnetic activity was firstly removed by vari- ational mode decomposition,and then we built a time-varying background field to eliminate the influence of local time on the data. Based on the established time-varying background field,we used the Swarm satellite magnetic field data to conduct a pre-earthquake anomaly analysis of the 2020 Jamaica earthquake. We calculated the amount of energy of the magnetic data inside the earthquake affected area,then compared with the threshold value of the time-varying back- ground field. If the difference between the amount of energy of a track inside the earthquake affected area and the corresponding background value is over the threshold value,the track was considered to be pre-earthquake anomalies. The results show that the cumulative number of anomalous tracks in function of the time shows accelerated growth from 50 days to 43 days before the earthquake. In addition,we also built day-side and night-side background fields to compare with the time-varying background field. By analyzing the differences between the anomalous orbits extracted based on the two methods,we find that the high-value background fields will be pulled down by the low-value background fields,which leads to some non-anomalous orbits being wrongly identified as anomalous orbits. For the same reason,the low-value background fields will be pulled up by the high-value background fields,which leads to some abnormal orbits cannot be recognized. It is because that the day-side and night-side back- ground fields were built by the data of multiple local times magnetic field data,which cannot identify the great variations of magnetic field at different local time. However,the time resolu- tion of time-varying background field is high,so it can highlight the great variations of mag-netic field at different local time. As a result,the establishment of time-varying background field is cru

关 键 词：蜂群卫星磁场 时变背景场 牙买加地震 震前异常提取 变分模态分解 

分 类 号：P315.72[天文地球—地震学]