2019年四川长宁M_(S)6.0地震前电离层TEC异常分析

Analysis of Ionospheric TEC Anomalies before the 2019 M_(S)6.0 Earthquake in Changning, Sichuan Province

2019年6月17日四川宜宾市长宁县发生M_(S)6.0地震。为了检测地震电离层电子浓度总含量(TEC)异常变化,采用自回归滑动平均模型(ARIMA)和先知(Prophet)两种方法来描述TEC时间序列,检测长宁地震前后TEC异常变化。地磁指数Kp,Dst,Ap和F10.7用于区分与太阳—地磁活动等空间因素相关的其他异常。结果显示,使用ARIMA方法,除了在地震发生前13天5:45 UTC检测到TEC数据时间序列中的显著电离层异常外,其他电离层异常变化全部发生在震后2~6 d;而使用Prophet方法在地震发生前16天7:45 UTC、13天9:30 UTC、5天8:30 UTC以及3天09:30 UTC检测到多处异常现象。综合分析表明,使用Prophet方法比ARIMA更易检测出震前异常。同时,Prophet由于其非线性学习的能力相对较强可作为地震电离层异常检测的鲁棒预测工具。

On 17 June 2019,an earthquake with M_(S)6.0 occurred near Changning,Yibin,Sichuan Province.In order to detect the anomalous changes of Total Electron Content(TEC)seismic ionospheric,Autoregressive Integrated Moving Average Model(ARIMA)and prophet are used to describe the TEC time series and detect TEC anomalies variations before and after the Changning earthquake.In this study,geomagnetic indices(i.e.K_(p),D_(st),Ap and F10.7)are used to distinguish pre-earthquake anomalies from the other anomalies related to the geomagnetic and solar activities.The result of ARIMA shows that apart from the significant ionospheric anomalies in TEC time series detected at 5:45 UTC,13 days before the earthquake,all the other ionospheric anomalies occurred 2~6 days after the event.While using Prophet method,multiple pre-earthquake anomalies are detected at 7:45 UTC before 16 days,9:30 UTC before 13 days,8:30 UTC before 5 days,and 09:30 UTC before 3 days.A comprehensive analysis indicates that the Prophet method is more likely to manifest anomalous states than traditional methods such as ARIMA.Meanwhile,due to its promising ability of nonlinearly learning,Prophet method is worthy of attention as a robust predictive tool for seismic ionospheric anomaly detection.