Enhancing reliability of seismo-ionospheric anomaly detection with the linear correlation between total electron content and the solar activity index F10.7: Nepal earthquake 2015

Abstract

There is still no consensus on seismo-ionospheric anomalies and coupling mechanism. One of important reasons is that multi- excitation factors of ionospheric disturbances interfere with the judgment of their source. In this paper, a Linear Model between TEC and F10.7 (LMTF) was built to detect seismo-ionospheric TEC anomalies before and after Nepal earthquake 2015. Firstly, LMTF and Kalman filter (KFM) were utilized to predict TEC and compare with the TEC from Global Ionosphere Map (GIM) for evaluating their prediction accuracies. The statistical results show that the mean square error (MSE), average absolute relative error (Δ¯) and the correlation coefficient (Corr) between the TEC from GIM and the prediction TEC are ±0.88 TECU, 1.55 and 0.94 and all approximately equal to those of KMF, when their time moving windows are all set to 30 days. Further considering the period of the solar, the time moving window could be set to 27 days. Then, Sliding Quartile Method (SQM), KFM and LMTF were utilized to detect TEC anomalies above epicenter, International GNSS stations in affected area and the globe during the period of 15 days before and 10 days after Nepal earthquake by comparison. The comparative results demonstrate that LMTF is more effective to detect the TEC anomaly caused by Nepal earthquake in temporal and spatial scale. Moreover, the characteristics of the TEC anomalies caused by Nepal earthquake using LMTF are in agreement with the results of previous studies on Wenchuan and Nepal earthquake cases. At last, the coupling mechanism was discussed based on the characteristics of seismo-ionospheric TEC anomalies. It is supposed that the mechanism of seismo-ionospheric TEC anomalies can be explained by the combination action of internal gravity waves (IGWs) generated by the solar terminator and the electric field in seismogenic zone formed by the electric field effect of geochemical process and the piezo-electric potential effect of rock.