Correlation Analysis for Total Electron Content Anomalies on 11th March, 2011

TL;DR

This paper introduces a correlation analysis method for detecting preseismic Total Electron Content (TEC) anomalies in the ionosphere, demonstrating its effectiveness in identifying anomalies before the 2011 Tohoku earthquake.

Contribution

It proposes a novel correlation-based approach to identify TEC anomalies, improving detection amidst noise and natural disturbances, with potential for earthquake prediction.

Findings

Detected TEC anomaly one hour before the 2011 Tohoku earthquake.

Demonstrated the effectiveness of correlation analysis in TEC anomaly detection.

Extended the application of correlation methods from radio communications to ionospheric studies.

Abstract

We can observe the changes of Total Electron Content, TEC, in ionosphere by analyzing the data from GNSS satellites. There are many reports about TEC anomalies after earthquakes, i.e. large earthquakes often disturb the ionosphere. Up to now, preseismic TEC anomalies have been reported in several papers. However, they are not so clear as coseismic TEC anomalies, and their analysis methods have some problems for practical earthquake prediction. One factor making it difficult to detect TEC anomalies is large noises in TEC data. Non-negligible TEC disturbances are caused by many natural mechanisms. To overcome this difficulty, we propose correlation analyses between one GNSS station and GNSS stations surrounding it. First, we model TEC time series over a few hours using polynomial functions of time. Second, we calculate prediction errors as the departure of the TEC time series from the models over time scale of a few minutes, and define it as the TEC anomaly. Third, we calculate the correlation between anomaly of one GNSS station and those at the surrounding stations. Although such a correlation method has long been used for radio communications, in particular for spread spectrum communications and very long baseline interferometry (VLBI) to increase SNR (signal to noise ratio), it has not been widely applied for TEC analyses. As a result of our method, we demonstrate that the correlation analysis let us detect TEC anomaly one hour before 2011 Tohoku-oki earthquake. In this paper, we examined the 2011 Tohoku-oki case extensively.