Challenges in the Detection of Ionospheric Pre-Earthquake Total Electron Content Anomalies (PETA) for Earthquake Forewarning

Abstract

Various studies have investigated the link between seismic activity and ionospheric precursory phenomena. Many of these retrospective case studies have supported the existence of pre-earthquake ionospheric anomalies by examining past earthquake events using a variety of analytical methods. Based on existing methodologies, however, the conversion of a retrospective analysis to a prospective forewarning scenario is not a straightforward process. The obstacles to its potential adoption stem mainly from assumptions made during data analysis and interpretation. In this study, several parameters pertaining to existing approaches for the detection of these ionospheric anomalies are highlighted and discussed, in particular ionosphere total electron content (TEC). A detailed examination is conducted to understand the roles that each of these parameters play in the detection process and the consequent difficulties when adopting them in a prospective analysis. These issues include accounting for variations in ionosphere characteristics owing to different measurement platforms (e.g. ground- and space-based observations) and statistical methods (e.g. standard deviation envelopes) used in detecting anomalies. Furthermore, the necessity of excluding space weather contributions in the underlying TEC fluctuations poses a challenge in determining the validity of observed ionospheric anomalies. The notion of an “earthquake preparation zone” is also evaluated in the context of the ionosphere, along with its implications in a forewarning scenario. These issues need to be addressed in current research in order to enable its possible application in earthquake forewarning.