Three-Dimensional Feature of Ionospheric Anomaly Prior to 2010 Maule Earthquake

The phenomenal discovery by Heki (Geophys Res Lett 38(17), 2011) [1] regarding an anomaly in the ionosphere a few minutes before a major earthquake has given hope. It has been a decade, and this research continues to develop and the latest development is the disclosure of the preseismic structure in three-dimensional. Based on the results of 3D tomography, this anomaly has positive (electron increase) in the lower and negative (electron decrease) components in the upper ionospheres. Muafiry and Heki (J Geophys Res Space Phys 125(10), 2020) [2] then suspected that the mechanism for this phenomenon was due to the transfer of electrons from the upper to the lower layer of the ionosphere triggered by surface electric charge. Nevertheless, this structure has only been identified in two significant earthquake events, the 2015 Illapel and the 2011 Tohoku-Oki Earthquakes to name. Further research regarding the existence of these two anomaly components needs to be explored extensively for other large earthquakes. In this study, an attempt to obtain these two components before the 2010 Maule Earthquake is conducted. Using phase difference of the microwave GPS signals from networks in some South American countries, the positive and negative components of the anomaly in the ionosphere before the earthquake are recorded in GPS-TEC time series. However, due to limited ray-path of GPS station-satellite signal pairs penetrated into the 3D tomography voxels, the negative anomaly component is not identified clearly at higher altitude as was previously found in two other large earthquakes. Such problem occurs because limited navigation satellites and stations are available at this time.