[M-IS09] Interdisciplinary studies on pre-earthquake processes

[MIS09-10] The 3-D ionospheric Ne disturbances prior to M9.0 Tohoku-Oki Earthquake on
March 11, 2011

*Rui Song¹, Katsumi Hattori^1,2,3, Chie Yoshino², Jann-Yenq LIU⁴ (1.Research Institute of Disaster Medicine, Chiba University, 2.Graduate School of Science, Chiba University, 3.Center for Environmental Remote Sensing, Chiba University, 4.Institute of Space Science, National Central University, Taiwan)

In this study, the three-dimensional (3-D) ionospheric electron density (Ne) disturbances prior to the 2011 M9.0 Tohoku-Oki Earthquake were analyzed by using the ground-based total electron content data sets provided by the global positioning system (GPS) Earth Observation Network (GEONET) in Japan. To retrieve the 3-D ionospheric Ne distributions, we developed an initial input-free algorithm, termed the improved constraint least square fitting (ICLSF) algorithm based on the computerized ionospheric tomography (CIT) technique. It has an excellent performance in visualizing ionospheric disturbances, owing to its independence of any initial guesses with only vertical direction constraints. Two kinds of ionospheric Ne anomalies were detected in our study. First, by calculating the percent Ne variations, we found remarkable negative Ne anomalies ranging from -20% to -60% around the epicenter on March 8, 2011, which is three days prior to the main shock. They lasted for more than ~20 hours in the lower altitudes of F2 layer in 190 - 250 km. Second, prominent continuous downward drift of Ne in the F2 layer with displacement of ~ 60 km was recognized immediately before the main shock during 04:52 - 05:30 UT in the west of the epicenter. Finally, we discussed the possible lithosphere-atmosphere-ionosphere coupling mechanism based the 3-D distribution of reconstructed ionospheric anomalies.