[M-IS04] Interdisciplinary studies on pre-earthquake processes

[MIS04-10] The 3-D ionospheric Ne disturbances prior to Tohoku-Oki Earthquake occurred on March 11, 2011

★Invited Papers

*Song Rui¹、服部 克巳¹、张 学民²、劉 正彦³ (1.千葉大学理学部、2.Institute of Earthquake Forecasting, China Earthquake Administration, China、3.Institute of Space Science, National Central University, Taiwan)

キーワード：Seismo-ionospheric effect、Computerized ionospheric tomography、Electron density pertubation

We detailly studied the three-dimensional (3-D) ionospheric electron density (Ne) disturbances prior to the 2011 M9.0 Tohoku Oki Earthquake in Japan by the ground-based total electron content data sets provided by the global positioning system (GPS) Earth Observation Network (GEONET). 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 mainshock. 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 mainshock during 04:52 - 05:30 UT west of epicenter. Finally, we discussed the possible triggering mechanism based on the 3-D CIT results.