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

[MIS04-P11] Seismo-ionospheric precursors in the ground-based GNSS total electron content and DMSP ion parameters associated with the 1999 M7.6 Chi-Chi earthquake

*Jann-Yenq LIU¹、Fu-Yuan CHANG²、Yun-Cheng WEN³、Chi-Yen LIN²、Yuh-Ing CHEN⁴ (1.Center for Astronautical Physics and Engineering, Department of Space Science and Engineering, Center for Space and Remote Sensing Research, National Central University、2.Center for Astronautical Physics and Engineering, Department of Space Science and Engineering, National Central University、3.Department of Space Science and Engineering, National Central University、4.Graduate Institute of Statistics, National Central University)

キーワード：Chi-Chi earthquake, total electron content, DMSP statllite, electric field, ion velocity

This study revisits the total electron content (TEC) derived from ground-based GPS receivers during the 21 September 1999 M7.3 Chi-Chi earthquake. It is found that TEC over the epicenter anomalously/significantly decrease in the afternoon period day 1, 3, and 4 before the Chi-Chi earthquake. We further statistically examine pre-earthquake ionospheric anomalies of TEC associated with M5.0 equal and greater earthquakes in Taiwan about 6 years before the Chi-Chi earthquake (1994/1/1-1999/9/20) and find the characteristic of seismo-ionospheric precursors (SIP) in the polarity (i.e., increase or decrease anomalies), local time, lead time, duration, etc. of these earthquakes. The statistical result shows that the SIP characteristic is TEC significantly/anomalously decreasing in the afternoon period day 1-5 before the earthquakes, which suggests that the anomalies appearing day 1, 3, and 4 before the Chi-Chi earthquake most likely are SIPs. The spatial analysis is conducted, which shows that TEC anomalously/significantly decrease specifically over the epicenter day 1, 3, and 4 before the Chi-Chi earthquake. To search possible causal mechanisms, which result in the decrease anomalies of the Chi-Chi earthquake, the equatorial ionization anomaly of TEC along the Taiwan longitude during September 1999 and plasma quantities of ion density, ion temperature, and ion velocity probed by DMSP (Defense Meteorological Satellite Program) satellites are examined. Results show that seismo-electric fields generated in the epicenter area before the Chi-Chi earthquake are essential.