本論文利用中位數參考，分析中壢電離層台(25°N, 121.2°E)紀錄之電離層??2層層峰(臨界)電漿頻率(foF2)持續變化，以及臺灣經度鏈一維和經度緯度二維電離層全電子含量(Total Electron Content, TEC)，重新審視臺灣1999年9月21日規模M7.7集集大地震電離層異常前兆。研究結果與先前結果十分吻合，證實foF2和TEC於集集地震前3與4天下午時段顯著異常減少、臺灣經度鏈上之電離層赤道異常峰(Equatorial Ionization Anomaly, EIA)明顯向赤道移動、集集震央上空TEC急遽減少。藉由統計和接收者操作特徵曲線(Receiver Operating Characteristic curve, ROC curve)分析1994-1999年foF2和TEC尋找臺灣地震時間電離層前兆之極性、領先天數、持續時間、地方時段等特性。結果顯示臺灣地區規模M?6.0地震前1-4天下午時段foF2和TEC顯著異常減少。前兆特性與集集地震個案吻合，說明電離層異常為可靠的地震前兆。利用全球電離層圖(Global Ionosphere Map, GIM)進行之空間前兆分析，說明TEC負異常集中出現於集集震央上空，再次證實地震電離層前兆之存在與可靠性。電離層EIA赤道向移動顯示集集地震前兆天在震央附近出現西向孕震電場，而DMSP人造衛星量測之離子速度，證實孕震電場約為1.2-1.6 mVm? 西向，此乃為地震電離層前兆之物理機制。最後統計分析1994-2019臺灣地區地震與TEC的關聯性，結果顯示集集地震前與後數年地震電離層異常前兆特性明顯不同。;To revisit seismo-ionospheric precursors (SIPs) of the 21 September 1999 Mw 7.7 Chi-Chi earthquake, this thesis applies the median base on the ionospheric critical frequency of foF2 sounded by the Chung-Li ionosonde (25°N, 121.2°E) and the total electron content (TEC) derived by ground-based GPS receivers in Taiwan. Current and previous results yield good agreements that foF2 and TEC significantly decrease in the afternoon period on day 3 and 4 before the Chi-Chi earthquake; the EIA (Equatorial Ionization Anomaly) prominently moves equatorward; and TEC drastically reduces specifically over the Chi-Chi epicenter. Statistical test and ROC (Receiver Operating Characteristic) curve are applied to find the characteristics of positive/negative polarity, lead day, duration, local time, etc. of increase temporal SIPs of foF2 and TEC in Taiwan during 1994–1999. Results show that the SIPs characteristics in Taiwan is significant decrease of the foF2 and TEC in the afternoon period day 1-4 before M? 6.0 earthquakes. The well agreement of Chi-Chi event with the characteristics indicates that SIPs of foF2 and TEC are reliable. The global ionosphere map (GIM) is used to conduct the SIP spatial analysis. Negative anomalies of GIM TEC frequently appear specifically over the epicenter, which confirms the existence of the Chi-Chi SIP. Meanwhile, the prominent equatorward motion implies that seismo-generated westward electric fields appear over the epicenter area. The ion velocity measured by DMSP (Defense Meteorological Satellite Program) satellite shows that the seismo-generated westward electric fields are of about 1.2-1.6 mV/m, which are the mechanism causing the Chi-Chi SIPs. Moreover, statistical analyses of TEC associated with earthquakes during 1994-2019 show that the characteristics has been significantly changed before (1994-1999) and after the Chi-Chi earthquake (2000-2019).
