電離層地震前兆之研究; A study of seismo-ionospheric precursor

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Title:	電離層地震前兆之研究;A study of seismo-ionospheric precursor
Authors:	卓裕榮;Yu-Jung Chuo
Contributors:	太空科學研究所
Keywords:	地震;電離層;全球定位系統;fof2;foF2;GPS;ionosphere;earthquake
Date:	2002-05-21
Issue Date:	2009-09-22 09:45:26 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	研究瑞里、集集和嘉義三個地震前電離層的變化情形，發現電離層最大電漿頻率foF2 會異常減少。另也由台灣地區GPS 接收網資料估算上空之全電子含量，發現赤道異常峰於地震前有向赤道方向移動的現象。進一步分析十四個規模6.0 以上的地震，發現異常的時間為地震前1~5 天內之1200-1700LT，且大多發生於地震之前一天。同時也發現地震前五天內清晨及黃昏時之散塊E 層電漿頻率foEs 也會異常增大。進一步分析1994-1999 六年間每日及期間規模5.0 以上地震前一天之foF2 資料。比較兩者之差異，確認前兆出現時間為1200-1700LT。利用互相關分析，發現地震前兆出現是於規模5.0 以上地震之前五天內。研究電離層地震前兆異常偏離量與地震規模、震央距離及震源深度之關係，發現偏離量變化會隨著地震規模的增加而增加，而卻隨著震央距離的增加而減少。至於偏離量與震源深度的關係則不明顯。經統計結果顯示，地震規模5.0 以上五天前發生電離層foF2 前兆的機會為74.1%，且地震的規模愈大出現前兆之機會也愈大。另外，電離層前兆後出現地震的機會為53.3%，這比地震發生之平均機會大1.6 倍。 ii In this dissertation, the ionospheric maximum plasma frequency, foF2, is applied to study ionospheric variations before the 3 strong Rei-Li, Chi- Chi, and Chia-Yi earthquakes. Results show that the foF2 signatures decrease before the three-earthquake onset. Meanwhile, the ionospheric total electron content (TEC) observed by the global positioning system (GPS) receivers in Taiwan area is also utilized to investigate these events. It is found that the equatorial anomaly crest of the GPS TEC moves equatorward and the associated TEC value significantly decreases 1-4 days before the three earthquakes. Further, the foF2 before fourteen M³6.0 earthquakes occurred in 1994-1999. It is found that the decreases appear at 1200-1700LT within 6 days before the onset of the earthquakes, and most likely appear 1 day before. On the other hand, a comparison between the day-to-day variability and anomalies in the foEs before the fourteen M³6.0 earthquakes shows that the foEs severly enhances during the sunrise and sunset periods. Further, a robust statistical technique is applied to identify anomalies in the foF2 appearing in the Taiwan area during 184 M³5.0 earthquakes occurred in 1994-1999. A stacking process and cross correlation analyses have uncovered not only the typical shape foF2 decreasing 1200-1700LT, but also the leading time 1-5 days the ionospheric precursors. Furthermore, simulation tests verify the superiority of the ionospheric precursor over a seismicity-based prediction process and confirm the significance of the ionospheric precursor related to the earthquakes. The statistics results show that the probabilities of observing the features 1-5 days prior to the forthcoming shocks is 74.1% and, on the other hand, the valid alarm rate of the ionospheric precursor is 53.3%.
Appears in Collections:	[Graduate Institute of Space Science] Department of Earth Sciences

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