台灣及中國災害性地震期間電離層層峰濃度與全電子含量異常研究

莊皓琨(Hau-Kun Jhuang)

指導教授 ： 劉正彥

國立中央大學/地球科學學院/太空科學研究所/博士(2014年)

摘要

本論文利用電離層探測儀及全球定位系統(Global Position System，GPS)分析地震期間電離層電子濃度之時空變化。首先利用電離層F2層峰濃度NmF2、GPS接收機反計算不同頻段訊號所推得之電離層全電子含量(Total Electron Content，TEC)、以及全球電離層圖(Global Ionospheric Maps，GIM)三種工具分析集集地震期間電離層之時空變化。比對台灣中壢、日本國分寺電離層探測儀記錄之NmF2時間變化，時間上發現集集地震引發之電離層負異常日。另外，分析台灣本地之GPS-TEC，發現其結果與電離層NmF2出現的異常日時間一致。進一步探討集集地震引發電離層之空間範圍，亦分析日本琉球GPS 0497接收機之TEC資料，異常結果也出現類似台灣GPS-TEC之負異常。為更確認異常之空間範圍，利用GIM之內差，建立虛擬觀測站含國分寺、φ120及其它三個不同地理經度的觀測站φ30、φ60、和φ90。結果顯示磁暴引起全球性之電離層負異常，而地震引起之電離層負異常，則是震央附近之區域性異常。應用類似分析，延伸以台灣地區 1997-1999 年144筆規模 M ≥ 5.0 地震期間之NmF2和TEC，統計研究台灣地區電離層地震時間前兆。同時比對1994-1999六年的NmF2及TEC資料，結果發現地震前後負異常有兩大發生時間點，一為地震前7日至後3日之 1000-1800 LT ，另一則為前7日至前1日之1600-2000 LT 。利用 GIM-TEC 之異常空間分布，以檢定地震之區域異常或是磁暴引起之全球異常。研究汶川地震期間之 GIM-TEC 變化，發現該地震會負異常多於正異常。地震前13、6、及5日，負異常位於震央附近與其共軛點之電離層，下午1200-1800LT及黃昏時段 1800-2200LT 皆低於 -2.9σ 。而正異常僅於地震前3日，出現於震央上空，但高出平均的差值卻無法通過 +2.5σ 門檻。統計研究1998年5月1日至2008年5月11日共33筆中國發生之 M ≥ 6.0 地震期間，結果顯示該 10 年期間電離層在地震前出現較多負異常，但是出現之時間卻與台灣 1000-2000LT 不同，為 2000-0400LT 。

關鍵字

電離層 ； 地震前兆

並列摘要

This dissertation studies ionospheric electron density variations by means of ionosonde and global position System (GPS). The ionospheric variations during Chi-Chi earthquake are the event study observed by 2 ionosondes Chungli, Taiwan and Kokunbunji, Japan, 4 local GPS receivers in Taiwan, and one at Okinawa, and 5 virtual GIM (Global Ionospheric Maps) 30˚E, 60˚E, 90˚E, 120˚E and Kokunbunji. The spatial analyses are employed to identify whether the earthquake or the geomagnetic disturbances cause the anomalous reductions. Moreover, we analyze the peak frequency and the peak electron density in the F2 layer (foF2 and NmF2), the peak density and the total electron content (TEC) during 1997 and 1999 associated with 144 M ≥ 5.0 earthquakes in Taiwan. The statistical results show that the anomalous reductions in NmF2 and TEC appear more frequently before than those after the earthquakes. By contrast, the anomalous enhancements appear less frequently before than those after the earthquakes. In general, the pre-earthquake departure of NmF2 and TEC from their associated medians is proportional to the earthquake magnitude. In Taiwan, the anomalous reductions appear not only at 1000-1800LT but also at 1600-2000LT. We further examine GIM-TEC during M8.0 Wenchuan earthquakes, and observe both the anomalous enhancement and reduction before the earthquake. It is found that the enhance anomaly appear less frequently than the reduce one. Therefore, the anomalous reductions appear on day 13, day 6, and day 5 before the earthquake while the anomalous enhancement appears on day 3 before the earthquake. The spatial analysis reveals that the depletion appears over the epicenter and its conjugate point, while the enhancement simply occurs around the epicenter. Apply the similar statistical analysis on the GIM-TEC of 33 M ≥ 6.0 earthquakes occurring in China during 1 May 1998 and 11 May 2008. Results show that the anomalous GIM-TEC reductions occur more frequently than those of the enhancements before the earthquakes. The precursors in Taiwan mainly appear during 1000-1800LT or 1600-2000LT while that in China mainly generally occurs during 2000-0400LT.

並列關鍵字

ionosphere ； earthquake ； precursor

參考文獻

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