在前兆現象研究中，目前似乎能找到地震活動之前的電磁場異常，而目前台灣區相關研究使用的是全島固定的全磁場監測，以及運用GPS分析天空中之電離層異常，本研究期能建立固定之電磁場監測網，以分析可能影響大地電磁訊號之相關研究。本研究主要分析與討論目前電磁監測系統內的資料變化，及其所可能相關之影響因素。 於大地電磁法的記錄中，我們可以發現視電阻率會有每日的變化，兩不同地區測站皆以一天一次變化為主，但影響之頻率與強度皆不同，另外澎湖站亦有很明顯全頻一天兩次之變化。日變化量可能與海水潮汐、太陽一天一次之起落影響有關，我們發現澎湖站長期之視電阻率資料在白天很不穩定，日落後晚上的資料較好。在日變化之下，我們亦能在視電阻率變化上，看見磁暴現象發生時之視電阻率變化，但相關影響大約只在磁暴發生的開始，磁暴後磁場降低會經過數天的回復時間，在視電阻率上看不見回復期之變化。 大地電場經過一年多的監測，發現全台各站有自己之變化趨勢，但在各自的主趨勢下，我們依舊能發現一些共通的反應變化，其中長達一個月以上之抬升回復反應，可能與地震活動相關，但其關聯性尚不清楚，亦有短時間之擾動可能與靠近台灣之颱風有關。 在地震活動之前的關聯，我們發現大地電磁法記錄上，福山站在地震活動之前數小時內會出現數十秒之週期振盪訊號，在地震發生後會有伴隨著地震波動的電磁擾動現象，但電磁場擾動訊號有起始之一兩秒的飄移訊號，其異常發生時間比地震波要來的慢。一年多全島地電場觀測記錄中，第一次島上規模6的地震活動發生於南投仁愛鄉，在長展距的大地電場監測中，我們發現了可能之近震央區的震前電場擾動訊號，以及其他接近同步反應之全台震後電磁場擾動。 Many electromagnetic anomalies are reported as precursors in many areas. In this study, we tried to build up the stationary recording system to measure the variations of natural electromagnetic field. The preliminary results will show some background changes in our system and variations which may relate to earthquakes and typhoon activities. We found the different daily cycles of resistivity in different frequency bands between Penghu and Fushan station. The solar wind activities would cause the daily changes on the electromagnetic field and also cause the resistivity changes between day and night. We found the statics of resistivity on nighttime data was better than the daytime data in Penghu station. The resistivity would also appear the large anomalies at the beginning of a magnetic storm. The data of the geoelectric field measurement system showed the electric filed in different sites were drifting in different trends in Taiwan in a year. There are two large and long raised on geoelectric field in 2012 and they may all relate to earthquakes. We found the short term changes in many stations and the largest anomaily in Nanau in the earily August and it would be related to the typhoon passed by Taiwan area. There were appeared some harmonic electromagnetic signals in seconds period before earthquake in our magnetotelluric records in Fushan. We also found the small drifting signals earlier then the seismic wave arriving time and the variations may with seismic wave. One large earthquake occurred in central Taiwan in March 2013, and there were recorded some changes just about 30 seconds before and 14 seconds after the earthquake in our geoelectric measuring. The early signal just appeared in stations nearby the epicenter in the central Taiwan. The late signals were found almost at the same time in whole Taiwan.
