台灣車籠埔鑽探計畫井下地震儀（Taiwan Chelungpu-fault Drilling Project Borehole Seismometers Array，簡稱TCDPBHS）安裝於1999年Mw 7.6集集地震最大同震變形（12m）之車籠埔斷層北段，運作時間為2006年中至2021年底約16年。井下地震儀所記錄之高品質地震波形，已有許多前人研究對於此研究區域產生之微地震及斷層帶特性進行深入的分析與探討。本研究分析TCDPBHS 2006年至2019年共14年間，長時間之連續波形紀錄的變化，用以瞭解測站的觀測數據品質在長時間的運行下有無顯著改變，分析之頻段範圍為0.01至1秒。首先，本研究優化轉檔程式，提高轉檔效率，並統整了TCDPBHS之長年維護紀錄，做出TCDPBHS之資料完整度圖，算得其資料完整率為84.23%。其次，本研究分析此14年間TCDPBHS連續波形資料，計算其功率譜密度之機率密度函數（Probabilistic Power Spectral Density，簡稱PPSD），並建立PPSD資料庫。再者，本研究分析PPSD的長期變化，發現儀器自安裝以來，其記錄之長期環境噪訊並無顯著變化，數值維持在 -150 dB至 -120 dB之間，顯示儀器運行至2019年仍運作良好。最後，本研究藉由不同方式分析PPSD資料特性，發現TCDPBHS能夠觀察到明顯的日夜變化、週變化、降雨及塊體崩塌事件，但在從環境噪訊來分辨微地震訊號上遇到挑戰。本研究確定了TCDPBHS於2006年至2019年間的資料品質穩定性及分析各種雜訊型態，這些結果將對TCDPBHS的未來研究提供基礎資訊，且此資料分析流程可直接應用於米崙斷層井下地震儀陣列。

The Taiwan Chelungpu-fault Drilling Project Borehole Seismometers (TCDPBHS) were installed between 947 m and 1274 m depth in an active thrust fault environment, which caused the Mw 7.6 Chi-Chi earthquake in Taiwan in 1999. The running time of TCDPBHS starts from the middle of 2006 to the end of 2021. In this paper, we analyze 14 years of continuous noise records of TCDPBHS from 2006 to 2019 between the period ranging from 0.01 and 1 second. First, we optimize the file conversion procedure of TCDPBHS to increase efficiency. We also combine the maintenance records and the existing files to get the data completeness, which is 84.23%. Second, we calculate the power spectral density (PSD) of each 10-minute record, then we calculate the probabilistic power spectral density (PPSD) of each month from 2006 to 2019. We find that there was no significant change between the PPSD distribution, which is between -150 dB and -120 dB, during these years. It indicates that TCDPBHS are well-operated. We establish a PPSD database for future studies based on our results. Last, we further investigate characteristics of PPSD in TCDPBHS and obtain diurnal and weekly variation of TCDPBHS due to human activities. We also discover that heavy rainfalls and landslides may increase noise level in TCDPBHS. We cannot identify microearthquake events from the ambient noise. This study helps us understand the stability of TCDPBHS from 2006 to 2019 as well as the different types of noise characteristics. The documented information will be useful for further studies of TCDPBHS. The data analysis process can be directly applied to the borehole seismometer array near Milun fault.

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