臺灣博碩士論文加值系統

本研究利用地震儀所紀錄之地動訊號分析台灣各測站附近的高頻噪訊及周遭環境噪訊的強度變化，除了解其與海氣環境參數的關聯之外，也據以檢驗各地震測站的運作效能與地震偵測能力，並建立台灣的噪訊模型供作日後地震觀測實驗的選站參考。
高頻噪訊是取用2006年至2009年中央研究院BATS地震網18個寬頻測站之連續紀錄，做帶通濾波後研究2-18 Hz高頻噪訊之時空變化，並比對溫度、氣壓、雨量及風速等氣象因子，找出影響各測站噪訊之主要因素。此部份研究結果顯示，臺灣之高頻噪訊主要受到雨量及風速之影響；其中西部測站的2 Hz噪訊有季節性的變化，呈現冬強夏弱之現象，與風速及氣壓呈正相關而與溫度呈負相關，推論應是受海浪影響。西部、墾丁及台東測站之噪訊較其他測站強，顯示平原、沿海及觀光區之高頻噪訊較大，受人為活動及海浪影響。臨近河流的測站，其噪訊在颱風影響臺灣過後比其他測站有延遲降回背景值的現象，與河床堆積物在水位升降過程中受到搬運的影響，不斷與河床產生撞擊有關。
周遭環境噪訊則是取用2006年7月1日至2008年6月30日之寬頻測站連續紀錄，測站選用BATS地震網、TAIGER計畫及中央氣象局地震網共95個地震測站，利用功譜密度機率函數（PDFs）之統計方法，計算各測站不同週期背景噪訊之強度分佈，並在不同的特徵頻段範圍內將噪訊強度轉換為功率，最後彙整出背景噪訊在空間及時間之分布型態並討論其涵義。結果顯示臺灣之高頻噪訊（〉 1 Hz）遠大於全球低噪訊模型，長週期則落在全球高、低噪訊模型之間。平原之噪訊高出山區20-50 dB，主要受都市化影響；西部沿海之噪訊高出東部海岸10-30 dB，可知西部沿海因鄰近台灣海峽淺水區，所以激發二次微地動的效率比東部顯著。0.1-1秒週期主要反映文明噪訊，因此有日變化及週變化；2-8秒週期為二次微地動，反映海浪噪訊，有年變化現象。井下100公尺的噪訊比地表低約20 dB，顯示井下站對地震紀錄較地表站有更好的偵測能力。

To characterize the ambient noise levels in the Taiwan region and to understand its relationship with climate parameters, we used two methods to analyze the continuous waveforms recorded at Taiwan broadband seismic stations. On the basis of these results, we are able not only to evaluate the station performance and provide crucial information for site selection, but also to realize the controlling factors of noise.
First, we extract the noise amplitude of 9 frequency bands in 2-18 Hz from seismic data collected at 18 BATS stations between 2006 and 2009. Then we compare these high-frequency noise amplitudes with ambient temperature, atmospheric pressure, rainfall and wind-speed, respectively. The results show that the high-frequency noise is affected by rainfall and wind-speed. However, 2 Hz noise exhibits seasonal variation for the stations in western Taiwan, which may reflect the seasonal change of wave climate. High-frequency noises in western Taiwan, Kenting and Taitung are larger than elsewhere, implying intensive human activities in these areas. Stations that are close to river are characterized by a delay of returning to background high-frequency noise level after typhoons.
Secondly, we follow the method proposed by MaNamara and Buland (2004) to compute the probability density functions of power spectral density (PDFs) of ambient noise. The data is collected at 95 broadband stations in BATS, TAIGER, and CWBSN from July 2006 to June 2008. The result shows that the high-frequency noise (〉 1 Hz) is much higher than the global low noise model. But the long-period noise is within the global high and low noise models. The spatial variation shows that noise level in the plain area is 20-50 dB higher than the mountainous area, and the noise level along the western coast is 10-30 dB higher than the eastern coast. This implies that the excitation of the secondary microseism is more effective in the shallower Taiwan Strait than in the deep Pacific. Noise amplitude in 1-10 Hz presents significant diurnal and weekly variation. Significant annual variation that is associated with the wave climate can be seen at temporal variation of the 2-8 s noise amplitude. We also verify that the borehole stations present lower noise level by about 20 dB when compared with corresponding surface stations. It means that the ambient noise could be much reduced by installing borehole seismic stations and therefore enhance the ability of detecting smaller earthquakes.

摘要 .................................... I
Abstract................................ III
誌謝 ..................................... V
目錄 ..................................... VI
圖目錄 ................................... IX
第 1 章 序論 ............................... 1
1.1 研究背景及動機 .......................... 1
1.2 論文範疇及架構 .......................... 3
第 2 章 前人研究 ............................ 4
第 3 章 研究方法 .................................. 12
3.1 高頻噪訊 ..................................... 12
3.1.1 資料來源及分析方法 .......................... 12
3.1.2 噪訊與氣象參數之比對 ......................... 18
3.2 臺灣周遭環境噪訊 .............................. 18
3.2.1 資料來源及分析方法 .......................... 18
3.2.2 功譜密度(Power Spectrum Density, PSD) ...... 21
3.2.3 計算周遭噪訊的時空分佈 ....................... 23
第 4 章 研究結果 .................................. 24
4.1 高頻噪訊 ..................................... 24
4.1.1 噪訊特徵 ................................... 24
4.1.2 噪訊與氣象參數之比對 ......................... 27
4.1.3 不同頻率之高頻噪訊在空間上的分布 .............. 31
4.2 臺灣周遭環境噪訊 .............................. 35
4.2.1 臺灣周遭環境噪訊模型 ......................... 35
4.2.2 噪訊的時間變化 ............................... 39
4.2.3 噪訊對空間分佈 ............................... 45
第 5 章 討論 ....................................... 51
5.1 高頻噪訊 ....................................... 51
5.1.1 噪訊特徵 ..................................... 51
5.1.2 噪訊與氣象參數之比對 .......................... 52
5.1.3 不同頻率之高頻噪訊在空間上的分布 ................ 53
5.2 臺灣周遭環境噪訊 ................................ 53
5.2.1 臺灣周遭環境噪訊模型 ........................... 53
5.2.2 噪訊的時間變化 ................................ 55
5.2.3 噪訊對空間分佈 ................................ 56
第 6 章 結論 ........................................ 58
6.1 高頻噪訊 ........................................ 58
6.2 周遭環境噪訊 .................................... 58
參考文獻 ............................................ 60
附錄A 高頻噪訊各站之噪訊特徵 .......................... 64
附錄B 高頻噪訊與氣象參數之比對 ......................... 74
附錄C 各測站噪訊之月變化圖 ............................ 80

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