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|Title: ||利用寬頻地震儀分析颱風期間的低頻訊號來源;Analysis Of Low Frequency Signals From Broadband Seismometers Records During Typhoons|
|Keywords: ||背景噪訊;環境噪訊;颱風;寬頻地震儀;時頻圖;ambient noise;spectrogram|
|Issue Date: ||2016-10-13 13:23:24 (UTC+8)|
|Abstract: ||寬頻地震測站所記錄到1 Hz至10 Hz的高頻背景噪訊通常與人為活動，如汽車、火車和工廠活動有關；而低於1Hz的低頻背景噪訊之主要來源有地表微地動、大氣現象和海浪與風之影響等。為了瞭解這些低頻噪訊來源，本研究選取了幾個具有不同路徑的颱風（2012年杜蘇芮、2013年潭美跟康瑞、2014年哈吉貝跟麥德姆）靠近台灣時的寬頻地震測站記錄，藉由與海象浮標、雨量及氣象觀測資料做交叉比對，來了解各項氣象因素對於寬頻地震測站中週期2秒以上之噪訊記錄的影響。|
;Broadband seismometers record signals over a wide frequency band, in which the high-frequency background noise is usually associated with human activities, such as cars, trains and factory-related activities. Meanwhile, the low-frequency signals are generally linked to microseisms, atmospheric phenomena and weather conditions. By comparing the broadband seismic data recorded during the pass of the typhoons with different moving paths, such as Doksuri in 2012, Trami and Kong-Rey in 2013, Hagibis and Matmo in 2014, the meteorological information, and the marine conditions, we attempt to understand the effect of the meteorological conditions on the low-frequency noise. The result shows that the broadband station located along the southwestern coast of Taiwan usually have relatively higher background noise value, while the inland stations were characterized by lower noise energy. This rapid decay of the noise energy with distance from the coastline suggests that the low frequency noise could be correlated with the oceanic waves. In addition, the noise energy level increases when the distance from the typhoon and the station decreases. The enhanced frequency range is between 0.1-0.5 Hz, which is consistent with the effect caused by the interference of oceanic waves as suggested by the previous studies. This observation indicates that the pass of typhoon may reinforce the interaction of oceanic waves and caused some influence on the seismic records. The positive correlation between the significant wave height and the noise energy could also give evidence to this observation. However, we found that the noise energy is not necessarily the strongest when the distance from typhoon and the station is the shortest. This phenomenon seems to be related to the typhoon path. When the typhoon track is perpendicular to the coastline, the change of noise energy is generally more significantly; whereas less energy changes are observed when the typhoon path is subparallel to the coastline. On the other hand, sometimes the energy of low frequency signal could increase without the inference of typhoons. After comparing the noise energy density with different meteorological and precipitation data, we found that the pressure change and the consecutive rainfall could be the main factors which affect the energy distribution. In summary, our result confirm that the broadband seismic data could indeed be influenced by the metrological conditions and marine environments. The contribution of each effect may vary. However, the main factors which control the low frequency noise energy should still be the wave height and the pressure.
|Appears in Collections:||[地球物理研究所] 博碩士論文|
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