敏督利颱風於民國93年7月2日侵襲台灣，引發「七二水災」造成嚴重的土砂災害，其中在南投縣神木村愛玉子溪即發生數起土石流事件，水土保持局設置於當地之神木土石流觀測站成功地收集到現場即時資料，本文主要將七二水災期間神木土石流觀測站地聲檢知器所測得之地聲（地表振動）時域訊號利用快速傅立葉轉換（FFT）與Gabor Transform進行分析，並討論土石流地聲在時域、頻域之相關特性，所獲得之結果可作為日後該地區訂定警戒基準之參考依據。分析結果顯示土石流地聲之頻率分佈範圍在10~150Hz之間；而由Gabor transform分析結果，發現土石流波湧前端之地聲訊號頻率分佈範圍約在10~30Hz，而波湧通過時地聲訊號之頻率分佈範圍則較為廣泛，至於尾流部分之主要頻率在60Hz左右；由序列式地聲檢知器之地聲訊號求得土石流波湧之平均流速約為13.3 ；此外，比較土石流地聲訊號之振動速率大小，發現裝設於混凝土結構物中之地聲檢知器，易受結構物影響而無法反應出土石流之規模大小。

Typhoon Mindulle attacked Taiwan on July 2nd 2004, and resulted in the "Flood on July 2". On July 2, it caused several debris flows in Aiyuzih creek, Shenmu Village, Sinyi Towship, Nantou County. The debris flow monitoring station in Shenmu set up by the Soil and Water Conservation Bureau, successfully colleted the real-time data. The objective of this study is to analyze and discuss the characteristics of the ground vibrations generated by debris flows that gathered from Shenmu debris flow monitoring station. The result we obtained can be utilized as reference for debris-flow warning thresholds at this region. The time-domain signals of ground vibrations were transformed into the frequency domain by using Fast Fourier Transform and into the Time-Frequency domain by using Gabor transform. The analysis of geophone data shows that the frequency of ground vibrations resulted from a real debris flow ranges from 10 to 150 Hz. By using Gabor Transform to analyze the ground-vibration signals, we find that at the instant before the appearance of peak amplitude in frequency domain, the spectrums concentrated around 30 Hz. When the ground-vibration signals reached the peak value, the distributions of frequency domain fell into a wider range. After the peak, the frequencies fall around 60 Hz. The average velocity of the debris-flow front-surge is figured as 13.3 m/s. In addition, comparison of the geophone data reveals that the geophone installed in the concrete bank revetment can't respond to the magnitude of the debris flow because of the influence of the structure.

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