本研究以地聲檢知器 (geophone)量測不同型態土石流流動時所產生之地聲，實驗量測所得地聲時域訊號經快速傅立葉轉換(FFT)及Gabor轉換分析，以求得地聲之頻域訊號及時間－頻率訊號。實驗依照水土保持手冊(1992)將土石流的類型區分為礫石型、一般型及泥流型。實驗結果顯示礫石型土石流地聲頻率主要在10到300Hz之間；而泥流型土石流的地聲頻率介於5到20Hz之間。一般型土石流的地聲頻率則介於兩者之間，當其土石材料中之礫石成份增加時，20到300Hz之地聲振幅會明顯增加。由此可知20到300Hz之地聲主要是由於礫石摩擦、撞擊實驗渠道底床所產生。本研究還利用每單位時間之地聲累積能量與互相關(cross-correlation)的方法來推算不同型態土石流波湧之平均流速。藉由推算的結果得知每單位時間之地聲累積能量較適合作為推算土石流之流速的方法。然而，當地聲檢知器地聲所測得土石流之地聲訊號不明顯時，便無法利用上述的兩種方法來推算其流速，如泥流型土石流之地聲訊號。

The purpose of this study is to investigate the ground vibration generated by different types of debris flows. The ground vibration was recorded by geophones. The ground-vibration signals in the time domain were transformed into the frequency domain by using the Fast Fourier Transform and into the Time-Frequency domain by using the Gabor Transform. According to the handbook of soil and water conservation (Soil and Water Conservation Bureau, 1992), debris flows was classified into three types, which are the bouldery type, the cobble-gravelly type, and the muddy type. The experimental results show that the frequency range of the ground vibration associated with the bouldery type debris flows is between 10 to 300Hz, while that of the muddy type debris flows is between 5 to 20Hz. However, the frequency range of the cobble-gravelly type debris flows includes both of the ranges. The frequency range of ground vibration between 20 to 300Hz becomes more apparent as larger grains were added to the experimental materials. Therefore, the frequency range between 20 to 300Hz was inferred to have resulted from collisions and friction between the cobbles and the channel bed. In this study, the accumulative energy method of the ground vibration per unit time and cross-correlation were used to calculate the velocity of different types of debris flows. The results of calculation show that the accumulative energy method of the ground vibration per unite time better than the other. However, the ground-vibration signals of debris flows measured by geophone were not obvious, such as the muddy type of debris flows. We can’t obtain the velocity of debris flows by using the methods above.

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