本研究目的為利用新型地震儀ES-1高靈敏度以及最低量測頻率至0.13 Hz的優點，量測土石流所產生的10 Hz以下低頻地表振動，希冀以低頻訊號經長距離傳輸後不易衰減的特性，提前偵測土石流波湧訊號，進而改善地聲檢知器(Geophone)量測範圍較小的缺點。本監測系統2013年於南投縣神木村愛玉子溪共量測到三起由2013年5月30日午後強降雨、蘇力颱風與潭美颱風所造成的強烈地表振動訊號。經鋼索檢知器與CCD攝影機相互比對後，確認2013年5月30日午後強降雨與蘇力颱風期間量測到的振動訊號為土石流所引發。在兩起土石流事件中，ES-1量測到土石流產生的最低頻率分別為4 Hz與2 Hz，突破以往土石流地表振動頻段主要在10至150 Hz的認知。在蘇利颱風事件中，由降雨資料與時頻分析比對，顯示降雨量與地表振動大小呈正相關，且土石流前端訊號於時頻譜圖上呈現指數型增加。另外，利用愛玉子溪上下游的ES-1量測的波湧時間差可估算此次土石流的平均流速。在此次土石流事件的頻域分析中，上下游儀器皆提前4分鐘量測到2 Hz訊號提升能量的現象，推估為土石流於愛玉子溪上游生成並開始流動所造成的地表震動，經由此特性，本研究可估算出土石流生成的大略位置。
本監測系統在運作期間，亦量測到其他地表震動源的訊號，分別為2013年3月27日的南投近震與2013年4月20日的中國雅安遠震。雖然本研究量測標的為由土石流所引起的地表振動訊號，但是藉由量測其他可能造成地表振動的來源，可釐清土石流地表振動與其他來源的特性差異。南投近震事件中，由於震央接近本系統測站，經時頻分析顯示，高頻地震波於短距離傳輸後仍存在，導致ES-1接收到高低頻夾雜的地表振動訊號。中國雅安遠震事件中，ES-1只量測到經過長距離傳輸後的1 Hz以下低頻震盪訊號。除了地震所引發的地表振動外，ES-1量測到午後強降雨導致河川流水增加與流水搬運河床土砂材料所造成的地表振動訊號，經時頻分析結果顯示河水與土砂材料所造成的地表振動多分布於10 Hz至60 Hz。本研究量測結果證實ES-1藉由在低頻段具高敏感度的優點，可提前量測土石流所引發的低頻地表振動訊號，亦可釐清土石流的時頻域特性。

The aim of this study is using the ES-1, a newly developed seismometer deployed along Aiyuzi Stream in Nantou County, Taiwan, to detect the low-frequency signals generated by debris flows. With the low attenuation of low-frequency signals after long distances, ES-1 is expected to improve the small detection area of a Geophone via its high sensitivity and capability of detecting low frequencies as low as 0.13 Hz to detect the ground vibration of debris flows in advanced. Strong ground vibrations were measured in the convectional rainfall event and two typhoon events. After the correlation of the CCD cameras and wire sensors, the vibration signals in convectional rain and Typhoon Soulik event were identified as being caused by debris flows. The lowest frequencies in the two events were 4 Hz and 2 Hz, respectively, which is lower than the conventional bandwidth of debris flows from 10 to 150 Hz. From the precipitation data and spectral analysis, the ground vibration had positive correlation with rainfall; further, the leading signals of the debris flows detected by ES-1 were exponentially increasing. If the 2 Hz signals were extracted for independent analysis, it could be observed that the low frequency signals were detected 4 minutes earlier both by upstream and downstream ES-1 sensors before the debris flow surges approached ES-1 sensors. This phenomenon is attributed to the ground vibrations caused by the debris flows formation and flowing at the upper reach; moreover, the approximate location where the debris flows generated can be calculated by this characteristic.
Before the summer rainy season, which spawns debris flows, the ES-1 system sensed ground vibrations from both local earthquakes and teleseism. Although the main objective of this study was detecting ground vibration from debris flows, measuring ground vibration from other seismic sources helps distinguish the characteristics of debris flow ground vibrations from others. In the event of local earthquakes, with the spectral analysis, ES-1’s spectral analysis received broad band frequency signals because of the short distance between the epicenter and the ES-1 station. In contrast, ES-1 only received low-frequency signals under 1 Hz from Ya-an in Sichuan Province of China. Besides seismic signals from earthquakes, ground vibrations from 10 to 60 Hz induced by increasing discharge and bed load transport from convectional rainfall were also detected by ES-1. From these results, the ES-1 was verified as capable of measuring low-frequency ground vibration signals generated by debris flows and clarifying the spatial-temporal frequency characteristics of debris flows.

1.Aki, K. (1980). Attenuation of shear-waves in the lithosphere for frequencies from 0.05 to 25 Hz. Physics of the Earth and Planetary Interiors, 21(1), 50-60.
2.Arattano, M. (1999). On the use of seismic detectors as monitoring and warning systems for debris flows. Natural Hazards, 20(2-3), 197-213.
3.Arattano, M., and Marchi, L. (2008). Systems and sensors for debris-flow monitoring and warning. [Review]. Sensors, 8(4), 2436-2452.
4.Arattano, M., and Moia, F. (1999). Monitoring the propagation of a debris flow along a torrent. [Article]. Hydrological Sciences Journal-Journal Des Sciences Hydrologiques, 44(5), 811-823.
5.Berti, M., Genevois, R., LaHusen, R., Simoni, A., and Tecca, P. R. (2000). Debris flow monitoring in the Acquabona watershed on the Dolomites (Italian Alps). Physics and Chemistry of the Earth Part B-Hydrology Oceans and Atmosphere, 25(9), 707-715.
6.Berti, M., Genevois, R., Simoni, A., and Tecca, P. R. (1999). Field observations of a debris flow event in the Dolomites. Geomorphology, 29(3-4), 265-274.
7.Bolt, B. A. (1976). Nuclear explosions and earthquakes. The parted vail.
8.Burtin, A., Bollinger, L., Vergne, J., Cattin, R., and Nabelek, J. L. (2008). Spectral analysis of seismic noise induced by rivers: A new tool to monitor spatiotemporal changes in stream hydrodynamics. [Article]. Journal of Geophysical Research-Solid Earth, 113(B5).
9.Burtin, A., Cattin, R., Bollinger, L., Vergne, J., Steer, P., Robert, A., et al. (2011). Towards the hydrologic and bed load monitoring from high-frequency seismic noise in a braided river: The "torrent de St Pierre", French Alps. [Article]. Journal of Hydrology, 408(1-2), 43-53.
10.Chu, C. R. (2013). Deployment of a fiber-optic sensing system for monitoring ground vibrations produced by debris flows National Cheng Kung University, Tainan.
11.Coussot, P., and Meunier, M. (1996). Recognition, classification and mechanical description of debris flows. [Review]. Earth-Science Reviews, 40(3-4), 209-227.
12.Feng, Z. Y. (2012). The seismic signatures of the surge wave from the 2009 Xiaolin landslide-dam breach in Taiwan. Hydrological Processes, 26(9), 1342-1351.
13.Gauer, P., and Issler, D. (2004). Possible erosion mechanisms in snow avalanches. In P. M. B. Fohn (Ed.), Annals of Glaciology, Vol 38 2004 (Vol. 38, pp. 384-392).
14.Gutowski, T. G., and Dym, C. L. (1976). Propagation of ground vibration: a review. Journal of Sound and Vibration, 49(2), 179-193.
15.Huang, C. J., Chu, C. R., Tien, T. M., Yin, H. Y., and Chen, P. S. (2012). Calibration and Deployment of a Fiber-Optic Sensing System for Monitoring Debris Flows. Sensors, 12(5), 5835-5849.
16.Huang, C. J., Shieh, C. L., and Yin, H. Y. (2004). Laboratory study of the underground sound generated by debris flows. Journal of Geophysical Research: Earth Surface (2003–2012), 109.
17.Huang, C. J., Yin, H. Y., Chen, C. Y., Yeh, C. H., and Wang, C. L. (2007). Ground vibrations produced by rock motions and debris flows. [Article]. Journal of Geophysical Research-Earth Surface, 112.
18.Hungr, O., Evans, S. G., Bovis, M. J., and Hutchinson, J. N. (2001). A review of the classification of landslides of the flow type. Environmental & Engineering Geoscience, 7(3), 221-238.
19.Hurlimann, M., Rickenmann, D., and Graf, C. (2003). Field and monitoring data of debris-flow events in the Swiss Alps. Canadian Geotechnical Journal, 40(1), 161-175.
20.Itakura, Y., Inaba, H., and Sawada, T. (2005). A debris-flow monitoring devices and methods bibliography. Natural Hazards and Earth System Science, 5(6), 971-977.
21.Johnson, A., and Rodine, J. (1984). Debris flow. Slope instability, 1984, 257-361.
22.Kogelnig, A., Hübl, J., Suriñach, E., Vilajosana, I., and McArdell, B. W. (2011). Infrasound produced by debris flow: propagation and frequency content evolution. Natural Hazards, 1-21.
23.Lay, T., and Wallace, T. C. (1995). Modern global seismology (Vol. 58): Academic press.
24.Marchi, L., Arattano, M., and Deganutti, A. M. (2002). Ten years of debris-flow monitoring in the Moscardo Torrent (Italian Alps). [Article]. Geomorphology, 46(1-2), 1-17.
25.Okuda, S., Okunishi, K., and Suwa, H. (1980). Observation of debris flow at Kamikamihori Valley of Mt. Yakedade. Paper presented at the Excursion Guidebook of the 3rd Meeting of IGU commission on Field Experiment in Geomorphology.
26.Pierson, T. (1980). Erosion and deposition by debirs flows at Mt Thomas, North-Canterbury, New-Zealand. Earth Surface Processes and Landforms, 5(3), 227-247.
27.Pierson, T. (1986). Flow behavior of channelized debris flows, Mount St. Helens, Washington. Hillslope processes, 269-296.
28.Roberts, P. M. (1989). A versatile equalization circuit for increasing seismometer velocity response below the natural frequency. Bulletin of the Seismological Society of America, 79(5), 1607-1617.
29.Sharpe, C. F. S. (1938). Landslides and related phenomena: a study of mass-movements of soil and rock: Columbia University Press New York.
30.Surinach, E., Vilajosana, I., Khazaradze, G., Biescas, B., Furdada, G., and Vilaplana, J. M. (2005). Seismic detection and characterization of landslides and other mass movements. Natural Hazards and Earth System Sciences, 5(6), 791-798.
31.Takahashi, T. (1981). Debris flow. Annual Review of Fluid Mechanics, 13, 57-77.
32.Takahashi, T. (1991). Debris flow. Rotterdam: Balkema.
33.Zhang, S. (1993). A comprehensive approach to the observation and prevention of debris flows in China. Natural Hazards, 7(1), 1-23.