台灣由於降雨豐沛且集中，加上地質破碎的自然條件，常在梅雨或颱風期間發生崩塌。崩塌事件可能造成人員傷亡以及財產損失，若能在崩塌前提出預警，便能夠有效降低損失。豪大雨期間地層中含水量的變化常成為崩塌預警的重要指標之一，然而在山坡地上進行地層含水量的觀測並不容易。近年來利用環境噪訊分析來推估地下組成或裂隙等構造的變化，已經被證實可作為一種環境變遷的監測工具。其原理是地下傳波介質的特性改變會影響尾波傳遞的時間，而導致傳波速度的變化。崩塌的成因來自塊體的有效應力降低，而地層中的含水是降低地質材料有效應力的重要因素。在崩塌發生前的地下含水量增加，便會導致傳波速度變慢，而可做為崩塌預警的指標之一。
本研究於苗栗縣南庄鄉鹿場以及嘉義縣竹崎鄉中心崙分別架設5組地震站，其中地震站分布分別貫穿或包圍潛在崩塌邊坡(地震站間距離為100公尺至600公尺)，藉此進行兩站間的環境噪訊分析。本研究所採用之噪訊分析是透過將兩地震站的小時地動訊號進行交互相關分析，再利用拉伸法以及移動窗格交互頻譜法計算速度變化，得出不同頻率段的速度變化率(dv/v)。本研究也收集鄰近邊坡的氣象觀測資料，觀察降雨量及氣溫與地下傳波速度的相關性。在兩種計算速度變化率的方法中，以移動窗格交互頻譜法所計算得到之dv/v的變動幅度較小，而拉伸法所計算得到的dv/v變動幅度可達到±10 %，且數值離散。在濾波波段為4-6 Hz的條件下，兩種dv/v的計算方法之結果都呈現降雨時傳波速度變快之現象。在濾波波段較高的條件時，以拉伸法所計算之dv/v則未與降雨有明顯之關係，而移動窗格交互頻譜法所計算之dv/v的變動仍與降雨有關。dv/v呈現日夜週期的波動則可能與氣溫變化有關。本研究認為在目前的設站條件下，利用移動窗格交互頻譜法計算兩地震站間尾波散射的波速變化率較適用於本研究區域。

In Taiwan, due to abundant rainfall and fractured geological setting, landslides frequently occur during the rainy seasons or typhoons. A landslide may cause casualties and property losses. If an early warning can be issued before the landslide, the loss can be effectively reduced. Changes in the water content of the formation during heavy rains often become one of the important indicators of landslide warnings. However, it is not easy to observe the water content of the formation on the hillside. In recent years, the use of ambient noise analysis to estimate changes in subsurface structures such as underground composition or fissures has been proven to be a useful monitoring tool for environmental changes. The principle is that changes in the characteristics of the underground wave-transmitting medium will affect the propagation time of the coda wave, resulting in changes in the wave-propagation velocity. The cause of landslide comes from the reduction of the effective stress of the sliding block, and the water content in the formation is an important factor in reducing the effective stress of geological materials. The increase in groundwater content before the landslide will cause the wave propagation velocity to slow down, which can be used as one of the indicators of landslide warning.
In this study, five seismic stations were equipped in Luchang, Miaoli County, and Zhongsinlun, Chiayi County, respectively. The seismic stations distributed through or surrounded the potential landslide slopes with the distance between seismic stations ranging between 100 m and 600 m, and the ambient noise analysis between the two stations is performed. The noise analysis used in this research is to conduct a cross-correlation analysis of the hourly ground motion signals of the two seismic stations, and then use the stretching method and the moving window cross spectrum (MWCS) method to calculate the velocity change, and obtain the velocity change rate of different frequency bands (dv/v). The study collects meteorological observation data to observe the correlation between rainfall, temperature, and underground wave velocity. The dv/v calculated by the MWCS method has a smaller variation range, while the dv/v calculated by the stretching method can reach ±10%, and the values are discrete. By using the 4-6 Hz filter, the results of the two dv/v calculation methods show the phenomenon that the wave propagation speed becomes faster during rainfall. When using a higher-frequency filter, the dv/v calculated by the stretching method has no obvious relationship with the rainfall, and the variation of the dv/v calculated by the MWCS method is still related to the rainfall. The fluctuation of dv/v in the day-night cycle may be related to temperature changes. This study summaries that under the current station conditions, using the MWCS method to calculate the rate of velocity change of coda wave between two seismic stations is more suitable for the study areas.

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