小林村山崩場址折射震測調查

Investigating the Hsiaolin landslide site by the seismic refraction method

施驊珮(Hua-Pei Shih)

指導教授 ： 王乾盈

國立中央大學/地球科學學院/地球物理研究所/碩士(2011年)

摘要

2009年八月莫拉克颱風帶來驚人的豪雨，四天之內累積超過2000公釐的降雨量，造成南台灣山區多處山崩。最不幸的是，高雄縣甲仙鄉小林村完全被山崩摧毀，造成超過400人死亡，此一極為罕見的事件值得深入研究。調查顯示這個村子遭到兩階段的掩蓋，第一次是山坡頂部土石大規模崩落，掩埋了位於河邊的村莊，河道也被堵塞而形成一個堰塞湖；接下來，河水潰堤帶來的岩屑又再次覆蓋了村子，一層疊在另一層之上，形成一個多層次的堆積構造。本報告使用傳統的折射震測法探測小林村山崩場址的沈積構造，並估算建築物遭掩埋的深度。
為了處理多層次的問題，我們根據傳統的「正負法」，發展出一套新的技術，來處理多層構造的折射震測資料。首先，鑑別出各層的走時曲線段落，並設計一套逆推公式來重建這些片段的走時曲線，其中加入若干條件限制，使得走時曲線的走向合理，如此可得到一條包含觀測和推算部分的完整走時曲線，再利用它來計算地底的折射層。
本研究得到如下的結果：
1) 原本的地面被掩蓋在地底下3-5公尺深處，此掩蔽層也就是第一層，是新的山崩物質組成，P波波速為400m/sec。
2) 第二層代表基盤上的原始沉積層，厚度約15~20公尺之間，此層可能堆積著舊的山崩碎屑物，P波波速為1500m/sec。
3) 基盤面相當不規則，出現若干弱帶，顯示古河流的截切面，或為古山崩遺留的痕跡。基盤P波波速約3000m/sec，係由泥岩和砂岩組成。
4) 另外，在原河流位址的剖面，基盤以上出現三層地層，最上面二層與「山崩及河水潰堤」的二次碎屑物堆積覆蓋一致

關鍵字

折射震測 ； 小林村

並列摘要

The violent rain induced by the 2009 Morakot typhoon, accumulated over 2000mm precipitation within 4days, caused widespread landslides in the southern Taiwan. The landslide at Hsiaolin village, unfortunately, completely destroyed the village and caused over 400 deaths. This is an extremely rare case worth detailed study. It is known that the village was covered twice. First, the massive landslide from the top hill overlaid the village at the riverside and blocked the river to form a barrier lake. Next, the lake dam collapsed and the debris covered the village area again. This forms a natural deposit situation having several layers, one above the other. In this study, we used the traditional refraction method to explore the layered deposition structure and to estimate the depths of building been buried.
Basing on the traditional Plus-Minus method, we developed a new analysis technique to resolve the multiple-layered structure for the refraction data. After identifying different segments of travel time curves for different layers, we design on inversion algorithm to reconstruct the travel time curve from these incomplete segments. Several constraints are emplaced to confine the travel-time curve trend, which may lead to a reasonable distribution. A complete travel time curve including the observed and estimated parts is thus formed, which is then used to calculate the underground refraction layer.
The results are as follows:
1) The original ground surface is buried under 3~5m depths at the village area The covered layer, i.e., the first layer, is composed of new landslide materials with the P velocity 400m/sec.
2) The second layer represents the original deposit layer above the basement. The thickness is between 15 and 20m, which may accumulate the old landslide debris. The P velocity is around 1500m/sec.
3) The basement surface is relatively irregular, which is marked by ancient river cuts as well as some weak zones. The basement has P velocity as 3000m/sec and consists of mudstones and sandstones.
4) The profile at the original river position possesses three layers above the basement. This agrees with the two times covering of the landslide material and the river debris.

並列關鍵字

Hsiaolin ； seismic refraction method

參考文獻

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