應用高精度數值地形精進臺北地區褶皺逆衝帶地質圖

Abstract

近年來高精度數值地形技術發展與電腦運算效能的提升，能在三維數值製圖環境下完整呈現出高精度數值地形，透過人為辨識、程式計算與ArcGIS套裝軟體建立三維空間下，對沉積岩區地表地形進行進行分析與辨識，並建立在前人累積的地質架構下，完成並檢核所繪製的高精度數值地質圖。研究區域位於北臺灣，為臺北盆地鄰近之西部麓山帶沉積岩，所出露地層分別由漸新世五指山層至上新世桂竹林層，地層走向與構造線受褶皺逆衝帶作用影響下分佈大致呈現東北-西南走向。利用高精度數值地形與計算衍伸所出的圖層進行地表地質構造的辨識，如利用坡度圖、日照陰影圖等，而坡度圖對於呈現沉積岩區的地表差異侵蝕尤其明顯，搭配數值地形位態計算，所增加位態包含岩層位態與斷層位態，並整合現有地質資料與野外查核，確認地層界線、岩性、構造位置與野外量測位態，近一步對所地表辨識的結果進行整體整合，建構出包含岩層線、斷層線與位態的三維地表線形數值資料。是以高精度數值地形進行三維地表地質辨識，可以提升製圖成果之解析度，研究成果為五萬分之一比例尺臺北地區褶皺逆衝帶地質圖，以及將研究區域分為三幅兩萬五千分之一比例尺臺北地區褶皺逆衝帶地質圖，圖幅名稱分別為臺北市、八堵與基隆，配合兩條地質剖面詳述區域中構造分佈。首次在沉積岩區利用三維數值地形製圖方式繪製出大面積的地質圖，呈現出三維數值地表地質圖，借由岩層與斷層的繪製，發現在三維數值地形製圖條件下不同於傳統二維地質圖上線形繪製的差異。本研究建構在現有的地質基礎與架構上，提供精進與革新現有沉積岩區地質圖之方法，證明可利用高精度數值地形在沈積岩區製圖，對於植被茂密、露頭稀少與交通不便之區域，此製圖方法更顯其重要性。

In recent years, with the advancement of high resolution DEM and computing powers, we have been able to construct and display high-resolution DEM in a three-dimensional environment. Through human identification, program calculation and ArcGIS software, this study set up a three-dimensional space to analyze and identify surface topography in sedimentary rock areas. Based on the geological background accumulated by the predecessors, the high-resolution DEM-derived geological maps were completed and checked. The study area is in northern Taiwan near the eastern part of the Taipei Basin and consists of sedimentary rocks from the Oligocene to the Pliocene times. The stratigraphic units and tectonic structures within the fold-thrust belt generally exhibit a northeast-southwest trend. In the study, three-dimensional geological maps were drawn through ArcGIS with high-resolution DEM. The slope map and hillshade map derived from high-resolution DEM and the DEM itself are used as the main three-dimensional terrain identification base maps. The interlayers of sandstone and shale or structures resulted from differential erosion were used for sedimentary rock layers identification to establish the structural features of the study area. The study has successfully produced a 1:50000 geological map of the Taipei Sedimentary Rock Area and three 1:25,000 small-area geological maps. Two geological profiles are drawn to show the distribution of structures in the area. For the first time, a large-area two-dimensional geological map was created by using three-dimensional numerical topography in the sedimentary rock area. A procedure of producing three-dimensional DEM geological map was proposed in this study. Through existing geological frameworks and data, this study provides mapping methods for the refinement and renovation of existing geological maps of sedimentary rock areas. This study demonstrates that high-resolution DEM can be used for mapping areas of sedimentary rocks, particularly for areas with dense vegetation, sparse exposure and inaccessibility.