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Fundamental and Environmental Geology
Resource Geology
Geological Hazard
Geological Information Service


:::Fundamental and Environmental Geology
  The objective of fundamental and environmental geology is to study the surface and subsurface geology of Taiwan and to present the results reflected upon geological maps to help characterize and examine major geological features like structure, stratigraphy, mineralogy, and paleontology. The CGS also undertakes projects across a wide spectrum of academic and practical concerns, including Quaternary studies, engineering and subsurface testing of metropolitan areas in Taiwan, research on slopeland areas surrounding metropolises, and marine geology mapping offshore of Taiwan. Key projects developed and implemented in 2017 are summarized as follows:
A. Geological Mapping
  The second edition of Penghu Islands sheet (scale 1/50,000 geological map) was published in December, 2017. In the second edition, a new unit of Gupoyu Formation and several latest Ar-Ar dating results of basalt were added to facilitate more in-depth understanding of the volcanic activities of Penghu, where basalt and sandstone are widely distributed. Pyroclastic and epiclastic rocks, calcareous sandstones, and Holocene deposits can also be found locally. Recently drilled cores and previous studies on local petrology, geochronology, geochemistry, and stratigraphy provide richer information for the reconstruction of the subsurface geology model of Penghu.

    The Hoping Sheet, a 2-year mapping project, aims to complete a scale 1/50,000 geological map of the Hoping area located in the metamorphic subzone of the Central Range, which is mainly composed of marble, schist, gneiss, and granitic rocks and marks the evolution of Tananao Schist in Mesozoic. Based on the recent studies of dating about Tananao Schist, Chiuchu Marble was formed by the subduction of the Pacific plate in early Jurassic. From Jurassic to Cretaceous, a melange (Tungao Schist) was formed by the subduction zone between a volcanic arc and a subduction zone, and I-type granitic rocks were formed through the migration of volcanic arc. In late Cretaceous, Tungao Schist and Wuta Schist were formed by the Nanao Orogeny. The Nansuao Formation and the Lushan Formation were younger than Tananao complex and may be deposited from Eocene to Miocene.

    The CGS has also started to build up the lithostratigraphic type locality and profiles of the Western Foothills Belt. Main tasks include the completion of geologic route maps with scale of 1/5,000 and stratigraphic column with a scale of 1/1,000 and the collection of rock samples of the Mushan, Taliao, Shihti, and Nankang formations. The project begins with regions in northern Taiwan and move on southward subsequently .
B. Mapping and Development of Geological Maps for Urban Hazard Prevention

The purpose of this study is to compose geohazard maps of major urban areas in Taiwan. In reaction against the soil liquefaction disasters triggered by the Meinong earthquake in 2016, the CGS initiated the composition of soil liquefaction susceptibility maps for urban areas in Taichung, Changhua, Yunlin and Chiayi and managed to complete the geohazard maps in 2017. New projects are launched in order to acquiring detailed information about soil liquefaction. The purpose of this project is to investigate and research on the soil re-liquefaction sites. Beishih Village of the Xinhua District Tainan City was selected to carry out this investigation.
    Soil liquefaction geohazard analysis identified thick sand layers and several thin layers of mud and rather loosely accumulated sand distributed beneath the ground surface to a depth of 30 meters in Dacheng Township of Changhua County, Baozhong Township and Tuku Township of Yunlin County, and Dongshih Township of Chiayi County. Due to the shallow groundwater table, mostly at 2 meters below the ground surface, and the extraction of groundwater for irrigation, these areas are at risk of experiencing soil liquefaction and serious ground subsidence.
    A new project of investigating soil re-liquefaction sites was launched in 2017, and the results indicated that the layers beneath the ground surface to a depth of 10 meters in the investigated areas were composed of bayhead delta deposits and fluvial sediments of the sedimentary environment, which in turn constituted mainly loosely accumulated fine sand and silts with low shear strength. High groundwater table was maintained in the shallow layers even during the dry season, which may render the investigated areas with loose sands vulnerable to soil liquefaction during strong earthquakes.
    This project can be expected to continue adding new functions to the urban geological information system. The documentary inquiry function and the geological database completed in this year provide engineering borehole and related geological documents for data retrieval. The soil liquefaction potential inquiry system facilitated by the Information Center of the Ministry of the Interior has been installed and made accessible to the general public on the Chunghwa Telecom cloud server. This system is managed by the CGS now to serve citizens interested in gathering the provided information.
    Changhua city: Geological map of engineering environment and Susceptibility map of geohazards.

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