Central Geological Survey, MOEA.

I. Geological Mapping

Geological mapping is the most fundamental task of the CGS. The outputs of geological mapping contain maps of the national geological structure, stratigraphy, historical geology, geological resources, and geological environmental conditions of Taiwan. They are essential for national planning, land development and environmental conservation.

The main tasks of geological mapping include:

A. Field surveys: With the aid of technological and positioning devices, geological phenomena are investigated, described, and recorded; at times, samples are collected.

B. Geological data analyses: Geological data analyses, dating of samples, analyzing geological structure, etc.

C. Geological map compilation: Compiling and integrating geological information into geological maps of various scales.

Significant Achievements

• 1974: Completed  Taiwan geological maps in the scale of 1/250,000 (1^st edition)

• 1986: Completed Taiwan geological maps in the scale of 1/500,000 (1^st edition).

• 2000: Completed Taiwan’s geological maps in the scale of 1/500,000 (2^nd edition).

• Since 1988: Publishing and updating the series of Taiwan’s geological maps and offs-shore islands’ geological maps in the scale of 1/50,000 .

II. Environmental and Engineering Geological Surveys

Using aerial photos and remote sensing images to integrate the high-resolution digital topographic maps produced by LiDAR(Light Detection And Ranging), it is not only possible to produce high-resolution Digital Elevation Model (DEM) maps, but interpret and update Taiwan's environmental geological data. Such tasks are often applied to practical hazard prevention and mitigation, and engineering developments.

Major works include:

• Engineering geological survey: Evaluating the geological environmental and engineering properties and potential geological hazards through borehole drilling, soil and rock sampling, and test analyzing.

• Environmental geological survey: With the aid of field investigations, remote sensing techniques and high- resolution LiDAR DEM to identify the information for landslides, dip slopes, potential large-scale landslides (deep-seated gravitational slope deformation), and riverbank erosions, etc.

• Compiling environmental and engineering geological maps and establishing database for various usage.

Significant Achievements

 • Since 1992: Completed the surveys on the environmental and engineering geology of Taipei, Kaohsiung and other urban areas of Taiwan.

 •Since 2002: Completed the surveys on the integral environmental geology for landslide hazard susceptibility around slope lands of urban areas, and establishing its databank.

• Since 2006: Completed geological surveys of the upper stream watersheds of flood-prone areas and established its databank.

• Since 2007: Completed the environmental geological surveys around mountainous settlements in order to enhance application for preventing slope land hazards.

• Since 2010: Completed national LiDAR program for DEM maps; started to conduct programs for analyzing geologically sensitive areas and hazard-prone areas.

• Since 2014: Completed delineating of the landslide- and landslip-prone areas of Taiwan.

• Since 2017: Launched supplementary investigation of potential large scale landslide and construction of “landslide and geological information cloud platform”.

• Since 2018: Launched overall review of the landslide- and landslip-prone areas of Taiwan.

III. Observation and Survey of Volcanic Activity

Long-term observation and monitoring for potential volcanic activity of the Tatun Volcanic Group (TVG) and the Kueishantao in northern Taiwan through geological background data collection and regionally geophysical exploration; developing research scheme for the youngest volcano of the TVG to identify its characteristics and geological history for assessing potentially hazards.

Major works include:

A. Monitoring the seismicity of northern Taiwan volcanic areas

B. Monitoring the variations of geochemical and geothermal characteristics in the TVG

C. Observing surface deformation in the TVG

D. Conducting aeromagnetic survey of on-shore and off-shore regions in northern and eastern Taiwan

E. Dating volcanic rocks in the TVG to facilitate analyses

Significant Achievements

• The low-velocity zones found at the depths of a few km in the shallow crust and 20 km in the deep crust beneath the TVG possibly represent a hydrothermal chamber and a magma reservoir respectively. Based on the volcanic tremors, very long period seismic earthquakes and swarm earthquakes that occasionally occurred in the TVG, the volcano-related hydrothermal activities in the Tatun volcanic area remain fairly energetic.

• The domestic execution ability of high resolution aeromagnetic survey was built and it produces the magnetic intensity grid with 100 m spacing. Based on the aeromagnetic dataset, the rock formations with high-magnetic susceptibility beneath the TVG extend in northeast-southwest direction and are consistent with the regional structures. The newly found high magnetic zones without specific landform patterns might represent the latent or eroded igneous rocks. The ring-shaped and radial high-magnetic rock bodies were found beneath the Kueishantao, and the ring-shaped one is approximately 9 km in diameter and more than 4 km in depth.