Central Geological Survey, MOEA

About: Central Geological Survey, MOEA is a government organization based out in Taipei, Taiwan. It is known for research contribution in the topics: Landslide & Fault (geology). The organization has 68 authors who have published 81 publications receiving 2037 citations. The organization is also known as: Jīngjì Bù Zhōngyāng Dìzhí Diàochá Suǒ.

Gamma Ray and Radon Anomalies in Northern Taiwan as a Possible Preearthquake Indicator around the Plate Boundary

Abstract: Taiwan is tectonically situated in an oblique collision zone between the Philippine Sea Plate (PSP) and the Eurasian Plate (EP). Continuous observations of gamma rays at the Yangmingshan (YMSG) station and soil radon at the Tapingti (TPT) station were recorded in the volcanic area and around a major fault zone, respectively, in Taiwan for seismic studies. A number of anomalous high gamma ray counts and radon concentrations at certain times were found. It is noted that significant increases of soil radon concentrations were observed and followed by the increase in gamma rays a few days to a few weeks before earthquakes that occurred in northeastern Taiwan. Earthquakes such as these are usually related to the subduction of the PSP beneath the EP to the north along the subduction zone in northern Taiwan (e.g., , April 20, 2015). It is suggested that the preseismic activity may be associated with slow geodynamic processes at the subduction interface, leading to the PSP movement triggering radon enhancements at the TPT station. Furthermore, the further movement of the PSP might be blocked by the EP, with the accumulated elastic stress resulting in the increase of gamma rays due to the increase in porosity and fractures below the YMSG station. The continuous monitoring of the multiple parameters can improve the understanding of the relationship between the observed radon and gamma ray variations and the regional crustal stress/strain in north and northeastern Taiwan.

Mountain Building Mechanisms in the Southern Central Range of the Taiwan Orogenic Belt - from Accretionary Wedge Deformation to Arc-Continental Collision

Abstract: Most researches consider the Taiwan Orogeny to be the result of an oblique arc–continental collision between the Philippine Sea Plate and Eurasia Plate. According to kinematic modeling, the mountains started to build from the north and progressively propagated southward at a rate of 60–90 km/my. Because of the oblique nature of the collision, the influence of the collision on mountain building resulted in the southern Central Range experiencing orogenic processes more recently than in the north. In order to test this model, we studied a critical area using zircon and apatite fission-track data to reveal the early exhumation history of the southern Central Range. We find that exhumation started about 6 Ma, which is earlier than the previously predicted timing of mountain building. We also find that the exhumation history can be separated into two stages: an initial stage starting at ca. 6 Ma and continuing to ca. 1 Ma with a slow uplift rate of b1 mm/yr; and a second stage starting at ca. 1 Ma until the present with a high uplift rate of 4–10 mm/yr. The initial stage of mountain building is considered to be related to accretionary wedge deformation as the South China Sea Plate subducted beneath the Philippine Sea Plate whereas the second stage mountain building resulted from the arc–continental collision. Combining the ages of isotopic dating and fission-track dating in the northern Central Range, we find that the northern Central Range also could start exhumation at ca. 6 Ma and that its exhumation history can also be separated into two stages with similar exhumation patterns and mechanisms to that of the southern Central Range. The most notable difference between the exhumation history of the northern and southern areas of the range is the more extensive degree of exhumation in the north; this could be attributed to the northern Central Range having experienced a longer collision history.

Deep-Seated Landslide Mapping and Geomorphic Characteristic Using High Resolution DTM in Northern Taiwan

Abstract: Open image in new window Torrential rainfall and local geologic structure play principal roles in triggering deep-seated landslide around mountainous area. Typhoon Morakot (2009), the most destructive event occurred in 2009, battered southern Taiwan and caused severe casualties in Siaolin Village. For the purpose of reducing the damage resulted from geological disaster, this study adopted high resolution topographic data which extracted from airborne LiDAR scanning to map the recent and ancient deep-seated landslides in northern Taiwan. In this study, a visualization technique of sky-view factor was performed to generate quasi-3D relief image map by overlapping slope gradient, topographic openness, and multiple direction hill-shading maps, allowing us to interpret precisely the feature of landslide zonation. The study area covers an area of 5502 km2. The landslide micro-topography interpretation were presented with main scarp and landslide mass in polygon pattern, it shows more than 200 deep-seated landslides located on Hsuehshan Range, Tatun volcano group, and Western foothills in northern Taiwan. The spatial distribution of landslide relates highly to the regional strike of formation and local drainage pattern. Additionally, the detrimental geomorphic and geologic factors are extracted to evaluate the landslide evolution. For high scarp ratio slope, it usually represents the landform of ancient landslide characterized with apparent slope deformations. This work also explores the relationship between geomorphic evolutions of landslide and susceptibility. The paper describes expert mapping method combing with topography enhancement technique and provides competent authority to assess landslide magnitude and reduce disaster risk.