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Fundamental and Environmental Geology
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Geological Hazard
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:::Geological Hazard

 

Geological hazard investigation has emerged in recent years to present a particularly sensitive aspect of geological research as it aims to study and identify all probabilities of geological hazards. In 2017, the CGS invested its efforts more specifically on investigating and monitoring active faults, landslides, and volcanoes.
A. Active Fault Observation and Research on Earthquake Potential, 4th Phase(1/4)
  This is a four-year (2017~2020), cross-disciplinary project integrating several geodetic studies. The adopted methods include observation by continuous/campaign-mode GPS stations, leveling measurement, and PS-InSAR. The results are expected to contribute to the probability analysis of active faults in Taiwan.
    Surface Deformation Analysis from Geodetic Data and Establishment of Fault Models (1/4): In this project, the geodetic data obtained by an island-wide continuous and campaign GPS network, precise leveling lines, and PS-InSAR are analyzed to measure the surface velocity field in this project, and the surface velocities are inverted to estimate the slip rate deficit and optimize fault geometry parameters by adopting the fault models. The surface velocity field and the derived fault parameters can be expected to help assess the probability analysis of major faults and to delineate the geologically sensitive areas of active faults.
    Improvement of Earthquake Probability Assessment for Active Faults and Parameter Analysis for Seismogenic Structures in Taiwan (1/4): The project reviewed the parameters of active faults in Central Taiwan and had the logic trees of the reviewed faults updated. For better examining fault geometry, the dip and depth of the reviewed faults were modified in line with subsurface relationship. The oblique slip (rake) was added to help calculate the net slip rate of fault plane. The maximum and the minimum values of the net slip rate were used as the upper and lower bounds, and the average value was used as the medium number in the logic tree branch. The 30-, 50-, and 100-year conditional probability for M ? 6.5 earthquakes of each fault in Central Taiwan were also evaluated.
    The project succeeded in monitoring ground deformation and keeping the GPS stations work well, although no new station was established in 2017. (Active Tectonics Division)
B. Research on Tectonic Characteristics of Major Active Faults, 3rd Phase(3/4)
 

This is the third phase of a four-year (2015-2018) project focusing on the study of the structural characteristics of major active faults in Taiwan. The project utilized geophysical methods for exploring the characteristics of the near surface fault structures in the Liuchia, Muchiliao, and Shihtan fault zones. The CGS completed more than 7,500m near surface profile using geoelectric resistivity, ground-penetrating radar, and high-resolution shallow reflection seismic methods. Field survey and morphostructural analysis were conducted to investigate the long-term slip rate of the Tachienshan Fault. The investigations of the Muchiliao Fault, Tuntzuchiao Fault, Hengchun Fault, and Lingding Fault were also advanced with field surveys and drilling in 14 sites with the total borehole length reaching 1,890 m, while the delineation and announcement of geologically sensitive areas for the Liuchia Fault were completed. The CGS will continue accumulating data of earthquake geology and render the data available for online inquiry so as to provide the public with valuable information concerning active faults in Taiwan. (Active Tectonics Division).

C. Research on Volcano Activity Observation in Northern Taiwan
  This four-year (2016~2019) project aims to continue the observation of volcanic activities in northern Taiwan, to improve monitoring methods and techniques, and to precisely evaluate the volcanic geometry beneath the Tatun Volcano Group (TVG) and the Kueishantao area. The results of this project obtained in 2017 are summarized below:
- Seismic and geochemical monitoring in the volcanic areas of northern Taiwan: The background data monitoring of volcano-related hydrothermal activities in northern Taiwan include 16 seismic stations, 5 hot springs, 6 volcanic gas sites and 4 geothermal wells. As indicated by both seismic and geochemical data, the volcanic activities in northern Taiwan remain stable.
- Age dating of volcanic rocks in Tatun Volcano Group: The project employs the U-Th-Ra and fission track dating techniques for age dating of the youngest volcanic rocks in the Cising volcano subgroup. The result of dating shows that age of Shamoushan lava dome extrusion should be younger than 16,000 yrs.
- Airborne magnetic survey in eastern Taiwan: The area surveyed in 2017 was located between Ruisui and Yuli townships. The high magnetic anomalies in shallow crust was closely related to ultrabasic rock bodies in the Central Range and the volcanic bodies in the Coastal Range. The NNE-trending high magnetic belts with magnetized vectors in nearly opposite directions indicated magnetization related to original geomagnetic reversal of oceanic crust before the arc-continent collision.
D. Development and Application of Innovative Technology for Landslide Observation and Landslide Susceptibility Assessment
  The purposes of this four-year project (2015~2018) include investigating environmental geology in slope areas, studying the rainfall thresholds for shallow landslides, and monitoring susceptible deep-seated landslides in 30 selected areas.
- Assessment on Rainfall Induced Shallow Landslide Susceptibility: Major works include the study of rainfall threshold for debris slide and updating of the environmental geological maps. In 2017, the study area focused on central Taiwan covered by 41 map sheets with a scale of 1/25,000. Integrating the data collected from landslides and field investigations, the "Rainfall-induced Landslide Early Warning Information System (RiLEWIS)" reports good validity and has been under ongoing improvement. Using high-resolution DEMs by airborne LiDAR, 235 rockslides are recognized or modified, and the average area is about 12 hectare in central Taiwan, meeting the definition of large-scale landslide. All the new data contribute to the updating of the environmental geological information system.
- Development and Application of Innovative Technology for deep-seated Landslide Observation: Geological survey, landslide investigation, field tests, instrumentations and observations were implemented in order to study the activity of 30 deep-seated landslide areas, including LuShan village, LuShan hotspring, HerYa, CuilLuan, Malieba, DingYuan in NanTou County, TaiHe, RuiLi, LeYe, KeZiLin, ChaoZhouHu, SheZiLiao, LongTou, ZhangNaoLiao, ShiBi in ChiaYi County, DaWu, XinJiaMu, DaLai, TaiWu in PingTung County and ZhuLin in Kaohsiung City, XiRoAn, TongBi in New Taipei City, MeiHua in HsinChu County, ShiBaGu in MiaoLi County and ErJiTuan in Kaohsiung City.
E. Integrating the Geo-Information of Large-Scale Landslide into Information Services for Slope Geohazard Prevention
  Since the typhoon Morakot severely devastated Taiwan in 2009, the CGS has initiated the project "Investigation and Analysis for Geologically Sensitive Areas under the Program of National Land Preservation." The CGS had established a 1m high-resolution digital elevation model (DEM) by utilizing the techniques of airborne LiDAR (Light Detection And Ranging) and the findings of geohazard interpretation accumulated from 2010-2016. This was the first time that high-resolution DEM was applied in Taiwan island-wide, facilitating the integration of DEM, satellite images and aerial photos to locate in an area of 4,200 square kilometers 1,074 potential sites of large-scale landside (larger than 10 ha) that might be triggered by gravitational slope deformation. In addition, 113 at-risk slope areas encompassing 103 residential communities had been identified. The findings of preliminary investigations of potential large-scale landslide over the past few years play a crucial role in helping the government reduce the impact of complex large-scale landslides. Making good use of advanced information technology, this project has accumulated essential data and developed effective observation techniques oriented to disaster prevention. Meanwhile, the project further helps promote industry-academia-government collaboration. With the Information Services for Disaster Prevention, more and more people, including researchers, professionals, and citizens, can obtain and share information about landslide prevention in Taiwan, thereby enhancing the public's geohazard awareness.

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