|
The geological hazard investigations include hazards caused by earthquakes, volcanic eruptions, fault activities, landslides, land subsidence, and other geological activity. Situated in a geologically dynamic area, this line of research is particularly sensitive and important in Taiwan. In recent years, the CGS has taken initiatives to study and identify possible geological hazards. In 2006, the CGS concentrated on developing a monitoring system on active faults, landslides and debris flow. |
| A. |
Active Fault Observation and Evaluation on Earthquake Potential |
| |
This multi-disciplinary project integrates studies of crustal strain, geochemistry and groundwater hydrology. These sub-projects use the techniques of observations by a cluster of borehole strainmeters, geochemical sensors, and piezometers. The results are expected to con-tribute to the evaluation of earthquake potential in western Taiwan.
| - |
The Deployment of Devices Observing Fault Activities and Data Analysis: In 2006, a fourth set of downhole earthquake observation instruments was installed in southwestern Taiwan at two locations: Tai-Sing and Jhong-Sing. In addition, a fifth set of downhole earthquake observation instruments was installed attwo locations: Da-Bang and Sin-Le. The borehole instruments included a strainmeter (GTSM), a piezometer and a seismometer. |
| - |
Geochemical Investigation and Research on Fault Activities in Taiwan: It will be helpful to better understand the mechanism and process of the fault/earthquake activity by gathering long-term observations of gas composition and water-level at appropriate sites near fault zones. This is a four-year project from 2005 to 2008. In 2006, two soil gas composition sites and one water-level observation recording station were constructed in the Chiayi-Tainan area. Long-term monitoring will verify the relationship between geochemical/water level variations and earthquake activity in the sub-project. |
|
| B. |
Earthquake Geological Investigation and DataBank Establishment on Active Faults |
| |
The goals of active fault investigation were: (1) pinpointing the fault location, (2) unraveling the nature of the fault, (3) analyzing fault activity, and (4) deciphering the recurrence period of the fault so as to mitigate seismic hazards. As scheduled, five faults should be investigated each year. Furthermore, a databank will also be developed to properly manage the data collected. The faults investigated in 2006 were located in central and eastern Taiwan.
| - |
The Sanyi reverse fault strikes EW from Tawo to Sanyi, and turns to nearly NS to the Tachia River. The timing of its last reactivation was likely within the Holocene. |
| - |
The Tachia fault, a blind thrust, probably extends southward to connect the Chingshui fault that is located in the west side of the Dadu Tableland. |
| - |
The Tiehchanshan fault is probably a branch of the Tachia and Chingshui faults. In addition, the linear scarp was also possibly formed by river erosion or other reasons, because there is no obvious geological and geophysical evidence along the lineament.
|
| - |
The Luyeh reverse fault strikes NS and dips to the east. It is a hanging wall fault, the Beinanshan Conglomerate and the footwall is slate. This fault is
very active because it cuts the young terraces and flood plane. |
| - |
The Lichi reverse fault strikes nearly NS and dips to the east with high angle. It has reactivat-ed several times recently, because there are some tectonic
-related landforms along the fault.
|
|
| C. |
The Investigation and Monitoring of Specific Geohazards in Metropolitan Taipei |
| |
During 2006, one downhole broadband seismograph, two surficial broadband seismographs, one automatic and continuous analyzer for hot-spring chemistry, and one geothermal monitoring string were installed in a volcanic area and Taipei Basin. A network consisting of nearly 40 broad-band seismic stations was deployed around the TVG and the Taipei Basin continuously to monitor seismicity. High mantle-derived 3He/4He and micro-earthquake swarm indicated a magma
chamber might exist beneath the Tatun Volcano Group (TVG).
| - |
A 1/25,000 scale geological map and the volcanic framework of the Huangzuishan subgroup of the TVG were established combining surficial field survey and
three boring cores of 495.7 m, 150.7 m, and 100 m respectively. Well preserved craters, domes, and lava platforms in the Huangzuishan subgroup formed the most beautiful stratovolcanic landforms in Taiwan. |
| - |
Airbone LiDAR was utilized to produce 2 m-resolution DTM and DSM of an area of 920 km2. The analysis and studies of topographic scarps and lineaments, river
cliffs and ancient channels, volcanic landforms, and fault-induced flooding were completed. |
| - |
In the northeastern offshore area, the resulting seismic reflection profiles revealed two normal fault zones located at the extension of two terrestrial
major thrusts, Jinshan fault and Kanjiao fault, towards the marine terrain. The reversal of fault type might indicate a significant geological event. |
|
| D. |
Landslide Investigation and Hazard Evaluation of Taiwan |
| |
This investigation aims to provide a better picture of when and where landslides might occur and thus help us to prevent them. Two projects were completed in
2006:
| - |
Investigation of Landslides of Kaohsiung and Pingtung County: Information was gathered on the land cover, surface drainage, morphology, surface material,
rock type, geological struc-ture, lineament, and earthquake data. The information was used, along with DTM, to develop an evaluation procedure for the slope
failure potential in Kaohsiung and Pingtung County. The methods to identify slope failures were aerial photo interpretation and field investigations. |
| - |
Field Displacement Monitoring and Slope Stability Analysis of Hungtsaiping landslide: The Hungtsaiping Landslide covers hundreds of hectares, which was
triggered by the Chi-Chi earthquake in 1999, and the sliding mechanisms were complicated. Newly developed fiber optic ground displacement and water
pressure/level sensing systems, coupled with remote sensing and other imaging techniques were used to monitor the status of the landslide. The mechanisms
include: rock mass slide, plane slide, shallow curved slide, shallow debris collapse, and river erosion. |
The investigation shows that a landslide is very likely to occur again. Technically, it will occur when the horizontal acceleration reaches 0.18 g or when
the horizontal and vertical accelerations simultaneously reach 0.11 g. Due to the continued existence of unfavorable factors, a massive landslide seems
inevitable if a major earthquake such as the Chi-Chi earthquake occurs again. |
| E. |
Geological Investigation of Debris Flow |
| |
This 5-year project is debuted in 2002,a subsidiary of the "National Land Conservation Plan" by the Executive Yuan. The main purposes of this project are:
| - |
to allocate the distribution of debris flow, sediments, landslides in watersheds |
| - |
to determine the properties of sediments and engineering properties of rock mass in watersheds. |
A geographic information system database with 379 debris flows was established, including the 30 debris flows caused by heavy rainfall during the Toraji typhoon in 2006. As well, a web GIS was designed to offer online search for debris flow.
The investigation area of debris flow during the 5-year project.
SWCB (Soil and Water Conservation Bureau) |
| F. |
Dynamic System for Monitoring the Geological Environments and Resources by Utilizing ROCSAT-2 (FORMOSAT-2) Images |
| |
Fiscal year 2006 was the second year since the project was proposed. The main goal of this project is to establish a dynamic monitoring system of geohazards,
geological environ-ments on the GIS platform by combining the real-time images produced by FORMOSAT-2. Some geological applications of FORMOSAT-2 imagery of
Taiwan have proven functional:
| - |
Developing the techniques of auto-classification for landslides and debris flow based on the spectral, textural, and spatial features extracted from the
FORMOSAT-2 imagery, and utilizing ground investigation data to calibrate the results of imagery auto-classification. This year the research focuses on the
analysis of the variations of landslides and debris flow in central and northern Taiwan. The CGS determined the occurrence criterion of landslides and
debris flow based on assimilating the data of rainfall recording stations using satellite imagery. |
| - |
Monitoring the coastline between the Toucian River and Yuanli, and between the Tainan and Kaohsiung areas. The results show that, around the mouth of the
Keya River in Hsinchu, the coastline has continued to retreat since the CGS started monitoring in 2005; the Wangzihliaoshan sand bar also showed retrograding
towards land. Moreover, a newly formed tidal inlet has occurred. |
| - |
Mapping the geological structures and lithology of the Central Mountain Range by the textures of FORMOSAT-2 images, the field measurement of reflectance,
and the multi- and hyper-spectral imagery obtained from ASTER and Hyperion. |
|
|
