Geological Hazard Investigations
Geological hazard investigations include the monitoring of earthquakes, volcanos activities, fault activities, landslides, land subsidence, coastal change, and hazards caused by other geologic processes. In order to understand the distribution and potential of geological hazards, the CGS undertakes various kinds of geological surveys and studies to provide the essential information for making decision on disaster prevention and mitigation plans.
The CGS currently focuses on the following fields:
- Active fault investigations.
- Landslide and potentially large-scale landslide investigations.
- Soil liquefaction investigations.
- Others, such as land subsidence, coastal erosion, tsunami, and volcanic investigations.
I. Active Fault Investigations
Faults cause major earthquakes and hazards in Taiwan. Since 1997, the CGS commenced the investigation of active faults to understand their geological nature, characteristics and recurrence interval.
The goals are as below:
A. Conducting active fault investigation with the methods of field survey, geodesy, borehole drilling, resistivity method, ground penetrating radar, seismic survey, and trenching.
B. Monitoring active faults with the methods of borehole strain meter (GTSM), continuous monitoring of environmental chemical gases, GPS, precise leveling, and PS-InSAR
C. Assessing fault reactivation probability by integrating parameters such as fault length, recurrence interval, the last active time and long-term slip rate.
D. Providing active fault information service for the general public by setting up web database with maps, reports and geodesy of active fault investigation.
• 1998: Publish the “Explanatory Test of the Active Fault Map of Taiwan. Scale 1:500,000.”
• 1999: Publish the "Surface rupture map and related geological reports of the Chi-Chi earthquake".
• 2000: Published the 2nd edition of " Explanatory Test of the Active Fault Map of Taiwan. Scale 1:500,000.”
• 2007: Published “Active Faults of Northern Taiwan: Explanatory Test for the Strip Maps of Active Faults. Scale 1: 25,000.” and “Active Faults of Southwestern Taiwan: Explanatory Test for the Strip Maps of Active Faults. Scale 1: 25,000.”
• 2008: Published “ Active Faults of Central Taiwan: Explanatory Test for the Strip Maps of Active Faults. Scale 1: 25,000.”
• 2009: Published “Active Faults of Eastern and Southern Taiwan: Explanatory Test for the Strip Maps of Active Faults. Scale 1: 25,000.”
• 2012: Published the "1/500,000 Active Fault Map of Taiwan: An Explanatory Text (2012 Edition)”.
II. Investigation of Landslide and Potentially Large-scale Landslide-prone Geology
Mountains occupy two-thirds of Taiwan's territory and many metropolitan areas of Taiwan are surrounded by slope lands. Due to the steep landform and complicated geological structure, earthquakes and torrential rains, along with heavy subtropical weathering and erosion, often trigger hazardous landslide and debris flows.
Since 1999, the CGS has carried out the following projects:
A. Investigation and analysis: evaluating aerial photos, high resolution LiDAR DEM and conducting field surveys to pinpoint landslide sites and potentially large-scale landslide sites.
B. Susceptibility evaluation: using geographic information system (GIS) and statistical methods to integrate data from on-site investigation, geomorphological data, geological data and other relevant data to model and analyze landslides.
C. Compilation of information: Compiling all data and information to map the distribution of potential landslide sites and susceptibility analyses.
• 1999 to 2006: Completed landslide inventory and hazard evaluation of Taiwan.
• 2002 to 2004: Completed geological investigation of the Chi-Chi earthquake induced landslides.
• 2007 to 2010: Conducted assessment and monitoring of the potential hazard of geologically sensitive areas.
• 2006 to 2013: Completed geological investigation and established database for the upstream watersheds of flood-prone areas.
• 2010 to 2015: Completed mapping island-wide high resolution LiDAR DEM maps and underwent geological investigation of potentially large-scale landslides after typhoon Morakot.
• 2011 to 2014: Strengthening application of geo-hazard investigation results in slope land areas.
III. Soil Liquefaction
Taiwan is located at the junction of plates and has frequent seismic activities. In the plain areas where the groundwater level is high and sediments are loose, soil liquefaction may be triggered by strong earthquakes.
Since 2010, the CGS started constructing the 3D geological information bank of soil liquefaction to make the public aware of its risk and thus to mitigate hazards. In 2016, due to severe damages caused by Meinong Earthquake in Tainan, where massive constructions were destroyed partly due to soil liquefaction. Hence, completing soil liquefaction data and making them available to the public becomes an important task of CGS.
The main works include:
A. Hydrogeological investigations in plain areas: establishing hydrogeological framework and groundwater conceptual models, and identifying major groundwater recharge areas, provide information to delineate the geologically sensitive areas
B. Completed hydrogeological surveys and assessing the groundwater resources in mountainous areas
C. Established a comprehensive hydrogeological database for public queries
• 2013: Completed compiling results of the survey and evaluation of soil liquefaction areas of Taipei and Kaohsiung cities..
• 2016: Compiled the survey and evaluation of areas of potential soil liquefaction hazards of Yilan, Hsinju, Taichung, Changhua, Yunlin, Chiayi, Tainan, and Pingtung urban areas.
• 2016: Published soil liquefaction information and completed a national inquiry system for soil liquefaction.