ScienceAsia 33 (2007): 257-264 |doi: 10.2306/scienceasia1513-1874.2007.33.257

Application of Enhanced Ground Geophysical Data to Active Fault Analysis in the Southern Sri Sawat Fault Segment, South of Srinakarin Dam, Western Thailand

Viriya Danphaiboonphon,^a,c,d Punya Charusiri^a* and Weera Galong^b

 
ABSTRACT:     The study area (approximately 5,000 m²) in Sri Sawat, Kanchanaburi province, is occupied by the Quaternary deposits and Triassic sedimentary rocks. This area is about 3 km to the south of the Srinakarin Dam located in the southern part of the Sri sawat fault. Main structural features in the area are northwesttrending normal faults as clearly recognized from aerial photographs and satellite imageries. The fault segments, common at the foothill, are dominated by Triassic sedimentary strata. The prime objective of this study is to recognize Quaternary fault zones using ground geophysical methods including magnetic, very low frequency electromagnetic (VLF-EM) and resistivity. Five survey lines of ground geophysical survey (100 m long) with traverse line of 10 m and 5 m of sample spacing interval are assigned in the northeast trending perpendicular to the inferred main geological structure. About 100 stations were selected for measurement, and all data were enhanced using the GEOSOFT and VLF PAK programs. The result indicates that, the fault zone shows higher resistivity values and lower magnetic and VLF-EM responses than those of the mudstone country rocks. The ground geophysical results reveal two systems of faults; both are shallow (at about 0-5 m below surface) and orient in the northwest-southeast trend with opposite dip directions. The fault almost at the northern end is very close to the foothill and is considered to be the major fault. This fault strikes in the northwest-southeast direction, dips to the southwest apparently less than 45° and crosscuts Triassic rocks. This major fault, however, is regarded as “less potentially active” fault. The other faultis regarded as the minor and antithetic fault, and located in the Quaternary deposit at southern end. It strikes northwest-southeast and dips to the northeast at the same angle. This fault is recorded as a minor fault possibly crosscutting the Quaternary colluvial sediments, and is considered to be the active fault.

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^a Earthquake and Tectonic Geology Research Unit, c/o Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand.
^b Bureau of Minerals, Department of Mineral Resources, Bangkok 10400, Thailand.
^c Present address: PTT Exploration and Production Public Company, 555 PTT Office Building, Vibhvadi- Rangsit Rd., Chatuchak, Bangkok 10900, Thailand.
^d E-mail address: d_viriya@yahoo.com

* Corresponding author, E-mail: cpunya@chula.ac.th

Received 13 Jun 2005, Accepted 15 Feb 2007