Bulletin of the Geological Society of Malaysia, Volume 43, Dec. 1999, pp. 653 - 665
1Department of Geology, Chulalongkorn University, Bangkok 10330, Thailand
2Geological Survey Division, Department of Mineral Resources, Bangkok 10400, Thailand
3Geophysical Subdivision, Meteorological Department, Bangkok, 10260, Thailand
Abstract: There was little awareness on earthquake hazards in Thailand until the country experienced the 1983 earthquake. Though Thailand has long been recognized as situated in the low seismicity region and there were not very much earthquake damaged events in her past history, there are more than 4,000 small to moderate quakes detected in Thailand and nearby since the installment of the worldwide seismograph network in 1902. After the establishment of National Earthquake Committee in 1984 and installment of 12 seismic network stations, more studies related to earthquakes have been generated. However, most of the qualified studies concern to some extent with the engineering properties related to the earth tremors.
At present it is recognized that many earthquake activities have a closely temporal and spatial relation to the fault movements. However, based on our study, the recent fault activities are more or less linked to the extrusion tectonics caused by the India-Asia collision during mid-Tertiary. There are at least three approaches to defining the active fault (AF) - general, engineering, and regulatory definitions, however, all of which use the age of the last past activity. The faults that do not meet general requirements are interpreted as either potentially active (PAF) or tentatively active (TAF). In the adoption of the active fault classification, the geological, geotectonic, geochronological, and seismological evidences allow us to group the faults in Thailand into 5-major fault zones (FZ), namely the northern, western-northwestern, central peninsular, southern peninsular, and eastern-northeastern FZs.
However, not all FZs are considered as the AF. Most faults of the central and southern peninsular and east-northeast FZs are inferred as PAF and TAF. Many faults belonging to the northern and western-northwestern FZs are regarded as the AF. Exception is the Mae Tha, Nam Pat and Pha Yao faults are inferred as TAF due to their subdued and deeply eroded morphology and scarps. Based upon the fault activity in conjunction with the seismic zoning maps, the seismic risk map of Thailand is proposed.