Prevention, Mitigation and Engineering Response for Geohazard in Thailand

Thailand is situated in SE Asia where most of the area has been under the influence of monsoonal type of weather. Geological settings of the country is believed to be the result of the collision between Indian and Eurasian plates. The collision has great influences on the topographic, weather and tectonic activities of the area for a long time. These factors are closely related to a number of serious geohazards of the area. Such geohazards include landslide and tsunami caused by a large distant earthquake along the Indian – Eurasian subduction zone. Important geohazard cases in Thailand have been discussed and landslide is focused in order to make an optimum risks assessment. There are three main landslide events occurred in Thailand. These landslides occurred in Nakhon Si Thammarat province in the south; Phetchabun province in the northeast; and Tak province in the west. The 2004’s Tsunami event was also unexpected one to a great number of people who live along the Andaman shorelines of the country. These events have generated awareness on landslide geohazard to the nation because it took many lives and damaged properties. As one of the key organization working on geohazard, the Department of Mineral Resources has carried out study programs in order to gain better understanding of such events and then set up activities for the prevention and mitigation for it via engineering approach. Most of our works are based upon not only a scientific approach but also concepts of people’s participatory. We have set up landslide warning networks for both local and regional ones for the high risked areas throughout the country. For tsunami, we have set up our measures via education, information transmission and evacuation plan for high risked areas. Our work has created awareness among people who have been or potentially been effected by such hazards to be well prepared for the event that has yet to come

The timing of strike-slip shear along the Ranong and Khlong Marui faults, Thailand

The timing of shear along many important strike-slip faults in Southeast Asia, such as the Ailao Shan-Red River, Mae Ping and Three Pagodas faults, is poorly understood. We present 40Ar/39Ar, U-Pb SHRIMP and microstructural data from the Ranong and Khlong Marui faults of Thailand to show that they experienced a major period of ductile dextral shear during the middle Eocene (48–40 Ma, centered on 44 Ma) which followed two phases of dextral shear along the Ranong Fault, before the Late Cretaceous (>81 Ma) and between the late Paleocene and early Eocene (59–49 Ma). Many of the sheared rocks were part of a pre-kinematic crystalline basement complex, which partially melted and was intruded by Late Cretaceous (81–71 Ma) and early Eocene (48 Ma) tin-bearing granites. Middle Eocene dextral shear at temperatures of ~300–500°C formed extensive mylonite belts through these rocks and was synchronous with granitoid vein emplacement. Dextral shear along the Ranong and Khlong Marui faults occurred at the same time as sinistral shear along the Mae Ping and Three Pagodas faults of northern Thailand, a result of India-Burma coupling in advance of India-Asia collision. In the late Eocene (<37 Ma) the Ranong and Khlong Marui faults were reactivated as curved sinistral branches of the Mae Ping and Three Pagodas faults, which were accommodating lateral extrusion during India-Asia collision and Himalayan orogenesis

Tectonic blocks and suture zones of eastern Thailand: evidence from enhanced airborne geophysical analysis

Airborne geophysical data were used to analyze the complex structures of eastern Thailand. For visual interpretation, the magnetic data were enhanced by the analytical signal, and we used reduction to the pole (RTP) and vertical derivative (VD) grid methods, while the radiometric data were enhanced by false-colored composites and rectification. The main regional structure of this area trends roughly in northwest-southeast direction, with sinistral faulting movements. These are the result of compression tectonics (sigma_1 in an east-west direction) that generated strike-slip movement during the pre Indian-Asian collision. These faults are cross-cut by the northeast-southwest-running sinistral fault and the northwest-southeast dextral fault, which occurred following the Indian-Asian collision, from the transpession sinistral shear in the northwest-southeast direction. Three distinct geophysical domains are discernible; the Northern, Central and Southern Domains. These three domains correspond very well with the established geotectonic units, as the Northern Domain with the Indochina block, the Central Domain with the Nakhonthai block, the Upper Southern Sub-domain with the Lampang-Chaing Rai block, and the Lower Southern Sub-domain with the Shan Thai block. The Indochina block is a single unit with moderate radiometric intensities and a high magnetic signature. The direction of the east-west lineament pattern is underlain by Mesozoic non-marine sedimentary rock, with mafic igneous bodies beneath this. The Nakhonthai block has a strong magnetic signature and a very weak radiometric intensity, with Late Paleozoic-Early Mesozoic volcanic rock and mélange zones that are largely covered by Cenozoic sediments. The boundaries of this block are the southern extension of the Mae Ping Faults and are oriented in the northwest-southeast direction. The Lampang-Chaing Rai and Shan Thai blocks, with very weak to moderate magnetic signatures and moderate to very strong radiometric intensities are dominated by marine clastic and igneous rocks or a northwest-southeast trending deformation zone of inferred Precambrian complexes, respectively. It is suggested that these tectonic plates collided against one another in a west-east direction