Defining earthquake - risk areas along the active faults in Lampang – Phrae area, northern Thailand using enhanced Landsat TM image data and GIS software programs

摘要

We applied results of both remote-sensing interpretation and field survey to map the settlement distribution as well as the active faults along the Lampang – Phrae Fault Zone, northern Thailand. The objective of this research work is to define seismic risk areas in Lampang - Phrae area using multi-disciplinary approaches. With the application of ENVI 3.4 software, we are able to process and enhance the Landsat TM5 and TM7 images using image registration, image mosaicking, image enhancement, and digital image interpretation. Based on geological, seismological, and geomorphic data, the Lampang – Phrae Fault Zone with the total length of 130 km and the width of 20 km are recognized. The fault zone can be subdivided into 10 segments as Ton Ngun Segment (18 km), Mae Paun Segment (20 km), Sobprab Segment (42 km), Ban Mai Segment (40 km), Long Segment (49 km), Thoen Segment (19 km), Wangchin Segment (74 km), Wangkhon Segment (28 km), Phrae Segment (48 km), and Mae Man Segment (13 km). Tectonic geomorphology and morphometric analysis indicate that along these fault segments the Ban Mai, Sobprab, Long, Thoen and Phrae segments are interpreted to represent the “most active faults”. Landsat image interpretation maps, topographic maps, political administration maps, active fault maps, morphometric maps, road net map, and population density data, were overlain, integrated and analyzed using ArcView 3.2 GIS software to point out the earthquake risk - areas. A strip zone measured equally from both sides of each fault segment covering the total width of 10 km was applied for defining earthquake ruptures in the seismic risk zones. Our result with the GIS application indicates that 7 densely populated district areas in the study area are seismically risked, including Wangchin, Thoen, Sobprab, Long, Muang Phrae, Sung Men, and Denchai district areas . Based on the overall result, we also inferred the most densely populated areas in Long and Sobprab districts have been regarded the most risk areas for fault - induced earthquakes.