Abstract
We applied remote sensing techniques and geomorphic index analysis to a study of the NE-SW-striking Thoen Fault, Lampang Basin, northern Thailand. Morphotectonic landforms, formed by normal faulting in the basin, include fault scarps, triangular facets, wine-glass canyons, and a linear mountain front. Along the Thoen Fault, the stream length gradient index records steeper slopes near the mountain front; the index values are possibly related to a normal fault system. Moreover, we obtained low values of the ratio of the valley floor width to valley height (0.44–2.75), and of mountain-front sinuosity (1.11–1.82) along various segments of the fault. These geomorphic indices suggest tectonic activity involving dip-slip displacement on faults. Although the geomorphology and geomorphic indices in the study area indicate active normal faulting, sedimentary units exposed in a trench at Ban Don Fai show no evidence of recent fault movement. In Ban Don Fai trench No. 2, accelerator mass spectrometry radiocarbon (AMS) ages and optically stimulated luminescence (OSL) ages indicate that deposition of the lowest exposed sedimentary unit occurred between 960 and 910 years ago. Therefore, the most recent movement upon the Ban Don Fai segment of the Thoen Fault occurred more than 960 years ago.
Highlights
Thailand is located to the east of the Andaman-Sumatra earthquake belt, and no large earthquake has recently occurred in this region
Most of the V f and Sm f values obtained for the Ban Mai, Ban Don Fai, and Sop Prap segments are low (0.44–2.75 for V f and 1.11–1.82 for Sm f ; Tables 1 and 2), which may indicate an area of weakly active tectonism characterized by normal dip-slip fault movement
The Thoen Fault is well defined by geomorphology, and is evident as sharp lineaments on aerial photographs and satellite images (Fig. 4), associated with morphotectonic landforms such as fault scarps, triangular facets, wine-glass canyons, and a linear mountain front
Summary
Thailand is located to the east of the Andaman-Sumatra earthquake belt, and no large earthquake (i.e., magnitude ≥6 on the Richter scale) has recently occurred in this region. Geomorphic indices, including the stream length gradient index (S L), the ratio of valley floor width to valley height (V f ), and mountain-front sinuosity (Sm f ), were used in the present study to identify tectonic activity within the Lampang Basin. Most of the V f and Sm f values obtained for the Ban Mai, Ban Don Fai, and Sop Prap segments are low (0.44–2.75 for V f and 1.11–1.82 for Sm f ; Tables 1 and 2), which may indicate an area of weakly active tectonism characterized by normal dip-slip fault movement. This result is encouraging in terms of the future use of OSL dating
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