Neotectonic evidences along the Three Pagoda Fault zone, Changwat Kanchanburi

Abstract

Three-Pagoda Fault (TPF) is located in Kanchanaburi province, western Thailand. Evidences from remote-sensing and field investigations indicate that the TPF is the NW-trending oblique-slip fault with the total length of about 222 km. It can be traced from southeastern Myanmar to western and central Thailand. Several approaches have been applied to figure out neotectonic evidences in the Kanchanaburi area. LANDSAT TM5, JERS-SAR, and aerial photographic interpretation as well as TL and ESR dating synthesis form the major task for this study. Evidences from geology, geometry, and geomorphology indicate that the TPF is delineated into 5 segments, that is Sangkhla Buri (8 km), Kanchanaburi (197.5 km), Thong Phaphum (69 km), Mae Ham Noi (31.5 km), and khwae Yai (125 km) Segments. Offset streams, triangular facets, fault scarps, shutter ridges, linear ridges, and beheaded streams, regarded as essential morphotectonic evidences, are frequently observed along the TPF. All these features point to the youthfulness of the Tpf activity. Four directions of faults and lineaments can be detected, i.e., NE, NW, N and E trends. Among these, the roughly NW-trending fault traces are observed to be the most prominent, and seem to post-date the other directions. The WNW-trending Mae Nam Noi segment is inferred to represent the youngest fault trace for this trend. Nine representative samples from fault gouges and fault-related sediments along the Sangkhla Buri and Kanchanaburi segments have been selected for dating. The geochonological results indicate 5 faulting events along these two fault segments, namely 1) 1,575-920 Ka, 2) 465-580 Ka, 3) 180 Ka, 4) 140-145 Ka, and 5) 20-22 Ka. These results and remote-sensing data advocate the activeness of the TPF within Quaternary period. The main right-lateral sense of movement and NW-trending of the TPF lead to the delineation of strain ellipsoid orientation, strongly suggesting the major stress axis in the N-S direction after Indian-Asian continental collision (40-45 Ma). It is also confirmed from other supporting evidences that the TPF may be active till present, as recognized from epicentral distribution, hot-spring location, and heat-flow data. However, more detailed geological investigations, particularly dating information, are required to specify the precise active-fault location.