Paleoearthquake investigations along the Khlong Marui fault zone, southern Thailand

Abstract

The Khlong Marui Fault Zone (KMF) in southern Thailand was selected for identifying its detailed characteristics and locating active faults. The remote-sensing and field data were applied for evaluating the occurrence of paleoseismicity in the study area. The main purposes of this study include events of earthquake faulting, paleoearthquake magnitudes, and slip rates of these fault movements. Results from the remote-sensing interpretation indicate that the KMF is the northeast-southwest trending oblique-slip fault which the major component is lateral and has a total length of about 150 km. The fault zone can be traced from Andaman Sea in the south through Phuket, Phan Nga, Krabi, and Surat Thani and extends northwards to the Gulf of Thailand. Sixteen fault segments, ranging in length from 10 to 55 km, were recognized, and some of which run and pass through Cenozoic basins. Based on the results of remotesensing interpretation together with the evaluation of geomorphic indices, earlier geophysical and ground surveys reveal that several morphotectonic features, have been identified in the middle part of the study area (Khao Phanom), especially the Khlong Marui fault segment, which is the longest of KMF. The results from two and earlier excavated paleoseismic trenches along the KMF indicate 4 paleoearthquake events with the lastest movement taking place in 2,000 years ago. It is also estimated that the movement along the segment was triggered by the earthquake with the maximum paleoearthquake magnitude of Mw 7.1. The slip rate of this fault segment is estimated as 0.4 – 0.5 mm/yr. Therefore, it is concluded that the KMF is still active till present, and the Khoa Phanom and Phang Nga segments, which were dextral active, are regarded as the active segments with the presentday sinistral sense of movement.