Neotectonics and pale earthquakes along Mae Hong Son Fault, northern Thailand

Abstract

Mae Hong Son Fault (MHSF) is a north-south-trending active fault in Northern Thailand. Last earthquake occurred on February, 1975 with a magnitude of 5.6 at Ban Tha Song Young in Tak Province. This study aims to describe morphological characteristics of MHSF using high (12.5m) resolution Digital Elevation Model (DEM) and to evaluate paleoearthquake magnitudes, recurrence intervals, and slip rates of MHSF by excavating paleoearthquake trenches. According to morphotectonic analysis, offset streams, linear valleys, triangular facets and scarplets were formed as a result of dextral movement within the active fault zone. There are two separate basins associated with the MHSF, which include the Mae Hong Son Basin to the north and the Mae Sariang Basin the south. Between these basins, fault displacements decrease towards Khun Yuam area suggesting a linkage zone in the Mae Hong Son strike-slip fault systems. Surface rupture length investigation from fault segments in both basins indicates maximum credible earthquake between M5.8 - M6.3. Nine paleoearthquake events were identified in Mae Hong Son Province based on trenching and road-cut outcrop studies, and optically stimulated luminescence (OSL) dating. The OSL ages of the events are 78,000, 68,000, 58,000, 48,000, 35,000, 30,000, 25,000, 8,000 and 3,000 years ago. The recurrence interval of earthquake events on the MHSF appears to be ca. 5,000 years, and the slip rate was estimated as ca. 0.04–0.15 mm/yr.