Seismic hazard map of Southern Thailand

Abstract

This research concentrates on the re-evaluation of the paleo-earthquake activities of the Khlong Marui Fault (KMF) and Ranong Fault (RNF) with an aim to establish of seismic hazard maps of southern Thailand. Based on the results of satellite image interpretation, field investigation and geochronological analyses, the KMF and RNF produced the maximum paleo-magnitudes of M[subscript W] 6.6 and M[subscript W] 6.2 at 2,000 and 9,000 years ago, respectively. The KMF has the mean recurrence interval of 2,200 years and the slip rates of 0.1-0.5 mm/yr whereas the RNF has the mean recurrence interval of 8,300 years and the slip rates of 0.04-0.17 mm/yr. The seismic sources include the line and area sources in southern Thailand and nearby region including the Sumatra-Andaman subduction zone. The probability seismic hazard analysis and the logic tree approach were applied. The hazard maps consist of maps showing mean peak ground accelerations and spectral accelerations at 0.2, 0.3, and 1.0 seconds with a 10%, 5%, 2% and 0.5% probability of exceedance in 50-year hazard levels for rock site condition. The results reveal that the highest hazard areas are in districts of Muang, Phanom, and Viphavadi (Surat Thani), Thap Put (Phang Nga), Plai Phraya (Krabi). The lowest hazard areas are in the southernmost part of Thailand (Yala, Pattani and Narathiwat). The maximum values of the mean peak ground acceleration for the 500–10,000 yr return period are 0.28g-0.52g and the maximum spectral accelerations at 0.2 seconds for the same return period are 0.52-0.8 g. These seismic hazard maps are useful as a guideline for future design of buildings, bridges and high hazard structures as dams for rock sites to resist earthquake forces. This preliminary result will be more helpful and accurate if the more detailed dating data, and horizontal ground acceleration results can be synthesized.