Analysis of Seismic Stations in Northern Thailand Using Hvsr (Horizontal-to-Vertical Spectral Ratios)

Abstract

Several major cities in Northern Thailand, situated within a sedimentary basin near active faults, face heightened seismic risks. This research investigates the effects of several earthquakes, magnitudes between 4.4 and 6.4, in northern Thailand from 2019 to 2023. The seismic activity impacted Chiang Mai, Chiang Rai, Mae Hong Son, Lampang, and Lamphun. The Horizontal Vertical Spectral Ratio (HVSR) method is utilized to examine strong ground motion data from northern Thailand gathered by the Department of Mineral Resources (DMR) and the Thai Meteorological Department (TMD). This approach is used to detect site response, classify, and ascertain basins’ natural frequency, providing essential insights for seismic analysis and hazard evaluation in the investigated area. The study targets nine stations, each recording at least nine ground motions and ten ambient noises. Significant amplification is noted at sites with stiff and soft soils, including CMPR, CMAI, and PHRS. Additionally, the research compares the calculated site natural frequency with the average shear wave velocity of the upper 30 m (Vs<inf>30</inf>), derived from Shuttle Radar Topography Mission (SRTM) from USGS and Multichannel Analysis of Surface Wave (MASW) data when accessible.