Shear-Wave Velocity Structure and Site Response Analysis of the Bangkok Basin for Seismic Hazard Assessment

Abstract The Bangkok basin in the lower Central Plain of Thailand is susceptible to ground shaking from moderate-to-large distant earthquakes due to its thick Quaternary sedimentary deposits. This study investigates deep shear-wave velocity structure and the associated ground response of the Bangkok basin using microtremor array measurement to characterize site effects in the basin. The deep shear-wave velocities at six sites in Bangkok and vicinity are calculated by a two-station spatial autocorrelation method using long-period accelerometers. A low-velocity layer with VS lower than 500 m/s is found at depths <200 m. The depth to bedrock with VS of 1000–1500 m/s is between 300 and 500 m. Bedrock with VS higher than 2000 m/s exists at depths >1000 m. Three-component microtremor observations at 115 sites in the study area suggest that the ground response in most areas has 2 predominant periods, 0.8–1.2 s and 2–5 s. The short-period ground response ranges between 0.3 and 1.2, s which increases toward the Gulf of Thailand and decreases toward Phra Nakhon Sri Ayutthaya province. The long periods range between 1.2 and 5.9 s. We also observe that the dominant ground response period of 0.7–2.5 s in central Bangkok corresponds to the damage reports of high rises and strong-motion data from the 2025 Mw 7.7 Myanmar earthquake.