Abstract
This study focuses on S-wave velocity structures in Yangon City, Myanmar, where the seismic safety of constructions is insufficient while strong ground shaking due to earthquakes nearby are expected in the near future. In this study, we investigated underground structures based on the horizontal-to-vertical spectral ratios (HVRs) of single-station microtremors as well as phase velocity estimated by array measurement of microtremors inside Yangon City, which can be used to simulate strong ground motions during future crustal earthquakes or used as information for microzonation studies. Microtremor explorations were conducted at 27 sites including one array site at the ground of University of Yangon. The observed results showed the consistent HVR peaks for the fundamental mode in the lower frequencies ranging from 0.7 to 1.3 Hz, while they showed also the other peaks at higher frequencies ranging from 20 to 40 Hz. The final S-wave velocity structures showed that the topmost layer may have a thickness of 1 to 2m with the S-wave velocity of 140m/s and that the 5th deepest layer exists at around 100m below the surface throughout the observed area, as the engineering bedrock with the S-wave velocity of 800m/s.
