Acquisition of Ground Information in Downtown Yangon for Bosai Operation Support System

抄録

Yangon is one of the most populated and socio-economically important cities in Myanmar. Unfortunately, it is located in a moderately active-seismic area, and significant damage and loss will be incurred if an earthquake occurs there in the future. The seismogenic Sagaing Fault passes 40 km to the E of Yangon, which has experienced several destructive earthquakes in the past. The urban area studied here, Kyauktada, Pazundaung, and Botahtaung townships, are located mostly on a soft alluvial plain, which is mainly composed of sand, silt, and clay, which are sediments prone to amplify seismic waves. The Yangon Bosai Operation Support System (BOSS), designed to establish a proper disaster management system based on the potential damage that a future earthquake might cause, is under development. BOSS has two components damage prediction and damage response – which are based on predicted damage and current response capability and practices in Myanmar. For damage prediction, major inputs include information on the underlying soils, building construction and associated fragility functions, based on different building types. Microtremor survey is a useful tool for reviewing underlying soil layer information, as this can significantly affect vulnerability assessments and the identification of potential damages. Microtremor surveys and analyses were therefore conducted at 88 sites throughout the studied urban areas to acquire key ground information for BOSS. Our analyses showed that the fundamental frequency of horizontal to vertical spectral ratio (H/V ratio) of microtremors generally ranged 0.6–2.4 Hz, while the peak amplitude was between 1.3 and 4.0. Soil thickness ranged 60–210 m, and the average shear wave velocity over the ground’s upper 30 m, V_s³⁰, was in the range 180–560 ms^-1. All outcomes from this research will become key input parameters for BOSS development in Yangon.