Publication: Seismic microzonation maps development and site classification considering deeper soil deposit
Date
2022-05-01
Authors
Lee, Jian Yee
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Abstract
The far field effect of earthquakes from neighbouring countries can be felt in Penang Island, which is contrary to the perception that Malaysia is seismic free. This hazard serves as a reminder of the importance of seismic study, particularly in light of local geological conditions and site classification. In Malaysia, there is a lack of study on the dynamic characteristics of soil. In addition, Malaysia National Annex introduced site period, Ts to classify ground for sediment depth more than 30 m, which needs to be further investigated. This thesis presents the ground structure of Penang Island for seismic microzonation maps development and site classification based on Vs,30 and Ts. This study applies microtremor single point and array observation methods to estimate the ground structure of Penang Island. Seismic microzonation maps and site classification maps of Penang Island were generated. Site response analysis and structural response analysis were conducted to study the appropriateness of site classification based on MS EN 1998-1:2015 (National Annex: 2017), considering site period for sediment exceeding 30 m in depth. The results show that Penang Island has a ground structure with a predominant frequency ranging from 1.45 to 7.4 Hz and Vs,30 in the range of 168 m/s to 468 m/s. The northeast (Georgetown) and western (Balik Pulau) regions of Penang Island show a low frequency and Vs,30 value, indicating that these areas have a soft ground structure. A relationship of predominant frequency (f) and sediment thickness (h) was developed, which can be expressed as h= 54.214f -1.032 . From the analysis results, the ground types with deeper sediment depth will have greater amplification factors and structural responses. It can conclude that Vs,30 is the xix main parameter to classify soil regardless of the sediment thickness. If the ground classification using Ts differs from those defined by Vs,30, the ground type should not be upgraded to a stiffer soil class when considering deeper sediment depth.