Development of Seismic Microzonation Maps for Low to Moderate Seismicity Regions Using Microtremor Observation Data

Abstract

Microzonation in low to moderate seismicity regions is not extensively used due to a lack of attention given. Accordingly, the structures are not designed for earthquake loading. However, these countries are susceptible to earthquake threat caused by local and far field earthquakes. The far field effect of earthquakes from neighbouring countries can be felt in Penang Island, Malaysia, 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 the light of the local geological conditions. This work presents the ground structure of Penang Island for seismic microzonation map development using a simpler and affordable method for low to moderate seismicity regions. Moreover, this study applies microtremor single point and array observation methods to estimate the ground structure of Penang Island. The estimated ground structures are validated using the available borelog data and the results show good agreement. The developed microzonation maps show that Penang Island has a ground structure with a predominant frequency ranging from 1.45 Hz 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. The study demonstrates a simple and affordable method that can be adopted by low to moderate seismicity countries to develop seismic microzonation maps.