Response spectra for long distance subduction earthquakes on soft soil sites

A stochastic seismological model has been developed for simulating earthquake ground shaking on rock sites in Singapore and the adjoining Malaysian Peninsula. Simulations from the model have been compared with recent earthquake events (12th September 2007) of M8.4 and M7.8 generated by the Sunda Arc Subduction Trench from a long distance in the range 600 km – 1000 km. It was concluded that existing attenuation models developed for worldwide applications may not provide realistic representation of such extreme magnitude-distance combinations. In this study, ground motion simulations for rock sites were extended to simulations for the more hazardous soft soil sites conforming to Class C and D of IBC 2006. Accelerograms recorded in downholes from recent major earthquake events along with borehole records of selected soil sites have been collated and archived. Response spectra and drift demands calculated from the recorded accelerograms have been compared with those simulated by program GENQKE (incorporating the attenuation behaviour of the region) and program SHAKE (incorporating the amplification effects of the individual soil sites). This comparative study could form the basis for the development of a realistic and reliable seismic demand model for the Singapore and Malaysian peninsular region.