ASSESSMENT OF CREDIBLE GROUND MOTION IN SINGAPORE DUE TO A GREAT SUMATRAN SUBDUCTION EARTHQUAKE

摘要

Singapore is located in a low-seismicity region, where earthquakes have never posed any real problem so far. However, huge but infrequent Sumatran subduction earthquakes might pose a real problem to medium- and high-rise buildings in Singapore when they occur. Bedrock motions in Singapore due to a hypothesised great Sumatran subduction earthquake that has a size similar to the 1833 event (Mw=9.0) are simulated using an extended reflectivity method, taking into account uncertainties in source rupture process. The random rupture models, considering the uncertainties in the rupture directivity, slip distribution, presence of asperities, rupture velocity and dislocation rise time, are made based on a range of seismologically possible models. The simulated bedrock motions have a very long duration of about 250 s with a predominant period between 1.8 and 2.5 s, which coincides with the natural periods of medium- and high-rise buildings widely found in Singapore. The 90-percentile horizontal PGA is estimated to be 33 gals and the 90-percentile horizontal spectral acceleration with 5% damping ratio is 100 gals within the predominant period range. The 90-percentile bedrock motion might generate base shear forces of a building higher than that required by the current design code, where seismic design has yet to be considered. This has not taken into account the effects of the local soil response that might amplify the bedrock motion.