Development of surface ground motion and spectral acceleration based on modified shear wave propagation analysis

The shear wave propagation analysis (SPA) is a method for developing surface ground motion and spectral acceleration by conducting seismic wave propagation from bedrock to surface elevation. The bedrock elevation and soil profile from bedrock through surface elevation are important information needed for SPA. The shear wave velocity, damping ratio, soil density and shear modulus are the four parameters that are needed for developing SPA. This paper describes a modified SPA for developing surface ground motion and spectral acceleration by conducting two different soil deposit model, actual and modified bedrock elevation models. The difference in the two models depends on the bedrock elevation used for SPA. The actual bedrock elevation model is conducted based on the real bedrock elevation observed using microtremor test. However, the second model is performed based on the final depth of soil boring investigation. The study was conducted at the Engineering Faculty of Diponegoro University. Based on the microtremor observation, the bedrock elevation was predicted at 50 metres below the surface level. However, two soil boring investigations conducted in this study area were stopped at 30 metres below the surface level. The surface ground motion and spectral acceleration developed from both models are almost equal. (paper)