SOIL AMPLIFICATION: A NUMERICAL STUDY

Abstract

From the previous Earthquakes’ records it is evident that Soil Amplification plays a major role in Amplifying or attenuating effects of damaging seismic waves. Soil amplification is mainly dependent on the local geology, topology and geotechnical conditions. Large degree of damage at an area during earthquake is highly dependent on the site dependent factors. Local site condition affects all three (duration, amplitude and frequency of ground motions). It is to be noted that each soil layer responds differently in a seismic event. Analytical models are unable to give solution for complex geological models hence to quantify these responses is a difficult task as it contains a lot of uncertainties. Various 1-D, 2-D and 3-D models are used to measure site amplification effects computationally using Numerical Methods such as Finite Difference method and with recent development in computational power and in software tools, the use of simulated time histories of ground motion has made the process easy and realistic. This study includes the computational simulation by generating SH and SV waves using staggered grid time-domain finite-difference (FD) program and calculating its interaction with different layers of soil and rock. The accuracy is validated by comparing the numerically computed soil amplification at resonance frequency with the analytical solutions. The point Earthquake induced in the numerical grid in form of Gabor wavelet as a source time function. Further, it presents the effects of impedance contrast (IC) at the basin-edge on the spectral amplification and complex mode transformation of Basin-Transduced Rayleigh waves in case of SV wave. The responses of basin-edge models reveal that surface wave get generated when SH and SV waves interact with basin edge. This paper also studies the impact of the complex interaction of basin edge induced surface waves, body waves and soil topography on spectral amplification with varying epicentral distance and Impedance contrast.