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Journal of Earth System Science

, Volume 117, Supplement 2, pp 731–748 | Cite as

Importance of quantification of local site effects based on wave propagation in seismic microzonation

  • S. Kumar
  • J. P. Narayan
Article

Abstract

This paper presents the three most important aspects of seismic microzonation namely prediction of fundamental frequency (F 0) of soil deposit, aggravation factor (aggravation factor is simply the extra spectral amplification due to complex 2D site effects over the 1D response of the soil column) and the spatial variability of the ground motion caused by the basin-edge induced Love waves. The predicted F 0 of single, double and three-soil-layered models revealed that the available empirical relations to predict the F 0 of layered soil deposits are inadequate. We recommend the use of analytical or numerical methods to predict such an important parameter based on wave propagation effects. An increase of amplitude of Love wave, strain level and average aggravation factor (AAF) with increase of impedance contrast was obtained. Based on the trend of rate of decrease of AAF and maximum strain with offset from the basin-edge, we can qualitatively infer that the effects of induced Love wave may reduce to a negligible value after a traveled distance of 6.5–10.0 λ F (where λ F is the wavelength corresponding to the F 0 of soil layer). The obtained increase of strain level with the decrease of distance between two receiver points used for the computation of strain reflects that structures having spatial extent smaller than the λ F may suffer damage due to the basin-edge induced surface waves. The fast rate of decrease of strain with the offset from the strong lateral discontinuity (SLD)/basin-edge may be attributed to the dispersive nature of Love wave. We can incorporate the increased spectral amplification due to the induced surface waves in the form of aggravation factor but till date we have no effective way to incorporate the effects of developed strain by induced surface waves in seismic microzonation or in building codes.

Keywords

Basin-edge effects surface waves aggravation factor spatial variability finite difference method 

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Copyright information

© Indian Academy of Sciences 2008

Authors and Affiliations

  1. 1.Department of Earthquake EngineeringIndian Institute of Technology RoorkeeRoorkeeIndia

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