Effect of Bedrock Depth on Site Amplification: A Parametric Study for Different Soil Types

Ritu Raj Nath(1*), Md. Hussain(2), Ravi Sankar Jakka(3)

(1) Research Scholar Dept. of Earthquake Engineering Indian Institute of Technology Roorkee, India
(2) Department of Civil Engineering, Aligarh Muslim University, India
(3) Asst. Professor Dept. of Earthquake Engineering Indian Institute of Technology Roorkee, India
(*) Corresponding author

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One of the most important parameters that determine the effect of local site condition on strong ground motion is the location of bedrock and its geomorphology. The depth of bedrock alters the dynamics of the system as a whole and thus has significant influence on amplification of the bedrock motion. The present study is an attempt to investigate the effect of bedrock depth on site amplification through the perspective of one dimensional ground response analysis. The study is extended to all three soil types of Indian peninsula in accordance with IS 1893 (Part I): 2002. Four earthquakes are considered to simulate near field and far field effects. Results are interpreted in terms of surface acceleration time history, response spectra at 5%, 10%, 15%& 20% damping, amplification spectrum and Fourier spectra at the surface. It has been observed that amplification of bedrock motion is a function of frequency content of the input motion and is closely correlated to bed rock depth. The study also reveals that peak ground acceleration for all soil types’ changes with the depth of bed rock.
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Local Site Effects; Bedrock Depth; Soil Type; Amplification Ratio; Response Spectrum

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