Seismic site response under variable shear wave velocity models: application to Jamshedpur, India

Abstract

This study evaluates the influence of shear wave velocity (Vs) characterization on seismic site response in Jamshedpur, India. To understand these effects, a one-dimensional equivalent linear ground response analysis has been performed for three distinct shear wave velocity inputs: Vs profiles obtained from the MASW method, Vs profiles obtained from established correlations between Vs and SPT-N values, and the mean shear wave velocity measured for the top 30 m of ground (Vs30). Subsurface conditions at 15 locations were characterized using Multichannel Analysis of Surface Waves (MASW) surveys and borehole investigations. The estimated Vs30 values range from 213 to 493 m/s and were used to categorize and describe these sites according to NEHRP seismic site classification, and the majority of sites fall in seismic site class C, and a few fall in seismic site class D. Four recorded ground motions with PGA values of 0.1 g, 0.16 g, 0.28 g, and 0.41 g have been used to evaluate site behavior under varying shaking intensities. The findings showed that predicted site response is more site-sensitive to the selected Vs model. Surface acceleration increased from 0.20 to 0.35 g, 0.4 to 0.7 g, 0.7 to 1.2 g, and 1 to 1.5 g for 0.10 g, 0.16 g, 0.28 g, and 0.41 g input motion, respectively. Computed amplification ratios varied across the study area, ranging from 1.0 to 5.1. Peak spectral acceleration (PSA) showed substantial spatial variability and increased with shaking intensity, depending on site conditions, input motion, and Vs representation. PSA values ranged from 0.3681 to 9.5938 g under input PGA values of 0.10–0.41 g, indicating significant resonance induced amplification despite moderate earthquake shaking. MASW based profiles tended to predict higher amplification and spectral acceleration values at several locations for moderate to strong shaking, as they were able to represent local subsurface heterogeneity and near-surface variability. Empirical correlation based profiles tend to underestimate PSA values, while Vs30 performs reasonably for low PGA but fails to reflect site-specific heterogeneity at higher PGA. The results can provide essential guidance for microzonation, seismic hazard assessment, and earthquake-resilient urban planning in Jamshedpur. The site specific ground response of Jamshedpur was assessed by equivalent linear ground response analysis utilizing three distinct shear wave velocity (Vs) models obtained from MASW method, shear wave velocity (Vs) and SPT-N correlations, and Vs30. MASW based Vs profiles yield higher and more site-sensitive PSA values, especially at medium to strong shaking levels, because they able to represent local subsurface heterogeneity and near-surface variability. The results obtained from Empirical correlation based Vs profiles underestimate PSA due to their unrealistically stiff velocity structure, while Vs30 based spectra perform reasonably at low PGA but misrepresent site-specific heterogeneity and tend to overestimate amplification at higher PGA. Comparison with the IS 1893 (2016) design spectra indicates that the codal plateau value of 2.5 g may underestimate seismic demand at several locations, particularly for short-period, low-rise, and stiff structures due to local site amplification. The study highlights considerable variation in ground response parameters across Jamshedpur, emphasizing the importance of detailed subsurface investigation in the area for seismic microzonation and earthquake resilient structures. The site specific ground response of Jamshedpur was assessed by equivalent linear ground response analysis utilizing three distinct shear wave velocity (Vs) models obtained from MASW method, shear wave velocity (Vs) and SPT-N correlations, and Vs30. MASW based Vs profiles yield higher and more site-sensitive PSA values, especially at medium to strong shaking levels, because they able to represent local subsurface heterogeneity and near-surface variability. The results obtained from Empirical correlation based Vs profiles underestimate PSA due to their unrealistically stiff velocity structure, while Vs30 based spectra perform reasonably at low PGA but misrepresent site-specific heterogeneity and tend to overestimate amplification at higher PGA. Comparison with the IS 1893 (2016) design spectra indicates that the codal plateau value of 2.5 g may underestimate seismic demand at several locations, particularly for short-period, low-rise, and stiff structures due to local site amplification. The study highlights considerable variation in ground response parameters across Jamshedpur, emphasizing the importance of detailed subsurface investigation in the area for seismic microzonation and earthquake resilient structures.