Seismic Site Response under Variable Shear Wave Velocity Inputs: Application to Jamshedpur, India

Local site conditions influence earthquake ground motions, mostly due to changes in subsurface characteristics and soil stiffness. The vertical propagation of shear waves is influenced by these parameters, which impact the amplification of ground motions. To understand these effects for Jamshedpur city, this study performed a one-dimensional equivalent linear ground response analysis for three distinct shear wave velocity inputs: Vs profiles obtained from the MASW test, Vs profiles obtained from established correlations between Vs and SPT-N values, and the mean shear wave velocity measured for the top 30 meters of ground (Vs30). Subsurface characterization was carried out at 15 locations through MASW testing and borehole investigations. The soil and rock profile for 15 representative boreholes has been evaluated. The mean Vs for the upper 30 m depth are used to categorize and describe these sites according to NEHRP seismic site categorization, and the majority of sites fall in seismic site class C, and 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 show that shear wave velocity is the primary factor governing surface motion in the region. MASW based profiles provide higher and more reliable spectral acceleration estimates, particularly for moderate to strong shaking, as they capture real stratification and near-surface variability. Empirical correlation based profiles tend to underestimate peak spectral acceleration, 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.