Evaluation of site-specific characteristics using microtremor measurements in the Gorakhpur city of Uttar Pradesh, India

Abstract

The microtremor measurements are carried out in and around the Gorakhpur city (Uttar Pradesh), India, overlain by alluvium at about 150 sites to understand the local site conditions. Horizontal-to-vertical spectral ratio (HVSR) confirms that the majority of sites have a predominant frequency of ~0.45 Hz, which may suggest the prevalence of thick soft sediments in the area. Conspicuously, a number of multiple peaks in HVSR curves at few sites may reflect the presence of different interfaces with significant impedance contrasts. Maximum amplification is observed of 4.0–5.3 to the NW–SE of the city, whilst few sites in the city are found to be associated with different values of peak amplification factor that varied between 2.0 and 4.0. It is also observed that the ground vulnerability index (Kg) in Gorakhpur city has values higher than 10.0 at most of the sites. Assimilation of 1-D velocity model for the city clearly shows that low shear wave velocity (~300 m/s) down to the depth of ~35 m, suggesting thick piles of sediments that may correspond to fluvial river system in the area, whilst the peak frequency of about 0.45 Hz may correspond to the Quaternary–Tertiary sediment boundary that may exist at deeper layers (~1000 m). The inference of this study may be used as inputs for earthquake risk management by reducing the severity of earthquake shaking through design of earthquake risk resilient structures. © 2021, Indian Academy of Sciences.