Browsing by Author "Yadav, Pawan Kumar"

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    Evaluation of site-specific characteristics using microtremor measurements in the Gorakhpur city of Uttar Pradesh, India
    (Springer, 2021) Shankar, Uma; Yadav, Pawan Kumar; Singh, A.P.; Gupta, Arun Kumar
    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.
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    Microtremor measurements in the India's holy city, Varanasi for assessment of site characteristics
    (Elsevier Ltd, 2021) Shankar, Uma; Kumari, Sangeeta; Yadav, Pawan Kumar; Singh, A.P.; Gupta, Arun Kumar
    Microtremor measurements are used for preliminary site effect of the Quaternary sediments of Varanasi in Indo-Gangatic plain, which is being planned as a Smart City of India. We evaluated site effects using single and arrays Microtremor measurements at various sites in the Varanasi City, Uttar Pradesh, India. At City, H/V spectral ratios using microtremor measurements indicate fundamental frequency range 0.37�0.63 Hz, corresponds amplification 5 to 14 times. This indicates that the deep thickness of the upper soft soil at about several hundreds of meters. Such huge amount of sediments deposition sources could be associated with fluvial rivers system in the area and sediment drain from Himalaya. The average peak frequency (~0.5) may reflect the Quaternary-Tertiary boundary. Microtremor array measurements at two sites were taken using circular arrays (30 and 60 m) which consists of three recording stations on the circumference of circle and one in the centre of circle. The Phase velocity dispersion of Rayleigh wave is calculated from array using SPAC method, and a 1-D shear wave velocity structure is determined by means of inversion processes. The top layers up to 50 m show shear velocities between 280 and 320 m/s and the velocities of underneath layer vary between 1500 and 1600 m/s till 100 m of depth. These results from the present study would be useful for future planning purposes as well as risk management and to reduce severity of earthquake effects in the study area. � 2021 Elsevier Ltd and INQUA
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    Site Characterization for Seismic Hazard Analysis in Gorakhpur City Using Shear Wave Velocity (Vs) from Ambient Noise Measurements
    (Springer, 2023) Yadav, Pawan Kumar; Shankar, Uma
    The Gorakhpur city experienced several high-intensity tremors because of ongoing seismic activities in the Himalayan region. Therefore, the characterization of its subsurface is crucial for a better assessment of the seismic hazards. Ambient noise measurements at 360 sites single-station and four array sites show the predominant frequency peak varies between 0.434 to 1.02�Hz from horizontal-to-vertical spectral ratio (HVSR) analysis and amplitude increasing toward the north with maximum amplification is 4.81. The structure of the shallow soft soil has been observed by frequency wavenumber (F�K) analysis. Joint inversion of the HVSR and Rayleigh wave dispersion curves reveals three layers of soft, dense and stiff soil sediments of varying thickness. The shear wave velocity (Vs) of the sediment varies between 280 to 1200�m/s from top soil to 100�m subsurface depth. The observed Vs models correspond to soil classifications ranging from soft soil to very dense soil and rock. � 2023, The Author(s), under exclusive licence to Indian Geotechnical Society.