Seismic Site Characterization of Rajasthan, India with special emphasis on Seismic Hazard Microzonation study for few major populated cities

Rajasthan, in northwestern India, lies within the Western Indian Shield's tectonic block. The state's landscape is dominated by the extensive Thar desert with diverse sand dunes, alluvial deposits, and areas featuring felsic lava flows, granitic plutons, and mafic lavas. The Aravalli range extends northeast-southwest, subducting beneath the Himalayan arc, marked by numerous parallel active faults. In the southwest, the Cambay Graben forms a rift zone with steep faults, and the north-south trending Konoi Fault at Jaisalmer is linked to intraplate seismicity. Although, Rajasthan is not classified as a high to very high-risk zone according to Bureau of Indian Standards, the emergence of unconventional seismic sources, such as induced seismicity related to anthropogenic activities like mining and reservoir-induced seismicity, underscores the evolving nature of seismic risks. The surrounding region of the state jolted time and again by several devastating earthquakes viz. 1935 Quetta earthquake of M_w 7.7 in Pakistan, 2001 Bhuj earthquake of M_w 7.6 in Gujrat and 1938 Satpura-valley earthquake of M_w 6.2 in Madhya Pradesh with MM Intensities ranging between V–VIII. Moreover, Rajasthan's increasing urbanization and infrastructure development necessitate a thorough assessment of surface-level seismic hazard in the area to safeguard lives, property, and critical infrastructure. By considering seismicity patterns, fault networks, and similarities in focal mechanisms, 12 areal seismogenic sources and additional active tectonic features were identified across various hypocentral depth ranges (0–25 km, 25–70 km and 70–180 km), and utilizing 15 Ground Motion Prediction Equations, including 6 Site-specific Next-Generation Spectral Attenuation models specific to West Central Himalaya, Kutch Region, and Central India tectonic provinces, yielded probabilistic Peak Ground Acceleration (PGA) at engineering bedrock ranging from 0.08 to 0.42 g. A exhaustive geophysical and geotechnical field investigations at 600 sites have been carried out to determine the effective shear wave velocity, ranging from 223 to 956 m/s, leading to the classification of the region into nine site classes: D4, D3, D2, D1, C4, C3, C2, C1, and B. Systematic 2D non-linear site response analysis has been performed using “PLAXIS 2D” and subsequently convolution of absolute site amplification factor with PGA on firm rock condition resulted in a surface-consistent hazard ranging from 0.10 to 0.68 g. A comprehensive seismic hazard microzonation study have also been presented for four major cities, namely Jaipur, Jaisalmer, Jodhpur, and Udaipur, taking into account their significant population and cultural heritage. The findings from this study will be crucial for earthquake hazard and risk assessments of the region.