| Abstract |
Abstract: The Indo-Gangetic basin is tectonically active, geologically complex, and geomorphologically diversified and has experienced major earthquakes over time in its stretch. This active megalopolis region lacks comprehensive seismic and geotechnical investigations. This study provides a correlation of topographic slope and shear wave velocity, utilizing a region-specific Vs30 model derived from joint modelling of Horizontal-to-Vertical Spectral Ratio (HVSR) and dispersion curves. Shuttle Radar Topography Mission (SRTM30) is considered to generate a new set of topographic-slope coefficients. The region predominantly corresponds to site Class D, as per NEHRP classification. The regional model provides a more accurate representation of seismic site conditions compared to the global model, which tends to overgeneralize and lacks site-specific setting. Seismic hazard maps generated for the Gorkha–Nepal Earthquake (2015) and Nepal–Bihar Earthquake (1934) scenarios show elevated risk in the northeastern region of southern Bihar. For the 2015 scenario, PGA (Peak Ground Acceleration) values in the high-risk eastern area range from 0.06 to 0.084 g, while the 1934 scenario shows values from 0.10 to 0.145 g. Spectral acceleration values at 0.2 and 1-sec periods also confirm greater ground motion potential in the eastern part, particularly around Patna and Nalanda. These findings provide critical insights for organizations such as National Disaster Management Authority of India (NDMA) and Geological Survey of India (GSI), helping to inform earthquake-resistant design, urban planning, and infrastructure development to improve resilience against future earthquakes in southern Bihar. Research highlights: This study emphasizes the importance of reliable, region-specific shear wave velocity (Vs30) data in assessing seismic hazards and classifying sites in southern Bihar. Several factors influence seismic hazard assessment, depending on soil conditions. Reliable, region-specific Vs30 (shear wave velocity) data is critical for seismic hazard assessment and site classification in southern Bihar. Soil conditions and subsurface features significantly impact seismic wave amplification. Development of a proxy-based Vs30 model regionalized to southern Bihar. Combines Horizontal-to-Vertical Spectral Ratio (HVSR) and surface wave dispersion curves for precise subsurface characterization. Regional Vs30 data from joint modeling improved seismic site classifications compared to global models. Significant differences were observed between the proposed regional model and the global model by Wald and Allen (2007). Regional model showed smaller residuals and better alignment with observed values. Demonstrates the effectiveness of combining HVSR, surface wave dispersion, and topographic slope analysis for localized Vs30 estimation. This research provides valuable insights for organizations such as the National Disaster Management Authority (NDMA) and the Geological Survey of India (GSI), which can use the data to inform earthquake-resistant design, smart city planning for Varanasi, Patna and Bihar Sharif highlighted by the Government of India’s Smart Cities Mission (SCM) initiatives, and major construction projects in Kaimur (Bhabua), Bhojpur, Buxar, Jehanabad, Rohtas significantly for southern Bihar. The study underscores the effectiveness of combining HVSR, surface wave dispersion, and topographic slope analysis for localized Vs30 estimation, ensuring a more reliable seismic hazard evaluation framework. © Indian Academy of Sciences 2025. |
