Integrated Earthquake Risk Assessment Using PSHA-Based Microzonation and Soil Vulnerability Index Maps of Urban Kathmandu Valley

The Kathmandu Valley, located in a seismically active region, has a long history of enduring significant earthquakes. Despite existing efforts, previous studies often lack comprehensive integration of seismic hazard data with vulnerability assessment, which is crucial for detailed earthquake risk evaluations. This study develops a comprehensive seismic risk assessment by integrating probabilistic seismic hazard analysis (PSHA) and soil vulnerability index map using Arc GIS. The PSHA, conducted with the R-CRISIS tool, estimates peak ground acceleration (PGA) across the region, while the soil vulnerability index is derived from nonlinear ground response analysis using DEEPSOIL. The seismic hazard analysis, reveals maximum peak ground accelerations (PGA) ranging from 0.345 g to 0.382 g over 50 years at a 10% probability of exceedance, corresponding to a return period of 475 years. The soil vulnerability index extending from 0.21 to 21.72, is applied here to assess the risk. Among the metropolitan cities and municipalities, Madhyapur Thimi emerged as the safest area, with 99.38% of its region classified as low-risk, while Shankharapur municipality was identified as the most vulnerable, with 88.01% of its area classified as high-risk. This study provides critical insights for seismic risk assessment in the Kathmandu Valley; however, further research should consider dynamic land use and urban development changes to continually refine and update these assessments.