A comparative statistical analysis of equivalent linear and nonlinear site response in the Kathmandu Valley, Nepal

This study presents a comparative assessment of equivalent linear (EL) and nonlinear (NL) site response analyses for the Kathmandu Valley, Nepal, using DEEPSOILTM based on borehole data from multiple locations and seismic input motions focusing on two significant events: the Gorkha (Mw 7.8, 25 April 2015) and Kobe, Japan (Mw 6.9, 17 January 1995) earthquakes. A statistical analysis, including Pearson correlation, normality tests, t-tests, and Mann-Whitney U tests, was conducted using MATLAB to examine the relationship between peak ground acceleration (PGA) and displacement under EL and NL conditions. Results show that the NL analysis better captures soil nonlinearity. The Gorkha NL case showed a strong inverse correlation (slope = –20.195, p = 0), indicating significant displacement reduction with increasing PGA. EL cases, in contrast, exhibited weaker trends, often overestimating. Boxplots further confirmed significant differences in PGA and displacement between events, especially under EL conditions. These findings highlight the critical importance of incorporating NL site response analysis in seismic hazard assessments. The Gorkha NL results reveal that NL models can reduce predicted displacement by more than 50% compared to EL models. This has direct implications for infrastructure resilience in earthquake-prone regions like the Kathmandu Valley, where site-specific NL analysis is essential for accurate seismic design and safety evaluation.