Seismic Microzonation of Kathmandu Valley: Integration of Borehole Data, Microtremor Survey, and Numerical Evaluation

Abstract

This Kathmandu Valley by integrating borehole data, microtremor survey results, and numerical evaluation techniques to assess soil liquefaction potential. Microtremor measurements were collected from 75 stations throughout the valley, and the vulnerability index (K_g) was calculated using Nakamura’s method, which factors in fundamental frequency and amplification characteristics. The resulting K_g values ranged from 0.091 to 13.463, highlighting the varying liquefaction risk across the valley. Borehole data from 29 excavation sites were used to validate the liquefaction potential, and a threshold K_g value was established in alignment with prior research benchmarks. Numerical evaluation through finite element modeling (FEM) using PLAXIS-2D was performed to further assess liquefaction susceptibility. The FEM analysis confirmed areas with a K_g value greater than 5 as highly vulnerable to liquefaction, while other regions exhibited low susceptibility. Liquefaction susceptibility maps identified critical high-risk zones, particularly in Kathmandu, including areas near Kantipath, Maitighar, and Teku, as well as in Lalitpur and Bhaktapur, such as near Chakupat, Patan Durbar Square, and Bhaktapur Durbar Square. This study demonstrates that integrating microtremor survey data, borehole information, and numerical analysis offers a comprehensive, reliable approach for seismic microzonation and liquefaction risk assessment in earthquake-prone regions like Kathmandu Valley.