Imaging the Basement Topography of the Kathmandu Basin, Central Nepal: A Passive Seismological Approach

Abstract

This study presents extensive data on resonance frequency, velocity structure and deep borehole data to explore the basement topography of the Kathmandu Basin. The fundamental resonance frequency across the basin varies from approximately 0.20 Hz to 8 Hz, with the lowest value occurring in the central region. The resulting basement map reveals two broad (~2.5 km wide) and deep (300–600 m) troughs extending southward from the north and merging in the basin’s center to form a major depression exceeding 600 m in depth. The study also identifies detailed geomorphic features, including partially exposed and buried ridges, deep paleo-river channels, and isolated hillocks within the basin. Variations in shear-wave velocity and the presence of deep basin structures likely contributed to the prolonged and amplified long-period ground motions that damaged tall buildings during the 2015 earthquake.