Critical Evaluation and Estimation of Shear Wave Structure and Horizontal to Vertical Spectral Ratio at Different Sites in Kathmandu Valley

The present study was conducted to determine the resonant frequency of the soil and to classify the subsurface soil based on the structure of the shear wave velocity. Five sites have been chosen for this reason, such as Pulchowk, Chhauni, Gaushala, Buddhanagar and Bhainsepati. Approximately 20 data were collected at each location, and then the structure of shear wave velocity and graph of amplification ratio with their spatial distribution were generated using software, i.e. Seisimager / Controller for Seismodule. The outcomes of both methods of study were then compared to the Gorkha Earthquake and borehole data amplitude. All these data and studies show that the sediments of the Kathmandu Valley depend on the frequency of the seismic waves, and in the peripheral area the wave velocity is greater than in the central part of the Valley. The outcome has also shown the silty-sand presence, Devastation is caused by clay and loose gravel soil with poor bearing capacity and elastic modulus at most of the sites. It was also noted that a non-intrusive microtremor analysis can be adopted for earthquake site characterization in the Kathmandu Valley, apart from a few limitations, which can be easily extended and expanded for Kathmandu in future seismic hazard and microzonation efforts. For most of the sites, the low velocity model is due to the presence of soft soil in that region that is responsible for most of the sites’ destruction. The findings have also shown that in the peripheral area, the parametric values of ground motion are greater than in the central part of the valley.

Author (s) Details

Mrs. Srijana Poudel
Central Department of Geology, Tribhuvan University, Kathmandu, Nepal.

Dr. Subesh Ghimire
Central Department of Geology, Tribhuvan University, Kathmandu, Nepal.

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