DETERMINATION OF SHEAR WAVE VELOCITY PROFILE OF BASIN SEDIMENT OF BHAKTAPUR USING AMBIENT VIBRATION

Abstract

Microtremors, often referred to as microseismic vibrations, are prevalent, weak, and low-amplitude oscillations that can be detected on the Earth's surface. Microtremor survey Method (MSM) at different sites of four municipalities of Bhaktapur district were performed to determine the shear wave velocity of the subsurface structure. Horizontal to Vertical Spectral ratio (HVSR) technique was employed to evaluate the predominant frequency of the ground using the collected ambient vibration data and found that frequencies ranges from 0.214 Hz to 7.81 Hz. Inversion of the observed spectral ratio was performed using an inversion algorithm to estimate the shear wave velocity profile and sediment depth of the selected sites which were validated from previous studies. Sediments depth in Bhaktapur and Madhyapur Thimi are found to be higher than Suryabinayak and Changurayan. The previously available underground structure was tuned from the generated output of this study and the output subsurface structure was used for preparation of 2D Fence diagram. 2D fence diagram of Bhaktapur Municipality was also developed in west-east direction and compared with previous study.