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Resonance frequency as a proxy for vulnerability as well as hazard assessment in the context of recent 6.4 Assam earthquake
  • Rajib Biswas,
  • Nilutpal Bora,
  • Debraj Bailung Sonowal
Rajib Biswas
Tezpur University

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Nilutpal Bora
IIT, Guwahati
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Debraj Bailung Sonowal
Tezpur University
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Abstract

We report here a preliminary investigation on site effects in a highly populated zone of academic importance. The study area is mostly characterized by its alluvial sediments. Due to its rapid development with construction of high-rise buildings and presence of active Kopili fault nearby, the site effects analysis in this area has become very crucial which is further fueled by a strongly felt earthquake of 6.4 M occurring recently; whose epicenter was just 40 Km away from this study area. Accordingly, an attempt is made to assess site related parameters by accruing ambient vibration records at 16 single stations covering. Via horizontal to vertical spectral ratio (HVSR) analysis, we estimate the resonant frequencies. Likewise, we compute the HVSR amplification values. Apart from this, liquefaction vulnerability indices were estimated for the study region. With a fair corroboration with borehole data, the findings reveal a low velocity zone. The heterogenous distribution of resonant frequencies and assorted amplification implicate a varying overburden thickness; thereby augmenting the Kg values at certain places. In the context of the recent 6.4 M earthquake, the results are poised to play a pivotal role so far hazard mitigation is concerned.