Estimation of ground response and local site effects for Vishakhapatnam, India

Ground motion intensity due to an earthquake changes as it disseminates through the soil media from bedrock to the surface. As the ground motion intensity and damage levels mainly depend upon the local site conditions, it is mandatory to carry out the detailed site-specific hazard studies to assure safety of the structure against seismic risk. In this research paper, an effort has been made to estimate seismic hazard associated with the city of Vishakhapatnam. The city lies in east coast region of southern India and falls under seismic zone II (IS 1893-2016 in Criteria for earthquake-resistant design of structures: part 1—general provisions and buildings, Bureau of Indian Standards, New Delhi, 2016). Seismic activity in the Eastern Ghats mobile belt region has increased due to subduction of Burma plate toward the Bay of Bengal, which resulted in activation of inactive faults and new fault development in the region. Therefore, increasing seismic risk and importance of the study area has motivated the researchers to carry out probabilistic seismic hazard assessment and estimation of local site effects using ground response analysis and microtremor testing. From the results, hazard maps were generated in terms of peak ground acceleration (surface, bedrock level), H/V frequency and H/V amplitude. The seismic hazard parameters, uniform hazard response spectrum and hazards curves from probabilistic seismic hazard assessment are further useful in design and construction of prominent structures. The peak ground acceleration at surface and bedrock, predominant frequency and H/V amplitude indicate the variation in local site conditions and will be of great help in seismic design of structures as well as retrofitting of the existing structures to withstand against seismic hazards. Hazard maps from the study will be helpful in further seismic microzonation studies and also identifying zones of potential seismic risk.