Ambient Noise HIV Spectral Ratio for Site Effect Estimation in Some Parts of the Greater Accra Region, Ghana.

Abstract

The soils in the Greater Accra Metropolitan Area (GAMA) soils have complex lithologies with varying spatial distribution mainly owing to bedrock, drainage, and topography. They are characterized by silty-sandy clays, heavy clays, and fine to coarse sand mostly in lower elevations, which grade to a range of gravely or highly quarzitic cobbly lateritic soils on higher grounds. The region is active seismically and has a history of earthquakes with destructive intensities occurring both recently and in the past. The recent surge in urbanization has made it possible to analyze and understand site effects in the region. The site effect plays a crucial role in planning and developing earthquake-resistant constructions as well as in estimating the damage caused by earthquakes. It is for this reason that the horizontal-to-vertical spectral ratio analysis has been used on ambient noise recorded in 13 sites in the region. Important site specific parameters such as the fundamental frequency, 𝑓0, of soft sediments and its corresponding amplification factor,𝐴0, alluvium thickness,𝐻0 and the soil vulnerability index,𝐾𝑔, have been estimated for the sites. The fundamental site frequency for the study area ranged between 0.73 𝐻𝑧 to 11.00 𝐻𝑧 with their corresponding amplification factor also ranging from 1.6 to 10.0. The alluvium thickness ranged between 2.61 𝑚 to 175.75 𝑚. The seismic vulnerability index which represents the likelihood of liquefaction ranged from 0.37 to 20.00. Tesano PS site appears to be the most vulnerable to earthquake destruction and liquefaction.