Evaluation of site amplification factors for shallow rock sites of Islamabad, Pakistan.

Abstract

Current seismic provisions in Building Code of Pakistan (BCP-2007), seismic site classifications, and corresponding site amplification factors were determined similar to Uniform Building Code (UBC-1997), which were based on the local site conditions of Western United States with low impedance contrast, deep sites, and high seismicity conditions. The use of these deep sites based amplification factors to the shallow sites may not be appropriate to capture shallow sites' response. In this study, we performed a non-linear site-specific response analysis suite to compute the amplification factors for the six (06) representative shallow bedrock sites of Islamabad, Pakistan. The computed amplification factors are compared with BCP-2007 code-based design estimates; it is found that BCP-2007 code-based guidelines underestimate amplification factors at a short period whereas overestimating at an extended period. The study's findings highlight the potential implications of current code-based amplification factors for Islamabad's shallow sites and suggest improving the current seismic guidelines.