Seismic Microzonation of the Peshawar Metropolitan Area, Pakistan, Based on One-Dimensional Nonlinear Site Response Analysis

Seismic resilient design of infrastructure is crucial in active regions. The infrastructure development of Pakistan is based on the Building Code of Pakistan (BCP-2007), which is based on the Uniform Building Code (UBC-1997). The UBC is further based on deep soil conditions in the western United States, which have low impedance contrast and high seismic conditions. Applying foreign seismic criteria can give in the determination of results that deviate from the target area's actual geotechnical and geological ground conditions, as these conditions vary from place to place. This study adapts a simple yet more precise technique of nonlinear site-specific seismic response analysis for designing seismic resilient structures rather than relying on the results which are based on the Peak Ground Acceleration only. Site-specific seismic amplification factors were calculated using Geographic Information System and a geotechnical engineering dataset of 42 standard penetration test in the metropolitan area of Peshawar City, Pakistan. Shear wave velocities (Vs) were calculated using 50 SPTN-VS correlations, and the results were validated using the available in situ measurements of shear wave velocity data. Furthermore, the average shear wave velocity (VSZ) and shear wave velocity up to 30m (VS30) were calculated, and sub-site classification of the study area was developed for microzonation. The General Quadratic/Hyperbolic (GQ/H) model was used, and a non-linear one-dimensional analysis of sixteen shallow sub-site profiles under twenty (20) ground motions had been carried out using DEEPSOIL software. The resulting site-specific amplification factors were compared with the suggested values from the BCP. It was found that BCP overestimates short-period amplification factors (Fa) for 12 profiles and long-period amplification factors (Fv) for all 16 proposed profiles. This study proposes site-specific GIS-based maps for the bedrock depth, National Earthquake Hazards Reduction Program site classes, short-period amplification factors (Fa) and long-period amplification factors (Fv), which will eventually enhance economic and safety aspects of the future infrastructure designs at the understudy region.