Evaluation of seismicity of Karachi city in the context of modern building codes

Abstract

Spectral acceleration is representative of seismic hazard in modern building codes as well as an important parameter used in seismic design these days. Karachi, an economic artery of Pakistan, is located in the vicinity of an active tectonic setting, i.e., triple junction, with uncertain seismicity. Keeping in view the modern seismic design practices, efforts are required to evaluate the seismic hazard of Karachi city in terms of spectral acceleration. This study is focused on the estimation of seismic hazard for the metropolitan city of Karachi in the context of modern building codes. The seismic potential of around 800–900-km circle was considered a threat for the city, and 13 seismic zones (A-1 to A-13) were identified as seismic sources. A seismicity model based on Gutenberg-Richter law was developed, identifying A-1 and A-11 as zones of high seismicity. The ground attenuation model recommended for the Middle East region proposed by Akkar and Bommer was utilized for the computation of different ground motion scenarios. Short-period, SS, and 1-s, S1, spectral acceleration values for considered region were calculated as 1.37 m/s2 and 0.41 m/s2, respectively. In addition, peak ground acceleration (PGA) values for Karachi city were observed to be in a range of 0.7–0.77 m/s2. The results of this study provide bases for the preparation of seismic risk maps, the estimation of earthquake insurance premiums, seismic zonation for region lying on Arabian and Indian plates, and the preliminary site evaluation of critical facilities.