Seismic Hazard Analysis of Pakistan

Abstract

This study is focused on the seismic hazard analysis of Pakistan with special emphasis on the development of input parameters. Initially, comprehensive catalogues of both historically reported and instrumentally recorded earthquakes of Pakistan was prepared using a wide range of data sources. Quality of the instrumental earthquake catalogue was assessed by the magnitude of completeness (Mc) using different methodologies, and Stepp’s methodology was found the most adequate. The attenuation relationships were derived by carrying out multiple regression analysis of the macro-seismic and strong motion data. Predicted values of peak ground acceleration (PGA) from these relationships were found in conformity with the observed values of PGA. However, proposed attenuation models somewhat overestimated PGA values in near field region for larger earthquakes (Mw > 7.0). It may be either due to the site nonlinearity effects resulting from high intensity of ground shaking or owe to the factors like geology of the area, fault type, directivity of the fault rupture and other source parameters. A comparison of PGA values assimilated by using Next Generation Attenuation relationships (NGAs) and newly developed attenuation models with the observed values also showed a close proximity, which demonstrates the robustness and applicability of these relations for a wide range of earthquakes. Seismo-tectonic model considering more than 50 faults and 18 seismic source zones provided a future reference for any seismic hazard studies concerning the study area. Deterministic seismic hazard assessment (DSHA) of federal capital and four provincial capitals revealed that Quetta (PGA = 0.35g, vmax = 45cm/sec) was more susceptible to seismic hazard than other cities as Quetta lies near to Chaman Fault, which demonstrated a maximum magnitude potential value of 8.3. Whereas Lahore, capital of the Punjab province, was found to be the least prone to earthquake hazard. Probabilistic seismic hazard assessment (PSHA) of these cities, and on 0.1o x 0.1o grid for 2%, 5% and 10% probability of exceedance in 50, 100 and 250 years in terms of total hazard curves, uniform hazard spectra and seismic hazard maps provided basis for future structural design and analysis. PSHA results also complemented the DSHA results showing Quetta as the most vulnerable to earthquakes. The seismic hazard maps, however, stressed the need to investigate some regions like Quetta and Muzaffarabad- Balakot areas in detail. The design response spectra (DRS) and compatible time histories were also developed for these cities of Pakistan in order to better design and analyze the future and existing structures. Among the methods used for the construction of DRS, the Newmark & Hall method was found the least conservative and International Building Code (IBC) the highest conservative. However, Building Code of Pakistan (BCP) yielded the intermediate values. The spectral acceleration values and PGA values derived from DRS compatible time histories were highest for the Quetta city.