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.