Analysis of Quetta-Ziarat earthquake of 29 October 2008 in Pakistan

An earthquake of magnitude 6.5 Mb occurred on 29 October 2008 near Chiltan hills, Balochistan Province, in Pakistan with a foreshock of magnitude 5.0 Mb. Depths of events were 15 and 12 km, respectively. The intensity of the mainshock was VIII in and around the Ziarat–Pashin areas while the Peak Ground Acceleration recorded at Quetta area (60 km from the epicenter) was 0.17 m/s2 (horizontal component) and 0.06 m/s2 (vertical component). For this study, 1,185 aftershocks ranging from 2.2 to 4.8 Mb were recorded till end of January 2009 using four portable instruments (1 s) installed in a radius of 40 km around the epicenter. As no surface rupture was found, the source mechanism and aftershocks were only tools for finding fault dimensions. The source mechanism was found to be strike slip for both events, and aftershock trend was NW–SE suggesting the strike slip nature of the fault. These results disagreed with the existing description of the fault system in the area which was previously thought to be thrust in nature.