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Ziarat Earthquake, October 2008

The Ziarat earthquake of October 2008 has been reported widely in the print and electronic media when on 29th October 2008, in Pishin and Ziarat District, 80 km NE of Quetta unusual pair of Mw=6.4 earthquakes occurred. The first tremor struck at 4:09 am local time (23:09 GMT) at a depth of 15 kilometer while the second one jolted the area at 5:35pm. The affected region is the mountainous area and extends from Ziarat to Pishin (Figure 4A). 300 people were killed by landslides and by the collapsing adobe structures. In the Ziarat District the villages of Warchum, Wam, Kala China, Kawas, Ahmadun, Gogai, Tangai, Spezanda were worst hit while in the Pishin District villages of Khushab, Balozia, Khanozai, Rodh Malazia and in the Harnai District the area of Zardalu suffered. Geology of the Ziarat, Gogai area The area is part of the Suleiman Fold Belt, which consists of sedimentary rocks of Jurassic to Pleistocene age. The exposed rocks in the aera (Fig. 2 and 3) are: the Parh group (Cretaceous), Bibai Formation (upper Cretaceous), Dungan Formation (Paleocene), Ghazij Formation (Eocene), including Nagri Formation, and the Dhok Pathan Formation (Miocene) of the Siwalik group. Tectonics of the area The Ziarat-Gogai area lies on the western margin of the Indian plate. Two major tectonic features can be traced on the surface: the Bibai nappe and Gogai nappe (Kazmi, 1979). The Bibai and Gogai nappes represent the southern boundary of the Muslimbagh Ophiolites (Fig. 4A). The Bibai nappe is situated in the Ziarat valley. The Ghazij Formation (Eocene) is overlain by the older rocks of Parh group (Cretaceous). The contact between these two formations is marked by thrust fault which is called Bibai thrust (Figure 2). The Bibai thrust fault can be traced eastward to Kach, Ahmadun, and Spera Ragha. No movement was detected following inspection of this thrust fault. The Gogai nappe is located in the Saro syncline, northeast of Ahmadun, adjacent to Gogai Village. The Bibai Formation and Dungan Limestone are exposed along the outer margin of the syncline. Earthquakes 29th October, 2008 The earthquake area falls in the Sulaiman Fold and Thrust belt, a region where geologically the younger rocks of Miocene and Pleistocene (Nagri, Dhock Pattan and Bostan Formations sedimentary rocks) have been folded and squeezed by forces associated with India-Eurasia collision. The earthquakes are located 80 km east of the Chaman fault, which is a major left lateral strike slip fault system. The two M6.4 main shocks occurred on 29th November 2008, in Pishin and Ziarat District, 70 km NE of Quetta. The first tremor struck at 4:09 am local time (23:09 GMT) at a depth of 15 kilometer while the second one jolted area at 5:35pm. The earthquakes appear to have occurred on a N60E fault that slipped 1.5 m right-laterally, and although it is shallow, no surface faulting has yet been observed.