Khadim’s Quetta

Surface rupture near Zardaaloo (Shahrigh) in the Ghazij Formation.

Din Mohammed Kakar

The following report is not an exhaustive and conclusive one; many technical details have been withheld to keep it simple and readable. However, the usage of geological terminology was not totally avoidable. Moreover, data gathered during the field trips, subsequent to the October earthquake, will be published in a relevant scientific journal at an appropriate time. It’s worth mentioning here that following the October earthquake I spent about a month in the affected areas, monitoring after-slip and direction of stress development, and, collected GPS data from Chaman to Harnai, Sanjavi, Qilla Saifullah and Muslimbagh.

Introduction

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.

Figure 1. Ziarat Pishin Intensity map showing mapped shaking intensity based partly on intensities observed by the University of Baluchistan field study team. The highest intensities in the epicentral region correspond to Intensity VIII. (courtesy of Stacey Martin, University of New Zealand).

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.

Figure 2. Shows the rocks exposed in Ziarat Valley: Dungan Limestone, Ghazij Formation, Parh Group & Bibai Volcanics.

Figure 3. In the Gogai valley Parh limestone, Goru Formation, Ghazij Formation and Dungan Limestone are exposed.

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.

Figure 4A. Geological Map of Ziarat-Pishin and Harnai area. The black stars show epicenters of the main shocks and aftershocks. A number of mapped NW trending faults are evident that are parallel to the inferred causal fault that slipped in the two M6.4 main shocks but no surface slip could be identified on the ground. The black squares are the locations of the nearest GPS points.

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.

Figure 4B.A satellite Image of the earthquake hit areas, showing main villages and the two major events.

Figure 5.  Shows the strike-slip focal mechanisms of the two main shocks with epicenters at Khanozai and Gogai areas, some aftershocks being in the northeastern side of the two main shocks. It also show the co-seismic slip vectors of the two nearest GPS points in the Kach and Surkhab Valley. The dashed black line joining the two points is the inferred fault that ruptured in a dextral sense at possibly 5-15 km depth. Future inSAR scenes may elucidate the precise location of the fault that slipped.

Global Positioning System (GPS)

GPS is Satellite based technology, measuring three components Latitude, longitude and altitude. GPS receivers use satellites to triangulate distances of ground based positions to millimeter accuracy. Repeated measurements of the same points provide a measure of displacements resulting from tectonic motions. We installed a continuous operating receiver in the grounds of the University of Balochistan in 2006. GPS measurements  reveal a SW motion of Quetta region relative to the Indian Plate at approximately 7 mm/yr. We also installed 12 chains of control points between Chaman and Harnai, six of which were measured at least once before the earthquakes.

Figure 6. GPS points with velocity vectors prior to the earthquake superimposed on the morphology of the region. The epicenters of the earthquakes (with their GMT dates) occurred north-east of Kach. The earthquakes were strike slip with a right lateral sense of motion and occurred below the cover of surface geology.

The observed signal suggests that as much as 75% of the sinistral shear signal at the plate boundary remains west of Quetta suggesting that other prominent strike slip faults are vulnerable to future slip. The present study not only confirms that the region continues to be seismically active but that the region vulnerable to future earthquakes extends throughout the thrust and fold belt.

Figure 7. A rupture of 60 m long fissure observed in Parh Limestone in Saro area Gogai. The orientation of this rupture is NW-SE, which coincides with fault plane of the recent earthquake.

Immediately after, the earthquake of 29th October, 2008, we installed GPS receivers at all points from Chaman to Harnai to measure co-seismic movement. The strain direction prior to the earthquakes leads us to infer a mean contraction rate of 5 mm/yr directed to the SE. The earthquake was strike-slip on a NW/SE plane. Thus the earthquake has enhanced this pre- earthquake compressional stress to the NE and east of the epicentral areas and reduced it to the SW and west. If we assume 1.5 m of desxtral slip beneath the region, we conclude that, the region where shallow reverse slip earthquakes may now become more probable is to the east of the epicenter. This includes the villages of Chohtair, Sanjavi, Duki and Loralai (red circle on the sketch). Deep strike-slip earthquakes are probable in line with the two large shocks (Yellow on the sketch) the areas fall Pishin, Gulistan and Chaman in the Northwest and Shahrig, Harnai, Sanjavi and Murree Bughti areas in the south. We plan to run precise models when we get data from all the GPS receivers in the region.

Figure 8. Shows a line depicting the subsurface strike slip fault that slipped in the 29th October 2008 earthquake. The red and yellow circles indicate areas of enhanced probability for future reverse slip or strike slip earthquakes respectively.

Figure 9A. Showing clustering of after shocks around the two main shocks.

Interferogram of the Area

An interferogram is a CCD camera recording of an optical interference pattern caused from laser light beam sharing between the incoming and outgoing beam of the interferometer. Any displacement of one part of the scene appears directly as a phase shift with respect to the rest of the scene.

In figure 9B the effects of earthquake can be clearly seen.  This is all preliminary, so there are many confusing fringes and large areas of lost coherence, but it appears as if it was NE-SW directed strike slip faulting up near KACH.  The complex signal at KACH is probably due to its extremely close proximity to the surface faulting (NE-SW trend just meters west of KACH.

Figure.9B:  showing incoherence, affecting a large area, between Kach and Kawas.

Landslides

Landslides, the downward and outward movement of slope-forming rock debris, have caused considerable damage to public and private property and a high number of causalities in the sliding prone areas. The most important factors that are directly related to the landslides are the bed rock geology, slope condition, seismicity, and precipitation.

Figure.10. Shapes and appearance of landslides

As earlier stated, that the Ziarat Gogai, Khost, Shahrig and Haranai valleys are within the Ghazij Formation. In these valleys, highly incompetent nature of the Ghazij Formation, tectonic structure of the area, and high angle slopes and deforestation in the area provided the base for instability of the slopes. The affected areas receive rain and snow fall from December to April. The earthquake of October 29, 2008 triggered a disastrous landsliding, destroying the villages of Wam, Warchom, Kala China, Killi Rudgai.

It is worth mentioning here that the Ziarat region, Goagai valley and Zardalu area lie within a high risk landslide zone, suggesting that future wet weathers and/or earthquakes may cause further devastating landslides.

Furthermore, during our filed observations, along the road of Ziarat Valley and on Harnai Road, up to Chapper Rift, several areas susceptible to landsliding  have also been identified . Landslides that have been brought close to failure will be de-stabilized further by rain and snow fall during the coming winter season. While landslides that occurred during the earthquake have probably used much of their available load therefore reducing the risk  of future large  scale landslides, except where forests have been stripped by the former slides.

A great need exists to quantitatively assess the hazard potential caused by earthquake-induced landslides.

Figure 12 & 13: Road cracks developed due to slope instability, were triggered by the recent earthquake. Fig. 12 shows a vertical displacement of 20 cm down to the right.

Figure: 14 & 15: showing nascent landslides that could be triggered by future heavy rain and snow falls.

Figure 16 &17: rock-falls in the Gogai and Ziarat areas.

Newly emerged springs

In various parts of the earthquake struck areas including the valley of Ziarat and Gogai, several newly emerged springs, mostly in the Parh limestone, were observed. The violent shaking of rocks may have developed new cracks and/or enlarged the existing cracks, further increasing the bulk permeability of the region leading to new springs or even the older faults in the area may have been reactivated thus causing the water to gush out from new escape routes.

Figures 20 & 21: showing newly emerged springs, in the Parh Limestone, near Ahmadun. In the background of Fig. 21 a water pond almost filled to the brim is visible, was in fact empty before the earthquake. Figures 22 & 23 show newly emerged springs in Parh Group in the Killi Spezandai of the Ziarat district. Fig. 23 is from Saro Tangai area.

Conclusions

1. The earthquakes appear to have occurred on a N60E fault that slipped 1.5 m right-laterally. Although the earthquake occurred at a shallow depth, no surface faulting has yet been observed.

2. The earthquake has enhanced pre- earthquake compressional stress to the NE and east of the epicentral areas and reduced it to the SW and west. It means that future shallow earthquake is probable in Chohtair, Sanjavi, Duki and Loralai.

3. Deep strike-slip earthquakes are probable in line with the two large shocks; the following areas could be affected: Pishin, Gulistan and Chaman in the Northwest and Khost, Shahrag, Harnai, and Murree Bughti areas in the south.

4. Ziarat, Gogai, Khost, Shahrag and Harnai valleys are within the Ghazij Formation. In these valleys, highly incompetent nature of the Ghazij Formation, tectonic set-up of the area, and high angle slopes, provided the base of instability for adobe houses, roads and other infrastructures.

5. The Ziarat, Gogai Valley, Zardalu areas fall within a high risk landslide area, that may result in further slides triggered by future wet weather or aftershocks.

6. On the way, along the road in the  Ziarat Valley and on Harnai Road, up to Chapper Rift, several areas prone to landsliding have been identified.

7. In most of the Ziarat District, the adobe structures either collapsed or damaged seriously. In Pishin District, the adjacent villages to the epicenter, i.e. Khanozai, Balozia, Pishin, Dilsoar, Rodgh Malazai, were also badly damaged.

8. In the earthquake affected areas, on the roads bordering the villages, due to the potential fall of huge blocks/rock falls, a potential threat to life exists.

Suggestions and Recommendations

• Pre-Disaster plan should be made for high seismic zone areas to avoid or minimize the effects of the future earthquake in Quetta, Pishin, Ziarat, Chaman, Nushki, Kalat, Khuzdar, and for the coastal regions.
• The implementation of the building codes should be ensured in high seismic zone areas. In addition to that, all existing public and private buildings should be surveyed and assessed for retrofitting to avoid or minimize the future earthquake effects.
• Mere payment of amount to the villagers in Ziarat and Pishin Districts, for reconstruction of their houses are not sufficient without giving them earthquake resistant design. It is also vital to insured the reconstruction of earthquake resistant adobe in earthquake hit areas.
• A great need exists to quantitatively assess the hazard potential caused by earthquake-induced landslides/ rock fall in Ziarat, Gogai, Rudh Malazai and Zardalu area to avoid further losses of life and property.
• The Road engineers should evaluate/asses the road conditions in Ziarat, Gogai, Rudh- Malazai and Zardalu area. Some of the bridges and earth filled causeways are near to failure and prone to slide/slump in the coming wet seasons.
• Dams in the earthquake hit areas are also need to be assessed as some of them are at verge of the failures.
• The fractured/ damaged houses (Adobe) in the earthquake hit areas are need to be demolished. These houses will be prone to collapsed due to rain and snow fall in the coming wet seasons.
• Reconstruction of the houses should be ensured on compact ground and may be avoided to reconstruct on incompetent rocks, near high angle slopes.

Acknowledgements

For the preparation of this report I sincerely acknowledge the technical support of Prof Roger Bilham and S. Walter of Colorado University, USA. I am equally indebted to Prof.  Dr. Akhtar Mohammad Kassi, Department of Geology, and Aimal Khan Kassi, Assistant Professor, Center of Excellence in Mineralogy, for their support and discussions during and after the fieldwork. Special thanks are due to Najeebullah Kakar, student of B.S 2^nd year, Department of Geology, who installed GPS in the field.

References

Kazmi, A.H., 1979: The Bibai and Gogai Nappes in the Kach-Ziarat Area of Northern Balochistan. Pages 333-339 In: Geodynamics of Pakistan (Editors: Farah & DeJong)

Niamatulla, M. et al., 1989: Emplacement of Bibai and Gogai Nappes, NW of Quetta. Geol. Bulletin University of Peshawar, v. 22

Kassi, A.M. & Kakar, D.M. 1992: Preliminary assessment of Landslides and gapping fissures near Sor Range Zharia China Quetta Disst. Balochistan, Pakistan Journal of  Earth Sciences Vol.1

(Din Mohammed Kakar is a faculty member at the Geology Department, Univeristy of Balochistan and can be contacted via e-mail:  dinkakar@yahoo.co.uk).