balochistan earthquake of september, 2013 and birth … archival/download.php?file=pdf...balochistan...

Open Access e-Journal Earth Science India- www.earthscienceindia.info Popular Issue, VII (I), January, 2014, p. 1-12

Balochistan Earthquake of September, 2013 and birth of islands

off the Makran Coast of southern Pakistan Arun Kumar

A team of scientists found bubbles rising from the surface of the island that caught fire when a match was lit, and it was suggested to be methane gas. They also suggested that the island is a “mud volcano”, created by methane gas forcing overlying sediments upwards during the violent shaking by the earthquake………….. Earlier, such islands emerged in 1999 and 2011 two km off the Makran coast. These islands were located south of a point near the confluence of the Hingol River and the Arabian Sea.

Tuesday, September 24, 2013, an earthquake measuring 7.8 on the Richter scale struck Awaran and Kech districts of Balochistan province of Pakistan. Its epicenter was located near Kharan area of this province (Figure 1). Few hours after this earthquake, the sea bed off the Gwadar coast of southern Pakistan rose and formed a new island 600 m offshore. Gwadar is around 400 km away from the epicenter of the earthquake. Initial reports said that the island was small; about 200 m long, 20 m high and 100 m wide (Figure 2). According to the later reports of the United States Geological Survey (USGS), this earthquake measured 7.7 on the Richter scale, and its epicenter was located 96 km north of Awaran at a depth of 20 km. The earthquake was the result of movements along the active Chaman Fault.

A team of scientists found bubbles rising from the surface of the island that caught fire when a match was lit, and it was suggested to be methane gas. They also suggested that the island is a “mud volcano”, created by methane gas forcing overlying sediments upwards during the violent shaking by the earthquake. This island is nothing more than a body of mud that will soon be eroded by the waves and will eventually disappear (Figure 3). A couple of days later two more islands emerged off the Balochistan coast of Ormara and Pasni.

The Makran coastal belt has extensive reserves of frozen methane as gas hydrates below the sea floor. Due to tectonic movements, fractures and fissures are formed in the sediments containing gas hydrates thus making conduits for pressurized methane gas to escape. This forces the overlying sediments that forms a dome-like structure and ultimately emerges as an island on the sea surface. Small domal structures may remain under water if they are not tall enough to emerge from the water surface. The gas samples from the Malan Island that emerged in March, 1999 contained methane, ethane, propane and butane. The gas is microbiologically generated bacterial methane and is not thermogenic.

Fifty five people were reported to have been killed by this earthquake. Aftershocks were felt all over Balochistan and adjoining Sindh. Minor tremors were also felt in cities like Karachi, Jacobabad, Khairpur, and as far away as New Delhi and Ahmedabad in India. AFP reports on September 25th stated that more than 260 people were killed. In a later report the deathfigure went up to 359 and affected hundreds of thousands of people(Yusuf, 2013).

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At least 15 people died and 50 were injured in another earthquake of 6.8 M that hit this region on Saturday, September 28, 2013. According to the USGS its epicenter was 96 km NE of Balochistan'sAwaran district and 14 km deep. Strong tremors were felt in different parts of the Balochistan and Sindh. The total death count from the two quakes has reached 374 and injured to over 825.

Figure 1: Map of Pakistan showing the location of epicenter of the September 24, 2013 earthquake. (http://earthquake.usgs.gov/earthquakes/eventpage/usb000jyiv#shakemap … pic.twitter.com/6Fb7myOsFY)



Figure 2: Photograph of the island off the coast of Gwadar, Balochistan Province, Pakistan. (Photo: Syed Ali Shah, Dawn.com, September 25, 2013)

Figure 3: The Island primarily constitutes of mud that will eventually be eroded by waves and will disappear over time. (Photo: Syed Ali Shah, Dawn.com, September 25, 2013)



Earlier, such islands emerged in 1999 and 2011 two km off the Makran coast. These islands were located south of a point near the confluence of the Hingol River and the Arabian Sea. An island of mud volcano suddenly appeared about three km offshore from Hingolon the Makran coast on November 16, 2010. The island was 90 m high and around three km long (Figure 4).This island has since disappeared due to erosion by waves. Appearance and disappearance of such islands of mud volcanoes are common phenomena in this region. Sometimes they even emerge without an earthquake. Almost a year back an island of almost similar size as present (September 24, 2013) had emerged at a similar distance from the Makran coast. More than 80 active mud volcanoes have been identified along the Makran coast.

Delisle et al. (2002) studied the activity, source and driving force of the venting of fluid mud in the coastal Makran and carried out surveys of two active onshore mud volcano fields and a newly born (March 1999) offshore mud volcano (Malan Island). They all line up along one NE / SW trending structural lineament: the axis of the Dhak Anticline. Isotopic data indicate a bacterial origin of the gas (mainly methane). Mixed benthic foraminiferal faunas and calcareous nannofloras suggest that the source level of the extruded mud is at a sub-surface depth of two to three km. An area of 160,000 m3 of mud was extruded from the sea floor at a water depth of 10 m within days after 15 March 1999, forming Malan Island which was destroyed within a few months by deep-reaching waves during the SW monsoon.

On 28 November 1945, Pasni and some parts of Ormara along the Balochistan coast were inundated by 12-15 m high tsunamis, when the 8.1M earthquake hit the Makran coast. More than 4000 people died and the giant waves brought to shore thousands of dead fish and destroyed many villages (Figure 5). An island (mud volcano) had also emerged in the same area after this earthquake which was eventually eroded away by the waves. Based on the modeling results of historical tsunamis in the Makran Subduction Zone (MSZ), Heidarzadeh et al. (2008) concluded that “either the extreme run-up of 12–15 m assigned for the 1945 Makran tsunami in the historical record was produced by a submarine landslide triggered by the parent earthquake, or that these reports are exaggerated. The other possibility could be the generation of the huge run-up heights by large displacements on splay faults.” This whole region is a possible site for a future large earthquake and tsunami.

Recurring frequency of earthquakes and tsunamis in the MSZ is estimated to be around 100-150 years. An earthquake from the MSZ area was also reported in 326 B.C. Seismic activity in the region was registered in the years 1008 and 1897.

Geology of the Makran Coast

Geology and petroleum potential of the Makran coast of Pakistan and Iran provides a

good source of information on the geology of this region (Harms, 1982). This is a region where the Indian, Eurasian and Arabian plates converge resulting in a high level of seismicity(Figure 6).The subduction zone of the Arabian plate underneath the Eurasian plate is known as the MSZ (Figure 7). The subduction pressure gradually builds over time and eventually gets released resulting into the generation of earthquakes. The longer the interval between two earthquakes, the larger will be the amount of built-up pressure that expectedly will result in the higher intensity of earthquakes. Major earthquakes in Pakistan result from



the movements along the Chaman Fault Zone (CFZ). The NASA website describes this fault as:

“The Chaman fault zone is part of the Eurasian-Indian plate boundary complex, with the Suleiman Ranges marking a jog to the east in the northern edge of the Indian continental plate. The Chaman zone has evolved from a thrust fault of the Arabian-Eurasian collisional complex to a strike-slip fault along the Eurasian-Indian transform boundary.The Arabian-Eurasian plate boundary, a subduction zone, is beneath the Indian Ocean to the south of the Makran region. Sedimentary rocks (turbidites) that were originally deposited on the seafloor have been scraped off as the Arabian plate is subducted beneath the Eurasian plate. They were then uplifted and folded into the Makran Ranges during that plate collision. As India moves northward, the east ends of the Makran folds (on the Eurasian plate) have been dragged to the north along the Chaman fault zone.” (Website 1).

Figure 4: The mud volcano that emerged offshore in Hingol, Balochistan (Photo: Suhail Yusuf, Dawn.com Sept 28, 2013)

The Chaman Fault is an active, over 850 km long, is a transform, left-lateral strike-slip fault and the slippage rate has been estimated to be 10 mm/yr or more. This fault extends southward to the triple junction where the Arabian Plate, Eurasian Plate and Indian Plate meet; this location is just off the Makran Coast of Pakistan. The fault runs northeast across Balochistan and on to NNE into Afghanistan. The Ghazaband and Ornach-Nal faults are often included as part of the Chaman Fault system. Owen Fracture Zone is the southern extension of the triple junction under the Arabian Sea and extends southwest to approximately 10ºN 57ºE in the Indian Ocean (Website 2).



Figure 5: The epicenter of the 28 November 1945 earthquake that generated tsunamis off the Makran coast of Pakistan and Iran (Pararas-Carayannis, 2006).

Figure 6: Tectonic boundaries ofthe Arabian Plate showing its margins with the Indian Plate, andthe Eurasian Plate (Seber et al., 2000).



Figure 7: TheMakranAccretionary Prism and the Makran Subduction Zone (MSZ) off the Makran coast of Pakistan and Iran showing location of mud volcanoes (Pararas-Carayannis, 2006).

Figure 8: A specimen of coral found on the island (Photo: Dawn.com, courtesy WWF).



Ornach-Nal and Chaman Faults are transform faults and they mark the boundary between the Indian Plate in the east and the Eurasian Plate in the west. This fault is the land expression of the Owen Fracture found in the Arabian Sea; it enters Balochistan at a distance of about 75 km northwest of Karachi (Website 3).

Smith et al. (2013) developed a 2-D thermal model of the subduction zone, which suggests that earthquakes ranging from 8.7- 9.2 M are probable approximately within 350 km of the area, with a reoccurrence frequency of 100-200 years.

Geology of the Makran Accretionary Wedge

The crust of the Arabian Plate below the Oman Abyssal Plain subducts to the north

under the Eurasian continent, thereby building the Makran Accretionary Wedge (Schlüter et al., 2002). Within the thick sediments entering the subduction zone, a major unconformity was identified separating a lower, shale and sand dominated deep sea sequence of assumed Cretaceous to Early Neogene age from the overlying Upper Miocene to the Recent clastic sequence. The mud-prone sediments of the lower sequence are interpreted to represent the main décollement of the Makran Accretionary Wedge. They are also regarded as the main source for rising mud diapirs and mud volcanoes along imbricated thrusts and anticlinal structures within the Makran Accretionary Wedge.

According to Koppa et al. (2000) Makran is one of the largest accretionary wedges on the globe which was formed by the convergence between the Eurasian and Arabian Plates. It is characterized by an extremely high sediment input of 7 km and a shallow subduction angle. A décollement is developed within the turbiditic sequence. More than 3 km of sediment bypasses the first accretionary ridges (underthrusting) and is transported to greater depth. This might help to explain the sparse earthquake activity associated with the subduction here.

Figure 9: A moray eel (Photo: Dawn.com, courtesy WWF).



Figure 10: A rock crab (Photo: Dawn.com, courtesy WWF).

Figure 11: A piece of coral (Photo: Dawn.com, courtesy WWF).



Figure 12: A fish and a crab (Photo: Dawn.com, courtesy WWF).

von Rad et al. (1996) reported on the discovery of a methane-hydrogen sulfide rich “cold seep” from the Makran Accretionary Prism off Pakistan (Arabian Sea). From the seeps isotopically light, bacterially formed methane is emanating that is partly oxidized. Fault-controlled pore fluid expulsion is due to the tectonic dewatering and degassing of the accretionary prism, whereas diffuse discharge of pore fluids is inferred from the widespread occurrence of tiny gas bubble tubes.

The Makran accretionary complex has a thick gas-hydrate-bearing horizon and due to reduced hydrostatic pressure and rising ocean bottom water temperatures, gas hydrates are progressively dissociated into hydrate water, methane and hydrogen sulphide. Due to the upward migration of fluids to the seafloor an abundance of randomly distributed gas seeps are observed at water depths of 350 to 800m (von Rad et al., 2000).

Prins et al. (2000) studied the input of terrigenous sediments along the continental margin off SW Pakistan based on sediment cores distributed along a transect from the upper slope to the abyssal plain and discussed spatial and temporal variations in sediment composition, sedimentation rate and turbidite frequency during the late Pleistocene-Holocene related to the changes in sea level, climate, and tectonic activity. They found that grain-size distributions of the hemipelagic and turbiditic sediments are a mixture of turbidite sand, turbidite silt or eolian dust, and fluvial mud. The eolian dust primarily came from the northern Arabian Peninsula and the Persian Gulf region, and the fluvial sediments from the Makran margin. The ratio of contributions of eolian and fluvial sediment was used as an indicator of continental aridity, i.e. summer monsoon intensity.



New island’s fauna

According to Ilyas (2013), the World Wide Fund for Nature-Pakistan (WWF-P) collected both living and dead specimens of invertebrate animals, fish and algae from the newly formed island (Figures 8-12). The specimens were initially identified as corals, seashells, coralline algae, dead fish, crabs and shrimps. They also identified four species of small encrusting and branching corals, sea cucumbers and dead fishincluded groupers, flat-head, moray eel and grunt.

Acknowledgements: I thank the editor of Dawn.comfor permitting me to use the published photographs fromthis online newspaper. A lot of information about the earthquake and the islandsin this article is based on the initial reports published in Dawn.com. I also thank my son Anshuman Kumar for linguistic improvements to this write-up.

References

Delisle, G., von Rad, U., Andruleit, H., von Daniels, C., Tabrez, A., Inam, A. 2002. Active mud volcanoes on- and offshore eastern Makran, Pakistan. International Journal of Earth Sciences, 91(1): 93-110. Harms, J.C., Cappel, H.N.; Francis, D.C., 1982.Title Geology and Petroleum Potential of the Makran Coast, Pakistan. Society of Petroleum Engineers, Marathon Oil Company, U.S.A. (http://www.onepetro.org/mslib/servlet/onepetropreview?id=00010423) Heidarzadeh, M., Pirooz, M. D., Zaker, N. H., Ahmet C. Yalciner, A. C., Mokhtari, M., AsadEsmaeily, A. 2008. Historical tsunami in the MakranSubduction Zone off the southern coasts of Iran and Pakistan and results of numerical modeling. Ocean Engineering, 35 (8–9): 774–786. Ilyas, F. 2013. Samples of sea organisms collected from new island. Dawn.com. September 30, 2013. Koppa, C., Fruehnb, J., Flueha, E. R., Reichertc, C., Kukowskia, N., Bialasa, J., Klaeschena, D. 2000. Structure of the Makransubduction zone from wide-angle and reflection seismic data. Tectonophysics, 329 (1– 4):171–191. Pararas-Carayannis, G. 2006.The potential of tsunami generation along the MakranSubduction Zone in the Northern Arabian Sea. Case Study: The earthquake and tsunami of November 28, 1945. Science of Tsunami Hazards, 24 (5): 358 Prins, M. A., Postmaa, G., Weltjeb, G. J. 2000. Controls on terrigenous sediment supply to the Arabian Sea duringthe late Quaternary: the Makran continental slope. Marine Geology, 169: 351–371. Seber, D., Steer, D., Sandvol, E. and Sandvol, C., Brindisi, C. and Barazangi, M. (2000). Design and development of information systems for the geosciences: An application to the Middle East. GeoArabia, v. 5(2): 269-295. Schlüter, H. U., Prexl, A., Gaedicke, Ch., Roeser, H., Reichert, Ch., Meyer, H., Daniels, C. von. 2002. The Makranaccretionary wedge: sediment thicknesses and ages and the origin of mud volcanoes. Marine Geology, 185 (3–4): 219–232. Smith1, G. L., McNeill1, L. C., Wang, K., Jiangheng He, J. and Henstock, T. L. 2013.Thermal structure and megathrustseismogenic potential of the Makransubduction zone. Geophysical Research Letters, 40 (8)1528–1533. von Rad, U., Röscha, H., Bernera, U., Geyhb, M., Marchiga, V. and Schulza, H. 1996. Authigenic carbonates derived from oxidized methane vented from the Makranaccretionary prism off Pakistan. Marine Geology, 136 (1–2): 55–77. von Rad, U., Berner, U., Delisle, G., Doose-Rolinski, H., Fechner, N., Linke, P., Lückge, A., Roeser, H. A., Schmaljohann, R., Wiedicke, M., Block, M., Damm, V., Erbacher, J.,Fritsch, J., Harazim, B., Poggenburg, J., Scheeder, G., Schreckenberger, B., von Mirbach, N. Drews, M., Walter, S., Ali Khan, A., Inam, A., Tahir, M., Tabrez, A. R., Cheema, A. H., Pervaz, M., Ashraf, M. 2000. Gas and fluid venting at the Makranaccretionary wedge off Pakistan. Geo-Marine Letters, 20 (1): 10-19. Yusuf, S. 2013.The ticking time bomb beneath Quetta. DAWN.com, September 28, 2013.



Web References Website 1: http://earth.jsc.nasa.gov/handbooks/arabianpages/chaman-title.htm Website 2:http://en.wikipedia.org/wiki/Chaman_Fault Website 3: http://baask.com/diwwan/index.php?topic=2902.0

About the author

Dr. Arun Kumar is an Adjunct Professor, Department of Earth Science, Carleton University 1125 Colonel By drive, Ottawa, ON K1S 5B6, Canada. Email: [email protected]


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