Iftikhar A Raja
VOLUME: 2 ISSUE: 1
Page No: 152-164
Iftikhar A Raja
Javed Iqbala, Ishtiaq A. K. Jadoonb, Iftikhar A Rajac
aDepartment of Earth Sciences,Abbottabad University of Science and Technology, Abbottabad, Pakistan
bDepartment of Earth Sciences
cDepartment of Environmental Sciences,
Iftikhar A Raja, THE BALOCHISTAN EARTHQUAKE 2013: EMERGENCE OF A NEW ISLAND IN THE ARABIAN SEA(2017)SDRP Journal of Earth Sciences & Environmental Studies 2(1)
A massive earthquake of 7.7 magnitude struck south-central Pakistan on September 24, 2013. The epicenter of the earthquake was 63 km north-north-east (NNE) of Awaran in Baluchistan. The earthquake caused the death of 386 people, leaving thousands homeless. The earthquake also affected different cities in Iran, India and Afghanistan. The fundamental cause of the earthquake was displacement along oblique-strike-slip fault at a depth of only 15 km (9.3 miles). The quake has created an island in the Arabian Sea which is an unusual in case of strike-slip faulting and it raises the question of the nature and original mechanism of the earthquake. The formation of the island indicates that there is a significant push of the northward moving Indo-Pakistani plate along with oblique-strike-slip faulting which was the original motion of the earthquake. These facts were discussed and explained in this paper.
Earthquakes or seismic tremor are a natural hazard caused by environmental factors, killing an increasing number of people. The increase in casualties may be due to the growth in population, towns growing into urban centres . Major population centres are often located along mountain ranges, with cities lying next to faults. Significant damage occurs when they rupture due to the proximity of vulnerable buildings . The degree of damage varies according to the intensity of the quake and local geological conditions. Close to the epicenter, the damage is direct, resulting in immediate destruction, such as collapsed buildings and destroyed infrastructure, broken installation, and indirect or secondary, resulting in fires, landslides, floods, etc.
The 2013 Balochistan earthquake struck along one of the most hazardous yet poorly studied tectonic plate boundaries in the world. The earthquake of 7.7 magnitude was likely centered on a southern strand of the Chaman Fault. The Chaman Fault is a large, active fault around 860 kilometers long, stretching along Pak-Afghan border region. It is one of the world’s major terrestrial transform faults that cross back and forth between Afghanistan and Pakistan, ultimately merging with some other faults and going to the Arabian Sea . One of the deadliest earthquakes ever in Southeast Asia occurred in 1935, on the northern Chaman Fault and destroyed the town of Quetta, killing more than 30,000 people.
Sometimes mountains are created and islands emerged when continents collide, causing tectonic faults to move. Most of these faults are locked in the upper crust, and sudden slipping in earthquakes mountain growth for example, in Nepal during 2015 Gorkha earthquake . The Balochistan 2013 earthquake undergoes similar situation and resulted in the creation of an Island off Gwadar coast Figure 1. The earthquake occurred on September 24, 2013, in the south central region of Pakistan . The earthquake was measured at 7.7 magnitude, and lasted for a very short time, 8 seconds, but degree of damage caused was enormous. Over 300,000 people have been affected across six districts. Awaran district near the epicenter was the most affected area, homes which were made up of mud and stone were demolished. This paper addresses the September 2013 Balochistan Earthquake, creation of island and discusses history of earthquakes in this particular region.
EARTHQUAKE SEPTEMBER 2013
At Pakistan standard time (PST) 16:29:48, (11:29:48 GMT), on September 24, 2013 a powerful earthquake struck the south-central part of Pakistan. The epicenter of the earthquake was 63 km NNE of Awaran district (26° 59' 58.92"N, 65° 30' 51.48"E). The location of the earthquake hit area is shown in Figure 2(a-b) .
The magnitude of the earthquake that lasted for 8 seconds was 7.7 on the Richter scale. The epicenter of the event is 69 km north of Awaran, Pakistan, and 276 km north-west of Karachi city, where over 11.6 million people resided .The earthquake shocks were also observed in neighbouring countries India, Iran and Afghanistan too. The earthquake was as a result of oblique-strike-slip type motion at shallow crustal depths. The location and mechanism of the earthquake are consistent with rupture within the Eurasian plate above the Makran subduction zone, Figure 3 . The event occurred within the transition zone between northward subduction of the Arabian plate beneath the Eurasian plate and northward collision of the Indian plate with the Eurasian plate. The intensity of the event over the distance is shown in “Distance vs Intensity” curve in Figure 4 .
The aftermath of the September 24, 2014 earthquake in Balochistan has been devastating. According to National Disaster Management Authority, Islamabad, the earthquake caused the death of about 386 people, injured 816 people, and made thousands of people homeless (totally damaged houses 32638, partially damaged houses 14118)  (Figure 5).
A subduction zone along the Makran coast was first time proposed about four decades ago  and found to be consistent with seismic activities  followed by field investigations . Several researchers assessed the tsunami hazard along the coast of Iran, Pakistan and Oman originating from the subduction process [11-13]. Heidarzadeh and his colleagues [14,15] performed deterministic analyses based on five magnitude 8.1 events and six magnitude 8.3 events, respectively, and Heidarzadeh and Kijko [16,17] carried out a probabilistic study based on three magnitude 8.1 sources associated with probabilities to propose what they labeled a “first generation” probabilistic tsunami hazard assessment (PTHA) for the region. There is a complex tectonics history of southern and central Pakistan at the regional scale, where Indian-Pakistani plate slides northward relative to the Eurasian plate in the east, and the Arabian plate subducts northward beneath the Eurasian plate in the Makran (earthquake epicenter region) [18-21]. These motions typically result in north-south to northeast-southwest strike-slip motion at the latitude of the September 24 earthquake that is primarily accommodated on the Chaman Fault, with the earthquake potentially occurring on one of the southern-most strands of this fault system . The dramatic formation of an island in the Arabia Sea raises questions about the original trigger and mechanism of the event for which deep investigation is required - Figure 6(a-d). It is also noted that out of 23 strong earthquakes (over 6.0 Mw) in Pakistan, 14 occurred in Balochistan which makes it one of the most prone province to earthquakes. The earthquake of 27 November 1945 - off the Makran coast (Balochistan) Mw 7.9,  also formed an island which disappeared later.
Although it is not unusual for earthquakes of this magnitude to change the coastline, or even deform the shape of the planet, for example; in 2010, an earthquake of 8.8 magnitude in Chile [created new coastlines in that country and changed the shape of the Earth enough to shorten our days by a fraction of second . However, in the case of strike-slip events like the current event, this is not usual. Only one strong earthquake occurred in the region during last few decades within 200 km of the current event; a magnitude 6.1 occurred in July 1990  killing 6 persons.
Balochistan earthquake 2013 was a powerful strike-slip earthquake leaving more than 100,000 homeless. Amidst the destruction, a new island was created offshore in the Paddi Zirr (West Bay) near Gwadar, Pakistan . The images in Figure 6(a-d) illustrate the emergence of the new island over Gwadar offshore and its approximate size [24, 25]. There is no island visible in the image (Figure 6a) in the area, snapped by the Operational Land Imager on Landsat 8 satellite on April 17, 2013. On September 26, 2013, Advanced Land Imager on NASA's Earth Observing-1 satellite captured an image of the emerging island, as shown in Figure 6b [24,25]. The island sits roughly one kilometer (0.6 miles) offshore of the town of Gwadar. The French Pleiades satellite further mapped the muddy hill's dimensions, Figure 6c .
Description The Island
The aerial photograph of the new island named “Zalzala Koh” or Gwadar Island, in Figure 6d , released by Pakistan's National Institute of Oceanography (PNIO) , suggests the gray-colored mound. The surface is covered in sea creatures such as dead fish and solid enough for people to walk on.
The island is partially composed of rock fragments, mud and sand. It is about 330 miles (533 kilometers) from Pakistan's largest city of Karachi and 75 miles (120 kilometers) from Iran border (Figure 1, 2a). The island is about 60 feet (18 meters) high, 100 feet (30 meters) wide and 250 feet (76 meters) long (Figures 1 and 6d). The new island may have formed by surface deformation produced by the earthquake or by the release of gas trapped in surface sediments due to ground shaking. The in situ geological observations show that the second mechanism is the most adequate since the surface of the island presented fissures and cracks indicating the escape of gas, which was also observed bubbling along the shores of the island. The combustion produced by open fire suggests that the gas was mainly methane. The occurrence of methane is a good clue for hydrocarbon prospecting in the area. Due to its unconsolidated nature it is probable that the island will soon be destroyed by marine abrasion. It is very obvious that there is fossil fuel source underneath seabed, the indication of methane gas confirms this claim and it is suggested to carry out deep investigations for hydrocarbon prospective.
DISCUSSION: Tectonic History - Seismicity and Seismic Hazards
Earthquake history of Pakistan shows that Balochistan Province is one of the most earthquake prone regions in Pakistan (Table 1 and 2). According to a map created by the Pakistan Meteorological Department (PMD), the country is divided into 4 zones based on expected ground acceleration (Figures 7&8). The areas surrounding Quetta, along the Makran coast and parts of the Khyber Pakhtun Khawa (KPK) province, along the Afghan border fall in Zone 4. According to the Global Seismic Hazard Assessment Program (GSHAP), the most vulnerable areas of Pakistan are parts of Balochistan province in and around Quetta stretching to the Afghan border and western parts of Balochistan, which include the Makran coast upto the Iranian border (Figures 7&8). These regions may expect to have maximum peak ground accelerations (PGA) ranging from 0.24g to 0.4g.
The Arabian, Eurasian and Indo-Pakistani plates are the main contributors to active tectonics and seismicity in Pakistan. Mountain orogeny in Pakistan is the result of compressional tectonics associated with collision of the Indian plate moving northwards at a rate of 48 mm/yr with respect to the Eurasian plate [27,28]. Continental thickening of the northern and western edge of the India subcontinent has produced the highest mountains in the world, including the Himalayan, Karakoram, Pamir and Hindu Kush ranges. Almost all of the earthquake activity and related deformation found in this region, as well as in adjacent parts of Afghanistan and India, are due to collisional plate tectonics.
In the western margin of the Tibetan Plateau, in the vicinity of southeastern Afghanistan and western Pakistan, the Indian plate translates obliquely relative to the Eurasian plate, resulting in a complex fold-and-thrust belt known as the Sulaiman Range. Faulting in this region includes strike-slip, reverse-slip and oblique-slip motion and often results in shallow, destructive earthquakes. The relatively fast moving left-lateral, strike-slip Chaman Fault system in southeastern Afghanistan accommodates translational motion between the Indian and Eurasian plates (Figure 9). In 1505, a segment of the Chaman Fault system near Kabul, Afghanistan ruptured causing widespread destruction of Kabul and surrounding villages. In the same region, the more recent 30 May 1935, M7.6 Quetta, Pakistan earthquake, occurred within the Sulaiman Range, killing between 30,000 and 60,000 people.
Off the south coast of Pakistan and southeast coast of Iran, the Makran trench is the present-day surface expression of active subduction of the Arabian plate beneath the continental Eurasian plate, which converges at a rate of approximately 20 mm/yr. Although the Makran subduction zone (Figure 9) has a relatively slow convergence rate, it has produced large devastating earthquakes and tsunamis. For example, the November 27, 1945 M8.0 mega-thrust earthquake  produced a tsunami within the Gulf of Oman and Arabian Sea, killing over 4,000 people. Northwest of this active subduction zone, collision of the Arabian and Eurasian plates forms the approximately 1,500-km-long fold and thrust belt of the Zagros Mountains, which crosses the whole of western Iran and extends into northeastern Iraq. Collision of the Arabian and Eurasian plates also causes crustal shortening in the Alborz Mountains and Kopet Dag in northern Iran. Eastern Iran experiences destructive earthquakes that originate on both strike-slip and reverse faults. For example, the 16 September 1978 M7.8 earthquake , along the southwest edge of the Dasht-e-Lut Basin killed at least 15,000 people.
The September 24, 2013 earthquake led to the formation of an island  which indicates that there is a significance push of northward moving Indo-Pak plate along with oblique-strike-slip fault which was the original cause of the earthquake. Based on Modified Mercalli Intensity Scale, the earthquake is very strong earthquake (intensity-VII). The island is just a big pile of mud from the seafloor that got pushed up. This area of the world seems to see so many of these features because the geology is correct for their formation. The underground pressure in this case came from expanding natural gas. Similar islands have appeared offshore, 700-kilometer (450-mile) of Makran coast in the past century [31,32]. The Makran coast is where the Arabian tectonic plate is pushed northward and downward to go underneath the Eurasian continental plate. The thick layer of mud and rock on the Arabian Plate is scraped off and has formed the land in southwestern Pakistan, southeastern Iran, and the shallow underwater area offshore.
The life of such islands is usually short. Underground gas cools down or escapes, leaving the crust to collapse and settle back down. Waves and tides may wash away the loose sand, soft clay, and mud. However such mud volcanoes and islands are a natural hazard and threat to navigation.
The September 24, 2013 earthquake was a drastic earthquake but resulted in less human and property loss due to its epicenter in less populated area, which killed about 386 people, injured 816 people, and made thousands of people homeless (totally damaged houses 32638, partially damaged houses 14118). It is concluded that:
We are thankful to Pakistan Meteorological Department (PMD) and Geological Survey of Pakistan (GSP) for useful data. The data from reports of National Disaster Management Authority (NDMA), Government of Pakistan, (Prime Minister’s Office), remained very helpful in this study.
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