Tuesday, September 24, 2013

PLANETARY TREMORS: Powerful 7.7 Magnitude Earthquake Strikes Southern Pakistan - Felt Throughout Asia; At Least 25 Dead; USGS Issues "RED ALERT," Giving A 73 Percent Chance Of 1,000 Or More Deaths!

September 24, 2013 - PAKISTAN - A 7.7-magnitude earthquake struck southern Pakistan on Tuesday, killing at least 25 people according to early reports.

USGS earthquake location map.

The U.S. Geological Survey placed the epicenter 41 miles north-northeast of Awaran in the province of Balochistan. Mir Qadoos Bezinjo, deputy speaker of the Balochistan Assembly, told NBC News that "over 25 people" have been killed in the Arawan district as a result of the quake.

The tremor occurred at 7:29 a.m. Eastern time (4:29 p.m. local time) and shook the Pakistani mountain region, according to the USGS. The quake was relatively shallow, occurring just 12 miles (20 km) below ground, raising the potential for violent shaking near the epicenter. 

Balochistan is Pakistan's largest but least populous province, with a population of just under 8 million in an area slightly smaller than Montana.

However, "moderate" to "rather strong" shaking (levels 4 and 5 on the 12-point Mercalli Intensity Scale) were estimated by the USGS across the heavily populated Indus River valley, home to some 140 million people.

The Times of India reported the tremor was felt as far away as New Delhi, the capital of neighboring India.
The earthquake was originally rated a 7.4 on the Richter scale but was later upgraded to a 7.8, and then revised to a 7.7. Following the temblor, the USGS issued a "Red Alert," giving a 73 percent chance of 1,000 or more deaths.

USGS earthquake shakemap intensity.


USGS earthquake shakemap intensity.


The quake was felt in Pakistan's largest city, Karachi, along the Arabian Sea. People in the city's tall office buildings rushed into the streets following the tremor, and Pakistani television showed images of lights swaying as the earth moved.

TV footage showed residents in Quetta, the capital of Baluchistan, coming out of their homes and offices in a panic. One man told Pakistan's Dunya television channel that he was sitting in his office when the building started shaking.

Other residents said people started reciting verses from Islam's holy book, the Quran, when the quake began.

USGS earthquake population exposure.


USGS earthquake damage estimates.


Baluchistan and neighboring Iran are prone to earthquakes.

A magnitude 7.8, which was centered just across the border in Iran, killed at least 35 people in Pakistan in April.

A 5.9-magnitude aftershock was reported near the epicenter just minutes after the initial quake.

Information from the Associated Press is included in this report. -
 TWC.

Tectonic Summary.
The September 24, 2013 M7.7 earthquake in south-central Pakistan occurred as the result of oblique-strike-slip type motion at shallow crustal depths. The location and mechanism of the earthquake are consistent with rupture within the Eurasia plate above the Makran subduction zone. The event occurred within the transition zone between northward subduction of the Arabia plate beneath the Eurasia plate and northward collision of the India plate with the Eurasia plate. The epicenter of the event is 69km north of Awaran, Pakistan, and 270km north of Karachi, Pakistan (population 11.6 million).


On a broad scale, the tectonics of southern and central Pakistan reflect a complex plate boundary where the India plate slides northward relative to the Eurasia plate in the east, and the Arabia plate subducts northward beneath the Eurasia plate in the Makran (western Pakistan). 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. Further, more in-depth studies will be required to identify the precise fault associated with this event. Although seismically active, this portion of the Eurasia plate boundary region has not experience large damaging earthquakes in the recent history. In the past 40 years, only one significant event (M6.1), which killed 6, has occurred within 200km of the September 2013 event, in July of 1990.

Seismotectonics of the Middle East and Vicinity.
No fewer than four major tectonic plates (Arabia, Eurasia, India, and Africa) and one smaller tectonic block (Anatolia) are responsible for seismicity and tectonics in the Middle East and surrounding region. Geologic development of the region is a consequence of a number of first-order plate tectonic processes that include subduction, large-scale transform faulting, compressional mountain building and crustal extension. 

Mountain building in northern Pakistan and Afghanistan is the result of compressional tectonics associated with collision of the India plate moving northwards at a rate of 40 mm/yr with respect to the Eurasia plate. 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. Earthquake activity and faulting found in this region, as well as adjacent parts of Afghanistan and India, are due to collisional plate tectonics. 

USGS plate tectonics for the region.


Beneath the Pamir-Hindu Kush Mountains of northern Afghanistan, earthquakes occur to depths as great as 200 km as a result of remnant lithospheric subduction. Shallower crustal earthquakes in the Pamir-Hindu Mountains occur primarily along the Main Pamir Thrust and other active Quaternary faults, which accommodate much of the region's crustal shortening. The western and eastern margins of the Main Pamir Thrust display a combination of thrust and strike-slip mechanisms. 

Along the western margin of the Tibetan Plateau, in the vicinity of southeastern Afghanistan and western Pakistan, the India plate translates obliquely relative to the Eurasia 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 India and Eurasia plates. 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 Arabia plate beneath the continental Eurasia plate, which converge at a rate of approximately 20 mm/yr. Although the Makran subduction zone 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 Arabia Sea, killing over 4,000 people. Northwest of this active subduction zone, collision of the Arabia and Eurasia 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 Arabia and Eurasia 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. 

Along the eastern margin of the Mediterranean region there is complex interaction between the Africa, Arabia and Eurasia plates. The Red Sea Rift is a spreading center between the Africa and Arabia plates, with a spreading rate of approximately 10mm/yr near its northern end, and 16mm/yr near its southern end (Chu, D. and Gordon, R. G., 1998). Seismicity rate and size of earthquakes has been relatively small along the spreading center, but the rifting process has produced a series of volcanic systems across western Saudi Arabia. 

Further north, the Red Sea Rift terminates at the southern boundary of the Dead Sea Transform Fault. The Dead Sea Transform is a strike-slip fault that accommodates differential motion between the Africa and Arabia plates. Though both the Africa plate, to the west, and the Arabia plate, to the east, are moving in a NNE direction, the Arabia plate is moving slightly faster, resulting in the left-lateral, strike-slip motion along this segment of the plate boundary. Historically, earthquake activity along the Dead Sea Transform has been a significant hazard in the densely populated Levant region (eastern Mediterranean). For example, the November 1759 Near East earthquake is thought to have killed somewhere between 2,000-20,000 people. The northern termination of the Dead Sea Transform occurs within a complex tectonic region of southeast Turkey, where interaction of the Africa and Arabia plates and the Anatolia block occurs. This involves translational motion of the Anatolia Block westwards, with a speed of approximately 25mm/yr with respect to Eurasia, in order to accommodate closure of the Mediterranean basin. 

The right-lateral, strike-slip North Anatolia Fault, in northern Turkey, accommodates much of the westwards motion between the Anatolia Block and Eurasia Plate. Between 1939 and 1999, a series of devastating M7.0+ strike-slip earthquakes propagated westwards along the North Anatolia Fault system. The westernmost of these earthquakes was the 17th August 1999, M7.6 Izmit earthquake, near the Sea of Marmara, killed approximately 17,000 people. 

At the southern edge of the Anatolia Block lies the east-west trending Cyprian Arc with associated levels of moderate seismicity. The Cyprian Arc represents the convergent boundary between the Anatolia Block to the north and the Africa Plate to the south. The boundary is thought to join the East Anatolia Fault zone in eastern Turkey; however no certain geometry or sense of relative motion along the entire boundary is widely accepted. - USGS.

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