Τρίτη 16 Απριλίου 2013

ΣΧΕΤΙΚΑ ΜΕ ΤΟ 2ο ΣΕΙΣΜΟ ΣΤΟ ΙΡΑΝ

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Extremely dangerous earthquake M 7.8 struck Iran-Pakistan border region

– Posted on April 16, 2013

A very strong earthquake magnitude 7.8 (USGS) struck Iran-Pakistan border region on Tuesday, April 16, 2013 at 10:44 UTC. By latest reports USGS calculated depth at 82 km, their initial report measured 15.2 km which placed it as extremely dangerous earthquake because of the shallow epicenter. With those numbers changed the estimated damage is far less than previously thought.
EMSC is reporting M 7.7 but at depth of 87 km, their initial report set depth at 135 km. Iranian Seismological Center reports M 7.5. at depth of 95 km, their initial report said depth was at only 18 km. GEOFON reported magnitude 7.7 and depth of 89 km. The information is now manually reviewed but still based on preliminary data.
At 12:27 UTC there is still no official information on damage and deaths. 100 rescuers are on their way to the epicenter area and will probably need approx. 5 hours to reach the epicenter area.
This is the second major earthquake to be felt in the region in less than a week. A destructive and deadly earthquake struck southern Iran on April 9, 2013 at 11:52 UTC.
GDACS is reporting that this earthquake can have a medium humanitarian impact based on the magnitude and the affected population and their vulnerability.
There are about 300 000 people living within 100 km radius.
Epicenter of the earthquake was 94 km E of Khāsh, Iran and 188 km SE of Zāhedān, Iran at coordinates 28.25 N ; 62.18 E as reported by EMSC.
Tremors were felt across the Gulf region and in New Delhi. Buildings in Sharjah, Dubai and Abu Dhabi were evacuated.
Earthquake was felt all over north India and reports were received from Indian cities of Chandigarh, Noida, Delhi, Ahmedabad, Amritsar, Jammu.
Being adjacent to Iran, strong tremors were felt in Pakistan’s cities of Islamabad, Karachi and Baluchistan region.
Tremors remained for short duration, but was strong enough to alert public. People rushed out of their offices and homes.

Magnitude	7.8
Date-Time	Tuesday, April 16, 2013 at 10:44:20 UTC Tuesday, April 16, 2013 at 03:44:20 PM at epicenter
Location	28.107°N, 62.053°E
Depth	82 km (51.0 miles)
Region	IRAN-PAKISTAN BORDER REGION
Distances	194 km (121 miles) SE (144°) from Zahedan, Iran 256 km (159 miles) NNW (336°) from Turbat, Pakistan 256 km (159 miles) WSW (250°) from Dalbandin, Pakistan 605 km (376 miles) NE (34°) from MUSCAT, Oman
Location Uncertainty	horizontal +/- 14.3 km (8.9 miles); depth +/- 2.9 km (1.8 miles)
Parameters	NST=175, Nph=175, Dmin=976.3 km, Rmss=0.98 sec, Gp= 32°, M-type=regional moment magnitude (Mw), Version=9
Source	Magnitude: USGS NEIC (WDCS-D) Location: USGS NEIC (WDCS-D)
Event ID	usb000g7x7

Tectonic summary by USGS

The April 16, 2013 M 7.8 earthquake east of Khash, Iran, occurred as a result of normal faulting at an intermediate depth in the Arabian plate lithosphere, approximately 80 km beneath the Earth’s surface. Regional tectonics are dominated by the collisions of the Arabian and India plates with Eurasia; at the longitude of this event, the Arabian plate is converging towards the north-northeast at a rate of approximately 37 mm/yr with respect to the Eurasian plate. Arabian plate lithosphere is subducted beneath the Eurasian plate at the Makran coast of Pakistan and Iran, and becomes progressively deeper to the north.
The subducted Arabian plate is known to be seismically active to depths of about 160 km. The frequency of moderate and large earthquakes within the subducted Arabian plate is not high compared with similar events in some other subducted plates worldwide, but several earthquakes have occurred within this slab in the region of today’s event over the past 40 years, including a magnitude 6.7 shock 50 km to the south in 1983. In January of 2011, a M 7.2 earthquake occurred approximately 200 km to the east, in a similar tectonic environment to the April 16 earthquake.

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.
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.
Featured image: EMSC + Google maps

http://thewatchers.adorraeli.com/2013/04/16/extremely-dangerous-shallow-earthquake-m-7-8-struck-iran-pakistan-border-region/