Earthquakes near Tabriz, Iran

Earthquakes with magnitudes 6.4 and 6.3 struck northwestern Iran on August 11, 2012. The earthquakes occurred midway between Lake Orumiyeh and the Caspian Sea. Separated by only 11 minutes and 10 kilometers (6 miles), both quakes were shallow, occurring less than 10 kilometers below ground. The quakes leveled mud-brick and concrete homes in about 230 villages, Al Jazeera reported, and by August 13, the death toll had passed 300. More than 3,000 people had been injured, and more than 16,000 people had been left homeless by the disaster.

This image shows the region where the earthquakes struck. Rings mark earthquake locations, and bigger, thicker rings indicate higher magnitudes. Note that this image only shows the large quakes that occurred on August 11, and aftershocks with a magnitude of 4.0 or greater that occurred through the afternoon of August 13. The red lines indicate faults. The earthquake locations and faults are superimposed on a digital elevation map, made from the ASTER Global Digital Elevation Model Version 2 (GDEM2). Lighter colors correspond with higher elevations.

The U.S. Geological Society (USGS) explained that the earthquakes occurred in the crust of the Eurasian Plate. In this region, the Arabian Plate moves roughly northward with respect to the Eurasian Plate, at about 26 millimeters (1 inch) per year, but the USGS stated that these earthquakes occurred about 300 kilometers (200 miles) east of the plate boundary. The event likely occurred as a result of an oblique strike-slip fault, where blocks of the Earth slide past each other, the USGS said, but because of the location was so far from a plate boundary, “precise identification of the causative fault(s) is difficult at this time.”

1. References

2. Al Jazeera. (2012, August 13) Thousands left homeless after Iran quakes. Accessed August 13, 2012.
3. Al Jazeera. (2012, August 13) Iran earthquake death toll continues to rise. Accessed August 13, 2012.
4. The Big Picture. (2012, August 13) Iran earthquakes. Boston Globe. Accessed August 13, 2012.
5. CBS/Associated Press. (2012, August 13) Iran earthquake death toll passes 300 day after search for survivors called off. Accessed August 13, 2012.
6. U.S. Geological Survey. (2011, August 11) M6.4 – 23km SW of Ahar, Iran. Accessed August 13, 2012.
7. U.S. Geological Survey. (2011, August 11) M6.3 – 32km WSW of Ahar, Iran. Accessed August 13, 2012.

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.

M6.3 - 32km WSW of Ahar, Iran

Event Time

1. 2012-08-11 12:34:35 UTC
2. 2012-08-11 17:04:35 UTC+04:30 at epicenter
3. 2012-08-11 17:04:35 UTC+04:30 system time

Nearby Cities

1. 32km (20mi) WSW of Ahar, Iran
2. 49km (30mi) ENE of Tabriz, Iran
3. 86km (53mi) E of Marand, Iran
4. 97km (60mi) NNW of Hashtrud, Iran
5. 282km (175mi) SE of Yerevan, Armenia

Tectonic Summary

The August 11, 2012 M 6.4 and M 6.3 earthquakes in northwestern Iran occurred as a result of oblique strike-slip faulting in the shallow crust of the Eurasia plate, approximately 300 km east of the plate boundary between the Eurasia and Arabia plates. The two earthquakes are separated by just 10 km in an east-west direction. Focal mechanisms, describing the style of faulting for the earthquakes, suggest slip on either fault planes striking roughly east-west, or those striking roughly north-south. Because these earthquakes are intraplate events, away from the main plate boundary structures in the region, precise identification of the causative fault(s) is difficult at this time, though their offset suggest they may be associated with an east-west striking structure.

On a broad scale, the seismotectonics of this region are controlled by the collision of the Arabia and Eurasia plates; at the latitude of the earthquakes, the Arabia plate moves almost due north with respect to the Eurasia plate at a rate of approximately 26 mm/yr. To the south of today’s earthquakes, towards Iraq and the Persian Gulf, tectonics are dominated by the Zagros fold and thrust belt. To the west, in Turkey, tectonics are dominated by strike-slip faulting on the East (in southern Turkey) and North (in northern Turkey) Anatolian fault zones, accommodating the westward motion of the Anatolian block as it is being squeezed by the converging Arabian and Eurasian plates. The August 11, 2012 earthquakes occurred in the broad, elevated Turkish-Iranian Plateau region between these regimes and the Alborz Mountains further east. The events are consistent with the distributed, dominantly strike-slip mechanisms of historic earthquakes nearby, and with the orientation of mapped faults in the region.

Over the past 40 years, seven earthquakes of M 6 or greater have occurred within 300 km of today’s events. The closest was a M 6.1 earthquake in February of 1997, approximately 100 km to the east, which caused 1100 fatalities. In October of 2011, a M 7.1 earthquake struck the region of Van in eastern Turkey, near the Iranian border 300 km to the west of the August 11, 2012 earthquakes, resulting in over 500 fatalities.

NPP's 'Blue Marble'

A 'Blue Marble' image of the Earth taken from the VIIRS instrument aboard NASA's most recently launched Earth-observing satellite - Suomi NPP.

The Visible/Infrared Imager Radiometer Suite or VIIRS is the primary imaging instrument onboard NPP, and it acquires data in 22 spectral bands covering visible, near-infrared, and thermal infrared regions of the electromagnetic spectrum.

The Eastern, Western, and Australian views were created by NASA scientist Norman Kuring. They are composite images using a number of swaths of the Earth's surface taken on January 4, 2012. The Arctic composite was collected on May 26, 2012 from the OceanColor group at Goddard/NASA.

Ouarkziz Impact Crater, Algeria

The Ouarkziz Impact Crater is located in northwestern Algeria, close to the border with Morocco. The crater was formed by a meteor impact less than 70 million years ago, during the late Cretaceous Period of the Mesozoic Era, or “Age of Dinosaurs.”

Originally called Tindouf, the 3.5-kilometer wide crater (image center) has been heavily eroded since its formation; however, its circular morphology is highlighted by exposures of older sedimentary rock layers that form roughly northwest to southeast-trending ridgelines. From the vantage point of an astronaut on the International Space Station, the impact crater is clearly visible with a magnifying camera lens.

A geologist interpreting this image to build a geological history of the region would conclude that the Ouarkziz crater is younger than the sedimentary rocks, as the rock layers had to be already present for the meteor to hit them. Likewise, a stream channel is visible cutting across the center of the structure, indicating that the channel formed after the impact had occurred. This Principal of Cross-Cutting Relationships, usually attributed to the 19th century geologist Charles Lyell, is a basic logic tool used by geologists to build relative sequence and history of events when investigating a region.

Satellites Observe Widespread Melting Event on Greenland

Nearly the entire ice sheet covering Greenland—from its thin coastal edges to its two-mile-thick center—experienced some degree of melting for several days in July 2012. According to measurements from three satellites and an analysis by NASA and university scientists, an estimated 97 percent of the top layer of the ice sheet had thawed at some point in mid-July, the largest extent of surface melting observed in three decades of satellite observations.

The data visualization above shows the extent of surface melting in Greenland on July 8 (left) and July 12, 2012 (right). The maps are based on observations from the Special Sensor Microwave Imager/Sounder (SSMI/S) on the U.S. Air Force’s DMSP satellite, from India’s OceanSat-2, and from the Moderate Resolution Imaging Spectroradiometer(MODIS) on NASA’s Terra and Aqua satellites. The satellites measure different physical properties at different scales, and they pass over Greenland at different times. Taken together, they provide a picture of an extreme melt event.

On July 8, satellites showed that about 40 percent of the ice sheet had undergone thawing at or near the surface. By July 12, the extent of melting spread dramatically beyond the norm. In the images above, areas classified as “probable melt” (light pink) correspond to sites where at least one satellite detected surface melting. Areas classified as “melt” (dark pink) correspond to sites where two or three satellites detected melting.

Every summer, a fraction of the surface of the Greenland ice sheet naturally melts. At high elevations, most melt water quickly refreezes in place. Near the coast, some of the melt is retained by the ice sheet and the rest is lost to the ocean.

In mid-July 2012, Son Nghiem of NASA’s Jet Propulsion Laboratory was analyzing radar data from the Indian Space Research Organisation’s Oceansat-2 satellite when he noticed that most of Greenland appeared to have undergone surface melting on July 12. “This was so extraordinary that at first I questioned the result,” said Nghiem. “Was this real or was it due to a data error?”

Nghiem consulted with Dorothy Hall, who studies the surface temperature of Greenland from NASA’s Goddard Space Flight Center. She confirmed that MODIS showed unusually high temperatures over the ice sheet surface and that melt was extensive. Colleagues Thomas Mote of the University of Georgia and Marco Tedesco of the City University of New York also confirmed the melt with passive-microwave data from the DMSP.

The extreme melting coincided with an unusually strong ridge of warm air—a “heat dome”—over Greenland. The ridge was one in a series that dominated Greenland’s weather between May and July 2012.

Even the area around Summit Station in central Greenland, which at two miles above sea level is near the highest point of the ice sheet, showed signs of melting. A National Oceanic and Atmospheric Administration weather station at Summit confirmed that air temperatures hovered above or within a degree of freezing for several hours from July 11 to July 12.

Such pronounced melting at Summit and across the ice sheet has not occurred since 1889, according to ice cores analyzed by Kaitlin Keegan at Dartmouth College. “Ice cores from Summit show that melting events of this type occur about once every 150 years,” said Lora Koenig, a NASA scientist and member of the team analyzing the satellite data. “With the last one happening in 1889, this event is right on time. But if we continue to observe melting events like this in upcoming years, it will be worrisome.”

“The Greenland ice sheet is a vast area with a varied history of change,” said Tom Wagner, NASA’s cryosphere program manager. “This event, combined with other natural but uncommon phenomena such as the large calving event earlier this week on Petermann Glacier, are part of a complex story.”

The Lights of London

Billions of people will see London through many different filters and lenses during the 2012 Olympic Games and Paralympic Games. None of those views will look quite like this one from the Suomi National Polar-orbiting Partnership satellite.

The image above shows London and the southern half of Great Britain as it appeared on the night of March 27, 2012. While most of the events in the 2012 Olympics will be held in the greater London area, several other cities and towns will host events, including: canoeing at Lee Valley White Water Center; sailing in Portland Harbour; rowing and canoeing at Eton Dorney; and cycling and mountain bike events at Hadleigh Farm.

The image was acquired by the Visible Infrared Imaging Radiometer Suite (VIIRS) on Suomi NPP, which includes a “day-night band” similar to images collected by the Operational Linescan System (OLS) flown on U.S. Defense Meterological Satellite Program (DMSP) satellites.

The day-night band observes light in a range of wavelengths from green to near-infrared, and uses light intensification to enable the detection of dim signals, according to Chris Elvidge, who leads the Earth Observation Group at NOAA’s National Geophysical Data Center and works on the VIIRS team.

“In wavelength-speak, the range for visible light is about 400 (blue light) to 700 (red light) nanometers, and the day/night band’s sensitivity is 500 to 900 nanometers,” said Steve Miller, a researcher in the Cooperative Institute for Research in the Atmosphere at Colorado State University. “There are a lot of satellites up there with sensitivity to this same range, but the special thing about the day/night band is its high sensitivity to very low amounts of this light. It can sense light 100,000 times fainter than the conventional visible light sensors. That makes it very sensitive to things like moonlight, city lights, among many other things.”

The night views of Earth are more than just a novelty. “Nightime lights are the least ambiguous remote sensing observation indicating the presence and magnitude of human activities and the density of development,” said Elvidge. Seeing Earth’s night lighting has practical applications in studying human populations, economic activity, habitat fragmentation and encroachment, and energy use. “We can actually look at cities and tell you how much energy is emanating from them,” Miller added, “something pretty useful for energy consumption studies.”

Other scientists use the nighttime views to choose sites for astronomical observatories, study the impact of nocturnal lighting, and to monitor power outages and natural disasters. In meteorology, the combination of VIIRS nighttime views and thermal imaging is valuable for things like differentiating high clouds from low clouds from fog banks.

Suomi NPP was launched from Vandenberg Air Force Base on October 28, 2011, and is the result of a partnership between NASA, the National Oceanic and Atmospheric Administration, and the Department of Defense.

Editor's Note: In the large image (below the main image), the lights in the Irish Sea, the English Channel, and the North Sea are likely a blend of fishing vessels and flares from offshore oil and gas platforms.

1. Related Reading

2. London 2012 Olympic and Paralympic Games (n.d.) Interactive Map–2012 Olympics. Accessed July 25, 2012.
3. NASA (n.d.) Suomi NPP. Accessed July 25, 2012.
4. NASA Earth Observatory (2008, April 22) Cities at Night: The View from Space.

Carbon Eaters on the Black Sea

This brilliant cyan pattern scattered across the surface of the Black Sea is a bloom of microscopic phytoplankton. The multitude of single-celled algae in this image are most likely coccolithophores, one of Earth’s champions of carbon pumping. Coccolithophores constantly remove carbon dioxide from the atmosphere and slowly send it down to the seafloor, an action that helps to stabilize the Earth's climate.

This image of this swirling blue bloom was captured on July 15, 2012, by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite. Note that the image is rotated so that north is to the right. Ocean scientist Norman Kuring of NASA’s Goddard Space Flight Center suggested the bloom was likely Emiliania huxleyi, though it is impossible to know the species for sure without direct sampling of the water.

Coccolithophores use carbon, calcium, and oxygen to produce tiny plates of calcium carbonate (coccoliths). Often called “stones” by researchers, coccoliths resemble hubcaps. During their lifespan, coccolithophores remove carbon from the air, “fix” or integrate it into what is effectively limestone, and take it with them to the seafloor when they die and sink or when they are consumed (and eventually excreted) by zooplankton and fish.

These micro-stones are thought to speed up the ocean’s biological pump, according to William Balch, a senior research scientist at the Bigelow Laboratory for Ocean Sciences and a member of the Suomi NPP science team. Without this dense calcium carbonate ballast for sinking particles to the depths, less carbon dioxide would be drawn down into the ocean. The net result would be higher atmospheric concentrations of carbon dioxide.

But as Balch points out, the ever-increasing amount of carbon dioxide in our air could upset this biological pump. Excess carbon dioxide is making the ocean more acidic, which may change the conditions that promote coccolithophore growth. “Ocean acidification is highly relevant to coccolithophores,” said Balch. “We are trying to understand if it would slow the ocean’s biological pump by inhibiting coccolithophore calcification. If they can’t calcify, they can’t make their limestone plates that pull all the sinking particulate carbon to the seafloor.”

Mine Collapse in Turkey

At 10 a.m. on February 10, 2011, disaster struck the Çöllolar coalfield in central Turkey, near the city of Elbistan. The northeastern wall of an open-pit mine collapsed, sending about 50 million tons of material into the mine. The debris buried and killed ten workers.

The collapse was the second at the same mine within a week. Four days earlier, a smaller landslide damaged the opposite wall and killed one person. According to a United Nations report, debris from the two landslides covered 2.73 square kilometers (1 square mile). The larger landslide extended 350 meters (1,150 feet) past the original perimeter of the pit. Inadequate drainage of the mine walls likely caused the landslides, according to Caner Zanbak, an environmental adviser to the Turkish Chemical Manufacturers Association.

The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite acquired this view of the landslide’s aftermath on June 7, 2011. Material from both landslides is visible in the mine pit on the left side of the image. See this blog post for a detailed satellite view of the boundary between the two debris fields. An aerial photograph of the two landslides is available here. The pit on the far right of the image is the Kislaköy mine, which was damaged in 2006 by a landslide.

The material mined at the Çöllolar coalfield is lignite, a brown type of coal that is generally younger and softer than bituminous or anthracite. Turkey relies on lignate for 21 percent of its electric power production, and the Afsin-Elbistan lignite basin contains about half of Turkey’s lignate reserves.

Turkey has the highest fatality rate for miners in the world, with 133 deaths for every 100,000 miners in Turkey, according to data released in 2011. As of June 19, 2012, the Çöllolar coalfield was still closed pending the outcome of a lawsuit. The bodies of nine of the workers killed had not yet been recovered from the debris.

• References

• Energy Newsletter Turkey. (2012, May 10). Afsin-Elbistan Latest Status Draft Site Report. Accessed June 9, 2012.
• Petley, Dave. (2011, March 9). The Astonishing Çöllolar Coalfield Landslide in Turkey. Accessed June 9, 2012.
• Today's Zaman. (2011, July 1). Turkey Ranks First in World List of Deadly Mine Accidents. Accessed June 9, 2012
• Tutluoglu, L. (2010, May 10). Two and Three Dimensional Analysis of a Slope Failure in a Lignite Mine. Accessed June 9, 2012.
• UNITAR. (2011, March 11). Post-Landslide Assessment for Çöllolar Coalfield Kahramanmaras, Turkey. Accessed June 9, 2012.

Dust Storm over the Persian Gulf

On June 2, 2012, a dust storm struck southeastern Iraq. Winds blew fine sediments toward the southeast, over the Persian Gulf, and into northeastern Saudi Arabia. Winds also kicked up streamers of dust in Qatar. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this natural-color image the same day.

Although most of the countries affected by the dust enjoyed some clear skies outside of the storm, dust completely obliterated Kuwait. On June 4, Kuwait Times reported that the storm had paralyzed the country, with visibility reduced to less than 500 meters (1,600 feet). Dust storm activity was expected to continue, although it was expected to benefit residents by lowering recent high temperatures.

1. References

2. Fattahova, N. (2012, June 4) Activities paralyzed as dust storm hits Kuwait - Weather to help reduce temperature.Kuwait Times. Accessed June 4, 2012.

Dust Storm over Afghanistan, Pakistan, and Iran

A dust storm stirred in the Hamun wetlands along the Iran-Afghanistan border on June 3, 2012. By the following day, the dust plumes had grown, spreading far south into Pakistan. The Moderate Resolution Imaging Spectroradiometer(MODIS) on NASA’s Aqua satellite acquired this natural-color image on June 4.

When moisture is scarce, areas like the Hamun wetlands transform to dry lakebeds, and the fine sediments provide material for dust storms. Multiple dry lakebeds occur along the borders between Iran, Afghanistan, and Pakistan, in addition to the Hamun wetland area. High temperatures can also contribute to dust storms by making air near the ground unstable. In such conditions, even light winds can loft dust into the air.

1. References

2. University Corporation for Atmospheric Research. Forecasting Dust Storms. (Registration required).

Dust over Iraq and Iran

The dust that blew over Syria and Iraq on June 18, 2012, continued its southeastward journey the following day. On June 19, the dust had spread to western Iran and the Persian Gulf.

This natural-color image from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite shows a camel-colored plume curving eastward along the Iraq-Iran border. That plume is thick enough to completely hide the land and water surfaces below. Thinner dust hovers over the Persian Gulf.