From the ABC 7 Weather team

Afghanistan: Geological Hotspot for Destructive Earthquakes

April 29, 2013 - 12:08 PM
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Some of the most beautiful terrain in the world is found in war-torn Afghanistan, also some of the most deadliest earthquakes form there.

Last Wednesday, right before 2PM local time (about 5:30 AM EST) an earthquake hit northeastern Afghanistan with a magnitude of 5.7 and a depth reported of 43 miles (or 70 kilometers) reported by the U.S. Geological Survey. The epicenter of the quake was about 15.5 miles (or 25 kilometers) northwest of the eastern Afghan city of Jalalabad (near the Pakistani border) and Jalalabad is about 110 miles east of the Afghanistan Capital, Kabul (Fig. 1).

 Fig. 1:

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Considering last Wednesday brought heavy and steady rains to much of Afghanistan, hundreds of the mud-brick dwellings that many citizens lived in throughout the country collapsed. With over 70 injuries, at least 18 people were killed in adjacent Nangarhar and Kunar provinces-and that death toll could be many more.

This earthquake was not only felt in Afghanistan, but it was also felt as far away as the Indian capital of New Delhi. This just happened to be the latest quake amidst the bundle of earthquakes that have already affected parts of Asia over the last month. Just 2 weeks ago, a 6.6 magnitude earthquake killed around 200 people in southwest China and just a few days after that, a 7.8 magnitude earthquake centered in Iran killed 41 people in Pakistan near the Iranian border. There was also a 7.8 magnitude earthquake centered in Iran that affected thousands of people in remote southeastern Pakistan.

Two of the most deadly earthquakes in recent history were on October 8, 2005 and May 30th, 1998. On October 8th, a 7.6-magnitude earthquake killed more than 80,000 people and left about 4 million homeless, mainly in Pakistan-controlled Kashmir and parts of northwestern province Khyber Pakhtunkhwa. On May 30th, a quake that  measured 6.9 on the Richter scale struck Takhar and Badakhshan provinces in Afghanistan. Between 4,000 and 4,500 people died as a result of that earthquake and more than 16,000 houses/dwellings were destroyed or damaged.

Tremors and earthquakes are regular events throughout Afghanistan, and more commonly in northern Afghanistan around the Hindu Kush and Pamirs mountain ranges (Pic 1 - 3). The Pamir Mountain range has commonly been referred to over time as the "Roof of the World” and penetrates through Tajikistan, Afghanistan, China, and Kyrgyzstan. The   Hindu Kush Mountains are some 500 miles long and 150 miles wide, with an elevation of 24,850 feet at its highest peak. The Hindu Kush mountain range covers around 2/3 of Afghanistan, which lies near the collision of the Eurasian and Indian tectonic plates (in fact, the colliding of those two plates is exactly how these mountain ranges formed).

Pic 1: Hindu Kush Mountains

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Pic 2: Hindu Kush Mountains
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Pic 3: Pamir Mountains in Afghanistan

 

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In this geological hot spot, Afghan seismicity is driven by the relative northward movements of the Arabian plate past western Afghanistan at 1.29 in/yr and of the Indian plate past eastern Afghanistan at 1.53 in/yr. These both collide with the southern part of the Eurasian plate at the rate of about 1.7 inches per year. Most of these earthquake tend to be prone in the northeastern part of the country where the effects of the plate collision are more pronounced. Fig. 2 shows not only the plates surrounding Afghanistan but short blue and green lines with dots that represent local orientations of greatest horizontal compressive stress. Stress orientations were calculated from focal mechanisms of shallow earthquakes (depths 40 km or less).

Fig. 2:

ZZZZZAfghanistan is laced with geological faults. (A fault is crack in the Earth's crust. Typically, faults are associated with, or form, the boundaries between Earth's tectonic plates). Below is a shuttle -radar topographic map of Afghanistan showing the locations of features thought to be probably or possible young faults. Chaman fault (Fig. 3 red and better shown in Fig. 4) and related faults, which extend from south-central Afghanistan to the northeastern corner, are the most active and hazardous faults. Colors: red = most hazardous, green: the least hazardous, blue: less active faults but still pose a hazard.

Fig. 3:

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Fig. 4 is a generalized seismic-hazard map of Afghanistan showing the level of shaking (or according to the USGS the peak ground acceleration measure as a percentage of the force of gravity) that is likely to occur with a 2-percent probability in the next 50 years. Warm colors show higher hazard and cool colors show lower hazard. The strongest expected shaking is concentrated on major active faults in eastern and northern Afghanistan.

Fig. 4:

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Although the north and eastern parts of Afghanistan are more prone to increased earthquake activity,  historical accounts do show that damaging earthquakes have occurred in seismically less active parts of the country.  Fig 5 shows the generalized boundary or the Indian and Eurasian tectonic plates (yellow line) and locations of historical earthquakes. dates of selected significant earthquakes are showing in bold. The red arrow shows the general direction and rate of the Indian plate movement. Yellow arrows show left-lateral sense of motion on the western plate margin.

Fig 5:

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The long history of Earthquake throughout much of Afghanistan and Asia highlights the need to understand the level of hazard in various parts of the country. By combining data from the USGS, on the locations, sizes and frequencies of earthquakes with the locations and estimated activity rates of major faults, scientists can hopefully better forecast the probable levels of future ground shaking and earthquakes to eventually save lives and continue to lend to the growth of Afghanistan.

*most information (including the Figures) were generated from USGS publications.
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