The Earth Story

The North Anatolian Fault – one of the world’s most dangerous It’s hard to say that there’s a single, most dangerous fault segment in the world, but if we started making a list, the North Anatolian fault would appear on it very quickly.

The North Anatolian Fault – one of the world’s most dangerous

It’s hard to say that there’s a single, most dangerous fault segment in the world, but if we started making a list, the North Anatolian fault would appear on it very quickly. The North Anatolian Fault is a strike-slip fault on the north side of Turkey. It accommodates motion related to the other major plate collisions in the area – the Arabian plate to the south is pushing to the north, creating the mountain belts in Iran. The East Anatolian Fault separates Turkey from the Arabian plate, and along these fractures Turkey is basically “getting out of the way”. It’s being squeezed by the collision and the whole landmass is being pushed to the West, leading to a large strike-slip fault in northern Turkey.

This image was published in a paper on the North Anatolian Fault in 1997 and it illustrates a unique property of this fault – a seismic series. In 1939 there was a large earthquake along the Eastern portion of this fault. Following that quake, there has been a century-long series of Earthquakes gradually farther to the west. Every time the fault ruptured, it broke along a specific segment and then the quake stopped. The portion where it stopped was then put under extra stress, and within at most a few decades, the next segment of the fault ruptured.

I highlighted that this image was published in 1997 because it is missing recent events. In 1999 a pair of large earthquakes struck along the North Anatolian Fault near Izmit, shown on this map in white. The largest moment magnitude event of the two was recorded at 7.4, and that large of a quake hitting a populated area led to over 17,000 deaths and over 50,000 injuries.

The 1999 quakes struck in a seismic gap, a part of the fault that was right up against the portion that broke in the 1967 quake but had itself not ruptured. After the large Izmit quake, there are still portions of the fault that have not broken; the most worrisome is a strand that runs north, just off the coast of Istanbul, a city with a population of over 14 million.

Very few faults around the world behave as predictably as the North Anatolian Fault. Usually changes in rock composition or motion direction along the fault mean that faults don’t break in the pattern seen on here. However, evidence obtained from previous earthquakes, either historical records or from surveys that actually dig across the fault, indicates that this type of sequence is normal for the North Anatolian fault. The fault initially ruptures in the East and then that break leads to earthquakes that progressively migrate to the West.

The North Anatolian Fault is therefore a very interesting seismic curiosity, a fault that is more regular than almost any on Earth…and a very dangerous place, because the most at-risk seismic gap on this fault is the portion closest to the major city of Istanbul.

We can’t say when it will happen, it could take decades, but the section of the fault near Istanbul is eventually going to produce a large earthquake. Any bit of preparation right now in Istanbul, in the form of disaster response plans and building codes, will save lives in the future.

The World Bank has described Istanbul as “one of the most proactive cities in the world in terms of safeguarding against seismic risks" and "a model for disaster risk management”, but there are still issues, particularly associated with poverty, at-risk structures, and the rapid population growth of the area (which around the world is often associated with some structures failing to meet building codes).

-JBB

Image credit: USGS https://en.wikipedia.org/wiki/North_Anatolian_Fault#/media/File:Slip-dist.png

Read more: http://bit.ly/1HiQLhA http://on.doi.gov/1gsIWz9 http://1.usa.gov/1IPBERf http://bit.ly/1TqwFcU http://bit.ly/1MkU9vM