Laying on the border between Europe and Asia, the mega city of Istanbul is one of the most impressive on either continent. Boasting a population of some 14 million people, the city split by the Bosphorous Strait is one of the most diverse and rapidly expanding in the world, yet an ominous portent hangs over it due to its location close to the North Anatolian Fault Zone.
Experts say that a major earthquake is due to strike the city within the next thirty years. Although construction firms have increasingly designed buildings with this consideration in mind, the event is still likely to be devastating on a human and economic level.
“It’s inevitable, a certainty,” Professor Okan Tuysuz, director of the Eurasia Institute of Earth Sciences at Istanbul’s Technical University, told the Guardian in 2006, “We know the scale. We know the place. We just don’t know exactly when…”
Now, Geoscientists and natural disaster management experts have used historical and archaeological data to determine just how powerful an earthquake in Istanbul’s metropolitan area could be.
The scientists from the GFZ German Research Centre for Geosciences, along with one colleague from the University of Southern California, analaysed historic earthquake maxima along the North Anatolian Fault Line. They concluded that although ‘mega quakes’ of magnitude M8 can be expected in the east of the region, the maximum earthquake magnitude expected in northwestern Turkey, including the Istanbul-Marmara region, is just M7.5.
“We have compiled a new catalogue on historical seismicity for the North Anatolian Fault Zone (NAFZ) dating back to 300 years BCE, thus, covering a time period of 2300 years.” explained seismologist from the GFZ Institute, Marco Bohnhoff, in a press release, “It is interesting to notice that in the North West of Turkey an earthquake with a magnitude larger than 7.5 has never been observed. On the other hand in eastern Turkey magnitudes of up to M8 are well documented”.
Earthquakes have plagued Istanbul throughout its history, dating back to its days as Constantinople. The 557 CE earthquake, which struck the Byzantine city as its citizens celebrated the run up to the winter solstice, was unprecedented in its devastation. Minor earthquakes had been common throughout the sixth century, but none had approached the ferocity of that in the winter of 557. According to the Greek poet Agathias Scholasticus, Constantinople was “almost completely razed to the ground”.
Almost a thousand years later, in 1509, another major earthquake struck Constantinople. With its epicentre in the Sea of Marmara, the earthquake had a magnitude of M7.2, leading to a tsunami and forty-five days of aftershocks. The devastating quake destroyed over a thousand homes, 109 mosques, and resulted in 10,000 fatalities.
The NAFZ extends across Northern Turkey, from the Northern Aegean Sea to the Caucasus, and is the site where the Anatolian tectonic plate meets with the Eurasian. Westward movement of the Anatloian plate causes it to interlock with the Eurasian, triggering an accumulation of stress which is released every several hundred years in the form of earthquakes.
“We were able to demonstrate that the smaller earthquake magnitudes in the west are closely linked to the earlier stage in fault-zone evolution there with an approx. age of eight million years.” explained Bonhoff, “In comparison the eastern part of the NAFZ with an age of twelve to thirteen million years, is older and more mature. The largest M8 earthquakes solely occur along the older eastern part that also has longer consistent segments”.
Of course, M7.5 earthquakes still have the potential to be a great hazard to the metropolitan area of Istanbul. The NAFZ passes just 20km away from the city’s historic centre, on the Marmara sea floor. As the 1509 Constantinople earthquake shows, a major seismic event there could be devastating.
The GFZ study reveals how historical data can be applied to predicting and preparing for future natural disasters. Through the catalogue of historical earthquakes compiled for the study, the team have estimated the maximum magnitude of a potential earthquake in Istanbul, which in turn has allowed an understanding of the seismic hazards facing the city, and could even inform building codes in the future.
For more information on the study: www.sciencedirect.com
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