Earthquake hazard for Istanbul

Istanbul is an ancient and beautiful city with a long history at the centre of major empires including the Roman, Byzantine, Latin and Ottoman. It is a city inundated with rich culture and history. In 2010 it was named a European Capital of Culture making it the world’s tenth most popular tourist destination. Home to over 13 million people it is also one of the most densely populated cities in Turkey.

A building destroyed in the 1999 Izmit earthquake

But this thriving and seemingly indestructible city sits on a loaded spring: The North Anatolian Fault. The most active and earthquake prone fault system in Turkey and the source of the 1999 magnitude 7.4 earthquake that killed nearly 18,00 people in the city of Izmit.

The North Anatolian Fault is about 1300km long running along the entire length of northern Turkey, from the Aegean Sea to the west to Lake Van to the east.

It has been known for a while now that earthquakes on the fault tend to follow a successive sequence, i.e. an earthquake rupture will often occur in the section of the fault proceeding the last rupture. The current sequence started in 1939 with the magnitude 7.9 Erzincan earthquake and has been progressing to the west in a series of 12 large earthquakes.

Researchers in 1997 used this observation to successfully predict the location of the 1999 Izmit earthquake (if not the exact time). Worryingly the Izmit earthquake ruptured less than 100km to the east of Istanbul. Further work has led other researchers to predict a major earthquake, possibly another magnitude 7.4 in the Istanbul region within the next 20 years!

Current westward progression of earthquakes along the North Anatolian Fault.

So what can we do? Firstly, we need to better understand the science behind the cause of earthquakes in this region. The FaultLab project based at the University of Leeds involves research into the nature of the North Anatolian Fault and the surface deformation during various stages of the earthquake cycle. A greater understanding of the fault system can be used in forecasting models to give a better idea of the seismic risk.

Secondly, more engineering work needs to be done to reinforce vulnerable buildings which would collapse in the event of ground shaking. In May 2012 the Turkish government passed a new Urban Transformation Law which stated that all buildings that did not conform to current earthquake hazard and risk criteria will be demolished and rebuilt.

Is it too late?

This effectively means nearly 7 million buildings throughout Turkey will be rebuilt to current earthquake standards over the next two decades! This massive project is expected to generate over USD 500 billion worth of construction industry over the next decade. Only last month, (February 2013) work began in Istanbul.

A new rail line currently under construction which runs beneath the Bosphorus Sea and links the east and western parts of the city will also be able to withstand moderate to high intensity shaking.

But the key question is: will Turkey and Istanbul in particular be able to finish all this redevelopment before the next major earthquake?

For all our sake, I certainly hope so!

Ekbal

More information:
[1] Progressive failure on the North Anatolian fault since 1939 by earthquake stress triggering, 1997, Geophysical Journal International, v 128, pp 594-604
[2] Parsons, T., Shinji, T., Stein, R. S., Barka, A. A., Dietrich, J. H.; Heightened Odds of Large Earthquakes Near Istanbul: An Interaction-Based Probability Calculation, 2000, Science, v 288, pp 661-665
[3] http://www.invest.gov.tr/en-US/infocenter/news/Pages/220213-turkey-urban-transformation-project-foreign-investors.aspx