2023 Turkey-Syria earthquake: rupture in the heart of a triple juction
The series of earthquakes on 6 February struck at the intersection of two extremely hazardous faults: the East Anatolian Fault and the Dead Sea Transform. These faults are the boundaries between three tectonic plates that converge in the so-called Maraş triple junction, near the town Kahramanmaraş. The small Anatolian tectonic plate, on which much of Turkey lies, is said to have shifted three meters to the southwest. But what is a triple junction, why are Turkey's faults so notorious, and, most astoundingly, why do so many people live there?
Author: Kathelijne Bonne. Top image: satellite image from NASA Visible Earth catalog.
Feb. 6, one of the largest earthquakes in the recent history of Turkey and the
world struck. The epicenter was 34 km west of the city of Gaziantep in southern
Turkey, close to the Maraş (or Marash) triple junction. The first and most
powerful quake had a magnitude of 7.8 (on the moment magnitude scale) and struck at 4:17 a.m. in the morning. A
series of aftershocks soon followed, some of them extremely powerful (7.7). Also in the following days, the USGS published the recording of several tremors in the
wide area with magnitudes of more than 4. A huge area in Turkey and Syria is affected and the earthquakes were felt far beyond the national borders.
Transform faults: strong earthquakes
Turkey lies atop a complex puzzle of tectonic plates bounded by large transform fault zones. In a transform fault, the tectonic plates move laterally past each other. During an earthquake, the lateral shear stress releases much more energy than in other faulting mechanisms. It is no coincidence that the world's most severe earthquakes occur in large transform zones such as Turkey, California (San Andreas Fault), New Zealand (Alpine Fault) and Haiti (Enriquillo-Plantain Garden Fault).
Although the area has been fairly calm seismically for over 50 years, disaster struck in the middle of a humanitarian crisis. With so much suffering around it is difficult to delve into the "technical" side of this multiple crisis while people are dying, but I must give it a try. The death toll has passed the thirty thousand mark. The injured and missing are uncountable. Relief efforts are slowed down because of the existing conflict, aftershocks, bad winter weather, unstable ruins, and insecurity in every possible sense. We can only hope there won't be disease outbreaks, even though history tells a different story: cholera broke out in the aftermath of the Haiti earthquake in 2010.
Remote geologists can only contribute by explaining why earthquakes happen. Every time a natural disaster occurs, I am asked why people go to live in such dangerous places at all. "If you, the geologists, know it's so dangerous there, why aren't those regions evacuated?" (Geologists are not usually listened to but that is not the answer to this question.) What are the solutions? And are poor people more affected by natural disasters than rich ones?
Let's start with the human "why" and then look at the geology of southern Turkey's devastating triple junction.
Mosaic of landscapes
Throughout history, people have always lived in earthquake-prone places because there are many natural advantages in those regions, mainly due to the huge diversity of landscapes and resources. In tectonically active regions, societies balance precariously between prosperity and devastation. Geographically, earthquake zones form a mosaic of elongated mountain-fringed valleys and plains, in which fertile river sediment is deposited. These were attractive places for settlements, and over time, for civilizations. There is always fresh running water, room for fields and irrigation systems, fertile soils and many mineral resources.
Earthquake zones are geologically complex, and precisely because of this, rock outcrops are very diverse (limestone, sandstone, volcanic rock, etc.). The subsurface is thus rich in ores and minerals. The minerals weather at the surface, that is, they dissolve in the soil so that they can be taken up by plant roots, leading to good productivity. In mountains, there is always plenty of precipitation, snowcaps last a long time, and there is year-round water to irrigate. River floods leave a layer of mud enriching the fields. The relief offers many opportunities for cattle to move between higher and lower pastures according to the season. There are also strategic advantages. The mountains themselves provide good hiding and viewing places, and escape, trade and migration routes for people. Often large cities grew out of exchange hubs on major trade routes. Turkey was one of the major hubs of the Silk Road.
The greatest cultures flourished in tectonically complex regions, such as Mesopotamia, Lebanon, Israel, the Greek and Roman Empires, the Indus Civilization, the Inca Empire and the Mayan Empire. Earthquakes, volcanic eruptions, landslides, tsunamis and floods were a regular scourge and more than once led to the fall of city-states and entire civilizations. History shows that people always eventually return, whether or not after a period of abandonment.
In the surroundings of the Maraş triple junction (with in the wider area: Gariantep, Aleppo, Hatay and Iskerendun) we find a huge diversity of landscapes that were certainly found attractive in ancient times, and still are today. The massifs of the Taurus Mountains are interspersed with elongated, flat valleys. The tributaries of the great Orontes, Ceyhan and Euphrates rivers deposit nutrient-rich sediment in these intermontane valleys.
Why not evacuate?
Evacuating an area of high earthquake risk is impossible. We are no longer a few million people on a vast planet but billions on a cramped planet, and besides, people don't usually move (far) away during sudden natural disasters. Again, we will see that cities will rise from the ashes, laboriously, but surely. Especially long-term and lingering conditions push people to flee en-masse, such as war, climate change and famine due to soil depletion and/or crop failures year after year.
Most of the world's population lives in a potentially dangerous place on the edges of continental plates, where natural hazards are high: The entire West Coast of the Americas, the other branches of the Ring of Fire (around the Pacific Ocean), the East African Rift, Southeast Asia, the Mediterranean, the huge Eurasian Mountain range that stretches from the Pyrenees, across the Alps, Turkey and Zagros to the Himalayas and Southeast Asia. There is no question of evacuating because then everyone would have to go inland, Siberia or the Sahara.
Natural disasters hit poor people harder, but with earthquakes this has not much to do with the nature of the disasters, but rather with poor housing and indifferent or weak governments. It is more difficult to escape in one piece from shabby houses or poorly maintained apartment blocks than from sturdy villas. Turkish engineers confirm that many flats from the 1990s are in a bad state, and often built illegally. Tampering with building permits happens all the time. Building regulations are getting stricter, though, especially after the massive 2010 Izmir earthquake. The very old structures that are still standing have turned out to be earthquake resistant so far, such as the Hagia Sofia in Istanbul, which also stands right above the huge North Anatolian fault, Turkey's northern fault zone.
In the eye of the triple junction
A triple junction is a place where three tectonic plates lie against each other. Plates are separated by large fault zones or discontinuities in the lithosphere (the rigid outer part of the Earth). The plates move relative to each other, but that movement is not gradual and continuous. Tensions build up for years and discharge in a shock, casing an earthquake. After the shock, the plates have shifted slightly and the stresses slowly begin to build up again.
A well-known triple junction is the Afar Triangle in Ethiopia. There, three plates diverge. Because of the divergence, there is volcanism as magma rises to the surface. There are also earthquakes but usually not major ones.
Turkey, the situation is different because instead of "normal"
faults, the country is bisected by the massive North and East Anatolian
transform faults. These are actually the boundaries of a small tectonic plate,
the Anatolian plate, sandwiched between the much larger Eurasian, Arabian and
African plates. Those big continents squeeze tiny Anatolia to the southwest,
and the current earthquake would have moved the tiny continent by three meters.
At the Maraş triple junction, the East Anatolian fault links up with the Dead
Sea Transform, which runs all the way through western Syria, Lebanon and Israel
to the Gulf of Aqaba and the Red Sea. Through the Afar Triangle, Turkey's rift
system is thus connected to the East African rift system, which also includes a
few less dangerous triple junctions.
Let's zoom out a bit: Two continent-wide geological structures converge at the site of the 2023 Turkish-Syrian earthquake: the East African rift system and the great Eurasian Mountain range.
What to do?
As interesting as the geology of the world's largest fault zones may be, one question keeps coming back. What can be done to protect people in tectonically active regions? Since those regions cannot be evacuated, there is only one solution: buildings must be designed earthquake-resistant, earthquake preparedness and readiness tightened and evacuation procedures must be able to be carried out efficiently at all times.
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- The Mediterranean Sea dried up almost completely during the Messinian Crisis.
- Mount St Helens erupted 40 years ago.
Article by Kathelijne Bonne, geologist and soil scientist. I also write on Good Climate News.
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