BGS news

The Kahraman Maraş earthquake sequence, Turkey/Syria, 2023

Two large earthquakes occurred within hours of each other on 6 February 2023.

14/02/2023

Evolution of the southern Turkey earthquake sequence along with mapped active faults (blue lines). BGS © UKRI. Earthquake information: ANSS Comprehensive Earthquake Catalog (USGS ComCat). Topography: Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010). Mapped faults: GEM Global Active Faults Database.

The devastating Kahraman Maraş earthquake sequence has caused widespread destruction and terrible loss of life across a large part of southern Turkey and northern Syria, with the collapse of thousands of buildings in populated areas throughout the region.

The earthquake sequence

The sequence started with a magnitude 7.8 earthquake at 01:17 UTC on 6 February 2023, rupturing a 200 km section of the north-east to south-west trending fault system that forms the boundary between the Anatolian and the Arabian tectonic plates. These plates are moving horizontally relative to each other at a speed of around 13 mm per year.

The earthquake took about 30 seconds to reach a maximum slip of around 3 m and resulted in intense shaking that lasted over a minute. Recorded ground accelerations at some sites close to the fault rupture exceeded 1.0 g. A few hours later, a magnitude 7.5 event occurred on a nearby branch of the fault system that trends east to west. This caused further strong ground shaking and destruction.

Previous seismicity in the area

The magnitude 7.8 earthquake was approximately 2.5 times bigger than the magnitude 7.4 Izmit earthquake in Turkey in 1999, which killed over 17 000 people, and was the same size as the magnitude 7.8 Erzincan earthquake in north-east Turkey in 1939, which killed over 32 000 people. The latter is considered the deadliest natural disaster in Turkey in the 20th century.

Although the earthquake risk in this part of southern Turkey was generally considered to be less than along the well-known Northern Anatolian Fault in northern Turkey, large and damaging earthquakes have struck here in the past. The city of Aleppo in northern Syria has been destroyed by several earthquakes in the last thousand years, including an earthquake in 1822 with over 20 000 fatalities.

The continuing hazard

Aftershocks are expected to cause moderate to severe ground shaking over a 300 to 500 km region for months to come. Some of these earthquakes may be several hundred kilometres away from other aftershocks and may be large enough to cause further damage, particularly to buildings that have already been weakened.

There have already been several aftershocks with a magnitude larger than 6.0. Our current understanding of the statistics of the aftershock process suggests that there may be several tens of earthquakes of this size or greater.

Over a period of months to years, the frequency of triggered seismicity (aftershocks) will reduce, with earthquake activity gradually returning to previous levels. Until then, earthquake hazard and risk in the region will remain heightened. This means that increased seismic hazard in the region where the two large earthquakes occurred is transient in nature, whilst longer seismic hazard estimates continue to be relevant.

Earthquake cascades

It is well established that large earthquakes can trigger seismicity on other nearby faults as the Earth’s Crust adjusts to the sudden change in stress. Both the permanent deformation caused by the initial earthquake and the passage of seismic waves through the Earth can trigger these subsequent earthquakes.

Other recent examples of this triggering process include the Kumamoto sequence on the island of Kyushu, Japan, in 2016, when a magnitude 6.5 earthquake was followed almost a day later by a magnitude 7.3 event. In Europe, the magnitude 6.0 Amatrice earthquake that occurred in Italy in 2016 was followed by the magnitude 6.5 Norcia earthquake two months later.

Although such cascading sequences of large-magnitude earthquake within short periods of time are relatively rare, investigation and analysis of these may promote a new understanding of the earthquake process.