On 6 February 2023, two earthquakes devastated southern and central Turkey and northern and western Syria. The first earthquake occurred at 04:17:35 TRT (01:17:35 UTC), measuring moment magnitude () of 7.8. The epicenter was west–northwest of Gaziantep. This strike-slip shock achieved a Mercalli intensity of XII (Extreme) around the epicenter and in Antakya. It was followed by a 7.7 earthquake, at 13:24:49 TRT (10:24:49 UTC). This earthquake was centered north-northeast from the first. There was widespread severe damage and tens of thousands of fatalities.

The 7.8 earthquake is the largest to strike Turkey since the 1939 Erzincan earthquake of the same magnitude, and jointly the second-largest in the country, after larger estimates for the 1668 North Anatolia earthquake. It is also one of the strongest earthquakes ever recorded in the Levant. It was felt as far as Egypt and the Black Sea coast of Turkey. There were more than 30,000 aftershocks in the three months that followed. The seismic sequence was the result of shallow strike-slip faulting along segments of the Dead Sea Transform, East Anatolian and Sürgü–Çardak faults.

Damaged roads, winter storms, and disruption to communications hampered the Disaster and Emergency Management Presidency's rescue and relief effort, which included 60,000 search-and-rescue workers, 5,000 health workers and 30,000 volunteers. Following Turkey's call for international help, more than 141,000 people from 94 countries joined the rescue effort.

There was widespread damage in an area of about , about the size of Germany. An estimated 14 million people, or 16 percent of Turkey's population, were affected. Development experts from the United Nations estimated that about 1.5 million people were left homeless.

The confirmed death toll in Turkey was 53,537; estimates of the number of dead in Syria were between 5,951 and 8,476. It is the deadliest earthquake in present-day Turkey since the 526 Antioch earthquake and the deadliest natural disaster in Turkey's modern history. It is also the deadliest in present-day Syria since the 1822 Aleppo earthquake; the deadliest earthquake or natural disaster worldwide since the 2010 Haiti earthquake; and the fifth-deadliest earthquake of the 21st century. The damage was estimated at US$150 billion in Turkey, or nine percent of its gross domestic product (GDP), and US$9 billion in Syria, or 18 percent of its GDP.

Tectonic setting Geology

Central southern Turkey and northwestern Syria are affected by the interaction between three tectonic plates: the African plate, Arabian plate, and Anatolian sub-plate. The boundary between the African and Arabian plates is represented by the Dead Sea Transform (DST)—a major zone of left-lateral strike-slip fault—it accommodates the relative northward movement of Arabia with respect to Africa. The northern end of the DST truncates at the East Anatolian Fault (EAF), another major left-lateral strike-slip fault zone that accommodates the overall westward movement of the Anatolian plate as it is extruded in that direction by the northward movement of the Arabian plate. The DST and EAF meet at the Marash triple junction. The EAF continues west of the triple junction, forming the boundary between the African and Anatolian plates, linking into the Cyprus arc to the west via the Latakia Ridge.

The EAF is subdivided into seven segments, from the northeast; the Karlıova, Ilıca, Palu, Pütürge, Erkenek, Pazarcık and Amanos segments. The Amanos segment is also considered part of the DST by some geologists, or a transitional structure between the EAF and DST by others. A northern strand to the EAF has also been recognized, including the Sürgü, Çardak, Savrun, Çokak, Toprakkale, Yumurtalık, Karataş, Yakapınar and Düziçi–İskenderun segments. The estimated slip rate on the main strand of the EAF system decreases south-westwards from per year on the Karlıova segment down to per year on the Amanos segment. On the northern strand, a slip rate of per year was estimated on the Çardak segment. The Sürgü-Çardak Fault is an east–west striking long fault that runs north of the EAF. It branches away from the EAF west of Çelikhan and extends westwards to Göksun.Erdik, M., Tümsa, M. B. D., Pınar, A., Altunel, E., and Zülfikar, A. C. 2023, A preliminary report on 6 February 2023, Earthquake in Türkiye, Comprising two segments; the Sürgü Fault runs between Çelikhan and Nurhak; the Çardak Fault runs between Nurhak and Göksun. Seismicity on the fault is low—the only associated earthquake was a M 6.8 event in 1544.

The northern part of the DST is subdivided into several segments, although there is some disagreement between scientists as to which faults should be assigned to the DST and which to the EAF, at the northernmost end of the structure. Following the 2013 "Active Fault Map of Turkey", seven DST segments are recognized in Turkey and neighbouring parts of Syria; the Afrin, Sermada, Armanaz, Hacıpaşa, Yesemek, Sakçagöz and Narlı segments.

Seismicity The EAF has produced large or damaging earthquakes in the past few hundred years along various segments, including the 1789 (M 7.2, Palu), 1795 (M 7.0, Pazarcık), 1866 (M 7.2 Karlıova), 1872 (M 7.2, Amanos), 1874 (M 7.1, Palu), 1875 (M 6.7, Palu), 1893 (M 7.1, Erkenek), 1971 (M 6.6, Karlıova) and 2020 (M 6.8, Pütürge) events. Other large historical earthquakes have been tentatively assigned to segments of the EAF, such as the 1114 and 1513 Marash earthquakes, both thought to have ruptured the Pazarcık segment.

The Palu and Pütürge segments in the east display a recurrence interval of about 150 years for M 6.8–7.0 earthquakes. The Pazarcık and Amanos segments in the west have recurrence intervals of 237–772 years and 414–917 years, respectively, for M 7.0–7.4 earthquakes. A research paper published by Earth and Planetary Science Letters in 2002 studied stress accumulation and increased seismic hazard along the East Anatolian Fault. The study concluded two sections of the fault with a considerably high potential for future earthquakes. One of these sections was in Elazığ and Bingöl, located between the rupture zones of the 1874 and 1971 earthquakes. The seismic gap ruptured during a 6.1 earthquake in 2010. The 2020 6.8 earthquake ruptured to the southwest between the 1893/1905 and 1874 earthquakes. Another seismic gap was located in Kahramanmaraş—this long section—according to the study, believed to last rupture in 1513 has the potential to produce magnitude 7.3 earthquakes.

Large earthquakes on the northern part of the DST include events in 115, 526, 587, 1138, 1170 and 1822, which resulted in several tens of thousands to several hundreds of thousands of fatalities.

Earthquake sequence

The first and largest earthquake in the sequence struck at 01:17 UTC. The United States Geological Survey (USGS) and Global Centroid Moment Tensor (GCMT) measured it at 7.8 and 7.8, respectively. GEOSCOPE reported 8.0 and Kandilli Observatory (KOERI) reported 7.7 and 7.4. It had an epicenter west of Gaziantep in Gaziantep Province, which is near the border with Syria. The earthquake hypocenter was at a depth of according to USGS and according to KOERI. The shock had a focal mechanism corresponding to strike-slip faulting.

It is one of the strongest ever recorded in Turkey, equivalent in magnitude to the 1939 Erzincan earthquake (7.8). These earthquakes are surpassed only by the larger estimates for the 1668 North Anatolia earthquake. Globally it was the strongest recorded since August 2021.

At 10:24 UTC, an earthquake measuring 7.5 according to USGS, 7.6 according to KOERI, or 7.7 according to Geoscope and the GCMT, struck with an epicenter near Ekinözü, 95 km northeast of the 7.8 event. It had a depth of according to the USGS, by KOERI, and by Geoscope. The shock was also the result of strike-slip faulting; it had an epicenter north of the previous large earthquake.

A reevaluation of the earthquakes using long-period coda moment magnitude obtained 7.95 ± 0.013 and 7.86 ± 0.012, respectively. These earthquakes were some of the largest Turkish earthquakes in over 2,000 years. Both earthquakes are the largest and only observed to occur on land within a short span of time.

Aftershocks

Over 570 aftershocks were recorded within 24 hours of the 7.8 earthquake and over 30,000 recorded by May 2023. An aftershock measuring 6.7 occurred about 11 minutes after the mainshock. There were 25 aftershocks 4.0 or greater recorded within six hours of the main tremor, according to the USGS. More than 12 hours later, the USGS had reported at least 54 aftershocks of 4.3 or greater magnitude, while the Turkish Disaster and Emergency Management Presidency (AFAD) recorded at least 120 total aftershocks.

The 7.8 earthquake had aftershocks distributed along about of the EAF. A 6.3 aftershock struck near Uzunbağ in Hatay Province on 20 February; the earthquake was the result of oblique-normal faulting. This 6.3 event produced an independent cluster of aftershocks with a similar focal mechanism. Aftershocks from the sequence also occurred in the Gulf of Alexandretta, consistent with a northwest–southeast striking fault that produced the large aftershock. This aftershock occurred because the 7.8 event transferred sufficient on another normal fault sufficient for it to fail.

The 7.7 earthquake triggered its own aftershock sequence, including two  6.0 aftershocks. Aftershocks of the second earthquake continued through at least 9 February. Thousands of aftershocks associated with this earthquake were distributed along an east–west trend corresponding to the Çardak Fault for about .

Seismology

A source model for the 7.8 earthquake produced by the USGS from observed seismic waves, taking into account preliminary rupture mapping from satellite data, uses three fault segments with individual lengths, widths, strikes and dips of > × , 028°/85° (Segment 1), > × , 060°/85° (Segment 2) and > × , 025°/75° (Segment 3). The mainshock produced a maximum slip of along Segment 2, beneath Sakarya in Kahramanmaraş Province, northeast of the junction where it meets Segment 1. Another zone of large slip estimated at occurred further northeast along Segment 2, northwest of Adıyaman.

The USGS source model for the 7.7 earthquake which struck nine hours later has three large fault segments with individual lengths, widths, strikes and dips of > × >, 276°/80° (Segment 1), > × >, 250°/80° (Segment 2) and ~ × >, 060°/80° (Segment 3). Maximum displacement occurred on Segment 1 at .

Three segments of the EAF were involved in the 7.8 rupture; the Amanos, Pazarcık and Erkenek segments. The earthquake ruptured ~ of the EAF, producing a maximum slip of up to ~ along the Pazarcık segment. The northern end of the rupture was about south of the 6.8 earthquake that struck in 2020. This section of the EAF, the Pütürge segment, between both earthquakes, may represent a seismic gap. The southern segment of the EAF rupture was at its termination, near Antakya. Slip peaked at from the surface to depth during the 7.7 earthquake; slip was at the surface. Slip along the fault was compact—mostly confined to within the Çardak Fault; it was also shallower—attenuating from . Slip during the 7.8 event extended to and for the 7.7 event. The 6.4 aftershock that struck Antakya on 20 February had a rupture area of × and produced a peak slip of at depth.

Preliminary analysis of the effects of stress changes caused by the 7.8 earthquake on the Çardak–Sürgü Fault, based on the USGS fault model, indicated up to 3 bars of added stress near the epicenter of the 7.7 shock, sufficient to trigger rupture on that zone, assuming that it was already close to failure. Stress on the Hatay Fault, source of the 20 February 6.4 aftershock, increased by 1 bar following the 6 February earthquakes.

Rupture propagation