Tehran – A strong earthquake of 6.2 size in the Marmara Sea, 40 km from Istanbul, Istanbul, at 12:49 pm local time on April 23, 2025. The mechanism of the earthquake is non-slip, and the epicenter of the earthquake is located about 10 km and 40 km southwest of Istanbul in the seas of Marmara.
The Istanbul region is seismically active due to its proximity to the North Anatolian fault (NAF) and has been the site of several major earthquakes throughout history. With a dominant dextral strike slip mechanism, this fault system is known for passing through northern Turkey and generating large earthquakes. Istanbul is at risk of major seismic events, and forecasts indicate that earthquakes can occur at any time. These events often follow a westward “movement” pattern, with stress being transmitted along the fault after each rupture. Earthquake movements indicate the westward progression of major ruptures since 1939, but the fault segment of the Marmara Sea was the most important segment without rupture since 1766. people.
The earthquake near Elginkan on August 17, 1668 (an estimated scale of M7.8–8.0) was one of the largest earthquakes in Anatolia history, causing extensive destruction from Elginkan to the Black Sea. 400 km of the fault system has burst. On May 22, 1766, an earthquake in the Marmara Sea (near Istanbul) section of the North Anatolian Fault, weighing about 7.4, destroyed parts of Istanbul, killing about 4,000-5,000 people. This last major burst in the Marmara Sea sector was the creation of the current seismic fissure near Istanbul.
In the south and east of the Marmara Sea, the earthquakes of August 17, 1999 and November 12, 1999 were 7.4 and 7.1 respectively, respectively, the last major rupture of this fault in southeastern Istanbul and in the Marmara Sea.
The Marmara section of the North Anatolian fault system has accumulated stress for 259 years since 1766 and has not ruptured.
Historically, Istanbul has experienced at least 34 major earthquakes in the last two,000 years. The last major earthquake in the region occurred in 1999 in Izmit, about 80 km southeast of Istanbul. This had devastating effects and highlighted the vulnerability of many of the city’s buildings. The current assessment shows that only about one-third of Istanbul’s buildings are structurally resilient to seismic activity.
The accumulation of stress along the North Anatolian Fault System (northern branch) near Istanbul and the presence of seismic gaps in the fault lock near Istanbul led to the presence of 65% to 70% of the chances of a major earthquake of a magnitude below 7 earthquake in this region by 2040. people.
A tsunami warning has also been issued following the earthquake on April 23, 2025. A major rupture occurs in the North Anatolia fault in the Marmara Sea, which can create a tsunami with waves of up to 10 meters.
The North Anatolian fault is a round, right-handed anti-slip fault with the Anatolian plate moving westward relative to the Eurasian plate at a rate of 2-3 cm a year. Complete rupture of the Marmara section of a fault about 150-200 km long can cause an earthquake of M7.0-7.8. The population density of Istanbul’s 16 million people and the presence of aging and vulnerable structures of about two-thirds of Istanbul’s buildings indicate that most of Istanbul’s population is in weak buildings that are exposed to the possibility of damage from the next major earthquake. In this coastal region, soft deposits along the Marmara coast enhance earthquake tremors. Liquefaction in coastal areas is another danger from the Istanbul earthquake, along with the possibility of tsunamis with a possible wave height of 5-10 meters. Of course, since 2013, important facilities (hospitals, bridges) can fail in this city. Earthquake early warning systems are operating, particularly due to the gas network and the safe closure of major Istanbul cities, which are effective in reducing secondary risks.
Future earthquakes in the North Anatolia Disorder Zone (NAFZ) near Istanbul are of great importance for geological, social and economic reasons. The northern branch of the North Anatolian fault north of the Marmara Sea (near Istanbul) has not ruptured since 1766 and has accumulated about 259 years of structural stress. This “locked” section is ready for a major earthquake to be delayed. With a 62-75% chance, the M7.0+ event could become a serious event location near Istanbul by 2040. The April 23, 2025 earthquake is considered, so the possibility of another earthquake will be reassessed, with a 6.2 magnitude earthquake potential likely to result in a domino effect close to a trapped fault fragment. Istanbul is a metropolitan city of about 16 million people, many of whom live in busy buildings, informal settlements or buildings built before 2000 that do not meet the modern earthquake code. Construction Quality: Despite stricter regulations following the 1999 Izmit earthquake, poor construction and illegal construction continue. 40% of Istanbul’s buildings are at risk of collapse. The soft sediments along the coastal regions of Istanbul – the golden horns – and the coast of Marmara can amplify tremors by 2-3 times. Istanbul is a turkey financial, cultural and logistics center, accounting for around 40% of GDP. Large earthquakes can disrupt the global supply chain (such as shipping from the Boshols Strait).
A major earthquake could cause tsunamis and liquefaction in Istanbul. Coastal areas and flatlands are at increased risk. Bridges, airports, hospitals, energy networks (such as natural gas pipelines) can become inoperable. Estimates suggest hundreds of thousands of deaths and millions of displaced people in the worst-case scenario. Due to the dense urban layout of Istanbul, emergency response is difficult.
A complete rupture of 150-200 km long of the northern branch of the North Anatolia Fault in the Marmara Sea could generate an earthquake of M7.4-7.8. Partial ruptures (e.g., length 50-100 km) can produce M7.0-7.4.
Since 1999, only 10% of vulnerable buildings have been remodeled. Financing and implementing earthquake regulations remains an important issue in Türkiye. Therefore, earthquakes of over 7 sizes near Istanbul are one of the natural disasters of the 21st century, with the possibility of an earthquake of M7.0-7.8, catastrophic loss of life, and serious economic consequences of the Türkiye and the region.