Affecting over 14 million people, nearly 16% of the national population, the recent twin quakes that occurred in southeastern Türkiye – mainly in Adana, Adiyaman, Diyarbakır, Gaziantep, Hatay, Kilis, Malatya, Osmaniye and Şanlıurfa – also resulted in strong tremors in several countries in the region, including Syria and Lebanon, within the space of fewer than 10 hours.
It's the second week after the deadly quakes, and the death toll has risen to 31,643, according to the Disaster and Emergency Management Authority (AFAD) on Monday. Some 147,934 survivors have been evacuated from the region to other provinces. It's been a week, but the pain of loss remains fresh.
After the deadly disaster shook the world, many lessons have been learned from the twin quakes, such as global unity, miracles in rescue operations, geographical changes, and of course, the importance of geography and construction – all these elements contribute to showing us how important it is to be prepared to avoid these catastrophes.
Since the earthquake, every citizen in Türkiye has been preoccupied with a fear of future tremors. Geologists from all over the world have tried to address the fear and explain the chance of another disaster. This scenario has created a zeal among youngsters to learn about geophysics to understand why and how quakes occur. The same enthusiasm inspired Daily Sabah to discuss the science behind the recent earthquakes in southern Türkiye and learn more about geophysics.
Geophysics engineer professor Murat Utkucu from the Department of Geophysical Engineering at Sakarya University explained the geophysics of the deadly quake: "The major and devastating magnitude 7.7 and 7.6 earthquakes demonstrated once more how earthquakes impact densely populated and industrialized areas. Both earthquakes that struck southeastern Türkiye occurred along the East Anatolian Fault Zone (EAFZ), one of the major tectonic elements running across the country. Along with the North Anatolian Fault Zone (NAFZ) that produced the notorious quake in 1999 with a magnitude of 7.5 in Izmit and 7.2 in Düzce, these faults accommodate the movement of the Anatolian Plate toward the west. This motion is the main cause of the earthquake generation along the faults. In addition to the other diffuse faults in western and eastern Türkiye, the country is one of the most earthquake-prone countries on Earth."
Regarding the recent earthquakes, Utkucu said: "The first earthquake struck just before sunrise, mostly catching people while they slept. Powerful enough to be shaken or to be felt from thousands of kilometers away, this shock ruptured a fault of about 250-300 kilometers (155-190 miles) as indicated by the aftershock distribution provided by the AFAD and the Kandilli Observatory and Earthquake Research Institute of Türkiye, as well as initial field studies and seismogram analysis by the institutes across the globe. For comparison, the 1999 Izmit earthquake ruptured a fault length of 150 kilometers along the NAFZ, and the 2020 Sivrice-Doğanyol earthquake of 6.7 along a section of the EAFZ slipped a fault length of 50 kilometers. This fact explains why the earthquake affected a broad area. The 7.7 earthquake released a seismic movement that was 50% larger than that of the 1999 Izmit and Düzce earthquakes combined (compare 5.5 x 1020 Nt.m to the sum of 3.2 x 1020 Nt.m). Strong aftershocks as large as 6.7 followed. As if that was not bad enough, our research at Sakarya University found that this earthquake triggered the second mainshock of 7.6 magnitude along a fault branch of the EAFZ called the Northern Branch.
"The second major tremor ruptured a fault perpendicular to the first one. The first mainshock, depending on the faulting type of the EAFZ, caused a damaged area in the northeast-southeast directions. Nevertheless, the second mainshock further broadened the damaged area in the east-west direction. Adding the magnitudes of both shocks, this is why we are facing a wide damage area that complicates the disaster relief efforts."
"The strength of the 7.7 tremor was no surprise because it involved a section of the EAFZ called the Maraş Seismic Gap, which has been known for its large earthquake quiescence for at least 500 years. The data from the trenches excavated along the fault indicated that the 1114 and 1513 earthquakes were the last to rupture the gap."
The current status of the fault lines has also been estimated in a project carried out by the author and supported by the Scientific and Technological Research Council of Türkiye (TÜBITAK). As an earthquake-prone country, doublet earthquakes with shocks close in location and timing are not uncommon in Türkiye. The doublets were 16 days apart in 1114, three months apart in 1766 and in 1999, and a month apart in 1866. None of these previous quakes occurred within hours of each other.
The magnitude of the first mainshock also surprised those researching earthquakes because historical seismology studies have suggested the maximum magnitude of large earthquakes along the EAFZ was 7.5-7.6. Considering the nature of the earthquake magnitude scale and the magnitude of the first mainshock, this means a considerable difference in size, he explained.
"Here at Sakarya University, our first analysis found that two or possibly three of the faults that caused previous quakes ruptured together for the current earthquakes. We know that the faster slipping NAFZ produced the 7.9-8.0 magnitude Erzincan earthquake in 1939 but we did not expect such a large earthquake along the EAFZ."
There are two well-defined seismic gaps in Türkiye, both along the NAFZ, namely the Yedisu Seismic Gap in the east of Erzincan and the East Marmara Sea Seismic gap, lying offshore Istanbul, between the Kartal district of Istanbul and the Marmara Ereğlisi town of Tekirdağ. The first was ruptured in 1784, and the latter in May 1766. Neither of the gaps has generated an earthquake large enough for crustal deformation relaxation, and 250 years are sufficient for them to produce magnitude 7.0 or larger earthquakes, meaning a high risk for a major earthquake.
All these factors demonstrate how high the chance of another major earthquake is and how vital earthquake science studies are in Türkiye. Anatolian lands have experienced dozens of significant earthquakes in the last millennia. The 1668 North Anatolian earthquake was believed to have been 8.0-8.1 magnitude. Even earthquakes that could be classified as “great” from a seismology perspective occur in this region. Earthquake science studies and education, earthquake safety and disaster management should be among the priorities in Türkiye. Despite all structural design procedures, the buildings are still collapsing. Considering the high standards of civil engineering in Türkiye and past experiences, the collapses are mostly due to the application process and lack or neglect of proper inspection during the construction process. Since, these problems could not be overcome in the short term, to mitigate earthquake risk, the necessity of short-building designs or giving priority to the risk rather than hazard should be discussed by the civil engineering community, Utkucu advised.
