The twin earthquakes that struck southern Türkiye and neighbouring Syria, and have killed more than 28,000 people as of Sunday were “extraordinary,” according to experts, as they stressed the need for more study on recent data in the wake of the strong tremors.
The magnitude 7.7 and 7.6 earthquakes, centred in the Kahramanmaras province, affected more than 13 million people across 10 provinces, including Hatay, Gaziantep, Adana, Adiyaman, Diyarbakir, Kilis, Malatya, Osmaniye, and Sanliurfa.
Several countries in the region, including Syria and Lebanon, felt the strong tremors that shook Türkiye in the space of less than 10 hours.
Tiziana Rossetto, a professor of earthquake engineering at University College London, told Anadolu Agency (AA) that it is known that the epicentre of the earthquake, Kahramanmaras, is very seismic.
“However, this was a very large event,” she said, adding that the first earthquake triggered the second earthquake on the different fault, on the East Anatolia fault.
“So what we have here a situation where you have one very large earthquake, which in itself is devastating, or could be devastating, followed in sequence very shortly by another extremely large earthquake,” Rossetto said.
“So, this is not a common event. And I don’t think it’s something that we think about, it’s definitely not something we think about within a seismic design setting,” she argued.
Rossetto also compared Monday’s quakes with the 1994 Northridge earthquake that hit the San Andreas fault in California.
She said the 6.7 magnitude California quake caused massive damage on infrastructure, bridges, roads, and buildings, however, there was a much lower level of energy release than the first earthquake in Türkiye, “which is at least 30 times more in terms of energy release.”
“So, you know, we can expect these large earthquakes to cause a lot of damage, but that’s why we need to be prepared,” the professor added.
It takes long time for the energy to accumulate to create such large earthquakes, Rossetto said.
“If the energy can be released in a number of very small earthquake events, which don’t cause a lot of ground shaking but are releasing energy constantly, and you know many times a year, or they can accumulate, the plates are essentially locked together and continuing to stress until the moment when they break. When they break, they release all of their energy.”
She, however, added that it is not certain that the next such powerful earthquake will happen in a time of 500 years.
The movements at the faults– small rearing of the faults or aftershocks – are happening now as the faults “sort of reestablish themselves in balance,” according to Rossetto.
Aftershocks will be happening in “over a number of weeks and reducing in size over time that we don’t know,” she said.
Raymond Durrheim, a geoscience professor at South Africa-based Witwatersrand University, told AA that the two earthquakes were exceptional in the way that they occurred in close regions to each other and at short intervals.
According to him, the earthquakes of magnitude 7.5 and above are observed almost every year around the world, but earthquakes of magnitude 7.7 and 7.6 in Türkiye, which are very close to each other on the fault line and occur nine hours apart, were “extraordinary.”
Echoing Rossetto, Durrheim said the first quake was more likely to have triggered a second tremor, as it obviously added to the tragedy.
At the same time, he said, there are too many people trapped in debris and waiting to be rescued, which is straining the resources of response teams.
Detailed analysis needed
Jordi Diaz, a seismologist from the Geosciencies Barcelona (GEO3BCN-CSIC), a centre of the Spanish Scientific Research Council specialised in geosciences, told AA that the twin quakes that hit Türkiye was “so big” and “strong,” and according to the statistics the biggest earthquake in the century.
Diaz said earthquakes of this magnitude occur 10 or 20 times in a year in the world, but earthquakes in Türkiye have some differences in terms of intensity.
The depth of the back-to-back tremors were very close to the surface, and the two earthquakes centred in residential areas, he said, explaining the reasons of big losses in Türkiye, also citing the poor construction of buildings.
Diaz said the earthquakes in Türkiye occurred in a region marked red in the seismic map. They were expected to happen in the region, but the exact time had not been known, he added.
“In earthquakes, we know the risk zones, but since we do not know the time, what we need to do is to get prepared in the best way and build resilient structures,” he urged.
The expert highlighted the need for a detailed analysis of the earthquakes in Kahramanmaras. He said there were earthquakes in two different fault lines in Türkiye and it is still being discussed whether the second quake was an aftershock or separate tremor.
Data from these earthquakes will certainly be used to record the progress in the earthquake analysis, he said, adding that segmental fault lines being sliced into fault shapes will help to better understand the geodynamic conditions of fault lines.
Recent data and seismic hazards may change existing regulations or monitored areas, according to Diaz.
He also warned that Istanbul, like many others, is a place at risk of a large and destructive earthquake, similar to Tokyo, Los Angeles and San Francisco.
He suggested that new buildings should be constructed with better earthquake resistance, logistic support should be strengthened and response teams should be prepared.