Researchers have determined that Turkey and Syria’s February 6 earthquake disaster was probably a “doublet”, a process in which the first quake triggers the second in a neighbouring fault.
ETH Zurich researcher Luca Dal Zilio and colleague Jean Paul Ampuero from Geoazur published a commentary on the quake catastrophe that killed tens of thousands in scientific journal Communications Earth & Environment. Dal Zilio spoke to ETH News about his and Ampuero’s findings.
Dal Zilio observed: “The two powerful earthquakes that hit Turkey and Syria on 6 February 2023 were of similar magnitude (7.8 and 7.6) and only nine hours apart. These events are referred to as an earthquake doublet because they are a pair of powerful earthquakes that have centroids closer than their rupture size and occur within a time frame that is shorter than the recurrence time inferred from the plate motion.”
He added: “There was long talk of an exceptionally strong aftershock. The second earthquake in this case wasn’t a typical aftershock, as it was almost as strong as the first one and occurred on a different, nearby fault. According to Bath’s Law, the largest aftershock is usually about 1.2 magnitudes smaller than the main earthquake. A series of earthquakes like the recent events in Turkey and Syria has its own unique features.”
Asked why an earthquake doublet probably occurred, the researcher said: “The first earthquake probably contributed to an increase in static stress in the area where the second event occurred. While this increase may not have been substantial, it could have been sufficient to set off the second event just hours later. This suggests that both faults were under critical stress. The first earthquake might have given a final nudge to the second fault zone, which had accumulated stress over decades and was already critically loaded. Further research will help us better understand this aspect of earthquake interaction.”
Dal Zilio also discussed the fact that Istanbul is at serious risk of suffering a major earthquake, something experts have warned of for a long time.
Turkey’s commercial and cultural capital, with a population of 16mn, is located on the North Anatolian Fault. The North Anatolian Fault and the East Anatolian Fault, which also runs through Turkey, are two of the most active fault systems in Europe and the world and thus pose a major seismic hazard.
Said Dal Zilio: “The North Anatolian Fault, on which Istanbul is located, also poses a significant risk. There were several earthquakes along this fault in the last century. These events have now left a seismic gap south of Istanbul and beneath the Sea of Marmara, a gap that has not been filled for 250 years. Seismologists often refer to such regions as seismic gaps because they are sections of a fault system where little or no seismic activity has occurred over an extended period of time, even though neighbouring sections have been affected by earthquakes.
“We assume that these are areas along a fault where stresses accumulate before releasing an enormous amount of energy all at once, which can result in powerful earthquakes.”