The first quake could have given a final push to the second fault zone, which had accumulated stress over decades and was already critically loaded.
The first of the two powerful earthquakes that struck Turkey and Syria on February 6 could give the ‘final push’ for the second, turning this event into an earthquake doublet .
Just nine hours apart and of similar magnitude these have centroids closer than their rupture size and occur within a time frame that is shorter than the recurrence time inferred from plate motion, the researcher explained in a statement. from ETH Zurich Luca Dal Zilio, co-author of a commentary on these recent quakes in Communications Earth & Environment .
It was not a replica
The second quake in this case was not a typical aftershock, as it was almost as strong as the first 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 quake .
According to Dal Zilio, the first earthquake likely 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 enough to trigger the second event just a few hours later. This suggests that both faults were under critical stress,” he explained.
Thus, he estimates that the first earthquake could have given a final push to the second fault zone, which had accumulated stress for decades and was already critically loaded.
Significant damage in earthquakes of this magnitude cannot be avoided , especially when cities are located exactly on seismically active fault lines, causing large surface displacements of six to eight meters.
In the opinion of this expert, this event underlines the need to better understand the strong movement of the ground near a fault and to update risk management practices, for example, calculating how the transfer of tension has changed the probability of danger in the region. . Ideally, we should also find out to what extent strong mainshocks have changed the stability of buildings and increased their vulnerability to aftershocks.
Separately, Dal Zilio commented that the North Anatolian Fault and the East Anatolian Fault, which run through Turkey , are two of the most active fault systems in Europe and the world, and therefore pose a seismic hazard. important for the region.
The North Anatolian Fault, on which Istanbul lies, also presents a significant risk. There have been several earthquakes along this fault in the last century. These events have now left a seismic gap south of Istanbul and below the Sea of Marmara, a gap that has not been filled in 250 years. Seismologists often refer to these regions as seismic breccias because they are sections of a fault system where little or no seismic activity has occurred for an extended period of time, even though neighboring sections have been affected by earthquakes .
“We assume these are areas along a fault where stresses build up before releasing a huge amount of energy all at once, which can result in powerful earthquakes,” he said.