The earthquake in Turkey was twofold: the first and second occurred on the neighboring fault

ETH Zurich researcher Luca Dal Zilio provides an insightful summary of recent earthquakes in Turkey and Syria, shedding light on the complex nature of this event. It discusses lessons that can be drawn from it to better understand and prepare for future seismic events in the region.

ETH News: You and your colleague Jean-Paul Ampero of Geoazur have just published commentary on the earthquakes that hit Turkey in early February in the Scientific Journal. Earth and Environment Communications. what’s new?

Luca Dal Ziliu: The two strong earthquakes that hit Turkey and Syria on February 6, 2023 were of the same magnitude (7.8 and 7.6) and only nine hours apart. These events are referred to as earthquake doubling because they are a pair of strong earthquakes that have mean trains closer than their rupture magnitude and occur in a time frame shorter than the repetition time inferred from the plate motion.

There was long talk of an exceptionally strong aftershock.

The second quake in this case was not a typical aftershock, as it was roughly the same magnitude as the first and occurred on a different nearby fault. According to Bath’s Law, the largest aftershock is usually about 1.2 magnitude smaller than the main earthquake. Seismic series like the recent events in Türkiye and Syria have their own unique features. Studying these events helps us learn more about earthquakes and improve our ability to predict them.

Why did a double earthquake happen?

Perhaps the first earthquake contributed to an increase in static stress in the region where the second event occurred. While this increase may not have been significant, it would have been enough to start the second event just hours later. This indicates that both bugs were under critical stress. The first earthquake may have given a final boost to the second fault zone, which had built up stress over decades and was already dangerously overloaded. More research will help us better understand this aspect of interaction with earthquakes.

What can be learned from your analysis of the reconstruction of towns and villages in the affected areas?

Massive damage in earthquakes of this magnitude is unavoidable, especially when cities are located exactly on seismically active fault lines, causing large surface displacements of six to eight metres. This event underscores the need to better understand strong ground motion near a fault and update risk management practices—for example, by calculating how pressure transfer changed the hazard probability in the area. Ideally, we should also find out to what extent strong earthquakes altered the stability of buildings and increased their vulnerability to aftershocks.

Have we not long been aware of the high seismic hazard and associated severe risks for this region?

Yes, various European institutes – including ETH Zurich and the Swiss Seismological Service – have put a lot of effort into calculating earthquake risk across Europe in recent years. Thanks to these efforts, we now have an earthquake risk Europe map Everyone can access it. This map shows that the North Anatolian Fault and the East Anatolia Fault – both of which run through Turkey – are two of the most active fault systems in Europe and the world, and therefore pose a significant seismic hazard to the region.

The North Anatolian Rift, on which Istanbul is located, also poses a great danger. There have been many earthquakes along this fault in the past century. These events have now left a seismic chasm south of Istanbul and under the Sea of ​​Marmara, a chasm that has not been filled for 250 years. Seismologists often refer to areas as seismic fissures because they are sections of a fault system in which little or no seismic activity has occurred over a long period of time, even though adjacent sections have been affected by earthquakes. We assume that these are areas along the fault where stresses build up before a massive amount of energy is released all at once, which can cause powerful earthquakes.

What does the future look like and what will happen next?

In short, the current focus is on dealing with the massive loss of life and property. In the coming months and years, several follow-up studies to our report will provide insight into this catastrophic event. We hope to be able to learn from this to make buildings safer and better prepared for such events. As scientists, we hope this event will provide valuable insights into fault mechanics and earthquake physics.