The first high-precision image of a seismic fault zone is changing our knowledge of earthquakes. The idea that earthquakes release stress in a single strong quake along a single fault plane may need to be corrected. Recent research by the Karlsruhe Institute of Technology (KIT) in collaboration with the German Earth Sciences Research Center GFZ and other international institutions shows that the earthquakes occurred in an area with many fault planes, some of them parallel.

According to the authors, the results of the study can help create more realistic models of earthquakes and earthquake hazards in subduction zones. The study was published in the journal Nature.

An international team led by KIT’s first author, Carolina Challumeau, investigated a series of earthquakes that occurred in Ecuador, on the west coast of South America. There, the Pacific plate has sunk beneath the continental South American plate. Subduction repeatedly leads to very strong earthquakes. The most recent series of earthquakes in Taiwan may also be linked to the sinking, with the main earthquake killing nine people and causing extensive damage off Taiwan’s east coast in early April.

The series of Ecuadorian earthquakes analyzed by the team began on March 12, 2022, and ended on May 26, 2022. The strongest earthquake (magnitude 5.8) occurred on March 27 and triggered several smaller aftershocks in a short time. At that time, there was a dense network of 100 seismometers in the region. It was created for High Resolution Imaging of the Subduction Fault in the Pedernales Earthquake Rupture Zone (HIPER for short) for a sea experiment.

Detailed analysis of seismic data

Thanks to the highly detailed data from the HIPER experiment and the use of artificial intelligence, researchers were able to map more than 1,500 earthquakes and their corresponding fault planes at very high resolution at a depth of 15 to 20 kilometers. First author Dr. from KIT Geophysical Institute (GPI). “We observed that the seismicity of earthquakes occurs in the primary zone – the main earthquake, so to speak – and in the secondary zone, that is, the aftershocks,” says Caroline Chalumeau. . “We observed in the primary zone that seismicity occurred on many different fault planes, often overlapping. In some places parallel seismically active planes emerged, in others only isolated ones.”

Parallelism of earthquakes is not associated with a specific depth. “We found indications that the previous idea of ​​the release of stress from a single strong earthquake along a single fault plane may be a thing of the past,” says Professor Andreas Rietbrock from GPI. “Instead we need to talk about a fault network in which a series of ruptures occur during a single earthquake.”

Analysis of a series of earthquakes in Ecuador also provides new information about aftershocks. Challumeau says the main earthquake first occurred near the epicenter and then gradually spread in other directions. From this he concludes that the distribution of aftershocks in the region is mainly controlled by aftershocks. Professor Onno Onken from GFZ says: “With this study, Caroline Chalumeau’s team has provided the first clear seismological image of a seismogenic plate boundary. On the one hand, it confirms existing geological observations, and on the other hand, it successfully explains the propagation of aftershocks with a new approach. Thus, for example, liquid Previous assumptions that the spread caused aftershocks have been refuted.”

The results are also important for assessing earthquake risk in subduction zones. “The research will have implications for future modeling of earthquakes as well as for aseismic slip, that is, plate movements without earthquakes,” says Andreas Rietbrock.