Recent research indicates that earthquakes in subduction zones do not happen on a single fault plane, as traditionally believed, but rather on a complex network of fault planes. This discovery, based on detailed seismic data collected in Ecuador and analyzed with AI, challenges conventional ideas about how seismic stress is released. The study also provides new insights into aftershock behavior, which could have a significant impact on future earthquake prediction and risk assessment in subduction zones.
The first high-precision image of a seismic fault zone revolutionizes our understanding of earthquakes.
The belief that earthquakes relieve stress through a single strong quake along a single fault plane may need to be revised. Recent research carried out by the Karlsruhe Institute of Technology (KIT), in collaboration with the GFZ German Research Centre for Geosciences and other international institutions, suggests that earthquakes occur within an area containing multiple fault planes, some of which are parallel.
According to the researchers, the study results can contribute to developing more accurate earthquake models and hazard assessments in subduction zones. The study has been published in the journal Nature.
The international team led by first author Caroline Chalumeau from KIT examined a series of earthquakes in Ecuador on the west coast of South America. The Pacific Plate is subducted under the South American Plate, leading to frequent severe earthquakes. The most recent sequence of earthquakes in Taiwan, where the main quake killed nine people and caused extensive damage on the east coast in early April, can also be attributed to subduction.
The illustration depicts the seismogenic zone, which is 100 to 600 meters thick, containing fault planes (5 to 20 meters thick) where the ruptures occur. Credit: Dr. Caroline Chalumeau, Dr. Hans Argurto-Detzel, Prof. Andreas Rietbrock, Dr. Michael Frietsch. Prof. Onno Oncken, Dr. Monica Segovia, Dr. Audrey Galve: Seismological evidence for a multifault network at the subduction interface. Nature, 2024. DOI: 10.1038/s41586-024-07245-y
The series of earthquakes in Ecuador analyzed by the team began on March 12, 2022, and ended on May 26, 2022. The most severe quake (magnitude 5.8) occurred on March 27 and triggered numerous smaller aftershocks over a short period. At that time, a dense network of 100 seismometers was in place in the region for the offshore experiment “High-resolution imaging of the subduction fault in the Pedernales Earthquake Rupture zone” (HIPER).
Detailed Seismic Data Analysis
Using the highly detailed data from the HIPER experiment and artificial intelligence, the researchers were able to map over 1,500 earthquakes and their respective fault planes at a depth of 15 to 20 kilometers in very fine detail. Dr. Caroline Chalumeau from the Geophysical Institute (GPI) at KIT explains, “We observed that earthquake activity in the main earthquake region took place on several different fault planes, often overlapping. Some areas had parallel seismically active planes, while others had only single ones.”
The quakes being similar was not linked to a specific depth. Professor Andreas Rietbrock from the GPI says that the previous belief that stress is released by one strong quake on one fault plane might be outdated. Instead, he suggests that a network of faults causes a series of ruptures within a single earthquake.
The analysis of the Ecuadorian quake series also gives new insights into aftershocks. According to Chalumeau, aftershocks first happened near the main quake's epicenter and then spread in other directions, showing that afterslip mainly controls their propagation in the region. Prof. Onno Oncken from the GFZ states that Caroline Chalumeau’s team has provided the first detailed seismological image of a seismogenic plate boundary. This confirms existing geological observations and explains the propagation of aftershocks with a new approach, refuting previous assumptions about fluid diffusion causing aftershocks.
The findings are also crucial for evaluating earthquake risk in subduction zones, influencing the future modeling of earthquakes and aseismic slips, which are plate movements without earthquakes, according to Andreas Rietbrock.
Reference: “Seismological evidence for a multifault network at the subduction interface” by Caroline Chalumeau, Hans Agurto-Detzel, Andreas Rietbrock, Michael Frietsch, Onno Oncken, Monica Segovia and Audrey Galve, 17 April 2024, Nature.
DOI: 10.1038/s41586-024-07245-y
