The Ridgecrest earthquake left permanent damage in the Earth's deep crust

When tectonic pressure is released during an earthquake, rocks slide, and the Earth's crust is damaged, like a gash in the skin. Like skin, scar-like wounds that remain after an earthquake can heal, and the damaged area can regain its strength over time. A study published in the journal Science suggests that this recovery may be limited to the upper layers of the crust only. Deeper crusts take longer to recover, or may not recover at all.

Permanent change in the deep cortex

The results came from what was supposed to be just a test of a new technology.

Jared Bryan, a geophysicist at the Massachusetts Institute of Technology (MIT) and first author of the new study, has been working to improve a way to study localized damage to the Earth's crust by measuring the speed at which seismic waves from distant earthquakes travel.

Brian wanted to use this technique to study volcanoes, but as a test, he turned to the sequence of the 2019 Ridgecrest earthquake in California, a magnitude 6.4 foreshock followed by a magnitude 7.1 mainshock. “What originally brought me to work in the Ridgecrest Fault Zone was that I wanted a clear signal that I could use to calibrate my approach,” Brian said. Conveniently, the area was readily available to seismic wave data from 34 permanent seismic stations within 74 miles (120 kilometers) of the fault zone.

Between 2015 and 2023, 5,500 earthquakes generated seismic signals that traveled through the Earth's crust and reached vertically to seismic stations, allowing the team to track seismic wave velocities before and after the Ridgecrest earthquake. Damage from earthquakes causes fractures in rocks, significantly slowing the passage of seismic waves through them. After testing, Brian planned to use this technique to study volcanoes. But the results were too interesting to give up.

Previous studies of damage from earthquakes have been limited to the shallow crust, typically less than 6 miles (10 km) deep, or results have been averaged across all depths.

“You can never know where these changes were in function of depth, and that is critical,” said Roland Borgmann, a geophysicist from the University of California, Berkeley, who was not involved in the study.

However, the technique the researchers used in the new study detects changes equally well throughout the entire cortical column, from the surface to 15 miles (25 kilometers) away. “What we were most excited about was using this method that allows us to image how things change in the ground beyond the depth we normally think about when doing this kind of work,” said William Frank, a geophysicist at MIT and co-author of the study.

By tracking seismic waves passing through the crust surrounding the Ridgecrest earthquake, the researchers saw that in the upper crust, the waves slowed and then returned to normal within months, suggesting that the crust had actually been damaged but was recovering.

The finding that the lower crust undergoes slow, progressive and permanent damage is “entirely new and innovative.”

However, seismic waveform data from a deeper depth, between 6 and 9 miles (10 and 15 km), indicated that damage accumulated more slowly and did not heal during the 3-year-plus time period analyzed after the earthquake. Data showing changes in waveforms are usually subtle, requiring precise quantification, but this was not the case with data from the deeper crust, Brian said. “I could visually see this permanent change at the time of the earthquake,” he said.

The finding that the lower crust undergoes slow, progressive and permanent damage is “entirely new and innovative,” Borgmann said.

Looking beyond Ridgecrest

Scientists suggest two possible outcomes for damage to the deep cortex. Either the damaged area will recover, albeit over decades or centuries rather than months, or the changes will be permanent, and the structure of the fault zone will gradually change with each earthquake.

Because the Ridgecrest area has not experienced as many earthquakes as more mature fault zones, it is possible that “we are watching these fault zones mature in real time,” Bryan said.

The team wants to apply the same method to more mature faults, such as the well-studied San Andreas zone to the west. If data indicate that the deeper crust of a mature fault zone heals after an earthquake, permanent damage at Ridgecrest could be a feature of fault evolution.

Research on recovery in the deep crust “will place important constraints on how we model this evolution and how that then impacts our future predictions about where and how earthquakes occur,” Frank said.

—Andrew Chapman (@andrewgchapman.bsky.social), science writer

Citation: Chapman, A. (2025), The Ridgecrest earthquake left permanent damage in Earth's deep crust, EOS, 106, https://doi.org/10.1029/2025EO250421. Published November 14, 2025. Text © 2025. The Authors. CC BY-NC-ND 3.0 Unless otherwise noted, images are subject to copyright. Any reuse without express permission of the copyright owner is prohibited.

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