New findings challenge old beliefs about earthquake causes

Credit: NASA.

Scientists at Brown University have discovered a new factor that significantly influences where and how earthquakes occur.

Their research shows that the geometry of fault networks plays a critical role in determining earthquake locations and strength.

This finding challenges the traditional belief that friction at fault lines is the primary cause of earthquakes.

The study, published in Nature, reveals that the way faults are aligned can impact earthquake activity.

Victor Tsai, a geophysicist at Brown University and one of the lead authors, explains that this discovery could improve our understanding of earthquake behavior.

“For a long time, geophysicists believed that earthquakes happened when stress at faults built up to the point where the faults rapidly slipped, releasing pressure in a process called stick-slip behavior,” said Tsai. “Our study paints a different picture and suggests that fault geometry might be more important than previously thought.”

Fault lines are boundaries where the Earth’s tectonic plates meet and move against each other. Traditionally, scientists believed that the type of friction at these faults determined whether they would slip smoothly (creep) or break suddenly (causing an earthquake). Unstable friction was thought to cause rapid slips and intense ground motions, while stable friction led to slow, steady movements.

Tsai and his team found that the complexity of fault geometry, such as bends, gaps, and stepovers in the rocks, might be more relevant. Their study used mathematical models and data from California’s fault zones, including the well-known San Andreas Fault. They analyzed this data from the U.S. Geological Survey and the California Geological Survey.

To illustrate their findings, the researchers compared fault lines to serrated saw teeth. When the teeth are fewer and less sharp, the rocks slide past each other smoothly, resulting in creep. However, when the teeth are more jagged and complex, they catch on each other, building up pressure until they break free, causing an earthquake.

This study builds on earlier research that looked at why some earthquakes generate more ground motion than others, even those of similar magnitude. The researchers found that blocks colliding inside a fault zone during an earthquake contribute to high-frequency vibrations. This led them to consider that geometrical complexity might also affect where and why earthquakes occur.

Their analysis showed that fault zones with more complex geometry and misaligned faults tend to have stronger ground motions and more earthquakes. In contrast, zones with more aligned faults experience smoother creep without earthquakes.

“Understanding how faults behave as a system is essential to grasp why and how earthquakes happen,” said Jaeseok Lee, a Brown graduate student and lead researcher. “Our research indicates that the complexity of fault network geometry is the key factor.”

The researchers acknowledge that more work is needed to fully validate their model. However, this initial work suggests that fault alignment is easier to measure than frictional properties, which could make it a valuable tool for earthquake prediction.

“The next step is to test this model beyond California and see how it holds up,” said Tsai. “This could be a new way of understanding how earthquakes happen.”

This research has the potential to revolutionize our understanding of earthquakes and improve prediction models, helping to better prepare for future seismic events.