# Earthquake damage may reach 60 miles beyond fault lines

> Researchers at UCLA have found evidence that active faults may weaken rocks across distances of up to about 100 kilometers. The study, published in Science on May 21, 2026, suggests that earthquake-prone regions can erode more easily far beyond the visible fault...

Canonical URL: https://www.argo.net/earthquake-damage-may-reach-60-miles-beyond-fault-lines/
Byline: UCLA Division of Physical Sciences
Published: 2026-07-14T15:55:14+00:00
Categories: Earth, News

![Fracture fault lines in rock](https://www.argo.net/wp-content/uploads/2026/06/fault_line.jpg)

Researchers at [UCLA](https://physicalsciences.ucla.edu/ucla-researchers-show-faults-reshape-earths-surface-far-beyond-previously-thought/) have found evidence that active faults may weaken rocks across distances of up to about 100 kilometers. The study, published in *Science* on May 21, 2026, suggests that earthquake-prone regions can erode more easily far beyond the visible fault trace.

The finding gives scientists a broader view of how earthquakes shape landscapes. A fault can lift mountains over geologic time. It can also leave nearby rock weaker, more fractured and easier for rivers and landslides to wear away.

The work was led by **Boontigan Kuhasubpasin**, a former doctoral student in UCLA's Department of Earth, Planetary and Space Sciences. UCLA professors **Seulgi Moon** and **Carolina Lithgow-Bertelloni** served as co-advisors. Moon is now a professor at ETH Zurich.

## Faults weaken rock far from the rupture

The study examined how **active faults** influence erosion across many landscapes. Previous field observations often focused on heavily crushed rock near a fault core. The UCLA-led analysis points to a much wider zone of weakened terrain.

Using a global dataset, the researchers found that erosional efficiency was elevated on average within about 15 kilometers of a fault trace. The effect then decreased with distance and could still be detected up to about 100 kilometers away.

That 100-kilometer reach is roughly 60 miles. It means a major fault system may affect hillslopes, rivers and sediment production across an entire region. The strongest effects appeared near reverse faults and faults longer than 140 kilometers.

The study frames this influence as **tectonic rock damage**. In simple terms, repeated strain and shaking can make near-surface rock less resistant. Once rock loses strength, ordinary erosion processes can remove it more efficiently.

## River sediment revealed the pattern

To measure erosion at a global scale, the team turned to river basins. Rivers collect sediment from the land around them, so their sand and gravel can preserve a signal of how fast the upstream landscape is wearing down.

The researchers used 1,744 erosion rates derived from **beryllium-10**. This rare isotope builds up in minerals when rock sits near Earth's surface and is exposed to cosmic rays. Its abundance helps scientists estimate how quickly a landscape is being stripped away.

When erosion is slow, surface rock remains exposed longer and accumulates more beryllium-10. When erosion is fast, rock is removed sooner and the isotope signal changes. By comparing many river basins, the team could look for global patterns.

The researchers then compared those erosion estimates with maps of active faults. A clear trend emerged. Basins closer to faults tended to show higher erosional efficiency and the effect faded outward from the fault trace.

This approach allowed the team to study more than one mountain range or earthquake zone. The dataset covered many geologic settings, which made it possible to separate fault influence from other familiar controls on erosion.

## Machine learning ranked the biggest controls

Landscapes wear down for many reasons. Rainfall, rock type, slope, tectonic uplift, vegetation and temperature can all matter. The researchers used **machine learning** to compare these factors across the global dataset.

Fault proximity emerged as a dominant control on erosional efficiency. In many tectonically active regions, it ranked ahead of precipitation and lithology. Lithology refers to the physical character of rock, including how hard or soft it is.

The models improved when the researchers added a measure of **seismic shaking**. That result supports the idea that earthquake motion contributes to long-range weakening. It also links the erosion pattern to a physical process that operates through time.

Machine learning can reveal statistical relationships across complex datasets. It still requires careful interpretation. In this case, the models pointed to a consistent association between fault distance, shaking and faster erosion.

The team's results suggest that tectonic activity shapes landscapes through more than uplift. Faults can help build relief while also making surrounding rock easier to erode. Those two effects can operate together across mountain belts.

## Shaking may open hidden fractures

The proposed mechanism begins with repeated earthquake shaking. Each earthquake sends waves through the surrounding crust. Over many events, that shaking may damage rock well beyond the narrow zone where rupture breaks the surface.

"We believe earthquake shaking may be a key reason for this phenomenon," said **Carolina Lithgow-Bertelloni** of UCLA.

The team suggests that shaking may create tiny cracks called microfractures. It may also weaken the contacts between mineral grains. These changes would reduce the strength of near-surface rock and make it more vulnerable to weathering.

Once rock is weakened, rivers can cut into it more easily. Hillslopes may fail more readily. Sediment can move downstream faster, changing river channels and affecting how valleys grow.

The study treats this mechanism as a likely explanation based on the observed patterns. The researchers measured erosion rates and compared them with fault properties and shaking estimates. They did this across a global dataset rather than watching individual cracks form underground.

## Southern California offered a close test

The researchers also examined Southern California, where active faults cut across a heavily studied region. The **San Andreas Fault** and nearby fault systems provide a natural test case for linking rock damage with erosion.

In that region, the team compared erosion patterns with seismic-wave behavior. Seismic waves tend to slow down when they pass through fractured or damaged rock. Slower wave speeds can therefore reveal zones where rock has been weakened.

The Southern California results matched the global picture. Areas near faults showed evidence of extensive damage and those same areas tended to erode more efficiently. The overlap strengthened the link between seismic damage and landscape change.

This regional test matters because Southern California has abundant geophysical data. It also has complex fault networks, steep landscapes and a long history of earthquake research. Those features made it useful for checking the broader global signal.

The findings do more than describe one famous fault. They show how a well-instrumented region can help explain a worldwide relationship between earthquakes, rock strength and erosion.

## Why hazard maps may need a wider lens

The study could influence how scientists think about landslides, sediment movement and mountain growth. If fault-related weakening extends dozens of miles, then the landscape effects of earthquakes may cover a wider area than many maps imply.

Weakened rock can affect landslide susceptibility. It can also influence how much sediment enters rivers after storms or earthquakes. Over time, that sediment can fill reservoirs, alter channels and reshape valleys.

The implications are especially important in tectonically active regions. Mountain belts form where Earth's crust is squeezed, lifted and broken. This study suggests that faults can also prepare surrounding rock for faster removal by erosion.

That wider view may help researchers improve models of **landscape evolution**. It may also help planners understand why some slopes fail more readily than expected. The result is a more connected picture of earthquakes and surface change.

The UCLA-led study leaves room for future work. Scientists still need to test how different fault types, rock properties and earthquake histories affect the size of the damage zone. The main signal is already striking. Faults may leave a long-lived mark across landscapes far beyond the place where the ground breaks.