Additional Coverage:
- California fault lines reach highest stress in 1,000 years as experts warn of mega quake risk (themirror.com)
A recent study from the University of Hawai‘i at Mānoa highlights growing concerns about two major California fault lines-the San Andreas and San Jacinto faults-where significant pressure is accumulating beneath the surface. Researchers warn that interactions between these faults could potentially trigger a devastating mega-earthquake.
The study reveals that strain levels along both fault systems are now “very high,” with stress building to comparable degrees. Of particular concern is the Cajon Pass area, often called the “earthquake gate,” where these faults intersect. An earthquake originating here could have widespread effects, impacting Los Angeles, San Bernardino, Riverside, and the Coachella Valley, with severe damage expected to homes and critical infrastructure.
Cajon Pass plays a unique role in earthquake dynamics, sometimes halting ruptures from crossing between faults, and other times allowing seismic activity to transfer from one fault to the other. A major quake in this region could disrupt key transportation routes, energy corridors, and railways vital to the Los Angeles metropolitan area.
Published in the journal JGR: Solid Earth, the study points out that although the San Andreas and San Jacinto faults have not experienced a significant earthquake near Los Angeles in over a century, the underlying pressure has been steadily mounting. Earthquakes occur as tectonic plates-massive sections of Earth’s crust-move, lock, and suddenly release built-up stress, sending seismic waves that shake the ground.
Lead author Liliane Burkhard emphasizes the gravity of the situation: stress levels on multiple segments of these faults are at or above the highest levels observed in the past 1,000 years. This raises the possibility of a large, combined rupture involving both fault systems.
Using computer simulations that modeled major earthquakes over the last millennium, the research team examined how stress accumulates and influences adjacent fault segments. The San Andreas Fault, stretching roughly 800 miles, marks the boundary where the Pacific Plate slides past the North American Plate.
As these plates slowly grind against each other, sections of the fault can become locked, building tension for years or even decades. When this tension finally overcomes friction, it causes sudden slippage and an earthquake.
The San Andreas is classified as a right-lateral strike-slip fault, meaning that when viewed across the fault, the opposite side moves to the right. The Pacific Plate moves northwest while the North American Plate moves southeast, creating ongoing strain along the fault line.
Simulations suggest that as stress builds simultaneously across both fault systems, their interactions become more likely. Burkhard explains that whether a rupture crosses from one fault to the other depends on how similarly stressed the faults are at that moment.
When stress levels rise together, the “earthquake gate” opens, allowing a rupture to propagate across both faults. Conversely, mismatched stress levels tend to stop the rupture at the junction.
The study acknowledges a key limitation: its model assumes that an earthquake releases all stored strain in one event, which may not fully reflect real fault behavior, where strain can be released partially or irregularly. Adjusting this assumption could change the precise stress estimates.
Importantly, the researchers clarify that this work is not a prediction of when the next major earthquake will occur. Instead, it aims to improve understanding of how large earthquakes could connect across Southern California’s fault systems, enhancing risk assessments and aiding in future preparedness planning.
As Burkhard notes, “This is not a prediction of when an earthquake will happen. Our goal is to map out realistic scenarios for how a big rupture could spread across multiple faults to better inform earthquake risk management.”