A new scientific study has raised concerns about earthquake risks in Southern California, warning that two of the region’s most significant fault systems, the San Andreas Fault and the San Jacinto Fault, are currently under more stress than at any point in the past 1000 years.
The research, led by experts from the University of Hawaii and the United States Geological Survey (USGS), has renewed discussions about the possibility of a major earthquake in one of the most densely populated parts of the United States.
Study tracks 1000 years of stress build-up
Researchers used an advanced physics-based computer model to examine how stress has accumulated along the two fault systems from 1000 CE to the present day.
Unlike traditional methods, the model simulates physical processes occurring beneath the Earth’s surface and tracks how tectonic plate movements gradually increase or release stress along fault lines over time.
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The findings suggest that enormous amounts of stress have accumulated beneath metropolitan areas including Los Angeles and Riverside, potentially increasing the risk of a future large-scale earthquake.
According to the study, stress levels on the Mojave South segment of the San Andreas Fault have reached approximately 2.8 megapascals (MPa).
Meanwhile, the Bernardino strand of the San Jacinto Fault has recorded even higher stress levels of about 3.6 MPa.
Researchers say these are the highest stress levels identified at these locations during the last millennium, indicating that rocks deep beneath the surface may be approaching their mechanical limits.
Cajon Pass identified as a key concern
One of the most significant findings of the study involves Cajon Pass, a geographical area where the San Andreas and San Jacinto fault systems come very close to one another.
Scientists consider this region a critical junction between the two fault networks.
According to the researchers, an earthquake beginning on one fault could potentially trigger movement on the other. If that were to happen, multiple fault segments could rupture simultaneously, creating a far larger and more destructive earthquake than a typical single-fault event.
Experts warn that a combined rupture involving both fault systems could generate an earthquake with a magnitude of 7.5 or higher, posing a serious threat to large parts of Southern California.
Long periods of quiet may signal greater risk
Historical records show that the Mojave South segment of the San Andreas Fault has not experienced a major earthquake since 1857.
Similarly, the Bernardino branch of the San Jacinto Fault last saw significant activity in 1968.
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Scientists note that such long periods without major seismic activity should not necessarily be viewed as reassuring. Instead, they may indicate that stress has continued to build over decades or even centuries.
When tectonic plates remain locked and fail to release accumulated energy through earthquakes, pressure continues to increase along the fault. This phenomenon is known as a seismic gap.
Because the Mojave South segment has remained largely quiet for more than 150 years, researchers believe a substantial amount of stored energy may now be trapped within the fault system.
Lead author Lillian Burkhard emphasised that the study does not predict when an earthquake will occur.
She noted that modern science still lacks the ability to determine the exact date or time of future earthquakes.
Instead, the goal of the research is to improve preparedness and help authorities better understand areas facing elevated seismic risk.
Findings could aid disaster planning
Researchers believe the data could play an important role in disaster management and urban planning efforts across cities such as Los Angeles, Riverside and San Bernardino.
The findings may help local governments strengthen building regulations to ensure that future structures are capable of withstanding stronger seismic forces.
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The study could also support efforts to reinforce aging infrastructure, including bridges, water pipelines and power grids, reducing the potential impact of a major earthquake if one occurs in the future.
First published on: Jun 16, 2026 05:54 PM IST
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