A new study raises serious concerns about the tectonic stability of Southern California, saying pressure is building at the Cajon Pass, a critical junction between the San Andreas and San Jacinto fault systems. The research, published in the Journal of Geophysical Research, says parts of these fault networks are under the highest tectonic stress measured in the last 1,000 years, and that the area could face a catastrophic earthquake in one of the most densely populated parts of the United States.
The analysis is based on a computer model that reconstructed 1,000 years of seismic rupture history in the region. Researchers found that the section known as the San Jacinto Bernardino segment is carrying the heaviest stress at the fault intersection, increasing the chance that it could trigger nearby systems. They describe Cajon Pass, about 50 miles from downtown Los Angeles, as an “earthquake gateway” because it can either block a quake’s spread or allow it to jump from one fault to another.
If energy jumps between the systems, the result could be a longer, larger and more complex quake than anything experienced in modern times. The researchers say understanding how these fault systems behave is crucial because the region serves millions of residents and is a vital corridor for transportation, energy and strategic commerce infrastructure. Over the past millennium, the faults have produced 36 earthquakes of magnitude 6.4 or higher and account for about 90% of the tectonic plate movement in the area.
The study does not predict when the next major release of energy will happen, and the researchers stress it is not an earthquake “weather forecast.” Still, they argue it shows that the most populated seismic zone in the United States is in a highly sensitive state after more than 100 years since the last major quake in these systems. Experts cited in the article say the apparent calm could be “the calm before the storm,” and that the findings should affect urban planning and emergency preparedness.
