California's most famous fault isn't rumbling—it's quietly tightening. A new study of the San Andreas and neighboring San Jacinto faults finds that sections near Cajon Pass, about 50 miles northeast of downtown Los Angeles, are now carrying more tectonic stress than at any time in the last 1,000 years. Researchers used a computer model built from a millennium of earthquake history, satellite measurements of plate movement, and estimates of crust rigidity, the Los Angeles Times reports. Their conclusion, per lead author Liliane Burkhard: The system is more "loaded" than at any point in the record, echoing conditions that preceded past multifault "joint ruptures."
The lull is unusual. The southern San Andreas typically produces major quakes every 100 to 250 years, but parts of it haven't ruptured in about 300. The relative silence concerns scientists. The long pause means energy has been accumulating since long before the 1994 Northridge quake, which was damaging but geographically limited. A repeat of an 1857 Fort Tejon-style event—around magnitude 7.8 or higher—could bring violent shaking across much of Southern California and thousands of casualties, according to USGS scenarios. The study doesn't predict when that will happen, but its authors say the takeaway is straightforward: The risk is persistent, and preparation, not panic, is in order.
- The study, published in the Journal of Geophysical Research: Solid Earth, can be found here.
- The full Times piece can be found here.
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