Study Finds California Faults Under Highest Stress in a Millennium

Researchers have determined that stress on California's major fault lines is at its highest level in a millennium, according to a study published in the Journal of Geophysical Research, Solid Earth. The analysis used a three-dimensional physics-based earthquake cycle model that incorporated geological records such as tree-ring anomalies and radiocarbon dates to assess the current stress state of the San Andreas and San Jacinto fault zones.

The model indicates that tectonic stresses along these faults have reached, and in some locations exceeded, the peak levels observed over the last thousand years. The greatest stress concentrations are located northeast of Los Angeles, near the Cajon Pass region, which the authors describe as an "earthquake gate" that can respond to changing stress conditions over centuries.

"The question of when and how the next major earthquake will occur in this region is one of the most pressing problems in applied geoscience," said lead author Liliane Burkhard, a geophysicist at the University of Bern.

"Our results provide a clearer, physics-based picture of the current stress state of the fault system, and the framework we developed is not just applicable to California, but also for other complex fault junctions worldwide," Burkhard added.

The study notes that the last major quake on the San Andreas system was the 1857 Fort Tejon event, which measured magnitude 7.9. While smaller earthquakes, such as the 1994 Northridge quake, have released some stress, the prolonged interval since the 19th-century event has allowed significant energy to accumulate. Scientists caution that the fault system could rupture at any time, potentially producing an earthquake larger than those recorded in recent history.