'The system is critically stressed': San Andreas and San Jacinto faults scarily close to major earthquake, study finds

Key Points:

• A new study reveals that the San Andreas and San Jacinto fault systems in Southern California are experiencing their highest tectonic stress levels in 1,000 years, increasing the risk of a major earthquake.
• The faults may rupture separately or together through an "earthquake gate" at Cajon Pass, where stress levels on both faults are currently extremely elevated and similar, potentially triggering a large, joint rupture.
• Historical data shows these faults have caused 36 significant earthquakes over the past millennium, with the last major event in 1857; a similar rupture today could be far more devastating due to increased population and infrastructure.
• Researchers used tree-ring records and sediment age data to model 1,000 years of earthquake activity, indicating the system is critically stressed and capable of a through-going rupture involving multiple fault segments.
• The study emphasizes the importance of this model for hazard assessment, infrastructure planning, and emergency preparedness, and suggests it could be applied globally to other fault junctions for better earthquake risk understanding.