New research highlighted on August 21, 2026, is drawing renewed attention to the movement of the San Andreas Fault in Northern California, with findings from a San José State University earthquake geologist indicating that a section of the fault in the Santa Cruz Mountains may be moving faster than previously estimated. The research has attracted attention because understanding how quickly faults move can help scientists better evaluate long-term earthquake hazards in California.
The research is led by Kim Blisniuk, an earthquake geologist and professor at San José State University. Her work examines the geological record preserved in landscapes to determine how faults have moved over thousands of years. San José State describes Blisniuk’s research as combining field mapping, laboratory analysis and geological dating to measure long-term fault movement.
The latest findings focus on the Santa Cruz Mountains portion of the San Andreas Fault. According to reporting on the research, earlier estimates of movement in this section were based on shorter records, while the new analysis examines evidence extending across roughly 10,000 years. That longer timeframe provides researchers with a broader view of how consistently the fault has moved over geological time.
One of the notable findings is that the fault’s long-term slip rate appears to remain relatively consistent rather than decreasing farther south as some previous interpretations had suggested. Researchers used evidence from landforms and geological materials to reconstruct past movement. Techniques associated with this type of research include high-resolution topographic information, field observations and geochronological analysis, allowing scientists to estimate when particular landscapes formed and how much they have subsequently shifted.
The significance of the finding lies in what fault movement can tell scientists about earthquake behavior. A faster long-term slip rate generally indicates that a fault is accommodating tectonic movement more rapidly. However, the research does not mean that a major earthquake is imminent or that scientists can predict when one will occur. Earthquake timing remains difficult to forecast, and fault-slip measurements are only one part of understanding seismic hazards.
The distinction is important for California residents. The San Andreas Fault is one component of a broader network of active faults throughout the state, and its behavior varies along different sections. Previous USGS-supported research involving Blisniuk and other scientists has documented significant differences in slip rates among strands of the San Andreas system in Southern California. A 2021 study, for example, identified the Mission Creek strand as a primary strand in part of Southern California and estimated a San Andreas slip rate of about 24 millimeters per year in the study area.
The new research also illustrates why scientists study geological evidence covering thousands of years rather than relying only on recent earthquakes. Written records and modern instruments provide valuable information, but the geological landscape can preserve evidence of earthquakes and fault movement that occurred long before modern monitoring systems existed.
For Southern California readers, the findings are relevant even though the new research concerns the Santa Cruz Mountains. The San Andreas Fault extends through much of California, including major sections of Southern California. USGS research has previously emphasized that understanding long-term fault movement is important for evaluating seismic hazards in the region.
The research should therefore be viewed as an improvement in scientific understanding rather than a warning of an immediate disaster. The findings refine estimates of how the fault has behaved over long periods and may help researchers improve models used to study earthquake hazards.
For residents, the practical takeaway is straightforward: earthquake preparedness remains important regardless of whether a particular study changes estimates of fault movement. Keeping emergency supplies available, knowing how to respond during shaking and reviewing household emergency plans are sensible preparedness measures for people living in earthquake-prone parts of California.
The August 21 findings are another example of how ongoing geological research continues to improve scientists’ understanding of California’s complex fault systems. As researchers gather more geological evidence and compare it with modern measurements, they can build increasingly detailed pictures of how faults move and how that movement contributes to the state’s long-term seismic landscape.
