Over the last 1,000 years, the fault has had major earthquakes about every 140 years. The last major earthquake on the Hayward fault was the great earthquake of 1868, which was (as of 2023) 155 years ago, which matches the average interval. Earthquake geologists have determined that the fault has accumulated enough strain energy for another event the size of the 1868 quake; however, they avoid the term "overdue" because earthquakes do not follow a schedule.1 The fault is ready for another one (are you?).
The Hayward fault is a strike-slip fault, meaning most of the movement is horizontal. There is about 8-10 mm of aseismic creep (steady movement without earthquakes) along the fault per year. Not enough for dramatic effects, but enough to crack sidewalks and twist doorways.
Links and References
- Hayward Fault Fact Sheet (California Geological Survey)
- Hayward Fault (Wikipedia)
- Active Traces of the Hayward Fault USGS. Includes maps and Google Earth virtual tour
- The Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2) (USGS)
- "Stop Saying 'Overdue'," Oaklandgeology.com