Faults versus plate boundaries
A fault is a fracture along which rock has moved. Some faults accommodate motion between plates; many others lie within plates or within a broad boundary zone.
BOUNDARIES
Loading the atlas...
Plate colours identify regions, not risk.
Available regional fault maps
The detailed layer uses the California part of the USGS Quaternary Fault and Fold Database, 2020 release. Click a trace for its recorded age and location certainty. It includes several Quaternary age classes, not only currently active faults; the separate offshore layer is not included.
How to read the source coverage
A gap in mapped coverage does not establish that faults are absent. Check each source for its survey area, publication date and definition of activity before comparing regions.
Questions about this map
Is every plate boundary a single fault?
No. A plate boundary may include several faults, a spreading ridge, a trench or a wide deformation zone.
Sources and map method
Plate outlines use Peter Bird's PB2002 model, distributed by Nordpil under the Open Data Commons Attribution licence. Coastlines and country outlines are Natural Earth public-domain data. Boundary detail is limited by the source model. Detailed California traces use the USGS Quaternary Fault and Fold Database, 2020 release. The separate offshore layer is omitted.
- USGS: Quaternary Fault and Fold Database, California layer (2020 release)
- California Geological Survey: Faulting in California (2018)
- California Geological Survey: Fault Activity Map
- USGS: Earthquakes in stable continental regions
- Map dataset sources and licences
- PB2002 geometry and licence
- Natural Earth terms
Country lookup compares simplified land outlines with the plate model. Boundaries and historical coastlines are modelled features. This atlas explains geography; it does not predict earthquakes or provide site-specific hazard estimates.