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Pacific Coastal & Marine Science Center

Coastal and Marine Earthquake Studies


The Cascadia Megathrust and Tectonic Stress in the Pacific Northwest

Orientation of faults predicted by the model.

Cartoon of Pacific Northwest stresses and faults; see full explanation below.


Red Symbols: Orientation of faults predicted by the model. Rectangle represents normal faulting, line with diamond ends represents thrust faulting, and X represents two possible orientations of strike-slip faulting (see faults).

Shaded Blue Regions: Regions deforming at a higher rate than the interior part of North America.

Yellow Dots: Recent and important historical earthquakes in the Pacific Northwest.

The model shown above provides the best fit to the present-day stress and deformation field. For this model, the basal shear traction along the Cascadia megathrust is 15 MPa. Sensitivity analysis demonstrates that basal shear traction lower or higher than 15 MPa result in a greater misfit to the stress data and style of faulting. Conversely, the present-day stress field appears to be insensitive to shear traction less than 30 MPa along the transform margins. (Many independent studies indicate that the long-term traction along the San Andreas is less than 20 MPa.)

If you cannot fully access the information presented here, please contact Eric Geist.