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Pacific Coastal & Marine Science Center

Coastal and Marine Earthquake Studies

 

The Cascadia Megathrust and Tectonic Stress in the Pacific Northwest

The Model

Forces contributing to Intraplate Stress

To understand the tectonic cause of stress and deformation in the Pacific Northwest, we need to consider not only forces acting along the Cascadia Subduction zone, but also forces acting along the tectonic margins to the north (Queen Charlotte fault) and to the south (San Andreas fault).

In addition, over millions of years, mountain ranges are built that locally affect stress and deformation within the North American plate (i.e., internal forces in diagram at right). In general, the present day state of stress depends, in part, on how the continent was deformed in the past. In other words, the present-day rate of deformation has a "memory" of past deformation episodes.

As one might be lead to believe from the previous discussion, modeling the deformation of continents is very complex. The model chosen for this study (LARAMY) was developed over several years by Dr. Peter Bird at UCLA (Earth and Space Sciences). This model incorporates many aspects of continental deformation observed in the field and laboratory measurements of how rocks deform under different pressure and temperature conditions. In particular, LARAMY is quite successful in modeling the formation of the Rocky Mountains using reconstructions of plate motions along the western margin of North America. For this study, however, we focus on the last time step of the model--the present day state of stress and rate of deformation.