Tectonic framework of the Northern California continental margin

The northern coast of California is one of the most seismically active regions in the continental United States. This activity is largely due to tectonic forces resulting from differing relative motions between three extensive lithospheric plates that meet in this region. These crustal plates are bounded by long fault systems-the Cascadia subduction zone, the San Andreas fault system, and the Mendocino fault- that accommodate these differences in plate motion and that are capable of periodically producing damaging earthquakes. Historic earthquake locations are concentrated in the victinity of the tectonically unstable intersection of these tthree plates and their bounding fault systems.