- Subduction Faults
- The Western United States is seismically active because two major plates, the Pacific Plate and the North American Plate. Intersect along the San Andreas fault line.
- This figure shows the North American plate and the Pacific Plate, with the San Andreas fault between them.
- In the Bay Area, the San Andreas fault has strike-slip movement, with each side sliding past the other. In the Los Angeles area, because of the bend in the fault, the San Andreas has some thrust movement.
- Further north, the North American plate and Pacific plate are pushing against each other. The Pacific plate is being pushed under the North American plate.
- This kind of fault is called a subduction zone fault.
- Oregon, Washington, and Alaska are all subject to huge earthquakes caused by this process. The 1964 Good Friday Alaska earthquake is an example.