San Andreas Fault & Western US Tectonics Quiz
Fault types, seismic zones, transform boundaries (10 questions).
San Andreas Fault & Western US Tectonics Quiz: Quick Study Notes
The San Andreas Fault is the most famous transform fault in the world, stretching roughly 800 miles through California. It marks the sliding boundary between the Pacific Plate and the North American Plate, creating a complex zone of seismic activity that defines the geology of the Western United States.
Transform boundary (Right-lateral strike-slip fault).
Pacific Plate (moves NW) & North American Plate (moves SE).
1906 San Francisco Earthquake (Magnitude 7.9).
Averages 20-35 mm/year (roughly the speed fingernails grow).
Key Takeaways
- The fault is a right-lateral strike-slip fault, meaning the opposite side moves to the right.
- It is not a single continuous crack but a system of parallel faults (Hayward, Calaveras, San Jacinto).
- Elastic Rebound Theory explains how rocks accumulate stress and snap, causing earthquakes.
- Some sections, like Parkfield, experience “aseismic creep” (steady movement), while others are “locked.”
- The fault ends at the Mendocino Triple Junction in the north and the Salton Sea in the south.
- The “Big One” refers to a hypothetical massive rupture (Mag 7.8+) on the southern segment.
Frequently Asked Questions
Will California eventually fall into the ocean?
No. This is a common myth. The San Andreas is a strike-slip fault, meaning the plates slide horizontally past each other, not away from each other. Los Angeles is slowly moving toward San Francisco, not into the sea.
How long is the San Andreas Fault?
The fault extends approximately 800 miles (1,300 kilometers) through California.
What is the “Big One”?
The “Big One” refers to a predicted high-magnitude earthquake (likely 7.8 or higher) on the southern section of the fault, which has not ruptured significantly in over 300 years.
Why do earthquakes happen along the fault?
Friction holds the rocks together while the tectonic plates continue to move. Stress builds up until it overcomes the friction, causing the rocks to snap past each other violently.
Are there volcanoes along the San Andreas Fault?
Generally, no. Volcanoes are typical of subduction zones or divergent boundaries. The San Andreas is a transform boundary involving lateral motion, which rarely produces volcanic activity.
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