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Q&A November 2007

Q If San Diego is at the edge of a tectonic plate, will we always keep moving/slipping?
Submitted by 6th grade students in the Geo educational program at Birch Aquarium at Scripps

AProbably the most straightforward answer to the question is YES.

san andreas fault Above, The San Andreas fault zone at Carrizo Plain in central California. (Photo courtesy of US Geological Survey)  Below, A number of small faults in the greater San Andreas Fault system run through the San Diego area. (Map: Tracy Sabin)


There are roughly 12 major tectonic plates that cover the surface of the earth. Movement at these plate boundaries has occurred for millions of years, and will continue for millions of years. In general, these plates move past each other at about the same rate that your fingernails grow. Friction at these boundaries causes stress to build, and it is the sudden release of this stored energy that produces an earthquake.

Motion at the San Andreas boundary is referred to as "strike slip," which means that the two plates are moving horizontally past each other. The motion between the two plates in California is further classified as "right lateral," meaning that any "object" on the opposite side of a fault appears to move to the right during or after an earthquake event. Though San Diego is not directly over the San Andreas Fault, there are many smaller right lateral faults within the wider San Andreas Fault system, such as the Rose Canyon Fault that runs directly through the city of San Diego.

faults map

San Diego and the Pacific plate will keep moving northward with respect to the North American plate. This means in about 2 million years, San Diego and San Francisco will be neighbors!

Jeff Babcock, project scientist, Institute of Geophysics and Planetary Physics

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Scripps Scientists take on questions from students curious about ocean and earth sciences


jeff babcock

"In about 2 million years, San Diego and San Francisco will be neighbors!"
— Jeff Babcock