The San Andreas Fault in California is a large crack in the earth’s crust which marks part of a plate boundary. The slow-moving North American plate is sliding in the same direction as the faster-moving Pacific plate. The plates are always moving, but where they touch each other, they often lock together. Eventually, one plate will jump forward suddenly or slip or break, causing an earthquake.
A map of the San Andreas Fault CALIFORNIA
North American Plate moving in same direction but SLOWER (by an average of 1 cm per year)
San Francisco
San Andreas Fault
Los Angeles Pacific Plate
moving relatively FASTER
Mexico
An aerial photograph of the San Andreas Fault 3.3 Tsunami Waves
When an earthquake occurs under the sea, it can trigger a tsunami. A tsunami is a huge tidal wave that moves very quickly towards the shore. These waves can cause a huge amount of damage along the coastline and can result in many deaths. See figure 2 for how a tsunami happens.
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Fun Fact!
If the movement of the plates at the San Andres Fault continues as estimated, Los Angeles will eventually slide past San Francisco – but not for a while yet!
