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the molten material, causing the plates to slowly drift or collide or move apart from each other. The plates interact with each other at the plate boundaries described earlier in the chapter. Earthquakes occur when stress builds up along these plate boundaries and is suddenly released. Tectonic plate interaction greatly impacts the Earth’s surface. Volcanoes form when molten rock (magma) rises to the surface through plate tectonic activity. Mountain ranges are the result of the collision and uplift of rocks in the crust. The North American San Andreas Fault is a strike-slip fault that represents a major fracture in the Earth’s crust. This fault stretches for over 800 miles (1,288 km) throughout the state of California. In some places, the fault can be 10 miles (16 km) deep. The San Andreas

is not a single continuous fault, but rather a fault zone made up of many segments. Movement along any segment can cause on earthquake.

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What Makes an Earthquake