It is broken into a mosaic of moving plates . As these plates move and shift against one another they release enormous amounts of energy in the form of earthquakes. The boundary between the Pacific plate and the North American plate is located along the coast of California. The movement or slip of the two plates past one another has created the San Andreas fault, the source of many earthquakes . This sequence shows the locations of strong earthquakes worldwide.
Earthquakes tend to be concentrated at the boundaries of Earth's plates.
Volcanoes are also more frequent along the plate boundaries. As oceanic plates are driven under continental plates, forcing them into the mantle, they begin to melt. This produces molten rock, which rises to the surface forming volcanoes . The locations of volcanoes which erupted between 1960 and 1995 are shown.