These conditions cause some lightweight materials to melt and rise to the surface to form volcanoes. As a result, long chains of volcanoes, called volcanic arcs, are located above subducted plates, usually above the location where the plate has reached a depth of about 100 km. Earthquakes Geologic deformation is usually very slow, measured in centimeters per year, so the dynamic processes that continually reshape the Earth are, for the most part, unnoticed. Earthquakes are an occasional reminder that this deformation is indeed taking place, and infrequent, but potentially damaging, large earthquakes pose a hazard that is all too often ignored. Earthquakes occur wherever two plates slip past one another, such as along the San Andreas Fault in California.
Earthquakes also occur where one plate slides under the other, as is happening in southern Alaska.
When two ridges are connected by a fault, this is called a transform fault, and the fault is the source of strike-slip events. When completed, your model will look something like the figure below. Follow the directions on the following pages to complete the model. Coloring with paint or magic markers can be added to enhance the model. Note that the shaded portions of the sea floor have the same magnetization as today, while the unshaded portions have reversed magnetization.