Earthquakes and volcanoes both signal Earth’s tectonic plate movements, or land shifts. The internal movements of these plates show up mostly in areas around the edges of the plates.
The large Pacific plate, under the Pacific Ocean, seems to be very active—it may even be rotating. The stress created where the oceanic plate meets the various continental plates around the Pacific Rim is commonly released in earthquakes and volcanoes.
Up to one million earthquakes are recorded every year. Although every single quake alters Earth’s crust, most of them are noticed only by seismographs.