Seismograph An instrument that records the motions of the Earth, especially earthquakes. Seismograph Station A site at which one or more seismographs are set up and routinely monitored. Seismologist A scientist who studies earthquakes. The instrumental aspects of seismology. An elongated region where two plates are being pulled away from each other.
New crust is formed as molten rock is forced upward into the gap.
Examples of spreading centers include the Mid-Atlantic Ridge and the East African Rift. Subduction The process in which one lithospheric plate collides with and is forced down under another plate and drawn back into the Earth's mantle. An elongated region along which a plate descends relative to another plate, for example, the descent of the Nazca plate beneath the South American plate along the Peru-Chile Trench. The value given is the depth below the surface of the mean spheroid. The mean spheroid is a uniform approximation to the true shape of the Earth.