Tectonic Plates Enviroments

There are three main plate tectonic environments: extensional,
transform, and compressional. Plate boundaries in different
localities are subject to different inter-plate stresses, producing
these three types of earthquakes. Each type has its own special

Rising and Sinking of Material From Mantle

In this view of a flattened-out mantle from the northwest, the blue blobs show where
colder, denser material is sinking into the mantle. Near the surface, most of the colder
material is in the ancient roots of continental cratons. Subducting slabs of oceanic
lithosphere also appear, being recycled into the mantle from oceanic trenches.

In this view from the southwest the red blobs are warmer plumes of less dense material,
rising principally into the ocean-ridge spreading centers. A huge plume seems to be
feeding spreading at the East Pacific Rise directly from the core. Most of the heat being
released from the earth's interior emerges at the fast-spreading East Pacific Rise.


The map above of Earth's solid surface shows many of the features caused by
plate tectonics. The oceanic ridges are the asthenospheric spreading centers,
creating new oceanic crust. Subduction zones appear as deep oceanic
trenches. Most of the continental mountain belts occur where plates are
pressing against one another. The white squares locate examples given here
of the different tectonic and earthquake environments.

A satellite view of the Sinai shows two arms of the Red Sea spreading ridge,
exposed on land.

The Far Side of The Moon

Extensional ridges exist elsewhere in the solar system, although they never
attain the globe-encircling extent the oceanic ridges have on Earth. This
synthetic perspective of a large volcano on Venus is looking up the large rift
on its flank.

Plate Tectonics, theory of global tectonics (geologic structural
deformations) that has served as a general framework for
understanding the structure, history, and dynamics of the earth's
crust. The theory is based on the observation that the earth's
crust is formed by 13 semirigid plates. The boundaries of these
plates are zones of tectonic activity, where earthquakes and
volcanic eruptions tend to occur.

John Newstrom

Fault Lines

The Blanco, Mendocino, Murray, and Molokai fracture zones are
some of the many fracture zones (transform faults) that scar the ocean
floor and offset ridges (see text). The San Andreas is one of the few
transform faults exposed on land.