The lithosphere (litho:rock; sphere:layer) is the strong, upper 100 km of the Earth. The lithosphere is the tectonic plate we talk about in plate tectonics. The asthenosphere (a:without; stheno:strength) is the weak and easily deformed layer of the Earth that acts as a “lubricant” for the tectonic plates to slide over.

The lithosphere is broken into giant plates that fit around the globe like puzzle pieces. These puzzle pieces move a little bit each year as they slide on top of a somewhat fluid part of the mantle called the asthenosphere. All this moving rock can cause earthquakes.

The lithosphere is divided into huge slabs called tectonic plates. The heat from the mantle makes the rocks at the bottom of lithosphere slightly soft. This causes the plates to move. The movement of these plates is known as plate tectonics.

The theory of plate tectonics states that the Earth’s solid outer crust, the lithosphere, is separated into plates that move over the asthenosphere, the molten upper portion of the mantle. Thus, at divergent boundaries, oceanic crust is created.

The heat from radioactive processes within the planet’s interior causes the plates to move, sometimes toward and sometimes away from each other. This movement is called plate motion, or tectonic shift.

The surface of the Earth is divided into 7 major and 8 minor plates.

There may be scientific consensus as to whether such plates should be considered distinct portions of the crust; thus, new research could change this list.

• African Plate.
• Antarctic Plate.
• Australian Plate.
• Caribbean Plate.
• Cocos Plate.
• Eurasian Plate.
• Nazca Plate.
• North American Plate.

They move at a rate of one to two inches (three to five centimeters) per year.

Some geologists favor convection currents in the mantle as the best explanation for plate tectonic movement. Convection movement in the uppermost layers of the mantle may pull on the lithospheric rocks, breaking them into huge plates that move slowly on the more plastic, lubricated surface of the asthenosphere.

Plate motions cause mountains to rise where plates push together, or converge, and continents to fracture and oceans to form where plates pull apart, or diverge. The continents are embedded in the plates and drift passively with them, which over millions of years results in significant changes in Earth’s geography.

Earthquakes that generate tsunamis most often happen where Earth’s tectonic plates converge, and the heavier plate dips beneath the lighter one. Part of the seafloor snaps upward as the tension is released. The falling debris displaces the water from its equilibrium position and produces a tsunami.

Most large tsunamis occur at convergent plate boundaries where two tectonic plates are crashing into each other. As the two plates collide one plate is forced down underneath the other. As this happens the leading edge of the top plate snags on the bottom plate and pressure starts to build.

In subduction zones we see convergent plate boundaries where two plates are colliding with each other and one of the plates is subducting back into the Earth. This type of plate boundary is particularly effective for causing tsunamis.