About Earthquakes & How They Are Formed

Tectonic Plates

• The Earth's crust, or lithosphere, is made up of many irregular sections of rock, known as tectonic plates. These vary in size, shape and thickness, and can be between 4 and 40 miles thick. Oceanic crust is thinner and denser than continental crust. There are many smaller plates and nine large plates; six of these are continental and three are oceanic. Convection currents in the magma below the tectonic plates cause them to move, and the way they affect each other when they come together can have a massive consequences on the world on the surface.

Converging

• Plates collide at convergent boundaries, with the denser of the two plates driven beneath the other. As the denser plate is pushed down, it begins to melt in the heat, creating magma. This magma is less dense than the rock surrounding it, so it begins to move up towards the surface through cracks in the crust. This creates mountains and volcanoes.

Diverging

• Divergent boundaries are created between two tectonic plates that are moving apart. This separation allows magma from the Earth's mantle to rise to the surface. New crust is created in this way, and oceans are made larger. Plates diverging can also create rifts on land, and can even completely separate land masses. Diverging boundaries are generally found under water.

Earthquake

• Tectonic plates can affect each other when they are moving alongside one another. This creates friction, and the plates can occasionally become locked together. The magma beneath is still moving, but the plates are locked into place, causing a build-up of kinetic energy. Eventually the plates become free, but the stored-up energy is released as an earthquake. The point where the earthquake originates is known as the hypocenter.

Energy

• Energy is released in three types of waves in an earthquake. Primary, or P-waves, are the first release of energy, and are moving at between 6 and 7 kilometers per second and so are felt as an abrupt jerk. Next come secondary, or S-waves, and these produce a prolonged side-to-side motion. They move more slowly than P-waves, at 3.5 to 4 km/s. Lastly come the surface waves, which radiate out from a central spot known as the epicenter. This is directly above the hypocenter, on the surface.