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Where do earthquakes strike?

Watch Dr David Thompson explain where earthquakes occur in the world and the reasons for this.

In this video, Dr David Thompson explains where earthquakes occur in the world and the reasons for this.

In Week 1, we looked at the differentiation or internal layering of the Earth. The top layer is the atmosphere and the thin top solid layer on which we walk is called the crust.

a cross section showing the subsurface layers of the Earth from inner core, outer core, mantle, crust and the atmosphere A cross-section of the Earth

Plate tectonics

The crust is made up of rigid sections, known as tectonic plates. Plates are continuously moving over the mantle (middle part of Earth) at different speeds and in different directions.

There are seven major plates on Earth and earthquakes typically occur at the boundaries where plates meet. There are different types of boundaries characterised by how plates interact at them.

Plate tectonics retrieved from USGS, Public Domain.

Plate boundaries

There are three types of boundaries; divergent, convergent and transform boundaries and it is here where earthquakes often occur.

A table showing how at divergent plate boundaries, plates are moving apart. At convergent plate boundaries plates are moving towards one another destroying Earth’s crust as they collide. At transform plate boundaries plates slide horizontally past one another Three main Tectonic Plates boundary types retrieved from Age of the Sage

Divergent plate boundary

These boundaries occur along spreading centres where plates are moving apart and new crust is created by magma pushing up from the mantle.

Picture two giant conveyor belts, facing each other but slowly moving in opposite directions as they transport newly formed oceanic crust away from the ridge crest.

Convergent plate boundary

At these boundaries, plates are moving towards one another destroying Earth’s crust as they collide.

At some of these boundaries one plate sinks under the other as they collide and the area where the plate sinks is referred to as a subduction zone.

At other boundaries the plates collide head-on and neither plate sinks under the other, both are forced upwards forming mountains.

Transform plate boundary

At these boundaries, two plates slide horizontally past one another.

Summary

As we discovered in Week 1, the movement of plates at Earth’s crust is a unique process on our planet. It drives change and causes some of the extreme events we experience. This movement is key to understanding why earthquakes occur.