What is an Earthquake
Focus and Epicenter?

Introduction
Where is the earthquake focus? The focus of an earthquake is the point where the rocks start to fracture. It is the origin of the earthquake. The epicenter is the point on land directly above the focus.

Focus of an Earthquake, USGS

Focus of an Earthquake, USGS

Focus of an earthquake
The focus is also called the hypocenter of an earthquake. The vibrating waves travel away from the focus of the earthquake in all directions. The waves can be so powerful they will reach all parts of the Earth and cause it to vibrate like a turning fork.

Epicenter of an earthquake
Directly above the focus on the Earth's surface is the earthquake epicenter. Earthquake waves start at he focus and travel outward in all directions. Earthquake waves do not originate at the epicenter.

News stories about earthquakes
Most news stories on earthquakes will list the epicenter of an earthquake and then tell how deep the earthquake was from the epicenter. Great earthquakes that occur in subduction zones may give an earthquake focus but they actually break along hundreds of kilometers. The 1960 Chilean earthquake broke along 800 kilometers of the fault line.

Richter scale used for shallow-focus earthquakes
Shallow-focus earthquakes occur between 0 and 40 miles deep. Shallow-focus earthquakes are much more common than deep-focus earthquakes. Crustal plates moving against each other produce most of the shallow-focus earthquakes here on Earth. These earthquakes are generally smaller and scientists use the Richter scale when measuring these earthquakes.

Energy released by shallow focus earthquakes
Shallow-focus earthquakes are much more dangerous than deep-focus earthquakes. They release 75% of all the energy produced by earthquakes each year. They are crustal earthquakes that are smaller than deep-focus earthquakes.

Deep-focus earthquakes use moment magnitude scale
Deep-focus earthquakes occur 180 miles or more below the Earth's surface. These earthquakes occur in island arc or deep ocean trenches where one plate is slipping over another in subduction zones. Great earthquakes where one plate is slipping over another plate in a subduction zone trigger deep-focus earthquakes. They are the largest earthquakes and scientists use the moment magnitude scale to measure them.

More Earthquake Links

P waves Find out more about P Waves that are produced by large and small earthquakes.

Love Waves Find out more about Love waves that can topple tall buildings during large earthquakes!

The Mercalli Scale Did you know there can be twelve different intensities of an earthquake but only one magnitude? Find out why!

Normal Fault Find out why miners often find valuable ore in sites where normal faults have occurred


Earthquake Focus Learn where the focus and epicenter of an earthquake are located and exactly what they are?

Haiti Earthquake The devastating Haiti earthquake occurred in a region prone to large earthquakes. Find out why these large earthquakes occur.

What Causes Earthquakes. Find out what causes earthquakes and other fascinating facts about when our planet shakes, rattles, and rolls.

Kids Fun Science The links on our home page include information about volcanoes, science activities, plate tectonics, the rock cycle and much more.