Learn about Earthquakes

You have probably heard the news about the devastating earthquake that struck the country of Haiti in January 2010.

Hundreds of thousands of people were killed and millions were left homeless. Even the country’s capitol was destroyed. Earthquakes are very powerful and scary natural occurrences. But did you know that not all earthquakes are like the one that happened in Haiti? In fact, earthquakes happen everyday. We just don’t feel them that often.

What is an earthquake?

Earthquakes are simply movements in the crust of the Earth. The crust is the Earth’s rocky outer layer and it is composed of the ground where we live and an inner sheet that is made of enormous rocks known as plates. Beneath these plates is a layer of hot, molten rocks known as magma. When a volcano erupts, it spews out magma in the form of lava. In between these plates are lines known as faults, which continually press against each other. Because underneath these plates is a fluid base of magma, they are prone to slipping, sliding, and crashing against one another. When the rocks along the faults give in, an earthquake occurs.

What is the difference between the focus and epicenter?

When you listen to the news about earthquakes, you usually hear words like “focus” and “epicenter”. Many reporters mistakenly use these two words interchangeably. The focus of an earthquake is always underground. It is where the slipping, and the sliding, and the crashing occur. But an earthquake causes waves that can travel thousands of miles through the rocks and up to the ground above.

The ground that is above the focus of the earthquake is known as the epicenter. This is where the earthquake is felt the strongest.


What are the parts of a fault?

To understand earthquakes better, you need to know the different parts of a fault. A fault has usually four different parts: the fault plane, the hanging wall, the footwall, and the fault trace. The fault plane is the flat surface of the fault and is usually where everything happens. When the fault is sloping, the upper side of the fault is called the hanging wall and the lower side is known as the footwall. The line that represents a fault is called the fault trace.

What are the kinds of faults?

There are three different kinds of faults: normal faults, reverse faults, and strike-slip faults. Both normal faults and reverse faults are known as dip-slip faults because the faults either move up or down. Normal faults have a hanging wall that drops down. They are caused by movements that force them apart. Reverse faults, on the other hand, have a hanging wall that moves up and are caused by movements that force them together. Strike-slip faults are different. They don’t move up or down. Instead, they move left or right. If you stand at the surface of the Earth along a fault trace, you will see that one side of the fault has either moved left or right.

What are seismic waves?

Earthquakes produce seismic waves and seismic waves, in turn, cause much of the earthquake damage done on the surface of the Earth. There are actually several kinds of seismic waves, but they are all waves that travel through the inside of the Earth and out to the surface. Scientists who study seismic waves are known as seismologists and they attempt to measure seismic waves with the use of a device known as a seismograph. Seismologists also try to find ways to reduce the damage done by seismic waves from strong earthquakes.

How does an aftershock happen?

Aftershocks are usually smaller earthquakes that occur in the wake of a first earthquake. The first earthquake is usually the strongest but we shouldn’t underestimate the power of aftershocks. They can happen in as little as two days after the first earthquake to as long as two months after. Seismologists usually try to find the epicenter of an earthquake to find out whether the following earthquakes were aftershocks or separate earthquakes. Aftershocks usually happen because the plates have not yet fully adjusted to their new position and they have to move a little bit more to fall into their new places more smoothly. The strength and number of aftershocks become less and less as time passes by.

Earthquakes can be very dangerous to life on the surface of the Earth, but they are dynamic and magnificent forces of nature that tell us we have a life to live and take care of. Learn more about these forces of nature by downloading our free earthquake worksheet and coloring page.