Earthquake Lesson: Causes, Effects, and Safety

Lesson Overview

• What Is an Earthquake?
• The Earth's Layers and Moving Plates
• Why Do Earthquakes Happen? (Tectonic Plates and Faults)
• How Do We Measure Earthquakes? (The Richter Scale)
• Where Do Most Earthquakes Occur? (The Ring of Fire)
• Can We Predict Earthquakes?
• Earthquake Safety: Do's and Don'ts

Have you ever heard about the ground suddenly shaking? Furniture might wobble and objects rattle. This shaking of the Earth is called an earthquake. Earthquakes can be surprising or scary, but learning about them helps us understand why they happen and how to stay safe. 

Did you know that the Earth actually shakes a little somewhere around the world almost every day? Most of these earthquakes are so small that only special instruments can detect them. In this lesson, we'll explore what earthquakes are, what causes them, how we measure them, and what to do if one happens.

What Is an Earthquake?

An earthquake is a sudden shaking or trembling of the ground. It happens when energy that's been stored in the Earth's crust is suddenly released. Think of it like a rubber band that has been stretched-if it snaps, it releases energy and vibrates. 

In an earthquake, rocks under the ground break or slip along cracks called faults, releasing energy in waves. These seismic waves travel through the ground, causing it to shake. Some earthquakes are so small you barely feel them, while others are strong enough to knock things over.

The Earth's Layers and Moving Plates

Earth's Layers: The Earth has a thin outer crust (where we live), a thick mantle, a liquid outer core, and a solid inner core.

Earth may seem like one solid ball, but it's made of layers, a bit like an onion or a layered cake. The main layers are the crust, the mantle, the outer core, and the inner core. The crust is the thin, outermost layer - and that's where we live! It's like the skin of an apple or the shell of an egg, relatively very thin compared to the other layers. 

Below the crust is the mantle, which is much hotter and can flow very slowly (though it's mostly solid rock). Deeper down, the outer core is hot liquid metal and the inner core is an even hotter solid metal ball.

Importantly, the Earth's crust isn't one unbroken piece. It's broken into huge puzzle pieces called tectonic plates. These plates fit together like pieces of a puzzle to form Earth's surface. They float on the softer, semi-fluid upper part of the mantle.

Because of the mantle's slow movements, the plates move too-very slowly. In fact, the continents on these plates drift just a few centimeters per year, about as fast as your fingernails grow! You won't notice this slow motion in daily life, but over millions of years it can move continents across the globe.

Why Do Earthquakes Happen? (Tectonic Plates and Faults)

Earthquakes mostly happen because of the movements of those tectonic plates. Since the plates are constantly shifting (even if we don't feel it), they can push into each other, pull apart, or slide past one another. The places where two plates meet are called plate boundaries, and these areas are often where earthquakes occur.

A fault is a crack or break in the Earth's crust along which movement happens. You can think of a fault as a boundary or edge between two blocks of rock. When plates push or slide against each other along a fault, sometimes they get stuck due to friction. They keep pushing, building up pressure, until suddenly the fault breaks loose and the rocks slip – this releases a burst of energy. That burst of energy shoots out in all directions as seismic waves, shaking the ground. This is an earthquake.

Here's an example: imagine pressing your hands together and trying to slide them. At first, friction keeps them from moving. If you push harder, eventually your hands will slip suddenly. That sudden slip is like an earthquake on a fault!

Why Earthquakes Happen:

• Plate Collision: When plates push into each other (converge), one might slide under the other or they crumple up to form mountains. This can cause powerful earthquakes as the crust suddenly shifts.
  
• Plate Sliding: When plates grind past each other sideways (like along California's San Andreas Fault), they can snag and then suddenly slip, causing earthquakes.

Most big earthquakes occur on faults at plate boundaries. However, earthquakes can also happen in the middle of plates if there are weaker zones in the crust. It's less common, but places not on major plate edges can still feel earthquakes once in a while.

How Do We Measure Earthquakes? (The Richter Scale)

When an earthquake happens, one of the first questions people ask is, "How strong was it?" Scientists measure earthquake strength using a magnitude scale. The most famous one is the Richter scale. Magnitude is a number that represents the amount of energy released by an earthquake.

To measure an earthquake, scientists use instruments called seismographs. A seismograph records the vibrations of the ground during an earthquake, creating a zig-zag line called a seismogram. By looking at these recordings, scientists calculate the earthquake's magnitude.

The Richter scale is designed so that each increase of 1 in magnitude means about ten times stronger shaking than the previous number. That means a magnitude 5 quake shakes about ten times more than a magnitude 4, and a magnitude 6 shakes ten times more than a 5.

Here is a simple comparison of magnitudes and their effects:

• Below Magnitude 4: Usually minor, often not felt by people.
• Around Magnitude 5: Moderate, felt by everyone nearby; minor damage possible.
• Magnitude 6–7: Strong, can cause significant damage to buildings in an area.
• Magnitude 8+: Extremely powerful, causing severe damage over a wide area (very rare).

Where Do Most Earthquakes Occur? (The Ring of Fire)

The "Ring of Fire": A map of the Pacific Ocean basin showing the Ring of Fire (in red), where many earthquakes and volcanoes happen around the edges of the Pacific Plate.

Earthquakes can happen anywhere there's a fault, but they are much more frequent in certain zones. The majority of the world's earthquakes occur along the boundaries of tectonic plates. One region stands out in particular: the Pacific Ring of Fire. This is a horseshoe-shaped belt around the edges of the Pacific Ocean where a large number of earthquakes and volcanoes occur.

On the map above, the red lines and dots outline the Ring of Fire. It follows the edges of the huge Pacific Plate-from New Zealand up through Asia and Japan, across to Alaska, and then down the west coasts of North and South America. In these areas, plates are colliding or sliding past each other, causing frequent earthquakes (and lots of volcanoes, too).

Take This Quiz:

Earthquake trivia quiz for kids

Can We Predict Earthquakes?

Unfortunately, the answer is no-at least not yet. Unlike weather forecasts, there is no reliable way to know exactly when or where the next earthquake will happen. Earthquakes start deep underground with little warning. Sometimes there are tiny tremors beforehand or reports of odd animal behavior, but nothing that can consistently predict a quake.

Scientists can estimate where earthquakes are likely over years, and some places have early-warning systems that give people a few seconds notice once a quake starts. But those are not true predictions-just quick reactions to an earthquake already happening. So in general, earthquakes strike without warning, which is why being prepared is so important.

Earthquake Safety: Do's and Don'ts

Knowing what to do during an earthquake can protect you from getting hurt. Earthquake safety is often taught as "Drop, Cover, and Hold On." This means if you feel the ground shaking:

Drop to the ground, take cover under something sturdy (like a table) while protecting your head and neck, and hold on until the shaking stops. This shields you from falling debris. Now, here are some key do's and don'ts for earthquake safety:

What to DO during an earthquake:

• Do take cover under a strong piece of furniture. If there's a table or desk nearby, get under it for protection.
• Do stay in the open if you're already outside. Move away from buildings, trees, or power lines to an open area, so nothing can fall on you.

What NOT to do during an earthquake:

• Don't stand near windows or glass. Windows can shatter during a quake. You want to be away from any glass that could break and hurt you.
• Don't run outside while everything is shaking. You could trip, and building debris might be falling. It's safer to drop and cover where you are until the shaking stops.
• Don't panic. This one can be hard, but remember what you've learned. Try to stay calm and focus on protecting yourself.

Once the shaking stops, it's important to carefully leave any damaged building. Be prepared for aftershocks (smaller quakes that can happen after the main earthquake) and be ready to Drop, Cover, and Hold On again if necessary. Stay away from damaged areas and listen to instructions from teachers, parents, or emergency officials.