What Is an Earthquake?

An earthquake happens when the ground suddenly shakes. This shaking is caused by movements inside the Earth. The Earth’s surface is made of large pieces of rock called tectonic plates. These plates are always moving, but very slowly.

Sometimes, the plates push against each other and get stuck. Over time, a lot of energy builds up. When the plates finally move, the energy is released as an earthquake. The ground can shake a little or a lot — depending on how much energy is released.

How Do We Measure Earthquakes?

Scientists use a tool called a seismograph to measure earthquakes. The strength of an earthquake is called its magnitude.

One common scale is the Richter scale:

• A small earthquake (below 4.0) may not be felt.

• A medium earthquake (4.0 to 6.0) can shake buildings.

• A strong earthquake (above 6.0) can cause a lot of damage.

Where Do Earthquakes Happen?

Earthquakes can happen anywhere, but they are most common near fault lines, where tectonic plates meet.

Some famous earthquake zones include:

• The Ring of Fire around the Pacific Ocean

• California’s San Andreas Fault

• Japan, which often experiences large earthquakes

Effects of Earthquakes

Earthquakes can cause many problems:

• Buildings and bridges can fall.

• Roads and pipelines can break.

• Tsunamis (giant sea waves) can happen after undersea earthquakes.

But earthquakes also help scientists learn about the Earth’s structure. They remind us that the Earth is always changing.

Staying Safe During an Earthquake

• If indoors, drop, cover, and hold on under a table or desk.

• Stay away from windows.

• If outside, move away from buildings and power lines.

• Be ready for aftershocks (smaller quakes that happen after the main one).

[Key Vocabulary]

[ Review Questions ]

1️⃣ What causes an earthquake?

2️⃣ What tool is used to measure earthquakes?

3️⃣ Where do earthquakes happen most often?

4️⃣ Name one effect of a strong earthquake.

5️⃣ What should you do to stay safe during an earthquake?