How Earthquakes Occur

What Causes An Earthquake?

The Earth’s upper layer is made of giant slabs of rock called tectonic plates, which move very slowly.

An earthquake occurs when the tectonic plates pull apart, slide past or bump into each other. 

• Faults: Cracks in the Earth’s crust where earthquakes are most likely to occur.
• Epicenter: The point on the Earth’s surface directly above where the earthquake starts.
• Seismic Waves: Waves of energy that travel through the Earth during an earthquake.

Frequency of Earthquakes

Some places have more earthquakes than others because they are located near tectonic plate boundaries. Example: Pacific Ring of Fire.

There are three main types of plate boundaries where earthquakes are common:

• Convergent Boundaries: Two plates collide, and one might go under the other, causing a strong earthquake.
• Divergent Boundaries: Two plates move away from each other, and magma rises to make new crust. This can also cause earthquakes.
• Transform Boundaries: Two plates slide past each other sideways. The friction and stress from this movement can lead to earthquakes.

Measuring Earthquakes

Scientists use special tools and scales to measure earthquakes. Here’s how they do it:

• Seismometers detect and record the vibrations from earthquakes. They create a seismograph, which shows the seismic waves.
• Richter Scale measures the magnitude, or energy, of an earthquake. Each whole number increase means the earthquake is ten times stronger. 
• Moment Magnitude Scale (Mw) is a newer, more accurate scale for big earthquakes. It measures the size of the fault area that slipped, how much it slipped, and the strength of the rocks.

Fun Facts

Here are some interesting facts about the earthquakes:

• The largest recorded earthquake was in Chile in 1960, with a magnitude of 9.5.
• Earthquakes can cause other natural disasters like tsunamis and landslides.
• There are over 500,000 detectable earthquakes yearly, but only about 100,000 are felt.
• The maximum number of earthquakes in the USA occurs along the western coast, particularly in California, which is part of the Pacific Ring of Fire.

Review

Let’s quickly recap what we learned about earthquakes:

• What is the point on the Earth’s surface directly above the earthquake’s start called? Epicenter
• What waves of energy travel through the Earth during an earthquake? Seismic Waves
• What are cracks in the Earth’s crust where earthquakes occur called? Faults
• What does the Richter Scale measure about an earthquake? Magnitude