Earthquakes - Definition, Examples, Quiz, FAQ, Trivia
Discover how Earth's moving plates create shaking ground and learn how to stay safe
What is an Earthquake?
An earthquake is a sudden shaking of the ground caused by movements deep within the Earth. When two pieces of Earth's crust suddenly slip past each other, they release energy that travels through the ground in waves, making the surface shake.
Earthquakes can be so small you can't feel them, or so big they change the landscape! Most earthquakes last less than a minute, but some powerful ones can last several minutes. About 500,000 detectable earthquakes occur each year, but only about 100 of them cause significant damage.
Did You Know?
The largest recorded earthquake was in Chile in 1960 with a magnitude of 9.5. It created tsunamis that traveled across the Pacific Ocean!
What Causes Earthquakes?
Earthquakes happen because our planet's surface is made of giant puzzle pieces called tectonic plates. These plates are always moving very slowly—about as fast as your fingernails grow! Most earthquakes occur at the boundaries where these plates meet.
There are three main ways plates interact:
Colliding
Plates push together, forming mountains
Pulling Apart
Plates move away from each other
Sliding Past
Plates grind against each other
When plates get stuck but keep trying to move, stress builds up. When the stress becomes too great, the rocks suddenly break or slip, causing an earthquake. The spot underground where the rock breaks is called the focus, and the place directly above it on the surface is called the epicenter.
Measuring Earthquakes
Scientists measure earthquakes using special instruments called seismographs. These machines record the ground movements caused by seismic waves. The record they produce is called a seismogram.
There are two main scales for measuring earthquakes:
Richter Scale
Measures the energy released by an earthquake. Each whole number increase means 10 times stronger shaking and 32 times more energy!
Mercalli Scale
Measures the effects and damage at specific locations. Uses Roman numerals from I (not felt) to XII (total destruction)
A magnitude 2.0 or less earthquake is called a microearthquake and isn't usually felt. Earthquakes between 4.5-6.0 cause damage over a limited area. Anything over 7.0 is considered a major earthquake that can cause serious damage over large areas.
Earthquake Safety
Knowing what to do during an earthquake can save your life! Remember these three important steps:
DROP
Drop down onto your hands and knees
COVER
Cover your head and neck under a sturdy table or desk
HOLD ON
Hold on until the shaking stops
Before an earthquake:
• Create an emergency plan with your family
• Prepare an emergency kit with water, food, and supplies
• Secure heavy furniture to walls
After an earthquake:
• Expect aftershocks
• Check for injuries and damage
• If you smell gas, leave immediately
• Listen to emergency broadcasts
Important!
During an earthquake, do NOT stand in a doorway. Modern building codes don't make doorways the safest place. Get under a table instead!
Earthquake Quiz
Test your earthquake knowledge with this 5-question quiz! Answer all questions to see how much you've learned.
Frequently Asked Questions
Here are answers to common questions about earthquakes:
Amazing Earthquake Facts
Discover fascinating information about earthquakes:
Moonquakes
Earth isn't the only place with quakes! "Moonquakes" occur on the Moon, caused by tidal forces from Earth and temperature changes. They can last up to 10 minutes!
Record Breaker
The most powerful earthquake ever recorded was the 1960 Valdivia earthquake in Chile, magnitude 9.5. It released energy equivalent to 1,000 atomic bombs!
Moving Cities
The 2011 Japan earthquake moved the city of Sendai 8 feet east and shifted Earth's axis by 6.5 inches! It also shortened the day by 1.8 microseconds.
Underwater Mountains
The longest mountain range on Earth is underwater! The Mid-Ocean Ridge stretches 40,000 miles around the planet and is where many earthquakes occur.
