This diagram shows an earthquake along a fault. The focus of the earthquake is where the energy is released underground. The epicenter is the spot on the Earth’s surface directly above the focus.
USGS and NPS
What Is an Earthquake?
The ground underfoot might seem like it’s not going anywhere but it is. It moves. If it moves all of a sudden the ground shakes. That’s an earthquake!
Earthquakes happen as pieces of the Earth’s crust move suddenly past one another at cracks called faults. Sometimes those pieces do not slide smoothly past one another. They get snagged on the rough surface of the fault. When the pieces of rock overcome the snags, there is an earthquake.
Each year, more than a million earthquakes happen. Most of these are so small that people do not feel the shaking. But some are large enough that people feel them, and a few of those are so large that they cause significant damage.
Earthquakes cause damage to buildings, bridges, and roads. Earthquakes can cause landslides and mudslides, too. If a large earthquake happens under the ocean it can cause a tsunami – a giant ocean wave or series of waves.
Scientists can figure out whether an earthquake is likely to happen in a place. However, unlike weather events, earthquakes can not be forecast ahead of time.
Shop Windows to the Universe Science Store!
Print copies of Spring 2011 issue of The Earth Scientist
, focusing on modernizing classroom seismology education, are available in our online store
. Thanks to IRIS
, the issue is also available as a free pdf
online at NESTA
You might also be interested in:
Some faults look strong and like they wouldn’t cause an earthquake. But it turns out that they can slip and slide like weak faults causing earthquakes. Scientists have been looking at one of these faults...more
A team of scientists from the United States was invited to visit Haiti in late January 2010 to look into the cause of the magnitude 7 earthquake that happened there. While there, the geologists will collect...more
Earthquakes occur regularly in Sumatra, Indonesia because it is located near the boundary of two of Earth's tectonic plates. Earthquakes can create tsunamis when the seafloor moves up or down rapidly....more
New research shows that part of the Whillians Ice Stream in West Antarctica moves more than two feet twice every day in an earthquake-like pattern equal to a Magnitude 7 earthquake. In an earthquake, stress...more
Plates at our planet’s surface move because heat in the Earth’s core causes molten rock in the mantle layer to flow. We used to think the Earth’s plates just surfed on top of the moving mantle, but now...more
Many forces change the surface of the Earth over time. The largest force that changes our planet’s surface is movement of Earth's outer layer in a process called plate tectonics. As shown in this picture,...more
Most people in San Francisco, CA were still asleep when an earthquake shook them awake early in the morning of April 18, 1906. It was a very strong earthquake. It lasted for only about a minute, but caused...more