Earthquake

An earthquake, also called a quake, tremor, or temblor, is the shaking of the Earth's surface. This shaking happens when energy suddenly releases deep inside the lithosphere, creating seismic waves. Earthquakes can be very small, so people can't feel them, or very big, so they can damage buildings.

The shaking occurs because of movements deep inside the Earth, especially along places called faults.

Earthquakes can happen naturally or because of human activities such as mining, fracking, and nuclear weapons testing. The point deep underground where the shaking starts is called the hypocenter, and the point on the ground above it is the epicenter. Big earthquakes can cause problems like making the ground act like liquid (soil liquefaction). If they happen underwater, they can sometimes create huge waves in the ocean called a tsunami.

Scientists study earthquakes to understand them better, and engineers design special buildings to stay safe during shaking. Earthquakes are not just a problem for Earth; similar events called marsquakes and moonquakes have been detected on other planets and moons, too.

Terminology

An earthquake is the shaking of Earth's surface caused by a sudden release of energy in the lithosphere, creating seismic waves. People also call earthquakes quakes, tremors, or temblors. These events can happen naturally or because of human actions, such as fracking or nuclear tests, and are usually caused by geological faults breaking apart. The place where an earthquake starts underground is called the hypocenter, while the spot on the ground directly above it is the epicenter.

Major examples

Main article: Lists of earthquakes

Some of the biggest earthquakes in history have caused damage and loss of life. The 1556 Shaanxi earthquake in China was one of the deadliest. It happened on January 23, 1556. Many people lived in homes carved into hillsides, and when the earthquake struck, many of these homes collapsed.

Another very powerful earthquake was the 1960 Chilean earthquake. It is the largest ever measured, reaching a magnitude of 9.5 on May 22, 1960. This earthquake showed how strong these natural events can be. Earthquakes near places where many people live or near the ocean can create big waves called tsunamis. These waves can cause more damage far away from where the earthquake starts.

Occurrence

Tectonic earthquakes happen when energy builds up and moves along a fault. When the stress becomes too big, it breaks free and sends out seismic waves. This is called the elastic-rebound theory.

There are three main types of faults that can cause earthquakes: normal, reverse (thrust), and strike-slip. These faults are found in different places and can cause earthquakes of different strengths. The energy from an earthquake gets much bigger with its size, so larger earthquakes have much more energy than smaller ones. Most earthquakes happen in a place called the Pacific Ring of Fire, but they can happen anywhere along plate edges.

Measurement and location

Main articles: Seismic magnitude scales and Seismology

Earthquakes are measured using special tools called seismometers. These tools record the seismic waves that move through the Earth during an earthquake. There are different ways to measure how strong an earthquake is. One old way is called the Richter scale, but scientists now mostly use the moment magnitude scale. This scale measures how much energy the earthquake released.

Earthquakes create different types of waves. Some waves, called P waves, move faster and push the ground as they pass. Others, called S waves, move slower and shake the ground up and down. These waves travel at different speeds depending on the rocks they move through. By measuring how long it takes these waves to reach different places, scientists can find out where an earthquake happened and how deep it was.

Effects

Earthquakes can shake the ground and sometimes break it apart. This can damage buildings and other structures. The shaking can feel stronger or weaker depending on how big the earthquake is, how close you are to where it starts, and what the land is like.

Earthquakes can also make the ground act like water for a short time, causing buildings to sink or tilt. They can trigger landslides and start fires by breaking power or gas lines. If an earthquake happens underwater, it can create big waves in the ocean called tsunamis. These waves can travel very fast and cause damage when they reach the shore. Earthquakes can also lead to floods if they break dams or cause landslides that block rivers.

Management

Prediction

Scientists study earthquakes to try and guess when and where they might happen next. They use many ways to research this, but even with lots of work, they can't say exactly when an earthquake will strike. Some people think certain weather might signal an earthquake, but this isn't proven.

Forecasting

Forecasting is a way to guess how likely earthquakes are in a place over many years. For areas where scientists know a lot about the faults, they can guess how likely a big earthquake is in the next few decades. There are also warning systems that can tell people an earthquake has started before the shaking comes, giving people a chance to find safety.

Preparedness

Engineers design buildings and bridges to stand up to earthquakes. Older buildings can be made stronger to be safer. Insurance can help people replace what is damaged. Governments and groups make plans to lower risks and get ready for earthquakes. Technology like artificial intelligence can help check buildings and plan safety steps. People can also get ready by securing heavy objects, knowing where utility shutoffs are, and learning what to do when the ground starts shaking. In coastal areas, getting ready also includes being ready for possible tsunamis from undersea earthquakes.

In culture

Different cultures have had many ideas about why earthquakes happen. In ancient Greece, some people thought earthquakes were caused by air vapors underground. Others, like Thales, believed they happened because of tension between earth and water. In Norse mythology, earthquakes were seen as the struggles of the god Loki. In Greek stories, Poseidon, the god of the sea, was responsible for earthquakes. Japanese folklore tells of a giant catfish named Namazu causing quakes. Taiwanese legends speak of a giant earth buffalo named Tē-gû.

Earthquakes also appear in many stories and books. Famous earthquakes, like the one in Kobe in 1995 or San Francisco in 1906, have inspired many tales. Some fictional stories focus on the sudden changes and what happens after, such as in The Earthquake in Chile or Haruki Murakami’s After the Quake. The "Big One," a powerful earthquake expected along California's San Andreas Fault, is a popular theme in many novels and films.

Outside of Earth

Main article: Quake (natural phenomenon)

Just like on Earth, shaking can happen on other worlds too. We call these events marsquakes on Mars and moonquakes on the Moon. This shows that Earth isn’t the only place where the ground moves.