Earthquake

An earthquake, also called a quake, tremor, or temblor, is the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. These events can range from being so weak that people can't feel them, to being so strong that they can lift objects and people into the air, damage buildings, and destroy entire cities. The shaking happens because of movements deep inside the Earth, especially along places called faults.

Earthquakes can happen naturally, or they can be caused by human activities such as mining, fracking, and nuclear weapons testing. The point deep underground where the shaking starts is called the hypocenter, while the point on the ground directly above it is the epicenter. Big earthquakes can cause many problems, like shaking the ground so much that it acts like liquid (soil liquefaction), and sometimes they can even trigger huge waves in the ocean called a tsunami if they happen underwater.

Some of the most powerful earthquakes ever recorded include the 1976 Tangshan earthquake in China and the 1960 Valdivia earthquake in Chile, which was the largest ever measured at 9.5 magnitude. To keep people safe, scientists study earthquakes to understand them better, and engineers design special buildings that can withstand the 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 the surface of Earth 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 a lot of damage and loss of life. The 1556 Shaanxi earthquake in China was one of the deadliest, happening on January 23, 1556. Many people lived in special homes carved into hillsides, and when the earthquake struck, many of these homes collapsed.

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

Occurrence

Tectonic earthquakes happen where there is enough stored energy to move along a fault plane. When stress builds up, it suddenly breaks free, releasing energy as seismic waves. This process, called the elastic-rebound theory, explains how earthquakes occur.

There are three main types of faults that can cause earthquakes: normal, reverse (thrust), and strike-slip. Each type occurs in different geological settings and can produce earthquakes of varying strengths. The energy released in an earthquake increases greatly with its magnitude, meaning larger earthquakes release much more energy than smaller ones. Most earthquakes happen in areas known as the Pacific Ring of Fire, but they can occur anywhere along plate boundaries.

Measurement and location

Main articles: Seismic magnitude scales and Seismology

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

Earthquakes create different types of waves. Some waves, called P waves, move faster and squeeze 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 what kind of rock they are moving through. By measuring how long it takes these waves to reach different places, scientists can figure out where an earthquake happened and how deep it was.

Effects

Earthquakes can shake the ground and sometimes break it apart, which can damage buildings and other structures. The strength of the shaking depends on how big the earthquake is, how close you are to where it starts, and what the land is like. Some places can feel stronger shaking even from smaller earthquakes because of the soil and rock there.

Earthquakes can also make the ground act like water for a short time, causing buildings to sink or tilt. They can trigger landslides, start fires by breaking power or gas lines, and even create big waves in the ocean called tsunamis if they happen underwater. These waves can travel very fast and cause a lot of 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 predict when and where they might happen next. They use many different methods, but even with lots of research, they can't yet say exactly when an earthquake will strike. Some people think certain weather conditions might signal an upcoming earthquake, but this isn't proven.

Forecasting

Forecasting is a way to guess the chance of earthquakes happening in a place over many years. For areas where scientists understand the faults well, they can estimate 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 reaches them, giving people a chance to find safety.

Preparedness

Engineers work to design buildings and bridges so they can withstand earthquakes. Older buildings can be strengthened to make them safer. Insurance can help people replace what is damaged. Governments and groups make plans to reduce risks and get ready for earthquakes. Technology like artificial intelligence can help check buildings and plan safety steps. Individuals can also prepare by securing heavy objects, knowing where utility shutoffs are, and learning what to do when the ground starts shaking. In coastal areas, preparedness also includes being ready for possible tsunamis triggered by undersea earthquakes.

In culture

Different cultures have had various explanations for earthquakes throughout history. In ancient Greece, some believed earthquakes were caused by air vapors underground, while others, like Thales, thought they resulted from 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, and 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 destruction and its aftermath, 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 similar to earthquakes can happen on other worlds. We call these events marsquakes on Mars and moonquakes on the Moon . These show that Earth isn't the only place where the ground moves and shakes.