# Earthquakes - Source: Kiddle (kids.kiddle.co), CC BY-SA 3.0, Kiddle encyclopedia, adapted from Wikipedia - Reading level: Grade 5 - Subjects: Rocks and Earthquakes, Nature, Science - Topics: earthquakes, earthquake, called, cause, earth's, people - Length: 1207 words, about 9 min - Published: 2026-07-29 - Original: - Page: - Open in Sprouts: An **earthquake** is when the Earth's surface shakes. This happens because of a sudden movement deep inside the Earth's crust. Earthquakes can be very powerful and cause a lot of damage. Earthquakes usually last only a short time, but they can happen again. They are caused by a quick release of energy in the Earth's crust. This energy creates waves called seismic waves that travel through the Earth. The study of earthquakes is called seismology. Scientists who study seismology look at how often, what kind, and how big earthquakes are. Earthquakes can be large or small. Big earthquakes can knock down buildings and cause injuries or even deaths. We measure earthquakes using tools called seismometers. The strength of an earthquake is often reported using the Richter scale. On this scale, an earthquake of 3 or less is barely felt. But a magnitude 7 or higher earthquake can cause damage over a very large area. If an earthquake happens under the ocean, it can create a giant wave called a tsunami. Tsunamis can cause as much damage and loss of life as the earthquake itself. Earthquakes can also cause landslides, where large amounts of rock and soil slide down a slope. ## How Earthquakes Happen Earthquakes are mostly caused by the movement of huge pieces of the Earth's outer layer, called tectonic plates. Imagine the Earth's crust as a giant puzzle made of these plates. When these plates push against each other, one might slide over or under the other. This movement can build mountains, cause earthquakes, and create [volcanoes](https://sprout.rootsofreason.org/r/kiddle/volcano-facts-for-kids). The edges where these plates meet are called fault lines. Sometimes, these plates get stuck as they try to move past each other. When they are stuck, stress builds up. Eventually, this stress becomes too much, and the plates suddenly slip. This sudden slip releases all the stored energy, causing the ground to shake. ### Types of Earthquake Faults There are three main types of geological faults that can cause earthquakes: - **Normal faults** happen where the Earth's crust is being pulled apart. - **Reverse faults** (also called thrust faults) occur where the Earth's crust is being pushed together and shortened. - **Strike-slip faults** are steep cracks where the two sides of the fault slide horizontally past each other. The famous San Andreas Fault in California is an example of a strike-slip fault. ## Earthquake Sequences Most earthquakes are part of a group that happens in the same area over time. Most of these groups are small tremors that don't cause much harm. - A **foreshock** is a smaller earthquake that happens before a larger one. The larger earthquake is called the mainshock. Foreshocks happen in the same area as the mainshock but are always weaker. - An **aftershock** is an earthquake that happens after a mainshock. Aftershocks are also in the same area as the mainshock and are smaller. They occur as the Earth's crust settles down after the big earthquake. - **Earthquake swarms** are a series of earthquakes that strike in a specific area over a short time. Unlike foreshocks and aftershocks, there isn't one clearly biggest earthquake in a swarm. All the quakes in the sequence are roughly the same size. For example, there was an earthquake swarm at Yellowstone National Park in 2004. Sometimes, earthquakes can happen in a sort of **earthquake storm**. This is when earthquakes hit a fault line in groups, with each one triggering the next. These storms can last for years, and some later earthquakes can be as damaging as the early ones. This happened along the North Anatolian fault in Turkey during the 20th century. ## Tsunamis: Ocean's Giant Waves A **tsunami** is a series of very fast-moving waves in the ocean. They are usually caused by powerful earthquakes under the sea. These waves can crash onto coastal areas, destroying houses and even wiping out entire towns. Unfortunately, we cannot stop tsunamis from happening. However, there are warning systems that can alert people before the giant waves reach the land. This gives people enough time to get to safety. ## Making Buildings Earthquake-Proof Some places, like [Japan](https://sprout.rootsofreason.org/r/kiddle/japan) or California, have many earthquakes and lots of people living there. In these areas, it's important to build houses and other buildings that can stand strong during an earthquake. This is called seismic design or "earthquake-proofing." Earthquake-proof buildings are made to resist the powerful forces of an earthquake. Their strength depends on how they are built, their shape, how their weight is spread out, and how stiff they are. Different combinations of these features are used. Buildings that are square, rectangular, or shell-shaped can often handle earthquakes better than very tall skyscrapers. To reduce stress, a building's ground floor can have very strong, hollow columns. The rest of the building can then be supported by flexible columns inside these hollow ones. Another way is to use rollers or rubber pads to separate the base of the building from the ground. This allows the building to sway safely during an earthquake. To help prevent a roof from collapsing, builders use lightweight materials for the roof. Outer walls are made with stronger, reinforced materials like steel or reinforced concrete. Flexible windows can also help keep the glass from breaking during a quake. ## Major Earthquakes in History ![Map of earthquakes 1900-](https://sprout.rootsofreason.org/media/kiddle-earthquakes-5eacf62414.png) Earthquakes (M6.0+) since 1900 through 2017 ![USGS magnitude 8 earthquakes since 1900](https://sprout.rootsofreason.org/media/kiddle-earthquakes-f56913b4f1.png) Earthquakes of magnitude 8.0 and greater from 1900 to 2018. The size of the bubbles shows how many people died. One of the deadliest earthquakes ever recorded was the 1556 Shaanxi earthquake in China. It happened on January 23, 1556, and killed over 830,000 people. Most homes in that area were yaodongs, which are dwellings carved into hillsides. Many people died when these homes collapsed. The 1976 Tangshan earthquake, which killed between 240,000 and 655,000 people, was the deadliest of the 20th century. The 1960 Chilean earthquake is the largest earthquake ever measured by a seismograph. It reached a magnitude of 9.5 on May 22, 1960. The energy it released was about twice as much as the next most powerful earthquake, the 1964 Alaska earthquake (March 27, 1964). The ten largest recorded earthquakes have all been megathrust earthquakes, which happen when one tectonic plate slides under another. However, only the 2004 Indian Ocean earthquake is also one of the deadliest in history. Earthquakes that cause the most deaths are often powerful ones that happen near cities or the ocean. Earthquakes near the ocean can create tsunamis that devastate communities thousands of kilometers away. Areas most at risk for many deaths include places where strong earthquakes are rare but powerful, and poorer regions that don't have strong building rules to protect against earthquakes. ## How Earthquakes Affect People ![Ghajn Hadid Tower closer view](https://sprout.rootsofreason.org/media/kiddle-earthquakes-2d3dfc0829.jpg) Ruins of the Għajn Ħadid Tower, which collapsed during the 1856 Heraklion earthquake The physical damage from an earthquake changes depending on how strong the shaking is and what kind of community is affected. Poorer and developing communities often suffer more severe and longer-lasting impacts than well-developed ones. Some effects can include: - Injuries and loss of life. - Damage to important services like roads, bridges, and public transport. - Interruption of water, power, sewer, and gas services. - Communication systems breaking down. - Loss of vital community services such as hospitals, police, and fire departments. - General damage to property. - Buildings collapsing or becoming unsafe. ## Picture credits - Phoenix7777, CC BY-SA 4.0 () - Cmglee, CC BY-SA 3.0 () - Joseph.j.zarb at English Wikipedia, CC BY-SA 3.0 ()