Earthquakes. Seismic waves and seismograph

28/04/2026

The online earthquake simulations on this page will help you understand how seismic waves are generated and act and how a seismograph works.

This Thematic Unit is part of our Earth Sciences collection

Earthquake

Sudden release of energy in the Earth’s crust in the form of seismic waves, caused by the movement of faults or tectonic plates.

Epicenter

Point on the Earth’s surface located vertically above the hypocenter; it is located using geographical coordinates.

Geological Fault

A fracture or zone of fracture between two blocks of rock that allows relative displacement between them, accumulating stress released in seisms.

Hypocenter

Point inside the Earth where the rupture that generates the seism originates; its depth is measured in kilometers (km).

Mercalli Scale

Qualitative scale that measures seismic intensity based on observed effects and damage to people and structures.

Plate Tectonics

Theory explaining the Earth’s lithospheric structure through the movement of large plates, whose interaction generates most earthquakes.

Richter Scale

Logarithmic scale that measures seismic magnitude (released energy) based on wave amplitude.

Seism

A synonym for earthquake, commonly used in technical contexts to refer to any vibratory movement of the earth.

Seismic Wave

Elastic wave that propagates the energy of an earthquake; its propagation speed is measured in kilometers per second (km/s).

Seismograph

Precision instrument used to detect, measure, and record Earth’s vibrations.

What are earthquakes

Earthquakes are natural phenomena that occur when there is a sudden release of energy in the earth’s crust. This release of energy can have devastating consequences, as it causes vibrations and movements on the Earth’s surface. Earthquakes occur mainly in areas of seismic activity, such as tectonic faults, where continental plates meet and move.

The seismograph and the Richter scale

A device called a seismograph is used to measure the intensity of earthquakes. The most common measure used to quantify the magnitude of an earthquake is the Richter scale, which quantifies the energy released during the event. Smaller earthquakes, generally below 4 on the Richter scale, are imperceptible to people, while earthquakes of magnitude greater than 7 can cause significant damage. The modified Mercalli scale is also used to assess the intensity of an earthquake based on the effects observed at different locations.

Effects of earthquakes

The effects of an earthquake can be catastrophic. Sudden ground shaking can cause buildings to collapse, roads to crack, and bridges to collapse. In addition, earthquakes can generate tsunamis in coastal areas.

Earthquakes can also have secondary consequences. Landslides, fires, and seismic aftershocks are common after an earthquake. These events can hamper rescue efforts and increase the number of casualties and overall destruction.

To mitigate the effects of earthquakes, construction techniques have been developed to make buildings more resistant to seismic shaking. Building codes and seismic standards are implemented in many earthquake-prone regions to ensure that structures are designed to withstand seismic stress.

Seismic monitoring

Seismic monitoring is an important tool for detecting and studying earthquakes. Networks of seismographs and other devices are used to measure and record ground motions. These data are used to better understand seismic activity, predict the occurrence of earthquakes, and alert at-risk populations.

In short, the online earthquake simulations will show you in an interactive and simple way how an earthquake acts. Don’t miss them!

Earthquake

Sudden release of energy in the Earth’s crust in the form of seismic waves, caused by the movement of faults or tectonic plates.

Epicenter

Point on the Earth’s surface located vertically above the hypocenter; it is located using geographical coordinates.

Geological Fault

A fracture or zone of fracture between two blocks of rock that allows relative displacement between them, accumulating stress released in seisms.

Hypocenter

Point inside the Earth where the rupture that generates the seism originates; its depth is measured in kilometers (km).

Mercalli Scale

Qualitative scale that measures seismic intensity based on observed effects and damage to people and structures.

Plate Tectonics

Theory explaining the Earth’s lithospheric structure through the movement of large plates, whose interaction generates most earthquakes.

Richter Scale

Logarithmic scale that measures seismic magnitude (released energy) based on wave amplitude.

Seism

A synonym for earthquake, commonly used in technical contexts to refer to any vibratory movement of the earth.

Seismic Wave

Elastic wave that propagates the energy of an earthquake; its propagation speed is measured in kilometers per second (km/s).

Seismograph

Precision instrument used to detect, measure, and record Earth’s vibrations.

Explore the exciting STEM world with our free, online, simulations and accompanying companion courses! With them you’ll be able to experience and learn hands-on. Take this opportunity to immerse yourself in virtual experiences while advancing your education – awaken your scientific curiosity and discover all that the STEM world has to offer!

Earthquake simulations

Waves
Seismograph

Seismic waves

Observe in this animation the differences between S-waves and P-waves.

Seismograph

Observe how a seismograph works. Modify the magnitude of the earthquake according to the Ritcher scale and see what happens.

Giants of science

“If I have seen further, it is by standing on the shoulders of giants”

Isaac Newton

Charles Lyell

1797

–

1875

Charles Lyell was a defender of uniformitarianism, he showed that present geological processes shaped Earth over millions of years. His work strongly influenced Darwin and modern geology

“The present is the key to the past”

René Just Haüy

1743

–

1822

René Just Haüy established the foundations of modern crystallography, showing that crystals have regular forms derived from an ordered internal structure. He founded crystallographic mineralogy

“Crystals reveal to us the secret geometry of nature”

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“If I have seen further, it is by standing on the shoulders of giants”

Isaac Newton

Alfred Lothar Wegener

1880

–

1930

Alfred Wegener formulated the theory of continental drift, proposing that the continents were once united in a supercontinent called Pangaea, laying the foundation of modern plate tectonics

“Continental drift explains the harmony of the coasts and the similarity of fossils on both sides of the ocean”

Alexander von Humboldt

1769

–

1859

Alexander von Humboldt integrated geology, climate, and biology observations to found modern geography, showing the connections between nature, climate, and life

“Nature is a living whole of interconnected forces”

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Test your knowledge

What geological processes lead to the sudden release of energy that produces an earthquake?

Earthquakes occur when tectonic plates—massive slabs of Earth’s crust—move continuously but do not slide smoothly past one another. Instead, they become locked due to friction and irregularities along their boundaries. As the plates keep pushing, tension builds up over long periods of time. When the accumulated stress exceeds the resistance holding the plates in place, they shift abruptly. This sudden movement releases energy in the form of seismic waves that travel through the ground and cause the shaking we experience. The magnitude of an earthquake depends on how much energy was stored and the size of the area where the rupture occurred.

How do seismic waves interact with Earth’s internal layers, and what information can scientists extract from their behavior?

Seismic waves travel at different speeds and follow different paths depending on the materials they pass through. Some waves can move through both solids and liquids, while others can only travel through solid layers. By studying how these waves change direction, slow down, or speed up, scientists can infer the composition, density, and physical state of Earth’s interior. This is how we know, for example, that the outer core is liquid and that the mantle contains regions with varying densities. Earthquakes therefore act as natural probes that reveal the planet’s internal structure.

Why do some earthquakes feel like a gentle wobble while others feel like a sudden jolt?

Because earthquakes don’t all release energy in the same way. Some generate rolling, wave‑like motions that feel smoother and last longer, while others produce sharp, abrupt movements. Your distance from the epicenter also matters: the closer you are, the more intense and sudden the shaking feels. And the type of ground beneath you plays a big role—soft soil can amplify vibrations, while solid rock transmits them more directly.

What happens if an earthquake occurs under the ocean—does that always mean a tsunami?

Not necessarily. A tsunami only forms if the earthquake causes a large vertical displacement of the seafloor. Many underwater earthquakes involve horizontal movement, where the plates slide past each other without lifting or lowering the ocean floor. In those cases, no tsunami is generated. Only when the seabed rises or sinks abruptly does it push the water column above it and create the massive waves associated with tsunamis.

How come some buildings survive strong earthquakes while others collapse even during smaller ones?

Because not all buildings are designed to handle seismic forces. Modern structures in earthquake‑prone regions use flexible materials, reinforced frameworks, and engineering systems that allow controlled movement without collapsing. Older or poorly built structures lack these protections. The type of ground also matters: a well‑designed building on soft soil may suffer more damage than a simpler one built on solid rock. Earthquake resistance depends on both the construction and the environment.