Shaking moves through the ground.
These shakes come from big quakes. They can travel deep inside the Earth. They can also move on top. They help us learn about our world. Can you feel the ground shake?
Shaking moves through the ground.
These shakes can come from big quakes. They can also come from volcanoes. These shakes travel in different ways.
Some shakes travel deep inside the Earth. These are called body waves. Other shakes move along the top. These are called surface waves.
Surface waves can cause more damage. They move the ground a lot.
Scientists use these shakes to study the world. They can even find where a quake started. It is amazing how the ground moves!
Shaking moves through the Earth in many ways. We call these shakes seismic waves.
They can come from earthquakes or volcanoes. Large landslides can also make them.
Scientists who study these waves are called seismologists. They use tools called seismometers to record the shakes.
There are two main types of waves. Body waves travel deep inside the Earth. Surface waves travel along the top. Surface waves move the ground a lot. This can cause more damage.
Body waves have two kinds. The first is the P wave. P waves are primary waves. They are the fastest waves. They can travel through solids and liquids. The second is the S wave. S waves are secondary waves. They move slower than P waves. S waves can only move through solids. They cannot travel through liquid. This helps scientists know the Earth has a liquid outer core.
By timing the waves, scientists can find where a quake started.
Seismic waves are vibrations that travel through a planet.
These waves carry energy through the ground or water. They can start from many different events. Earthquakes and volcanic eruptions are common causes. Large landslides or man-made explosions also create them. Scientists called seismologists study these moving waves. They use special tools like seismometers to record them.
These tools help us understand how the Earth moves.
Waves are divided into two main groups. Body waves travel through the inside of the Earth. Surface waves travel along the top layer instead.
Surface waves move the ground more than body waves. This larger motion often causes more damage during a quake. Body waves have two specific types called P waves and S waves. P waves are primary waves because they arrive first. They move very fast through solids and liquids. S waves are secondary waves that arrive later. They can only move through solid material.
People have studied these waves for a long time. A mathematician named Siméon Denis Poisson identified the two body waves in 1830. Later, Lord Rayleigh predicted surface waves in 1885. He described Rayleigh waves, which move like water waves. Augustus Edward Hough Love created a model for Love waves in 1911. These waves move horizontally along the Earth's surface. Dr. Robert Stoneley also found a special type of boundary wave. His work helped us see how waves move between different materials.
Scientists use many numbers to describe these waves. In air, P waves travel at 330 meters per second. They move at 1450 meters per second in water. In hard granite, they reach about 5000 meters per second. S waves are usually only 60% as fast as P waves. Some Earth vibrations take a long time to pass. A "breathing" mode called 0S0 lasts about 20 minutes. Another mode called 0S2 lasts about 54 minutes. A twisting motion called 0T2 lasts about 44 minutes.
These waves act like a giant X-ray for our planet. Because waves bend or bounce, we can see inside. This is called refraction or reflection. When S waves cannot pass through the liquid outer core, they leave a shadow. This fact helped Richard Dixon Oldham show the core is liquid. By timing different waves, scientists can find a quake's starting point. They use three different stations to find the exact hypocenter.
This helps us map the hidden world beneath our feet.
Seismic waves are mechanical waves of acoustic energy that travel through a planetary body.
These waves carry energy released by various events. Common sources include earthquakes, volcanic eruptions, and magma movement. They can also result from large landslides or man-made explosions. Seismologists study these vibrations to understand the Earth. They record the data using seismometers, accelerometers, or hydrophones in water.
Scientists must distinguish these waves from seismic noise, which is persistent, low-amplitude vibration from many sources.
The speed of a seismic wave depends on the medium it travels through. This velocity is determined by the density and elasticity of the material. As waves move deeper through the crust and mantle, their velocity tends to increase. However, velocity drops sharply when waves move from the mantle into the outer core.
This change in speed occurs because the physical properties of the Earth change with depth. Scientists use the refraction and reflection of these waves to research the Earth's internal structure. This process is similar to how light bends when it enters water.
Seismic waves are categorized into two main groups: body waves and surface waves. Body waves travel through the interior of the Earth. Their paths are controlled by the material's density and modulus, which is its stiffness. The modulus changes based on temperature, composition, and the material phase.
Surface waves travel across the Earth's surface instead of through the interior. Surface waves decay more slowly with distance than body waves. Because their particle motion is larger, surface waves often cause more damage.
Body waves consist of two specific types: Primary (P) waves and Secondary (S) waves. Siméon Denis Poisson, a French mathematician, recognized this distinction in 1830. P waves are compressional, longitudinal waves. They are pressure waves that travel faster than other waves, so they arrive at stations first. P waves can travel through any material, including fluids. In air, they move at 330 m/s. In water, they move at 1450 m/s, and in granite, they reach about 5000 m/s. S waves are shear waves that are transverse in nature. They arrive after P waves and move the ground perpendicular to the wave's direction. S waves can only travel through solids because fluids do not support shear stresses. S waves typically move at about 60% of the speed of P waves.
Surface waves also have distinct types, such as Rayleigh waves and Love waves. John William Strutt, Lord Rayleigh, predicted Rayleigh waves in 1885. These waves move in a manner similar to waves on the surface of water. They are slower than body waves, moving at roughly 90% of the S wave velocity. Love waves are horizontally polarized shear waves that exist in layered media. Augustus Edward Hough Love created a mathematical model for them in 1911. These waves usually travel slightly faster than Rayleigh waves.
Another type is the Stoneley wave, which travels along a solid-fluid boundary. Dr. Robert Stoneley described these interface waves in his research.
Large earthquakes can trigger free oscillations, which are standing waves within the Earth. These result from interference between two surface waves traveling in opposite directions. Rayleigh wave interference creates spheroidal oscillations, while Love wave interference creates toroidal oscillations.
Some spheroidal modes include the "breathing" mode (0S0), which lasts about 20 minutes. The "rugby" mode (0S2) lasts about 54 minutes. Toroidal modes include the 0T2 mode, which describes a twisting of the hemispheres every 44 minutes. The first observations of these oscillations occurred during the 1960 earthquake in Chile.
Seismology provides vital data about the Earth's composition. Because S waves cannot pass through liquids, their absence in the outer core proved that the layer is liquid. This was demonstrated by Richard Dixon Oldham. By measuring the different travel times of P and S waves, scientists can locate a quake's hypocenter.
This is done by finding the intersection of circles from at least three different observation stations. These waves act as a tool to map the hidden structures of our planet.
Where will your curiosity go next?
🖼️ Images & Media (9)
More to explore
✨ What else?
Related topics you might enjoy
🪜 Step back
Simpler topics to build understanding
What is Nepedia?
A free, ad-free encyclopedia for children. Every article is written at five reading levels, so the same page works for a five-year-old and a fifteen-year-old — use the level switcher above to see this one change. No account needed to read.