Seismic wave facts for kids

Seismic waves are like vibrations or shakes that travel through the Earth. Think of them as ripples in a pond, but through solid ground! They can be caused by big events like earthquakes, volcanic eruptions, or even large explosions made by people. These waves move through the different layers of our planet. How fast they go depends on what kind of material they are traveling through. When they hit something different, they might bounce off or change direction. Scientists use special tools called seismographs to detect and record these waves.

What Causes Seismic Waves?

Seismic waves are created when a lot of energy is suddenly released in the Earth. The most common cause is an earthquake. When an earthquake happens, it sends out a burst of energy. This energy travels as seismic waves, making the ground shake in all directions from where the earthquake started. Other things that can cause these waves include underground explosions and volcanic eruptions.

Types of Seismic Waves

Seismic waves are split into two main groups: body waves and surface waves. Body waves travel deep through the Earth's inside. Surface waves, on the other hand, move along the Earth's outer layer, like ripples on water.

Body Waves: Traveling Through Earth

Body waves are special because they can travel all the way through the Earth's interior. There are two types of body waves: primary waves and secondary waves.

Primary Waves (P-waves)

Primary waves, often called P-waves, are the fastest seismic waves. This means they are the first ones to arrive at a location when an earthquake happens. That's why they are called 'primary'!

P-waves can travel through solids, liquids, and even gases. In solid rock, they can move super fast, about 7 to 8 kilometers (4 to 5 miles) per second. Their speed changes when they go through liquids or gases. As P-waves move, they push and pull the ground back and forth. It's like a Slinky toy being squeezed and stretched.

Secondary Waves (S-waves)

Secondary waves, or S-waves, arrive after the primary waves. This is why they are called 'secondary'. S-waves are a bit slower than P-waves, traveling at about 3 to 4 kilometers (1.8 to 2.5 miles) per second.

Unlike P-waves, S-waves cannot travel through liquids or air. They can only move through solid materials. When S-waves pass, they make the ground move up and down or side to side. This movement is at a right angle to the direction the wave is traveling. S-waves temporarily change the shape of the material they pass through.

Surface Waves: Shaking the Ground's Surface

Surface waves travel along the Earth's outer layer, or surface. They usually arrive after both P-waves and S-waves. These waves are created when body waves (P-waves and S-waves) reach the surface. There are two main types of surface waves.

Rayleigh Waves

Rayleigh waves are named after a scientist called John William Strutt Rayleigh. When these waves travel, the ground moves in an oval shape, similar to how water moves in ocean waves. The speed of Rayleigh waves depends on the type of solid material they are moving through. These waves help us understand why the ground shakes during an earthquake. Rayleigh waves are usually slower than Love waves.

Love Waves

Love waves are named after another scientist, A.E.H. Love. When Love waves pass, particles in the ground move side to side. This movement is at a 90-degree angle to the direction the wave is traveling. The speed of Love waves also depends on the type of solid they are in. By studying Love waves, scientists can even learn about the thickness of the Earth's crust. Love waves typically travel faster than Rayleigh waves.

How Scientists Detect Seismic Waves

Seismic waves are detected and recorded by special instruments called seismographs. Since primary waves travel faster, they are recorded by seismographs before secondary waves.

Scientists use the time difference between the arrival of P-waves and S-waves to figure out where an earthquake started. By using data from at least three different seismograph stations, they can pinpoint the exact location. Studying seismic waves also helps us learn a lot about what the Earth's layers are made of.

Images for kids

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  Body waves and surface waves

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  p-wave and s-wave from seismograph

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  Velocity of seismic waves in Earth versus depth. The negligible S-wave velocity in the outer core occurs because it is liquid, while in the solid inner core the S-wave velocity is non-zero

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  The sense of motion for toroidal 0T1 oscillation for two moments of time.

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  The scheme of motion for spheroidal 0S2 oscillation.Dashed lines give nodal (zero) lines. Arrows give the sense of motion.

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  The hypocenter/epicenter of an earthquake is calculated by using the seismic data of that earthquake from at least three different locations. The hypocenter/epicenter is found at the intersection of three circles centered on three observation stations, here shown in Japan, Australia and the United States. The radius of each circle is calculated from the difference in the arrival times of P- and S-waves at the corresponding station.

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  P- and S-waves sharing with the propagation

See also

In Spanish: Onda sísmica para niños