# What Are Surface Waves? - Definition, Types & Examples

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• 0:01 Waves of Warning
• 0:52 What Is a Surface Wave?
• 1:43 Types
• 2:24 More Examples of Surface Waves
• 3:11 Lesson Summary

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Lesson Transcript
Instructor: Suzanne Rebert

Suzanne has taught college economics, geography, and statistics, and has master's degrees in agricultural economics and marine affairs (marine resource management).

You may think of a surface wave as just a bunch of moving water or--in the case of an earthquake--moving dirt. Find out more about surface waves, and take a quiz to test your understanding.

## Waves of Warning

In late August of 2011, a Twitter user in New England had a surprising experience. A few minutes before 2 p.m. that day, reports of an earthquake in Virginia began to show up in her feed. A little over a minute later, a mild earthquake rocked her own city. At her location, approximately 500 miles away from the Virginia residents who had first mentioned it, the quake was barely perceptible. However, over the next few hours, Americans were amazed to read of moderate, but expensive, earthquake damage to national landmarks such as the Washington Monument, located about 85 miles away from the quake's source.

What was going on? Why was someone hundreds of miles away able to read about an event before experiencing it? The answer isn't time travel, but the differential speeds of primary and surface waves.

## What Is a Surface Wave?

In physics, a surface wave can occur along any boundary of two different substances. The seismic type of surface wave happens at the boundary between air and rockâ€”the surface of the earth. In other words, this is not a wave that travels in a relatively straight line through the earth from the earthquake's focus, or breakage point of subsurface rock, to the observer's location.

Paths through the deep layers of the earth are the quickest routes from the focus to the human or seismometer observing the quake. Therefore, the seismic waves that take that path are the first to arrive, and scientists call these the body waves. They include the P- and S-waves. Our New England Twitter user was hit by the P- and S-wave just seconds after they were generated in the capital, but she didn't feel them. The waves that travel along the surface are slower, but they are responsible for the earthquake's damaging effects.

## Types

Surface waves are classified by the type of motion they transmit. Two of the most important types are Rayleigh waves and Love waves.

Rayleigh waves have an up-and-down rolling motion that many people describe as feeling like riding in a ship on the ocean. They are also called 'surface roll' waves.

Love waves have a back-and-forth motion, like a sidewinder rattlesnake traveling over the sand.

The combination of the Rayleigh waves' vertical rolling action and the horizontal stresses from the Love waves is the source of most direct damage from earthquakes (i.e., damage not caused by secondary effects like a fire or tsunami). Both of these wave types are named for the scientists who predicted them.

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