Love wave

Love waves are a specific type of seismic wave that travels along the surface of the Earth. In the field of seismology, these are known as surface waves. They are also sometimes called Q waves or lateral waves in German. Unlike body waves, which move through the interior of the planet, Love waves move horizontally. They are described as horizontally polarized waves. This means the motion of the ground is perpendicular to the direction the wave is traveling. They are a distinct class of seismic energy, separate from P-waves, S-waves, and Rayleigh waves.

To understand how a Love wave works, we must look at how different layers of the Earth interact. These waves are the result of interference from many shear waves, also called S-waves. For a Love wave to form, there must be a low velocity layer sitting on top of a higher velocity layer. This top layer is an elastic layer that is guided by the material beneath it. One side of this layer is welded to an elastic half space. The other side borders a vacuum. This specific structure allows the S-waves to combine and create the horizontal shifting motion we see during an earthquake.

The movement of particles during a Love wave follows a very specific pattern. The motion forms a horizontal line that is perpendicular to the wave's propagation. As you look deeper into the material, the movement changes. It can decrease to a specific point called a node. After hitting a node, the motion may increase and decrease again as you examine deeper layers. The amplitude, which is the maximum amount of particle motion, often decreases rapidly as you go deeper. Because these waves are confined to the surface, their strength is most intense at the top.

Mathematics allowed scientists to understand these waves before they were fully observed. Augustus Edward Hough Love predicted the existence of these waves mathematically in 1911. His findings were published by the Cambridge University Press. Later, in 1967, the work was published again by Dover in New York. Scientists use complex equations to describe this movement. They often use the conservation of linear momentum of a linear elastic material to model it. One common way to solve these mathematical problems is through the propagator matrix method, also called the matricant approach.

Love waves have unique speeds compared to other seismic waves. They travel at a lower velocity than both P-waves and S-waves. However, they travel faster than Rayleigh waves. One of their most important features is how they lose energy over distance. Body waves travel in three dimensions, so they lose strength quickly. Love waves stay on the surface, so their amplitude decays only as 1/r. This means they decay much more slowly than body waves. Because they stay strong for a long time, they can be very dangerous.

Because of this slow decay, Love waves are highly destructive. They are often the most destructive waves outside the immediate area of the earthquake's focus or epicentre. In fact, Love waves are what most people feel directly when an earthquake occurs. In very large earthquakes, these waves can be so powerful that they travel around the entire Earth several times. They continue to move and vibrate the ground before they finally dissipate. This ability to carry energy over vast distances makes them a major concern for seismologists.

Sometimes, people notice that animals like cats and dogs act strangely before an earthquake. It was once thought that these animals could predict an earthquake. However, the science suggests a different reason. Animals are simply more sensitive to ground vibrations than humans are. They are able to detect the subtler body waves, such as P-waves and S-waves, that arrive before the Love waves. By the time the large, horizontal shifting of the Love waves reaches a location, the animals have already felt the earlier, smaller vibrations.