Earthquakes are caused by the movement of tectonic plates. This is because these plates are in constant motion and release energy during this movement. Earthquakes can be caused by volcanic eruptions, which are considered a wave of energy of natural origin. What we perceive are seismic waves that come from within the Earth. There are different types of earthquakes. seismic waves And all of them are represented in a seismogram. For more information on how to measure earthquakes, you can read how earthquakes are measured.
How earthquakes form
An earthquake is a tremor on the Earth's surface resulting from the sudden release of energy from within the Earth. This energy release comes from the movement of tectonic plates, which release energy as they move. They can vary in size and intensity. Some earthquakes are so weak that they are not clearly felt. Others, however, They are so violent that they destroy citiesIn this context, it is important to consider how earthquakes can change the elastic properties of the Earth's crust.
The set of earthquakes that occur in a region is known as seismic activity. It refers to the frequency, type, and size of earthquakes experienced in that location over a period of time. On the Earth's surface, these earthquakes manifest as ground shaking and brief displacement. To better understand these phenomena, it is recommended to read about seismicity and its importanceIf you're interested in seismic activity in Spain, there are resources on the country's five most aggressive earthquakes.
They occur almost everywhere on the planet, both at the edges of tectonic plates and along faults. We know that our planet has four main internal layers: inner core, outer core, mantle and crust. The top of the mantle is made up of a rock structure where there are certain convection currents which are those that promote the movement of tectonic plates and, with it, earthquakes.
Seismic waves
As we mentioned before, the formation of an earthquake is due to the expansion of seismic waves occurring within the planet. We define seismic waves as a type of elastic wave produced by the propagation of temporary alterations in the stress field, which results in slight movements of tectonic plates. Although we refer to the movement of tectonic plates as such, we should know that this movement is so slight that it is almost imperceptible. Over the years, tectonic plates move at a slower pace than they did millions of years ago. The continents only move an average of 2 centimeters a year. This is barely perceptible to humans.
It's worth noting that there are different types of seismic waves that can be produced artificially. For example, humans can create artificial seismic waves through the use of explosives or gas extraction techniques such as fracking. These methods can help us better understand the lithospheric plates and their behavior. Understanding seismic waves is vital to seismology, which studies the distribution of these phenomena.
Types of seismic waves
Let's look at the main types of seismic waves that exist and their characteristics. As we mentioned before, seismic waves travel from the Earth's interior to the Earth's crust. However, that's not all. For a more in-depth analysis of the characteristics of earthquakes, it may be helpful to know: How earthquakes are measured and its impact on the earth.
Internal waves are those that travel inside the earth. We know that the composition of our planet's interior is quite complex. This is derived from the information that exists in the existence of different types of seismic waves that follow curved paths. It's an effect similar to that of the refraction of light waves.
P waves are defined as waves that occur in highly compressed soils and are waves expanded in the direction of propagation. The main characteristic of these seismic waves is that they can move through any material, regardless of its state. On the other hand, we have S waves. This type of wave travels transversely to the direction of propagation. Furthermore, they have a lower speed than P waves. so they appear much later in the field. These waves cannot propagate through fluids.
Seismology is the science that is responsible for studying the occurrence of earthquakes. This is how the spatial-temporal distribution, the mechanisms at the source, and the release of energy are studied. The study of the propagation of seismic waves produced by earthquakes provides information about their internal structure, the regions they form, and their distribution of density and elastic constants. Thanks to seismic waves, a great deal of information about the Earth's interior has been obtained.
Importance
Thanks to these seismic waves, we know that they are produced by earthquakes and are determined by the mechanics of elastic media. This means that their speed depends on the elastic characteristics of the medium in which they develop, and their distribution can be studied by observing the travel times and amplitudes of these waves. As mentioned before, there are two types of seismic waves. These propagate at different speeds. The fastest and the first are P waves. These correspond to what are known as longitudinal waves.
The latter have a lower velocity and are transverse in nature. These are called S waves. The study of these waves is carried out by the laws of reflection and refraction, since our planet is made up of layers that have different materials and composition. The trajectories and arrival time are determined considering the flat layers, each of which has a constant speed or considering the spherical earth.
On the Earth's surface and in other discontinuities in the crust, other types of waves are produced. Because they propagate along the surface, they are called surface waves. These waves propagate at lower speeds than S waves and their magnitude is also lower, since they decrease with depth. There are two types of this type of surface waves: Rayleigh waves and Love waves. The first are of vertical movement and the second are of horizontal movement.
I hope that with this information you can learn more about seismic waves and their characteristics.