When an earthquake occurs, we must know what its records are to be able to intuit if there may be more aftershocks. The place where the movement of the ground is recorded is the seismogram. The seismogram is the graph where the records measured by the seismograph are recorded. The main function of the seismograph is to measure the speed and type of seismic wave produced during an earthquake.
In this article we are going to tell you how a seismogram works and what is the importance of earthquake records.
How an earthquake forms
The first thing is to know how an earthquake is formed. As we know, the earth's crust is divided into tectonic plates. The interaction between these tectonic plates is the main cause of earthquakes. Nevertheless, is not the only one. Any process that can achieve large amounts of energy contained in the rocks is enough to generate earthquakes. The size of such earthquakes will depend on the area of stress concentration and other factors.
We are going to talk now about what are the factors that can cause an earthquake:
- Tectonic plates: As we mentioned before, there are numerous earthquakes that originate from the shifting of certain tectonic plates that make up the Earth's crust. These earthquakes generate various types of waves that are recorded by a seismograph and displayed on a seismogram. These earthquakes typically affect large areas of land and are the most common cause of problems.
- Volcanic: This is a less common source of earthquakes, but it can also cause an earthquake. If a volcano erupts violently, it can generate a large amount of shaking that affects all nearby areas. Although it can generate earthquakes, its range of action is much smaller compared to tectonic earthquakes. If you'd like more information on this topic, you can read about the relationship between earthquakes and volcanic eruptions.
- By sinking: if the continuous erosive action of groundwater has taken place inside the crust, they leave a vacuum and end up giving up the weight of the upper part. This fall of the earth is generating vibrations known as earthquakes. Their frequency is very low and they affect to a very small extent.
- Landslides: It may also happen that the weight of the mountain itself can produce some earthquakes by causing landslides along the faults. They are generally not large earthquakes, but rather small waves.
- Atomic explosions: They are carried out during human experiments on atomic bombs. Apparently it has been possible to verify that there is a correlation between seismic movements and the explosion of atomic bombs.
What is a seismogram
When the earthquake begins to send waves from the hypocenter to the epicenter, a device known as a seismograph is responsible for measuring the magnitude of these waves. The record of all seismic waves are noted on the seismogram. Seismogram can collect all the information of an earthquake. In it, the hours, intensity, speed and distance at which the earthquake takes place are recorded.
Because the speeds of the different types of waves are different, they can provide a wealth of information about the earthquake itself. P waves are the primary waves that have the highest speed. S waves are those that travel at a slower speed. They are called surface waves. The difference in speed between each type of wave is used to determine the location of the earthquake's focus. For more information on this process, you can consult how the magnitude of an earthquake is measured.
How we measure an earthquake
The energy of the earthquake travels in the form of vibrations. These seismic waves are recorded by a seismograph. This device indicates the intensity and magnitude of the seismic wave vibrations. The seismogram is plotted in a series of zigzags on the paper where, finally, all the intensity of the waves that the earthquake has had will be represented.
This is where we can see the time, location, and intensity of the earthquake based on the information revealed by the seismogram. It can also reveal information about the type of rock through which the seismic waves passed.
The measurements available on seismograms belong to the Richter magnitude scale. This magnitude scale was created in 1935 by seismologist Charles Richter, and the values range from 1 to the open end. This is a quantitative measurement. It measures the seismic energy released in each earthquake, regardless of its intensity. Its measurement is based primarily on the amplitude of the wave recorded by the seismogram.
Until today, this is the best known and most used way to classify earthquakes. In theory there are no limits on this scale, but a scale of 9 already means total destruction. The largest earthquake that has happened in history took place in Chile in 1960 and reached 9.5 on the Richter scale. In addition, seismograms record natural or artificial ground movement, information that is closely related to natural phenomena.
The seismometer has two components: a horizontal one and a vertical one. It is capable of recording the signal with both components plus a third, vertical one. The purpose is to be able to determine the correct speed of seismic waves and be able to properly locate the hypocenter of the earthquakeBy knowing the hypocenter of the earthquake, we can know where the epicenter will be located vertically.
Seismogram and record
A seismogram can be used to visualize the speed of seismic waves, which are typically surface waves or body waves (P waves and S waves). The first wave recorded is the P wave, as it has the highest speed.
According to the type of seismic event there are several types of seismogram. There are seismograms for local, regional, teleseismic events, nuclear explosions, large earthquakes, volcanic movement and volcanic earthquakesAll of these types generate different signals with their own characteristics that help the seismogram reveal what type of event has occurred.
I hope that with this information you can learn more about the seismogram.