When an earthquake occurs, we need to know what its records show in order to anticipate whether there might be aftershocks. The recording of ground movement is called a seismogram . A seismogram is the graph where the readings from the seismograph are displayed. The main function of the seismograph is to measure the speed and type of seismic wave produced during an earthquake.
In this article we'll tell you how a seismogram works and what the importance of earthquake records is.
How an earthquake forms
The first step is understanding how an earthquake forms. As we know, the Earth's crust is divided into tectonic plates. The interaction between these tectonic plates is the primary cause of earthquakes . However, it is not the only one. Any process that can release large amounts of energy stored in rocks is sufficient to generate earthquakes. The magnitude of these earthquakes will depend on the area where the stress is concentrated 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 an earthquake begins sending waves from the hypocenter to the epicenter, a device known as a seismograph measures the magnitude of these waves. The recording of all seismic waves is noted on a seismogram. A seismogram can gather all the information about an earthquake. It records the time, intensity, speed, and distance at which the earthquake occurs.
Because the speeds of different types of waves vary, they can provide valuable information about the earthquake itself. P-waves are the primary waves, which travel at a higher speed. S-waves travel at a slower speed and are called surface waves. The difference in speed between these two types of waves is used to pinpoint the earthquake's epicenter. For more information on this process, you can consult how earthquake magnitude is measured.
How we measure an earthquake
The energy of an earthquake travels in the form of vibrations. These seismic waves are recorded by a seismograph. This instrument indicates the intensity and magnitude of the seismic wave vibrations. The seismogram displays a series of zigzags on paper, ultimately representing the full intensity of the earthquake's waves.
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.
To this day, this is the most well-known and widely used method for classifying earthquakes. In theory, there are no limits on this scale, but a magnitude 9 already signifies total destruction. The largest earthquake ever recorded occurred in Chile in 1960 and reached 9.5 on the Richter scale. Furthermore, seismograms record the natural or artificial movement of the ground, information that is closely related to natural phenomena.
The seismometer has two components: a horizontal and a vertical one. It is capable of recording the signal with both of these components, as well as a third, vertical component. The purpose is to determine the correct speed of seismic waves and accurately locate the hypocenter of the earthquake . Knowing the hypocenter of the earthquake allows us to determine the vertical location of the epicenter.
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.
Depending on the type of seismic event, there are several types of seismograms. There are seismograms for local events, regional events, teleseismic events, nuclear explosions, large-magnitude earthquakes, volcanic activity, and volcanic earthquakes . All 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.