Again and again our earth quakes and destruction occurs. At this point we want to explain to you how earthquakes occur and what exactly an earthquake is.
The structure of the earth
To understand what exactly happens in an earthquake, you need to know how our earth is constructed: it consists of a solid shell, the so-called Earth’s crust. This crust floats on a liquid layer of magma. This layer forms the Earth’s mantle. And in the interior of the earth there are the outer and inner Earth core.
A giant moving puzzle
The solid earth’s crust is not a coalesced shell: It consists of seven larger and innumerable smaller pieces, which almost resemble a puzzle. They are called Plates. Europe, the continent on which Germany is located, is situated on the Eurasian Plate, for example.
At the edges of these plates displacements occur again and again. That is because they swim on a liquid underground.
If you have brought milk to the boil in a pot and then let it cool, a thin skin forms on its surface. If you then move the milk carefully, i.e. set the liquid in motion, the milk skin cracks or pushes together in other places.
This is exactly what happens to the earth’s crust. Only on a much larger scale. Earthquakes occur at the points where the skin tears apart, is pushed together, or pushes past each other. These places are also called Fracture zones. But they do not have to lie only at plate edges. Sometimes even a closed plate cracks open. This is how a fracture zone is formed within a plate.
In most cases, the plates interlock at a depth of several kilometers and not directly at the earth’s surface. Scientists call this the Earthquake focus or also Hypocenter. At the earth’s surface above this earthquake focus, at the so-called Epicenter, the quake is strongest.
When the earth makes waves
An earthquake causes the earth to vibrate:
Similar to a stone that throws waves when you drop it into water, waves form in the earth and on the earth’s surface.
Geologists distinguish between three types of waves:
- There are on the one hand the primary waves or briefly P-waves. They spread fastest in the earth’s interior.
- The so-called secondary waves or S-waves for short are only half as fast as P-waves. They also move through the earth’s interior.
- Then there are the surface waves. If a P- or an S-wave has propagated to the earth’s surface, it can no longer be propagated further upwards, but only to the sides. These waves are the most dangerous, because they make the earth vibrate the most and cause the most destruction. But they are also the slowest waves and are therefore measured last.
Where does the earth shake?
Earthquakes cannot be predicted, but one can estimate the danger of an area with the help of empirical values. On the picture below you can see a world map. In the dark red colored areas the danger of earthquakes is very high.
How are earthquakes measured??
The strength of an earthquake is measured with Richter scale described. It takes its name from the American scientist Charles F. Judge who developed the scale.
The strength is measured with the following values:
- to 1: measurable only by instruments
- 2 – 3: only slightly felt by people
- 4 – 5: slight damage
- 6 – 7: great damage
- from 8: very destructive earthquake
Earthquakes are measured with the help of Seismographs. These are instruments that record small movements of the ground. The recording of the tremors on paper, film or computer is called a seismogram.
In the case of earthquakes one usually finds the values of the Richter scale in the news. Today, however, earthquake researchers mainly use the Moment Magnitude Scale. Like the Richter scale, it is given in numbers up to 8 and higher. The Richter scale is considered inaccurate for stronger earthquakes. Moment magnitude no longer calculates the energy of the quake, but the length of the fracture in the earth’s crust.