Earthquake: Usually refers to the phenomenon of ground shaking within a certain range caused by the sudden release of stress in a certain part of the earth's crust. Earthquakes are actually a very common geological phenomenon, but due to the complexity and elusiveness of the crust we live in, the currently accepted explanation by geologists is caused by plate movements caused by tectonic movements.
According to data, in 2021 alone, more than 20 earthquakes of magnitude 5 or above occurred in the mainland, causing direct economic losses of 10.7 billion yuan.
So what are the basic elements of an earthquake?
1. Focal point: usually refers to the area that causes earthquakes or releases crustal stress;
2. Epicenter: Compared with the source, the epicenter refers to the corresponding area projected from the source area to the ground, and it is also the earliest ground position to receive the vibration;
3. Source depth: refers to the distance from the above source to the epicenter;
4. Epicenter distance: refers to the distance from the seismic network to the source;
5. Isoseismic line: the connection of points of the same earthquake causing equal damage degree (can also become intensity) on the ground (can be understood by referring to the definition of contour).
So what are the characteristics of earthquakes:
For us living on the surface, the three characteristics are the most prominent, one is sudden, strong earthquakes occur in an instant. The second is destructive, which can lead to landslides, ground subsidence and uplift, surface dislocation, mountain and river diversion more serious, and cause tsunamis. The third is that it has a strong chain type, often a strong earthquake is accompanied by a series of secondary earthquakes that have been repeated many times or even many years.
However, students living by the sea do not need to worry, earthquakes to cause tsunamis also need to be large enough, and the depth of the epicenter is shallow, the seaside is close to the deep sea, and the way the source is wrong is up and down, etc., to cause a tsunami.
After an earthquake, it must not be taken lightly, because as long as there is a causal connection in the same geological structure zone or the same source, it can be called the same earthquake sequence.
Usually divided by the magnitude of the earthquake, the larger earthquake in an earthquake sequence is often called the main shock, the rest is called aftershock, for the general earthquake, there is rarely a single earthquake often accompanied by aftershocks and foreshocks.
However, if the difference between each tremor in the sequence of earthquakes is not obvious, it can also be called a group seismic effect, such as the Xingtai earthquake in 1966.