Earthquakes are vibrations in the ground that originate below the surface of the earth. They arise through mass shifts, mostly as a result of movements of tectonic plates at fracture joints in the lithosphere, the outermost layer of the earth’s body, which includes the earth’s crust and the outermost part of the earth’s mantle. Volcanic activity, collapses or subsidence of underground cavities, landslides, large landslides or blasts are the cause. Earth layers according to chemical properties: (1) Earth’s crust, (2) Earth’s mantle, (3) Earth’s core (4) lithosphere, (5) asthenosphere (6) outer core of the earth, (7) inner core of the earth.
When submarine landslides occur or when oceanic volcanoes erupt, the sudden vertical displacement of large parts of the ocean floor creates so-called tsunamis, which move at speeds of up to 800 kilometers per hour. These are barely noticeable on the open sea. However, if they run out in the shallower water, the wave crest steepens and in extreme cases can reach a height of 100 meters. Tsunamis occur most frequently in the Pacific, which is why the states bordering the Pacific have set up an early warning system, the Pacific Tsunami Warning Center. Usually do not consist of just a single tremor, but usually result in more. In this context, earthquakes can be divided into three phases: Fore-shocks, main shocks and aftershocks. Earthquakes that occur more frequently over a longer, limited period of time are called swarms or swarms of earthquakes. These occur particularly in volcanically active regions; the majority of recorded earthquakes are too weak to be perceived by humans.
On the other hand, strong earthquakes, which are counted as natural disasters, can destroy buildings, trigger landslides and tsunamis, or change the shape of the earth’s surface. The science of earthquakes is called seismology. With one exception, the ten strongest earthquakes since 1900 occurred in the Pacific Ring of Fire, the subduction zone around the Pacific. Pacific Ring of Fire, According to an analysis by the Karlsruhe Institute of Technology, more than 35. 000 natural catastrophe events in the last 115 years have killed a total of 2.23 million people worldwide as a result of earthquakes. The number may seem large at first glance, but in comparison to the 47 million deaths that the two world wars claimed in just 8 years, for example, it is just “a drop in the ocean”.
What types of earthquakes are there, Tectonic earthquakes 90% of all earthquakes are precisely this type of earthquake. It is caused by tectonic activity or movement of tectonic plates at depths of 10 to 15 kilometers. These can either move apart, towards one another or past one another. If the plates tilt or get caught in their movement, mechanical stresses build up within the rock. If the shear strength of the rocks is exceeded, these tensions are discharged in the form of jerky movements of the earth’s crust. The energy released during this process is 100 times the energy of a hydrogen bomb .
It is therefore hardly surprising that these earthquakes are among the strongest ever. Volcanic earthquakes Also known as magmatic earthquakes, these are tremors in volcanically active areas, which are caused by magma movements in the area of the magma body. They can also occur when there is no volcanic activity on the surface. As a rule, igneous quakes occur as swarms of earthquakes. At 7% volcanic earthquakes occur relatively rarely, are mostly weak and hardly stronger than magnitude.
Movement of hot water underground causes slight seismicity very close to the surface. These quakes can also occur like swarms and are mostly weak. Induced earthquakes As the name suggests, these quakes are induced by an external force – in the given case by humans in the form of interventions in the geology. As a result of these activities, there is a change in the rock stress in a shallow focus depth of less than 5 kilometers. Induced earthquakes can be caused by the extraction of raw materials such as coal, ore, natural gas or crude oil, grouting, hydraulic fracturing (fracking), reservoirs, Geothermal systems and explosions – for example in quarries or in the form of underground tests.
Induced earthquakes usually reach a magnitude between 3 and 6 collapse earthquakes, where naturally occurring cavities, for example in karst areas or in pieces of salt, can collapse and cause quakes near the surface of the earth. Even if they only reach a very low magnitude, for example 0.4, they can still be clearly felt. These quakes are shallow and are caused by sudden freezing of large amounts of water in the ground or in the rock underground. The frozen water expands, creating tensions that discharge in the form of small vibrations. The magnitude of the frost quake is often so small that it cannot even be determined. At most, a rumbling noise can be heard on the surface. Precipitation Heavy precipitation and snowmelt also lead to swarmquakes in individual areas, although these have a very low magnitude. Earthquake strength To be able to compare earthquakes with one another, their strength must first be determined. Since a direct measurement of the energy released by an earthquake is not possible due to the depth of the focal process alone, different scales were developed for this purpose. Intensity The very first scales, which were used at the end of the 18th to the end of the 19th century, were only capable of Describe the intensity of an earthquake, ie the effects on people, animals, structures and natural objects such as mountains or water. The 12-part Mercallis scale, for example, which was first introduced in 1902, is based solely on a subjective assessment of the auditory and sensory observations as well as the damage effect on the environment. About 60 years later, the Mercallis scale was first developed into the MSK scale, then the EMS scale, and these intensity scales are still used today.
The determination is made by means of questionnaires. The evaluated data are then recorded graphically in so-called isoist cards. Surveys of this kind are only possible in relatively densely populated areas. Magnitude Only from the second half of the 19th century onward, through the constant optimization of seismometers, was it possible to carry out objective measurements or measurements based on physical quantities. This resulted in the development of magnitude scales. Location-dependent amplitude values, which are recorded at seismological measuring stations, are used to determine the strength of the earthquake. Although the moment magnitude scale is currently the most common magnitude scale among scientists, the media in particular adhere to the Richter scale introduced in the 1930s. This is used to measure seismic waves in a logarithmic scale. In order to be able to record the magnitude of the earthquake exactly, the seismograph must ideally be positioned 100 km from the source of the earthquake. In addition to the energy of the quake, the direction and distance of the earthquake can also be derived from the recordings. If the earthquake measuring station is too far from the epicenter and at the same time the strength of the earthquake is too great (from magnitude 6), the Richter scale can only be used to a limited extent.
Nevertheless, due to the simple calculation and the comparability with older earthquake classifications, it is still used in seismology today. How can earthquakes be predicted? Some of them show up in the change of geophysical measurable quantities, such as the inclination of the ground, seismic speed or the electromagnetic properties of the rock. Phenomena such as the concept of seismic calm, according to which the seismic background activity or The steady occurrence of smaller earthquakes in a potentially endangered region decreases over a longer period of time and thus points to a future major event, however, are based on statistical observations. The most reliable predictions to date allow the radon method, which records the quantities in which the noble gas is Radon leaks from the earth. Before the quake, the amount of radon in the water of manholes increases up to four times the usual amount. Seismologists assume that shortly before an earthquake, deep underground rock layers suddenly become cracked, permeable and expand. This leads to the release of radon, which penetrates the soil and concentrates under the surface of the earth. The boreholes along the San Andreas Fault, The most famous example of such measurements, which are examined for their extent every week. In early February 1975, snakes around the northeastern Chinese city of Haicheng awoke prematurely from their hibernation to flee from the earthquake that hit the city a few days later laid in ruins. At that time, seismologists became aware of the behavior of the animals, took appropriate measurements and had the city evacuated in good time. During the seaquake, which triggered a devastating tsunami 40 kilometers off the coast of Indonesia on Christmas 2004, elephants and other animals fled in Sri Lanka inland, long before the first tidal waves hit. We know from elephants that they are able to perceive infrasound over great distances through the sensitive soles of their feet. It is believed that this was how they felt the tremors of the seaquake, as infrasound travels faster in rocks than in water.
Such reports of animals behaving strangely hours or days before a quake and showing escape reactions have been around since Documented antiquity. So far, science has not found a clear explanation for this. One thesis, for example, assumes that the friction in the rock and the strong pressure create electrical currents, which in turn break down the water in fine cracks in the rock. This creates positively charged particles, which are absorbed by the animals as aerosols through the breath and cause them to release serotonin. While serotonin is commonly known as the “happiness hormone,” too much can cause anxiety. The ability to sense approaching earthquakes doesn’t seem to be limited to specific animal species. Conspicuous behavior of mice, toads, rats, snakes or bats can be used as a kind of early warning system, just like that of birds, dogs, cats, horses, cows, pigs, goats, elephants or fish. Exact prediction using instruments cannot At this point it must be mentioned that both measurable and statistically determinable precursor phenomena can vary greatly in their temporal course and their magnitude. In many cases, individual or several precursor phenomena do not occur at all. Since the instrumental effort that would be required for the complete recording of these effects cannot be realized, the possibility of an exact prediction of earthquakes is not to be expected in the near future either, even if the seismologists have certain data that indicate an earthquake , the population is not given an early warning of every single earthquake.
Due to the economic damage and possible mass panic or mass hysteria, early warnings are only issued if the number of earthquake victims to be expected is estimated to be very large and the earthquake can also be precisely predicted in space and time.Earthquake records – the strongest earthquakes,Largest earthquake magnitude so far there were two quakes which reached a strength of 9.5 on the Richter scale. The Valdivia earthquake occurred in 1960 in the Pacific off the coast of Chile, which not only destroyed the small town, but also triggered a 25 meter high tsunami. Due to the strong foreshocks, however, a large part of the population moved to safety, so that the number of victims was comparatively low at 1,655. The same strength was measured in an earthquake near Alaska in 1964. Highest tsunami wave The most powerful tsunami to date was triggered by a seaquake in the Pacific and was about 85 meters high. It hit the Yaeyama Islands, now part of Japan, and claimed the lives of more than 13,000 people. Correct behavior in a (severe) earthquake Before an earthquake Anyone living in an earthquake-prone area should familiarize themselves well with their surroundings: What seismic sources are there in the area? How strong were previous earthquakes in this region? Is the house built safely? Is there a risk of soil liquefaction, landslides or tsunamis? This also applies to emergency shelters and potential evacuation routes, as well as to routes to supply centers, hospitals, workplaces, family members and friends.
To avoid danger, all furniture in the building should be firmly anchored to the wall and fragile or heavy objects should only be placed near the floor. This is especially true for places where you spend a lot of time, such as your bed, desk, etc. If you want to go on holiday in an earthquake-prone area, also has the opportunity to find out about potential dangers as well as how to deal with them both at the tour operator and in the hotel. Especially in tsunami areas, it is important to know evacuation routes in advance and to know where to find assembly points for tourists in an emergency. During the earthquake In many regions where earthquakes occur frequently, earthquake exercises are already held in schools, which students should use the correct behavior learn. If you are in a building, the basic rules are as follows.To avoid falling, crouch down and protect your head with your arms from falling objects: To avoid falling, crouch down and protect yourself Use your arms to protect your head from falling objects: For example, next to a stable inner wall or under a stable table: For example, next to a stable inner wall or under a stable table: Leave the building as soon as the vibrations have subsided Anyone who is in an older building without adequate protection at the time of the earthquake should do so Leave within seconds if there is a chance. Elevators must be avoided at all costs! The safest places outdoors are away from power poles, buildings, bridges, trees and slopes. These should be visited as soon as possible in the event of an earthquake. Vehicles should be kept on the roadside. After an earthquake In principle, the instructions of the authorities must be followed. The danger of aftershocks should also be considered. If your house was severely damaged in the earthquake, should not be entered under any circumstances. If possible, it is advisable to switch off supply lines and go to an evacuation center with the prepared emergency equipment. Tsunami areas are mostly equipped with alarm systems. If there is a danger or if there is no such alarm system, stretches of coast must be left as quickly as possible using existing evacuation routes. If these are not accessible or not available, heights should be visited. Even skyscrapers that have been spared from the earthquake are a safe alternative. Anyone staying outside of Europe should contact their own European embassy after a disaster, which will assist you in the further course and, if necessary, organize a return trip as well, that after an earthquake the rescue and care of the injured has top priority.Special case: swarms of earthquakes Even if most swarms of earthquakes do not cause any dangerous or large tremors, the uncertainty and fear is usually great. These are particularly noticeable at night and can disrupt sleep. If you are vacationing in such an area, even if there is no imminent danger, you should consider returning. Talking to the tour operator in advance is definitely a good idea to make sure that you get rebooking or refunds. Otherwise, keep calm. If the building you are staying in shows signs of structural damage such as small cracks in the wall, etc., it is advisable to have an expert check it out.