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§ 21. Earthquakes (textbook)

§ 21. Earthquakes


1. Remember that exercise lithospheric plate motions.

2. Which forces cause movements lithospheric plates?


Occurrence earthquakes.Earthquakes - is tremors, which are accompanied by fluctuations in Earth's surface. They are causing the Earth's internal forces that are moving lithospheric plates. These forces cause discontinuities deep crust. In the immediate area of the gap shifts crust. For several seconds inside the rock shifted a few centimeters or even meters in horizontal and vertical directions. It generates a sudden earthquake.

Place at depths where there is a gap and shift the earth's crust, called center of the earthquake. It can located at various depths - from several tens to 700 km. Of depth depends on the power of shaking the earth's surface: the deeper, the weaker. Of cell in all directions apply powerful seismic wave. It can be likened to waves from a stone thrown into water. Seismic wave oscillations of the earth's solid passes over long distances. It is through recoil species in the depths and zavalyuyutsya buildings on the surface. Distributed fluctuations rocks very quickly - up to 7 km / sec.

Over center of the Earth's surface is epicenter earthquake (From the Greek "Epi"- Above). In the midst of strength of the strongest aftershocks. Off from him, it decreases. Seismic wave covers a huge area. For example, in 1977 when the earthquake occurred epicenter in Carpathians, Then far away in Moscow, in homes pohytuvalysya chandeliers. If the earthquake epicenter is located on the seabed, the arise moretrusy. Then large floor area can quickly collapse. This in turn causes strong giant wave - Tsunami. They obrushuyutsya great destructive force on the coast, destroying everything in its path.

Destructive strength earthquakes. Among dangerous forces of nature have always been the worst earthquake disaster for humans. They begin suddenly occurring lightning and have a destructive force. Strong earthquakes are called Disaster(From Greek - "death", "end"). Eyewitnesses describe it as terrible natural phenomenon. Earth dull drone and sigh, shakes like ocean waves, and horbytsya shudders underfoot, and formed deep cracks abyss curved iron rails of railways, bridges falling, dying under the rubble of buildings people outbreak of fire from damaged gas and electric networks. During the catastrophic earthquake in 1960 in Chile (South America) and hit the mountain blocked the path of a river basin formed, began to act volcanoes, their fiery roztikalasya lava in all directions. And that's an incomplete list of the effects of earthquakes.

For assessing their strength using a 12-point scale. Pushing force in the 1-3 points attributed to weak (they feel only seismographs). Magnitude 6 points are considered strong (observable light damage buildings), 7 - very strong (cracking of the building), at 11-12 points - catastrophic (Destroyed almost everything). Each year on Earth occurs about 100 thousand earthquakes. Catastrophic earthquakes are rare - on average once every few years. Every year in the world of them killed 10 thousand people.


Fig. Aftermath of the earthquake


Development Seismology.Earthquakes studying science seismology.In many countries, seismologists conduct surveillance of the conduct of the Earth cortex. They assist devices, seismographs. They measure and automatically record the smallest shocks that occur in any part of the globe.

Important Seismology task is the prediction of earthquakes. Unfortunately, modern science can not yet accurately predict them. More or less accurately you can determine the area and power earthquake, but the beginning is very difficult to predict. So the best way reduce the loss - is to prepare for an earthquake. This building Earthquake buildings that can withstand 10-point earthquake. In countries where often These are terrible events, schools teach children proper behavior during earthquake.

Seismologist found that in some parts of the world earthquakes almost never, and in other they occur frequently. Their common is a certain regularity. Earthquakes occur on the boundaries of lithospheric plates, places them in tears and collision - vdovzh earth faults cortex. There, piled pressure subsoil time low earthquakes. Land issues like steam. Often these spaces coincide with mountainous areas (Mount Caucasus, Central Asia, North і South America). When scientists caused earthquake epicenters on the map, it appears that they are focused on seismic zones of the Earth - Pacific, Mediterranean йі  Atlantic. In Ukraine there are earthquakes in Carpathians (Power to 9 points) and Crimea (Up to 7 points).

Earthquakes - One of the clearest evidence of the existence in the depths of powerful internal forces, huge internal energy of the Earth.

FAQ task

1. As an earthquake occurs?

2. What cell different from the earthquake epicenter?

3. At what scale of earthquake strength measured?

4. How dangerous moretrusy? What areas are tsunamonebezpechnymy?

5. In which parts of the Earth  frequently earthquakes? Name and show the seismic zone map of the Earth.

6. Where earthquakes happen in Ukraine?