Earthquake are short lived vibrations

Earthquake is a sudden and short-lived vibrations caused by soil erosion of rocks, magmatic activity (volcanic earthquake) or tectonic disturbances (tectonic earthquake) in the lithosphere and part of the Earth's mantle. For instance, studying earthquakes is engaged in seismology, geophysics branch. Earthquake occurs in the interior of the Earth, this place is called the focus or hypocenter. As a matter of fact, place on earth where the strongest earthquake felt called epicenter.

Hypocenter can be shallow, at a depth of 70 kilometers below the Earth's surface. It is usually in areas of inter-plate spacing. Hypocenters can be medium deep (70 to 300 kilometers below the surface). Then, deep (300 to 730 kilometers below the earth's surface). They are mostly in subduction zones. An earthquake with a deeper focus from 730 km, to now is not recorded.

Seismic vibrations spread from the focus on all sides with progressive elastic seismic wave. The fastest are the longitudinal waves that oscillate in the direction of expansion, squeezing and stretching the material through which they pass. Transverse waves vibrating perpendicular to the direction of expansion, 1.7 times are slower than P-waves and spread only through solid rock. Of course, long waves are the slowest, make them circular and horizontal component and the effect of them is poor.

The earthquake was the strongest in the epicenter. This is a place on Earth's surface directly above the hypocentre and in his nearest surroundings (epicentral area). Curve of the travel time of seismic waves to individual places in the epicentral distance is called the time tables. Power of seismic impact depends on the depth hypocentre, distance to the epicenter, features of the floor. In solid rock earthquake was weaker than in independent ground, the presence of groundwater, strength building and another.

An earthquake is an endogenous process. These are processes that result from the heat in the Earth's interior. As a result of such processes are the result of tectonic plate movement. They resulting in tremors of the Earth's crust due to the release of large amounts of energy.

There are two measures that describe the earthquake. These are the magnitude and intensity. The magnitude of the earthquake represents energy released during an earthquake. It is expressed on the Richter scale, which has a value from 0 to 9. Of course, the intensity of an earthquake depends on several factors. Factors are amount of energy released, hypocentre depth, distance to the epicenter and the structure of the Earth's crust.
 

Richter scale or magnitude scale:

- Below 2.0 (Micro) - Micro-earthquakes do not feel. In fact, there are about 8.000 per day.
- 2.0 to 2.9 (Minor) - Generally not felt, but they are recorded by seismographs. There are about 1.000 per day.
- 3.0 to 3.9 (Minor) - Often felt but rarely cause damage. There are 49.000 per year (estimate).
- 4.0 to 4.9 (Light) - It is substantially shaking furniture. Significant damage is rare. There are 6.200 per year (estimate).
- 5.0 to 5.9 (Range) - Causes damage to weaker buildings in rural regions. Minor damage to modern buildings. There are 800 a year.
- 6.0 to 6.9 (Strong) - May cause damage to populated areas (160 km from the epicenter). There are 120 a year.
- 7.0 to 7.9 (Great) - Causes serious damage to a large area. There are 18 per year.
- 8.0 to 8.9 (Devastating) - can cause enormous damage and a thousand kilometers from the epicenter. There are 1 in one year.
- 9.0 to 9.9 (Devastating) - The catastrophic earthquake. It can destroyed most of the buildings within a few thousand kilometers. There are 1 in 20 years.
- 10,0+ (Epic) - They never recorded. Extremely rare (unknown).
 

Most of Earthquake are tectonic

In type of earthquake that must be given is tectonic, which has about 90% of cases, which occur tectonic movements. Such are the strongest earthquakes and affect larger areas. Zone tectonic earthquakes are related to the inter-plate movement and occur when subduction and seafloor spreading. There's volcanic in 7% of cases, are following the eruption of the volcano and the smaller the range. The weakest and smallest range are collapsed in 3% of cases, resulting from the collapse of the material that imparts underground cavities or rockfalls and landslides.

Earthquake spreads in seismic waves. The lines on the map that connect points of equal magnitude earthquake called isoseismal lines. According to the mode and speed of expansion, earthquakes can be with longitudinal or primary and secondary or transverse waves.

Longitudinal the fastest and vibrate in the direction of expansion. Transverse cause vertical oscillation of particles and spread only through solid materials. The surface waves cause circular or horizontal oscillation and may have the strongest effect (depending on the geological structure of the terrain). Earthquakes with it's epicenter on the seabed may cause waves such as tsunamis that can reach a height of 30 meters.

It is estimated that in one year there are an 900.000 earthquakes. For example, magnitude to 2.5 (on the Richter scale). Stronger are more rare and appear every 5 to 10 years. Countries where most earthquake happens are Chile, Japan and Indonesia. The most striking seismic zone in the Pacific, ring of fire (53% of all earthquakes) and in the Mediterranean-Alpine-Himalayan area (41%). Quiet or aseismic areas are in zones of old mountains and masses (the Canadian Shield, the Russian plate).