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| | Earthquake Measuring Devices:
Special instruments - seismographs are used for detecting and recording all forms of seismic waves. In most cases the seismograph has a bob with a spring fastening, which, during an earthquake, remains stationary while other parts of the instrument (body, supports) start moving and are displaced with respect to the bob. Some seismographs are sensitive to horizontal motion while others - to vertical. Waves are recorded by a vibrating stylus on a moving paper strip. Electronic seismographs (without a paper strip) also exist.
The forecasting station Atropatena automatically and independently records 3D vibrations and transmits this information to the Central Database, situated in the USA (La Habra). Since 2007, after opening the first station Atropatena-AZ, the short-term forecasting of earthquakes is regularly received in Praesidium of the International Academy of Sciences (Health and Ecology), Austria, Innsbruck), in the Pakistan Academy of Sciences (Islamabad,Pakistan) and the University Gadjah Mada (Jakarta,Indonesia). In 2009, the Global network for the forecasting of earthquakes (GNFE) started to function fully for the short-term forecasting of earthquakes and a prompt transmission of this information to member countries of Global network. This fact has been widely highlighted in international print media. One of the basic differences of the new forecasting technology of earthquakes is that, not only the place, intensity and time are predicted during the forecast but also the number of expected powerful earthquakes. On the basis of analysis and the interpretation of records "gravitogram", according to a special procedure, the Scientific Research Institute for forecasting and the study of earthquakes issues short-term forecasts of powerful earthquakes (3 - 7 days prior to tremors), which is put on the site "Central Database" (GNFE).
An earthquake is underground tremors and vibrations on the surface of the Earth, induced by natural causes (predominantly by tectonic processes) or (sometimes) artificial processes (explosions, filling of water reservoirs, caving-in of underground cavities of mining works). Insignificant tremors can also be invoked by lava upsurges during volcanic eruptions.
About one million earthquakes occur annually on the Earth, but the majority of them are so insignificant that they remain unnoticed. Really powerful earthquakes, capable of causing extensive damages, occur once in every two weeks on the planet. The majority of them occur at the bottom of oceans and hence are not accompanied by catastrophic consequences (if the earthquake under the ocean occurs without a tsunami).
Earthquakes are mostly known for the destruction which they are capable of. The destruction of buildings and structures are due to vibrations of the soil or gigantic tidal waves (tsunami), arising due to seismic displacements at the bottom of the sea.
The international network for the observation of earthquakes records even the most remote and insignificant earthquakes.
Earthquakes are caused by the quick displacement of section of the earth's crust as a whole during the plastic (fragile) deformation of elastic-stress rocks in the seismic centre. The majority of seismic centers arise near the Earth's surface.
Seismic waves and their measurement:
The sliding of rocks along the crack is prevented by friction in the beginning. Due to this, energy, causing movement, accumulates in the form of elastic stresses of rocks. When the stress reaches a critical point, exceeding the frictional force, a sudden rupture of rocks takes place with mutual displacement; stored energy, being released, induces wave vibrations of the earth's surface - earthquakes. Earthquakes can also occur due to the collapse of rocks in folds, when elastic stress exceeds the ultimate strength of the rocks and they cleave, forming ruptures.
Seismic waves, generated by earthquakes, propagate into all directions from the seismic center like a sound wave. The point, in which the shift of the rock begins is called the focus, seismic center or hypocentre, and the point on the earth's surface over the seismic center – the epicentre of the earthquake. Shock waves propagate to all directions from the seismic center , and their intensity decreases as they move away.
The velocity of seismic waves can reach up to 8 km/sec.
Types of seismic waves:
Seismic waves are divided into compression waves and transverse waves.
Compression waves or longitudinal seismic waves, cause vibrations of the rock particles, through which they propagate, along the direction of the wave, conditioned by the alternation of sections of compression and rarefaction in the rocks. The rate of propagation of compression waves is 1.7 times more than the speed of transverse waves, hence, the compression waves are recorded first by seismic stations. Compression waves are also called primary (P-waves). The speed of P-waves is equal to the speed of sound in the corresponding rock. When the frequency of P-waves is more than 15 Hz, these waves can be heard as an underground rumble and roar.
Transverse seismic waves make the particles of rocks oscillate perpendicularly to the direction of the wave. Shear waves are also called secondary (S-waves).
There exists a third type of elastic waves - long or surface waves (L-waves). Particularly, these waves cause heavy damage. |
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Since Tuesday's earthquake in the US went strangely unnoticed for many residents of the earthquake areas, our very own Doxieone has "patented" a simple yet effective
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Humorous image-good luck.
