What is an earthquake ?
Referred earthquake , earthquake or earthquake shaking or jerking terrain generally produced by tectonic or volcanic unrest. In some regions of America the word earthquake is used to indicate minor earthquakes and earthquake for higher intensity . Learn more about volcanoes here Original Title : Aftershock : Earthquake in New York
Production year : 1999
Duration : 110 MIN
Directed by Mikael Salomon
With: Tom Skerritt , Sharon Lawrence, Charles S. Dutton,
synopsis
A major earthquake affecting the city that never sleeps.
tremor
The origin of the vast majority of earthquakes in a release of energy product of volcanic activity or tectonic plates.
Tectonic earthquakes often occur in areas where the concentration of forces generated by the boundaries of tectonic plates resulting in readjustment movements inside and on the surface of the Earth. That is why the earthquakes of tectonic origin are intimately associated with the formation of faults. They usually occur at the end of a cycle called seismic cycle , which is the period of time during which strain accumulates in the interior of the Earth is suddenly released later . This release corresponds to the earthquake , after which the deformation begins to build again .
Although plate tectonics and volcanic activity are the main cause why earthquakes occur , there are many other factors that can lead to earthquakes : rockfalls on the slopes of the mountains , caverns collapse abrupt variations in atmospheric pressure cyclones and even human activity. These mechanisms generate low magnitude events that generally fall in the range of microearthquakes , tremors that can only be detected by seismographs.
The interior point on Earth where the earthquake occurs is called seismic focus or hypocenter , and the point of the surface that is directly vertically above the hypocenter , and therefore is the first affected by the shake - scores name epicenter.
The earthquake is propagated by elastic waves ( like sound ) from the hypocenter . Seismic waves come in three main types : two are body waves that only travel through the interior of the Earth and the third type corresponds to surface waves , and are responsible for the destruction of works and loss of life .
Longitudinal waves , primary or P : type of body waves that propagate at a speed of between 8 and 13 km / s in the same direction as the vibration of the particles. Circulate inside the Earth , through both liquids and solids . They are the first to record the measuring instruments seismographs , hence the name "P" or primary .
Transverse waves , secondary or S : body waves is slower than the above ( between 4 and 8 m / s ) and propagate normal to the direction of vibration of particles. Only pass through solids and recorded second in the measuring apparatus.
Surface waves : are the slowest of all ( 3.5 km / s ) and are the product of the interaction between P and S waves along the surface of the Earth. They are producing more damage. They spread from the epicenter and are similar to the waves that form on the surface of the sea. Such waves are those recorded last in seismographs .
Classes tremors
Volcanic : directly related to volcanic eruptions. Are of low intensity and forgone some distance from the volcano.
Tectonic : settings originate in the lithosphere . The hypocenter located usually located 10 to 25 kilometers deep , although some cases have come to detect depths of up to 70 kilometers.
Batisismos : its origin is unclear , characterized in that the hypocenter is located at large depths ( 300-700 km) , and outside the limits of the lithosphere.
Registration intensity of Earthquakes
Apparatus used for the graphic record of earthquakes are called seismographs , and is becoming embodied graph where the amplitude and duration of the passage of waves seismogram .
The intensity is measured by the destructive effects that the earthquake has had on human goods and to do a qualitative scales expressed in " degrees " the above effects are used. The most used are the Mercalli and Richter:
The Richter Scale is a logarithmic scale used to measure the energy released by an earthquake.
Mercalli Scale : a qualitative scale is used to measure "intensity" or the effects of earthquakes on buildings, structures and people.
They are called the isoseismal curves connecting the points where the earthquake has had equal intensity and are located surrounding the epicenter. The homosistas curves are the connecting points where the earthquake was felt at the same time .
Geographical Distribution Not all regions of the Earth are equally prone to seismic shaking. Studying the distribution of the hypocenter of the various earthquakes that have occurred throughout history, it has been divided the Earth's surface in three different areas :
Seismic regions : weak areas very prone to suffer large crustal earthquakes. Often coincide with regions where newly formed mountain ranges rise.
Penisísmicas Regions: waves in which only weak earthquakes are recorded and not very often .
Aseismic regions: very stable areas of the earth's crust where earthquakes rarely recorded.