Earthquake

An earthquake, earthquake or earthquake also called (from the Greek "σεισμός" tremor) or tierra1 tremor is a shaking of the ground which is produced by the collision of tectonic plates and the release of energy in the course of a sudden reorganization of materials Earth's crust to overcome the state of mechanical equilibrium. The most important and frequently occur when the stored elastic potential energy released in the gradual deformation of rocks adjacent to an active fault plane, but can also occur for other reasons, for example about volcanic processes, by collapse of karst cavities or landslides.
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Origin
The origin of earthquakes is in the accumulation of energy that occurs when materials inside the earth move, seeking the balance from unstable situations are the result of volcanic and tectonic activities, which occur mainly at the edges plate.
Although tectonic and volcanic activities are the main causes of the earthquakes are generated, there are many other factors that may cause: falling rocks on the slopes of the mountains and the collapse of caverns, abrupt changes in atmospheric pressure by cyclones and even human activity. These mechanisms generate events of low magnitude that generally fall in the range of microearthquakes, tremors that can only be detected by seismographs.
Locations
Tectonic earthquakes often occur in areas where the concentration of forces generated by the boundaries of tectonic plates lead to adjustment movements at home and on the surface of the Earth. This is why earthquakes or earthquakes of tectonic origin are closely associated with the formation of geological faults. They usually occur at the end of a cycle called the seismic cycle, which is the period during which strain accumulates in the interior of the Earth would later be released suddenly. This release corresponds to the earthquake, after which the strain begins to accumulate again.
The point within Earth where the earthquake occurs is called the earthquake focus or hypocenter, and the point of the surface is directly perpendicular to the hypocenter, and that, therefore, is the first affected by the shake-receives name epicenter.
In an earthquake can be distinguished:
• hypocenter, deep inner zone where the earthquake occurs.
• epicenter, the surface area perpendicular to the hypocenter, which more strongly affect seismic waves.
The probability of occurrence of earthquakes of a certain size in a given region is given by a Poisson distribution.
Spread


Damage caused by the earthquake of 1960 in Valdivia, Chile. It is the strongest earthquake recorded in the history of mankind, with 9.5 degrees on the Richter scale.
The earthquake is spread by elastic waves (similar to the sound) from the hypocenter. Seismic waves are presented in three main types:
• 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. Circulating inside the Earth, crossing both liquid and solid. They are the first recorded seismographs measuring instruments, hence the name "P".
• Transverse waves, secondary or S: Body waves are slower than the previous ones (between 4 and 8 km / s) and propagated normal to the direction of vibration of the particles. Only pass through solids and recorded in second place in the measuring apparatus.
• Surface waves: they 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. Are those that produce more damage. They spread from the epicenter, and are similar to the waves that form on the surface of the sea. Such waves are recorded on seismographs last place.
Geological faults
A fault is a fracture between two blocks of rock, which can slide relative to one another parallel to the fracture. Each of these blocks sudden slip occurs on a condom. There are three types of failures: failures and slip direction, normal faults and reverse faults. Failures are failures vertical direction (or almost vertical) where the blocks move horizontally. This horizontal movement may be of the right side or left side type, depending on whether an observer standing on a block is the block in front moves to the right or left. Normal faults are slanted fractures with blocks that slide vertically, mainly. In this case, the blocks are called roof and floor, the ceiling is the block which lies on the fracture angle. If the roof of the fault moves down, the failure rate is normal. Otherwise, it is a reverse fault. When the movement of the blocks is a combination of horizontal and vertical movement of a fault oblique speech.
Elastic waves


Damage from the 1906 earthquake in San Francisco, USA.
The energy released during an earthquake is spread by the Earth in the form of elastic waves called P waves, S waves and surface waves of Love and Rayleigh. P waves cause the ground to move forward and backward in the same direction in which they propagate (compression waves) produce S waves move perpendicular to the direction of propagation (shear waves) and waves Love and Rayleigh produce horizontal and longitudinal elliptic-soil, respectively. For its ability to pass through the interior of the Earth, P and S waves are also known as body waves. Unlike the latter, as its name implies, only surface waves travel near the earth's surface. The P wave, being the fastest, is the first to register at a seismic station. It spreads through the crust at an average speed of 6 km / s. The S wave is slower and spreads at a speed of approximately 60% of the P wave velocity
Induced Earthquakes
Today it is certain that if injected into the subsurface, either as a result of waste disposal in solution or suspension, or the extraction of hydrocarbons, is raised with a sudden increase in pore pressure, an intensification of seismic activity in regions already under heavy strain. Soon it should better control these earthquakes induced and, therefore, to provide, perhaps, induced small earthquakes could avoid triggering an earthquake of greater magnitude.
Magnitude and Intensity Scales


There were 358.214 earthquakes of varying intensity between 1963 and 1998.
• Richter Scale, also known as local magnitude scale (ML) is an arbitrary logarithmic scale that assigns a number to quantify the effect of an earthquake.
• The scale seismic moment magnitude is a logarithmic scale used to measure and compare earthquakes. It is based on measuring the total energy released in an earthquake. It was introduced in 1979 by Thomas C. Hanks and Hiroo Kanamori as the successor to the Richter scale.
• The Mercalli Scale is a seismic 12-point scale developed to assess the intensity of earthquakes through the effects and damage to various structures. Named after the Italian physicist Giuseppe Mercalli.
• Scale-Sponheuer Medvedev-Karnik, also known as MSK and MSK-64, is a macroseismic intensity scale used to assess the strength of earth movements based on the destructive effects on human constructions and the change of appearance the field and in the degree of involvement among the population. Has twelve degrees of intensity, the lowest being the number one, expressed in Roman numerals to avoid the use of decimals.