Contenido

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Las ondas sísmicas son ondas elásticas que se propagan en materiales sólidos o fluidos. Pueden dividirse en ondas de cuerpo, que viajan por el interior de los materiales; ondas de superficie, que viajan a lo largo de superficies o interfaces entre materiales; y modos normales, una forma de onda estacionaria.

body waves

There are two types of body waves: pressure waves or primary waves (P waves) and shear waves or secondary waves (S waves). P waves are longitudinal waves that involve compression and expansion in the direction in which the wave moves and are always the first waves to appear on a seismogram as they are the fastest moving waves through solids. S waves are transverse waves that move perpendicular to the direction of propagation. S waves are slower than P waves. Therefore, they appear later than P waves on a seismogram. Fluids cannot support transverse elastic waves due to their low shear resistance, so S waves only propagate in solids.[17]​.

Surface waves

Surface waves are the result of the interaction of P and S waves with the Earth's surface. These waves are dispersive, meaning that different frequencies have different speeds. The two main types of surface waves are Rayleigh waves, which have both compressional and shear motions, and Love waves, which are purely shear. Rayleigh waves are the result of the interaction of vertically polarized P waves and S waves with the surface and can exist in any solid medium. Love waves are formed by horizontally polarized S waves that interact with the surface, and can only exist if there is a change in elastic properties with depth in a solid medium, which is always the case in seismological applications. Surface waves travel more slowly than P waves and S waves because they are a result of these waves traveling along indirect paths to interact with the Earth's surface. Because they travel along the Earth's surface, their energy decays less rapidly than that of body waves (1/distance vs. 1/distance), so the shaking caused by surface waves is generally stronger than that of body waves, and primary surface waves are often the largest signals in earthquake seismograms. Surface waves are strongly excited when their source is near the surface, such as in a shallow earthquake or near-surface explosion, and are much weaker for deep seismic sources.[17]​.

Normal modes

Both body and surface waves are traveling waves; However, large earthquakes can also cause the entire Earth to "ring" like a resonant bell. This chime is a mixture of normal modes with discrete frequencies and periods of approximately one hour or less. Normal mode motion caused by a very large earthquake can be observed up to a month after the event.[17] The first observations of normal modes were made in the 1960s, when the arrival of higher fidelity instruments coincided with two of the largest earthquakes of the century: the 1960 Valdivia earthquake and the 1964 Alaska earthquake. Since then, Earth's normal modes have provided us with some of the strongest constraints on the deep structure of the Earth. Earth.

One of the first attempts at the scientific study of earthquakes occurred after the Lisbon earthquake of 1755. Other notable earthquakes that spurred major advances in the science of seismology include the Basilicata earthquake of 1857, the Valdivia earthquake of 1960, the San Francisco earthquake of 1906, the Alaska earthquake of 1964, the Indian Ocean earthquake of 2004, and the Great East Japan Earthquake. of 2011.

Seismometers are sensors that detect and record the movement of the Earth caused by elastic waves. Seismometers can be installed on the Earth's surface, in shallow vaults, in wells, or underwater. A complete set of instruments that records seismic signals is called a seismograph. Networks of seismographs continuously record ground motions around the world to facilitate monitoring and analysis of global earthquakes and other sources of seismic activity. The rapid localization of earthquakes makes tsunami warnings possible because seismic waves travel considerably faster than tsunami waves. Seismometers also record signals from non-seismic sources ranging from explosions (nuclear and chemical), to local wind noise[18] or anthropogenic activities, to incessant signals generated on the ocean floor and coasts induced by ocean waves (global microseism), to cryospheric events associated with large icebergs and glaciers. Seismographs have recorded meteorite impacts on the ocean with energies of up to 4.2 × 10 J (equivalent to that released by a ten kiloton explosion of TNT), as well as a series of industrial accidents and bombs and terrorist attacks (a field of study called forensic seismology). An important long-term motivation for global seismographic monitoring has been the detection and study of nuclear tests.

Because seismic waves typically propagate effectively by interacting with the Earth's internal structure, they provide high-resolution, non-invasive methods for studying the planet's interior. One of the first important discoveries (suggested by Richard Dixon Oldham in 1906 and definitively demonstrated by Harold Jeffreys in 1926) was that the Earth's outer core is liquid. Since S waves do not pass through liquids, the liquid core causes a "shadow" on the side of the planet opposite the earthquake where no direct S waves are observed. Furthermore, P waves travel much more slowly through the outer core than through the mantle.

By processing the readings of many seismometers using seismic tomography, seismologists have mapped the Earth's mantle with a resolution of several hundred kilometers. This has allowed scientists to identify convection cells and other large-scale features, such as large provinces of low shear rate near the core-mantle boundary.[19]

Earthquake prediction

Earthquake prediction is the forecast of the probable timing, location, magnitude and other important characteristics of an upcoming seismic event. Seismologists and others have attempted to create effective systems for accurately predicting earthquakes, such as the VAN method. Most seismologists do not believe that a system that provides timely warnings for individual earthquakes has yet been developed, and many believe that such a system would be unlikely to give useful warnings of impending seismic events. However, there are more general forecasts that routinely predict seismic hazard. These predictions calculate the probability that an earthquake of a given magnitude will affect a specific location over a given time distance, and are commonly used in earthquake engineering.

Public controversy over earthquake prediction arose after Italian authorities charged six seismologists and a government official with involuntary manslaughter in connection with the 6.3 magnitude earthquake in L'Aquila, Italy, on April 5, 2009. The charge has been widely perceived as an accusation of failure to predict the earthquake and has drawn condemnation from the American Association for the Advancement of Science and the American Geophysical Union. The indictment alleges that at a special meeting held in L'Aquila the week before the earthquake struck, scientists and officials were more interested in appeasing the population than in providing adequate information about earthquake risk and preparedness.[20]

Seismology of Mexico

The Mexican Republic is located in one of the most seismically active regions in the world, located within the area known as the Circum-Pacific Belt where the greatest seismic activity on the planet is concentrated.

The high seismicity in Mexico is mainly due to the interaction between the North American, Cocos, Pacific, Rivera and Caribbean plates, as well as local faults that run along several states, although the latter are less dangerous. The North American Plate separates from the Pacific Plate but rubs against the Caribbean Plate and collides with the Rivera and Cocos Plates, hence the incidence of earthquakes.[21]​.

In the country, five tectonic plates converge that interact all the time, and this relative displacement generates an accumulation of stress that is released with tremors of different magnitudes; The particular interaction of the Cocos plate with the North American plate causes the most relevant earthquakes.[22] Statistical data from the National Seismological Service "Servicio Seismológico Nacional (Mexico)") (SSN) indicate that about 200 earthquakes are recorded per year (average of the last two decades) with magnitude greater than 4 on the seismological moment magnitude scale (Mw).[23]​.

engineering seismology

Engineering seismology is the study and application of seismology for engineering purposes.[24] It is generally applied to the branch of seismology that deals with the evaluation of the seismic hazard of a location or region for the purposes of earthquake engineering. It is, therefore, a link between earth sciences and civil engineering.[25] Seismological engineering has two main components. First, the study of the history of earthquakes (for example, historical[25]​ and instrumental[26]​ catalogs of seismicity) and tectonics[27]​ to evaluate the earthquakes that could occur in a region and their characteristics and frequency of occurrence. Second, study the strong ground motions generated by earthquakes to evaluate the shaking expected from future earthquakes of similar characteristics. These strong ground motions can be observations from accelerometers or seismometers or those simulated by computer using various techniques,[28]​ which are then often used to develop ground motion prediction equations[29]​ (or ground motion models).

Contenido

.

Las ondas sísmicas son ondas elásticas que se propagan en materiales sólidos o fluidos. Pueden dividirse en ondas de cuerpo, que viajan por el interior de los materiales; ondas de superficie, que viajan a lo largo de superficies o interfaces entre materiales; y modos normales, una forma de onda estacionaria.

body waves

There are two types of body waves: pressure waves or primary waves (P waves) and shear waves or secondary waves (S waves). P waves are longitudinal waves that involve compression and expansion in the direction in which the wave moves and are always the first waves to appear on a seismogram as they are the fastest moving waves through solids. S waves are transverse waves that move perpendicular to the direction of propagation. S waves are slower than P waves. Therefore, they appear later than P waves on a seismogram. Fluids cannot support transverse elastic waves due to their low shear resistance, so S waves only propagate in solids.[17]​.

Surface waves

Surface waves are the result of the interaction of P and S waves with the Earth's surface. These waves are dispersive, meaning that different frequencies have different speeds. The two main types of surface waves are Rayleigh waves, which have both compressional and shear motions, and Love waves, which are purely shear. Rayleigh waves are the result of the interaction of vertically polarized P waves and S waves with the surface and can exist in any solid medium. Love waves are formed by horizontally polarized S waves that interact with the surface, and can only exist if there is a change in elastic properties with depth in a solid medium, which is always the case in seismological applications. Surface waves travel more slowly than P waves and S waves because they are a result of these waves traveling along indirect paths to interact with the Earth's surface. Because they travel along the Earth's surface, their energy decays less rapidly than that of body waves (1/distance vs. 1/distance), so the shaking caused by surface waves is generally stronger than that of body waves, and primary surface waves are often the largest signals in earthquake seismograms. Surface waves are strongly excited when their source is near the surface, such as in a shallow earthquake or near-surface explosion, and are much weaker for deep seismic sources.[17]​.

Normal modes

Both body and surface waves are traveling waves; However, large earthquakes can also cause the entire Earth to "ring" like a resonant bell. This chime is a mixture of normal modes with discrete frequencies and periods of approximately one hour or less. Normal mode motion caused by a very large earthquake can be observed up to a month after the event.[17] The first observations of normal modes were made in the 1960s, when the arrival of higher fidelity instruments coincided with two of the largest earthquakes of the century: the 1960 Valdivia earthquake and the 1964 Alaska earthquake. Since then, Earth's normal modes have provided us with some of the strongest constraints on the deep structure of the Earth. Earth.

One of the first attempts at the scientific study of earthquakes occurred after the Lisbon earthquake of 1755. Other notable earthquakes that spurred major advances in the science of seismology include the Basilicata earthquake of 1857, the Valdivia earthquake of 1960, the San Francisco earthquake of 1906, the Alaska earthquake of 1964, the Indian Ocean earthquake of 2004, and the Great East Japan Earthquake. of 2011.

Seismometers are sensors that detect and record the movement of the Earth caused by elastic waves. Seismometers can be installed on the Earth's surface, in shallow vaults, in wells, or underwater. A complete set of instruments that records seismic signals is called a seismograph. Networks of seismographs continuously record ground motions around the world to facilitate monitoring and analysis of global earthquakes and other sources of seismic activity. The rapid localization of earthquakes makes tsunami warnings possible because seismic waves travel considerably faster than tsunami waves. Seismometers also record signals from non-seismic sources ranging from explosions (nuclear and chemical), to local wind noise[18] or anthropogenic activities, to incessant signals generated on the ocean floor and coasts induced by ocean waves (global microseism), to cryospheric events associated with large icebergs and glaciers. Seismographs have recorded meteorite impacts on the ocean with energies of up to 4.2 × 10 J (equivalent to that released by a ten kiloton explosion of TNT), as well as a series of industrial accidents and bombs and terrorist attacks (a field of study called forensic seismology). An important long-term motivation for global seismographic monitoring has been the detection and study of nuclear tests.

Because seismic waves typically propagate effectively by interacting with the Earth's internal structure, they provide high-resolution, non-invasive methods for studying the planet's interior. One of the first important discoveries (suggested by Richard Dixon Oldham in 1906 and definitively demonstrated by Harold Jeffreys in 1926) was that the Earth's outer core is liquid. Since S waves do not pass through liquids, the liquid core causes a "shadow" on the side of the planet opposite the earthquake where no direct S waves are observed. Furthermore, P waves travel much more slowly through the outer core than through the mantle.

By processing the readings of many seismometers using seismic tomography, seismologists have mapped the Earth's mantle with a resolution of several hundred kilometers. This has allowed scientists to identify convection cells and other large-scale features, such as large provinces of low shear rate near the core-mantle boundary.[19]

Earthquake prediction

Earthquake prediction is the forecast of the probable timing, location, magnitude and other important characteristics of an upcoming seismic event. Seismologists and others have attempted to create effective systems for accurately predicting earthquakes, such as the VAN method. Most seismologists do not believe that a system that provides timely warnings for individual earthquakes has yet been developed, and many believe that such a system would be unlikely to give useful warnings of impending seismic events. However, there are more general forecasts that routinely predict seismic hazard. These predictions calculate the probability that an earthquake of a given magnitude will affect a specific location over a given time distance, and are commonly used in earthquake engineering.

Public controversy over earthquake prediction arose after Italian authorities charged six seismologists and a government official with involuntary manslaughter in connection with the 6.3 magnitude earthquake in L'Aquila, Italy, on April 5, 2009. The charge has been widely perceived as an accusation of failure to predict the earthquake and has drawn condemnation from the American Association for the Advancement of Science and the American Geophysical Union. The indictment alleges that at a special meeting held in L'Aquila the week before the earthquake struck, scientists and officials were more interested in appeasing the population than in providing adequate information about earthquake risk and preparedness.[20]

Seismology of Mexico

The Mexican Republic is located in one of the most seismically active regions in the world, located within the area known as the Circum-Pacific Belt where the greatest seismic activity on the planet is concentrated.

The high seismicity in Mexico is mainly due to the interaction between the North American, Cocos, Pacific, Rivera and Caribbean plates, as well as local faults that run along several states, although the latter are less dangerous. The North American Plate separates from the Pacific Plate but rubs against the Caribbean Plate and collides with the Rivera and Cocos Plates, hence the incidence of earthquakes.[21]​.

In the country, five tectonic plates converge that interact all the time, and this relative displacement generates an accumulation of stress that is released with tremors of different magnitudes; The particular interaction of the Cocos plate with the North American plate causes the most relevant earthquakes.[22] Statistical data from the National Seismological Service "Servicio Seismológico Nacional (Mexico)") (SSN) indicate that about 200 earthquakes are recorded per year (average of the last two decades) with magnitude greater than 4 on the seismological moment magnitude scale (Mw).[23]​.

engineering seismology

Engineering seismology is the study and application of seismology for engineering purposes.[24] It is generally applied to the branch of seismology that deals with the evaluation of the seismic hazard of a location or region for the purposes of earthquake engineering. It is, therefore, a link between earth sciences and civil engineering.[25] Seismological engineering has two main components. First, the study of the history of earthquakes (for example, historical[25]​ and instrumental[26]​ catalogs of seismicity) and tectonics[27]​ to evaluate the earthquakes that could occur in a region and their characteristics and frequency of occurrence. Second, study the strong ground motions generated by earthquakes to evaluate the shaking expected from future earthquakes of similar characteristics. These strong ground motions can be observations from accelerometers or seismometers or those simulated by computer using various techniques,[28]​ which are then often used to develop ground motion prediction equations[29]​ (or ground motion models).