Geophysics

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Geophysics
Geophysics, the study of the Earth by quantitative physical methods, especially by seismic, electromagnetic, and radioactivity methods. The theories and techniques of geophysics are employed extensively in the planetary sciences in general.

The field of geophysics includes the branches of:

    * Seismology (earthquakes and elastic waves)
    * Gravity and geodesy (the Earth's gravitational field and the size and form of the earth)
    * Atmospheric science, which includes:

        * Atmospheric electricity and terrestrial magnetism (including ionosphere, Van Allen belts, telluric currents, Radiant energy, etc.)
        * Meteorology and Climatology, which both involve studies of the weather.
        * Aeronomy, the study of the physical structure and chemistry of the atmosphere.

    * Geothermometry (heating of the Earth, heat flow, volcanology, and hot springs)
    * Hydrology (ground and surface water, sometimes including glaciology)
    * Physical oceanography
    * Tectonophysics (geological processes in the Earth)
    * Geodynamics (numerical study of the inner Earth)
    * Exploration and engineering geophysics
    * Geophysical Engineering
    * Geodesy
    * Glaciology
    * Petrophysics
    * Applied geophysics
    * Mineral Physics
    * Engineering geology
Planetary science
Planetary science, also known as planetology and closely related to planetary astronomy, is the science of planets, or planetary systems, and the solar system. Incorporating an interdisciplinary approach, planetary science draws from diverse sciences and may be considered a part of the Earth sciences, or more logically, as its parent field. Research tends to be done by a combination of astronomy, space exploration (particularly unmanned space missions), and comparative, experimental and meteorite work based on Earth. There is also an important theoretical component and considerable use of computer simulation. Astrogeology is a major component of planetary sciences.

Planetary science studies objects ranging in size from micrometeoroids to gas giants, their composition, dynamics and history.
Contents
SeismologyGreek seismos = earthquake and logos = word) is the scientific study of earthquakes and the propagation of elastic waves through the Earth. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes (such as explosions). A related field that uses geology to infer information regarding past earthquakes is paleoseismology. A recording of earth motion as a function of time is called a seismogram.

Earthquakes, and other sources, produce different types of seismic waves. These waves travel through rock, and provide an effective way to image both sources and structures deep within the Earth. There are three basic types of seismic waves in solids: P-waves (called body waves), and S-waves (surface waves). The two basic kinds of surface waves (Rayleigh and Love), can be fundamentally explained in terms of interacting P- and/or S-waves.

Pressure waves, also called Primary waves or P-waves, travel at the greatest velocity within solids and are therefore the first waves to appear on a seismogram. P-waves are fundamentally pressure disturbances that propagate through a material by alternately compressing and expanding (dialating) the medium, where particle motion is parallel to the direction of wave propagation. For a visual example of this movement, try laying a coil (like a Slinky) on a flat surface. Tap lightly on one end, and you will see the coil compress and then expand along the whole length of the coil. This is a P-wave-like phenomenon.

S-waves, also called Shear waves or secondary waves, are transverse waves that travel slower than P-waves and thus appear later than P-waves on a seismogram. Particle motion is perpendicular to the direction of wave propagation. Shear waves do not exist in fluids such as air or water.

Surface waves travel more slowly than S-waves, however, because they are trapped in the vicinity of the Earth's surface, they can be much larger in amplitude than body waves, and can form the largest signals seen in earthquake seismograms. They are particularly strongly excited when the seismic source is close to the surface of the Earth.

One of the earliest important discoveries (suggested by Richard Dixon Oldham in 1906 and definitively shown by Harold Jeffreys) in 1926) was that the outer core of the Earth is liquid. Pressure waves (P-waves) pass through the core. Transverse or shear waves (S-waves) that shake side-to-side require rigid material so they do not pass through the outer core. Thus, the liquid core causes a "shadow" on the side of the planet opposite of the earthquake where no direct S-waves are observed. The reduction in P-wave velocity of the outer core also causes a substantial delay for P waves penetrating the core from the (sesimically faster velocity) mantle.

Seismic waves produced by explosions or vibrating controlled sources are the primary method of underground exploration. Controlled source seismology has been used to map salt domes, faults, anticlines and other geologic traps in petroleum-bearing rocks, geological faults, rock types, and long-buried giant meteor craters. For example, the Chicxulub impactor, which is believed to have killed the dinosaurs, was localized to Central America by analyzing ejecta in the cretaceous boundary, and then physically proven to exist using seismic maps from oil exploration.
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Using seismic tomography with earthquake waves, the interior of the Earth has been completely mapped to a resolution of several hundred kilometers. This process has enabled scientists to identify convection cells, mantle plumes and other large-scale features of the inner Earth.

Seismographs are instruments that sense and record the motion of the Earth. Networks of seismographs today continuously monitor the seismic environment of the planet, allowing for the monitoring and analysis of global earthqaukes and tsunami warnings, as well as recording a variety of seismic signals arising from nonearthquake phenomena such as large meteors entering the atmosphere, pressure variations on the ocean floor induced by ocean waves (the global microseism), cryospheric events associated with large icebergs and glaciers, or underground nuclear tests. Above-ocean meteor strikes as large as ten kilotons of TNT, (equivalent to about 4.2 × 1013 J of effective explosive force) have been reported.
Atmospheric sciences
 is an umbrella term for the study of the atmosphere, its processes, the effects other systems have on the atmosphere, and the effects of the atmosphere on these other systems.

Meteorology includes atmospheric chemistry and atmospheric physics with a major focus on weather forecasting. Climatology is the study of atmospheric changes (both long and short-term) that define average climates and their change over time, due to both natural climate variability and anthropogenic climate variability.

Atmospheric science has been extended to the field of planetary science and the study of the atmospheres of the planets of the solar system.    * Earth science
    * Hydrometeorology
    * Weather
    * Oceanography
    * Atmospheric Chemistry
    * Atmospheric dispersion modeling
Meteorology
interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting. Meteorological phenomena are observable weather events which illuminate and are explained by the science of meteorology. Those events are bound by the variables that exist in Earth's atmosphere. They are temperature, pressure, water vapor, and the gradients and interactions of each variable, and how they change in time. The majority of Earth's observed weather is located in the troposphere.

Meteorology, climatology, atmospheric physics, and atmospheric chemistry are sub-disciplines of the atmospheric sciences. Meteorology and hydrology comprise the interdisciplinary field of hydrometeorology.

Interactions between our atmosphere and the oceans are part of coupled ocean-atmosphere studies. Meteorology has application in many diverse fields such as the military, energy production, farming, shipping and construction.
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Climatology
Climatology is the study of climate, scientifically defined as weather conditions averaged over a period of time,[1] and is a branch of the atmospheric sciences
Differences with meteorology

In contrast to meteorology, which studies short term weather systems lasting up to a few weeks, climatology studies the frequency and trends of those systems. It studies the periodicity of weather events over years to millennia, as well as changes in long-term average weather patterns, in relation to atmospheric conditions. Climatologists, those who practice climatology, study both the nature of climates - local, regional or global - and the natural or human-induced factors that cause climates to change. Climatology considers the past and can help predict future climate change.

Phenomena of climatological interest include the atmospheric boundary layer, circulation patterns, heat transfer (radiative, convective and latent), interactions between the atmosphere and the oceans and land surface (particularly vegetation, land use and topography), and the chemical and physical composition of the atmosphere. Related disciplines include astrophysics, chemistry, ecology, geology, geophysics, glaciology, hydrology, oceanography, and volcanology.
Hydrology
<img src="http://upload.wikimedia.org/wikipedia/commons/thumb/0/05/Land_ocean_ice_cloud_1024.jpg/250px-Land_ocean_ice_cloud_1024.jpg" alt="" />

Yδρoλoγια, Yδωρ+Λoγos, Hydrologia, the "study of water") is the study of the movement, distribution, and quality of water throughout the Earth, and thus addresses both the hydrologic cycle and water resources. A practitioner of hydrology is a hydrologist, working within the fields of either earth or environmental science, physical geography or civil and environmental engineering.

Domains of hydrology include hydrometeorology, surface hydrology, hydrogeology, drainage basin management and water quality, where water plays the central role. Oceanography and meteorology are not included because water is only one of many important aspects.

Hydrological research is useful in that it allows us to better understand the world in which we live, and also provides insight for environmental engineering, policy and planning.