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Definition
| the region below the lithosphere, variously estimated as being from fifty to several hundred miles (eighty-five to several hundred kilometers) thick, in which the rock is less rigid than that above and below but rigid enough to transmit transverse seismic waves. |
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| Seismic waves are waves that travel through the Earth or other elastic body, for example as the result of an earthquake, explosion, or some other process that imparts forces to the body. Seismic waves are also continually excited on Earth by the incessant pounding of ocean waves (referred to as the microseism) and the wind. Seismic waves are studied by seismologists, and measured by a seismograph, which records the output of a seismometer, or geophone. For seismic studies of oil reservoirs, hydrophones may give additional information. |
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a relatively rigid and immobile region of continental portions of the earth's crust. |
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convection currents [image] |
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| Density is the amount of anything in a certain space; the quantity of a matter in a given area. Hot liquids are less dense than cold liquids. Currents are a flow of water, air, or any liquid (or gas). Convection currents are circular currents or movement within a liquid (or gas) due to different densities of the hotter and cooler parts. |
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deep-focus earthquakes [image] |
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Definition
| A deep-focus earthquake is an earthquake that occurs at depths between 300 and 700 km beneath the Earth's surface.[1] Their cause is still not entirely understood since subducted lithosphere at that pressure and temperature regime should not exhibit brittle behavior. They are believed to be associated with mineralogical phase changes within the slab, such as olivine transforming into a more compact spinel structure. Deep focus earthquakes usually occur within subduction zones at oceanic-continental convergent boundaries. |
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Term
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Definition
| An earthquake (also known as a tremor or temblor) is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes are recorded with a seismometer, also known as a seismograph. The moment magnitude of an earthquake is conventionally reported, or the related and mostly obsolete Richter magnitude, with magnitude 3 or lower earthquakes being mostly imperceptible and magnitude 7 causing serious damage over large areas. Intensity of shaking is measured on the modified Mercalli scale. |
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| The epicenter or epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates. The word derives from the Greek ἐπίκεντρον (epikentron), "occupying a cardinal point", from ἐπί (epi), "on, upon, at" + κέντρον (kentron), "centre"[1]. |
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| planar rock fractures which show evidence of relative movement |
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| an earthquake's underground point of origin or hypocenter |
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| a location above a hot upwelling plume of mantle. |
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| In the Earth, the lithosphere includes the crust and the uppermost mantle which is joined to the crust across the mantle. The lithosphere is underlain by the asthenosphere, the weaker, hotter, and deeper part of the upper mantle. |
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| Mantle convection is the slow creeping motion of Earth's rocky mantle in response to perpetual gravitationally unstable variations in its density. Material near the surface of the Earth, particularly oceanic lithosphere, cools down by conduction of heat into the oceans and atmosphere, then thermally contracts to become dense, and then sinks under its own weight at convergent plate boundaries. This subducted material sinks to some depth in the Earth's interior where it is prohibited, by inherent density stratification, from sinking further. This stoppage creates a thermal boundary layer where sunken material soaks up heat via thermal conduction from below, and may become buoyant again to form upwelling mantle plumes. |
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Pangaea, Pangæa or Pangea (IPA: /pænˈdʒiːə/[1], from παν, pan, meaning entire, and Γαῖα, Gaea, meaning Earth in Ancient Greek) was the supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration [2]. |
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P-waves are type of elastic wave, also called seismic waves, that can travel through gasses (such as sounds), elastic solids and liquids, including the Earth. P-waves can be produced by earthquakes and recorded by seismometers. The name P-wave stands for primary wave, as the P-wave is the fastest among the abusive waves, compared to the S-waves. |
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Definition
| Ridge-push is a proposed mechanism for plate motion in plate tectonics. Because mid-ocean ridges lie at a higher elevation than the rest of the ocean floor, gravity causes the ridge to push on the lithosphere that lies farther from the ridge. |
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| A type of seismic wave, the S-wave, secondary wave, or shear wave (sometimes called an elastic S-wave) is one of the two main types of elastic body waves, so named because they move through the body of an object, unlike surface waves. |
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Definition
A type of seismic wave, the S-wave, secondary wave, or shear wave (sometimes called an elastic S-wave) is one of the two main types of elastic body waves, so named because they move through the body of an object, unlike surface waves. |
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shallow-focus earthquake [image] |
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Definition
| The majority of tectonic earthquakes originate at the ring of fire in depths not exceeding tens of kilometers. Earthquakes occurring at a depth of less than 70 km are classified as 'shallow-focus' earthquakes, while those with a focal-depth between 70 and 300 km are commonly termed 'mid-focus' or 'intermediate-depth' earthquakes. In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, deep-focus earthquakes may occur at much greater depths (ranging from 300 up to 700 kilometers).[4] These seismically active areas of subduction are known as Wadati-Benioff zones. Deep-focus earthquakes occur at a depth at which the subducted lithosphere should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep-focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure.[5] |
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| Plate motion is partly driven by the weight of cold, dense plates sinking into the mantle at trenches.[25] There is considerable evidence that convection is occurring in the mantle at some scale. The upwelling of material at mid-ocean ridges is almost certainly part of this convection. Some early models of plate tectonics envisioned the plates riding on top of convection cells like conveyor belts. However, most scientists working today believe that the asthenosphere is not strong enough to directly cause motion by the friction of such basal forces. Slab pull is most widely thought to be the greatest force acting on the plates. Recent models indicate that trench suction plays an important role as well. However, it should be noted that the North American Plate, for instance, is nowhere being subducted, yet it is in motion. Likewise the African, Eurasian and Antarctic Plates. The overall driving force for plate motion and its energy source remain subjects of ongoing research. |
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| In seismology, several types of surface waves are encountered. Surface waves, in this mechanical sense, are commonly known as either Love waves (L waves) or Rayleigh waves,a seismic wave is a wave that travels through the Earth, often as the result of an earthquake or explosion. Love waves have transverse motion (movement is perpendicular to the direction of travel, like light waves), whereas Rayleigh waves have both longitudinal (movement parallel to the direction of travel, like sound waves) and transverse motion. Seismic waves are studied by seismologists and measured by a seismograph or seismometer. Surface waves span a wide frequency range, and the period of waves that are most damaging is usually 10 seconds or longer. Surface waves can travel around the globe many times from the largest earthquakes. |
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| A terrane in geology is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted — "sutured" — to crust lying on another plate. The crustal block or fragment preserves its own distinctive geologic history, which is different from that of the surrounding areas (hence the term "exotic" terrane). The suture zone between a terrane and the crust it attaches to is usually identifiable as a fault. |
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thin-skinned thrusting [image] |
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Definition
| An accretionary wedge or accretionary prism is formed from sediments that are accreted onto the non-subducting tectonic plate at a convergent plate boundary. Most of the material in the accretionary wedge consists of marine sediments scraped off from the downgoing slab of oceanic crust but in some cases includes the erosional products of volcanic island arcs formed on the overriding plate. |
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Definition
| A volcanic belt is a large volcanically active region. Other terms are used for smaller areas of activity, such as volcanic fields. Volcanic belts are found above zones of unusually high temperature (700-1400°C) where magma is created by partial melting of solid material in the Earth's crust and upper mantle. These areas usually form along tectonic plate boundaries at depths of 10-50 km. For example, volcanoes in Mexico and western North America are mostly in volcanic belts, such as the Trans-Mexican Volcanic Belt that extends 900 km from west to east across central-southern Mexico and the Northern Cordilleran Volcanic Province in western Canada. |
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volcanic island arc [image] |
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Definition
A volcanic arc is a chain of volcanic islands or mountains formed by plate tectonics as an oceanic tectonic plate subducts under another tectonic plate and produces magma. There are two types of volcanic arcs: oceanic arcs (commonly called island arcs, a type of archipelago) and continental arcs. In the former, oceanic crust subducts beneath other oceanic crust on an adjacent plate, while in the latter case the oceanic crust subducts beneath continental crust. In some situations, a single subduction zone may show both aspects along its length, as part of a plate subducts beneath a continent and part beneath adjacent oceanic crust. |
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| A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot, molten rock, ash, and gases to escape from below the surface. Volcanic activity involving the extrusion of rock tends to form mountains or features like mountains over a period of time. |
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