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Topic: Subduction zone


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In the News (Thu 18 Apr 19)

  
  NationMaster - Encyclopedia: Subduction zone
Subduction zones are associated with the deepest earthquakes on the planet.
Subduction Zone Biology: Because subduction zones are the coldest parts of the Earth's interior and life cannot exist at temperatures >150°C, subduction zones are almost certainly associated with the deepest (highest pressure) biosphere.
Subduction zones are usually marked by deep ocean trenches that often exceed 6 mi (10 km) compared to the ocean's overall depth of 2 to 4 mi (3 to 5 km).
www.nationmaster.com /encyclopedia/Subduction-zone   (270 words)

  
 Sinking coastlines may precede large subduction zone quakes
If coastal subsidence is common before subduction zone quakes, areas such as those ringing the Pacific Rim could be on the lookout for subsidence as a warning of possible future megathrust quakes like the Dec. 26 9.0 Sumatra-Andaman Islands earthquake, the researchers say.
Subduction zones are areas where one of the Earth's tectonic plates slips under another, raising mountain ranges along the margin sprinkled with volcanoes.
Quakes occur when the edge of the overlying plate sticks to the subducting plate, causing a slight dip nearest the zone and a slight bulge farther away.
www.eurekalert.org /pub_releases/2005-01/uoc--scm012005.php   (1263 words)

  
 subduction zone - Encyclopedia.com
subduction zone large-scaled narrow region in the earth's crust where, according to plate tectonics, masses of the spreading oceanic lithosphere bend downward into the earth along the leading edges of converging lithospheric plates where it slowly melts at about 400 mi (640 km) deep and becomes reabsorbed.
Subduction zones are usually marked by deep ocean trenches that often exceed 6 mi (10 km) compared to the ocean's overall depth of 2 to 4 mi (3 to 5 km).
A pattern of earthquakes of shallow, intermediate, and deep focus occurs along the same angle as the descending plate, which is steeply inclined (30°-60°) toward the continent behind the trench in a zone called the Benioff Zone, discovered by the U.S. seismologist Hugo Benioff.
www.encyclopedia.com /doc/1E1-subducti.html   (1097 words)

  
  Subduction Summary
Subduction zones are associated with the deepest earthquakes on the planet.
Some subducted slabs seem not to be able to penetrate the major discontinuity in the mantle that lies at a depth of about 670 km, whereas other subducted oceanic plates can penetrate all the way to the core-mantle boundary.
Subduction Zone Biology: Because subduction zones are the coldest parts of the Earth's interior and life cannot exist at temperatures >150°C, subduction zones are almost certainly associated with the deepest (highest pressure) biosphere.
www.bookrags.com /Subduction   (1744 words)

  
 Cascadia Megathrust Earthquakes
The Cascadia Subduction Zone is a very long sloping fault that stretches from mid-Vancouver Island to Northern California.
The width of the Cascadia Subduction Zone fault varies along its length, depending on the temperature of the subducted oceanic slab, which heats up as it is pushed deeper beneath the continent.
Earthquake size is porportional to fault area, and the Cascadia Subduction Zone is a very long sloping fault that stretches from mid-Vancouver Island to Northern California.
www.pnsn.org /HAZARDS/CASCADIA/cascadia_zone.html   (303 words)

  
 The Seismogenic Zone Experiment (SEIZE): Science Plan   (Site not responding. Last check: )
1) is one manifestation of the diversity of subduction zones.
A shallowly dipping subduction zone thrust provides a large fault surface that is accessible to study by a combination of drilling and ongoing monitoring using passive and active seismology.
The décollement zone is the shallow, seaward manifestation of the seismogenic zone megathrust.
www.ldeo.columbia.edu /res/pi/margins/MARGINSnet4/SEIZE_sci_plan_old.html   (7481 words)

  
 The Seismogenic Zone Experiment (SEIZE): Science Plan
1) is one manifestation of the diversity of subduction zones.
A shallowly dipping subduction zone thrust provides a large fault surface that is accessible to study by a combination of drilling and ongoing monitoring using passive and active seismology.
The décollement zone is the shallow, seaward manifestation of the seismogenic zone megathrust.
www.geo.ua.edu:16080 /AMG/OldMargins/SEIZE_sci_plan.html   (7435 words)

  
 Subduction
This is clearly not the origin of subduction zone igneous activity because subduction zones are primarily places where one plate is moving down beneath the other.
The water escaping from the descending slab is probably the primary cause of volcanic activity at subduction zones.
In subduction zones that affect continental crust, and in areas where continents have come into collision, huge amounts of intermediate to felsic intrusive rock are formed.
www.stmarys.ca /conted/webcourses/GEO/GEO99/pubigneous/subduction.html   (1285 words)

  
 Subduction Zone: World of Earth Science
Subduction zones occur at collision boundaries where at least one of the colliding lithospheric plates contains oceanic crust.
In accord with plate tectonic theory, collision boundaries are sites where lithospheric plates move together and the resulting compression causes either subduction (where one or both lithospheric plates are driven down and destroyed in the molten mantle) or crustal uplifting that results in orogeny (mountain building).
The subducting oceanic crust pushes the continental crust upward into mountain chains (e.g., the Andes) and may contribute lighter molten materials to the overriding continental crust to form volcanic arcs (e.g., the "ring of fire"; a ring of volcanoes bordering the Pacific Rim.
science.enotes.com /earth-science/subduction-zone   (591 words)

  
 Great Earthquakes   (Site not responding. Last check: )
We find that slab pull at these subduction zones is small, indicating that the slab is weakened by the compressional stresses that are exerted on it by the overriding plate.
Alternatively, if the motion of the overriding plate is away from the subduction zone, as in (b), the seismic coupling between the slab and the overriding plate will be small, resulting in back-arc extension and only moderate-sized earthquakes.
This drives a circulation in the upper mantle that tends to push the overriding plate toward the subduction zones, thus increasing the compressional interaction at the subduction zone.
www.jhu.edu /eps/faculty/conrad/resproj/geq/geq.html   (1214 words)

  
 CCALMR TSUNAMI!
The Cascadia Subduction Zone (CSZ) extends from southern British Columbia to northern California.
The length of the crosshatched area is the approximate length of the postulated fault rupture for a magnitude 8.8 earthquake on the Cascadia subduction zone.
An extensive subsidence zone is visible off the coast of Oregon and Washington, leading to subsidence at the shoreline that does not match coseismic subsidence inferred from studies by Curt Peterson of buried wetland soils.
www.ccalmr.ogi.edu /tsunami   (849 words)

  
 Dynamic Earth - subduction zones   (Site not responding. Last check: )
Subduction zones are the flip side of mid-ocean ridges in plate tectonics.
These earthquake zones coincide with panels of anomalously high seismic velocities (high velocities are generally thought to represent cold mantle) suggesting plates diving down.
Computer models can predict the temperature structure of subduction zones and indicate that the downgoing slab can be many hundreds of degrees cooler than the surrounding mantle.
earth.leeds.ac.uk /dynamicearth/subduction/index.htm   (492 words)

  
 Shock Dynamics: Oceanic Crust
There remains substantial disagreement and uncertainty about the significance of different processes influencing subduction initiation, the material properties of tectonic plates, and even whether it is possible to initiate a totally new subduction zone in isolation from an existing one." (Gurnis p.
Hence, it is unlikely that compositional buoyancy contrast across these weak zones would develop throughout their evolutionary histories." "Therefore, it is physically implausible why one side of an old ridge, or transform [fault] or fracture zone prefers to sink while the other side chooses to rise under any deviatoric stresses." (Niu p.
Initiation of Subduction Zones as a Consequence of Lateral Compositional Buoyancy Contrast within the Lithosphere: a Petrological Perspective.
www.newgeology.us /presentation8.html   (1192 words)

  
 Sediment could be a major factor in biggest subduction zone earthquakes
But not all subduction zones are created equal, and University of Washington researchers believe they have found a key to determine which subduction zones – or which specific areas within a subduction zone – might produce the most severe shaking when they rupture.
As the subducting plate slides beneath the upper plate, stress begins to build where the plates meet and the upper plate can deform to create a large structure called a forearc basin.
It appears the most severe subduction zone earthquakes occur in areas where such sediment-filled basins are found, but the reasons aren't exactly clear.
www.physorg.com /news10375.html   (901 words)

  
 Cyberwest - River sediment buildup may be a factor in certain subduction zone earthquakes
Subduction zones — areas of offshore ocean floors where two tectonic plates meet, with one sliding beneath the other — are often where powerful earthquakes occur, including quakes in Indonesia in 2004, Alaska in 1964, Chile in 1960 and the Pacific Northwest in 1700.
As the subducting plate slides beneath the upper plate, stress begins to build where the plates meet and the upper plate can deform to create a large structure — "a forearc basin." The basin, a bowl-shaped depression, fills with sediment from nearby rivers that empty into the ocean.
As the top part of the subducting plate meets more resistance and travels at a slower speed than the bottom part of the plate, greater strain is created in the plate.
www.cyberwest.com /geology/cascadia-subduction-zone-earthquake.shtml   (806 words)

  
 Subduction zone tsunami by John Silveira Issue #94
That was caused by an earthquake on a similar subduction zone.
But in a subduction zone, the tectonic plates move over and under each other, and when the earth under the ocean moves up or down like that suddenly, it moves an incredible amount of water that creates a tsunami.
The earthquake was generated at a subduction zone, like the one you have here off the coast, but it was barely felt by people on land.
www.backwoodshome.com /articles2/silveira94.html   (6763 words)

  
 Vic Camp - Subduction zone volcanism
Subduction zone volcanism occurs where two plates are converging on one another.
As the subducting slab descends to greater and greater depths, it progressively encounters greater temperatures and greater pressures which cause the slab to release water into the mantle wedge overlying the descending plate.
The volcanoes produced by subduction zone volcanism are typically stratovolcanoes.
www.geology.sdsu.edu /how_volcanoes_work/subducvolc_page.html   (359 words)

  
 Subduction Zone, Active Continental Margins - John Seach
A subduction zone is a region where the oceanic lithosphere descends into the mantle.
Subduction zones produce the majority of volcanoes observed by humans.
Subduction zone volcanoes are often explosive and are the world's most dangerous.
www.volcanolive.com /subduction.html   (78 words)

  
 Interseismic coupling and asperity distribution along the Kamchatka subduction zone
North of ∼53°N, the subduction interface experiences significant aseismic slip, consistent with the lower seismic moment release in M ≤ 8.5 earthquakes along this portion of the subduction zone.
The GPS velocities are consistent with a boundary element forward model in which historic earthquake rupture zones are represented as locked asperities, surrounded by a zero shear stress subduction interface loaded by plate convergence.
Models in which the complete rupture zones of historic earthquakes are considered locked greatly overpredict the degree of kinematic coupling.
www.agu.org /pubs/crossref/2005/2005JB003648.shtml   (429 words)

  
 Earthquake Information for Port Orford, Oregon
The Cascadia subduction zone is the convergent boundary between the large North America plate and the small Juan de Fuca and Gorda plates to the west.
Subduction earthquakes such as those that occur off the Oregon coast are particularly effective in generating tsunamis.
As a tsunami nears the shore, it both slows in speed and grows in height so that a tsunami unnoticed at sea, may grow to be several meters or more in height as it reaches land.
www.portorford.org /community/earthquake.html   (209 words)

  
 Cascadia Subduction Zone   (Site not responding. Last check: )
In 1989, we piggybacked on an multichannel seismic reflection survey offshore to conduct an onshore/offshore experiment to image a transect across the margin from the subduction zone deformation front to the Willamette Valley (funded by NSF).
In 1993 and 1994, with colleagues from USGS and from Stanford, Lehigh, and Rice Universities) we moved to northern California to image the southern Cascadia subduction zone and northern San Andreas Fault (funded by NSF and USGS).
Trehu, A.M., G. Lin, E. Maxwell, C. Goldfinger, A seismic reflection profile across the Cascadia subduction zone offshore central Oregon: new constraints on the deep crustal structure and on the distribution of methane in the accretionary prism, Jour.
quakes.oce.orst.edu /Trehu/Ships/index.html   (251 words)

  
 Earth's Interior & Plate Tectonics
Subduction is the main method of cooling the mantle below 100 kilometers (62.5 miles).
If the lithosphere is young and thus hotter at a subduction zone, it will be forced back into the interior at a lesser angle.
Plates collide and are destroyed as they descend at subduction zones to produce deep ocean trenches, strings of volcanoes, extensive transform faults, broad linear rises, and folded mountain belts.
www.solarviews.com /eng/earthint.htm   (1396 words)

  
 On Subduction & Plate Tectonics
I disagree, it is an observation, and because the subduction of slabs is an observed fact, all of Brown's arguments to the contrary are rendered moot.
The double zone may be due to transformational faulting, as olivine along the edges of a metastable olivine wedge becomes warmer and transforms to spinel [8-11].
We suggest that with the absence of a pull from the detached lithosphere the upper part of the Australian plate in the region of the SDSZ is resistant to subduction, and thus the downward displacements caused by large earthquakes in the adjoining regions result in a localized rebound.
www.tim-thompson.com /subduction.html   (2256 words)

  
 Subduction Zone Processes   (Site not responding. Last check: )
Fluids expelled from subducted or accreted sediments transport chemical constituents both within the sediment section, thereby assisting in diagenesis and hydrocarbon concentration, and to the seafloor, supplying nutrients to chemosynthetic animal communities.
While the three-dimensional architecture of subduction zones and their accretionary prisms has been well-characterized in some locations around the world, our understanding of the time dependence of the processes affecting them is poor for the simple technological reason that time-series observations at long time scales are difficult to obtain at sea.
Curves for several fault geometries are given; parameters are fault dip, and widths of the locked zone and a transition zone where inter-seismic slip varies from zero to the full plate rate (derived from Hyndman and Wang, 1995; curves from model of Thatcher and Rundle, 1984).
www.neptune.washington.edu /pub/white_paper/scidriv3.html   (2063 words)

  
 CVO Website - Plate Tectonics and Sea-Floor Spreading
The Cascadia subduction zone off the coast of Washington, Oregon, and northern California is a convergent boundary between the large North America plate and the small Juan de Fuca plate to the west.
In sum, the subduction of the Juan de Fuca plate beneath the North America plate is believed to directly or indirectly cause most of the earthquakes and young geologic features in Washington and Oregon.
A 90-kilometer gap free of young volcanoes between Mount Rainier and Glacier Peak is landward of that part of the subducting plate with the least average dip to a depth of 60 kilometers.
vulcan.wr.usgs.gov /Glossary/PlateTectonics/description_plate_tectonics.html   (8248 words)

  
 Subduction   (Site not responding. Last check: )
Subduction is the process in which one plate is pushed downward beneath another plate into the underlying mantle when plates move towards each other.
The jerky movement, as well as the friction between the plates causes much heat, and together with the heat from the mantle and from radioactive decay, causes the subducted plate to melt.
The boundary of such plate movements is 'destructive' as part of the plate melts during subduction and is destroyed.
library.thinkquest.org /17457/platetectonics/5.php   (214 words)

  
 Benioff zone Summary
Benioff zones are dipping, roughly planar zones of increased earthquake activity produced by the interaction of a downgoing oceanic crustal plate with an overriding continental or oceanic plate.
Benioff zones are found in subduction zones that form by the collision of two crustal plates of dissimilar density and thickness, for example an oceanic and continental plate.
The earthquake zones that parallel the great oceanic trenches are typically inclined from 40 to 60 degrees from the horizontal and extend several hundred kilometers into the mantle along trends that reach thousands of kilometers in length.
www.bookrags.com /Benioff_zone   (527 words)

  
 Reyners--Plate coupling, Hikurangi subduction zone
Abstract Recent dense deployments of portable seismographs along the Hikurangi subduction zone have provided insights into the structure and seismic strain regime of the subducted and overlying plates, and the nature of plate coupling at the shallow part of the plate interface.
Farther to the northeast, the downdip width of the inferred locked portion of the plate interface progressively decreases, and subduction thrust events of about MW 6.9 are estimated for the northern part of the Raukumara Peninsula.
In the south of the subduction zone, changes in coupling arise principally from changes in the thickness of the subducted plate, whereas in the north they are mainly due to changes in thickness of the overlying plate.
www.rsnz.org /publish/nzjgg/1998/30.php   (261 words)

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