Open main menu
Home
Random
Recent changes
Special pages
Community portal
Preferences
About Wikipedia
Disclaimers
Incubator escapee wiki
Search
User menu
Talk
Dark mode
Contributions
Create account
Log in
Editing
Subduction
(section)
Warning:
You are not logged in. Your IP address will be publicly visible if you make any edits. If you
log in
or
create an account
, your edits will be attributed to your username, along with other benefits.
Anti-spam check. Do
not
fill this in!
===Earthquakes and tsunamis=== [[File:Global subducted slabs USGS.png|thumb|Global map of subduction zones, with subducted slabs contoured by depth|350 px]] {{Main|Megathrust earthquake}} Elastic strain caused by plate convergence in subduction zones produces at least three types of earthquakes. These are deep earthquakes, megathrust earthquakes, and outer rise earthquakes. Deep earthquakes happen within the crust, megathrust earthquakes on the subduction interface near the trench, and outer rise earthquakes on the subducting lower plate as it bends near the trench. Anomalously deep events are a characteristic of subduction zones, which produce the deepest quakes on the planet. Earthquakes are generally restricted to the shallow, brittle parts of the crust, generally at depths of less than twenty kilometers. However, in subduction zones quakes occur at depths as great as {{Convert|700|km|mi|abbr=on}}. These quakes define inclined zones of seismicity known as [[Wadati–Benioff zone]]s which trace the descending slab.{{sfn|Stern|2002|pp=17-18}} Nine of the ten largest earthquakes of the last 100 years were subduction zone megathrust earthquakes. These included the [[1960 Valdivia earthquake|1960 Great Chilean earthquake]] which at M 9.5 was the largest earthquake ever recorded, the [[2004 Indian Ocean earthquake and tsunami]], and the [[2011 Tōhoku earthquake and tsunami]]. The subduction of cold oceanic lithosphere into the mantle depresses the local [[geothermal gradient]] and causes a larger portion of Earth's crust to deform in a more brittle fashion than it would in a normal geothermal gradient setting. Because earthquakes can occur only when a rock is deforming in a brittle fashion, subduction zones can cause large earthquakes. If such a quake causes rapid deformation of the sea floor, there is potential for [[tsunami]]s. The largest tsunami ever recorded happened due to a [[2004 Indian Ocean earthquake and tsunami|mega-thrust earthquake on December 26, 2004]]. The earthquake was caused by subduction of the Indo-Australian plate under the Eurasian plate, but the tsunami spread over most of the planet and devastated the areas around the Indian Ocean. Small tremors which cause small, nondamaging tsunamis, also occur frequently.{{sfn|Stern|2002|pp=17-18}} A study published in 2016 suggested a new parameter to determine a subduction zone's ability to generate mega-earthquakes.<ref>{{Cite journal|last1=Bletery|first1=Quentin|last2=Thomas|first2=Amanda M.|last3=Rempel|first3=Alan W.|last4=Karlstrom|first4=Leif|last5=Sladen|first5=Anthony|last6=Barros|first6=Louis De|date=2016-11-25|title=Mega-earthquakes rupture flat megathrusts|journal=Science|language=en|volume=354|issue=6315|pages=1027–1031|doi=10.1126/science.aag0482|issn=0036-8075|pmid=27885027|bibcode=2016Sci...354.1027B|doi-access=free}}</ref> By examining subduction zone geometry and comparing the degree of lower plate curvature of the subducting plate in great historical earthquakes such as the 2004 Sumatra-Andaman and the 2011 Tōhoku earthquake, it was determined that the magnitude of earthquakes in subduction zones is inversely proportional to the angle of subduction near the trench, meaning that "the flatter the contact between the two plates, the more likely it is that mega-earthquakes will occur".<ref>{{Cite news|url=https://www.sciencedaily.com/releases/2016/11/161124150207.htm|title=Subduction zone geometry: Mega-earthquake risk indicator|work=ScienceDaily|access-date=2017-06-21|language=en}}</ref> [[Outer trench swell|Outer rise]] earthquakes on the lower plate occur when normal faults oceanward of the subduction zone are activated by flexure of the plate as it bends into the subduction zone.<ref>{{cite journal |url=https://sites.google.com/site/daniggcc/research-interests/former-research/tonga-kermadech-subduction | title=Slab pull effects from a flexural analysis of the Tonga and Kermadec Trenches (Pacific Plate) |author=Garcia-Castellanos, D. |author2=M. Torné |author3=M. Fernàndez | journal=Geophys. J. Int. | volume=141 | issue=2 | pages=479–485 | doi=10.1046/j.1365-246x.2000.00096.x | year=2000|bibcode = 2000GeoJI.141..479G | doi-access=free | hdl=10261/237992 | hdl-access=free }}</ref> The [[2009 Samoa earthquake and tsunami|2009 Samoa earthquake]] is an example of this type of event. Displacement of the sea floor caused by this event generated a six-meter tsunami in nearby Samoa. Seismic tomography has helped detect subducted lithospheric slabs deep in the mantle where no earthquakes occur.<ref name=":0" /> About one hundred slabs have been described in terms of depth and their timing and location of subduction.<ref name="Van der Meer-2017">{{cite web|url=http://www.atlas-of-the-underworld.org/|title=Atlas of the Underworld {{!}} Van der Meer, D.G., van Hinsbergen, D.J.J., and Spakman, W., 2017, Atlas of the Underworld: slab remnants in the mantle, their sinking history, and a new outlook on lower mantle viscosity, Tectonophysics|website=atlas-of-the-underworld.org|language=en-GB|access-date=2017-12-02}}</ref> The great seismic discontinuities in the mantle, at {{Convert|410|km|mi|abbr=on}} depth and {{Convert|670|km|mi|abbr=on}}, are disrupted by the descent of cold slabs in deep subduction zones. Some subducted slabs seem to have difficulty penetrating the major [[Transition zone (Earth)|discontinuity]] that marks the boundary between the upper mantle and lower mantle at a depth of about 670 kilometers. Other subducted oceanic plates have sunk to the [[core–mantle boundary]] at 2890 km depth. Generally, slabs decelerate during their descent into the mantle, from typically several cm/yr (up to ~10 cm/yr in some cases) at the subduction zone and in the uppermost mantle, to ~1 cm/yr in the lower mantle.<ref name="Van der Meer-2017" /> This leads to either folding or stacking of slabs at those depths, visible as thickened slabs in seismic tomography. Below ~1700 km, there might be a limited acceleration of slabs due to lower viscosity as a result of inferred mineral phase changes until they approach and finally stall at the [[core–mantle boundary]].<ref name="Van der Meer-2017" /> Here the slabs are heated up by the ambient heat and are not detected anymore ~300 Myr after subduction.<ref name="Van der Meer-2017" />
Edit summary
(Briefly describe your changes)
By publishing changes, you agree to the
Terms of Use
, and you irrevocably agree to release your contribution under the
CC BY-SA 4.0 License
and the
GFDL
. You agree that a hyperlink or URL is sufficient attribution under the Creative Commons license.
Cancel
Editing help
(opens in new window)