Editing Subduction (section)

===Deep structure===
The arc-trench complex is the surface expression of a much deeper structure. Though not directly accessible, the deeper portions can be studied using [[geophysics]] and [[geochemistry]]. Subduction zones are defined by an inclined zone of [[earthquake]]s, the [[Wadati–Benioff zone]], that dips away from the trench and extends down below the volcanic arc to the [[Transition zone (Earth)|660-kilometer discontinuity]]. Subduction zone earthquakes occur at greater depths (up to {{Convert|600|km|mi|abbr=on}}) than elsewhere on Earth (typically less than {{Convert|20|km|mi|abbr=on}} depth); such deep earthquakes may be driven by deep [[phase transformation]]s, [[thermal runaway]], or dehydration [[embrittlement]].<ref>{{cite journal | last1 = Frolich | first1 = C. | year = 1989 | title = The Nature of Deep Focus Earthquakes | journal = Annual Review of Earth and Planetary Sciences | volume =  17| pages =  227–254| doi = 10.1146/annurev.ea.17.050189.001303 | bibcode = 1989AREPS..17..227F}}</ref><ref>{{cite journal |last1=Hacker |first1=B. |display-authors=etal |year=2003 |title=Subduction factory 2. Are intermediate-depth earthquakes in subducting slabs linked to metamorphic dehydration reactions? |url=http://www.geol.ucsb.edu/faculty/hacker/viz/Hacker03_SubFac2_Intermediate_depth_earthquakes.pdf |journal=Journal of Geophysical Research |volume=108 |issue=B1 |pages=2030 |doi=10.1029/2001JB001129 |bibcode=2003JGRB..108.2030H }}</ref> [[Seismic tomography]] shows that some slabs can penetrate the [[lower mantle]]<ref name=":0">{{cite journal |last1=Domeier |first1=Mathew |last2=Doubrovine |first2=Pavel V. |last3=Torsvik |first3=Trond H. |last4=Spakman |first4=Wim |last5=Bull |first5=Abigail L. |title=Global correlation of lower mantle structure and past subduction |journal=Geophysical Research Letters |date=28 May 2016 |volume=43 |issue=10 |pages=4945–4953 |doi=10.1002/2016GL068827 |pmid=31413424 |pmc=6686211 |bibcode=2016GeoRL..43.4945D |doi-access=free }}</ref><ref>{{cite journal |last1=Faccenna |first1=Claudio |last2=Oncken |first2=Onno |last3=Holt |first3=Adam F. |last4=Becker |first4=Thorsten W. |title=Initiation of the Andean orogeny by lower mantle subduction |journal=Earth and Planetary Science Letters |year=2017 |volume=463 |pages=189–201 |doi=10.1016/j.epsl.2017.01.041 |bibcode=2017E&PSL.463..189F |hdl=11590/315613 |hdl-access=free }}</ref> and sink clear to the [[core–mantle boundary]].<ref>{{cite journal |last1=Hutko |first1=Alexander R. |last2=Lay |first2=Thorne |last3=Garnero |first3=Edward J. |last4=Revenaugh |first4=Justin |title=Seismic detection of folded, subducted lithosphere at the core–mantle boundary |journal=Nature |date=2006 |volume=441 |issue=7091 |pages=333–336 |doi=10.1038/nature04757 |pmid=16710418 |bibcode=2006Natur.441..333H |s2cid=4408681 }}</ref> Here the residue of the slabs may eventually heat enough to rise back to the surface as [[mantle plume]]s.<ref>{{cite journal |last1=Li |first1=Mingming |last2=McNamara |first2=Allen K. |title=The difficulty for subducted oceanic crust to accumulate at the Earth's core-mantle boundary |journal=Journal of Geophysical Research: Solid Earth |date=2013 |volume=118 |issue=4 |pages=1807–1816 |doi=10.1002/jgrb.50156 |bibcode=2013JGRB..118.1807L |doi-access=free }}</ref>{{sfn|Stern|2002|p=1}}