Editing Cascadia subduction zone (section)

===Earthquake effects===
[[Megathrust earthquake]]s are the most powerful earthquakes known to occur, and can exceed [[Moment magnitude scale|magnitude]] 9.0, which releases 1,000 times more energy than magnitude 7.0 and 1 million times more energy than a magnitude 5.0.<ref name=Nedimovic/><ref>{{Cite web|last=Haas|first=Ryan|date=2015-03-09|title=What Is A 9.0 Earthquake?|url=https://www.opb.org/news/series/unprepared/what-is-a-90-earthquake-/|url-status=live|access-date=2021-06-21|website=Oregon Public Broadcasting|language=en|archive-url=https://web.archive.org/web/20150126173645/http://www.opb.org:80/news/series/unprepared/what-is-a-90-earthquake-/ |archive-date=2015-01-26 }}</ref><ref>{{Cite web|title="How Much Bigger…?" Calculator|url=https://earthquake.usgs.gov/education/calculator.php|url-status=live|access-date=2021-06-21|publisher=United States Geological Survey|department= Earthquake Hazards Program|archive-url=https://web.archive.org/web/20190928152746/https://earthquake.usgs.gov/education/calculator.php |archive-date=2019-09-28 }}</ref> They occur when enough energy (stress) has accumulated in the "locked" zone of the fault to cause a rupture. The magnitude of a megathrust earthquake is proportional to length of the rupture along the fault. The Cascadia subduction zone, which forms the boundary between the Juan de Fuca and North American plates, is a very long sloping fault that stretches from mid-Vancouver Island to Northern California.<ref name="Nedimovic" />

Because of the great length of the fault, the Cascadia subduction zone is capable of producing very large earthquakes if rupture occurs along its entire length. Thermal and deformation studies indicate that the region 60 kilometers (about 40 miles) [[Strike and dip|downdip]] (east) of the deformation front (where plate deformation begins) is fully locked (the plates do not move past each other). Further downdip, there is a transition from fully locked to [[Aseismic creep|aseismic sliding]].<ref name=Nedimovic>{{cite journal | last1 = Nedimović | first1 = Mladen R. | last2 = Hyndman | first2 = Roy D. | last3 = Ramachandran | first3 = Kumar | last4 = Spence | first4 = George D. | title=Reflection signature of seismic and aseismic slip on the northern Cascadia subduction interface | journal=[[Nature (journal)|Nature]] | volume=424 | issue=6947 | date = 24 July 2003 | pages=416–420 | pmid=12879067 | doi=10.1038/nature01840|bibcode = 2003Natur.424..416N | s2cid = 4383885 }}</ref>

In 1999, a group of Continuous [[Global Positioning System]] sites registered a brief reversal of motion of approximately 2 centimeters (0.8&nbsp;inches) over a 50 kilometer by 300 kilometer (about 30 mile by 200 mile) area. The movement was the equivalent of a 6.7 magnitude earthquake.<ref name=Dragert2001>{{cite journal | last1 = Dragert | first1 = Herb | last2 = Wang | first2 = Kelin | last3 = James | first3 = Thomas S. | title=A silent slip event on the deeper Cascadia subduction interface | journal=[[Science (journal)|Science]] | volume=292 | issue=5521 | date = 25 May 2001 | pages=1525–1528 | pmid=11313500 | doi=10.1126/science.1060152|bibcode = 2001Sci...292.1525D | s2cid = 10928887 | doi-access = free }}</ref> The motion did not trigger an earthquake and was only detectable as silent, non-earthquake seismic signatures.<ref name=rogers2003>{{cite journal | last1 = Rogers | first1 = Garry | last2 = Dragert | first2 = Herb | title=Episodic tremor and slip on the Cascadia subduction zone: the chatter of silent slip | journal=[[Science (journal)|Science]] | volume=300 | issue=5627 | date = 20 June 2003 | pages = 1942–1943 | pmid=12738870 | doi=10.1126/science.1084783|bibcode = 2003Sci...300.1942R | s2cid = 2672381 | doi-access = free }}</ref>

In 2004, a study conducted by the Geological Society of America analyzed the potential for land subsidence along the Cascadia subduction zone. It postulated that several towns and cities on the west coast of Vancouver Island, such as [[Tofino]] and [[Ucluelet]], are at risk for a sudden, earthquake initiated, 1–2 m subsidence.<ref>{{cite journal |title=Coseismic subsidence in the 1700 great Cascadia earthquake: Coastal estimates versus elastic dislocation models| first1 = Lucinda J. | last1 = Leonard | first2 = Roy D. | last2 = Hyndman | first3 = Stéphane | last3 = Mazzotti | s2cid = 62833386 | doi = 10.1130/B25369.1 | journal = [[GSA Bulletin]] | volume = 116 | issue = 5–6 | pages = 655–670 | bibcode = 2004GSAB..116..655L |year=2004}}</ref>