Editing Cascadia subduction zone (section)

==History==

===Tradition===
{{Main|Thunderbird and Whale}}

There are no contemporaneous written records of the [[1700 Cascadia earthquake]]. Orally transmitted legends from the [[Olympic Peninsula]] area tell of [[Thunderbird and Whale|an epic battle between a thunderbird and a whale]]. In 2005, seismologist Ruth Ludwin set out to collect and analyze anecdotes from various [[Native Americans in the United States|First Nations]] groups. Reports from the [[Huu-ay-aht First Nations|Huu-ay-aht]],<ref name=NatGeo/> [[Makah]],<ref name=NatGeo/> [[Hoh Indian Tribe of the Hoh Indian Reservation|Hoh]],<ref name=AMNH/> [[Quileute]],<ref name=Smithsonian/><ref name=AMNH/> [[Yurok people|Yurok]],<ref name=Smithsonian/> and [[Duwamish tribe|Duwamish]]<ref name=Smithsonian/> peoples referred to earthquakes and saltwater floods. This collection of data allowed the researchers to come up with an estimated date range for the event; the midpoint was in the year 1701.<ref name=NatGeo/>

===Ghost forests===
[[File:Neskowin Ghost Forest - 2016.jpg|thumb|Stumps of trees at the Neskowin Ghost Forest]]
[[File:Neskowin Ghost Forest Stump Close Up.jpg|thumb|Large tree stump protruding from beach sand]]

During low tide one day in March 1986, paleogeologist [[Brian Atwater]] dug along [[Neah Bay]] with a ''nejiri gama'', a small hand hoe. Under a top layer of sand, he uncovered a distinct plant—[[arrowgrass]]—that had grown in a layer of marsh soil. This finding was evidence that the ground had suddenly sunk under sea level, causing saltwater to kill the vegetation. The event had happened so quickly that the top layer of sand sealed away the air, thus preserving centuries-old plants.<ref name = Discover/>

In 1987, Atwater mounted another expedition paddling up the [[Copalis River]] with Dr. David Yamaguchi, who was then studying the eruptions of [[Mount St. Helens]].<ref name = Discover/> The pair happened upon a section of "[[ghost forest]]", so-called due to the dead, gray stumps left standing after a sudden inundation of salt water had killed them hundreds of years ago.<ref name = AMNH>{{cite web|url=http://www.amnh.org/explore/science-bulletins/earth/documentaries/tsunami-science-reducing-the-risk/ghosts-of-tsunamis-past|title=Ghosts of Tsunamis Past|publisher=American Museum of Natural History|access-date=15 July 2015|archive-url=https://web.archive.org/web/20180828035721/https://www.amnh.org/explore/science-bulletins/earth/documentaries/tsunami-science-reducing-the-risk/ghosts-of-tsunamis-past/|archive-date=28 August 2018|url-status=dead}}</ref> Originally thought to have died slowly due to a gradual rise in sea level,<ref name = "Schulz2015" >{{cite magazine|last=Schulz|first=Kathryn|author-link=Kathryn Schulz|url=http://www.newyorker.com/magazine/2015/07/20/the-really-big-one|title=The Really Big One: An earthquake will destroy a sizable portion of the coastal Northwest. The question is when.|date=July 20, 2015|magazine=[[The New Yorker]]|access-date=July 14, 2015}}</ref> closer inspection yielded a different story: the land plummeted up to two meters during an earthquake.<ref name=AMNH/> Having initially tested [[spruce]] using [[Dendrochronology|tree-ring dating]], they found that the stumps were too rotted to count all the outer rings. However, upon having examined those of the [[Thuja plicata|western red cedar]] and comparing them to the living specimens meters away from the banks, they were able to approximate their year of death. There were rings up until the year 1699, indicating that the incident had occurred shortly thereafter. Root samples confirmed their conclusion, narrowing the time frame to the winter of 1699 to 1700.<ref name = NatGeo>{{cite magazine|url=http://news.nationalgeographic.com/news/2003/12/1208_031208_tsunami.html|archive-url=https://web.archive.org/web/20031211072304/http://news.nationalgeographic.com/news/2003/12/1208_031208_tsunami.html|url-status=dead|archive-date=December 11, 2003|title=Did North American Quake Cause 1700 Japanese Tsunami?|author=Stefan Lovgren|magazine=National Geographic|date=8 December 2003|access-date=15 July 2015}}</ref><ref name = Discover />

As with the arrowgrass site, the banks of the Copalis River are lined with a layer of marsh followed by a layer of sand. Jody Bourgeois and her team went on to demonstrate that the sand cover had originated with a tsunami surge rather than a storm surge.<ref name=AMNH/>

In 1995, an international team led by Alan Nelson of the [[USGS]] further corroborated these findings with 85 new samples from the rest of the [[Pacific Northwest]]. All along British Columbia, Washington State, and Oregon, the coast had fallen due to a violent earthquake and been covered by sand from the subsequent tsunami.<ref name=Discover/>

A further ghost forest was identified by Gordon Jacoby, a [[Dendrochronology|dendrochronologist]] from Columbia University, {{convert|60|ft|m}} underwater in [[Lake Washington]]. Unlike the other trees, these suffered from a landslide rather than a dip in the fault during a separate event around 900 CE.<ref name = Smithsonian/>

===Activity===
In the 1960s, underground fractures were uncovered by oil companies in [[Puget Sound]]. These were believed to be inactive through the 1990s.<ref name = Smithsonian>{{cite magazine|url=http://www.smithsonianmag.com/science-nature/future-shocks-83897640/?no-ist|title=Future Shocks: Modern science, ancient catastrophes and the endless quest to predict earthquakes|magazine=Smithsonian Magazine|author= Kevin Krajick|date=March 2005|access-date=15 July 2015}}</ref>

In the 1980s, geophysicists [[Thomas H. Heaton|Tom Heaton]] and [[Hiroo Kanamori]] of [[California Institute of Technology|Caltech]] compared the generally quiet Cascadia to more active subduction zones elsewhere in the [[Ring of Fire]]. They found similarities to faults in Chile, Alaska, and Japan's [[Nankai Trough]], locations known for [[megathrust earthquake]]s, a conclusion that was met with skepticism from other geophysicists at the time.<ref name = Discover>{{cite magazine|url=http://discovermagazine.com/2012/extreme-earth/01-big-one-earthquake-could-devastate-pacific-northwest|title=The Giant, Underestimated Earthquake Threat to North America|magazine=Discover Magazine|date=13 March 2012|author= Jerry Thompson|access-date=15 July 2015}}</ref>

===Orphan tsunami===

A 1996 study published by seismologist [[Kenji Satake]] supplemented the research by Atwater et al. with tsunami evidence across the Pacific.<ref name=NatGeo/> Japanese annals, which have recorded natural disasters since approximately 600&nbsp;CE,<ref name = "Schulz2015" /> had reports of a sixteen-foot tsunami that struck the coast of [[Honshu Island]] during the [[Genroku]] era.<ref name=Discover/><ref name=NatGeo/> Since no earthquake had been observed to produce it, scholars dubbed it an "[[orphan tsunami]]".<ref name="Schulz2015" /> Translating the [[Japanese calendar]], Satake found the incident had taken place around midnight of 27–28&nbsp;January 1700, ten hours after the earthquake occurred. The original magnitude 9.0 earthquake in the Pacific Northwest had thus occurred around 9 pm Pacific Standard Time on 26 January 1700.<ref name="Schulz2015" />