Cascadia subduction zone

Cascadia earthquake sources

The 1700 Cascadia Earthquake was a magnitude 8.7 – 9.2 megathrust earthquake that occurred in the Cascadia subduction zone in 1700. The earthquake involved the Juan de Fuca Plate underlying the Pacific ocean, from mid-Vancouver Island in southwest Canada off British Columbia to northern California, along the Pacific Northwest coast. The length of the fault rupture was about 1000 kilometers (600 miles) with an average slip of 20 meters. Image File history File links Size of this preview: 420 × 599 pixelsFull resolution (495 × 706 pixel, file size: 23 KB, MIME type: image/png) Cascadia subduction zone. ... Image File history File links Size of this preview: 420 × 599 pixelsFull resolution (495 × 706 pixel, file size: 23 KB, MIME type: image/png) Cascadia subduction zone. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... The moment magnitude scale was introduced in 1979 by Tom Hanks and Hiroo Kanamori as a successor to the Richter scale and is used by seismologists to compare the energy released by earthquakes. ... A megathrust earthquake is an interplate earthquake where one tectonic plate slips beneath (subducts) another. ... Structure of the Cascadia subduction zone Area of the Cascadia subduction zone The Cascadia subduction zone is a very long sloping fault that stretches from northern Vancouver Island to northern California. ... This article is about the natural seismic phenomenon. ... A map of the Juan de Fuca Plate The Juan de Fuca Plate, named after the explorer, is a tectonic plate arising from the Juan de Fuca Ridge, and subducting under the northerly portion of the western side of the North American Plate. ... Pacific redirects here. ... Vancouver Island is separated from mainland British Columbia by the Strait of Georgia and the Queen Charlotte Strait, and from Washington by the Juan De Fuca Strait. ... Motto: Splendor sine occasu (Latin: Splendour without diminishment) Capital Victoria Largest city Vancouver Official languages English (de facto) Government Lieutenant-Governor Steven Point Premier Gordon Campbell (BC Liberal) Federal representation in Canadian Parliament House seats 36 Senate seats 6 Confederation July 20, 1871 (6th province) Area  Ranked 5th Total 944... This article is about the U.S. state. ... The Pacific Northwest from space The Pacific Northwest, abbreviated PNW, or PacNW is a region in the northwest of North America. ...

The Cascadia Earthquake caused a tsunami that struck the coast of Japan, and may also be linked to the Bonneville slide. For other uses, see Tsunami (disambiguation). ... The original Bridge of the Gods was created by the Bonneville Slide, which dammed the Columbia River (see also Columbia River Gorge) in the modern-day Pacific Northwest of the United States in the eighteenth century. ...

Evidence of the earthquake

Evidence supporting the occurrence of the 1700 earthquake has been gathered into the 2005 book, The Orphan Tsunami of 1700, by geologist Brian Atwater and others. The Geologist by Carl Spitzweg A geologist is a contributor to the science of geology, studying the physical structure and processes of the Earth and planets of the solar system (see planetary geology). ... // Overview Brian Franklin Atwater is a geologist who works for the United States Geological Survey and is also a research professor at the University of Washington. ...

The evidence suggests that it took place at about 9:00 PM on January 26, 1700. Although there were no written records in the region at the time, the earthquake's precise date is nevertheless known from Japanese records of a tsunami that has not been tied to any other Pacific Rim earthquake. The most important clue linking the tsunami in Japan and the earthquake in the Pacific Northwest comes from studies of tree rings (dendrochronology) which show that red cedar trees killed by lowering of coastal forests into the tidal zone by the earthquake have outermost growth rings that formed in 1699, the last growing season before the tsunami. Oral traditions also exist among the region's original inhabitants, although these do not specify the date. is the 26th day of the year in the Gregorian calendar. ... Events January 1 - Russia accepts Julian calendar. ... The growth rings of an unknown tree species, at Bristol Zoo, England Pinus taeda Cross section showing annual rings, Cheraw, South Carolina Pine stump showing growth rings Dendrochronology or tree-ring dating is the method of scientific dating based on the analysis of tree-ring growth patterns. ... Binomial name Thuja plicata Donn ex D.Don Thuja plicata (Western Redcedar) is a species of thuja, an evergreen coniferous tree in the cypress family Cupressaceae, native to the northwestern United States and southwestern Canada, from southern Alaska and British Columbia south to northwest California and inland to western Montana. ... Oral tradition or oral culture is a way of transmitting history, literature or law from one generation to the next in a civilization without a writing system. ...

Future threats

The geological record reveals that "great earthquakes" (those with magnitude 8 or higher) occur in the Cascadia subduction zone about every 500 years on average, often accompanied by tsunamis. There is evidence of at least 13 events at intervals from about 300 to 900 years with an average of 590 years. Previous earthquakes are estimated to have occurred in 1310 AD, 810 AD, and 170 BC. The moment magnitude scale (a successor to the Richter Scale), was introduced in 1979 by Tom Hanks and Hiroo Kanamori and is used by seismologists to compare the energy released by earthquakes. ... Structure of the Cascadia subduction zone Area of the Cascadia subduction zone The Cascadia subduction zone is a very long sloping fault that stretches from northern Vancouver Island to northern California. ... For other uses, see Tsunami (disambiguation). ...

As the subduction zone ruptured in a magnitude 9 earthquake, it sent a strong tsunami to the coast. The shaking lasted for about 4 or more minutes, triggering landslides. Then the tsunami would have hit land, destroying structures at the coast. This was probably the strongest earthquake to strike the Contiguous United States in recorded history. The continental United States refers (except sometimes in U.S. federal law and regulations) to the largest part of the U.S. that is delimited by a continuous border. ...

As displayed in the 2004 Indian Ocean Earthquake, great damage comes from subduction zone tsunamis. In the case of a future Cascadia earthquake, however, most of the damage would probably be from the earthquake itself due to the urban areas, most notably Seattle, Portland, Vancouver, Victoria, and Tacoma, with vulnerable structures like brick buildings and highrises, being located along internal waterways, rivers, and bays, and not on the Pacific coast itself and therefore sheltered from the full brunt of a tsunami. The Cascadia coast is armed with various tsunami alerts and escape routes. The 2004 Indian Ocean earthquake, known by the scientific community as the Sumatra-Andaman earthquake,[1] was a great undersea earthquake that occurred at 00:58:53 UTC (07:58:53 local time) December 26, 2004 with an epicentre off the west coast of Sumatra, Indonesia. ...

Some other subduction zones have such earthquakes every 100–200 years; the longer interval here results from slower plate motions.

The rate of convergence between the Juan de Fuca Plate and the North American Plate is 40 mm/yr. [1] A map of the Juan de Fuca Plate The Juan de Fuca Plate, named after the explorer, is a tectonic plate arising from the Juan de Fuca Ridge, and subducting under the northerly portion of the western side of the North American Plate. ...  The North American plate, shown in brown The North American Plate is a tectonic plate covering most of North America, extending eastward to the Mid-Atlantic Ridge and westward to the Cherskiy Range in East Siberia. ... A millimetre (American spelling: millimeter), symbol mm is an SI unit of length that is equal to one thousandth of a metre. ... A year (from Old English gÄ“r) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ...

Similar megathrust earthquakes

Other megathrust earthquakes are the slightly more powerful 1964 Alaskan Good Friday Earthquake measured at magnitude 9.2, the 1960 Great Chilean Earthquake measured at 9.5, The Kamchatka quake measured at 9.0, and the 2004 Indian Ocean earthquake at 9.2. Earthquake Damage, Anchorage The Good Friday Earthquake (also called the Great Alaska Earthquake) of Friday, March 27, 1964 (Good Friday, a Christian holy day associated with a historical earthquake[1]), 5:36 P.M. AST (03:36 3/27 UTC) had a magnitude of 9. ... The moment magnitude scale (a successor to the Richter Scale), was introduced in 1979 by Tom Hanks and Hiroo Kanamori and is used by seismologists to compare the energy released by earthquakes. ... Map showing the areas affected by the tsunami The Great Chilean Earthquake or Valdivian Earthquake (Terremoto de Valdivia in Spanish) of 22 May 1960 is the most intense earthquake ever recorded, rating a 9. ... The Kamchatka earthquakes were a pair of megathrust earthquakes occurring off the coast of the Kamchatka Peninsula, in Russia on October 16, 1737, and on November 4, 1952, in the magnitude of ~9. ... The 2004 Indian Ocean earthquake, known by the scientific community as the Sumatra-Andaman earthquake,[1] was a great undersea earthquake that occurred at 00:58:53 UTC (07:58:53 local time) December 26, 2004 with an epicentre off the west coast of Sumatra, Indonesia. ...

See also New Madrid Earthquakes, which are estimated to have measured magnitude 7.5–8.0. The New Madrid Earthquake, the largest earthquake ever recorded in the contiguous United States, occurred on February 7, 1812. ...

See also

• Geology of the Pacific Northwest
• List of earthquakes

The Pacific Northwest region of the United States is still geologically active. ... The following is a list of major earthquakes. ...

External links and references

• National Resources Canada: evaluation of Cascadia subduction zone hazards
• USGS on the Cascadia earthquake
• Repository of information on the Cascadia earthquake
• Japanese tsunami descriptions
• Science Daily on the Cascadia Earthquake & Japanese evidence
• Canadian source with a nice map
• earthquake.usgs.gov/ on possible tie to the Bonneville Slide
• 300th anniversary article
• Lessons from surviving a tsunami
• The Orphan Tsunami of 1700
• Seattle scenario description