Gorda Plate

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A map of the Gorda and neighboring Juan de Fuca Plates subducting under the North American plate Juan de fuca plate.png
A map of the Gorda and neighboring Juan de Fuca Plates subducting under the North American plate

The Gorda Plate, located beneath the Pacific Ocean off the coast of northern California, is one of the northern remnants of the Farallon Plate. It is sometimes referred to (by, for example, publications from the USGS Earthquake Hazards Program) [1] as simply the southernmost portion of the neighboring Juan de Fuca Plate, another Farallon remnant.

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Unlike most tectonic plates, the Gorda Plate experiences significant intraplate deformation inside its boundaries. Numerous faults have been mapped in both the sediments and basement of the Gorda Basin, which is in the interior of the plate south of 41.6°N. [2] Stresses from the neighboring North American Plate and Pacific Plate cause frequent earthquakes in the interior of the plate, including the 1980 Eureka earthquake (also known as the Gorda Basin event). [3]

The easterly side is the Cascadia subduction zone where the plate subducts under the North American Plate in northern California. The southerly side is a transform boundary with the Pacific Plate along the Mendocino Fault. The westerly side is a divergent boundary with the Pacific Plate forming the Gorda Ridge. This ridge provides morphological evidence of differing spreading rates, with the northern portion of the ridge being narrow, and the southern portion being wide. [4] The northerly side is a transform boundary with the Juan de Fuca Plate, the Blanco Fracture Zone.

The subducting Gorda Plate is connected with the volcanoes in northern California, namely, Mount Shasta and Lassen Peak. Lassen Peak last erupted in 1914–1917. [5]

See also

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<span class="mw-page-title-main">North American Plate</span> Large tectonic plate including most of North America, Greenland and part of Siberia

The North American Plate is a tectonic plate containing most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of 76 million km2 (29 million sq mi), it is the Earth's second largest tectonic plate, behind the Pacific Plate.

<span class="mw-page-title-main">Juan de Fuca Plate</span> Small tectonic plate in the eastern North Pacific

The Juan de Fuca Plate is a small tectonic plate (microplate) generated from the Juan de Fuca Ridge that is subducting beneath the northerly portion of the western side of the North American Plate at the Cascadia subduction zone. It is named after the explorer of the same name. One of the smallest of Earth's tectonic plates, the Juan de Fuca Plate is a remnant part of the once-vast Farallon Plate, which is now largely subducted underneath the North American Plate.

<span class="mw-page-title-main">Farallon Plate</span> Ancient oceanic plate that has mostly subducted under the North American Plate

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<span class="mw-page-title-main">Nazca Plate</span> Oceanic tectonic plate in the eastern Pacific Ocean basin

The Nazca Plate or Nasca Plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru–Chile Trench, of the Nazca Plate under the South American Plate is largely responsible for the Andean orogeny. The Nazca Plate is bounded on the west by the Pacific Plate and to the south by the Antarctic Plate through the East Pacific Rise and the Chile Rise respectively. The movement of the Nazca Plate over several hotspots has created some volcanic islands as well as east–west running seamount chains that subduct under South America. Nazca is a relatively young plate both in terms of the age of its rocks and its existence as an independent plate having been formed from the break-up of the Farallon Plate about 23 million years ago. The oldest rocks of the plate are about 50 million years old.

<span class="mw-page-title-main">Pacific Plate</span> Oceanic tectonic plate under the Pacific Ocean

The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million km2 (40 million sq mi), it is the largest tectonic plate.

<span class="mw-page-title-main">Explorer Plate</span> Oceanic tectonic plate beneath the Pacific Ocean off the west coast of Vancouver Island, Canada

The Explorer Plate is an oceanic tectonic plate beneath the Pacific Ocean off the west coast of Vancouver Island, Canada, which is partially subducted under the North American Plate. Along with the Juan de Fuca Plate and Gorda Plate, the Explorer Plate is a remnant of the ancient Farallon Plate, which has been subducted under the North American Plate. The Explorer Plate separated from the Juan de Fuca Plate roughly 4 million years ago. In its smoother, southern half, the average depth of the Explorer plate is roughly 2,400 metres (7,900 ft) and rises up in its northern half to a highly variable basin between 1,400 metres (4,600 ft) and 2,200 metres (7,200 ft) in depth.

<span class="mw-page-title-main">Cascadia subduction zone</span> Convergent plate boundary that stretches from northern Vancouver Island to Northern California

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<span class="mw-page-title-main">Cape Mendocino</span> Cape in Mendocino County, California, United States

Cape Mendocino, which is located approximately 200 miles (320 km) north of San Francisco, is located on the Lost Coast entirely within Humboldt County, California, United States. At 124° 24' 34" W longitude, it is the westernmost point on the coast of California. The South Cape Mendocino State Marine Reserve and Sugarloaf Island are immediately offshore, although closed to public access due to their protected status. Sugarloaf Island is cited as California's westernmost island.

<span class="mw-page-title-main">Mendocino Fracture Zone</span> Geologic fracture zone and transform boundary near northern California

The Mendocino Fracture Zone is a fracture zone and transform boundary over 4000 km long, starting off the coast of Cape Mendocino in far northern California. It runs westward from a triple junction with the San Andreas Fault and the Cascadia subduction zone to the southern end of the Gorda Ridge. It continues on west of its junction with the Gorda Ridge, as an inactive remnant section which extends for several hundred miles.

<span class="mw-page-title-main">Mendocino Triple Junction</span> Point where the Gorda plate, the North American plate, and the Pacific plate meet

The Mendocino Triple Junction (MTJ) is the point where the Gorda plate, the North American plate, and the Pacific plate meet, in the Pacific Ocean near Cape Mendocino in northern California. This triple junction is the location of a change in the broad plate motions which dominate the west coast of North America, linking convergence of the northern Cascadia subduction zone and translation of the southern San Andreas Fault system. This region can be characterized by transform fault movement, the San Andreas also by transform strike slip movement, and the Cascadia subduction zone by a convergent plate boundary subduction movement. The Gorda plate is subducting, towards N50ºE, under the North American plate at 2.5 – 3 cm/yr, and is simultaneously converging obliquely against the Pacific plate at a rate of 5 cm/yr in the direction N115ºE. The accommodation of this plate configuration results in a transform boundary along the Mendocino Fracture Zone, and a divergent boundary at the Gorda Ridge. This area is tectonically active historically and today. The Cascadia subduction zone is known to be capable of producing megathrust earthquakes on the order of MW 9.0.

<span class="mw-page-title-main">Gorda Ridge</span> Tectonic spreading center off the northern coast of California and southern Oregon

The Gorda Ridge, aka Gorda Ridges tectonic spreading center, is located roughly 200 kilometres (120 mi) off the northern coast of California and southern Oregon. Running NE – SW it is roughly 300 kilometres (190 mi) in length. The ridge is broken into three segments; the northern ridge, central ridge, and the southern ridge, which contains the Escanaba Trough.

<span class="mw-page-title-main">Juan de Fuca Ridge</span> Divergent plate boundary off the coast of the Pacific Northwest region of North America

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<span class="mw-page-title-main">Explorer Ridge</span> Mid-ocean ridge west of British Columbia, Canada

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<span class="mw-page-title-main">Geology of the Pacific Northwest</span> Geology of Oregon and Washington (United States) and British Columbia (Canada)

The geology of the Pacific Northwest includes the composition, structure, physical properties and the processes that shape the Pacific Northwest region of North America. The region is part of the Ring of Fire: the subduction of the Pacific and Farallon Plates under the North American Plate is responsible for many of the area's scenic features as well as some of its hazards, such as volcanoes, earthquakes, and landslides.

<span class="mw-page-title-main">Pacific-Farallon Ridge</span> Spreading ridge during the Late Cretaceous

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The 1992 Cape Mendocino earthquakes occurred along the Lost Coast of Northern California on April 25 and 26. The three largest events were the M7.2 thrust mainshock that struck near the unincorporated community of Petrolia midday on April 25 and two primary strike-slip aftershocks measuring 6.5 and 6.6 that followed early the next morning. The sequence encompassed both interplate and intraplate activity that was associated with the Mendocino Triple Junction, a complex system of three major faults that converge near Cape Mendocino. The total number of aftershocks that followed the events exceeded 2,000.

<span class="mw-page-title-main">Geology of the Pacific Ocean</span> Overview about the geology of the Pacific Ocean

The Pacific Ocean evolved in the Mesozoic from the Panthalassic Ocean, which had formed when Rodinia rifted apart around 750 Ma. The first ocean floor which is part of the current Pacific Plate began 160 Ma to the west of the central Pacific and subsequently developed into the largest oceanic plate on Earth.

The 1932 Eureka earthquake occurred on June 6 at 00:44:26 local time along the northern coastal area of California in the United States. With a moment magnitude of 6.4 and a maximum Mercalli intensity of VIII (Severe), this earthquake left one person dead from a falling chimney and several injured. The shock was the largest in the area since 1923 and was felt in southern Oregon and northern California.

References

  1. "National Earthquake Information Center (NEIC)". usgs.gov. Archived from the original on 25 June 2012. Retrieved 12 December 2014.
  2. Gulick, S., Meltzer, A., and S. Clarke (1998) Seismic structure of the southern Cascadia subduction zone and accretionary prism north of the Mendocino triple junction. Journal of Geophysical Research-Solid Earth, 103(B11).
  3. "Historic Earthquakes". usgs.gov. Retrieved 12 December 2014.
  4. Riddihough, R. P. (1980). Gorda plate motions from magnetic anomaly analysis. Earth and Planetary Science Letters, 51(1), 163-170.
  5. Clynne Clynne, Michael; Christiansen, Daniel; Stauffer, Peter; Hendley, James (21 May 2015). "Eruptions of Lassen Peak, California, 1914 to 1917 — A Centennial Commemoration". usgs.gov. U.S. Department of the Interior.

41°12′N126°24′W / 41.2°N 126.4°W / 41.2; -126.4