| Juan de Fuca plate | |
|---|---|
 | |
| Type | Micro |
| Approximate area | 250,000 km2 (96,000 sq mi)[1] |
| Movement1 | North-east |
| Speed1 | 26 mm/year (1.0 in/year) |
| Features | Pacific Ocean |
| 1Relative to theAfrican plate | |
TheJuan de Fuca plate orJuan de Fuca microplate is a smalloceanictectonic plate (microplate) generated from theJuan de Fuca Ridge that issubducting beneath the northerly portion of the western side of theNorth American plate at theCascadia subduction zone.[2] It is named after theexplorer of the same name. One of the smallest of Earth's tectonic plates, the Juan de Fuca microplate is a remnant part of the once-vastFarallon plate, which is now largely subducted underneath the North American plate.
In plate tectonic reconstructions, the Juan de Fuca microplate is referred to as the Vancouver plate between the break-up of the Farallon platec. 55–52Ma and the activation of theSan Andreas Fault c. 30 Ma.[3]
The Juan de Fuca microplate system has its origins withPanthalassa'soceanic basin andcrust. This oceanic crust has primarily beensubducted under theNorth American plate, and theEurasian plate. Panthalassa's oceanic plate remnants are understood to be the Juan de Fuca,Gorda,Cocos and theNazca plates, all four of which were part of theFarallon plate.
The Juan de Fuca microplate is bounded on the south by theBlanco fracture zone (running northwest off the coast ofOregon), on the north by theNootka Fault (running southwest offNootka Island, nearVancouver Island,British Columbia) and along the west by thePacific plate (which covers most of thePacific Ocean and is the largest of Earth's tectonic plates). The Juan de Fuca microplate itself has since fractured into three pieces, and the name is applied to the entire plate in some references, but in others only to the central portion. The three fragments are differentiated as such: the piece to the south is known as theGorda plate and the piece to the north is known as theExplorer plate. The separate pieces are demarcated by the large offsets of the undersea spreading zone.
This subducting plate system has formed theCascade Range, theCascade Volcanic Arc, and thePacific Ranges, along the west coast ofNorth America from southernBritish Columbia to northernCalifornia. These in turn are part of the PacificRing of Fire, a much larger-scale volcanic feature that extends around much of the rim of thePacific Ocean.
The lastmegathrust earthquake at the Cascadia subduction zone was the1700 Cascadia earthquake, estimated to have amoment magnitude of 8.7 to 9.2. Based oncarbon dating of localtsunami deposits, it is inferred to have occurred around 1700.[4] Evidence of this earthquake is also seen in theghost forest along the bank of theCopalis River in Washington. The rings of the dead trees indicate that they died around 1700, and it is believed that they were killed when the earthquake occurred and sank the ground beneath them causing the trees to be flooded by saltwater.[5] Japanese records indicate that atsunami occurred inJapan on 26 January 1700, which was likely caused by this earthquake.[6]
In 2008, smallearthquakes were observed within the Juan de Fuca microplate. The unusual quakes were described as "more than 600 quakes over the past 10 days in a basin 150 miles [240 km] southwest ofNewport". The quakes were unlike most quakes in that they did not follow the pattern of a large quake, followed by smaller aftershocks; rather, they were simply a continual deluge of small quakes. Furthermore, they did not occur on the tectonic plate boundary, but rather in the middle of the plate. The subterranean quakes were detected onhydrophones, and scientists described the sounds as similar to thunder, and unlike anything previously recorded.[7]
The basaltic formations of the Juan de Fuca microplate could potentially be suitable for long-term CO2 sequestration as part of acarbon capture and storage (CCS) system. Injection of CO2 would lead to the formation of stable carbonates. It is estimated that 100 years of UScarbon emissions (at current rate) could be stored securely, without risk of leakage back into the atmosphere.[8][9]
In 2019, scientists from theUniversity of California, Berkeley, published a study inGeophysical Research Letters in which they reported that by utilizing data from over 30,000 seismic waves and 217 earthquakes to create a three-dimensional map, they had revealed the existence of a hole in the subducted part of the Juan de Fuca microplate, and speculated that the hole is an indication of a 150 kilometres (93 mi) deep tear in the plate along a "preexisting zone of weakness". According to William B. Hawley and Richard M. Allen, the authors of the study, the hole may be the cause of volcanism and earthquakes on the plate, and is causing deformation of the offshore part of the plate. The deformation may cause the plate to fragment, with the remaining un-subducted small pieces becoming attached to other plates nearby.[10][11]
In 2016, a geophysical study was published on the possible presence of a layer of buoyant material between the Earth'slithosphere and theasthenosphere under the Juan de Fuca microplate. The study extends the theory of partial melt in thelithosphere-asthenosphere boundary to subduction zones, specifically in theconvergent margins.[12]
Using teleseismic body-wavetomography, a low-velocity zone of thickness 50~100 km in the sublithospheric region beneath the Juan de Fuca microplate was detected. The observation, along with fluid-mechanical calculations that factor inCouette andPoiseuille flows, support the hypothesis of the accumulation of a buoyant material, characterized by low viscosity. The exact source of this anomaly remains unknown, although its highly-conductive nature and low-seismic wave velocity are well observed.[13]
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