inset) has evolved rapidly since it detached from the Juan de Fuca plate 5 Myr ago. Derek J. Thorkelson, in Encyclopedia of Geology (Second Edition), 2021. 19.1). This group of faults offset accretionary wedge sediments that underlie the continental shelf and slope in the forearc of the Cascadia subduction zone [781]; some faults also offset the overlying sedimentary section and the underlying oceanic basalts of the subducting Juan de Fuca Plate. The California landscape is, in part, a relict of this ancient subduction zone setting. Furthermore, they did not occur on the tectonic plate boundary, but rather in the middle of the plate. Moving apart about 25 mm/yr. The three segments subduct beneath North America at different rates. For more than one hundred million years prior to initiation of the San Andreas Fault (at 29 million years ago), the Farallon plate underwent subduction beneath California. In the south it borders the San Andreas fault and west by the Pacific plate. Such features are expected to be present within about 200 miles inland of an active continental coastline. The (geologically) significant shortening in the NE-SW direction shows significant strain build-up that will need to be released in an earthquake. 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. Offshore, beneath the Pacific Ocean, the Juan de Fuca Plate is being forced under, or subducted beneath, the western edge of the North American Plate. The overall topography shown in a Raisz landform map in Fig. This westward pull stretches the North American plate, thus creating normal faults. This is a classic subduction-related tectonic landscape in which accretion has caused uplift along the coast, subduction has created a volcanic highland in the Cascade Mountains, and the intervening Puget Sound/Willamette Valley forms a basin known as the forearc basin. The Juan de Fuca ridge system, a NNE-oriented intermediate-rate spreading center, is located at the boundary between the Pacific plate and the Juan de Fuca plate system. ), 1981. The last megathrust earthquake at the Cascadia subduction zone was the 1700 Cascadia earthquake, estimated to have a moment magnitude of 8.7 to 9.2. Beth Pratt-Sitaula, ... Donna Charlevoix, in Developments in Structural Geology and Tectonics, 2019. It is internal deformation that leads to earthquake hazard. The first has to do with the age of the subducting plate. The San Andreas Fault extends from the vicinity of Cape Mendocino southward to the Salton Sea. Vincent S. Cronin, in Encyclopedia of Geology (Second Edition), 2021. The heavy line with double arrow along the Coast Range follows the crest of an anticlinal flexure. The forcing of this slab across the Cordillera was the likely impetus that elevated the Middle-Southern Rocky Mountains from sea level beginning 75 million years ago as discussed in Chapter 14. Figure 10. The second reason has to do with the relatively slow rate of subduction in association with the Willapa, Columbia, Umpqua, Rogue, and other rivers that contribute copious amounts of sediment to the coastline. The third, the Explorer segment, is off the Canadian coast. Answer should at least include some mention of San Andreas Fault system and movement between the Pacific and North American Plates. The fault line, does not need to be seen, as it shifts and twitches in the darkness, for it is felt in waves of mud, clay and dirt. 6). The Juan de Fuca plate extends for about 600 miles (965km) from Vancouver Island in Canada, down to Cape Mendocino. This oceanic crust has primarily been subducted under the North American Plate, and the Eurasian Plate. Some of the more recent earthquakes include a magnitude 6.7 quake in 1949 and again in 1965, a magnitude 5.6 quake in 1996, and a magnitude 6.8 earthquake in 2001. Over 500 years, that would be 3.5–4 m. We would expect that both stations would move southest in the next plate boundary earthquake. Both shortening and right-lateral strike slip occur along the MTF. Meager in British Columbia, and the southern terminus at Mount Lassen in northern California, correspond with the northern and southern termini of the Juan de Fuca plate. Axis 2 = negative (contraction)—this is the axis in the NE-SW orientation. The Mendocino triple junction between the North American, Pacific, and Juan de Fuca Plates (Figs. The average rate of convergence between the Juan de Fuca segment and North America over the past 5 million years is between 9.8 and 13.8 feet per 100 years and the direction is about 49 degree east of north, which implies oblique subduction. The subterranean quakes were detected on hydrophones, and scientists described the sounds as similar to thunder, and unlike anything previously recorded. The Osceola Mudflow was by far the largest, extending all the way to the Seattle suburbs. Rotation direction = negative (clockwise), Strain ellipse extension (positive, zero, or negative): Axis 1 = positive Axis 2 = negative. Although it is the largest of the three segments, the Juan de Fuca segment is less than 275 miles wide measured from spreading ridge to subduction zone. The relationship between topography and tectonics is well displayed in Fig. Even though it has been under active tectonic development for hundreds of millions of years, we will discover in Part II of this book that much of the present-day Cordilleran structural form and landscape has developed during only the past 40 million years, and in many places, within the past 17 million years. The terrane is bordered by lower seismic velocity subduction complex at about 100 km distance (75 km from deformation front). Velocities > 5 km sec−1 may indicate igneous rocks that may sustain strain energy for seismic release. Crustal structure models across the northeastern Pacific rim (see Fig. Juan de Fuca Diagram. The Pacific Plate is moving northwest compared to North America. Joseph A. DiPietro, in Geology and Landscape Evolution (Second Edition), 2018. Schematic cross-section showing shallow subduction (underplating) of the Paleo-Pacific (Farallon) plate beneath the North American plate. Far to the north, subduction of the Pacific plate beneath Alaska is generating the Aleutian volcanic arc. Whereas the two volcanic arcs consist mainly of explosive, steep-sided stratovolcanoes with mainly calc-alkaline compositions, the slab window volcanic field consists of more mafic, less explosive volcanoes with gentler slopes and more alkalic compositions. Analysis of disrupted sediment suggests that as many as 12 powerful subduction-related earthquakes have occurred in the past 7700 years, about one every 642 years. Using a pencil, draw a line on the seafloor to show where new ocean crust and lithosphere is forming now (zero millions of years old). The approach here is to gain a first-order impression of how the North American, Juan de Fuca, and Pacific plates might interact in the vicinity of the triple junction—a first impression that can be refined with the inclusion of additional kinematic or geodynamic data. The modern plate boundary of western Canada and northwestern United States. Open triangles are seismometers and filled triangles are shot points on land. For the northern fragment, see, "Sizes of Tectonic or Lithospheric Plates", "Seaside, Oregon, Tsunami Pilot Study GIS, USGS Data Series 236, home page", "The Earthquake That Will Devastate the Pacific Northwest", "Fault slip and seismic moment of the 1700 Cascadia earthquake inferred from Japanese tsunami descriptions", "Unusual Earthquake Swarm Off Oregon Coast Puzzles Scientists", "Carbon dioxide sequestration in deep-sea basalt", "Sub-seafloor Carbon Dioxide Storage Potential on the Juan de Fuca Plate, Western North America", "The Fragmented Death of the Farallon Plate", "A Tectonic Plate Under Oregon Is Being Slowly Ripped Apart", National Geographic on Japanese records verifying an American earthquake, https://en.wikipedia.org/w/index.php?title=Juan_de_Fuca_Plate&oldid=1014735121, Short description is different from Wikidata, Wikipedia articles with WorldCat-VIAF identifiers, Creative Commons Attribution-ShareAlike License, This page was last edited on 28 March 2021, at 20:13. [4] Japanese records indicate that a tsunami occurred in Japan on 26 January 1700, which was likely caused by this earthquake. Beginning about 80 million years ago, rather than subducting directly into the mantle at a (normally) steep angle as shown in Fig. 7B); in other words, assume that convergent deformation will be shared equally by the two plates along the boundary. Presently, the, Problems and Solutions in Structural Geology and Tectonics, Developments in Structural Geology and Tectonics, , is an active continental margin that involves three tectonic plates: the North American plate, the Pacific plate, and the, Cordilleran Sedimentary Basins of Western Canada Record 180 Million Years of Terrane Accretion, The Sedimentary Basins of the United States and Canada (Second Edition), ). Key evidence for large destructive earthquakes was the discovery of rapidly drowned marshes and tree stands. Volcanism associated with the Northern Cordilleran slab window varies profoundly from one side to the other. USGS Fact sheet 2005–3036. Cascadia subduction zone is where young (4–8 Ma) Juan de Fuca plate subducts at a slow convergence rate (ENE-ward at 4 cm y−1) with high regional sedimentation rate beneath the North American continent (Fig. Fig. The underplated slab remained coherent all the way to Wyoming and Colorado. Injection of CO2 would lead to the formation of stable carbonates. There are additional reasons for an active tectonic landscape across the Cordillera. 5.6B, there is evidence that the Farallon plate subducted at such a shallow angle that it underplated the Cordilleran crust as depicted in Fig. (d) Nicaragua margin model. These reactions release fluids (H2O and CO2) into the solid upper mantle above the subducting plate that disturb equilibrium conditions, causing mantle rock to melt. The transforms have collectively forced the rifting (the separation) of Baja California from Mexico resulting in the opening of the Gulf of California. The place where they meet is the Cascadia subduction zone. The West Coast Trail Express provides a shuttle bus service in season, May 1 to September 30, picking up and dropping off passengers at Victoria, Sooke, Jordon River, China Beach, Sombrio Beach, Port Renfrew, and Nanaimo. The coastal stations have higher velocities. Figure 19.1. Figure 5.13. The Cascadia Subduction Zone has not produced an earthquake since 1700 and is building up pressure where the Juan de Fuca Plate is subsiding underneath the North American plate. 7. More specifically, P234 is west of the San Andreas Fault, and the other two stations are east of the main fault trace. The plate is … 5.6B. The Siletz terrane is exposed basement rock of the Cascadia forearc, which consists of accreted oceanic crust and seamounts about 50 Ma. Input data for finite modeling of Mendocino triple junction. Over time, the Gulf will continue to open and Baja California will slide northward with Los Angeles, eventually reaching San Francisco and beyond. The Juan de Fuca Plate system has its origins with Panthalassa's oceanic basin and crust. A small piece of California, including Los Angeles, is west of the San Andreas Fault. The Juan de Fuca and Gorda ridges mark the divergent plate boundary (the spreading ridge) with the Pacific plate. The catastrophic eruption on May 18, 1980, was the deadliest and most costly volcanic event in U.S. history, and resulted in 75 fatalities and the loss of 250 homes, 47 bridges, 24 km of railway, and ∼ 300 km of highway. FIGURE 4. (1998a) reported that the dip angle of the subducting plate is only a few degrees at about 47° N. The accretionary wedge is well developed and an increase of seismic velocity to > 4 km sec−1 seems to be due to dehydration, compaction, and diagenesis. The much smaller Gorda segment is subducting below the Klamath Mountains at a similar angle, but possibly at a slower rate between about 6.5 and 9.8 feet/100 years, particularly in its southern part. Subduction of the Juan de Fuca plate causes melting and magma generation in the mantle, which rises to the surface to create the Cascade volcanoes. (a) Topographic changes of Mount St. Helens measured from aerial photographs and laser imaging (LiDAR) showing rapid growth of a new lava dome, the whaleback-shape extrusion, and the deformed glacier. Our tomographic images clearly show the Juan de Fuca plate diving into the mantle beneath Oregon and continues east of the High Cascades with a dip of 50 reaching a depth of 400 km. Arrows indicate direction each plate is moving relative to the hotspot reference frame of Wang et al. The Juan de Fuca Plate is bounded on the south by the Blanco Fracture Zone (running northwest off the coast of Oregon), on the north by the Nootka Fault (running southwest off Nootka Island, near Vancouver Island, British Columbia) and along the west by the Pacific Plate (which covers most of the Pacific Oceanand is the largest of Earth's tectonic plates). Rotation also does not involve internal accumulation of strain, so it is more relevant to understanding overall tectonic movements than earthquake hazard. The avalanche reduced the elevation of the mountain summit by ∼ 400 m and formed a 1.6 km-wide crater (Figure 26). Rainier is probably the most dangerous volcano in this respect because of the relatively large population in its lowland drainages. It is estimated that 100 years of US carbon emissions (at current rate) could be stored securely, without risk of leakage back into the atmosphere. This landscape is a direct consequence of subduction of the Juan de Fuca plate. Fig. Our landscape shutters, our equilibrium sways. (Eds. 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. Volcanism associated with the Northern Cordilleran slab window varies profoundly from one side to the other. U.S. Geological Survey Professional Paper 1250, 844 pp. Figure 28. (b), (c) Within about 30 s after the collapse, the debris avalanche, lateral blast, and vertical eruption begin as the cryptodome is exposed. Seattle Fault Map Strait of Juan de Fuca Fault Map The Puget Sound faults under the highly populated Seattle and Puget Sound region of Washington state form a regional network of interrelated seismologic geologic faults. In this model, Explorer microplate, born about 5 Ma, accounts for strain partitioning between Juan de Fuca plate and the Queen Charlotte transform. 1. (d) Within the next 30 s, the summit block had slid and the lateral blast had stopped, and the vertical eruption was in full fury. North of the Vancouver Island, the Pacific plate and the much smaller Yukatat terrane have a strong northward component of motion, relative to North America, that is taken up by the Queen Charlotte-Fairweather dextral transform fault. The Cascadia subduction zone is a giant fault off the coast of the Pacific Northwest, where the Juan de Fuca tectonic plate plunges under the North American plate, building strain throughout the region and prompting fears of ‘The Big One’ when it explodes. Strait Of Juan De Fuca, Washington Depth: 42 km 2018-11-06 02:25:45 UTC 1.7 magnitude , 24 km depth Ault Field , Washington , United States We can make the same sort of assumption to locate the future trace of the San Andreas Fault half-way between the slightly divergent edges of the North American and Pacific plates. (Note that no geological, geophysical, or geodynamic information is used in making this first-order assumption. In this model, Explorer microplate, born about 5 Ma, … Schematic cross sections through Mount St. Helens showing the succession of events during the 1980 climactic eruption. 5.11, Juan de Fuca plate ends in southern Canada and the Cascadia trench is replaced by the Queen Charlotte transform fault. Figure 27 shows a generalized map of the impacts and deposits from the 1980 eruption. Trehu et al. Reproduced from Lipman, P.W., Mullineaux, D.R. Half spreading rates on its western plate boundaries are of the order of 25–35 mm/yr so that, by the time Juan de Fuca plate material reaches the Cascadia subduction plate boundary, the plate is maximally 11 Myr old. Map of western North America showing the plate tectonic configuration. The Nootka fault is the boundary between the Explorer and the Juan de Fuca plates, and Juan de Fuca plate regional seismicity and crustal age superimposed over grayscale bathymetry. (1998a). 5.11, is an active continental margin that involves three tectonic plates: the North American plate, the Pacific plate, and the Juan de Fuca plate. To these events we can add Late Pennsylvanian-Early Permian (c.300 Ma) uplift of a series of mountains from Colorado to Texas known as the Ancestral Rocky Mountains. Tectonic plates on the western coast of Canada and the United States. The unusual quakes were described as "more than 600 quakes over the past 10 days in a basin 150 miles [240 km] southwest of Newport". 19.4, is one of coastal mountains, an inland valley, and a tall, active volcanic, mountain range. For the purposes of a first-order kinematic model, assume that the future Pacific-Juan de Fuca plate boundary will be located half-way between the current boundaries as rotated over 1 Myr (Fig. USGS National Atlas digital shaded relief elevation map of the Cascadia Subduction complex. The Cascadia trench marks the subduction zone with the North American plate. The problem with landslides and avalanches high on the mountaintop is that they could result in down-valley mudflows capable of destroying towns. Commotion in the Ocean. Along this fault, the Pacific plate is moving northwestward relative to the North American plate at an approximate rate of 16.4 feet per 100 years (5 cm/year). Map showing the tectonic setting of the Gulf of California. EARTHQUAKES, FAULTS, AND PLATES As part of the investigation, H.F. Reid proposed the elastic rebound theory of earthquakes, where materials at distance on opposite sides of the fault move smoothly relative to each other, but friction on the fault “locks” each side and prevents it from slipping. 4a–c). In this case, we will use a hotspot reference frame to define the motion of each plate, with plate velocities from the HS4-EW-MORVEL56 model published in 2017 by Chengzu Wang, Richard Gordon, and Tuo Zhang, with location data compiled by Peter Bird. 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. The Gulf began to open only 5–6 million years ago and is the most recent rifting event to affect the United States. The most recent large-scale terrane accretion in the United States ended along the Washington-Oregon coast about 49 million years ago as discussed in Chapter 19. Part of the Century of Earthquakes poster. As the Pacific and North American plates diverge slightly, the remnants of the underplated Paleo-Pacific (Farallon) plate may be acting as a mechanical couple that helps drag the North American plate westward with the Pacific plate. Figure 19.2. Figure 5.12. Each year, seismologists with the Geological Survey of Canada record and locate more than 1000 earthquakes in western Canada. The San Andreas transform plate boundary continues southward as a series of transform fault segments within the Gulf of California that connect small divergent plate segments. In discussions that follow, we refer to the collection of orogenic events that created the Cordilleran Mountains as the Cordilleran orogeny. 19.1, the Juan de Fuca and Gorda segments. This plate is moving northeastward relative to North America along a convergent plate boundary such that the Juan de Fuca plate is subducting beneath the North American plate at the Cascadia trench at an approximate rate between 9.8 and 13.8 feet per 100 years. A subduction zone and an ocean basin have existed continuously off the west coast since at least the Antler orogeny. Deep reflection seismic shows that the top of the down-going Juan de Fuca plate is about 30 km beneath western Vancouver Island (Yorath et al., 1985; Hyndman et al., 1990; Cook et al., 1991). In addition, the volcanic arc to slab window transition is marked by the presence of adakites, which are volcanic rocks with compositions consistent with melting of the subducted oceanic crust. A triple junction offshore Vancouver Island is hypothesized to be evolving at the junction of Juan de Fuca Ridge and Nootka fault (Rohr and Furlong, 1995). The Juan de Fuca tectonic plate, which is off the coast of British Columbia, Washington and Oregon, is being forced underneath the North American Plate. Forearc crustal structure changes significantly along strike (Trehu et al., 1994; Flueh et al., 1998a) (Fig. The Explorer segment may no longer be subducting. The oldest rocks on the Juan de Fuca and Gorda segments are less than 10 million years old. Prior to its present-day tectonic setup, the Cordillera experienced at least five orogenic events, and similar to the Appalachians, none of the events affected the entire Cordilleran Mountain system. Instead of snapping and fracturing, it was thought that the subducting plate was deforming like warm wax. Seismic velocities are much higher than observed by Flueh et al. Moreover, except for the northernmost section of the Juan de Fuca plate, no prior seismic data were available from the central 50–250 km of the plate interior to link the lines of Nedimović et al. The bulging of the north flank is clearly shown by the pre-1980 and precollapse profiles. The Cordillera, during this time, was involved in numerous terrane accretion events, but was never involved in major continent–continent collision of the magnitude seen in the Appalachians. The arrow shows the direction of convergence. Such recent tectonic change is in contrast to the rest of the country, which has seen little tectonic change over the past several hundred million years. California has a similar landscape except that the inland mountain range (the Sierra Nevada) is not volcanic and the plate boundary is the San Andreas transform fault rather than a subduction zone. Generalized map showing the impacts and deposits of the 1980 climactic eruption in the vicinity of Mount St. Helens. Figure 5.11. The deformation may cause the plate to fragment, with the remaining un-subducted small pieces becoming attached to other plates nearby. The Cascadia Subduction Zone (CSZ) is a 1,000 km (620 mi) long dipping fault that stretches from Northern Vancouver Island to Cape Mendocino in northern California. (b) Topographic profiles along a N–S axis through Mount St. Helens’ crater showing the new lava dome relative to the south crater rim, 1980 crater floor, 1980–1986 lava dome, and 2000 glacier surface. The Juan de Fuca Plate off the coast of Washington is moving northeast compared to North America. 5.11 (or Fig. Portland lies near the Cascadia Subduction zone, where the Juan de Fuca plate is diving beneath the North American plate. Accreted terranes in the Cordillera (as well as in the Appalachians) were later dismembered and shuffled along strike-slip faults, thus complicating the collision history. The slab dips shallower compared with its counterparts to north and south, which have a dip of 65 (Harris, et al., 1991; Rasmussen and Humphreys, 1988). Modeling of 1 Myr of finite motion at the PC-NA-JF triple junction indicates growing boundary mismatches that are somewhat typical for triple junctions. Beyond 62 miles depth, the subducting plate becomes hot enough to undergo metamorphic reactions. The Juan de Fuca … New Juan de Fuca … The Mendocino triple junction marks the transition to the Juan de Fuca plate that extends north to about the southern tip of Queen Charlotte Islands; the Juan de Fuca Plate is moving eastward and is being subducted beneath North America at up to 46 mm/year relative to North America (Cascadia subduction zone). USGS Special Interest Publication, US Government Printing Office, Washington DC, 56. Smaller earthquakes, some large enough to be felt, occur on average every 5 years or so. [2] It is named after the explorer of the same name. (a) The volcano in the early morning of May 18. Google image of the north side of Mount St. Helens showing the collapse of 1980 and the numerous volcanic landslides and debris flows (no vertical exaggeration). Yes, it looks like a reasonable average of the other three. Panthalassa's oceanic plate remnants are understood to be the Juan de Fuca, Gorda, Cocos and the Nazca plates, all four of which were part of the Farallon Plate. CSZ, Cascadia Subduction Zone; MTF, Mendocino Transform Fault; SAF, San Andreas Fault. Landslides and avalanches off the slopes of Mt. If present-day plate motions continue, Los Angeles will slide northward and will reach the city of San Francisco in about 12 million years. There are several probable causes for active deformation so far inland. Transform faults in the Pacific Northwest. The general location of the PC-NA-JF triple junction shifts about 36 km to the northwest in 1 Myr, relative to the hotspot reference frame. 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