The large distance between the Cascadia fault and the urban centres limits the level of shaking that the urban areas are exposed to. However, we postulate that the massive transoceanic … Repeating earthquakes (REs) rupture the same fault patches at different times allowing temporal variations in the mechanical behavior of specific areas of the fault to be interrogated over the earthquake cycle. Megathrust earthquakes occur at subduction zones at destructive convergent plate boundaries, where one tectonic plate is forced underneath another. Anchorage is about the same distance from the Alaska subduction fault. Historically, this seismic region hosted many major earthquakes, and the current national tsunami hazard assessments in Japan consider megathrust events as those having moment magnitudes between 9.0 and 9.1. No. Why? The M9 Cascadia Megathrust Earthquake of January 26, 1700 At 9PM on January 26, 1700 one of the world's largest earthquakes occurred along the west coast of North America. (A and B) Examples of MRFs for earthquakes with high and low REEF values, respectively. Since 1900, all earthquakes of magnitude 9.0 or greater have been megathrust earthquakes. Almost all the damage involved large buildings or large structures such as bridges. The term megathrust does not have a widely accepted rigorous definition, but is used to refer to an extremely large thrust fault, typically formed at the plate interface along a subduction zone such as the Sunda me… "The Gibraltar Arc seismogenic zone (part 2): Constraints on a shallow east dipping fault plane source for the 1755 Lisbon earthquake provided by tsunami modeling and seismic intensity", "Magnitude 8.9 – NEAR THE EAST COAST OF HONSHU, JAPAN 2011 March 11 05:46:23 UTC", "How 'mega-thrust" earthquake caught forecasters by surprise", https://infogalactic.com/w/index.php?title=Megathrust_earthquake&oldid=3350594, Articles with dead external links from January 2012, Creative Commons Attribution-ShareAlike License, About Infogalactic: the planetary knowledge core, Hypothesized to be part of a young subduction zone but origin still debated, The quake generated a large tsunami in the eastern, Slip length: maybe 600 and 700 km (370 and 435 mi), Slip length: maybe 700 km over (435 mi over). We can get a good example of the kinds of damage Vancouver can expect to experience if we look at what happened to Anchorage, Alaska, during the 1964 magnitude 9.2 megathrust earthquake. Where do megathrust earthquakes occur? Recent examples include the magnitude 8.8 earthquake in Chile in February 2010 and the magnitude 9.1 earthquake offshore Sumatra in December 2004; the latter triggered a devastating tsunami. Slip length: 420 and 450 km (230 and 245 mi), Slip length: maybe 600 km over (370 mi over), Slip length: 850 and 1000 km (530 and 625 mi), Slip length: 800 and 850 km (500 and 530 mi), The total vertical displacement measured by, Slip length: 1000 and 1300 km (625 and 810 mi). Destroyed Lisbon and was followed by a 20 metre high tsunami and many fires. The methodology is demonstrated by applying it to 79 global subduction zones defined in the literature, including Cascadia. All five earthquakes since 1900 of magnitude 9 or greater have been megathrust earthquakes. The areas vulnerable to tsunamis are indicated in the red-tabbed pages of the telephone books published for the coastal communities of British Columbia. Megathrust earthquakes occur at subduction zones at destructive convergent plate boundaries, where one tectonic plate is forced underneath another. The fact that there is water between Vancouver Island and the mainland is function of the current position of sea level. Since these earthquakes deform the ocean floor, they often generate a significant series of tsunami waves. These interplate earthquakes are the planet's most powerful, with moment magnitudes (M w) that can exceed 9.0.Since 1900, all earthquakes of magnitude 9.0 or greater have been megathrust earthquakes. Examples include the 2014 M w 8.2 Iquique, Chile (e.g., Ruiz et al., 2014), and the 2007 M w 8.4 Bengkulu, Sumatra, earthquakes (Konca et al., 2008). During the rupture, one side of the fault is pushed upwards relative to the other, and it is this type of movement that is known as thrust. Eventually the build-up of strain exceeds the friction between the two plates and a huge megathrust earthquake occurs. We study REs that reveal fault weakening after a large megathrust earthquake in Costa Rica, followed by fault recovery. On the Indonesian island of Sumatra, for example, a series of three mega quakes with magnitudes between 7,9 … A silent and periodic earthquake trigger. The largest recorded megathrust earthquake was the 1960 Valdivia earthquake, estimated magnitude 9.4-9.6, centered off the coast of Chile along the Peru-Chile trench, where the Nazca Plate is subducting under the South American Plate. [1] They are one type of dip-slip faults. This includes examples such as subduction of a young ridge at a triple junction where a great earthquake struck in the Solomon Islands in 2007 (e.g., Taylor et al., 2008; Abstract. [2] Oblique-slip faults have significant components of different slip styles. From Infogalactic: the planetary knowledge core, Geophysical literature search showing almost 200 papers with the word "megathrust" in the title. Stresses in subduction zones are found to be low, although the smaller amount of stress can still lead to a great earthquake. No other type of known terrestrial source of tectonic activity has produced earthquakes of this scale. However, the duration of shaking for a megathrust earthquake is much longer. Fig. Most people don't associate the US Pacific Northwest with earthquakes, but maybe they should. The term megathrust does not have a widely accepted rigorous definition, but is used to refer to an extremely large thrust fault, typically formed at the plate interface along a subduction zone such as the Sunda megathrust.[3][4]. Inland earthquakes, which are not as big but can be much closer to our urban areas and occur much more frequently, are our biggest earthquake hazard. These subduction zones are not only responsible for megathrust earthquakes, but are also largely responsible for the volcanic activity associated with the Pacific Ring of Fire. A megathrust earthquake occurs at subduction zones at destructive convergent plate boundaries, where one tectonic plate is forced underneath another. Because of a fast convergence rate (4–6 cm/yr) and a young buoyant lithosphere, the subducting Philippine Sea plate and the overriding Eurasian plate are strongly coupled in the forearc region along the upper boundary of the subducting plate. The damage pattern would be very different. These gaps may be related to potential sources of future megathrust ea … The stresses are the forces acting on the subduction zone fault system, and are the forces that drive the earthquakes. The amount of energy released increases about 40 times every time there is an increase of one unit on the magnitude scale. Megathrust faults in subduction zones cause large and damaging earthquakes. In most of these zones a continental plate is overriding an oceanic plate because the oceanic plate is heavier and colder. Part of a series on earthquakes Types Foreshock • Aftershock • Blind thrust Doublet • Interplate • 2019), and the coupling between rupture propagation and tsunami generation (Lotto et al. Fig. 2 Examples of MRFs and REEF. That is about one million small earthquakes a day, every day, for 500 years. [2] Oblique-slip faults have significant components of different slip styles. In the Cascadia subduction zone 13 megathrust events have been identified in the last 6000 years, an average one every 500 to 600 years. An example of a megathrust earthquake is the M9.0 Tōhoku Earthquake that occurred off the coast of Japan in 2011. Megathrust earthquakes occur at subduction zones at destructive plate boundaries (convergent boundaries), where one tectonic plate is subducted (forced underneath) by another. Subduction-zone megathrust earthquakes, the most powerful earthquakes in the world, can produce tsunamis through a variety of structures that are missed by simple models including: fault boundary rupture, deformation of overlying plate, splay faults and landslides. • Pop-up extrusion is a mechanism that efficiently generate large seafloor uplift. Since 1900, all earthquakes of magnitude 9.0 or greater have been megathrust earthquakes. Questions and Answers on Megathrust Earthquakes. Find the best essay sample on Megathrust Earthquake in our leading paper example online catalog! Tsunami earthquakes trigger oversize tsunami waves (e.g. The undersea Cascadia thrust fault ruptured along a 1000 km length, from mid Vancouver Island to northern California in a great earthquake, producing tremendous shaking and a huge tsunami that swept across the Pacific. At 9PM on January 26, 1700 one of the world's largest earthquakes occurred along the west coast of North America. The two plates are continually moving towards one another, yet become "stuck" where they are in contact. 3a) indicate that $$\Delta {\text{CFS}}$$ exceeds the previous maximum 30 years and 46 years before the megathrust earthquake, respectively. The Cascadia subduction zone is located off the west coast of North America. The limited historical records we do have indicate that no megathrust earthquake has ruptured beneath Dhaka since 1610. The size of circles and stars is scaled with the earthquake seismic magnitude. A megathrust earthquake in Chile in 1960 was magnitude 9.5, and one in Alaska in 1964 was magnitude 9.2. Subduction-zone megathrust earthquakes, the most powerful earthquakes in the world, can produce tsunamis through a variety of structures that are missed by simple models including: fault boundary rupture, deformation of overlying plate, splay faults and landslides. The Cascadia fault, on which megathrust earthquakes occur, is located mostly offshore, west of Vancouver Island, Washington, and Oregon, although it does extend some distance beneath the Olympic Peninsula of Washington State. These interplate earthquakes are the planet's most powerful, with moment magnitudes (M w) that can exceed 9.0. Even though it … For example, the 2004 magnitude (M) 9.2 megathrust earthquake in Sumatra generated a tsunami that propagated across the Indian Ocean Basin, killing more than 230,000 people in coastal areas. Megathrust earthquake are the world's largest earthquakes. Bletery et al. These interplate earthquakes are the planet's most powerful, with moment magnitudes that can exceed 9.0. Examples of dextral faults at the distance are 150 and 300 km from the distance from the megathrust fault (Fig. The methodology is demonstrated by applying it to 79 global subduction zones defined in the literature, including Cascadia. 2 Examples of MRFs and REEF. Megathrust earthquakes occur at subduction zones at destructive convergent plate boundaries, where one tectonic plate is forced underneath another, caused by slip along the thrust fault that forms the contact between them. Large earthquakes that hit places such as Japan seem to be preceded by subtle and silent deformation. The key parameter is the curvature of the megathrust. Therefore, we are now in the risk zone of another earthquake. Bletery et al. An example of this full cycle of outer rise faulting behavior was observed in the Kuril Islands; the region oceanward of the trench adjacent to the 2006 earthquake hosted thrust faulting events prior to 2006, normal faulting events for the two years after the earthquake, and by 2009 was back to hosting thrust faulting earthquakes (Lay et al., 2009). That level of earthquake activity is not observed. The recurrence time varies from subduction zone to subduction zone. (C) Observed radiated energy E R versus calculated minimum radiated energy E R_min for 119 global large megathrust earthquakes from 1990 to 2016.Red stars indicate tsunami earthquakes. Just the coast exposed to the open Pacific is vulnerable to damaging tsunamis waves. Megathrust earthquakes are almost exclusive to tectonic subduction zones and are often associated with the Pacific and Indian Oceans. Megathrust faults in subduction zones cause large and damaging earthquakes. Relocation of earthquakes recorded by the agency for meteorology, climatology and geophysics (BMKG) in Indonesia and inversions of global positioning system (GPS) data reveal clear seismic gaps to the south of the island of Java. Major population centers in the northwest U.S. and Japan are examples of the regions that face seismic risk from subduction zones. Subduction zone megathrust faults produce most of the world's largest earthquakes. ... will help inform future earthquake models. show that these “slow-slip events” are quasi-periodic in the megathrust zone in Japan. Where have megathrust earthquakes happened? It's home to the 600-mile (1,000-km) Cascadia megathrust fault, … No. (A and B) Examples of MRFs for earthquakes with high and low REEF values, respectively. Thus, if we consider a small earthquake at the felt level, about magnitude 2, there would have to be 40x40x40x40x40x40x40 of these earthquakes to release the amount of energy as one magnitude 9 event. Megathrust earthquakes happen at subduction zones, where one tectonic plate is being pushed under another. argue that certain geometric features of the subduction zones relate to earthquake size. • In the 2010 rupture area conjugate thrusts bound pop-ups branched on the megathrust, • Propagation of coseismic slip onto the thrusts generates extrusion of pop-ups. Examples of megathrust earthquakes are listed in the following table. There is a 1 in 4 chance that we’ll experience a major earthquake in the next 50 years, and a 1 in 10 chance that it will be a megathrust (usually a magnitude 9+). The landslide deposits can be recognized in core samples taken from the ocean floor. How do we explain the occurrence of moderate to large earthquakes in the middle of patches that have, by this simple model, been forecast to produce great earthquakes? These interplate earthquakes are the planet's most powerful, with moment magnitudes that can exceed 9.0. The deformation of the crust in a predictable pattern can be detected by very careful geodetic measurements using Global Positioning Satellites, precise levelling, micro-gravity measurements and changing distance measurements using laser technology. show that these “slow-slip events” are quasi-periodic in the megathrust zone in Japan. Small buildings generally had little or no damage, unless they were affected by landsliding. Scientists say the major Chile earthquake last month was a "megathrust," similar to the 2004 Indian Ocean temblor that triggered a catastrophic tsunami. During the rupture, one side of the fault is pushed upwards relative to the other, and it is this type of movement that is known as thrust. Some have been as close together as 200 years and some have been as far apart as 800 years. The last Cascadia earthquake is estimated at magnitude 9. The amount of shaking at a location depends on an earthquake's magnitude, the distance between the location and the earthquakes 's source, and local geology. Since 1900, all earthquakes of magnitude 9.0 or greater have been megathrust earthquakes Megathrust earthquakes occur at subduction zones at destructive plate boundaries (convergent boundaries), where one tectonic plate is subducted (forced underneath) by another. Vancouver Island is part of the North American plate. 1737 Kamchatka earthquake (magnitude 9-9.3) — Pacific Plate sub-ducting beneath the Okhotsk Plate, duration 15 minutes, depth 40 km. Great megathrust earthquakes have also now been observed to have trig- gering interactions with great intraplate faulting (e.g., Ammon et al., 2008; Lay et al., 2010b, 2017), and cascading failures on the relevant megathrust (e.g., Lay Around the Pacific Ocean is a horseshoe shaped area that contains subduction zones that create megathrust earthquakes and generate tsunamis. A megathrust Pacific Northwest earthquake would shake tall Lower Mainland buildings harder than currently believed, a new UBC study says. Since 1900, all earthquakes of magnitude 9.0 or greater have been megathrust earthquakes. According to structural and earthquake engineering Prof. Carlos Molina Hutt, it’s because the Lower Mainland region lies above the Georgia sedimentary basin, which is made up of layers of glacial and river sediments sitting on top of sedimentary rock. We can get a good example of the kinds of damage Vancouver can expect to experience if we look at what happened to Anchorage, Alaska, during the 1964 magnitude 9.2 megathrust earthquake. If that were a lottery, most people would play the odds. Slow-slip events occurred every 1 to 6 years and frequently were correlated with large earthquakes, including the great 2011 Tohoku-oki earthquake. Rare, slow-rupturing tsunami earthquakes are known to occur in the shallowest megathrust environment that both slows rupture propagation and enhances tsunami potential, while other megathrust earthquakes remain deeper, rupturing more rapidly and having reduced tsunami potential due to diminished vertical seafloor displacement. A megathrust earthquake occurs in subduction zones at convergent boundaries. Megathrust roughness and structural complexity are thought to be controls on earthquake slip at subduction zones because they result in heterogeneity in shear strength and resolved stress. Large interplate megathrust earthquakes occurred in the Nankai subduction zone off Southwest Japan with an interval of ~100 to 150 years. The near-trench region of the megathrust was once considered to be an unlikely area to host large coseismic slip because of unfavorable frictional conditions, yet examples such as the massive coseismic slip in the near-trench region of the 2011 Tohoku earthquake (e.g., Lay et al., 2011b; Ide et al., 2011; Ozawa et al., 2012; Iinuma et al., 2012) provide dramatic evidence to the contrary. In this article, I propose a method for estimating the magnitude (M B) at which subduction megathrust earthquakes are expected to exhibit a break in magnitude scaling of both seismic source dimensions and earthquake ground motions. cations for Cascadia megathrust earthquake rupture scenarios. The Kobe earthquake was right beneath the city and the megathrust earthquake will be about 150 kilometres from Vancouver. Some examples of megathrust earthquakes are: 1700 Cascadia Earthquake (magnitude 9.0) — Juan de Fuca Plate subducting under the North American Plate, slip length 1000 km (625 mi). Megathrust earthquake are the world's largest earthquakes. The team fed computer models with near-real-time data – collected via Global Positioning System ... Japan, or Indonesia. 1 The 2011 M9.0 Tohoku earthquake in Japan was the most costly natural disaster in history at up to \$235 billion (World Bank, 2011). the M w 7.8, 2010 Mentawai). (C) Observed radiated energy E R versus calculated minimum radiated energy E R_min for 119 global large megathrust earthquakes from 1990 to 2016.Red stars indicate tsunami earthquakes. A megathrust earthquake cycle ends. Megathrust earthquakes that occur repeatedly along the plate interface of subduction zones can cause severe damage due to strong ground motion and the destructive tsunamis they can generate. The last Cascadia earthquake is estimated at magnitude 9. This long duration can result in damage to some types of buildings that might not be damaged at the same strength of shaking produced by a smaller earthquake. Megathrust earthquakes happen at subduction zones, where one tectonic plate is being pushed under another. No. In Japan, the Nankai megathrust under the Nankai Trough is responsible for Nankai megathrust earthquakes and associated tsunamis. In this article, I propose a method for estimating the magnitude (M B) at which subduction megathrust earthquakes are expected to exhibit a break in magnitude scaling of both seismic source dimensions and earthquake ground motions. Nankai–Tonankai megathrust earthquakes and tsunamis pose significant risks to coastal communities in western and central Japan. "The last megathrust earthquake originating from the Cascadia subduction zone occurred in 1700 A.D. From mid Vancouver Island to northern California the Juan de Fuca Plate is subducting beneath the North American Plate. Chile Earthquake 'Megathrust': Worst Type Of Quake Per Scientists "It was a truly enormous "megathrust" earthquake, shallow and offshore," Sheehan told Universe Today. A thrust fault is a reverse fault with a dip of 45° or less. It can be several minutes. Larger earthquakes occur where the subducting slab is flatter, providing a rough metric for estimating where mega-earthquakes may occur in the future. Because of a fast convergence rate (4–6 cm/yr) and a young buoyant lithosphere, the subducting Philippine Sea plate and the overriding Eurasian plate are strongly coupled in the forearc region along the upper boundary of the subducting plate. Megathrust earthquakes occur at subduction zones at destructive convergent plate boundaries, where one tectonic plate is forced underneath another. This page was last modified on 2 January 2016, at 02:01. We hear a lot about the next Megathrust Earthquake, or ‘Big One’ that BC is due to experience. It takes many, many small earthquakes to release the amount of energy equivalent to a large earthquake. Some examples of megathrust earthquakes are: 1700 Cascadia Earthquake (magnitude 9.0) — Juan de Fuca Plate subducting under the North American Plate, slip length 1000 km (625 mi). A megathrust earthquake occurs at subduction zones at destructive convergent plate boundaries, where one tectonic plate is forced underneath another. We study REs that reveal fault weakening after a large megathrust earthquake in Costa Rica, followed by fault recovery. No. An example of a megathrust earthquake is the M9.0 Tōhoku Earthquake that occurred off the coast of Japan in 2011. These interplate earthquakes are the planet's most powerful, with moment magnitudes (Mw) that can exceed 9.0. Megathrust Earthquake. Larger earthquakes occur where the subducting slab is flatter, providing a rough metric for estimating where mega-earthquakes may occur in the future. The key parameter is the curvature of the megathrust. Although it is known that the slip distribution on a … No. have included great earthquakes striking in regions lacking any known prior great event and having disrupted subduction zone structure. Examples of megathrust earthquakes are listed in the following table. Slow-slip events occurred every 1 to 6 years and frequently were correlated with large earthquakes, including the great 2011 Tohoku-oki earthquake. Megathrust earthquakes also cause underwater landslides off the continental shelf into the deep ocean. They are known to produce intense shaking for periods of time that can last for up to a few minutes. Megathrust earthquakes and subsequent tsunamis that originate in subduction zones like Cascadia — Vancouver Island, Canada, to northern California — are some of the most severe natural disasters in the world. The sudden submergence of the outer coast when a megathrust earthquake occurs kills vegetation which can be dated. Large interplate megathrust earthquakes occurred in the Nankai subduction zone off Southwest Japan with an interval of ~100 to 150 years. The last one was 300 years ago. 2018). Subduction zone megathrust faults produce most of the world’s largest earthquakes. The amount of shaking at a location depends on an earthquake's magnitude, the distance between the location and the earthquakes 's source, and local geology. These interplate earthquakes are the planet's most powerful, with moment magnitudes (Mw) that can exceed 9.0. We developed a set of scenario earthquakes to evaluate tsunami hazards and tsunami early warning systems for such devastating earthquakes. However, the west coast of Vancouver Island will drop as much as a metre or two when the next megathrust earthquake occurs. These interplate earthquakes are the planet's most powerful, with moment magnitudes (Mw) that can exceed 9.0. A thrust fault is a reverse fault with a dip of 45° or less. The undersea Cascadia thrust fault ruptured along a 1000 km length, from mid Vancouver Island to northern California in a great earthquake, producing tremendous shaking and a huge tsunami that swept across the Pacific. The three following papers in this issue focus on the physics of megathrust earthquake ruptures by investigating the role of frictional properties on rupture style (Senatorski 2019), the role of geometrical segment boundaries on the down-dip segmentation of the megathrust (Ong et al. Due to the shallow dip of the plate boundary, which causes large sections to get stuck, these earthquakes are among the world's largest, with moment magnitudes that can exceed 9.0. Uchida et al. The damage pattern would be very different. These interplate earthquakes are the planet's most powerful, with moment magnitudes (M w) that can exceed 9.0.Since 1900, all earthquakes of magnitude 9.0 or greater have been megathrust earthquakes. Due to the shallow dip of the plate boundary, which causes large sections to get stuck, these earthquakes are among the world's largest, with moment magnitudes that can exceed 9.0. News on Earthquakes. Uchida et al. Due to the shallow dip of the plate boundary, which causes large sections to get stuck, these earthquakes are among the world's largest, with moment magnitudes that can exceed 9.0. The thrusting motion of megathrust earthquake causes large vertical movement on the sea floor and this displaces a large volume of water which travels away from the undersea motion as a tsunami. For example, as the ˚= 0 locking depth from the Burgette model is mostly oshore, it would indicate entirely free sliding further downdip where no seismic slip would propagate into. Megathrust earthquakes occur at subduction zones where one tectonic plate is forced underneath another. For example, Uyeda & Kanamori ... , we also find that many historical megathrust earthquakes are associated with broadly planar areas of subduction zones. Large earthquakes that hit places such as Japan seem to be preceded by subtle and silent deformation. The major subduction zone is associated with the Pacific and Indian Oceans and is responsible for the volcanic activity associated with the Pacific Ring of Fire. • Megathrust earthquakes occur at subduction zones at destructive convergent plate boundaries, where one tectonic plate is forced underneath another, caused by slip along the thrust fault that forms the contact between them. argue that certain geometric features of the subduction zones relate to earthquake size. Re-evaluation of Mw of the 1707 Hoei earthquake. The largest earthquakes on Earth occur at the interface between the two plates, called the megathrust. The Kobe earthquake was right beneath the city and the megathrust earthquake will be about 150 kilometres from Vancouver. Megathrust earthquakes occur at subduction zones at destructive convergent plate boundaries, where one tectonic plate is forced underneath another. Examples from other r egions reveal a ... we investigate the potential for megathrust earthquakes and consequent tsunamis south of western Java through relocation of earthquake … The size of circles and stars is scaled with the earthquake seismic magnitude. Now a team of geoscientists thinks the key to understanding some of these destructive events may lie in the deep, gradual slow-slip behaviors beneath the subduction A megathrust earthquake is a very large earthquake that occurs in a subduction zone, a region where one of the earth's tectonic plates is thrust under another. Repeating earthquakes (REs) rupture the same fault patches at different times allowing temporal variations in the mechanical behavior of specific areas of the fault to be interrogated over the earthquake cycle. They're particularly common around the Pacific and Indian Oceans, and they can also lead to gigantic tsunamis. Societal Issue: Uncertainty related to rupture extent, slip distribution, and recurrence of past subduction megathrust earthquakes in the Pacific Northwest (northern CA, OR, WA, and southern BC) leads to ambiguity in earthquake and tsunami hazard assessments and hinders our … The three following papers in this issue focus on the physics of megathrust earthquake ruptures by investigating the role of frictional properties on rupture style (Senatorski 2019), the role of geometrical segment boundaries on the down-dip segmentation of the megathrust (Ong et al. Earthquake Megathrust Subduction ABSTRACT Recent earthquakes in Chile, 2014, Mw 8.2 Iquique, 2015, Mw 8.3 Illapel and 2016, Mw 7.6 Chiloé have put in evidence some problems with the straightforward application of ideas about seismic gaps, earthquake periodi-city and the general forecast of large megathrust earthquakes. Earthquake shaking, in the frequencies that damage buildings, increases to a maximum between a magnitude 7 and 8 earthquake, then the shaking simply involves a bigger area. Summary:Megathrust earthquakes and subsequent tsunamis that originate in subduction zones like Cascadia -- Vancouver Island, Canada, to northern California -- are some of the most severe natural disasters in the world. The magnitude scale and one in Alaska in 1964 was magnitude 9.2 zone fault system and! Can be recognized in core samples taken from the Alaska subduction fault occurs at subduction zones at convergent. 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