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Topic: Megathrust

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	Megathrust earthquake - Wikipedia, the free encyclopedia
		A megathrust earthquake is an interplate earthquake where one tectonic plate slips beneath (subducts) another.
		Due to the size of the tectonic plates and the shallow dip of the plate boundary, these earthquakes are among the world's largest, with moment magnitudes that can exceed 9.0.
		All five earthquakes since 1900 of magnitude 9 or greater have been megathrust earthquakes.
	en.wikipedia.org /wiki/Megathrust_earthquake (278 words)

	Troubled Times: Megathrust (Site not responding. Last check: 2007-11-03)
		A megathrust fault is the boundary between a subducting and an overriding plate.
		Megathrust earthquakes have never been observed in the short (~150 year) written history of the west coast of Canada, but there is compelling evidence that they did occur in prehistorical times.
		The landward extent of the rupture is an important factor for the shaking hazard at the inland cities of Victoria and Vancouver.
	www.zetatalk.com /theword/tword10p.htm (354 words)

	BBC - Science & Nature - Horizon (Site not responding. Last check: 2007-11-03)
		Megathrust earthquake only occur on a particular kind of fault.
		Heaton pointed to the existence of Native American legends that might be describing a megathrust earthquake that had happened before written records began.
		However, building to survive a megathrust earthquake is a major challenge.
	bbc.co.uk /sn/tvradio/programmes/horizon/megaquake_prog_summary.shtml (1090 words)

	Cascadia earthquake - Wikipedia, the free encyclopedia
		The 1700 Cascadia Earthquake was a magnitude 8.7 – 9.2 megathrust earthquake in 1700.
		The rate of convergence between the Juan de Fuca Plate and the North American Plate is 40 mm/yr.
		Other megathrust earthquakes are the slightly more powerful 1964 American Good Friday Earthquake measured at magnitude 9.2, the 1960 Great Chilean Earthquake measured at 9.5, and the 2004 Indian Ocean earthquake at a minimum of 9.0.
	en.wikipedia.org /wiki/Cascadia_Earthquake (529 words)

	New Tool For Predicting Mega Earthquakes
		Within subduction zones are enormous faults called megathrusts, the places where the two tectonic plates meet and interface one another.
		Megathrusts are the source of the largest and most devastating earthquakes on Earth.
		From the reflection data, Nedimovic and his coauthors mapped the locked zone on the megathrust along the northern Cascadia margin, which hosts the populous cities of Vancouver and Seattle.
	www.scienceagogo.com /news/20030711002304data_trunc_sys.shtml (1003 words)

	Implications: Tectonic Stress in the Pacific Northwest - USGS WR CMG (Site not responding. Last check: 2007-11-03)
		Measurements of uplift along coastal Washington and Oregon have been interpreted that the Cascadia megathrust is currently locked--typical of the deformation that occurs in the period between major earthquakes along a subduction zone megathrust.
		The predicted long-term uplift is significantly higher in coastal British Columbia and is ascribed to shortening of the continent perpendicular to the Queen Charlotte fault.
		An increase in the basal shear traction along the Cascadia megathrust from south to north is not necessary to explain the clockwise rotation of the compressive stress axis that is associated with the Cascade Convergence Stress Province.
	walrus.wr.usgs.gov /stress/implications.html (538 words)

	Caltech Press Release, 12/30/2004, Kerry Sieh
		The contact between the two plates is an earthquake fault, sometimes called a "megathrust." Figure 3 The two plates do not glide smoothly past each other along the megathrust but move in "stick-slip" fashion.
		The section of the subduction megathrust that runs from Myanmar southward across the Andaman Sea, then southeastward off the west coast of Sumatra, has produced many large and destructive earthquakes in the past two centuries Figure 5.
		During rupture of a subduction megathrust, the portion of Southeast Asia that overlies the megathrust jumps westward (toward the trench) by several meters, and upward by 1-3 meters (3-10 feet).
	pr.caltech.edu /media/Press_Releases/PR12628.html (835 words)

	What is a megathrust earthquake?
		The apparent inactivity within the zone of contact between the Juan de Fuca and North American plates suggests that either the two plates are locked together and are accumulating strain or that the contact zone is well lubricated and the plates are moving smoothly past each other.
		After the earthquake, the strain accumulated is released and vertical deformation results in the over-riding plate that is the reverse of that seen during stress build up.
		These phenomena could be important indications that we may be due for a megathrust quake sometime in the future.
	www.em.gov.bc.ca /Mining/Geolsurv/Surficial/quake/eq4.htm (624 words)

	Earthquake Scenario and Probabilistic Ground Shaking Maps for the Portland, Oregon, Metropolitan Area
		The scenario maps are for a moment magnitude (MW) 9.0 earthquake along the megathrust of the Cascadia subduction zone and a hypothetical MW 6.8 event on the Portland Hills fault.
		These include (1) earthquake scenario maps for a MW 9 megathrust event along the Cascadia subduction zone and a nearby crustal earthquake of MW 6.8 on the Portland Hills fault and (2) probabilistic maps for approximate return periods of 500 and 2,500 years (10% and 2% probability of exceedance in 50 years, respectively).
		The megathrust along the Cascadia subduction zone was modeled as being 1,000 km long, 115 km wide, and dipping 10° to the east.
	nwdata.geol.pdx.edu /DOGAMI/IMS-16/Text/IMS-16-CD-TEXT.html (7234 words)

	Evidence for possible precursor events of megathrust earthquakes on the west coast of North America -- Hawkes et al. ...
		Evidence for possible precursor events of megathrust earthquakes on the west coast of North America -- Hawkes et al.
		Evidence for possible precursor events of megathrust earthquakes on the west coast of North America
		Megathrust earthquakes in western North America may be preceded
	bulletin.geoscienceworld.org /cgi/content/abstract/117/7-8/996 (543 words)

	Disaster News Network: Vancouver: facing huge quake?
		Nedimovic looked at a section of the margin known as a megathrust, a region of serious seismic pressure, capable of generating massive earthquakes every few hundred years.
		In this case, seismologists have determined that this particular megathrust fires off a quake with a magnitude of 9 or greater every 200 to 800 years.
		This finding may have profound implications on disaster planning in that area, Nedimovic said — or at least he hopes it does, considering the level of danger that region will face in the future (even though he admits that could be hundreds of years in the future).
	www.disasternews.net /news/news.php?articleid=1978 (579 words)

	Seismic Reflection Data: Revealing Locations And Potentials For Mega Earthquakes -- The Earth Institute at Columbia ... (Site not responding. Last check: 2007-11-03)
		This graph from the paper published in Nature shows the locked (1), transition (2), and slow-slip (3) zones of the northern Cascadia megathrust inferred from (a), the extent and character of the megathrust reflections and (b), thermal and dislocation modeling.
		The northern Cascadia margin study was funded by the National Earthquake Hazards Reduction Program of the United States Geological Survey and by the Geological Survey of Canada.
		Mladen Nedimovic and his collaborators are submitting a proposal to National Science Foundation to carry out a megathrust seismic hazards characterization study along the southern Alaska margin.
	www.earthinstitute.columbia.edu /news/2003/story08-08-03.html (832 words)

	Preliminary Earthquake Report : Italy imc (Site not responding. Last check: 2007-11-03)
		The devastating megathrust earthquake of December 26, 2004, occurred on the interface of the India and Burma plates and was caused by the release of stresses that develop as the India plate subducts beneath the overriding Burma plate.
		Preliminary locations of larger aftershocks following the megathrust earthquake show that approximately 1200 km of the plate boundary slipped as a result of the earthquake.
		As with the recent event, megathrust earthquakes often generate large tsunamis that cause damage over a much wider area than is directly affected by ground shaking near the earthquake's rupture.
	italy.indymedia.org /mail.php?id=701949 (413 words)

	CNRS - Are silent earthquakes heralds of megathrust earthquakes in subduction zones ?
		CNRS - Are silent earthquakes heralds of megathrust earthquakes in subduction zones ?
		Recent findings obtained by different teams in two subduction zones, one in Japan, and the other in the Cascadia region (Pacific Northeast) are compared in an article published in the September 24, 2004, issue of Science by two researchers from the Department of Seismology (IPG Paris/CNRS/Université Paris 7).
		In the other subduction zones where there is no reliable record of the past occurrence of megathrust earthquakes, it is not known yet if such signals of activity might be detected, but structural exploration using seismic imaging can help locate a seismogenic segment.
	www2.cnrs.fr /en/314.htm (929 words)

	Honolulu Star-Bulletin News /2005/01/03/
		A magnitude-9.5 megathrust earthquake off the coast of Chile in 1960, the largest quake ever recorded, created a tsunami that killed 61 people on the Big Island and caused $23 million in damage.
		Other such over-under slippages that have affected Hawaii are the magnitude-9 quake in Kamchatka, Russia, in 1952, the 9.1 quake in the Andreanoff Islands, Alaska, in 1957 and the 9.2 quake in Prince William Sound, Alaska, in 1964, the U.S. Geological Survey said.
		The quake originated in a megathrust area, but some scientists feel it should not have created a tsunami because the magnitude of the quake, variously calculated at magnitude 7.1 to 7.8, was too small.
	starbulletin.com /2005/01/03/news/story4.html (479 words)

	StarIQ.com - NewsScope March 5
		Megathrust earthquakes are produced by a sudden slip between a subducting and overriding tectonic plate, and are the world's rarest and most massive earthquakes.
		The 1700 megathrust quake measured about 9.0 in magnitude and created a tsunami that swept across the Pacific Ocean to strike Japan, a timed event recorded by Japanese scholars.
		On the theory that a region's earthquakes are reactions to the megathrust earthquake as the fault lines settle and shift over the years, the megathrust earthquake can be used as a foundation horoscope and forecasting tool.
	www.stariq.com /pagetemplate/article-printer.asp?pageid=2250 (773 words)

	Sinking coastlines may precede large subduction zone quakes
		If coastal subsidence is common before subduction zone quakes, areas such as those ringing the Pacific Rim could be on the lookout for subsidence as a warning of possible future megathrust quakes like the Dec. 26 9.0 Sumatra-Andaman Islands earthquake, the researchers say.
		Seismologists estimate that the period between megathrust quakes along the Cascadia Subduction Zone, where the Pacific, Juan de Fuca and Gorda Oceanic plates creep under the North American plate, ranges from hundreds to thousands of years.
		The three sequences corresponded to megathrust quakes and tsunamis 3,000 years ago, 1,840 years ago and 1,670 years ago, though the core revealed a fourth event 300 years ago not accompanied by a tsunami but showing precursory subsidence as well as sudden subsidence due to a quake.
	www.eurekalert.org /pub_releases/2005-01/uoc--scm012005.php (1263 words)

	Aceh-Andaman earthquake What happened and what's next? : Nature
		This seemed to signal that about 25% of the Sunda megathrust, the great tectonic boundary along which the Australian and Indian plates begin their descent beneath Southeast Asia, had ruptured.
		This early controversy about the length of the megathrust rupture created a gnawing ambiguity about future dangers to populations around the Bay of Bengal.
		It seems that the section of the Sunda megathrust immediately to the south, off the coast of northern Sumatra, is now closer to failure.
	www.nature.com /nature/journal/v434/n7033/full/434573a.html (1120 words)

	On Shaky Ground 2 Why
		The megathrust is the locked boundary between them.
		The locked part of the subduction interface is known as the megathrust.
		All of the worlds greatest earthquakes (magnitude 8.5 and larger) are associated with ruptures of megathrusts.
	sorrel.humboldt.edu /~geodept/earthquakes/shaky2_why.html (846 words)

	Strain Accumulation Along the Cascadia Subduction Zone
		The geodetic networks from Cape Mendocino to the Strait of Juan de Fuca for which horizontal strain rates are measurable span almost the entire forearc region of the CSZ (Figure 24.1).
		In general, the directions and magnitudes of the strain rates are consistent with strain accumulation predicted by a megathrust that is mostly slipping at the plate convergence rate, but locked at shallow depths.
		However, we find no evidence that the megathrust is segmented by shallow regions where strain is not accumulating, so the hypothesis that the strain could be released by a single great earthquake cannot be rejected.
	seismo.berkeley.edu /annual_report/ar99_00/node28.html (1430 words)

	British Columbia Earthquake Resources & Information
		This earthquake occurred on the Cascadia Fault, the boundary between the North American and Juan de Fuca plates.
		This type of large earthquake is now known as a megathrust earthquake.
		Burried tidal marsh or coastal forest soils point to sudden land subsidence of about 1 metre occuring at the same time from Vancouver Island to Northern California.
	www.dsuper.net /~innotech/quake/1700.htm (603 words)

	Sumatran Plate Boundary Project Details Pages
		This map shows the inferred rupture area of the March 28, 2005 M 8.7 Banyak Islands earthquake with respect to large ruptures of the Sumatran megathrust in the past two centuries.
		Preliminary aftershock data show that the rupture extended from the southeastern limit of the 2004 M 9.3 Aceh/Andaman earthquake to the equator, a minimum distance of 300 km.
		Large earthquakes in 1907 and 1861 occurred along this portion of the megathrust.
	tectonics.caltech.edu /sumatra/details/sumatraBanyakEQ28march2005.html (92 words)

	Megathrust article
		In the next megathrust quake here, seismologists believe, most land from Cape Mendocino to about Coos Bay probably will be thrust up.
		The reason for the dire predictions is that megathrust subduction earthquakes do not work in the same way as quakes along vertical faults, with which Californians are all too familiar.
		While scientists know megathrust subduction quakes have occurred and must occur again, an important question remains.
	www.northcoast.com /~mbailey/MysteryoftheMegathrustarticle.htm (2719 words)

	CDNN News :: Megathrust Sumatra Earthquake Equals One Million A-Bombs
		'Megathrust' Sumatra earthquake equal to one million A-Bombs
		BANDA ACEH, Indonesia (28 Dec 2004) -- Scientists describe the devastating earthquake off the island of Sumatra as a "megathrust" — a grade reserved for the most powerful shifts in the Earth's crust.
		The term does not entirely capture the awesome power of the fourth largest earthquake since 1900, or the tsunami catastrophes it spawned for coastal areas around the Indian Ocean.
	www.cdnn.info /industry/i041228c/i041228c.html (709 words)

	Convergent Margins
		The three-dimensional structure and inferred geometric controls on the asperity of the megathrust again emphasizes the need for a grid of seismic coverage.
		Seismic imaging of the top of the subducting plate coupled with heat flow measurements and other observations have been used to delineate the seismically active part of the megathrust for seismic hazard evaluation [ Hyndman and Wang, 1993; Dragert et al., 1994].
		The igneous terrane thins dramatically to the north in the vicinity of the Puget Sound where seismicity both in the crust and on the megathrust is more commonly observed.
	www.agu.org /revgeophys/broche01/node4.html (1077 words)

	Tremors may mean 'Big One' on its way (Site not responding. Last check: 2007-11-03)
		That locked zone is where the next megathrust earthquake is expected to come from when it suddenly releases.
		But he said the slip is important because it is the only predictable event related to earthquakes, and it may hold clues as to when and where a megathrust will occur.
		That's energy being stored for the next big megathrust earthquake and on top of that regular motion we have this cycle that adds a little more stress every 14 months.
	www.freerepublic.com /focus/f-news/1486692/posts (2632 words)

	Asian Earthquake 26th Dec 2004 - How The Earthquake Affected Earth
		The Dec 26th 2004 Indonesian megathrust earthquake quickened Earth's rotation and changed our planet's shape.
		NASA scientists studying the Indonesian earthquake of Dec. 26, 2004, have calculated that it slightly changed our planet's shape, shaved almost 3 microseconds from the length of the day, and shifted the North Pole by centimeters.
		This one was not usual: The devastating megathrust earthquake registered nine on the new "moment" scale (modified Richter scale), making it the fourth largest 'quake in one hundred years.
	www.firstscience.com /SITE/ARTICLES/asianearthquake.asp (401 words)

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