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Topic: Benioff zone

	Subduction - Wikipedia, the free encyclopedia
		It is at subduction zones that the Earth's lithosphere, oceanic crust, sedimentary layers, and trapped water are recycled into the deep mantle.
		Subduction zones are associated with the deepest earthquakes on the planet.
		Subduction Zone Biology: Because subduction zones are the coldest parts of the Earth's interior and life cannot exist at temperatures >150°C, subduction zones are almost certainly associated with the deepest (highest pressure) biosphere.
	en.wikipedia.org /wiki/Subduction_zone (1167 words)

	Subduction Zones (Site not responding. Last check: 2007-10-13)
		Benioff Zones: Earthquakes in and around deep ocean trenches are principally produced by motions on thrust faults, indicating compression (converging plates).
		The farther from the trench, the deeper the earthquakes are.
		These earthquakes of the Benioff Zone (or Wadati-Benioff Zone) occur near the upper surface of the descending plate (or slab).
	www.columbia.edu /~vjd1/subd_zone_basic.htm (514 words)

	Introduction
		The Alaska Aleutian subduction zone is characterized by the Pacific plate descending beneath the North American plate, causing an abundance in seismic activity in the crust and along the Wadati-Benioff zone.
		The Alaska subduction zone is characterized by the Pacific plate descending beneath the North American plate, causing an abundance of seismic activity in the crust and along the Wadati-Benioff zone down to a depth of approximately 200km.
		The aftershock zone of the 1938 Alaskan earthquake and the preshock event of February 6, 1964 apparently form a separate asperity to the aftershock zone of the great Alaskan earthquake of March 28, 1964, which itself is composed of two asperities, the PWS and the Kodiak asperities.
	www.geo.utep.edu /pub/wesley/proposal.htm (2793 words)

	Lifelines and earthquake hazards in the greater Seattle area
		It is at this knee where the largest Benioff zone earthquakes occur: both the 1949 event near Olympia (southwest of Tacoma) and the 1965 event near the Seattle-Tacoma International Airport occurred at the knee.
		But we expect that Benioff zone earthquakes as large as magnitude 7.5 are expected everywhere west of the eastern shores of Puget Sound.
		The Seattle fault forms the south margin of the Seattle basin; the lack of coincidence on the map between the fault zone and the buried basin margin reflects the south dip of the Seattle fault—at depth, the fault is farther south.
	geomaps.wr.usgs.gov /pacnw/lifeline/eqhazards.html (1960 words)

	Deep Quakes in Washington and Oregon
		For example, a magnitude 7.5 Benioff Zone quake beneath Oaxaca, Mexico occurred on Sept. 30, 1999.
		Benioff Zone earthquakes usually have dip-slip, or normal faulting, and no large aftershocks.
		These earthquakes are caused by mineral changes as the plate goes to deeper depths and is exposed to increased temperature and pressure.
	www.geophys.washington.edu /SEIS/PNSN/INFO_GENERAL/platecontours.html (664 words)

	Amateur Geologist Structured Geological Glossary: Plate Tectonics
		The subduction zone is the area between the two plates, somewhat like a giant reverse fault.
		A narrow zone defined by earthquake foci and tens of kilometers thick dipping from the surface under the Earth's crust.
		Zone of earthquake foci produced near the surface of and within the subducted lithosphere.
	www.amateurgeologist.com /content/glossary/tectonics/tectonics.html (1219 words)

	Washington DGER: Earthquakes
		The Cascadia subduction zone, which is the convergent boundary between the North America plate and the Juan de Fuca plate, lies offshore from northernmost California to southernmost British Columbia.
		Earthquakes are caused by the abrupt release of this slowly accumulated strain.
		Intraplate or Benioff zone earthquakes occur in the subducting Juan de Fuca plate at depths of 25-100 km.
	www.dnr.wa.gov /geology/hazards/equakes.htm (1590 words)

	subduction zone - HighBeam Encyclopedia
		subduction zone large-scaled narrow region in the earth's crust where, according to plate tectonics, masses of the spreading oceanic lithosphere bend downward into the earth along the leading edges of converging lithospheric plates where it slowly melts at about 400 mi (640 km) deep and becomes reabsorbed.
		Subduction zones are usually marked by deep ocean trenches that often exceed 6 mi (10 km) compared to the ocean's overall depth of 2 to 4 mi (3 to 5 km).
		A pattern of earthquakes of shallow, intermediate, and deep focus occurs along the same angle as the descending plate, which is steeply inclined (30°-60°) toward the continent behind the trench in a zone called the Benioff Zone, discovered by the U.S. seismologist Hugo Benioff.
	www.encyclopedia.com /doc/1E1-subducti.html (437 words)

	PACIFIC NORTHWEST - SEATTLE - THE EARTHQUAKE OF 28 FEBRUARY 2001 IN THE STATE OF WASHINGTON, U.S.- by Dr. George ...
		The epicenter, the focal depth and preliminary tensor analysis indicate that the mechanism for this earthquake was due to tensional (normal) faulting which occurred along the subducting Benioff seismic zone of the Juan de Fuca tectonic plate.
		It parallels the offshore Cascadia Subduction Zone and it is the continuation of extensive faulting that results from the same subducting San Juan de Fuca plate as it forces further its way into the earth's upper mantle, underneath the North American plate.
		Crossection of the Subducting Juan De Fuca Plate showing the distribution of deeper earthquake hypocenters (and temperatures) along the Benioff zone and the shallower hypocenters on the northern extensions of the Western Rainier and Mt. St.
	www.drgeorgepc.com /Earthquake2001USSeattle.html (1786 words)

	Convergent Margins
		Active subduction is taking place, along these convergent plate boundaries, as evidenced by the zone of earthquakes, called a Benioff Zone, that begins near the oceanic trenches and extends to deeper levels in the direction of plate motion.
		As one zone of the crystal is precipitated the liquid immediately surrounding the crystal becomes depleted in the components necessary for further growth of the same composition.
		Some zones are partially dissolved and new compositions are precipitated that are more in equilibrium with the chemical compositions, pressures, and temperatures present in the part of the magma chamber into which the crystal is transported.
	www.tulane.edu /~sanelson/geol212/converg_margins.htm (3672 words)

	FAQs on Pacific Northwest Earthquakes
		The first of these is the "Cascadia Subduction Zone", a 1000 km long thrust fault which is the convergent boundary between the Juan de Fuca and North American plates and is the most extensive fault in the Pacific Northwest area.
		This zone is the continuation of the extensive faulting that results as the subducting plate is forced into the upper mantle.
		Large subduction zone earthquakes of magnitude 7.5 or greater are the most frequent cause of tsunamis, as the vertical displacement of the sea floor along the subduction zone fault results in displacement of the water above.
	www.geophys.washington.edu /SEIS/PNSN/INFO_GENERAL/faq.html (2975 words)

	Physical Geology Notes
		Benioff zone: A zone in the upper mantle, usually beneath an oceanic trench, where a cool, brittle plate, being subducted back into the mantle, gives rise to deep earthquakes.
		subduction zone: A zone, usually an oceanic trench, where a plate is being subducted back into the mantle.
		transition zone: the region of the mantle at depths between 400 and 670 km where the seismic velocities rise continuously from the upper to the lower mantle regions.
	ruby.colorado.edu /~smyth/G101glos.html (3068 words)

	BSSA, Volume 95:5 (Site not responding. Last check: 2007-10-13)
		In the southern CSZ beneath northwestern California, a Wadati–Benioff zone is present to a depth of about 40 km, but no large Gorda block earthquakes have been observed in the downgoing slab, although large events have occurred near the trench axis.
		Based on these analyses and comparisons with other subduction zones worldwide, the lack of shallow intraslab earthquakes in the central CSZ is not unusual.
		The young plate age, slower convergence rate, and the insulating effect of the Siletz terrane above the plate are factors that probably lead to the hot temperatures in this portion of the slab.
	www.seismosoc.org /publications/BSSA_html/bssa_95-5/04132.html (503 words)

	Glossary
		A dipping planar (flat) zone of earthquakes that is produced by the interaction of a descending oceanic crustal plate with a continental plate.
		Such zone of the earth's crust, which embraces the entirety of living organisms.
		The sum total of sediment's petrographic, palaeontological characteristics, which determined by the physical, geographical, geological terms of razing and accumulating zone.
	library.thinkquest.org /03oct/00904/eng/szoj.htm (1449 words)

	Geotimes:August2001:News Notes
		In addition to the usual Benioff quakes, data from the last 35 years show a cluster of earthquakes 300 kilometers deep and several hundred kilometers west of the WBZ.
		The second piece of evidence is the slower-than-expected speed of P and S waves in the region where the unusual earthquakes occur.
		The speed of seismic waves at the mantle’s transition zone is constrained mainly by temperature and petrology.
	www.agiweb.org /geotimes/aug01/Buoyant_slabs.html (755 words)

	Convergent Margins and Subduction
		In addition, siesmicity associated with subduction zones may result in significant earthquake and tsunami hazards in contiguous areas.
		Elsewhere plate boundaries of three types exist: divergent or spreading (e.g., mid-oceanic ridges), convergent (e.g., subduction zones), and strike-slip (e.g., the San Andreas fault zone in California or oceanic transform faults).
		Convergent margins are among the world's most seismogenic zones, and are characterized by progressively deeper earthquakes as one proceeds from trench to back-arc region - at most convergent margins, these earthquake foci define a dipping plane (the Wadati-Benioff zone, or WBZ) which corresponds to a fault zone between subducting oceanic lithosphere and the overriding plate.
	www.ruf.rice.edu /~leeman/billarcmaps.html (611 words)

	Benioff Zone - John Seach
		The Benioff Zone is the active seismic zone in a subduction zone.
		The upper zone is the top of the subducting slab.
		The main Benioff Zone is 10-20 km below where deformation of the slab produces a focus of earthquakes.
	www.volcanolive.com /benioff.html (40 words)

	Wadati-Benioff zone - Wikipedia, the free encyclopedia
		A Wadati-Benioff zone (also Benioff-Wadati zone or Benioff zone) is a deep active seismic area in a subduction zone.
		The deep earthquakes along the zone allow seismologists to map the three dimensional surface of a subducting slab of oceanic crust and mantle.
		The term was named for the two seismologists, Hugo Benioff of the California Institute of Technology, and Kiyoo Wadati of the Central Meteorological Observatory of Japan who independently discovered the zones.
	en.wikipedia.org /wiki/Benioff_zone (127 words)

	High-Resolution Studies of Intraslab Seismicity.
		Such a tendency toward localization in the crust or near the crust-mantle boundary in some subduction zones is a natural outcome of the dehydration embrittlement/fault reactivation/eclogite model (Figure 2b) whereas it is less obvious how top-side slab failure might be explained solely by the generic slab model.
		Wadati-Benioff zones commonly are not continuous structures, and in many zones intraslab earthquakes are restricted to tight clusters in certain depth intervals.
		Some of these correspond to places where the Wadati-Benioff zone changes geometry rapidly and hence may accommodate the membrane deformations that evidently accompany rapid changes in slab dip [ Cahill and Isacks, 1992].
	www.agu.org /revgeophys/kirby01/node9.html (478 words)

	REDWORD (Site not responding. Last check: 2007-10-13)
		Subduction of the Pacific plate is occurring at an angle of 45 degrees to a depth of 100 to 150 km which marks t he location of the Benioff zone beneath the volcanic front and Redoubt Volcano.
		Earthquakes of the Cook Inlet region are primarily derived from the Benioff zone which consists of an upper shallow thrust portion extending from the Aleutian trench to about 50 km depth and a more steeply dipping portion reaching a maximum depth of 250 k m behind the volcanic arc.
		Seismic data reveals that the Benioff zone is well-developed, 20-30 km thick and dipping approximately 35-40 degrees beneath the Cook Inlet volcanoes.
	www.gly.uga.edu /petrology/redoubt/REDWORD.HTML (1459 words)

	Plate Tectonics
		Inclined zone of earthquake foci adjacent to oceanic trench slopes downward under the overriding plate.
		The destruction of the oceanic lithosphere caused earthquakes down to depths of 700 to 800 km (440-500 miles), explaining the presence of the deepest earthquakes adjacent to oceanic trenches.
		The term subduction zone was coined to refer to locations marked by Wadati-Benioff zones where the oceanic lithosphere is consumed adjacent to a trench.
	www.mhhe.com /earthsci/geology/mcconnell/pte/pt.htm (1066 words)

	Earthquakes
		The most famous zone of continental convergence is the Himalaya, which formed by convergence of India and Asia.
		The 1964 Alaska earthquake was a subduction zone earthquake of magnitude 9.2.
		Deeper earthquakes occur as the subducting plate descends into the mantle and is subjected to strong compressional and tensional forces.
	www.efn.org /~agrush/introgeo/Lect_9.html (1225 words)

	[No title]
		Determine the dip and depth extent of the Wadati-Benioff zone along five different subduction zone transects.
		You should select transects across a) the Tonga/Kermadec subduction zone, b) the Peru-Chile Trench subduction zone, c) the Aleutian subduction zone, d) the Kuril Trench subduction zone, e) the Java Trench subduction zone.
		Assess the hypothesis, “Narrow chains of volcanoes occur approximately 100 km over the Wadati-Benioff zone at subducting plate boundaries.” Use observations along your five transects.
	zephyr.rice.edu /department/faculty/niu/ESCI324/Lab_2.doc (754 words)

	Geology Department, University of Otago, New Zealand
		Shallow earthquakes tend to occur to the southeast of this seismic zone, while the deeper ones occur towards the northwest.
		This pattern of deeper earthquakes towards the northwest of North Island reflects the northwest dip (or slope) of the boundary between the two plates (the Benioff zone).
		The subduction zone in the north is linked to the subduction zone in the south by a series of very large faults that run through Marlborough (Marlborough Fault System) and down the west coast of South Island (Alpine Fault).
	www.otago.ac.nz /geology/features/earthquake/earthquakes.htm (513 words)

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