DOCSLIB.ORG

Subduction Zones”

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Subduction Zones” EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Open Access Open Access Biogeosciences Biogeosciences Discussions Open Access Open Access Climate Climate of the Past of the Past Discussions Open Access Open Access Earth System Earth System Dynamics Dynamics Discussions Open Access Geoscientific Geoscientific Open Access Instrumentation Instrumentation Methods and Methods and Data Systems Data Systems Discussions Open Access Open Access Geoscientific Geoscientific Model Development Model Development Discussions Open Access Open Access Hydrology and Hydrology and Earth System Earth System Sciences Sciences Discussions Open Access Open Access Ocean Science Ocean Science Discussions Open Access Solid Earth, 4, 129–133, 2013 Open Access www.solid-earth.net/4/129/2013/ Solid Earth doi:10.5194/se-4-129-2013 Solid Earth Discussions © Author(s) 2013. CC Attribution 3.0 License. Open Access Open Access The Cryosphere The Cryosphere Discussions Introduction to the special issue on “Subduction Zones” S. J. H. Buiter1,2, F. Funiciello3, and J. van Hunen4 1Geological Survey of Norway, Geodynamics Team, Leiv Eirikssons vei 39, 7040 Trondheim, Norway 2University of Oslo, The Centre for Earth Evolution and Dynamics, 0316 Oslo, Norway 3Universita` Roma Tre, Dipartimento di Scienze, L.go S. Leonardo Murialdo 1, 00146, Rome, Italy 4Durham University, Department of Earth Sciences, Durham DH1 3LE, UK Correspondence to: S. J. H. Buiter ([email protected]) 1 The subduction process dip, nature of the overriding plate, back-arc tectonic regime, behaviour at the 660 km-discontinuity, seismicity, and vol- canic productivity of the arc (e.g., Jarrard, 1986; Pacheco et The discoveries in the previous century of continental drift, al., 1993; Heuret and Lallemand, 2005; Acocella and Funi- convection in Earth’s mantle, and the formation of oceanic ciello, 2009; Heuret et al., 2011; Hayes et al., 2012). lithosphere at mid-ocean ridges set the stage for the reali- Subduction is a complex dynamic process, which occurs sation that oceanic material is continuously recycled back over long timescales and to large depths and integrates small- into the mantle (e.g., Wegener, 1918; Holmes, 1931; Run- scale with large-scale phenomena. This process can, there- corn, 1956; Hess, 1962; Vine and Matthews, 1963; Wilson, fore, only be understood by adopting a multidisciplinary ap- 1966). This idea is also confirmed by evidence that no in situ proach integrating geological observations and geophysical oceanic lithosphere older than ca. 270 Ma exists on Earth imaging of regions of past and present subduction, with geo- (Muller¨ et al., 2008; Fig. 1a). The process of sinking of cold chemical fingerprinting of materials recycled in the subduc- oceanic lithosphere into the mantle, occurring at convergent tion system, and studies of subduction dynamics in space and margins, is called subduction. time. The direct association with devastating earthquakes and Subduction is not only responsible for mixing surface ma- active volcanism signifies a social need for an understand- terial back to the deep Earth and introducing significant ing of all aspects of this process. Decades of research have chemical variation back into the mantle (Christensen and furthered our understanding of the large-scale kinematics of Hofmann, 1994), but also for driving plate motions (Forsyth subduction processes and the close links between subducting and Ueda, 1975), mountain building and the growth of new lithosphere, mantle flow, and surface deformation. However, continental crust (Davidson and Arculus, 2006). Subduction past research has made it very clear that several fundamen- also deeply modifies the thermal structure of the mantle and tal questions remain unanswered. We therefore considered it accounts for arc volcanism, in addition to causing substan- timely to bring together a selection of papers that highlight tial surface (vertical and horizontal) deformations and re- the current state of subduction research. leasing most of the seismic energy of the Earth. The sub- duction process plays, therefore, a key role in the geody- namical and geochemical phenomena that shape our Earth 2 The Subduction Zones special issue and, for this reason, has led to a more-than-average atten- tion from the Earth Science community. But, despite these In this special issue we follow the subducting lithosphere on efforts, subduction still holds many enigmas and open ques- its journey from the surface to the lower mantle (Fig. 1b). tions. The most important are embedded in the lack of a Using tomographic imaging, numerical modelling, and field common behaviour of global subduction zones (e.g., Uyeda observations, the contributing articles outline several chal- and Kanamori, 1978). Some subduction zones are long-lived, lenges in the subduction system. In the text below, references such as the Andes subduction zone, which is over 100 million to articles in the special issue are in italics. years old, whereas others have just initiated, such as the New Subduction zones are associated with thrust earthquakes Hebrides and Puysegur subduction zones. Present-day sub- on the interplate contact and with intermediate-to-deep slab duction zones are also diverse in terms of trench motion, slab seismicity, posing a serious threat to communities living Published by Copernicus Publications on behalf of the European Geosciences Union. 130 S. J. H. Buiter et al.: Introduction “Subduction Zones” Steinberger et al.; a) Warren van Keken et al. Ramachandran Tavani & Hyndman Bottrill et al. Tong et al. Jaxybulatov et al. Subduction zone Age of ocean crust Continent Continental shelf 0 50 100 150 200 250 Ma b) Trench 1 Arcay (2012); Ramachandran & Hyndman (2012) 1 5 2 Tong et al. (2012); 2 van Keken et al. (2012) 4 3 3 Bentson & van Keken (2012) 4 Warren (2013) 410 km 5 Li & Hampel (2012); Tavani (2012) 6 Bottrill et al. (2012); 660 km 6 Magni et al. (2012); Jaxybulatov et al. (2013) Slab 7 Chertova et al. (2012); 7 Steinberger et al. (2012) Fig. 1. (a) Map of present-day subduction systems, and (b) schematic subduction zone cross-section with areas of study of the Subduction Zones special issue indicated as dashed boxes. Age of ocean crust from Muller¨ et al. (2008). close to these convergent regions (Fig. 1a). Previous stud- elling results with observations, it suggests a moderate-to- ies have found that faults in the upper part of a subduc- strong viscosity reduction of the asthenosphere due to meta- tion zone are susceptible to changes in ice and water loads somatism of the mantle wedge. (e.g., Chochran et al. 2004; Luttrell and Sandwell, 2010). Li The thermal structure of a subduction system is important and Hampel (2012) use 2-D finite element models to show for understanding subduction seismicity, slab dehydration, that glacial–interglacial sea level variations can be responsi- arc volcanism and geochemistry. Bengtson and van Keken ble for significant stress variations within convergent plates (2012) investigate to which extent the common approach of and, in turn, for the earthquake cycle of subduction thrust using 2-D cross-sections provides a reasonable image of the faults. Earthquakes are promoted during sea-level fall and 3-D system. 3-D numerical models of the thermal structure delayed during sea-level rise. Arcay (2012) finds that sub- and the flow regime in the mantle wedge show that 2-D cross- duction interplate dynamics are strongly dependent on both sections are reasonable for arcs that have minor along-strike ductile and brittle strength parameters. The evolution of the variations. However, a full 3-D model is unavoidable to sim- depth of the brittle-to-ductile transition and the kinematic de- ulate strongly curved subduction systems, such as the Mar- coupling depth along the subduction interface are both in- ianas, where significant 3-D mantle flow is induced in the fluenced by the interplate friction coefficient and the mantle mantle wedge by the subduction process. wedge strength. When comparing the thermochemical mod- Solid Earth, 4, 129–133, 2013 www.solid-earth.net/4/129/2013/ S. J. H. Buiter et al.: Introduction “Subduction Zones” 131 When an oceanic basin closes and continental lithosphere raphy to constrain fluids released from the young and hot enters a subduction zone, the positive buoyancy of the conti- Cascadia subducting lithosphere. The seismic velocities indi- nental crust will resist subduction, leading to a slow-down, cate substantial amounts of serpentinite in the forearc mantle, and ultimately to the end of subduction (e.g., McKenzie, lending itself towards weakness, which has important conse- 1969). Continental collision is accompanied by severe crustal quences for earthquake potential and collision tectonics. Sig- and lithospheric deformation, mountain building, slab break- nificant silica deposition at the base of the lower crust makes off, metamorphism, and the exhumation of high and ultra- it a primary contributor to the average composition of the high pressure [(U)HP] rocks. Warren (2013) reviews mech- continental crust. The Pacific slab subducting under north- anisms to subduct continental crust to (U)HP conditions and east Japan is an example of a cold subduction system due exhume the rocks back to Earth’s surface. The record of ex- to the high convergence rate and old age of the subducting humation is complicated by the fact that exhumation mecha- lithosphere. Tong et al. (2012) present P- and S-wave seis- nisms may change in time and space within the same subduc- mic tomography that image fluids released from dehydration tion zone. Buoyancy and external tectonic forces drive ex- of the subducting Pacific lithosphere under the 2011 Iwaki humation, but the changing spatial and temporal dominance earthquake area and Fukushima nuclear power plant location.
Load more

Recommended publications
  • Ocean Trench
    R E S O U R C E L I B R A R Y E N C Y C L O P E D I C E N T RY Ocean trench Ocean trenches are long, narrow depressions on the seafloor. These chasms are the deepest parts of the ocean—and some of the deepest natural spots on Earth. G R A D E S 5 - 12+ S U B J E C T S Earth Science, Geology, Geography, Physical Geography C O N T E N T S 11 Images, 1 Video, 2 Links For the complete encyclopedic entry with media resources, visit: http://www.nationalgeographic.org/encyclopedia/ocean-trench/ Ocean trenches are long, narrow depressions on the seafloor. These chasms are the deepest parts of the ocean—and some of the deepest natural spots on Earth. Ocean trenches are found in every ocean basin on the planet, although the deepest ocean trenches ring the Pacific as part of the so-called “Ring of Fire” that also includes active volcanoes and earthquake zones. Ocean trenches are a result of tectonic activity, which describes the movement of the Earth’s lithosphere. In particular, ocean trenches are a feature of convergent plate boundaries, where two or more tectonic plates meet. At many convergent plate boundaries, dense lithosphere melts or slides beneath less-dense lithosphere in a process called subduction, creating a trench. Ocean trenches occupy the deepest layer of the ocean, the hadalpelagic zone. The intense pressure, lack of sunlight, and frigid temperatures of the hadalpelagic zone make ocean trenches some of the most unique habitats on Earth.
    [Show full text]
  • Geologists Suggest Horseshoe Abyssal Plain May Be Start of a Subduction Zone 8 May 2019, by Bob Yirka
    Geologists suggest Horseshoe Abyssal Plain may be start of a subduction zone 8 May 2019, by Bob Yirka against one another. Over by the Iberian Peninsula, the opposite appears to be happening—the African and Eurasian plates are pulling apart as the former creeps east toward the Americas. Duarte noted that back in 2012, other researchers conducting seismic wave tests found what appeared to be a dense mass of unknown material beneath the epicenter of the 1969 quake. Some in the field suggested it could be the start of a subduction zone. Then, last year, another team conducted high-resolution imaging of the area and also found evidence of the mass, confirming that it truly existed. Other research has shown that the area just above the mass experiences routine tiny earthquakes. Duarte suggests the evidence to date indicates that the bottom of the plate is peeling away. This could happen, he explained, due to serpentinization in which water percolates through plate fractures and reacts with material beneath the surface, resulting A composite image of the Western hemisphere of the in the formation of soft green minerals. The soft Earth. Credit: NASA mineral layer, he suggests, is peeling away. And if that is the case, then it is likely the area is in the process of creating a subduction zone. He reports that he and his team members built models of their A team of geologists led by João Duarte gave a ideas and that they confirmed what he suspected. presentation at this past month's European The earthquakes were the result of the process of Geosciences Union meeting that included a birthing a new subduction zone.
    [Show full text]
  • 3.16 Oceanic Plateaus A.C.Kerr Cardiffuniversity,Wales,UK
    3.16 Oceanic Plateaus A.C.Kerr CardiffUniversity,Wales,UK 3.16.1 INTRODUCTION 537 3.16.2 FORMATION OF OCEANIC PLATEAUS 539 3.16.3 PRESERVATIONOFOCEANIC PLATEAUS 540 3.16.4GEOCHEMISTRY OF CRETACEOUSOCEANICPLATEAUS 540 3.16.4.1 GeneralChemicalCharacteristics 540 3.16.4.2 MantlePlumeSource Regions ofOceanic Plateaus 541 3.16.4.3 Caribbean–ColombianOceanic Plateau(, 90 Ma) 544 3.16.4.4OntongJavaPlateau(, 122 and , 90 Ma) 548 3.16.5THE INFLUENCE OF CONTINENTALCRUST ON OCEANIC PLATEAUS 549 3.16.5.1 The NorthAtlantic Igneous Province ( , 60 Ma to Present Day) 549 3.16.5.2 The KerguelenIgneous Province ( , 133 Ma to Present Day) 550 3.16.6 IDENTIFICATION OF OCEANIC PLATEAUS IN THE GEOLOGICAL RECORD 551 3.16.6.1 Diagnostic FeaturesofOceanic Plateaus 552 3.16.6.2 Mafic Triassic Accreted Terranesinthe NorthAmericanCordillera 553 3.16.6.3 Carboniferous to CretaceousAccreted Oceanic Plateaus inJapan 554 3.16.7 PRECAMBRIAN OCEANICPLATEAUS 556 3.16.8ENVIRONMENTAL IMPACT OF OCEANICPLATEAU FORMATION557 3.16.8.1 Cenomanian–TuronianBoundary (CTB)Extinction Event 558 3.16.8.2 LinksbetweenCTB Oceanic PlateauVolcanism andEnvironmentalPerturbation 558 3.16.9 CONCLUDING STATEMENTS 560 REFERENCES 561 3.16.1 INTRODUCTION knowledge ofthe oceanbasins hasimproved over the last 25years,many moreoceanic plateaus Although the existence oflarge continentalflood havebeenidentified (Figure1).Coffinand basalt provinceshasbeenknownfor some Eldholm (1992) introduced the term “large igneous considerabletime, e.g.,Holmes(1918),the provinces” (LIPs) asageneric term encompassing recognition thatsimilarfloodbasalt provinces oceanic plateaus,continentalfloodbasalt alsoexist belowthe oceans isrelatively recent. In provinces,andthoseprovinceswhich form at the early 1970s increasingamounts ofevidence the continent–oceanboundary (volcanic rifted fromseismic reflection andrefraction studies margins).
    [Show full text]
  • Geometrical Effects of a Subducted Seamount on Stopping Megathrust
    GEOPHYSICAL RESEARCH LETTERS, VOL. 40, 1–6, doi:10.1002/grl.50509, 2013 Geometrical effects of a subducted seamount on stopping megathrust ruptures Hongfeng Yang,1,2 Yajing Liu,1,3 and Jian Lin1 Received 6 March 2013; revised 18 April 2013; accepted 25 April 2013. [1] We have numerically simulated dynamic ruptures along rich sediments into seismogenic zone [Bangs et al., 2006]. a “slip-weakening” megathrust fault with a subducted The presence of entrained fluid-rich sediments in the vicinity seamount of realistic geometry, demonstrating that of a subducted seamount would reduce effective normal seamounts can act as a barrier to earthquake ruptures. Such stress and lubricate the thrust interface, leading to little barrier effect is calculated to be stronger for increased elastic strain accumulation and thus inhibiting coseismic seamount normal stress relative to the ambient level, for ruptures [Mochizuki et al., 2008; Singh et al., 2011]. Further- larger seamount height-to-width ratio, and for shorter more, it was proposed that seamount subduction may create seamount-to-nucleation distance. As the seamount height a complex fracture network in the overriding plate, making it increases from 0 to 40% of its basal width, the required unfavorable for the generation of large earthquakes [Wang increase in the effective normal stress on the seamount to and Bilek, 2011]. Thus, the specific mechanisms for stop ruptures drops by as much as ~20%. We further subducted seamounts to stop coseismic ruptures could be demonstrate that when a seamount is subducted adjacent to complex and remain open for debate. the earthquake nucleation zone, coseismic ruptures can be [3] Previous numerical studies have modeled a subducted stopped even if the seamount has a lower effective normal seamount as a patch under elevated effective normal stress stress than the ambient level.
    [Show full text]
  • Distribution and Sedimentary Characteristics of Tsunami Deposits
    Sedimentary Geology 200 (2007) 372–386 www.elsevier.com/locate/sedgeo Distribution and sedimentary characteristics of tsunami deposits along the Cascadia margin of western North America ⁎ Robert Peters a, , Bruce Jaffe a, Guy Gelfenbaum b a USGS Pacific Science Center, 400 Natural Bridges Drive, Santa Cruz, CA 95060, United States b USGS 345 Middlefield Road, Menlo Park, CA 94025, United States Abstract Tsunami deposits have been found at more than 60 sites along the Cascadia margin of Western North America, and here we review and synthesize their distribution and sedimentary characteristics based on the published record. Cascadia tsunami deposits are best preserved, and most easily identified, in low-energy coastal environments such as tidal marshes, back-barrier marshes and coastal lakes where they occur as anomalous layers of sand within peat and mud. They extend up to a kilometer inland in open coastal settings and several kilometers up river valleys. They are distinguished from other sediments by a combination of sedimentary character and stratigraphic context. Recurrence intervals range from 300–1000 years with an average of 500–600 years. The tsunami deposits have been used to help evaluate and mitigate tsunami hazards in Cascadia. They show that the Cascadia subduction zone is prone to great earthquakes that generate large tsunamis. The inclusion of tsunami deposits on inundation maps, used in conjunction with results from inundation models, allows a more accurate assessment of areas subject to tsunami inundation. The application of sediment transport models can help estimate tsunami flow velocity and wave height, parameters which are necessary to help establish evacuation routes and plan development in tsunami prone areas.
    [Show full text]
  • Mantle Hydration and Cl-Rich Fluids in the Subduction Forearc Bruno Reynard1,2
    Reynard Progress in Earth and Planetary Science (2016) 3:9 Progress in Earth and DOI 10.1186/s40645-016-0090-9 Planetary Science REVIEW Open Access Mantle hydration and Cl-rich fluids in the subduction forearc Bruno Reynard1,2 Abstract In the forearc region, aqueous fluids are released from the subducting slab at a rate depending on its thermal state. Escaping fluids tend to rise vertically unless they meet permeability barriers such as the deformed plate interface or the Moho of the overriding plate. Channeling of fluids along the plate interface and Moho may result in fluid overpressure in the oceanic crust, precipitation of quartz from fluids, and low Poisson ratio areas associated with tremors. Above the subducting plate, the forearc mantle wedge is the place of intense reactions between dehydration fluids from the subducting slab and ultramafic rocks leading to extensive serpentinization. The plate interface is mechanically decoupled, most likely in relation to serpentinization, thereby isolating the forearc mantle wedge from convection as a cold, potentially serpentinized and buoyant, body. Geophysical studies are unique probes to the interactions between fluids and rocks in the forearc mantle, and experimental constrains on rock properties allow inferring fluid migration and fluid-rock reactions from geophysical data. Seismic velocities reveal a high degree of serpentinization of the forearc mantle in hot subduction zones, and little serpentinization in the coldest subduction zones because the warmer the subduction zone, the higher the amount of water released by dehydration of hydrothermally altered oceanic lithosphere. Interpretation of seismic data from petrophysical constrain is limited by complex effects due to anisotropy that needs to be assessed both in the analysis and interpretation of seismic data.
    [Show full text]
  • OCEAN SUBDUCTION Show That Hardly Any Commercial Enhancement Finney B, Gregory-Eaves I, Sweetman J, Douglas MSV Program Can Be Regarded As Clearly Successful
    1982 OCEAN SUBDUCTION show that hardly any commercial enhancement Finney B, Gregory-Eaves I, Sweetman J, Douglas MSV program can be regarded as clearly successful. and Smol JP (2000) Impacts of climatic change and Model simulations suggest, however, that stock- Rshing on PaciRc salmon over the past 300 years. enhancement may be possible if releases can be Science 290: 795}799. made that match closely the current ecological Giske J and Salvanes AGV (1999) A model for enhance- and environmental conditions. However, this ment potentials in open ecosystems. In: Howell BR, Moksness E and Svasand T (eds) Stock Enhancement requires improvements of assessment methods of and Sea Ranching. Blackwell Fishing, News Books. these factors beyond present knowledge. Marine Howell BR, Moksness E and Svasand T (1999) Stock systems tend to have strong nonlinear dynamics, Enhancement and Sea Ranching. Blackwell Fishing, and unless one is able to predict these dynamics News Books. over a relevant time horizon, release efforts are Kareiva P, Marvier M and McClure M (2000) Recovery not likely to increase the abundance of the target and management options for spring/summer chinnook population. salmon in the Columbia River basin. Science 290: 977}979. Mills D (1989) Ecology and Management of Atlantic See also Salmon. London: Chapman & Hall. Ricker WE (1981) Changes in the average size and Mariculture, Environmental, Economic and Social average age of PaciRc salmon. Canadian Journal of Impacts of. Salmonid Farming. Salmon Fisheries: Fisheries and Aquatic Science 38: 1636}1656. Atlantic; Paci\c. Salmonids. Salvanes AGV, Aksnes DL, FossaJH and Giske J (1995) Simulated carrying capacities of Rsh in Norwegian Further Reading fjords.
    [Show full text]
  • Controls of Subduction Geometry, Location of Magmatic Arcs, and Tectonics of Arc and Back-Arc Regions
    Controls of subduction geometry, location of magmatic arcs, and tectonics of arc and back-arc regions TIMOTHY A. CROSS Exxon Production Research Company, P.O. Box 2189, Houston, Texas 77001 REX H. PILGER, JR. Department of Geology, Louisiana State University, Baton Rouge, Louisiana 70803 ABSTRACT States), intra-arc extension (for example, convergence rate, direction and rate of the Basin and Range province), foreland absolute upper-plate motion, age of the de- Most variation in geometry and angle of fold and thrust belts, and Laramide-style scending plate, and subduction of aseismic inclination of subducted oceanic lithosphere tectonics. ridges, oceanic plateaus, or intraplate is caused by four interdependent factors. island-seamount chains. It is crucial to Combinations of (1) rapid absolute upper- INTRODUCTION recognize that, in the natural system of the plate motion toward the trench and active Earth, the major factors may interact and, overriding of the subducted plate, (2) rapid Since Luyendyk's (1970) pioneer attempt therefore, are interdependent variables. De- relative plate convergence, and (3) subduc- to relate subduction-zone geometry to some pending on the associations among them, in tion of intraplate island-seamount chains, fundamental aspect(s) of plate kinematics a historical and spatial context, their aseismic ridges, and oceanic plateaus and dynamics, subsequent investigations effects on the geometry of subducted litho- (anomalously low-density oceanic litho- have suggested an increasing variety and sphere can be additive, or by contrast, one sphere) cause low-angle subduction. Under complexity among possible controls and variable can act in opposition to another conditions of low-angle subduction, the resultant configurations of subduction variable and result in total or partial cancel- upper surface of the subducted plate is in zones.
    [Show full text]
  • Lecture 4: OCEANS (Outline)
    LectureLecture 44 :: OCEANSOCEANS (Outline)(Outline) Basic Structures and Dynamics Ekman transport Geostrophic currents Surface Ocean Circulation Subtropicl gyre Boundary current Deep Ocean Circulation Thermohaline conveyor belt ESS200A Prof. Jin -Yi Yu BasicBasic OceanOcean StructuresStructures Warm up by sunlight! Upper Ocean (~100 m) Shallow, warm upper layer where light is abundant and where most marine life can be found. Deep Ocean Cold, dark, deep ocean where plenty supplies of nutrients and carbon exist. ESS200A No sunlight! Prof. Jin -Yi Yu BasicBasic OceanOcean CurrentCurrent SystemsSystems Upper Ocean surface circulation Deep Ocean deep ocean circulation ESS200A (from “Is The Temperature Rising?”) Prof. Jin -Yi Yu TheThe StateState ofof OceansOceans Temperature warm on the upper ocean, cold in the deeper ocean. Salinity variations determined by evaporation, precipitation, sea-ice formation and melt, and river runoff. Density small in the upper ocean, large in the deeper ocean. ESS200A Prof. Jin -Yi Yu PotentialPotential TemperatureTemperature Potential temperature is very close to temperature in the ocean. The average temperature of the world ocean is about 3.6°C. ESS200A (from Global Physical Climatology ) Prof. Jin -Yi Yu SalinitySalinity E < P Sea-ice formation and melting E > P Salinity is the mass of dissolved salts in a kilogram of seawater. Unit: ‰ (part per thousand; per mil). The average salinity of the world ocean is 34.7‰. Four major factors that affect salinity: evaporation, precipitation, inflow of river water, and sea-ice formation and melting. (from Global Physical Climatology ) ESS200A Prof. Jin -Yi Yu Low density due to absorption of solar energy near the surface. DensityDensity Seawater is almost incompressible, so the density of seawater is always very close to 1000 kg/m 3.
    [Show full text]
  • Twenty Years of Subduction Zone Science: Subduction Top to Bottom 2 (ST2B-2)
    Twenty Years of Subduction Zone Science: Subduction Top to Bottom 2 (ST2B-2) G.E. Bebout*, Dept. of Earth and Environmental Sciences, Lehigh University, Bethlehem, Pennsylvania 18015, USA; D.W. Scholl, emeritus, United States Geological Survey, Menlo Park, California 94025, USA, and University of Alaska Fairbanks, Fairbanks, Alaska 99775, USA; R.J. Stern, Dept. of Geosciences, University of Texas at Dallas, Richardson, Texas 75083, USA; L.M. Wallace, University of Texas Institute for Geophysics, Austin, Texas 78758, USA, and GNS Science, Lower Hutt, New Zealand; and P. Agard, Institut des Sciences de la Terre de Paris, UPMC Université Paris 06, CNRS, Sorbonne Universités, Paris, France ABSTRACT become increasingly interested in the pro- resultant publication encourages continued No other plate-tectonic setting has cess since the term was introduced by efforts along these lines. attracted such diverse, multidisciplinary White et al. (1970; also see the prescient “SUBCON” (Subduction Conference) research as convergent margins. Under- sketch of a subduction zone by Coats, was held in Avalon, Santa Catalina Island, standing the dynamics of subduction is 1962) on the heels of the plate tectonic rev- California, USA, on 12–17 June 1994, particularly important for realistic assess- olution. Subduction zones are where litho- largely funded by the United States ment of associated hazards such as earth- sphere is recycled into the mantle and they Geological Survey (USGS) but with addi- quakes, tsunamis, and volcanic eruptions. provide the third dimension for the tional support from the National Science A number of recent initiatives have been ~55,000 km length of convergent plate Foundation (NSF).
    [Show full text]
  • Tsunami Hazard Posed by Earthquakes on the Hikurangi
    CONFIDENTIAL This report has been prepared by the Institute of Geological and Nuclear Sciences Limited (GNS Science) exclusively for and under contract to EQC Research Foundation. Unless otherwise agreed in writing, all liability of GNS Science to any other party other than EQC Research Foundation in respect of the report is expressly excluded. The data presented in this Report are available to GNS Science for other use from May 2008 Project Number: EQC Project 06/521 Confidential 2008 CONTENTS TECHNICAL ABSTRACT.......................................................................................................III LAYMAN’S ABSTRACT.........................................................................................................IV KEYWORDS ............................................................................................................................V 1.0 INTRODUCTION ..........................................................................................................6 2.0 METHODOLOGY .........................................................................................................7 2.1 Deformation modelling .................................................................................................. 7 2.2 Tsunami modelling ........................................................................................................ 7 2.3 Limitations of modelling................................................................................................. 8 2.4 Run-up estimation ........................................................................................................
    [Show full text]
  • What's the Difference?
    New Zealand American Submarine Ring of Fire 2007 What’s The Difference? FOCUS SEATING ARRANGEMENT Volcanic processes at convergent and divergent Classroom style if students are working individu- tectonic plate boundaries ally, or groups of two to four students GRADE LEVEL MAXIMUM NUMBER OF STUDENTS 9-12 (Earth Science) 30 FOCUS QUESTION KEY WORDS How do volcanic processes differ at convergent Volcano and divergent tectonic plate boundaries? Caldera Hot spot LEARNING OBJECTIVES Ring of Fire Students will be able to compare and contrast Asthenosphere volcanoes at convergent and divergent plate Lithosphere boundaries. Magma Fault Students will be able to identify three geologic Transform boundary features that are associated with most volcanoes Convergent boundary on Earth. Divergent boundary Subduction Students will be able to explain why some volca- Tectonic plate noes erupt explosively while others do not. BACKGROUND INFORMATION MATERIALS The Submarine Ring of Fire is an arc of active vol- Copies of “Submarine Volcanism Worksheet,” canoes that partially encircles the Pacific Ocean one copy for each student or student group Basin, including the Kermadec and Mariana Islands in the western Pacific, the Aleutian Islands AUDIO/VISUAL MATERIALS between the Pacific and Bering Sea, the Cascade (Optional) Computer projection equipment to Mountains in western North America, and numer- show downloaded video materials ous volcanoes on the western coasts of Central America and South America. These volcanoes TEACHING TIME result from the motion of
    [Show full text]