DOCSLIB.ORG

4. Detection of Tsunamigenic Earthquakes

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

Study commissioned by Defra Flood Management The threat posed by tsunami to the UK June 2005 Statement of Use Dissemination Status Internal/External: Approved for release to Public Domain Keywords: tsunami, earthquakes, flood forecasting, flood warning, flood risk Research Contractor This report was produced by: British Geological Survey Murchison House West Mains Road Edinburgh EH9 3LA The work was carried out by a consortium with the following membership: British Geological Survey HR Wallingford Met Office Proudman Oceanographic Laboratory Project Manager Dr David Kerridge, [email protected] Defra Project Officer Mr David Richardson, [email protected] This document is also available on the Defra website www.defra.gov.uk/environ/fcd/studies/tsunami Department for Environment, Food and Rural Affairs, Flood Management Division Ergon House, Horseferry Road, London SW1P 2AL. Telephone 0207 238 3000 www.defra.gov.uk/environ/fcd © Queen’s Printer and Controller of HMSO 2005 Copyright in the typographical arrangement and design rests with the Crown. This publication (excluding the logo) may be reproduced free of charge in any format or medium provided that it is reproduced accurately and not used in a misleading context. The material must be acknowledged as Crown copyright with the title and source of the publication specified. The views expressed in this document are not necessarily those of Defra. Its officers, servants or agents accept no liability whatsoever for any loss or damage arising from the interpretation or use of the information, or reliance on views contained herein. Published by the Department for Environment, Food and Rural Affairs Departmental Foreword We welcome this thorough and detailed report and are grateful for the efforts of all the specialists concerned who completed the work at very short notice. This study has confirmed that Tsunamic events in the North East Atlantic and North Sea are possible but rare. In most plausible circumstances it is likely that such an event would be contained by current defences, designed to resist storm surges, for all major developed areas. We note, however, that any event of this type would be different in character from a storm surge and, in particular could occur at any time of the year without, for example, the build up of prior meteorological conditions associate with winter storms. We also note that there is some uncertainty about potential impacts of a wave that might be generated from a Lisbon-type earthquake in South West England, South Wales and Southern Ireland and that it may be possible to resolve some of this uncertainty through further more detailed modelling. We therefore propose to undertake further short term research that will: • Refine the potential impact envelope in the South West of England, South Wales (and Southern Ireland) from Lisbon-type events; • Give more consideration to the difference between tsunami-type events and storm surge waves in terms of coastal impact • Study typical impacts of near-coast events (e.g. on North Sea coast recreational beaches and other facilities seaward of defences) to identify the potential degree of hazard. In the light of these further investigations we will review the priority for further specific public awareness and/or emergency planning activities. However, because these types of event are so infrequent, we agree that warning systems are only sustainable if they are regularly used also for other purposes. We will therefore in the meantime: • Encourage discussions between the Environment Agency, Met Office and POL regarding a programme of selective improvements to the tide gauge network in terms of measurement frequency and data handling in light of the report recommendations and the further impacts work noted above. Also improvements in access to real-time data from gauges in other countries. All of these could have some benefits for normal storm forecasting. And with ODPM: • Encourage others to work on relevant enhancement and development of the European Broadband seismic network, data analysis and interpretation to support the aims identified in this report, especially the monitoring of potential near-field events as these will have other benefits for seismic research. • Encourage further dialogue between Met Office and British Geological Survey regarding routes for effective advice and warning dissemination relating to seismic events of all types with potentially hazardous consequences for the UK. We believe that this is a measured and appropriate response to the potential for the type of low probability events outlined in this report. Flood Management Division Defra June 2006 i ii Contents Executive Summary ......................................................................................... 1 1. Introduction .................................................................................................. 5 2. Possible sources of tsunamis affecting the UK ........................................ 7 2.1 Introduction .................................................................................................. 7 2.2 Possible tsunami sources............................................................................. 8 2.2.1 UK coastal waters .............................................................................. 9 2.2.2 NW European continental slope....................................................... 12 2.2.3 Plate boundary area west of Gibraltar.............................................. 20 2.2.4 Canary Islands ................................................................................. 23 2.2.5 Mid-Atlantic Ridge............................................................................ 24 2.2.6 Eastern North America continental slope ......................................... 25 2.2.7 Caribbean ........................................................................................ 26 2.3 Preliminary conclusions ............................................................................. 29 3. Models of tsunami propagation from potential source areas ................ 31 3.1 Introduction ................................................................................................ 31 3.2 Tsunami modelling ..................................................................................... 31 3.2.1 Generation of an initial tsunami profile............................................. 31 3.2.2 Propagation of tsunami to the coast................................................. 32 3.2.3 Estimate magnitude of tsunami waves at the coast ......................... 33 3.2.4 Estimation of tsunami inundation ..................................................... 35 3.3 Description of the numerical models .......................................................... 37 3.3.1 Results from Lisbon 1755 type tsunami ........................................... 40 3.3.2 Results from any North Sea tsunami with an origin that of the 1931 earthquake................................................................................................ 41 3.3.3 Results from tsunamis arising from a volcanic collapse on La Palma .................................................................................................................. 42 3.3.4 Celtic Sea......................................................................................... 42 3.4 Discussion of modelling results.................................................................. 43 3.5 Assessment of in-land flooding .................................................................. 58 3.5.1 A ‘first-order’ approach..................................................................... 58 3.5.2 Joint probability of different factors influencing flooding................... 58 4. Detection of tsunamigenic earthquakes .................................................. 60 4.1 Seismic characteristics of tsunamigenic earthquakes and slides............... 60 4.2 Tsunami earthquakes................................................................................. 61 4.3 Location, mechanism and depth ................................................................ 62 4.4 Submarine slides and landslides entering the sea ..................................... 63 4.5 Review of the current state and capability of seismograph networks ......... 65 4.5.1 Seismic monitoring equipment ......................................................... 65 4.5.2 Data processing ............................................................................... 66 4.5.3 Description of seismograph networks relevant to tsunami warning for northwest Europe...................................................................................... 67 4.5.4 Response to tsunamigenic events with the potential to have an impact on the UK ...................................................................................... 70 4.5.5 Strategy for tsunami monitoring in the UK and northwest Europe.... 71 4.5.6 Summary.......................................................................................... 73 5. Detection of tsunami using oceanographic and remote sensing instrumentation.............................................................................................. 75 5.1 Introduction ................................................................................................ 75 iii 5.2 Tsunami travel times................................................................................... 75 5.3 Technologies for tsunami detection ...........................................................
Recommended publications
  • Propagation of the Storegga Tsunami Into Ice-Free Lakes Along the Southern Shores of the Barents Sea

    Propagation of the Storegga Tsunami Into Ice-Free Lakes Along the Southern Shores of the Barents Sea

    Propagation of the Storegga tsunami into ice-free lakes along the southern shores of the Barents Sea Anders Romundset a,* - [email protected] Stein Bondevik a,b – [email protected] a Department of Geology, University of Tromsø, Dramsvegen 201, NO-9037 Tromsø, Norway b Sogn og Fjordane University College, Postboks 133, NO-6851 Sogndal, Norway * Correspondence to: Anders Romundset, Department of Geology, University of Tromsø, Dramsvegen 201, NO-9037 Tromsø, Norway. Telephone: (47) 77 64 62 06, E-mail: [email protected] Abstract There is clear evidence that the Storegga tsunami, triggered by the giant Storegga slide offshore western Norway 8100-8200 years ago, propagated into the Barents Sea. Cores from five coastal lakes along the coast of Finnmark in northern Norway reveal major erosion and deposition from the inundation of the tsunami. The deposits rest on a distinct erosional unconformity and consist of graded sand layers and re-deposited organic remains. Some of the organic remains are rip-up clasts of lake mud, peat and soil and suggest strong erosion of the lake floor and neighbouring land. In this part of the Arctic coastal lakes are usually covered by > 1 m of solid lake ice in the winter season. The significant erosion and deposition of rip-up clasts indicate that the lakes were ice free and that the ground was probably not frozen. We suggest that the Storegga slide and tsunami event happened sometime in the summer season; between April and October. Minimum run-up has been reconstructed to 3-4 m. KEYWORDS: Storegga; Tsunami deposits; Finnmark; Barents Sea; Holocene; 1.
  • I. Convergent Plate Boundaries (Destructive Margins) (Colliding Plates)

    I. Convergent Plate Boundaries (Destructive Margins) (Colliding Plates)

    I. Convergent plate boundaries (destructive margins) (colliding plates) 1. Plates collide, an ocean trench forms, lithosphere is subducted into the mantle 2. Types of convergence—three general classes, created by two types of plates —denser oceanic plate subsides into mantle SUBDUCTION --oceanic trench present where this occurs -- Plate descends angle average 45o a. Oceanic-continental convergence 1. Denser oceanic slab sinks into the asthenosphere—continental plate floats 2. Pockets of magma develop and rise—due to water added to lower part of overriding crust—100-150 km depth 3. Continental volcanic arcs form a. e.g., Andes Low angle, strong coupling, strong earthquakes i. Nazca plate ii. Seaward migration of Peru-Chile trench b. e.g., Cascades c. e.g., Sierra Nevada system example of previous subduction b. Oceanic-oceanic convergence 1. Two oceanic slabs converge HDEW animation Motion at Plate Boundaries a. one descends beneath the other b. the older, colder one 2. Often forms volcanoes on the ocean floor 3. Volcanic island arcs forms as volcanoes emerge from the sea 200-300 km from subduction trench TimeLife page 117 Philippine Arc a. e.g., Aleutian islands b. e.g., Mariana islands c. e.g., Tonga islands all three are young volcanic arcs, 20 km thick crust Japan more complex and thicker crust 20-35 km thick c. Continental-continental convergence— all oceaninc crust is destroyed at convergence, and continental crust remains 1. continental crust does not subside—too buoyant 2. two continents collide—become ‘sutured’ together 3. Can produce new mountain ranges such as the Himalayas II. Transform fault boundaries 1.
  • Landslide Generated Tsunamis : Numerical Modeling

    Landslide Generated Tsunamis : Numerical Modeling

    Sektion 2.5: Geodynamische Modellierung, GeoForschungsZentrum Potsdam Landslide generated tsunamis - Numerical modeling and real-time prediction Dissertation zur Erlangung des akademischen Grades Doktor der Naturwissenschaften (Dr. rer. nat.) in der Wissenschaftsdisziplin Geophysik eingereicht an der Mathematisch-Naturwissenschaftlichen Fakultät der Universität Potsdam vorgelegt von Sascha Brune Potsdam, den 29. Januar 2009 This work is licensed under a Creative Commons License: Attribution - Noncommercial - Share Alike 3.0 Germany To view a copy of this license visit http://creativecommons.org/licenses/by-nc-sa/3.0/de/deed.en Published online at the Institutional Repository of the University of Potsdam: URL http://opus.kobv.de/ubp/volltexte/2009/3298/ URN urn:nbn:de:kobv:517-opus-32986 [http://nbn-resolving.org/urn:nbn:de:kobv:517-opus-32986] Abstract Submarine landslides can generate local tsunamis posing a hazard to human lives and coastal facilities. Two major related problems are: (i) quantitative estimation of tsunami hazard and (ii) early detection of the most dangerous landslides. This thesis focuses on both those issues by providing numerical modeling of landslide- induced tsunamis and by suggesting and justifying a new method for fast detection of tsunamigenic landslides by means of tiltmeters. Due to the proximity to the Sunda subduction zone, Indonesian coasts are prone to earthquake, but also landslide tsunamis. The aim of the GITEWS-project (German- Indonesian Tsunami Early Warning System) is to provide fast and reliable tsunami warnings, but also to deepen the knowledge about tsunami hazards. New bathymetric data at the Sunda Arc provide the opportunity to evaluate the hazard potential of landslide tsunamis for the adjacent Indonesian islands.
  • The Role of Subducting Plate Rheology in Outer-Rise Seismicity: Implications for Japan and South American Subduction Systems

    The Role of Subducting Plate Rheology in Outer-Rise Seismicity: Implications for Japan and South American Subduction Systems

    Syracuse University SURFACE Syracuse University Honors Program Capstone Syracuse University Honors Program Capstone Projects Projects Spring 5-1-2015 The role of subducting plate rheology in outer-rise seismicity: Implications for Japan and South American subduction systems Karolina Lubecka Follow this and additional works at: https://surface.syr.edu/honors_capstone Part of the Geology Commons, Geophysics and Seismology Commons, and the Tectonics and Structure Commons Recommended Citation Lubecka, Karolina, "The role of subducting plate rheology in outer-rise seismicity: Implications for Japan and South American subduction systems" (2015). Syracuse University Honors Program Capstone Projects. 830. https://surface.syr.edu/honors_capstone/830 This Honors Capstone Project is brought to you for free and open access by the Syracuse University Honors Program Capstone Projects at SURFACE. It has been accepted for inclusion in Syracuse University Honors Program Capstone Projects by an authorized administrator of SURFACE. For more information, please contact [email protected]. The role of subducting plate rheology in outer-rise seismicity: Implications for Japan and South American subduction systems A Capstone Project Submitted in Partial Fulfillment of the Requirements of the Renée Crown University Honors Program at Syracuse University Karolina Lubecka Candidate for B.S. Degree and Renée Crown University Honors May 2015 Honors Capstone Project in Earth Science Capstone Project Advisor: _______________________ Dr. Robert Moucha Capstone Project Reader: _______________________ Dr. Gregory Hoke Honors Director: _______________________ Stephen Kuusisto, Director Date: May 5, 2015 i Abstract The outer rise is a subtle ridge on the seafloor located near an oceanic trench where a down-going lithospheric plate begins to bend and thus fault prior to subducting at the subduction zone.
  • ~Ertif Ied by 3 0 7 Thesis S Uperv Isg.Rn.:T::.··__....---

    ~Ertif Ied by 3 0 7 Thesis S Uperv Isg.Rn.:T::.··__....---

    1 A GRAPHIC DISPLAY OF PLATE TECTONICS IN THE TETHYS SEA by Anthony B. Williams S.B. California Institute of Technology (1965) SUBMITTED IN PARTIAL FULFILLMENT OF THE 3.EQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE at the MASSACHUSETTS INSTITUTE OF ·rECHNOLOGY August, 1971 ignature of Author Signature redacted Department oj;t=Earth and Planetary Science _S_ig_n_a_tu_r_e_r_e_d_a_c_te_d__ ~ ,_, , ~ertif ied by 3 0 7 Thesis S uperv isg.rn.:t::.··__....--- .. Signature redacted ccepted by Chairman, Departmental Committee on Graduate Students 77 Massachusetts Avenue Cambridge, MA 02139 MITLibraries http://Iibraries.mit.edu/ask DISCLAIMER NOTICE Due to the condition of the original material, there are unavoidable flaws in this reproduction. We have made every effort possible to provide you with the best copy available. Thank you. Some pages in the original document contain text that runs off the edge of the page. 2 ABSTRACT The hypothesis of plate tectonics is applied to the Mediterranean Sea region in order to explain its Tertiary mountain chains and to derive previous positions for the component plate fragments. Consuming plate boundaries are selected on geophysical and geological grounds, and are assumed connected through modern oceanic regions by shearing and accreting boundaries. The resultant plate fragments are rotated to fit geological and morphological similarities, and the timing of tectonic events, without violating available constraints. The cumulative rotations are plotted to illustrate behind-arc spreading in the western Mediterranean basins and closure upon the Adriatic and Ionian seas from east and west following northward motion of the central Alpine plate fragment. I 3 TABLE OF CONTENTS -Abstract .
  • Serpentine Volcanoes

    Serpentine Volcanoes

    2016 Deepwater Exploration of the Marianas Serpentine Volcanoes Focus Serpentine mud volcanoes Grade Level 9-12 (Earth Science) Focus Question What are serpentine mud volcanoes and what geological and chemical processes are involved with their formation? Learning Objectives • Students will describe serpentinization and explain its significance to deep-sea ecosystems. Materials q Copies of Mud Volcano Inquiry Guide, one copy for each student group Audio-Visual Materials q (Optional) Interactive whiteboard Teaching Time One or two 45-minute class periods Seating Arrangement Groups of two to four students Maximum Number of Students 30 Key Words Mariana Arc Serpentine Mud volcano Mariana Trench Serpentinization Peridotite Image captions/credits on Page 2. Tectonic plate 1 www.oceanexplorer.noaa.gov Serpentine Volcanoes - 2016 Grades 9-12 (Earth Science) Background Information NOTE: Explanations and procedures in this lesson are written at a level appropriate to professional educators. In presenting and discussing this material with students, educators may need to adapt the language and instructional approach to styles that are best suited to specific student groups. The Marina Trench is an oceanic trench in the western Pacific Ocean that is formed by the collision of two large pieces of the Earth’s crust known as tectonic plates. These plates are portions of the Earth’s outer crust (the lithosphere) about 5 km thick, as well as the upper 60 - 75 km of the underlying mantle. The plates move on a hot, flexible mantle layer called the asthenosphere, which is several hundred kilometers thick. The Pacific Ocean Basin lies on top of the Pacific Plate. To the east, new crust is formed by magma rising from deep within Images from Page 1 top to bottom: the Earth.
  • Methane Hydrate Stability and Anthropogenic Climate Change

    Methane Hydrate Stability and Anthropogenic Climate Change

    Biogeosciences, 4, 521–544, 2007 www.biogeosciences.net/4/521/2007/ Biogeosciences © Author(s) 2007. This work is licensed under a Creative Commons License. Methane hydrate stability and anthropogenic climate change D. Archer University of Chicago, Department of the Geophysical Sciences, USA Received: 20 March 2007 – Published in Biogeosciences Discuss.: 3 April 2007 Revised: 14 June 2007 – Accepted: 19 July 2007 – Published: 25 July 2007 Abstract. Methane frozen into hydrate makes up a large 1 Methane in the carbon cycle reservoir of potentially volatile carbon below the sea floor and associated with permafrost soils. This reservoir intu- 1.1 Sources of methane itively seems precarious, because hydrate ice floats in water, and melts at Earth surface conditions. The hydrate reservoir 1.1.1 Juvenile methane is so large that if 10% of the methane were released to the at- Methane, CH , is the most chemically reduced form of car- mosphere within a few years, it would have an impact on the 4 bon. In the atmosphere and in parts of the biosphere con- Earth’s radiation budget equivalent to a factor of 10 increase trolled by the atmosphere, oxidized forms of carbon, such as in atmospheric CO . 2 CO , the carbonate ions in seawater, and CaCO , are most Hydrates are releasing methane to the atmosphere today in 2 3 stable. Methane is therefore a transient species in our at- response to anthropogenic warming, for example along the mosphere; its concentration must be maintained by ongoing Arctic coastline of Siberia. However most of the hydrates release. One source of methane to the atmosphere is the re- are located at depths in soils and ocean sediments where an- duced interior of the Earth, via volcanic gases and hydrother- thropogenic warming and any possible methane release will mal vents.
  • Presentation on Pacific Plate and Associated Boundaries

    Presentation on Pacific Plate and Associated Boundaries

    PACIFIC PLATE AND ASSOCIATED BOUNDARIES The Pacific Plate • Pacific Plate is the largest plate and an oceanic plate. • It shares its boundaries with numerous plates namely; North American Plate.(Convergent and transform fault) Philippine Plate.(Convergent) Juan de Fuca Plate.(Convergent) Indo – Australian Plate.(Convergent, Transform Fault) Cocos Plate.(Divergent) Nazca Plate.(Divergent) Antarctic Plate.(Divergent,Transform Fault) Types of Plate Boundaries • Convergent Boundary: Subduction zones where two plates converges. Eg; Aleutian Islands(Alaska) • Divergent Boundary: Spreading centres where two plates move away from each other. Eg; East Pacific Rise (MOR, Pacific Ocean). • Transform Faults: Boundary where two plates slide past each other. For Eg. ; San Andreas Fault. BOUNDARY WITH ANTARCTIC PLATE DIVERGENT BOUNDARY • Pacific – Antarctic Ridge TRANSFORM FAULT • Louisville Seamount Chain Pacific – Antarctic Ridge Pacific – Antarctic Ridge(PAR) is located on the seafloor of the South Pacific Ocean. It is driven by the interaction of a mid oceanic ridge and deep mantle plumes located in the eastern portion of East Pacific Ridge. Louisville Seamount Chain It is the longest line of seamount chain in the Pacific Ocean of about 4,300 km, formed along the transform boundary in the western side between Pacific plate and Antarctic plate. It was formed from the Pacific Plate sliding over a long – lived centre of upwelling magma called the Louisville hotspot. BOUNDARY WITH PHILIPPINE PLATE CONVERGENT BOUNDARY • Izu – Ogasawara Trench • Mariana Trench Izu – Ogasawara Trench It is an oceanic trench in the western Pacific Ocean. It stretches from Japan to northern most section of Mariana Trench. Here, the Pacific Plate is being subducted beneath the Philippine Sea Plate.
  • Hadal Trenches Are Dynamic Hotspots for Early Diagenesis in the Deep Sea ✉ Ronnie N

    Hadal Trenches Are Dynamic Hotspots for Early Diagenesis in the Deep Sea ✉ Ronnie N

    ARTICLE https://doi.org/10.1038/s43247-020-00087-2 OPEN Hadal trenches are dynamic hotspots for early diagenesis in the deep sea ✉ Ronnie N. Glud 1,2 , Peter Berg3, Bo Thamdrup 1, Morten Larsen1, Heather A. Stewart 4, Alan J. Jamieson5, Anni Glud1, Kazumasa Oguri1,6, Hamed Sanei 7, Ashley A. Rowden8,9 & Frank Wenzhöfer 1,10,11 The deepest part of the global ocean, hadal trenches, are considered to act as depocenters for organic material. Relatively high microbial activity has been demonstrated in the deepest 1234567890():,; sections of some hadal trenches, but the deposition dynamics are thought to be spatially and temporally variable. Here, we explore sediment characteristics and in-situ benthic oxygen uptake along two trenches with contrasting surface primary productivity: the Kermadec and Atacama trenches. We find that benthic oxygen consumption varies by a factor of about 10 between hadal sites but is in all cases intensified relative to adjacent abyssal plains. The benthic oxygen uptake of the two trench regions reflects the difference in surface production, whereas variations within each trench are modulated by local deposition dynamics. Respiratory activity correlates with the sedimentary inventories of organic carbon and phy- todetrital material. We argue that hadal trenches represent deep sea hotspots for early diagenesis and are more diverse and dynamic environments than previously recognized. 1 Department of Biology, University of Southern Denmark, Nordcee and HADAL, 5230 Odense M, Denmark. 2 Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan. 3 Department of Environmental Sciences, University of Virginia, 291 McCormick Road, Charlottesville, VA 22904-4123, USA.
  • Habitat Heterogeneity of Hadal Trenches Considerations And

    Habitat Heterogeneity of Hadal Trenches Considerations And

    Progress in Oceanography 161 (2018) 47–65 Contents lists available at ScienceDirect Progress in Oceanography journal homepage: www.elsevier.com/locate/pocean Habitat heterogeneity of hadal trenches: Considerations and implications for T future studies ⁎ Heather A. Stewarta, , Alan J. Jamiesonb a British Geological Survey, Lyell Centre, Research Avenue South, Edinburgh EH14 4AP, UK b School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne NE1 7RU, UK ARTICLE INFO ABSTRACT Keywords: The hadal zone largely comprises a series of subduction trenches that do not form part of the continental shelf- Bottom topography slope rise to abyssal plain continuum. Instead they form geographically isolated clusters of deep-sea Hadal zone (6000–11,000 m water depth) environments. There is a growing realization in hadal science that ecological fl Ocean oor habitat patterns and processes are not driven solely by responses to hydrostatic pressure, with comparable levels of Oceanic trenches habitat heterogeneity as observed in other marine biozones. Furthermore, this heterogeneity can be expressed at Sediment distribution multiple scales from inter-trench levels (degrees of geographical isolation, and biochemical province), to intra- trench levels (variation between trench flanks and axis), topographical features within the trench interior (se- dimentary basins, ridges, escarpments, ‘deeps’, seamounts) to the substrate of the trench floor (seabed-sediment composition, mass movement deposits, bedrock outcrop). Using best available bathymetry data combined with the largest lander-derived imaging dataset that spans the full depth range of three hadal trenches (including adjacent slopes); the Mariana, Kermadec and New Hebrides trenches, the topographic variability, fine-scale habitat heterogeneity and distribution of seabed sediments of these three trenches have been assessed for the first time.
  • SUBDUCTION ZONES • Most Subduction Zones Are Found in the Pacific Ocean

    SUBDUCTION ZONES • Most Subduction Zones Are Found in the Pacific Ocean

    ANOTHER MEXICAN EARTHQUAKE! Magnitude 7.1, Tuesday Sept. 19, 2017 Why is there no oceanic crust older than 200 million years? SUBDUCTION • If new oceanic crust is being continuously created along the earth’s spreading ridge system, then we must find some way to re-cycle it back into the mantle. [WHY? –otherwise the earth would be expanding!!!!] • Old oceanic crust (>200 million years) is returned to the mantle at the deep ocean trenches. • These are known as SUBDUCTION ZONES • Most subduction zones are found in the Pacific Ocean. This means that the Pacific Ocean is shrinking and the Atlantic Ocean is expanding. Convection in the mantle Lithosphere Recap Lithosphere (or plate) – is rigid and is composed of crust and upper mantle. Thickness varies from 10-150 km. Asthenosphere – is soft, plastic and convecting. Melting of the asthenosphere produces volcanic rocks at ocean ridges. SUBDUCTION Cross-section through the southern Pacific Ocean New oceanic crust and lithosphere are created at the East Pacific Rise Old oceanic crust and lithosphere are subducted at deep ocean trenches (Tonga trench and Chile trench). Kamchatka Pacific Ocean trench Aleutian trench Japan trench Costa Rica trench Marianas trench Tonga trench Chile trench East Pacific Rise Notice that the trenches are often curved with the convex side facing the direction of subduction. This is because the earth is spherical Consequently by observing the curvature of the trench we can easily determine which side is being subducted Details of a subduction zone • Slab of lithosphere descends back into the mantle at a deep ocean trench. • Earthquakes trace the descent of the slab into the mantle (Benioff Zone).
  • Methane Hydrate Stability and Anthropogenic Climate Change

    Methane Hydrate Stability and Anthropogenic Climate Change

    Biogeosciences, 4, 521–544, 2007 www.biogeosciences.net/4/521/2007/ Biogeosciences © Author(s) 2007. This work is licensed under a Creative Commons License. Methane hydrate stability and anthropogenic climate change D. Archer University of Chicago, Department of the Geophysical Sciences, USA Received: 20 March 2007 – Published in Biogeosciences Discuss.: 3 April 2007 Revised: 14 June 2007 – Accepted: 19 July 2007 – Published: 25 July 2007 Abstract. Methane frozen into hydrate makes up a large 1 Methane in the carbon cycle reservoir of potentially volatile carbon below the sea floor and associated with permafrost soils. This reservoir intu- 1.1 Sources of methane itively seems precarious, because hydrate ice floats in water, and melts at Earth surface conditions. The hydrate reservoir 1.1.1 Juvenile methane is so large that if 10% of the methane were released to the at- Methane, CH , is the most chemically reduced form of car- mosphere within a few years, it would have an impact on the 4 bon. In the atmosphere and in parts of the biosphere con- Earth’s radiation budget equivalent to a factor of 10 increase trolled by the atmosphere, oxidized forms of carbon, such as in atmospheric CO . 2 CO , the carbonate ions in seawater, and CaCO , are most Hydrates are releasing methane to the atmosphere today in 2 3 stable. Methane is therefore a transient species in our at- response to anthropogenic warming, for example along the mosphere; its concentration must be maintained by ongoing Arctic coastline of Siberia. However most of the hydrates release. One source of methane to the atmosphere is the re- are located at depths in soils and ocean sediments where an- duced interior of the Earth, via volcanic gases and hydrother- thropogenic warming and any possible methane release will mal vents.