DOCSLIB.ORG

Active Continental Margin

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Active Continental Margin Encyclopedia of Marine Geosciences DOI 10.1007/978-94-007-6644-0_102-2 # Springer Science+Business Media Dordrecht 2014 Active Continental Margin Serge Lallemand* Géosciences Montpellier, University of Montpellier, Montpellier, France Synonyms Convergent boundary; Convergent margin; Destructive margin; Ocean-continent subduction; Oceanic subduction zone; Subduction zone Definition An active continental margin refers to the submerged edge of a continent overriding an oceanic lithosphere at a convergent plate boundary by opposition with a passive continental margin which is the remaining scar at the edge of a continent following continental break-up. The term “active” stresses the importance of the tectonic activity (seismicity, volcanism, mountain building) associated with plate convergence along that boundary. Today, people typically refer to a “subduction zone” rather than an “active margin.” Generalities Active continental margins, i.e., when an oceanic plate subducts beneath a continent, represent about two-thirds of the modern convergent margins. Their cumulated length has been estimated to 45,000 km (Lallemand et al., 2005). Most of them are located in the circum-Pacific (Japan, Kurils, Aleutians, and North, Middle, and South America), Southeast Asia (Ryukyus, Philippines, New Guinea), Indian Ocean (Java, Sumatra, Andaman, Makran), Mediterranean region (Aegea, Cala- bria), or Antilles. They are generally “active” over tens (Tonga, Mariana) or hundreds (Japan, South America) of millions of years. This longevity has consequences on their internal structure, especially in terms of continental growth by tectonic accretion of oceanic terranes, or by arc magmatism, but also sometimes in terms of continental consumption by tectonic erosion. Morphology A continental margin generally extends from the coast down to the abyssal plain (see Fig. 1 and entry “▶ Morphology Across Convergent Plate Boundaries”). It typically includes a continental platform gently dipping seaward and a talus with a steeper slope down to the trench. In detail, active continental margins offer a wide spectrum of morphologies from narrow and steep ones (e.g., Porto Rico) to wide and flat ones (e.g., Mediterranean “Ridge” which is a huge evaporitic accre- tionary wedge). In general, the continental shelves bordering active margins are narrower than those *Email: [email protected] *Email: [email protected] Page 1 of 6 Encyclopedia of Marine Geosciences DOI 10.1007/978-94-007-6644-0_102-2 # Springer Science+Business Media Dordrecht 2014 Fig. 1 Schematic view of an active continental margin after Lallemand et al. (2005) along passive margins. The trench marks the deepest seaward termination of the active continental margin. It coincides with the surface trace of the subduction fault marking the boundary between the converging plates. Its depth generally ranges between 2 and 7 km depending on the age of the subducting plate (young plate like Juan de Fuca – shallow trench) and the amount of trench fill sediment (thick trench fill like Makran – shallow trench). Birth, Life, and Death The discovery of microdiamonds in two billion-year-old rocks in Canada attests to ultrahigh- pressure metamorphism compatible with subduction in the early Proterozoic (Cartigny et al., 2004). The ongoing processes responsible for the sinking of the lithosphere at that time probably differed from those at present since the Earth was hotter than today. For modern subduction zones, Seiya Uyeda, in 1984, has proposed two modes of subduction mechanisms: a forced one (Chilean type) in contrast with a spontaneous one (Mariana type), further used by many authors like Stern and Bloomer (1992). These notions should now be replaced by compressional versus extensional subduction, based on the observation of the dominant strain within the overriding plate and not on the cause of the subduction itself (Heuret and Lallemand, 2005). Indeed, the observation of nascent or young (less than 10 million years old) subduction zones in the western Pacific has shown that all of them result from ongoing collisions and plate boundaries reorganization (Lallemand et al., 2005). None of them can be simply explained by the spontaneous sinking of an old and dense oceanic lithosphere under its own weight. The main driving force for subduction, after it initiates and develops down to a depth of about 200 km, is the slab pull exerted by the excess mass of the slab with respect to the surrounding mantle (Turcotte and Schubert, 1982; Hassani et al., 1997). The mantle convection around a subduction mainly results from the dynamics of the plate subduction, not the opposite (Kincaid and Sacks, 1997). Once the subduction process is launched, it becomes stable over millions of years unless an oceanic plateau, an island arc, or a continental block reaches Page 2 of 6 Encyclopedia of Marine Geosciences DOI 10.1007/978-94-007-6644-0_102-2 # Springer Science+Business Media Dordrecht 2014 the subduction zone. If this occurs, subduction may stop in the collision zone and jump to another place where a new oceanic subduction may develop (Taiwan, New Guinea, Philippines, Indonesia, etc.). In a few cases, continental subduction prevails for tens of millions of years before plate reorganization (Himalaya, Weissel et al., 1980; Shemenda, 1992). Tectonic Activity Earthquakes The subduction process generates large stresses within both converging plates as well as along the subduction interface. Part of the stress is intermittently released seismically (seismic cycle). The largest earthquakes are produced by the so-called subduction earthquakes, i.e., the seismic expres- sion of mega-ruptures along the frictional part of the plate interface, also called “seismogenic zone” (M9.0 2011 Tohoku earthquake, M9.2 2004 Sumatra earthquake, etc.). These particular earthquakes dissipate at least 85 % of the total seismic energy released in the world (Scholz, 1990). The reason is that the subduction interfaces are the largest faults on Earth (up to several hundred km, even 1,000 + km long) accommodating the largest slips (up to several tens of meters). Kanamori (1977) has shown that the seismic moment for great earthquakes is proportional to the faulted area and the slip on the fault. In addition to the subduction earthquakes, intraplate earthquakes may also occur either in the overriding plate, especially if compressive or extensive stress is transmitted from the subduction zone, or the downgoing plate (commonly called slab when it subducts into the mantle). The intraslab earthquakes include (Fig. 2) the flexural earthquakes caused by plate bending near the trench, the intermediate earthquakes (down to about 300 km) resulting from the down-dip stress (often extensional as a result of the slab pull) or the unbending processes necessary to unfold the slab as it penetrates into the mantle, and the deep earthquakes (down to the discontinuity between the upper and lower mantle at 660–670 km). For further details, see also the following entries: “▶ Subduction,”“▶ Earthquake,” and “▶ Seismogenic Zone.” Volcanism Most subduction zones are marked by a volcanic arc located at a distance between 100 and 300 km landward from the trench and 110 Æ 20 km above the subducting slab. Arc magmatism results from the dehydration of the crust and overlying sediment carried by the downgoing oceanic plate. Such dehydration occurs at various depths depending on pressure/temperature conditions, but those occurring below the convective mantle wedge trigger melting and metasomatism of the mantle and subsequent rise of magmas. The explosivity of the volcanism is attributed to the high volatile content in the magma, especially H2O. Calc-alkaline, potassic calc-alkaline, and shoshonitic series characterize the arc volcanoes lying on continental crust. For further details, see entry “▶ Island Arc Volcanism, Volcanic Arcs.” Terrane Collision/Accretion and Mountain Building Oceanic plates may carry seamounts, plateaus, active or fossil island arcs, and active or fossil spreading centers. Moreover, they may be attached to continents. Thus, it follows logically that during long period of activity of an oceanic subduction, collisions with buoyant features carried by the subducting plate occur. Collisions may be frontal like the Ontong-Java plateau with the Solomon arc or oblique like the Philippine Mobile Belt (Lallemand, 1999). Collisions along active continental margins often give rise to the accretion of crustal slivers (e.g., Izu-Bonin arc accretion in Japan; Tamura et al., 2010) or even large-size exotic terranes of oceanic or continental affinities such as the Page 3 of 6 Encyclopedia of Marine Geosciences DOI 10.1007/978-94-007-6644-0_102-2 # Springer Science+Business Media Dordrecht 2014 Fig. 2 Global view of an oceanic subduction zone with an old slab sinking at a high rate in order to get deep earthquakes after Lallemand et al. (2005). The isotherms are deflected along the top of the cold descending slab. Phase changes occur at various temperature/pressure (depth) conditions. This is why they occur at different depths in the slab. Different types of earthquakes (shallow, intermediate, and deep) and stable minerals are described. Variations in the mean density of the slab is indicated in the left column as the main phase transitions occur Caribbean (Antilles) or the Okhotsk (Russia) plateaus, the Panama-Choco (Colombia, Panama) or the Halmahera (Philippines) arcs, and the Qiantang, the Lhasa, or the South China continental blocks (e.g., Lallemand et al., 1998;
Load more

Recommended publications
  • (2019): Upper-Mantle Density Structure in the Philippine Sea and Adjacent Region and Its Relation to Tectonics
    Originally published as: Liang, Q., Chen, C., Kaban, M. K., Thomas, M. (2019): Upper-mantle density structure in the Philippine Sea and adjacent region and its relation to tectonics. - Geophysical Journal International, 219, 2, pp. 945—957 DOI: http://doi.org/10.1093/gji/ggz335 This article has been accepted for publication in Geophysical Journal International ©The Author(s) 2019. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Geophys. J. Int. (2019) 219, 945–957 doi: 10.1093/gji/ggz335 Advance Access publication 2019 July 30 GJI Gravity, Geodesy and Tides Upper-mantle density structure in the Philippine Sea and adjacent region and its relation to tectonics Downloaded from https://academic.oup.com/gji/article-abstract/219/2/945/5541063 by Geoforschungszentrum Potsdam user on 06 September 2019 Qing Liang,1,2 Chao Chen,1,2 Mikhail K. Kaban2,4 and Maik Thomas2,3 1Institute of Geophysics and Geomatics, China University of Geosciences, Wuhan 430074, P.R. China. E-mail: [email protected]; [email protected] 2Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Potsdam 14473,Germany 3Institute of Meteorology, Freie Universitat¨ Berlin, Berlin 12165,Germany 4Schmidt Institute of Physics of the Earth RAS, Moscow 123242, Russia Accepted 2019 July 20. Received 2019 June 14; in original form 2019 February 27 SUMMARY The evolution of the Philippine Sea Plate (PSP) since Jurassic is one of the key issues in the dynamics of lithosphere and mantle. The related studies benefited mostly from seismic tomography which provides velocity structures in the upper mantle.
    [Show full text]
  • Coastal and Marine Ecological Classification Standard (2012)
    FGDC-STD-018-2012 Coastal and Marine Ecological Classification Standard Marine and Coastal Spatial Data Subcommittee Federal Geographic Data Committee June, 2012 Federal Geographic Data Committee FGDC-STD-018-2012 Coastal and Marine Ecological Classification Standard, June 2012 ______________________________________________________________________________________ CONTENTS PAGE 1. Introduction ..................................................................................................................... 1 1.1 Objectives ................................................................................................................ 1 1.2 Need ......................................................................................................................... 2 1.3 Scope ........................................................................................................................ 2 1.4 Application ............................................................................................................... 3 1.5 Relationship to Previous FGDC Standards .............................................................. 4 1.6 Development Procedures ......................................................................................... 5 1.7 Guiding Principles ................................................................................................... 7 1.7.1 Build a Scientifically Sound Ecological Classification .................................... 7 1.7.2 Meet the Needs of a Wide Range of Users ......................................................
    [Show full text]
  • Articles Ranging in Resents Both Gravitational Acceleration and the Effect of Bed Size from Tens of Meters to a Few Centimeters in Diameter
    Nat. Hazards Earth Syst. Sci., 6, 671–685, 2006 www.nat-hazards-earth-syst-sci.net/6/671/2006/ Natural Hazards © Author(s) 2006. This work is licensed and Earth under a Creative Commons License. System Sciences Numerical simulation of tsunami generation by cold volcanic mass flows at Augustine Volcano, Alaska C. F. Waythomas1, P. Watts2, and J. S. Walder3 1U.S. Geological Survey, Alaska Volcano Observatory, Anchorage, AK, USA 2Applied Fluids Engineering Inc., Long Beach, CA, USA 3U.S. Geological Survey, Cascades Volcano Observatory, Vancouver, WA, USA Received: 18 April 2006 – Revised: 22 June 2006 – Accepted: 22 June 2006 – Published: 26 July 2006 Abstract. Many of the world’s active volcanoes are situated 1 Introduction on or near coastlines. During eruptions, diverse geophysical mass flows, including pyroclastic flows, debris avalanches, Many of the world’s active volcanoes are located within a and lahars, can deliver large volumes of unconsolidated de- few tens of kilometers of the sea or other large bodies of wa- bris to the ocean in a short period of time and thereby gen- ter. During eruptions, large volumes of volcaniclastic debris erate tsunamis. Deposits of both hot and cold volcanic mass may enter nearby water bodies, and under certain conditions, flows produced by eruptions of Aleutian arc volcanoes are this process may initiate tsunamis (Tinti et al., 1999; Tinti exposed at many locations along the coastlines of the Bering et al., 2003). Worldwide, tsunamis caused by volcanic erup- Sea, North Pacific Ocean, and Cook Inlet, indicating that tions are somewhat infrequent (Latter, 1981); however, doc- the flows entered the sea and in some cases may have ini- umented historical cases illustrate that loss of life and prop- tiated tsunamis.
    [Show full text]
  • Subsidence and Growth of Pacific Cretaceous Plateaus
    ELSEVIER Earth and Planetary Science Letters 161 (1998) 85±100 Subsidence and growth of Paci®c Cretaceous plateaus Garrett Ito a,Ł, Peter D. Clift b a School of Ocean and Earth Science and Technology, POST 713, University of Hawaii at Manoa, Honolulu, HI 96822, USA b Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA Received 10 November 1997; revised version received 11 May 1998; accepted 4 June 1998 Abstract The Ontong Java, Manihiki, and Shatsky oceanic plateaus are among the Earth's largest igneous provinces and are commonly believed to have erupted rapidly during the surfacing of giant heads of initiating mantle plumes. We investigate this hypothesis by using sediment descriptions of Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) drill cores to constrain plateau subsidence histories which re¯ect mantle thermal and crustal accretionary processes. We ®nd that total plateau subsidence is comparable to that expected of normal sea¯oor but less than predictions of thermal models of hotspot-affected lithosphere. If crustal emplacement was rapid, then uncertainties in paleo-water depths allow for the anomalous subsidence predicted for plumes with only moderate temperature anomalies and volumes, comparable to the sources of modern-day hotspots such as Hawaii and Iceland. Rapid emplacement over a plume head of high temperature and volume, however, is dif®cult to reconcile with the subsidence reconstructions. An alternative possibility that reconciles low subsidence over a high-temperature, high-volume plume source is a scenario in which plateau subsidence is the superposition of (1) subsidence due to the cooling of the plume source, and (2) uplift due to prolonged crustal growth in the form of magmatic underplating.
    [Show full text]
  • Seafloor Mapping of the Continental Slope of the U.S. Atlantic Margin to Study Submarine Landslides That Could Trigger Tsunamis
    Seafloor Mapping of the Continental Slope of the U.S. Atlantic Margin to Study Submarine Landslides that Could Trigger Tsunamis An additional Report to the Nuclear Regulatory Commission Job Code Number: N6480 By Atlantic and Gulf of Mexico Tsunami Hazard Assessment Group Seafloor Mapping of the Continental Slope of the U.S. Atlantic Margin to Study Submarine Landslides that Could Trigger Tsunamis An Additional Report to the Nuclear Regulatory Commission By Atlantic and Gulf of Mexico Tsunami Hazard Assessment Group: Uri ten Brink, David Twichell, Jason Chaytor, Bill Danforth, Brian Andrews, and Elizabeth Pendleton U.S. Geological Survey, Woods Hole Coastal and Marine Science Center, Woods Hole, Massachusetts, USA This reports provides additional information to the report Evaluation of Tsunami Sources with Potential to Impact the U.S. Atlantic and Gulf Coasts, submitted to the Nuclear Regulatory Commission on August 22, 2008. October 15, 2010 NOTICE FROM USGS This publication was prepared by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report, or represent that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. Any views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.
    [Show full text]
  • 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.
    [Show full text]
  • Plate Tectonics Says That Earth’S Plates Move Because of Convection Currents in the Mantle
    Bellringer Which ocean is getting smaller and which ocean is getting bigger due to subduction and sea floor spreading? Plate Tectonic Theory Notes How Plates Move • Earth’s crust is broken into many jagged pieces. The surface is like the shell of a hard-boiled egg that has been rolled. The pieces of Earth’s crust are called plates. Plates carry continents, oceans floors, or both. How Plates Move • The theory of plate tectonics says that Earth’s plates move because of convection currents in the mantle. Currents in the mantle carry plates on Earth’s surface, like currents in water carry boats on a river, or Cheerios in milk. How Plates Move • Plates can meet in three different ways. Plates may pull apart, push together, or slide past each other. Wherever plates meet, you usually get volcanoes, mountain ranges, or ocean trenches. Plate Boundaries • A plate boundary is where two plates meet. Faults form along plate boundaries. A fault is a break in Earth’s crust where blocks of rock have slipped past each other. Plate Boundaries • Where two plates move apart, the boundary is called a divergent boundary. • A divergent boundary between two oceanic plates will result in a mid-ocean ridge AND rift valley. (SEE: Sea-Floor Spreading) • A divergent boundary between two continental plates will result in only a rift valley. This is currently happening at the Great Rift Valley in east Africa. Eventually, the Indian Ocean will pour into the lowered valley and a new ocean will form. Plate Boundaries • Where two plates push together, the boundary is called a convergent boundary.
    [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]
  • Exploring Submarine Arc Volcanoes Steven Carey University of Rhode Island, [email protected]
    University of Rhode Island DigitalCommons@URI Graduate School of Oceanography Faculty Graduate School of Oceanography Publications 2007 Exploring Submarine Arc Volcanoes Steven Carey University of Rhode Island, [email protected] Haraldur Sigurdsson University of Rhode Island Follow this and additional works at: https://digitalcommons.uri.edu/gsofacpubs Terms of Use All rights reserved under copyright. Citation/Publisher Attribution Carey, S., and H. Sigurdsson. 2007. Exploring submarine arc volcanoes. Oceanography 20(4):80–89, https://doi.org/10.5670/ oceanog.2007.08. Available at: https://doi.org/10.5670/oceanog.2007.08 This Article is brought to you for free and open access by the Graduate School of Oceanography at DigitalCommons@URI. It has been accepted for inclusion in Graduate School of Oceanography Faculty Publications by an authorized administrator of DigitalCommons@URI. For more information, please contact [email protected]. This article has This been published in or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The approval portionthe ofwith any permitted articleonly photocopy by is of machine, reposting, this means or collective or other redistirbution SP ec I A L Iss U E On Ocean E X P L O R ATIO N Oceanography , Volume 20, Number 4, a quarterly journal of The 20, Number 4, a quarterly , Volume O ceanography Society. Copyright 2007 by The 2007 by Copyright Society. ceanography Exploring O ceanography Society. All rights All reserved. Society. ceanography O Submarine Arc Volcanoes or Th e [email protected] Send Society. ceanography to: correspondence all B Y S T even C A R E Y an D H A R A LDUR SIGURD ss O N Three quarters of Earth’s volcanic activ- although a significant part of arc volca- tion of tsunamis (Latter, 1981).
    [Show full text]
  • The Sub-Crustal Stress Field in the Taiwan Region
    Terr. Atmos. Ocean. Sci., Vol. 26, No. 3, 261-268, June 2015 doi: 10.3319/TAO.2014.12.04.01(T) The Sub-Crustal Stress Field in the Taiwan Region Robert Tenzer1, * and Mehdi Eshagh 2 1 The Key Laboratory of Geospace Environment and Geodesy, School of Geodesy and Geomatics, Wuhan University, Wuhan, China 2 Department of Engineering Science, University West, Trollhättan, Sweden Received 22 May 2014, revised 3 December 2014, accepted 4 December 2014 ABSTRACT We investigate the sub-crustal stress in the Taiwan region. A tectonic configuration in this region is dominated by a col- lision between the Philippine oceanic plate and the Eurasian continental margin. The horizontal components of the sub-crustal stress are computed based on the modified Runcorn’s formulae in terms of the stress function with a subsequent numerical differentiation. This modification increases the (degree-dependent) convergence domain of the asymptotically-convergent series and consequently allows evaluating the stress components to a spectral resolution, which is compatible with currently available global crustal models. Moreover, the solution to the Vening Meinesz-Moritz’s (VMM) inverse isostasy problem is explicitly incorporated in the stress function definition. The sub-crustal stress is then computed for a variable Moho geometry, instead of assuming only a constant Moho depth. The regional results reveal that the Philippine plate subduction underneath the Eurasian continental margin generates the shear sub-crustal stress along the Ryukyu Trench. Some stress anomalies asso- ciated with this subduction are also detected along both sides of the Okinawa Trough. A tensional stress along this divergent tectonic plate boundary is attributed to a back-arc rifting.
    [Show full text]
  • Visualization of the Geophysical Settings in the Philippine Sea Margins by Means of GMT and ISC Data
    Central European Journal of Geography and Sustainable Development 2020, Volume 2, Issue 1, Pages: 5-15 ISSN 2668-4322, ISSN-L 2668-4322 https://doi.org/10.47246/CEJGSD.2020.2.1.1 Visualization of the geophysical settings in the Philippine Sea margins by means of GMT and ISC data Polina Lemenkova* Ocean University of China, College of Marine Geo-sciences, 238 Songling Rd, Laoshan, 266100, Qingdao, Shandong, China; [email protected] Received: 22 February 2020; Revised: 12 March 2020; Accepted: 20 March 2020; Published online: 25 March 2020 _________________________________________________________________________________________________________________________ Abstract: The presented research aimed to perform geophysical modelling (gravity and geoid) and to evaluate the spatio-temporal variation of the marine geological data (distribution and depth of earthquakes) using combination of the Generic Mapping Tools (GMT) and available sources from the International Seismological Centre (ISC-EHB) that produce data on earthquakes as part of seismic survey and regional research projects. The target study area is a Philippine Sea basin (PSB) with two focused marginal areas: Philippine Trench and Mariana Trench, two hadal trenches located in the places of the tectonic plates subduction. Marine free-air gravity anomaly in the PSP shows higher values (>80 mGal) of the gravity fields structure at the volcanic areas and Philippine archipelago. Current study presented comparative geophysical analysis, and mapping free-air gravity and geoid in the Philippine Sea basin area. As a result of this study, the average level of earthquakes located in the Philippine Trench and Mariana Trench areas were compared, and those located in the Philippine archipelago are determined to be in the souther-western part (area of west Mindanao, south-west Visayas islands), while Luzon Islands shown shallower located earthquakes.
    [Show full text]
  • Santa Monica Mountains National Recreation Area Geologic Resources Inventory Report
    National Park Service U.S. Department of the Interior Natural Resource Stewardship and Science Santa Monica Mountains National Recreation Area Geologic Resources Inventory Report Natural Resource Report NPS/NRSS/GRD/NRR—2016/1297 ON THE COVER: Photograph of Boney Mountain (and the Milky Way). The Santa Monica Mountains are part of the Transverse Ranges. The backbone of the range skirts the northern edges of the Los Angeles Basin and Santa Monica Bay before descending into the Pacific Ocean at Point Mugu. The ridgeline of Boney Mountain is composed on Conejo Volcanics, which erupted as part of a shield volcano about 15 million years ago. National Park Service photograph available at http://www.nps.gov/samo/learn/photosmultimedia/index.htm. THIS PAGE: Photograph of Point Dume. Santa Monica Mountains National Recreation Area comprises a vast and varied California landscape in and around the greater Los Angeles metropolitan area and includes 64 km (40 mi) of ocean shoreline. The mild climate allows visitors to enjoy the park’s scenic, natural, and cultural resources year-round. National Park Service photograph available at https://www.flickr.com/photos/ santamonicamtns/albums. Santa Monica Mountains National Recreation Area Geologic Resources Inventory Report Natural Resource Report NPS/NRSS/GRD/NRR—2016/1297 Katie KellerLynn Colorado State University Research Associate National Park Service Geologic Resources Division Geologic Resources Inventory PO Box 25287 Denver, CO 80225 September 2016 U.S. Department of the Interior National Park Service Natural Resource Stewardship and Science Fort Collins, Colorado The National Park Service, Natural Resource Stewardship and Science office in Fort Collins, Colorado, publishes a range of reports that address natural resource topics.
    [Show full text]