DOCSLIB.ORG

TECTONICS of the RYUKYU ISLAND ARC Koshiro

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
TECTONICS of the RYUKYU ISLAND ARC Koshiro J. Phys. Earth,26, Suppl., S 301-S 307, 1978 TECTONICS OF THE RYUKYU ISLAND ARC KoshiroKIZAKI GeologicalLaboratory, Universityofthe Ryukyus, Naha, Japan (ReceivedJune 14,1978; Revised August 26, 1978) The geologicaland structuralcontrast between the north and centralRyukyus and the southRyukyus has been significantsince the Late Mesozoic. The differenceseems to correspondto that of the nature of the Philippine Sea floorfacing the Ryukyus, i.e. the Daito Ridgesand Amami plateauto the northand deeperbasin to the south. The north and centralRyukyus were a separatetectonic unit from thesouth Ryukyus from theLate Meso- zoicto Middle Tertiary.Subsequently they have unitedto form an islandarc as the islandgroups shifted southeastwards with differentrates in the Late Tertiaryto Quater- nary. 1. Introduction The Ryukyu islandsare a typicalisland arc, 1,200km long, lying between Kyushu and Taiwan at the northwestern Pacificmargin. They are composed of the Ryukyu Trench on the Pacificside, a row of islands,a volcanicbelt and the Okinawa Trough on the continentalmargin. The islandsare divided morphologicallyas well as geologically into threegroups: the north Ryukyu Osumi islands,the centralRyukyu Amami and Oki- nawa islands,and the south Ryukyu Miyako and Yaeyama islands. They are separated by the Tokara Channel and the Miyako Depression,which representstrike-slip fault zones. The structuralframework ofthe islandswas studiedby KONISHI (1965).His structural zonation paralleledthe zonation of the pre-Miocene basement complex of Southwest Honshu: the Ryukyu islandswere interpretedas the southwesterncontinuation of Outer Zone of Southwest Japan modified into an echelon configurationby the left-lateraltrans- current dislocationsof the Tokara Channel and the Miyako Depression. NAKAGAWA (1974)correlated the islandarc system of the Ryukyu islandswith that of NortheastJapan. In thispaper, the author attempts to discussthe islandarc system from a differentpoint of view. Recent investigationsverified that the geologicaland structuraldiscontinuity of the north-centralRyukyus and south Ryukyu issignificant. The geologicaland struc- turalhistories of both islandgroups are quitedifferent throughout the period of Mesozoic to Miocene. Thereafter,the islandgroups united into a singleisland arc. 2. Basementof theIslands The basement rocks of centralRyukyu are composed of Late Paleozoic eugeosyn- clinalsediments, including slate, chert, limestone and diabasicgreen rocks,whereas the Yaeyama metamorphic rocks-phyllite,black schistsand green schistsincluding the glau- cophane schistfacies rocks-are seen only in south Ryukyu. The Late Paleozoiceugeosynclinal sediments are correlatedto the Upper Paleozoic groups of Kyushu and Shikoku to the north and alsoto those of Taiwan to the south. The structuraltrend of the basement group isnot necessarilyparallel to the general trend of the S 301 S 302 K. KIZAKI Fig. 1. Structural trend of the Paleozoic group in the Ryukyu Islands. island arc but is more or less diverse (Fig. 1). The variation of the fold axes of the Paleo- zoic group seems to have resulted from the later dislocations than the deformations of the Mesozoic orogeny. The Yaeyama metamorphic rocks are constructed mainly of two fold systems with different orientations. The principal fold, which trends in NW-SE direction, has a wave- length of several kilometers and is clearly oblique to the trend of the island arc. The preferred orientation of minerals is parallel to the fold axis. A minor fold with EW axes is superimposed on the principal fold. Shear zones and faults are well developed parallel to the minor fold. Blocks of the metamorphic rocks crop out locally through the Lower Miocene sandstone formation along the EW faults. It seems therefore that the EW fault- ing was activated parallel to the island arc in the Middle to Late Miocene. Paleomagnetic study of the Eocene volcanic rocks reveals a clockwise rotation of 40° of the Yaeyama islands (south Ryukyu) resulting in the present NW-SE trend of the meta- morphic rocks (SASAJIMA, 1977). The original trend, therefore, should be in east-west direction parallel to the present direction of the island arc. Radiometric ages of the Yaeyama metamorphic rocks are 174my (K-Ar method), 195my (Rb-Sr method) (SHIBATA et al., 1968, 1972). The Sambagawa metamorphic rocks representing facies similar to the Yaeyama metamorphics, have ages of 82-102my, which are much younger than the Yaeyama rocks. But the Sangun metamorphic rocks indicate similar ages of 159-175my. Both Sambagawa and Sangun rocks are from Honshu, Shikoku and Kyushu. The green schist of the Tananao belt of Taiwan is re- Tectonics of the Ryukyu Island Arc S 303 ported to have much younger ages of 82-14my (YEN, 1975). The Yaeyama metamorphic rocks then seem to be correlatedto the Sangun rocks so far as the radiometricages are concerned. The originalsedimentary rocks are consideredto be of the Late Paleozoic age but no fossilshave yet been found from the metamorphic rocks. 3. The ShimantoBelt The terraneof the Shimanto supergroup of Late Mesozoic to Early Tertiaryage con- tinuessouthwards to the north-centralRyukyus from Kyushu, Shikoku and Honshu where the supergroup signifiesthe geosynclinalsediments in the outer belt of Southwest Japan on the Pacificside. The upper horizon of the supergroup in centralRyukyu is composed of thick and coarse sandstonescontaining Eocene nummulites. The distributionof the supergroup islimited to the north-centralRyukyus, whereas calcareouslittoral sediments intercalatedwith andesiteand pyroclasticrocks of Eocene age are seen in south Ryukyu (SHIRAO etal., 1 976). The Shimanto supergroup of the north-centralRyukyus isseverely deformed to form isoclinalfolds and SE-verging thrustfaults. It is alsoslightly metamor- phosed to black and green phyllitesand partlyto green schists. The Eocene formation of south Ryukyu shows differentsedimentation faciesfrom thatof the northern islandsand no deformationand metamorphism exceptmere tiltingand laterfaulting. The area of south Ryukyu has thereforebeen a part of stableland mass sincethe Eocene sedimentation. KONISHI (1965) stated that the Eocene basin of south Ryukyu formed an inner stablezone againstthe Shimanto belt,which formed the outer mobile zone of the islandsarc. Accordingly,the islandsof south Ryukyu have had to shiftmore rapidlysouthwards so as to form the presentRyukyu islandarc. 4. Miocene and Eocene Volcanism The inner zone of the north-centralRyukyus representsa line of recent volcanic islands,some of which are stillactive forming a presentvolcanic front. The basement of the volcanoesis constructedusually of volcanicand pyroclasticrocks of Miocene to Plio- cene age which are alteredto show greenishcolor by hydrothermal solution. Thus, they are collectivelycalled "Green Tuff Volcanics"of Neogene age similarto those in the main Japanese islands. Marine geologicalinvestigations demonstrated that the volcanic and pyroclasticrocks are distributedin a 100km wide zone in the inner zone and the Okinawa Trough of the north-centralRyukyus, but not of south Ryukyu (HONZA, 1977). Pyroclasticrocks and andesiteflows are found conformably within the Eocene littoral sediments in south Ryukyu (SHIRAO et al.,1976). Their occurrence seems to be similar to that of the "Green tuff"rocks, but the age isquite different.Moreover, the pyroxene andesitesof south Ryukyu show a lower alkali-limeindex (58.3)than those fromthe Mio- cene andesites(61.8) of the north-centralRyukyus (MATSUMOTO, 1964). The Eocene volcanism cannot be tracedto Taiwan but might be correlated withthat of the Philippines. Here again, the contrastof volcanism in age and characteris remarkable between the north-centralRyukyus and south Ryukyu (Fig.2). 5. Distributionof the Yaeyama Group The Yaeyama group, distributedin the Yaeyama islandsof south Ryukyu, the northern part of Taiwan and the Senkaku islands,is composed mainly of sandstone with S 304 K. KIZAKI Fig.2. "GreenTuff Volcanism" in Mioceneand Eocene. intercalationsof mudstone and ischaracterized by coal beds,cross laminae and tracefossils signifyinglittoral sediments. Palynologicalinvestigation reveals the age of the sedimentsto be the Lower Miocene (TAKAHASHI and MATSUMOTO, 1964). The group is correlatedwith the Lower Miocene seriesof Taiwan and northern Kyushu by the heavy mineral assemblage also (OBARA and MATSUMOTO, 1964). The mineral compositionis of zircon,tourmaline, garnet, and often associatedwith rutile,staurolite and monazite. These minerals are probably sup- plied fromgranite and gneiss,which are never found in the neighbouringislands nor Tai- wan, but are abundant in the southeastcoastal area of China. Therefore,the geological development of south Ryukyu should be interpretedin connectionwith the geology of the southeastChina. The Yaeyama group is slightlytilted structurally and faulted. This again shows that the Yaeyama islandsand theirenvirons have been in stableconditions since Early Miocene. 6. The ShimajiriBasin It isnot untilthe LatestMiocene during the depositionof the Shimajirigroup, that the north-centralRyukyus and south Ryukyu formed a common basin throughout the Ryukyu islands. The sedimentsof the group, which are composed mainly of siltstoneinterbedded sand- Tectonics of the Ryukyu Island Arc S 305 Table 1. Marine geological and structuralcontrast of the north-central Ryukyus to south Ryukyu around the Ryukyu islands after HONZA (1977). stone and tuffin the upper part,range from the Upper Miocene to the Lower Pleistocene according to the investigationof
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]
  • Effects of Constructing a New Airport on Ishigaki Island
    Island Sustainability II 181 Effects of constructing a new airport on Ishigaki Island Y. Maeno1, H. Gotoh1, M. Takezawa1 & T. Satoh2 1Nihon University, Japan 2Nihon Harbor Consultants Ltd., Japan Abstract Okinawa Prefecture marked the 40th anniversary of its reversion to Japanese sovereignty from US control in 2012. Such isolated islands are almost under the environment separated by the mainland and the sea, so that they have the economic differences from the mainland and some policies for being active isolated islands are taken. It is necessary to promote economical measures in order to increase the prosperity of isolated islands through initiatives involving tourism, fisheries, manufacturing, etc. In this study, Ishigaki Island was considered as an example of such an isolated island. Ishigaki Island is located to the west of the main islands of Okinawa and the second-largest island of the Yaeyama Island group. Ishigaki Island falls under the jurisdiction of Okinawa Prefecture, Japan’s southernmost prefecture, which is situated approximately half-way between Kyushu and Taiwan. Both islands belong to the Ryukyu Archipelago, which consists of more than 100 islands extending over an area of 1,000 km from Kyushu (the southwesternmost of Japan’s four main islands) to Taiwan in the south. Located between China and mainland Japan, Ishigaki Island has been culturally influenced by both countries. Much of the island and the surrounding ocean are protected as part of Iriomote-Ishigaki National Park. Ishigaki Airport, built in 1943, is the largest airport in the Yaeyama Island group. The runway and air security facilities were improved in accordance with passenger demand for larger aircraft, and the airport became a tentative jet airport in May 1979.
    [Show full text]
  • Changes in the Way of Traditional Cloth Makings and the Weavers’ Contribution in the Ryukyu Islands Toshiyuki Sano Nara Women’S University, Too [email protected]
    University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Textile Society of America Symposium Proceedings Textile Society of America 9-2014 Changes in the Way of Traditional Cloth Makings and the Weavers’ Contribution in the Ryukyu Islands Toshiyuki Sano Nara Women’s University, [email protected] Yuka Matsumoto Follow this and additional works at: http://digitalcommons.unl.edu/tsaconf Part of the Art and Design Commons, and the Art Practice Commons Sano, Toshiyuki and Matsumoto, Yuka, "Changes in the Way of Traditional Cloth Makings and the Weavers’ Contribution in the Ryukyu Islands" (2014). Textile Society of America Symposium Proceedings. 885. http://digitalcommons.unl.edu/tsaconf/885 This Article is brought to you for free and open access by the Textile Society of America at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Textile Society of America Symposium Proceedings by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Changes in the Way of Traditional Cloth Makings and the Weavers’ Contribution in the Ryukyu Islands Toshiyuki Sano and Yuka Matsumoto This article is based on a fieldwork project we conducted in 2013 and 2014. The objective of the project was to grasp the current state of how people are engaged in the traditional ways of weaving, dyeing and making cloth in the Ryukyu Islands.1 Throughout the project, we came to think it important to understand two points in order to see the direction of those who are engaged in manufacturing textiles in the Ryukyu Islands. The points are: the diversification in ways of engaging in traditional cloth making; and the importance of multi-generational relationship in sustaining traditional cloth making.
    [Show full text]
  • Contrasting Volcano Spacing Along SW Japan Arc Caused by Difference
    www.nature.com/scientificreports OPEN Contrasting volcano spacing along SW Japan arc caused by diference in age of subducting lithosphere Yoshiyuki Tatsumi1,2*, Nobuaki Suenaga3, Shoichi Yoshioka2,3, Katsuya Kaneko 1,2 & Takumi Matsumoto4 The SW Japan arc built by subduction of the Philippine Sea (PHS) plate exhibits uneven distribution of volcanoes: thirteen Quaternary composite volcanoes form in the western half of this arc, Kyushu Island, while only two in the eastern half, Chugoku district. Reconstruction of the PHS plate back to 14 Ma, together with examinations based on thermal structure models constrained by high- density heat fow data and a petrological model for dehydration reactions suggest that fuids are discharged actively at depths of 90–100 km in the hydrous layer at the top of the old (> 50 Ma), hence, cold lithosphere sinking beneath Kyushu Island. In contrast, the young (15–25 Ma) oceanic crust downgoing beneath Chugoku district releases fuids largely at shallower depths, i.e. beneath the non- volcanic forearc, to cause characteristic tectonic tremors and low-frequency earthquakes (LFEs) and be the source of specifc brine springs. Much larger amounts of fuids supplied to the magma source region in the western SW Japan arc could build more densely-distributed volcanoes. Subduction zone volcanoes tend to exhibit regular spacing along a volcanic arc, although the spacing of volcanoes within individual arcs is ofen variable from arc to arc1, 2. A broad positive correlation between the linear density of active volcanoes and the rate of plate convergence suggests that the faster subduction contributes to greater melt production in the mantle wedge3–5.
    [Show full text]
  • Constraints on the Moho in Japan and Kamchatka
    Tectonophysics 609 (2013) 184–201 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Review Article Constraints on the Moho in Japan and Kamchatka Takaya Iwasaki a, Vadim Levin b,⁎, Alex Nikulin b, Takashi Iidaka a a Earthquake Research Institute, University of Tokyo, Japan b Rutgers University, NJ, USA article info abstract Article history: This review collects and systematizes in one place a variety of results which offer constraints on the depth Received 1 July 2012 and the nature of the Moho beneath the Kamchatka peninsula and the islands of Japan. We also include stud- Received in revised form 12 November 2012 ies of the Izu–Bonin volcanic arc. All results have already been published separately in a variety of venues, and Accepted 22 November 2012 the primary goal of the present review is to describe them in the same language and in comparable terms. Available online 3 December 2012 For both regions we include studies using artificial and natural seismic sources, such as refraction and reflec- tion profiling, detection and interpretation of converted-mode body waves (receiver functions), surface wave Keywords: Kamchatka dispersion studies (in Kamchatka) and tomographic imaging (in Japan). The amount of work done in Japan is Japan significantly larger than in Kamchatka, and resulting constraints on the properties of the crust and the upper- Crustal structure most mantle are more detailed. Upper-mantle structure Japan and Kamchatka display a number of similarities in their crustal structure, most notably the average Moho crustal thickness in excess of 30 km (typical of continental regions), and the generally gradational nature of the crust–mantle transition where volcanic arcs are presently active.
    [Show full text]
  • Subducting Oceanic High Causes Compressional Faulting In
    Available online at www.sciencedirect.com Tectonophysics 466 (2009) 255–267 www.elsevier.com/locate/tecto Subducting oceanic high causes compressional faulting in southernmost Ryukyu forearc as revealed by hypocentral determinations of earthquakes and reflection/refraction seismic data ⁎ Yvonne Font a, , Serge Lallemand b a Géosciences Azur, UMR IRD–CNRS–UPMC–UNSA 6526, 06235 Villefranche-sur-Mer, France b Géosciences Montpellier, UMR CNRS–UM2 5243, CC.60, UM2, place E. Bataillon, 34095 Montpellier, France Available online 22 November 2007 Abstract Absolute earthquake hypocenter locations have been determined in the area offshore eastern Taiwan, at the Southernmost Ryukyu subduction zone. Location process is run within a 3D velocity model by combining the Taiwanese and neighboring Japanese networks and using the 3D MAXI technique. The study focuses on the most active seismic cluster in the Taiwan region that occurs in the forearc domain offshore eastern Taiwan. Earthquakes distribute mainly along 2 active planes. The first one aligns along the subduction interface and the second one, shallower affects the overriding margin. Focal mechanisms within the shallow group indicate that nodal planes are either compatible with high-angle back- thrusts or low-angle thrusts. The active seismic deformation exclusively indicates reverse faulting revealing that the forearc basement undergoes trench-perpendicular strong compression. By integrating the seismological image into the regional context, we favor the hypothesis in which the dense seismicity occurring offshore marks the activity of en-échelon high-angle reverse faults accommodating the uplift of a broken piece of Ryukyu Arc basement, called Hoping Basement Rise. The uplift is inferred to be caused by the subduction of an oceanic relief, either exotic block, seamount or oceanic crust sliver.
    [Show full text]
  • Large and Repeating Slow Slip Events in the Izu-Bonin Arc from Space
    LARGE AND REPEATING SLOW SLIP EVENTS IN THE IZU-BONIN ARC FROM SPACE GEODETIC DATA （伊豆小笠原弧における巨大スロー地震および繰り返し スロー地震の宇宙測地学的研究） by Deasy Arisa Department of Natural History Sciences Graduate School of Science, Hokkaido University September, 2016 Abstract The Izu-Bonin arc lies along the convergent boundary where the Pacific Plate subducts beneath the Philippine Sea Plate. In the first half of my three-year doctoral course, I focused on the slow deformation on the Izu Islands, and later in the second half, I focused on the slow deformation on the Bonin Islands. The first half of the study, described in Chapter V, is published as a paper, "Transient crustal movement in the northern Izu–Bonin arc starting in 2004: A large slow slip event or a slow back-arc rifting event?". Horizontal velocities of continuous Global Navigation Satellite System (GNSS) stations on the Izu Islands move eastward by up to ~1 cm/year relative to the stable part of the Philippine Sea Plate suggesting active back-arc rifting behind the northern part of the arc. We confirmed the eastward movement of the Izu Islands explained by Nishimura (2011), and later discussed the sudden accelerated movement in the Izu Islands detected to have occurred in the middle of 2004. I mainly discussed this acceleration and make further analysis to find out the possible cause of this acceleration. Here I report that such transient eastward acceleration, starting in the middle of 2004, resulted in ~3 cm extra movements in three years. I compare three different mechanisms possibly responsible for this transient movement, i.e. (1) postseismic movement of the 2004 September earthquake sequence off the Kii Peninsula far to the west, (2) a temporary activation of the back-arc rifting to the west dynamically triggered by seismic waves from a nearby earthquake, and (3) a large slow slip event in the Izu-Bonin Trench to the east.
    [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]
  • Philippine Sea Plate Inception, Evolution, and Consumption with Special Emphasis on the Early Stages of Izu-Bonin-Mariana Subduction Lallemand
    Progress in Earth and Planetary Science Philippine Sea Plate inception, evolution, and consumption with special emphasis on the early stages of Izu-Bonin-Mariana subduction Lallemand Lallemand Progress in Earth and Planetary Science (2016) 3:15 DOI 10.1186/s40645-016-0085-6 Lallemand Progress in Earth and Planetary Science (2016) 3:15 Progress in Earth and DOI 10.1186/s40645-016-0085-6 Planetary Science REVIEW Open Access Philippine Sea Plate inception, evolution, and consumption with special emphasis on the early stages of Izu-Bonin-Mariana subduction Serge Lallemand1,2 Abstract We compiled the most relevant data acquired throughout the Philippine Sea Plate (PSP) from the early expeditions to the most recent. We also analyzed the various explanatory models in light of this updated dataset. The following main conclusions are discussed in this study. (1) The Izanagi slab detachment beneath the East Asia margin around 60–55 Ma likely triggered the Oki-Daito plume occurrence, Mesozoic proto-PSP splitting, shortening and then failure across the paleo-transform boundary between the proto-PSP and the Pacific Plate, Izu-Bonin-Mariana subduction initiation and ultimately PSP inception. (2) The initial splitting phase of the composite proto-PSP under the plume influence at ∼54–48 Ma led to the formation of the long-lived West Philippine Basin and short-lived oceanic basins, part of whose crust has been ambiguously called “fore-arc basalts” (FABs). (3) Shortening across the paleo-transform boundary evolved into thrusting within the Pacific Plate at ∼52–50 Ma, allowing it to subduct beneath the newly formed PSP, which was composed of an alternance of thick Mesozoic terranes and thin oceanic lithosphere.
    [Show full text]
  • Interplate Coupling Along the Central Ryukyu Trench Inferred from GPS/Acoustic
    Interplate coupling along the central Ryukyu Trench inferred from GPS/acoustic seafloor geodetic observation Mamoru Nakamura University of the Ryukyus The Ryukyu trench is a major convergent plate boundary where the Philippine Sea plate is subducting at a rate of about 8 cm/yr. Large earthquakes have not been reported along the Ryukyu subduction for the last 300 years. Because the rate of release of seismic moment in the Ryukyu Trench over the last 80 years is 5% in consideration of the plate convergence rate, interseismic coupling in the trench is assumed to be weak.The GPS measurements by Japan Geographical Survey Institute also show the southward motion of Ryukyu arc, which is due to extensional rifting of Okinawa Trough. Backslip by the interplate coupling between the subducting Philippine Sea plate and the overriding Eurasian plate cannot have been detected in the GPS network along the Ryukyu Islands. We have started the GPS/acoustic seafloor observation to detect the inter-plate coupling in the central Ryukyu trench. For this measurement, we used a system capable of performing two main tasks: precise acoustic ranging between a ship station (observation vessel) and seafloor transponders, and kinematic GPS positioning of observation vessels. The seafloor reference point was set at about 33 km landward from the axis of the Ryukyu trench (southeast of Okinawa Island). A set of three acoustic transponders has been installed on the seafloor, at a depth of about 2900m. The transponders are placed to form a triangular. Five campaign observations were carried out for the period from January 2008 to November 2009.
    [Show full text]
  • Origin of Marginal Basins of the NW Pacific and Their Plate Tectonic
    Earth-Science Reviews 130 (2014) 154–196 Contents lists available at ScienceDirect Earth-Science Reviews journal homepage: www.elsevier.com/locate/earscirev Origin of marginal basins of the NW Pacificandtheirplate tectonic reconstructions Junyuan Xu a,⁎, Zvi Ben-Avraham b,TomKeltyc, Ho-Shing Yu d a Department of Petroleum Geology, China University of Geosciences, Wuhan, 430074, China. b Department of Geophysics and Planetary Sciences, Tel Aviv University, Ramat Aviv 69978, Israel c Department of Geological Sciences, California State University, Long Beach, CA 90840, USA d Institute of Oceanography, National Taiwan University, Taipei, Taiwan article info abstract Article history: Geometry of basins can indicate their tectonic origin whether they are small or large. The basins of Bohai Gulf, Received 4 March 2013 South China Sea, East China Sea, Japan Sea, Andaman Sea, Okhotsk Sea and Bering Sea have typical geometry Accepted 3 October 2013 of dextral pull-apart. The Java, Makassar, Celebes and Sulu Seas basins together with grabens in Borneo also com- Available online 16 October 2013 prise a local dextral, transform-margin type basin system similar to the central and southern parts of the Shanxi Basin in geometry. The overall configuration of the Philippine Sea resembles a typical sinistral transpressional Keywords: “pop-up” structure. These marginal basins except the Philippine Sea basin generally have similar (or compatible) Marginal basins of the NW Pacific Dextral pull-apart rift history in the Cenozoic, but there do be some differences in the rifting history between major basins or their Sinistral transpressional pop-up sub-basins due to local differences in tectonic settings. Rifting kinematics of each of these marginal basins can be Uplift of Tibetan Plateau explained by dextral pull-apart or transtension.
    [Show full text]
  • Moho Depth Variations in the Taiwan Orogen from Joint Inversion of Seismic Arrival Time and Bouguer Gravity Data
    Tectonophysics 632 (2014) 151–159 Contents lists available at ScienceDirect Tectonophysics journal homepage: www.elsevier.com/locate/tecto Moho depth variations in the Taiwan orogen from joint inversion of seismic arrival time and Bouguer gravity data Zhiwei Li a,⁎, Steven Roecker b, Kwanghee Kim c,YaXud, Tianyao Hao d a State Key Laboratory of Geodesy and Earth's Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, China b Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180, USA c Department of Geological Sciences, Pusan National University, Busan 609-735, Republic of Korea d Key Laboratory of Oil and Gas Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China article info abstract Article history: The joint inversion of different geophysical datasets is an effective means to reduce the non-uniqueness and Received 4 March 2014 improve the reliability of geophysical inversion. In this study, seismic arrival time and Bouguer gravity datasets Received in revised form 3 June 2014 are jointly inverted to obtain an image of 3-D velocity structures in the Taiwan orogen. The model obtained Accepted 9 June 2014 from joint inversion fits the arrival time observations at least as well as when inverted individually, and the Available online 16 June 2014 gravity observations are much better fit when included in the inversion, implying a reduction in ambiguity by si- multaneously modeling the disparate datasets. Moho depth variations estimated by the 3-D P wave velocity Keywords: Tomography model suggest a maximum Moho depth of 56 km located beneath the Backbone Central Range, and the trend Joint inversion of the Moho is largely consistent with the topography of the Central Range with eastward, asymmetric crustal Seismic arrival time thickening.
    [Show full text]