DOCSLIB.ORG

Methane-Rich Plumes in the Suruga Trough (Japan) and Their Carbon Isotopic Characterization

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Methane-Rich Plumes in the Suruga Trough (Japan) and Their Carbon Isotopic Characterization ELSEVIER Earth and Planetary Science Letters 160 (1998) 97±105 Methane-rich plumes in the Suruga Trough (Japan) and their carbon isotopic characterization U. Tsunogai a,Ł,J.Ishibashia, H. Wakita a,1,T.Gamob a Laboratory for Earthquake Chemistry, Faculty of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan b Ocean Research Institute, University of Tokyo, Minami-dai, Nakano-ku, Tokyo 164, Japan Received 18 August 1997; accepted 27 April 1998 Abstract 13 The carbon isotopic compositions (Ž CCH4) of the methane-rich buoyant plumes, observed in the oxygenated hemipelagic sea waters of the Suruga Trough, Japan, are discussed in relation to their sources. During a survey made in May 1996, two layers of anomalous methane-rich plumes, both of which centred at the same station about a few tens of kilometres off the coast, were found in the Suruga Trough. The deeper plume (ca. 2100 m depth, with a maximum methane concentration of 13 nmol=kg) had already been detected by a previous survey in 1986 at the same station, whereas the shallower plume (ca. 1000 m depth, with a maximum methane concentration of 10 nmol=kg) was newly discovered. 13 The estimated end-member Ž CCH4 value (59 š 3½ PDB) for the deeper plume suggests a microbial origin of the methane, probably derived from some shallow (surface) layer of sediment. The plume could be supplied from a continuous cold ¯uid seepage on the sea ¯oor of the Suruga Trough. On the other hand, the shallower plume is characterized by more 13 13 C-enriched end-member methane (Ž CCH4 D38 š 2½ PDB), presumably produced by the thermogenic degradation of organic matter. Since thermogenic methane should originate from a deeper part (more than 1000 m) of the sedimentary layer, it is unlikely that the thermogenic methane reaches the sea water by normal transport processes. The shallower plume may be a result of some sudden, catastrophic event on the sea ¯oor, such as earthquakes. 1998 Elsevier Science B.V. All rights reserved. Keywords: methane; carbon; isotopes; Suruga Bay; earthquakes 1. Introduction front of the Philippine sea plate, subducting beneath the plates of the Japanese Islands (Fig. 1). During a 1.1. Suruga Trough and anomalous methane hydrographic survey in November 1986, anomalous enrichment methane enrichment (a methane plume) was detected in the bottom sea water at 34ë400N, 138ë360E (station The Suruga Trough, which is the northern exten- 18 in Fig. 1) in the Suruga Trough (Fig. 2). Methane sion of the Nankai Trough, is the northern convergent enrichment in sea water, together with heat, Fe, Mn, Ł Corresponding author. Present address: Department of Environmental Physics and Engineering, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502, Japan. Tel.: C81 (45) 924-5555; Fax: C81 (45) 924-5554; E-mail: [email protected] 1 Present address: Faculty of Intercultural Studies, Gakushuin Women's College, 3-20-1 Toyama, Shinjuku-ku, Tokyo 162-8650, Japan. 0012-821X/98/$19.00 1998 Elsevier Science B.V. All rights reserved. PII S0012-821X(98)00075-2 98 U. Tsunogai et al. / Earth and Planetary Science Letters 160 (1998) 97±105 Fig. 1. Map showing the locations of sampling stations (circle D November, 1986 and square D 29 May, 1996), bottom topography of the Suruga Trough, and the epicentre of a magnitude 4.7 earthquake on 27 May, 1996 (star). Sectional contour map of methane concentration in Fig. 3 is constructed along the central axis of the trough (line A±B). and 3He enrichment, are well known indicators for methane (maximum concentration: ca. 200 nmol=kg) sea-¯oor hydrothermal activity, because hydrother- on the southern slope of Funka Bay, Japan, at a depth mal ¯uids are highly enriched in these compounds of about 50 m. relative to background sea water (e.g. [1]). However, In order to study the geochemical cycle of in spite of an observed high methane concentration methane in the ocean, we must clarify the geo- of more than 15 nmol=kg, this plume did not show chemical, geological, geophysical, and hydrologi- any of the other hydrothermal signatures. The plume, cal characteristics of sources of such methane-rich therefore, may be caused by some cold venting ¯uids plumes. Thus on 29 May, 1996, we revisited the Su- other than hydrothermal ¯uids, a possibility indi- ruga Trough during the KT96-8 Expedition of R=V cated also by later discoveries of numerous methane- Tansei Maru (University of Tokyo) in order to bet- rich cold ¯uid seepage sites at the adjacent Nankai ter understand the origins of methane in the plume Trough (e.g. [2]). observed in 1986. Observations of such anomalous, probably non- hydrothermal plumes in sea water have also been 1.2. Stable carbon isotopic composition of methane reported elsewhere. At a depth of several hundred metres in the Northwest Caribbean Sea, Brooks [3] The stable carbon isotopic composition of found methane-rich plumes (at a maximum concen- methane offers useful information for discerning the tration of more than 100 nmol=kg), possibly supplied origin of methane. The methane emitted by sea- from the Jamaica Ridge. Horibe et al. [4] have found ¯oor hydrothermal systems in sediment-poor envi- a methane-rich plume (at a maximum concentra- ronments is extremely enriched in 13C with a carbon 13 tion of ca. 3 nmol=kg) at a depth of approximately isotopic ratio (Ž CCH4) ranging from 25 to 8 3000 m in an open-ocean water column in the Mari- ½PDB, indicating an inorganic origin [7,8]. On the ana Trough, western Paci®c, of unknown origin [5]. other hand, organic-rich marine sediments produce Watanabe et al. [6] have found a large source of extremely 13C-depleted methane with a Ž13Cof50 U. Tsunogai et al. / Earth and Planetary Science Letters 160 (1998) 97±105 99 residual methane [17]) is suf®ciently slow relative to the diffusion of methane in sea water, we can study the origin of methane in methane-rich plumes by 13 Ž CCH4 measurements. Except for some recent works [18±21], how- ever, previous studies of the marine geochemistry of methane have lacked carbon isotopic data because they have dealt with oxygenated sea water which has 13 insuf®cient CH4 for traditional Ž CCH4 determina- tion. New isotope-ratio-monitoring gas chromatog- raphy=mass spectrometry (irm±GC=MS) systems re- quire much smaller samples for isotopic analyses (e.g. [22]). We have developed an analytical sys- tem which is capable of on-line simultaneous anal- yses of concentration and Ž13C values of low-level methane in sea water using irm±GC=MS, similar to the method developed by Popp et al. [19]. 2. Experiment Water was sampled on 29 May 1996 at stations 10, 11, 18, 19, and 20 (Fig. 1), which are located al- Fig. 2. Vertical CH4 pro®les at station 18 in the Suruga Trough most on the axis (deepest line) of the Suruga Trough. measured in 1986 (circle) and 1996 (square). The samples were collected with a 12-port Rosette multisampler (10-l Niskin bottles) attached to a Neil to 110½ PDB, as a result of microbial production Brown Mark III CTD system with a sonar pinger. Se- in the anoxic sedimentary layer (e.g. [9]). Methane- rial hydrographic measurements were made with the 13 rich cold seep ¯uids show similar Ž CCH4 values CTD system. The sampling was focused on depths as marine sediments, which are the main source of below 1000 m, because the methane plume was pre- methane in the ¯uids [10±13]. Sediment-rich hy- viously observed at depths below 1500 m (Fig. 2). drothermal systems supply methane with intermedi- Discrete sample analyses of salinity and dissolved ate Ž13C values, ranging from 30 to 50½ PDB oxygen were made using a salinometer (Autolab [7,14], due to thermogenic degradation of organic Industries) and the standard Winkler method. matter in the sediment. Methane in deeply buried ma- For CH4 content and isotopic analysis, a water rine sediments sometimes show similar Ž13Cvalues sample was slowly transferred into a ca. 530-ml as sediment-rich hydrothermal ¯uids for two possi- glass vial, which contained a Te¯on coated magnetic ble reasons: (1) thermal degradation of organic mat- stirrer of 5 cm length. After an approximately 2-fold ter under the in¯uence of elevated temperature (e.g. volume over¯ow to prevent air contamination, 3 [11,15]); (2) microbial production using extremely ml of saturated HgCl2 solution (6%wt) was slowly 13 C-enriched CO2 [16]. In the Nankai Trough, the added as a preservative. The vial was then sealed southern extension of the Suruga Trough, one may with a grey butyl rubber stopper and stored in the ®nd such 13C-enriched thermogenic methane in the dark at room temperature until analysis. In order to sedimentary layer about 1000 m below the sea ¯oor prevent seal breakage due to increases in volume [15]. If we can assume that some secondary alter- caused by temperature increases after sealing, about 13 nation of Ž CCH4 in the seawater column (i.e. bio- 1 ml of sample in each bottle was discarded without logical consumption in oxygenated seawater which contact with air, using a needle syringe through the 13 may result in enhancement of Ž CCH4 values of rubber stopper within an hour after sealing. 100 U. Tsunogai et al. / Earth and Planetary Science Letters 160 (1998) 97±105 The analytical system consisted sequentially of Table 1 a He-sparging bottle of water (80 ml=min carrier Observed concentration (CH4 in nmol=kg) and carbon isotopic Ž13 gas ¯ow), a CO2-trapping port with alkaline so- composition ( C in ½ PDB) of methane together with depth (D), water temperature (T), salinity (S) and oxygen concentration lution, a gas dryer (Na®on tubing), a liquid N2 (O ) temperature trap (150-mm-long column packed with 2 13 Porapak-Q), and a liquid N2 temperature cryofocus- D (m) T (ëC) S (PSU) O2 (ml=l) CH4 Ž C ing (5-mm-long column packed Porapak-Q) [13,19].
Load more

Recommended publications
  • Cambridge University Press 978-1-108-44568-9 — Active Faults of the World Robert Yeats Index More Information
    Cambridge University Press 978-1-108-44568-9 — Active Faults of the World Robert Yeats Index More Information Index Abancay Deflection, 201, 204–206, 223 Allmendinger, R. W., 206 Abant, Turkey, earthquake of 1957 Ms 7.0, 286 allochthonous terranes, 26 Abdrakhmatov, K. Y., 381, 383 Alpine fault, New Zealand, 482, 486, 489–490, 493 Abercrombie, R. E., 461, 464 Alps, 245, 249 Abers, G. A., 475–477 Alquist-Priolo Act, California, 75 Abidin, H. Z., 464 Altay Range, 384–387 Abiz, Iran, fault, 318 Alteriis, G., 251 Acambay graben, Mexico, 182 Altiplano Plateau, 190, 191, 200, 204, 205, 222 Acambay, Mexico, earthquake of 1912 Ms 6.7, 181 Altunel, E., 305, 322 Accra, Ghana, earthquake of 1939 M 6.4, 235 Altyn Tagh fault, 336, 355, 358, 360, 362, 364–366, accreted terrane, 3 378 Acocella, V., 234 Alvarado, P., 210, 214 active fault front, 408 Álvarez-Marrón, J. M., 219 Adamek, S., 170 Amaziahu, Dead Sea, fault, 297 Adams, J., 52, 66, 71–73, 87, 494 Ambraseys, N. N., 226, 229–231, 234, 259, 264, 275, Adria, 249, 250 277, 286, 288–290, 292, 296, 300, 301, 311, 321, Afar Triangle and triple junction, 226, 227, 231–233, 328, 334, 339, 341, 352, 353 237 Ammon, C. J., 464 Afghan (Helmand) block, 318 Amuri, New Zealand, earthquake of 1888 Mw 7–7.3, 486 Agadir, Morocco, earthquake of 1960 Ms 5.9, 243 Amurian Plate, 389, 399 Age of Enlightenment, 239 Anatolia Plate, 263, 268, 292, 293 Agua Blanca fault, Baja California, 107 Ancash, Peru, earthquake of 1946 M 6.3 to 6.9, 201 Aguilera, J., vii, 79, 138, 189 Ancón fault, Venezuela, 166 Airy, G.
    [Show full text]
  • Title On-Land Active Thrust Faults of the Nankai‒Suruga Subduction Zone
    CORE Metadata, citation and similar papers at core.ac.uk Provided by Kyoto University Research Information Repository On-land active thrust faults of the Nankai‒Suruga subduction Title zone: The Fujikawa-kako Fault Zone, central Japan Author(s) Lin, Aiming; Iida, Kenta; Tanaka, Hideto Citation Tectonophysics (2013), 601: 1-19 Issue Date 2013-08 URL http://hdl.handle.net/2433/176993 Right © 2013 Elsevier B.V. Type Journal Article Textversion author Kyoto University *Manuscript Click here to download Manuscript: 4..Lin_Tectono_text-R1.doc Click here to view linked References 1 2 On-land active thrust faults of the Nankai-Suruga subduction 3 4 zone: the Fujikawa–kako Fault Zone, central Japan 5 6 7 8 Aiming Lin1*, Kenta Iida2, and Hideto Tanaka2 9 10 11 12 1 13 Department of Geophysics, Graduate School of Science 14 15 Kyoto University, Kyoto 606-8502, Japan 16 17 2Graduate School of Science and Technology, Shizuoka Univ., 18 19 Ohya 836, Shizuoka 422-8529, Japan 20 21 22 23 24 25 26 27 28 29 30 *Corresponding author 31 32 Dr. Aiming Lin 33 34 Department of Geophysics 35 36 Graduate School of Science 37 38 39 Kyoto University 40 41 Kyoto 606-8502, Japan 42 43 Email: [email protected] 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 1 2 Abstract 3 4 5 This paper describes the tectonic topography that characterizes recent thrusting 6 7 8 9 10 along, the on-land active fault zone of the Nankai-Suruga subduction zone, called the 11 12 13 14 Fujikawa–kako Fault Zone, located near the triple junction of the Eurasian (EUR), 15 16 17 18 Philippine Sea (PHS), and North American (NA) plates, in the western side of Mt.
    [Show full text]
  • Seismic Activities Along the Nankai Trough
    ῔ΐῑῐῒ῕ Bull. Earthq. Res. Inst. Univ. Tokyo Vol. 12 ῍,**-῎ pp. +2/ῌ+3/ Seismic Activities along the Nankai Trough Kimihiro Mochizuki+῎* and Koichiro Obana,῎ +) Earthquake Research Institute, University of Tokyo ,) Japan Marine Science and Technology Center Abstrcat Occurrences of large earthquakes with estimated magnitudes as large as 2 along the Nankai Trough have been well documented in historical materials, and the oldest documented earthquake dates back to A.D. 02.. The recurrence periods are fairly constant, and are approximately ,** years for the earthquakes occurring before +-0+, and about +** years for those after +-0+. However, the number of smaller earthquakes observed by the on-land seismic stations is very small. Both seismic and tectonic couplings along the interface between the overriding and subducting plates are estimated to be nearly +**ῌ from seismic and geodetic data. Therefore, it has been considered that relatively simple physics govern the generation of the historical large earthquakes along the Nankai Trough. With the availability of abundant information on large earthquakes and modern data sets from dense seismic and geodetic networks, the Nankai Trough is one of the best-studied seismo- genic zones. Although improvements have been seen in estimating the fault-plane parameters for the historical earthquakes, there still remain important unanswered questions, such as if there have been unidentified earthquakes that fill in the ,**-year recurrence period. Estimates of precise fault-plane parameters are being demanded to have a better understanding of earthquake genera- tion. One of the most important topics is where the updip limit of the seismogenic zone is located. The location had not been resolved by on-land seismic observations.
    [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]
  • Tsunami Deposits and Earthquake Recurrence Along the Nankai
    Tsunami deposits and earthquake recurrence along the Nankai, Suruga and Sagami Troughs OSAMU FUJIWARA1 and JUNKO KOMATSUBARA1 1: Active Fault Research Center, AIST, C7, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan ([email protected]) INTRODUCTION Histories of great (M~8) subduction-zone earthquakes inferred from tsunami deposits span 3000 years for the Nankai and Suruga Troughs and nearly 10,000 years for the Sagami Trough. The inferred histories contain variable recurrence intervals. The shortest recurrence intervals, 100-200 years for the Nankai Trough and 150-300 years for the Sagami Trough, are similar to those known from written earthquake and tsunami records in the last 1300 years. Longer intervals inferred from the tsunami deposits probably reflect variability in rupture mode, incompleteness of geologic records, and insufficient research. 130E 140E GEOLOGICAL SETTING The Nankai, Suruga and Sagami Troughs comprising the northeastern subduction margin of the Philippine Sea plate are 40N seismically active areas in the world. The Philippine Sea plate converges with overriding plates at a rate of 49-42 mm/year along the Nankai Trough and 27 mm/year around the Sagami Trough (Seno et al., 1993, 1994). Several source areas (segments) 35N Japan are located along these troughs, each of which are 100 - 150 km long along the trough axis and potentially excites M8-class Trench earthquake accompanied by large tsunami and coastal uplift or subsidence. Earthquakes and tsunamis occurred from these areas have repeatedly damaged the Pacific coast of Japan, including Tokyo Nankai Trough and Osaka metropolitan areas. Trench Trench Izu-Ogasawara Izu-Ogasawara Fig.
    [Show full text]
  • Seismotectonic Modeling of the Repeating M 7-Class Disastrous Odawara Earthquake in the Izu Collision Zone, Central Japan
    Earth Planets Space, 56, 843–858, 2004 Seismotectonic modeling of the repeating M 7-class disastrous Odawara earthquake in the Izu collision zone, central Japan Katsuhiko Ishibashi Research Center for Urban Safety and Security/Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501, Japan (Received February 16, 2004; Revised July 15, 2004; Accepted July 21, 2004) Odawara City in central Japan, in the northernmost margin of the Philippine Sea (PHS) plate, suffered from severe earthquake disasters five times during the last 400 years with a mean repeat time of 73 years; in 1633, 1703, 1782, 1853 and 1923. In this region, non-volcanic Izu outer arc (IOA), the easternmost part of the PHS plate, has been subducted beneath Honshu (Japanese main island), and volcanic Izu inner arc (IIA) on the west of IOA has made multiple collision against Honshu. I hypothesize ‘West-Sagami-Bay Fracture’ (WSBF) beneath Odawara, a north-south striking tear fault within the PHS plate that has separated the descending IOA crust from the buoyant IIA crust, through examinations of multiple collision process and the PHS plate configuration. WSBF is considered a blind causative fault of the 1633, 1782 and 1853 M 7 Odawara earthquakes, and is inferred to have ruptured also during the 1703 and 1923 great Kanto earthquakes simultaneously with the interplate main fault. A presumable asperity on WSBF just beneath Odawara seems to control the temporal regularity of earthquake occurrence. Though WSBF has not yet been detected directly, it is considered an essential tectonic element in this region, which might be a fracture zone with a few or several kilometer thickness actually.
    [Show full text]
  • 26. Stratigraphic Synthesis of the Dsdp-Odp Sites in the Shikoku Basin, Nankai Trough, and Accretionary Prism1
    Hill, I.A., Taira, A., Firth, J.V., et al., 1993 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 131 26. STRATIGRAPHIC SYNTHESIS OF THE DSDP-ODP SITES IN THE SHIKOKU BASIN, NANKAI TROUGH, AND ACCRETIONARY PRISM1 Kevin T. Pickering,2 Michael B. Underwood,3 and Asahiko Taira4 ABSTRACT The stratigraphy of the Deep Sea Drilling Project/Ocean Drilling Program drill sites in the northern Shikoku Basin and Nankai Trough area are reviewed in the context of data from ODP Site 808, and interpreted with generalized depositional models for the Nankai Trough and Shikoku backarc basin. Backarc rifting between about 27 and 14 Ma caused the partitioning of the Shikoku Basin early in its history into a western (e.g., DSDP Sites 442 and 297) and eastern Shikoku Basin (e.g., DSDP Sites 443 and 444), separated by the linear and topographically high spreading ridge and the Kinan seamount chain. Pliocene terrigenous turbidites recovered at DSDP Site 297 appear to have been restricted to southwest of the spreading center; therefore, terrigenous turbidity currents coming from the Suruga Trough, to the east-northeast, do not appear to have been capable of overspilling the ridge crest, and if they overspilled the confines of the trench would have been confined to the eastern Shikoku Basin. We therefore believe that the terrigenous turbidites at Site 297 probably were delivered to the Shikoku Basin via Ashizuri Canyon at the western end of Shikoku, which lacks volcanoes of this time interval and is therefore a better candidate source for the more quartzo- feldspathic sands rather than the Izu collision zone.
    [Show full text]
  • Stress and Displacement Fields in the Northeastern Japan Island Arc As Evaluated with Three-Dimensional Finite Element Method and Their Tectonic Interpretations
    Stress and Displacement Fields in the Northeastern Japan Island Arc as Evaluated with Three-Dimensional Finite Element Method and Their Tectonic Interpretations 著者 Sato Kachishige 雑誌名 The science reports of the Tohoku University. Fifth series, Tohoku geophysical journal 巻 31 号 3-4 ページ 57-100 発行年 1988-06 URL http://hdl.handle.net/10097/45308 Tohoku Geophys. Journ. (Sci. Rep. TOhoku Univ., Ser. 5), Vol. 31, No. 3, 4, pp. 57-99, 1988 Stress and Displacement Fields in the Northeastern Japan Island Arc as Evaluated with Three- Dimensional Finite Element Method and Their Tectonic Interpretations KACHISHIGE SAT 0 International Latitude Observatory of Mizusawa, Mizusawa, Iwate Pref. 023 (Received March 25, 1988) Abstract : Numerical experiments for evaluation of the stress and displacement fields within the northeastern Japan island arc were performed by using three-dimensional finite element method. We study mainly the accumulation process of the stress within the arc by imposing boundary conditions as realistically as possible upon the plate-interaction models. Since this arc has very different structures in its southern and northern parts, calculations were separately made for these two parts. They roughly correspond to the Kanto and Tohoku districts, respectively. The patterns of calculated vertical displacement fields at the earth's surface are generally similar to the observed ones in the models of both parts. As to the stress, in the southern part, it is large not only in the shallower portion of the thrust zone between the subducting and overriding plates, but also in the deeper portion where two subducting slabs collide beneath the land area.
    [Show full text]
  • Takuya NISHIMURA Disaster Prevention Research Institute, Kyoto University E-Mail: [email protected]
    G3.6 D1727 Short-term SSEs in the Kanto region, central Japan using GNSS data for a quarter century ©Takuya Nishimura. All rights reserved Takuya NISHIMURA Disaster Prevention Research Institute, Kyoto University E-mail: [email protected] Key points ・ More than 179 short- and imtermidiate- term SSEs (SSEs) with a duration of up to 80 day are detected using 26-years-long GNSS data in the Kanto region, central Japan. ・Two distinctive SSE clusters where relative plate motion is fully released by s-SSEs are found along the Sagami Trough. ・ SSEs rarely overlap shallow tremors and regular M>7 earthquakes along the Japan Trench. However, they overlap M5-6 interplate earthquakes considerably. Detection of small short-term SSEs using GNSS Data Kanto Double Subduction Zone and Boso SSEs The Kanto region, central Japan is situated under complex tectonics Start We apply the method of Flowchart of SSE analysis Nishimura et al. (2013) and where the Philippine Sea and the Pacific plates subduct from the Sagami Trough and the Japan Trench, respectively (Fig. 4).Several SSEs were Pre-process of GNSS data Fault model Nishimura (2014) to detect Remove offsets and estimation reported by the previous studies [e.g., Ozawa et al., 2014]. Recently, postseismic transient Rectangular fault on a jump associated with Remove noisy data Nishikawa et al. found tremors along the Japan trench However, plate interface short-term SSEs in GNSS spatiotemporal distribution of SSEs on both plates still remains unclear. Duration estimation time-series and estimate Spatial filtering Stacking method of crustal deformation (Miyaoka and their fault models from NA Yokota, 2012) (Fig.
    [Show full text]
  • A Block-Fault Model for Deformation of the Japanese Islands Derived from Continuous GPS Observation
    LETTER Earth Planets Space, 52, 1095–1100, 2000 A block-fault model for deformation of the Japanese Islands derived from continuous GPS observation Manabu Hashimoto1, Shin’ichi Miyazaki2, and David D. Jackson3 1RCEP, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan 2Geographical Survey Institute, Kitasato 1, Tsukuba, Ibaraki 305-0811, Japan 3Department of Earth and Space Sciences, UCLA, Los Angeles, CA 90095-1567, U.S.A. (Received February 3, 2000; Revised August 3, 2000; Accepted August 9, 2000) We interpret the continuous GPS data for the Japanese islands from 1996 to 1999 using the model of Hashimoto and Jackson (1993). In this model crustal deformation is represented by a combination of rigid block motions and deformation due to slip deficits along the fault-bounding blocks. Hashimoto and Jackson used 19 blocks, 104 faults, and geodetic data spanning 100 years. In the present work we assume the same fault and block geometry, and we use only the continuous GPS data. Compared to the previous study, the motions of the major blocks are a bit larger: 107 ± 8 mm/yr for the Pacific plate, 47 ± 2 mm/yr for the Philippine Sea plate, and 24 ± 2 mm/yr for the Izu block, all relative to the Amurian plate. The estimated slip directions on active inland faults are now more consistent with geological estimates. Slip deficit rates exceed 10 mm/yr along the Itoigawa-Shizuoka Tectonic Line, Shinanogawa Seismic Zone, Atotsugawa fault, Hanaori fault, Arima-Takatsuki Tectonic Line, Rokko faults, Median Tectonic Line, and southern boundary of the Beppu-Shimabara graben.
    [Show full text]
  • Geotectonic Framework of Japanese Convergent Margin
    MARINE FRONTIERS ABSTRACTS 429 TAIRA, ASAHIKO, and HIDEKAZU TOKUYAMA, Ocean Research Institute, University of Tokyo, Tokyo, Japan Geotectonic Framework of Japanese Convergent Margin A synthesis of recent marine geophysical and geologic investigations around Japan uses data obtained by the Ocean Research Institute of the Uni• versity of Tokyo (including the Japan-France KAIKO Project), the Hydro- graphic Office and Geological Survey of Japan, and the Japan National Oil Company. This work reveals the contrasting characteristics of forearc and back-arc morphotectonics around Japanese subduction zones. From the north, the following features can be summarized. The Kuril Trench off Hokkaido shows a pile of trench deposits as much as 2-sec two-way traveltime in thickness. Despite this thickness, there is little evi• dence of deformation related to the accretionary processes. We propose that subduction of the thick trench fill is occurring at this boundary. The Japan Trench is characterized by massive slumping processes and debris accumulation at the toe of the overriding plate. The Dai-tchi Kashima seamount at the trench has been broken in half by normal faulting related to bending of the oceanic lithosphere into the subduction zone. Forearc subsi• dence is also evident on various profiles. We believe that the inner wall of the Japan Trench has been eroded tectonically at least from the Miocene to the Pliocene. Three plates interacting at the trench triple junction (Japan, Sagami, and Ogasawara Trenches) created a complex framework of convergent margin tectonics, including highly oblique convergence, forearc sliver collision, and pull-apart basin. The conspicuous features observed in the Izu-Bonin arc are forearc ophio- lite (serpentinite diapir) and back-arc rifting close to the volcanic arc.
    [Show full text]
  • An Overview of the Izu-Bonin-Mariana Subduction Factory
    An Overview of the Izu-Bonin-Mariana Subduction Factory Robert J. Stern Geosciences Department University of Texas at Dallas Box 830688 Richardson TX 75083-0688 [email protected] Matthew J. Fouch* Carnegie Institution of Washington Department of Terrestrial Magnetism 5241 Broad Branch Road, NW Washington, DC 20015 Simon L. Klemperer Department of Geophysics Stanford University Stanford CA 94305-2215. [email protected] * now at: Department of Geological Sciences Arizona State University P.O. Box 871404 Tempe, AZ 85287-1404 [email protected] Submitted 10/00, Revised 9/01 ABSTRACT The Izu-Bonin-Mariana (IBM) arc system extends 2800km from near Tokyo, Japan to Guam and is an outstanding example of an intra-oceanic convergent margin (IOCM). Inputs from sub-arc crust are minimized at IOCMs and mantle-to-crust fluxes can be more confidently assessed than for arcs built on continental crust. The history of the IBM IOCM since subduction began about 43 Ma may be better understood than for any other convergent margin. IBM subducts the oldest seafloor on the planet and is under strong extension. The stratigraphy of the western Pacific plate being subducted beneath IBM varies simply parallel to the arc, with abundant off-ridge volcanics and volcaniclastics in the south that diminish to the north, and this seafloor is completely subducted. The Wadati-Benioff Zone varies simply along strike, from dipping gently and failing to penetrate the 660 km discontinuity in the north to plunging vertically in the south into the deep mantle. The northern IBM arc is about 22km thick, with a felsic middle crust; this middle crust is exposed in the collision zone at the northern end of the IBM IOCM.
    [Show full text]