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  • 1
    Electronic Resource
    Electronic Resource
    Constraints on the state of in situ effective stress and the mechanical behavior of ODP Leg 186 claystones in the Japan Trench forearc (2004)
    Melbourne, Australia : Blackwell Science Pty
    The @island arc 13 (2004), S. 0 
    Details
    ISSN: 1440-1738
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract   The Japan Trench forearc offshore Honshu Island in northeast Japan, where the 130-m.y.-old Pacific oceanic plate is presently subducted, was drilled during the Ocean Drilling Program Leg 186. Results from mechanical and sedimentological studies of claystones recovered from Sites 1150 and 1151 in the overlying erosional forearc wedge are reported in the present study. Although many physical properties are similar in the seismic (Site 1150) and aseismic portion (Site 1151) of the shallow forearc, Site 1150 displayed a higher abundance of open fractures, two prominent fault zones and enigmatic pore fluid signatures in the claystones. The abundance of weak mineral phases, together with high smectite contents (from X-ray diffraction), control the low friction coefficients of 0.33–0.39 of the claystones in ring-shear experiments. Results from triaxial testing proposed overall low magnitudes of in situ effective vertical stress, with somewhat lower values at Site 1150 than at Site 1151. Similarly, samples from Site 1150 displayed slightly higher pore fluid pressures than those at Site 1151. The high sediment porosities, which are in part also a result of intact diatom tests (from scanning electron microscope), together with the anomalous fluid signatures and elevated pore fluid pressures, could very likely result from upward migration and influx of deep-seated waters. Dewatering reactions at depth result in enhanced pore fluid pressure transients along out-of-sequence thrusts and consequently lower effective stress. At depths greater than that of Leg 186 drilling, elevated pressure–temperature conditions trigger mineral transformation and cementation, which result in increasing friction, unstable sliding and seismic rupture. Such earthquakes could have repeatedly disaggregated the consolidated claystone fabrics at the seismic site, and could be responsible for differences in yield strength and cementation when compared to the aseismic Site 1151.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1440-1738.2003.00423.x
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  • 2
    Electronic Resource
    Electronic Resource
    Evidence for fluid flow in the Japan Trench forearc using isotope geochemistry (Cl, Sr, B): Results from ODP Site 1150 (2004)
    Melbourne, Australia : Blackwell Science Pty
    The @island arc 13 (2004), S. 0 
    Details
    ISSN: 1440-1738
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract  Interstitial pore waters from Ocean Drilling Program Site 1150, where ∼1200 m of sub-sea-floor sediment from the upper Japan Trench forearc were recovered, were analyzed for element concentrations and Cl, Sr and B isotopes. Although chlorinity showed profound down-hole freshening to values as low as ∼310 mm (0.55 × seawater) in the deeper part of the claystone-dominated succession, both Sr and B concentrations showed an overall increase. Sr reached concentrations of up to 〉250 µm (∼3.00 × seawater), whereas B-enrichment was even stronger (3920 µm; i.e. 9.30 × seawater). The strong variations in concentration correspond to fractionation reactions in the deep, tectonically deformed part of the forearc. The heavily fractured portion of Site 1150 (from ∼700 m to the total depth of the hole) has two shear zones that very likely act as conduits that expel deep-seated fluids to the sea floor. These fluids not only showed the strongest freshening of Cl, but were also characterized by low δ37Cl measurements (down to −1.1‰), the heaviest δ11B measurements (∼40–46‰) and the least radiogenic 87Sr/ 86Sr measurements. The profound isotope anomalies together with the excursions in element concentrations suggest that diagenetic processes operate at that depth. These include clay mineral diagenesis, alteration of tephra from the Japan and Izu Arcs, and possibly transformation of biogenic silica from abundant diatoms. Given the strong enrichment of some mobile elements (e.g. Sr, B, Li), enhanced fluid flow through permeable penetrative faults through the forearc (like the shear zones at Site 1150) could be an efficient mechanism for back-flux of those elements from the deep forearc into the hydrosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1440-1738.2003.00424.x
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  • 3
    Electronic Resource
    Electronic Resource
    Cross-section through the frontal Japan Trench subduction zone: Geochemical evidence for fluid flow and fluid–rock interaction from DSDP and ODP pore waters and sediments (2004)
    Melbourne, Australia : Blackwell Science Pty
    The @island arc 13 (2004), S. 0 
    Details
    ISSN: 1440-1738
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract  Fluids and sediments from Deep Sea Drilling Project/Ocean Drilling Program Legs (56, 57, 87 and 186) along a transect extending from the subducting plate, across the midslope and upper slope of the Japan Trench forearc were analyzed for B and B isotopes in order to assess their composition and fluid–sediment interaction. At the reference Site 436 on the subducting plate, changes in B contents and B isotopes are controlled by the lithology and diagenesis only. The midslope Sites 440 and 584 showed stronger variations in the B geochemistry, which can be related to diagenesis and tectonic dewatering along faults. The strongest changes in the B geochemistry were observed on the upper slope Sites 1150 and 1151, where profound down-hole freshening (chlorinities as low as ∼310 mmol) coincides with a B enrichment (up to 9.3 × seawater concentration). The B isotope pore fluid profile of Site 1150 displayed a bimodal variation with depth, first increasing to values more positive than seawater, then shifting to lower signatures typical for deep-seated fluids, whereas Site 1151 showed a constant B decrease with depth. Sites 1150 and 1151 sediments showed B increases with depth to values as high as ∼164 p.p.m. and isotopic compositions ranging from ∼+4 to −9‰. A linear decrease in Bsolid/Bfluid ratio, suggests that B geochemistry of the upper slope sites is controlled by fluid–rock interaction and deep-seated fluid flow, whereas constant Bsolid/Bfluid ratios were observed at the reference site on the incoming plate. This fluid overprint is probably caused by normal faults in the sediment cover which might be interconnected to deep thrusts in the underlying Cretaceous accreted wedge. This suggests that the erosive Japan Trench margin is characterized by back-flux of deep-seated, B-enriched fluids into the ocean, which is facilitated by extensional normal faulting as a result of tectonic erosion and subsidence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1440-1738.2003.00425.x
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  • 4
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    Geotechnical Characteristics and Slope Stability Analysis on the Deeper Slope of the Ligurian Margin, Southern France (2014)
    Springer
    In:  In: Landslide Science for a Safer Geoenvironment. Springer, Heidelberg, Germany, pp. 549-555. ISBN 978-3-319-04995-3
    Details
    Publication Date: 2015-09-24
    Description: Submarine slope failures of various types and sizes are common along the tectonic and seismically active Ligurian margin, northwestern Mediterranean Sea, primarily because of seismicity up to ~M6, rapid sediment deposition in the Var fluvial system, and steepness of the continental slope (average 11°). We present geophysical, sedimentological and geotechnical results of two distinct slides in water depth 〉1,500 m: one located on the flank of the Upper Var Valley called Western Slide (WS), another located at the base of continental slope called Eastern Slide (ES). WS is a superficial slide characterized by a slope angle of ~4.6° and shallow scar (~30 m) whereas ES is a deep-seated slide with a lower slope angle (~3°) and deep scar (~100 m). Both areas mainly comprise clayey silt with intermediate plasticity, low water content (30–75 %) and underconsolidation to strong overconsolidation. Upslope undeformed sediments have low undrained shear strength (0–20 kPa) increasing gradually with depth, whereas an abrupt increase in strength up to 200 kPa occurs at a depth of ~3.6 m in the headwall of WS and ~1.0 m in the headwall of ES. These boundaries are interpreted as earlier failure planes that have been covered by hemipelagite or talus from upslope after landslide emplacement. Infinite slope stability analyses indicate both sites are stable under static conditions; however, slope failure may occur in undrained earthquake condition. Peak earthquake acceleration from 0.09 g on WS and 0.12 g on ES, i.e. M5–5.3 earthquakes on the spot, would be required to induce slope instability. Different failure styles include rapid sedimentation on steep canyon flanks with undercutting causing superficial slides in the west and an earthquake on the adjacent Marcel fault to trigger a deep-seated slide in the east.
    Type: Book chapter , NonPeerReviewed
    DOI: 10.1007/978-3-319-04996-0_84
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    OceanRep: Book chapter
  • 5
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    How Stable Is the Nice Slope? – An Analysis Based on Strength and Cohesion from Ring Shear Experiments (2013)
    Springer
    In:  In: Submarine Mass Movements and Their Consequences. Springer, Heidelberg, Germany, pp. 189-199. ISBN 978-3-319-00971-1
    Details
    Publication Date: 2015-09-24
    Description: The upper shelf of the landslide-prone Ligurian Margin (Western Mediterranean Sea) off Nice well-known for the 1979 Airport Landslide is a natural laboratory to study preconditioning factors and trigger mechanisms for submarine landslides. For this study low-stress ring shear experiments have been carried out on a variety of sediments from 〉50 gravity cores to characterise the velocity-dependent frictional behaviour. Mean values of the peak coefficient of friction vary from 0.46 for clay-dominated samples (53 % clay, 46 % silt, 1 %) sand up to 0.76 for coarse-grained sediments (26 % clay, 57 % silt, 17 % sand). The majority of the sediments tested show velocity strengthening regardless of the grain size distribution. For clayey sediments the peak and residual cohesive strength increases with increasing normal stress, with values from 1.3 to 10.6 kPa and up to 25 % of all strength supported by cohesive forces in the shallowmost samples. A pseudo-static slope stability analysis reveals that the different lithologies (even clay-rich material with clay content ≥50 %) tested are stable up to slope angles 〈26° under quasi-drained conditions
    Type: Book chapter , NonPeerReviewed
    DOI: 10.1007/978-3-319-00972-8_17
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    OceanRep: Book chapter
  • 6
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    Styles and productivity of mud diapirism along the Middle American Margin, Part II: Mound Culebra and Mounds 11 and 12 (2005)
    Springer
    In:  In: Mud volcanoes, geodynamics and seismicity. , ed. by Martinelli, G. and Panahi, B. NATO science series : Series 4, Earth and environmental sciences, 51 . Springer, Dordrecht, pp. 49-76. ISBN 1-402-03203-X
    Details
    Publication Date: 2019-09-23
    Type: Book chapter , PeerReviewed
    DOI: 10.1007/1-4020-3204-8_5
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    OceanRep: Book chapter
  • 7
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    On the consolidation state of sediments from the accretionary prism offshore Vancouver Island, North Cascadia Margin (2022)
    Springer
    Details
    Publication Date: 2024-02-07
    Description: Sediment geotechnical properties are an important component of geohazard analyses and studies on submarine slope failures on continental margins. The northern Cascadia margin is a region of repeated subduction earthquakes and related geohazards including devastating tsunamis. Despite several drilling campaigns at this margin mostly for gas hydrate studies, sediment geotechnical properties are lacking to date. We therefore investigated a set of 20 half-round samples from four drill sites of Integrated Ocean Drilling Program (IODP) Expedition 311 along a margin-perpendicular transect. Samples were analysed for Atterberg properties (liquid limit, plasticity limit, plasticity index) and consolidation state (pre-consolidation stress, over-consolidation ratio, initial void ratio and compression index). Results of these parameters are in good agreement with similar studies at the southern Cascadia margin from Ocean Drilling Program (ODP) Leg 204 and are regarded robust, despite the long time-span between sample recovery in 2005 and our analyses. Individual results are interpreted at each of the drill sites and reflect the overall tectonic state of the location within the accretionary prism. An interplay of site-specific tectonic forcing, including thrust faulting, uplift, folding, and erosion appears to govern the depth-dependent consolidation state of the sediments.
    Type: Article , PeerReviewed
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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