Abstract
Fluid venting in accretionary prisms, which feeds chemosynthetic biological communities, occurs mostly on the marginal thrust ridge. New seismic data for the marginal ridge of the Cascadia prism show significantly lower velocity than that in the adjacent oceanic basin and place important constraints on the interpretations of why fluid venting occurs mostly on the marginal ridge. We employed a finite-element method to analyze a typical fault-bend folding model to explain the phenomenon. The fault in the model is simulated by contact elements. The elements are characterized not only by finite sliding along a slide line, but also by elastoplastic deformation.
We present the results of a stress analysis which show that the marginal ridge is under subhorizontal extension and the frontal thrust is under compression. This state of stress favors the growth of tensile cracks in the marginal ridge, facilitates fluid flow and reduces seismic velocities therein; on the other hand, it may close fluid pathways along the frontal thrust and divert fluid flow to the marginal ridge.
Similar content being viewed by others
References
Agar, S. M. (1990),The Interaction of Fluid Processes and Progressive Deformation during Shallow Level Accretion: Examples from Shimanto Belt of SW Japan, J. Gephys. Res.95, 9133–9147.
Bebout, G. E. (1919),Geometry and Mechanisms of Fluid Flow at 15 to 45 km depths in an Early Cretaceous Accretionary Complex, Geophys. Res. Lett.18, 923–926.
Boulegue, J., Iiyama, J. T., Charlon, J.-L., and Jedwab, J. (1987),Nankai Trough, Japan Trench and Kuril Trench, Geomechanical Fluids.
Carson, B. (1977),Tectonically-induced Deformation of Deep-sea Sediments off Washington and Oregon: Mechanical Consolidation, Mar. Geol.24, 289–307.
Carson, B., Holmes, M. L., Umstet, D, Strasser, J. G., andJohnson, H. P. (1990),Fluid Expulsion from the Cascadia Accretionary Prism: Evidence from Poresity Distribution, Direct Measurements, and GLORIA Imagery, Philos, Trans. R. Soc. London A335, 331–340.
Cloos, M. (1984),Landward-dipping Reflectors in Accretionary Wedges: Active Dewatering Conducts? Geology12, 519–522.
Cochrane, G. R., Moore, J. C., MacKay, M. E., andMoore, G. F. (1994),Velocity-porosity Model of the Oregon Accretionary Prism from Multichannel Seismic Reflection Data, J. Geophys. Res.99, 7033–7043.
Coward, M. P., Nell, P. R., andTalbot, J.,An analysis of strains is associated with the Moine Thrust Zone, Assynt, Northwest Scotland. InStructural Geology of Fold and Thrust Belts (eds. Mitra, S., and Fisher, G. W.) (John Hopkins Univ. Press 1992) pp. 105–122.
Davis, D., Suppe, J., andDahlen, F. A. (1983),The Mechanics of Fold-and-thrust belts, J. Geophys. Res.88, 1153–1172.
Dix, D. H. (1955),Seismic Velocities from Surface Measurements, Geophysics20, 68–86.
Fisher, D. M., andBrantley, S. L. (1992),Models of Quartz Overgrowth and Vein Formation: Deformation and Episodic Fluid Flow in an Ancient Subduction Zone, J. Geophys. Res.97, 20043–20061.
Hamilton, E. L. (1978),Sound Velocity-density Relations in Sea-floor Sediments and Rocks, J. Acoust. Soc. Am.63, 366–377.
Henry, P., andWang, C.-Y. (1991),Modeling of Fluid Flow and Pore Pressure at the Toe of the Oregon and Barbados Accretionary Wedges, J. Geophys. Res.96, 20109–20130.
Horath, F. (1989),Permeability evolution in the Cascadia Accretionary Prism: Examples from the Oregon Prism and Olympic Peninsula Melanges. M.Sc. Thesis, University of California, Santa Cruz.
Kulm, L. D., von Huene, R., andShipboard Scientific Party (1973),Shipboard Site Report: Site 174 and Site 175, Initial Rep. Deep Sea Drill. Proj.18, 97–212.
Kulm, L. D. et al. (1986),Oregon Subduction Zone: Venting, Fauna, and Carbonates, Science231, 561–566.
Le Pichon, X. et al. (1987),Nankai Trough and Zenisu Ridge: A Deep-sea Submersible Survey, Earth Planet. Sci. Lett.83, 285–299.
Lewis, B. T. R.,Changes in P and S velocities caused by subduction related accretion off Washington/Oregon. InShear Waves in Marine Sediments (Hovem; Richardson; and Stol, eds.) (Kluwer Academic Publications 1990).
MacKay, M. E., Moore, G. F., Cochrane, G. R., Moore, J. C., andKulm, L. D. (1992),Landward Vergence and Oblique Structural Trends in the Oregon Margin Accretionary Prism: Implications and Effect on Fluid Flow, Earth Planet. Sci. Lett.109, 477–491.
McPherson, R. C., andDengler, L. A. (1992),The Honeydew Earthquake, California Geology, 31–39.
Moore, J. C., Orange, D., andKulm, L. D. (1990),Interrelationship of Fluid Venting and Structural Evolution: Alvin Observations from the Frontal Accretionary Prism, Oregon, J. Geophys. Res.95, 8795–8808.
O'Connell, R., andBudiansky, B. (1974),Seismic Velocities in Dry and Saturated Cracked Solid, J. Geophys. Res.79, 5412–5425.
Riddihough, R. P. (1984),A Model for Recent Plate Interaction off Canada's West Coast, Can. J. Earth. Sci.14, 384–396.
Screaton, E. J., Wuthrich, D. R., andDreiss, S. J. (1990),Permeabilities, Fluid Pressures, and Flow Rates in the Barbados Ridge Complex, J. Geophys. Res.95, 8997–9007.
Seely, D. R.,The significance of landward vergence and oblique structural trends on trench inner slopes. InIsland Arcs, Deep Sea Trenches, and Back-Arc Basins (eds. Talwani, M., and Pitman, W. C. III) (Amer. Geophys. Union Maurice Ewing Series 1, Washington D.C. 1977) pp. 187–198.
Shi, Y., Wang, C.-Y., andvon Huene, R. (1989),Hydrogeological Modeling of Porous Flow in the Oregon Accretionary Prism, Geology17, 320–323.
Snavely, P. D., Jr., andMiller, J. The central Oregon continental margin, lines WO76-4 and WO76-5 Seismic images of modern convergent margin tectonic structure (ed. von Huene, R.) In AAPG Stud. Geol. Vol.26, pp. 24–29.
Suess, E., Carson, B., Ritger, S., Moore, J. C., Jones, M. L., Kulm, L. D., andCochrane, G., (1985),Biological communities at vent sites along the subduction zone off Oregon. InThe Hydrothermal Vents of the Eastern Pacific: An Overview (ed. Jones, M. L.) Biol. Soc. Wash. Bull.6, 474–484.
Suppe, J. (1983),Geometry and Kinematics of Fault-bend Folding, Am. J. Sc.283, 648–721.
Taner, M. T., andKoehler, F. (1969),Velocity Spectra-digital Computer Derivation and Applications of Velocity Functions, Geophys.34, 859–881.
Vrolijk, P. J. (1987),Tectonically-driven Fluid Flow in the Kodiak Accretionary Complex, Alaska, Geology15, 466–469.
Wang, C.-Y., Shi, Y., Hwang, W.-T., andChen, H. (1990),Hydrogeologic Processes in the Oregon-Washington Accretionary Complex, J. Geophys. Res.95, 9009–9033.
Westbrook, G. K. (1991),Geophysical Evidence for the Role of Fluids in Accretionary Wedge Tectonics, Philos, Trans. R. Soc. London A335, 227–242.
Westbrook, G. K., andSmith, M. T. (1983),Long Decollements and Mud Volcanoes: Evidence from the Barbados Ridge Complex for the Role of High Pore Pressure in the Development of an Accretionary Wedge, Geology11, 279–285.
Author information
Authors and Affiliations
Additional information
On leave from Peking University, Beijing, 100871, China
Rights and permissions
About this article
Cite this article
Cai, Y., Wang, Cy., Hwang, Wt. et al. The effect of fault-bend folding on seismic velocity in the marginal ridge of accretionary prisms. PAGEOPH 145, 637–646 (1995). https://doi.org/10.1007/BF00879593
Received:
Revised:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00879593