Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Evidence for fault weakness and fluid flow within an active low-angle normal fault

Abstract

Determining the composition and physical properties of shallow-dipping, active normal faults (dips < 35° with respect to the horizontal) is important for understanding how such faults slip under low resolved shear stress and accommodate significant extension of the crust and lithosphere. Seismic reflection images1 and earthquake source parameters2 show that a magnitude 6.2 earthquake occurred at about 5 km depth on or close to a normal fault with a dip of 25–30° located ahead of a propagating spreading centre in the Woodlark basin. Here we present results from a genetic algorithm inversion of seismic reflection data, which shows that the fault at 4–5 km depth contains a 33-m-thick layer with seismic velocities of about 4.3 km s-1, which we interpret to be composed of serpentinite fault gouge. Isolated zones exhibit velocities as low as 1.7 km s-1 with high porosities, which we suggest are maintained by high fluid pressures. We propose that hydrothermal fluid flow, possibly driven by a deep magmatic heat source, and high extensional stresses ahead of the ridge tip have created conditions for fault weakness and strain localization on the low-angle normal fault.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Bathymetry map of the study area showing the location of RV Maurice Ewing EW9510 multichannel seismic (MCS) reflection line 1374.
Figure 2: Multichannel seismic line 1374.
Figure 3: Velocity structure of the fault zone flattened along the fault–basement contact determined by genetic algorithm inversion of every fifth trace from CMPs 1480 to 1630 of MCS line 1374.
Figure 4: Normal-moveout-corrected CMP gathers 1500 (a) and 1600 (b) from MCS line 1374.

Similar content being viewed by others

References

  1. Mutter, J. C., Mutter, C. Z., Abers, G. & Fang, J. Seismic images of low-angle normal faults in the western Woodlark Basin where continental extension yields to seafloor spreading. Eos Trans AGU 74, 412 (1993).

    Article  Google Scholar 

  2. Abers, G. A., Mutter, C. Z. & Fang, J. Shallow dips of normal faults during rapid extension: Earthquakes and normal faults in the Woodlark-D'Entrecasteaux rift system, Papua New Guinea. J. Geophys. Res. 102, 15301–15317 (1997).

    Article  ADS  Google Scholar 

  3. Taylor, B. et al. Proc. ODP Init. Rep. [CD-ROM] 180, (Ocean Drilling Program, College Station, 1999).

    Google Scholar 

  4. Taylor, B., Mutter, C., Goodliffe, A. & Fang, J. Active continental extension: the Woodlark Basin. JOI/USSAC Newsl. 9, 1–4 (1996).

    Google Scholar 

  5. Davies, H. L. & Smith, I. E. Geology of Eastern Papua. Geol. Soc. Am. Bull. 82, 3299–3312 (1971).

    Article  ADS  Google Scholar 

  6. Anderson, E. M. The Dynamics of Faulting and Dyke Formation with Application to Britain (Oliver and Boyd, Edinburgh, 1942).

    Google Scholar 

  7. Byerlee, J. D. Friction of Rocks. Pure Appl. Geophys. 116, 615–626 (1978).

    Article  ADS  Google Scholar 

  8. Rice, J. R. in Fault Mechanics and Transport Properties of Rock (eds Evans, B. & Wong, T.-F.) 475–503 (Academic, San Diego, 1992).

    Google Scholar 

  9. Byerlee, J. D. Friction, overpressure and fault normal compression. Geophys. Res. Lett. 17, 2109–2112 (1990).

    Article  ADS  Google Scholar 

  10. Sen, M. K. & Stoffa, P. L. Rapid sampling of model space using genetic algorithms: examples from seismic waveform inversion. Geophys. J. Int. 108, 281–292 (1992).

    Article  ADS  Google Scholar 

  11. Widess, M. B. How thin is a thin bed? Geophysics 49, 1637–1648 (1984).

    Article  Google Scholar 

  12. Ostrander, W. J. Plane-wave reflection coefficients for gas sands at nonnormal angles of incidence. Geophysics 49, 1637–1648 (1984).

    Article  ADS  Google Scholar 

  13. Shuey, R. T. A simplification of the Zoeppritz equations. Geophysics 50, 609–614 (1985).

    Article  ADS  Google Scholar 

  14. Tucholke, B. E. & Lin, J. A geological model for the structure of ridge segments in slow spreading ocean crust. J. Geophys. Res. 99, 11937–11958 (1994).

    Article  ADS  Google Scholar 

  15. Wyllie, M. R. J., Gregory, A. R. & Gardner, G. H. F. An experimental investigation of factors affecting elastic wave velocities in porous media. Geophysics 23, 459–493 (1958).

    Article  ADS  Google Scholar 

  16. Marone, C., Raleigh, C. B. & Scholz, C. H. Frictional behavior and constitutive modeling of simulated fault gouge. J. Geophys. Res. 95, 7007–7025 (1996).

    Article  ADS  Google Scholar 

  17. Mutter, J. C. & Karson, J. A. Structural processes at slow-spreading ridges. Science 257, 627–634 (1992).

    Article  ADS  CAS  Google Scholar 

  18. Taylor, B., Goodliffe, A. M. & Martinez, F. How continents break up: Insights from Papua New Guinea. J. Geophys. Res. 104, 7497–7512 (1999).

    Article  ADS  Google Scholar 

  19. Tucholke, B. E., Lin, J. & Kleinrock, M. C. Megamullions and mullion structure defining oceanic metamorphic core complexes on the Mid-Atlantic Ridge. J. Geophys. Res. 103, 9857–9866 (1998).

    Article  ADS  Google Scholar 

  20. Mutter, J. C., Mutter, C. Z. & Fang, J. Analogies to oceanic behaviour in the continental breakup of the western Woodlark Basin. Nature 380, 333–336 (1996).

    Article  ADS  CAS  Google Scholar 

  21. Goldberg, D. E. Genetic Algorithms in Search, Optimization and Machine Learning (Addison-Wesley, Reading, MA, 1989).

    MATH  Google Scholar 

  22. Ganley, D. C. A method for calculating synthetic seismograms which includes the effects of absorption and dispersion. Geophysics 46, 1100–1107 (1981).

    Article  ADS  Google Scholar 

  23. Taylor, B., Goodliffe, A., Martinez, F. & Hey, R. Continental rifting and initial sea-floor spreading in the Woodlark basin. Nature 374, 534–537 (1995).

    Article  ADS  CAS  Google Scholar 

Download references

Acknowledgements

We thank W. Menke, C. Scholz, S. Carbotte, A. Lerner-Lam and D. Goldberg for helpful discussions and R. Detrick and W. Bosworth for comments that improved this Letter. J.F. and J.M. were supported under a grant from JOI/USSAC. We thank the captain and crew of the RV Maurice Ewing for MCS data acquired on EW9510. ODP Leg 180 drilling results used in this study were obtained thanks to the efforts of the captain and crew of the DV JOIDES Resolution; A. Klaus and the TAMU scientific support staff; co-chiefs P. Houchon and B. Taylor and the ODP Leg 180 Scientific Party.

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to J. S. Floyd.

Rights and permissions

Reprints and permissions

About this article

Cite this article

Floyd, J., Mutter, J., Goodliffe, A. et al. Evidence for fault weakness and fluid flow within an active low-angle normal fault. Nature 411, 779–783 (2001). https://doi.org/10.1038/35081040

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI: https://doi.org/10.1038/35081040

This article is cited by

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing