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.

Motion in the north Iceland volcanic rift zone accommodated by bookshelf faulting

Abstract

Along mid-ocean ridges the extending crust is segmented1 on length scales of 10–1,000 km. Where rift segments are offset from one another, motion between segments is accommodated by transform faults that are oriented orthogonally to the main rift axis. Where segments overlap, non-transform offsets with a variety of geometries2 accommodate shear motions. Here we use micro-seismic data to analyse the geometries of faults at two overlapping rift segments exposed on land in north Iceland. Between the rift segments, we identify a series of faults that are aligned sub-parallel to the orientation of the main rift. These faults slip through left-lateral strike-slip motion. Yet, movement between the overlapping rift segments is through right-lateral motion. Together, these motions induce a clockwise rotation of the faults and intervening crustal blocks in a motion that is consistent with a bookshelf-faulting mechanism, named after its resemblance to a tilting row of books on a shelf3. The faults probably reactivated existing crustal weaknesses, such as dyke intrusions, that were originally oriented parallel to the main rift and have since rotated about 15° clockwise. Reactivation of pre-existing, rift-parallel weaknesses contrasts with typical mid-ocean ridge transform faults and is an important illustration of a non-transform offset accommodating shear motion between overlapping rift segments.

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: Automated microseismic event location, showing intense activity between volcanic rift segments.
Figure 2: Sub-parallel array of left-lateral strike-slip faults in the Askja–Kverkfjöll relay zone.
Figure 3: A typical strike-slip event, showing clear arrivals and a well-constrained focal mechanism.
Figure 4: Right-lateral transform motion across the Askja–Kverkfjöll relay zone.

Similar content being viewed by others

References

  1. MacDonald, K. C. et al. A new view of the mid-ocean ridge from the behaviour of ridge axis discontinuities. Nature 335, 217–225 (1988).

    Article  Google Scholar 

  2. Grindlay, N. R., Fox, P. J. & Macdonald, K. C. Second-order ridge axis discontinuities in the South Atlantic: morphology, structure and evolution. Mar. Geophys. Res. 13, 21–49 (1991).

    Article  Google Scholar 

  3. Mandl, G. Tectonic deformation by rotating parallel faults: the ‘bookshelf’ mechanism. Tectonophysics 141, 277–316 (1987).

    Article  Google Scholar 

  4. Einarsson, P. Plate boundaries, rifts and transforms in Iceland. Jökull 58, 35–58 (2008).

    Google Scholar 

  5. Hjartardóttir, A. R., Einarsson, P. & Sigurdsson, H. The fissure swarm of the Askja volcanic system along the divergent plate boundary of N Iceland. Bull. Volcanol. 71, 961–975 (2009).

    Article  Google Scholar 

  6. Hjartardóttir, A. R. & Einarsson, P. The Kverkfjöll fissure swarm and eastern boundary of the Northern Volcanic Rift Zone, Iceland. Bull. Volcanol. 74, 143–162 (2012).

    Article  Google Scholar 

  7. Sigvaldason, G. E., Annertz, K. & Nilsson, M. Effect of glacier loading deloading on volcanism—postglacial volcanic production-rate of the Dyngjufjoll area, central Iceland. Bull. Volcanol. 54, 385–392 (1992).

    Article  Google Scholar 

  8. Bayasgalan, A., Jackson, J., Ritz, J-F. & Carretier, S. Field examples of strike-slip fault terminations in Mongolia and their tectonic significance. Tectonics 18, 394–411 (1999).

    Article  Google Scholar 

  9. DeMets, R., Gordon, G., Argus, D. F. & Stein, S. Effect of recent revisions to the geomagnetic reversal timescale on estimates of current plate motions. Geophys. Res. Lett. 21, 2191–2194 (1994).

    Article  Google Scholar 

  10. Rögnvaldsson, S., Gudmundsson, A. & Slunga, R. Seismotectonic analysis of the Tjörnes Fracture Zone, an active transform fault in north Iceland. J. Geophys. Res. 103, 117–130 (1998).

    Article  Google Scholar 

  11. Árnadóttir, Th., Geirsson, H. & Einarsson, P. Coseismic stress changes and crustal deformation on the Rekjanes Peninsula due to triggered earthquakes on June 17, 2000. J. Geophy. Res. 109, B09307 (2004).

    Article  Google Scholar 

  12. Einarsson, P. & Sæmundsson, K. Earthquake epicenters 1982–1985 and volcanic systems in Iceland (Map). (Menningarsjóður, Reykjavı´k, 1987).

  13. Einarsson, P. Earthquakes and present day tectonism in Iceland. Tectonophysics 189, 261–279 (1991).

    Article  Google Scholar 

  14. Þorbjarnardóttir, B. S., Gudmundsson, G. B., Hjaltadóttir, S. & Roberts, M. J. Seismicity in Iceland during 2006. Jökull 57, 45–60 (2007).

    Google Scholar 

  15. Hjartardóttir, A. R. Fissure swarms of the Northern Volcanic Rift Zone, Iceland Masters thesis, Univ. Iceland (2013).

  16. Nicholson, C., Seeber, L., Williams, P. & Sykes, L. R. Seismicity and fault kinematics through the eastern Transverse Ranges, California: Block rotation, strike-slip faulting and low angle thrusts. J. Geophys. Res. 91, 4891–4908 (1986).

    Article  Google Scholar 

  17. Einarsson, P. Mapping of Holocene surface ruptures in the South Iceland Seismic Zone. Jökull 60, 121–138 (2010).

    Google Scholar 

  18. Searle, R. C. & Hey, R. N. Gloria observations of the propagating rift at 95.5°W on the Cocos-Nazca spreading centre. J. Geophys. Res. 88, 6433–6447 (1983).

    Article  Google Scholar 

  19. Wetzel, L. R., Wiens, D. A & Kleinrock, M. C. Evidence from earthquakes for bookshelf faulting at large non-transform ridge offsets. Nature 362, 235–237 (1993).

    Article  Google Scholar 

  20. Copley, A. & Jackson, J. Active tectonics of the Turkish–Iranian plateau. Tectonics 25, TC6006 (2006).

    Article  Google Scholar 

  21. Larson, R. L. et al. Roller-bearing tectonic evolution of the Juan Fernandez microplate. Nature 356, 571–575 (1992).

    Article  Google Scholar 

  22. Soosalu, H. et al. Lower-crustal earthquakes caused by magma movement beneath Askja volcano on the north Iceland rift. Bull. Volcanol. 72, 55–62 (2009).

    Article  Google Scholar 

  23. Key, J., White, R. S., Soosalu, H. & Jakobsdóttir, S. S. Multiple melt injection along a spreading segment at Askja, Iceland. Geophys. Res. Lett. 38, 1–5 (2012).

    Google Scholar 

  24. Drew, J., White, R. S., Tilman, F. & Tarasewicz, J. Coalescence microseismic mapping. Geophys. J. Int. 195, 1773–1785 (2013).

    Article  Google Scholar 

  25. Tarasewicz, J., Brandsdóttir, B., White, R. S., Hensh, M. & Thorbjarnardóttir, B. Using microearthquakes to track repeated magma intrusions beneath the Eyjafjallajökull stratovolcano, Iceland. J. Geophys. Res. 117, B00C06 (2012).

    Article  Google Scholar 

  26. Lomax, A., Virieux, J., Volant, P. & Berge, C. Advances in Seismic Event Location (Kluwer, 2000).

    Google Scholar 

  27. Key, J. Tracking Melt with Lower Crustal Earthquakes at Askja, Iceland (Univ. Cambridge, 2012).

    Google Scholar 

  28. Martens, H. R. & White, R. S. Triggering of microearthquakes in Iceland by volatiles released from a dyke intrusion. Geophys. J. Int. 194, 1738–1754 (2013).

    Article  Google Scholar 

  29. Waldhauser, F. & Ellsworth, W. A double-difference earthquake location algorithm: Method and application to the northern Hayward fault, California. Bull. Seismol. Soc. Am. 90, 1353–1368 (2000).

    Article  Google Scholar 

  30. Reasenberg, P. & Oppenheimer, D. H. FPFIT, FPPLOT, FPPAGE: Fortran computer programs for calculating and displaying earthquake fault-plane solutions. USGS Open-file Report. 85–739 (1985).

Download references

Acknowledgements

Seismometers were borrowed from the Natural Environment Research Council SEIS-UK (loans 914 and 968), and the work was financially supported by a research grant and studentships from the NERC and Shell. We thank S. Steinþórsson, H. Soosalu and all those who have assisted in fieldwork in Iceland since 2009. We are grateful to Á. R. Hjartardóttir and P. Einarsson for providing raw data on fracture orientations and for helpful comments on the manuscript, and A. Copley for advice. The Icelandic Meteorological Office kindly provided additional data from their seismometers in northeast Iceland. Dept. Earth Sciences, Cambridge contribution number ESC3000.

Author information

Authors and Affiliations

Authors

Contributions

All authors participated in data collection and the interpretation of results. Data processing of the microseismic swarms was carried out by R.G.G., with the addition of picks for the easternmost swarm by R.S.W. The manuscript was written by R.G.G and R.S.W.

Corresponding author

Correspondence to Robert G. Green.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supplementary Information (PDF 1688 kb)

Supplementary Information

Supplementary Information (XLSX 17 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Green, R., White, R. & Greenfield, T. Motion in the north Iceland volcanic rift zone accommodated by bookshelf faulting. Nature Geosci 7, 29–33 (2014). https://doi.org/10.1038/ngeo2012

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/ngeo2012

This article is cited by

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