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A four-year study of shear-wave splitting in Iceland: 2. Temporal changes before earthquakes and volcanic eruptions

By
T. Volti
T. Volti
1
School of Geosciences, University of Edinburgh, Grant Institute West Mains Road, Edinburgh, EH9 3JW, UK (e-mail: tvolti@glg.ed.ac.uk; scrampin@ed.ac.uk)
2
Japan Marine Science and Technology Centre Yokahama, 237-0061, Japan
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S. Crampin
S. Crampin
1
School of Geosciences, University of Edinburgh, Grant Institute West Mains Road, Edinburgh, EH9 3JW, UK (e-mail: tvolti@glg.ed.ac.uk; scrampin@ed.ac.uk)
3
Edinburgh Anisotropy Project, British Geological Survey Edinburgh EH9 3LA, UK
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Published:
January 01, 2003

Abstract

This chapter reports temporal variations in the time-delays between split shear-waves before both earthquakes and volcanic eruptions in Iceland. The hypothesis is that during a build-up of stress, crack distributions in a large volume surrounding the immediate source zone are modified until the level of cracking reaches fracture criticality, when shear strength is lost, rocks fracture, and earthquakes, or some types of eruptions occur. In one two-year period, when volcanic and magmatic activity appeared to be low, changes in shear-wave splitting in SW Iceland were observed routinely before earthquakes with magnitudes between M3.5 and M5.1. Assuming a linear relationship between earthquake magnitude and the rate of increasing crack aspect-ratio in this comparatively narrow amplitude range, the time and magnitude of a M5 earthquake was successfully stress-forecast. These results confirm a new understanding of pre-fracturing deformation of in situ rock that has implications over a wide range of situations where the crust undergoes changes at low levels of deformation below those at which rocks fracture. Potential applications of this new understanding include monitoring hydrocarbon production, as well as stress-forecasting earthquakes and some volcanic eruptions.

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Contents

Geological Society, London, Special Publications

New Insights into Structural Interpretation and Modelling

D. A. Nieuwland
D. A. Nieuwland
Vrije Universiteit Amsterdam, The Netherlands
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Geological Society of London
Volume
212
ISBN electronic:
9781862394605
Publication date:
January 01, 2003

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