Françoise Bergerat (1), Jacques Angelier (1), and Agust Gudmundsson (2)
(1) ESA 7072, Université P. et M. Curie, Paris, France
(2) Geological Institute, University of Bergen

The South Iceland Seismic Zone (SISZ) is an E-W trending left-lateral transform zone connecting two segments of the Mid-Atlantic ridge. The SISZ developed recently, as a result of the eastward jump of the oceanic rifting in Iceland. Because this transform zone has not reached a stage of maturity, the E-W sinistral shear is not tightly localised in the upper crust but still expressed in a complex, 20 km wide system of fractures and faults. Large earthquakes occurred during historical times along series of N-S dextral faults. As an example, we analyse the Leirubakki Fault of the eastern SISZ. Although this fault is located close to the trace of a large 1912 earthquake, its rupture occurred earlier during historical times. Our work included (1) reconnaissance of the fault trace based on aerial photograph analysis and field study, (2) GPS mapping to reconstruct the morphology of the rupture zone, and (3) measurements of structures along the fault, including orientations and amplitudes. We thus identify a pattern of dextral segments that connect typical push-up structures, with specific angular relationships between these features and the general trend of the earthquake fault. The fracturing process involved development of near-surface strike-slip segments, oblique relative to the underlying shear zone. Estimates of shortening amounts and rock volumes involved in push-up development lead to estimate the thickness of the section affected by this particular deformation.

Francoise BERGERAT
Laboratoire de Tectonique CNRS-UPMC
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