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Cruise report 26SIRENA 2 / D274 Cruise RRS Discovery Govan, Sept, 12 th – Ponta Delgada, Oct, 1 st , 2003----------------------------------------------------------------------------------------------------------------------IV –Along-track dataIV - 1 the "Terceira survey"The exact geometry of the Africa/Eurasia boundary within the Azores Archipelago is poorly known.However seismicity data indicate that part of this major structural feature runs between the islandsof Saõ Miguel and Terceira.This section of the plate boundary, known as the Terceira Ridge, consist of several deep troughsand linear ridges. Some of these ridges were studied during a TOBI side-scan survey (AZORRE 98cruise), sail by R/V Urania within the framework of a cooperation between the SOC, theIGM/Bologna and the University of Algarve at Faro. This cruise allowed the sonar imaging of asector between the Hirondelle Basin and Terceira Is. TOBI images show that this area is intensivelyfractured and shows a complex morphology, with a dominant 140°N structural trend.A bathymetry survey, to be used as a framework for the interpretation of TOBI images, and to allowthe study of the fault population, was sailed during D274. Magnetics and gravity data were, as wasthe case for all D274 tracks, recorded along the Terceira survey tracks.Figure IV-1-1: Tracks sailed during the Terceira survey (on Sept. 29 th and 30 th , 2003).