Tr. J. of Earth Sciences

Abstract: Detail mapping of active fault zones bounding four travertine masses in the Gediz and Menderes grabens of western Turkey revealed that they are divided into geometric fault segments up to 13 km long. Fissures, supplying the carbonate-rich waters that give rise to the travertines are preferentially developed at the ends of the fault segments or in extensional step-over zones where the offset between the fault strands is about 1 km or more. The deposition of travertines in such structural settings is probably a consequence of the network of fissures supplying the carbonate-rich waters being highly interconnected where extensional strains were complex. It follows that during a neotectonic survey directed at finding active faults and identifying potentially hazardous segment boundaries it might be worthwhile searching for, and surveying, late Quaternary travertine bodies. Because the orientations of fissures and the long axes of fissure-ridges are related to local stresses in and around step-over zones, caution should be exercised when employing fissure orientations during regional palaeostress reconstructions. The main boundary faults penetrating down at depths probably act as the main deep conduits for the carbonate-rich thermal waters to ascend to the surface along the graben margins in the study area. However, at shallow depths in step-over zones and adjacent to fault tips, waters also probably flow through the complex fracture networks that commonly occur in these areas