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The Gülbahç e Geothermal Field is located on the eastern margin of the Karaburun Peninsula, about 45 km from the city ofİzmir, western Anatolia, Turkey. The stratigraphy of the study area is represented by a Miocene volcano-sedimentary succession, including several sedimentary and volcanic units. These units overlie the basement rocks of the Karaburun Platform and Bornova Flysch Zone which consist of sandstones, shales and carbonate blocks. These rock units are cut and deformed by a series of NW-SE-to NE-SW-trending faults, extending from Sıgacık Bay to Gülbahç e Bay. Structural studies suggest that while most of the geothermal systems in western Anatolia are controlled by normal faults, the geothermal system at Gülbahç e is controlled by a strike-slip dominated shear zone, previously named theİzmir-Balıkesir Transfer Zone. Along the fault zone, associations of active fault segments accommodate deep circulation of hydrothermally modified sea water, and thus the resulting negative flower structure is the primary control mechanism for the geothermal system.Hydrogeochemical properties of the field show that surface temperature of fluid ranges from 30 to 34 • C. Geothermal fluids in Gülbahç e have high salinity (EC > 34 mS/cm) and low enthalpy. Piper and Schoeller diagrams indicate that geothermal fluid is in the NaCl facies. Chemical geothermometers suggest that the reservoir temperature is around 53-136 • C. The isotopic data (oxygen-18, deuterium and tritium) suggest that geothermal fluids are formed by local recharge and deep circulation of sea water.

U‐Th dating of carbonate veins in connection with active tectonics has recently been used as an attractive tool for constraining the absolute timing of late Quaternary crustal deformations. In this study, for the first time we correlate U‐Th ages of travertine deposits in coseismic fissures along the North Anatolian Fault Zone with records of paleoseismological studies supported by historical earthquake catalogued data. U‐Th ages are assessed in relation to the recurrence interval and the size and epicenter distance of major Holocene earthquakes. Our statistical evaluations on age correlations indicate that the carbonate vein precipitation is concentrated in eight different periods along the North Anatolian Fault Zone. The periods are well correlated with historical earthquake records and with previous dating results of the nearby trench studies. At least six of the periods correspond to the earthquakes reported in the historical catalogues. The age correlations of carbonate precipitation intervals for the last millennium show a recurrence along the eastern North Anatolian Fault Zone with a mode at 130–330 years that is consistent with a previously proposed paleoseismic recurrence interval of the fault. Recorded events in carbonate veins indicate a close‐epicenter (d < 200 km) and high‐intensity (I > VI) paleoearthquakes. Our results suggest that coseismic carbonate veins could be used to determine paleoseismic records as a supplementary tool to augment paleoseismological techniques. This tool has advantages over traditional paleoseismological methods for the understanding of long‐term earthquake behavior, particularly for prehistoric late Pleistocene events which cannot be dated easily by traditional paleoseismological methods.

IntroductionThe E-W-running Büyük Menderes and Gediz grabens, with their prominent morphologies, have attracted the attention of many researchers in the study of the Late Oligocene to Recent extension of West Anatolia. Being symmetric to each other, both zones in the Central Menderes Massif represent narrow intracontinental deformation belts with complex structural history and display multiple basin developments (Figure 1). The Büyük Menderes Graben (BMG) is limited by a regional detachment in the north. The basin is surrounded by the E-W-running Küçük Menderes Graben in the north and by the Muğla-Yatağan Basin and Kale-Tavas Molas Basin in the far south. Four Mio-Pliocene depressions (from west to east, the Çine, Bozdoğan, Karacasu, and Denizli basins) having overall N-S trends are situated just south of the BMG (Figure 1).Modes of development of variously oriented grabens in this region have received little attention. Although there is a hypothesis called the supradetachment transtensional mechanism (Yılmaz et al., 2000;Çemen et al., 2006;Çiftçi et al., 2011;Gessner et al., 2013), it is not substantiated by considerable structural or depositional field data from N-S running grabens. The previous studies in the BMG and in the vicinity of the BMG revealed a complicated and sometimes conflicting Neogene deformation history. For instance, formation of the Söke Basin in the west tip during the Early to Late Miocene was explained in terms of N-S extension (either detachment or high-angle faultrelated) (Sümer et al., 2013). On the other hand, both N-S compression- (Gürer et al., 2009) and N-S extension-related sedimentary basins (Emre and Sözbilir, 1987;Cohen et al., 1995;Bozkurt, 2000) were reported in the central part of the BMG in the Middle and Late Miocene. Further east in the Denizli Basin, the extension direction turns to NNW (or NE and NW) (Kaymakçı, 2005;Koçyiğit, 2005). This brief account suggests that further multidisciplinary detailed studies are still required in unexplored areas in order to reconcile or negate the existing conflicting views and provide more detailed structural history in the BMG and its vicinity.In this study we focused on the stratigraphic, sedimentological, and structural characteristics of the Karacasu and Bozdoğan (K&B) basins just south of the Abstract: The Karacasu and Bozdoğan basins, which trend obliquely to modern grabens in the Central Menderes Massif, are investigated in terms of morphology, basinfill architecture, and structure. Evaluation of the previous geophysical and new structural data indicates that the basins are symmetrical grabens mostly running in a N-S direction. Analysis of sedimentary facies of the basins' infill supports the simple graben model by revealing lateral alluvial/colluvial fans in basin margins and axial fluvial/lacustrine environments in a central trough. The long-term changes between fluvial and lacustrine conditions in the basins are attributed to paleoclimatic origin. Paleostress analysis of slickensides substantiates that the basins were deformed...

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