Shallow seismic study of the geothermal areas in the Gülbahçe Bay and İzmir Gulf (Aegean Sea, Western Turkey)

The two seismic units, i.e., the basement and the basin sediments are interpreted as Miocene and Plio-Quaternary deposits, respectively. The basin sediments of approximately 255 m thickness are risen and compressed through the active strike-slip faults, GF1–GF3 extending in N–S direction towards the outer Gülbahçe Bay. These compressed sediments are interpreted as upwelling zones with weak reflection character and internal frequency attenuation. The most significant one is marked as a possible mud diaper zone with a ~320 m width and the approximately 500 m. A synthetic model of the field data gathered from the diaper indicates that the top of the diapir is characterised by a strong positive reflection character while the internal diaper is represented by polarity reversals and weak reflections due to a velocity decrease with depth. Moreover, phase changes are observed at the border of the diapiric structure. A relatively thicker basin sediment unit of approximately 700 m was observed on the pro-delta sediments of the Gediz River and the sediments below in the İzmir Gulf. The active strike-slip faults, İF1–İF5 deform the basement and basin deposits. Moreover, two active normal faults, İF6 and İF7 are marked from inner to outer part of the gulf. The seismic attribute sections indicate weak reflection zones and frequency attenuation particularly both inside the pro-delta sediments and the sediments below. Observations suggest to us the existence of possible fluid and/or gas discharges and saturations in the Gülbahçe Bay and İzmir Gulf.