SEISMIC EVENTS IN THE UPPER MIOCENE – PLIOCENE SEDIMENTARY SUCCESSION IN THE GULF OF ?ZM?R (WESTERN ANATOLIA): IMPLICATIONS FOR HYDROCARBON PROSPECTIVITY

摘要

>An analysis of multi‐channel seismic reflection data integrating reflection tomography, pre‐stack depth migration, AVO analysis, seismic modelling and seismic attribute analysis was used to investigate the Miocene – Quaternary stratigraphy of the Gulf of ?zmir, western Anatolia. In this area, the east‐west oriented Gediz graben intersects with the NE‐SW oriented Bak?r?ay Graben. A velocity‐depth model together with pre‐stack depth migration allowed two seismic stratigraphic units (SSU1 and SSU2) to be distinguished. These units can be correlated with the stratigraphic succession at the offshore Fo?a‐1 well and correspond to the Upper Miocene to Recent Bozk?y, Ularca and Bayrami? Formations with a combined thickness of 1.75 km. The units rest on acoustic basement (SSU3) which has a basin‐and‐ridge morphology, and which corresponds to the Lower‐Middle Miocene Yuntda? Volcanics. A number of lateral velocity variations were identified. In particular, a ~90 m wide and ~500 m long lenticular‐shaped low‐velocity zone with an interval velocity of 1.68 km/s was identified in the Quaternary Bayrami? Formation. The structure is bounded by negative reflections whose amplitude increases with offset at the top and by strong positive reflections whose amplitude increases with offset at the base, interpreted as possible bright and flat spots respectively. These amplitude events point to the presence of gas‐saturated sediments within the study area. The lenticular structure is bounded by strike‐slip faults on either side, and by a Miocene – Pliocene unconformity surface below and by shales of the Bayrami? Formations above. It is therefore interpreted as a possible structural – stratigraphic trap. The strike‐slip faults may allow the migration of hydrocarbons from source rocks located at greater depths. The presence of a low‐velocity zone above the lenticular structure reaching up to seafloor may indicate the upward leakage of hydrocarbons from the trap. These observations will contribute to future hydrocarbon exploration activities in the study area.