Reflection traveltime tomography: A 2d case study from gulf of Izmir (Turkey)

In this study, reflection traveltime tomography has been carried out on a multichannel seismic reflection data in the İzmir Gulf to obtain a velocity-depth model of the study area for the first time. The time-migrated seismic sections were interpreted stratigraphically before reflection traveltime tomography application. The raw shot gathers improved by performing preliminary data-processing steps such as noise elimination by editing, muting, notch filtering and spherical gain recovery. Migrated seismic sections produced by using conventional data processing scheme in previous studies were interpreted stratigraphically in detail. The interfaces defined on the migrated time sections were picked on the improved common shot gathers. Travel times calculated by ray tracing were used during travel time inversion adopting SIRT (Simultaneous Iterative Reconstruction Technique) algorithm to estimate the local interval velocities. These interval velocities estimated in each iteration were used for calculating the shape and depth of the interfaces in the study area. The velocity field is updated by minimizing the travel time residuals. Tomogram revealed that the velocity model of a sedimentary sequence of four seismic units with a thickness of about 1 km in the offshore Foça that are separated by five different interfaces (H1-H5). The interval velocities of these sedimentary sequences vary between 1.5-2.6 km/s. The acoustic basement (H5) constitutes a basin geometry that deepens to 800 meters from west to east and gets shallow up to 440 meters in the east forming a ridge. In addition to this, the sediment units in the basins deepen from west to east in accordance with the basin geometry. The investigation provided that the reflection traveltime tomography method is a good tool to obtain stratigraphical properties of layers in depth and to estimate an accurate interval velocity model of the seismic unit.