Shear-Wave Velocity Structure in the Adana Basin of Southern Turkey by Ambient Noise Tomography

The Adana Basin located in a tectonically active region of southern Turkey is known to be one of the major Neogene basins with thick sedimentary deposits. Hence, investigation of its 3-D seismic velocity structure is important in terms of seismic hazard evaluation as well as its hydrocarbon potential. We investigate the shear-wave velocity structure of the Adana Basin by using the method of ambient noise tomography. The vertical-component continuous seismic data recorded by 21 broadband stations located in and around the basin were used for the extraction of the Green's functions obtained from three-year stacks of cross correlations between 210 station pairs. A total of 138 paths were selected based on signal-to-noise ratio and minimum distance criteria. We measure the Rayleigh wave group velocities in the period range of 8 to 25 s using the multiple filtering method. By performing a series of checkerboard tests, the optimal cell size in tomographic imaging was found to be 20 x 20 km. We obtain an adequate resolution in the center of the basin. The resolution gets slightly deteriorated around the edges since there are fewer paths available. Tomographic images of Rayleigh wave group velocities suggest that the lateral variation of velocity structure is captured in a way that is correlated with the geology. Estimation of 1-D shear-wave velocity models from the inversion of localized group velocities at each tomography cell provides us with the 3-D characterization of sediment thickness and shear-wave velocity variation across the basin.