Constraining crustal and uppermost mantle structure beneath station TBZ (Trabzon, Turkey) by receiver function and dispersion analyses

We jointly invert teleseismic radial-component receiver functions and regional Rayleigh and Love surface-wave group velocities for 1-D shear-wave velocity structure beneath station TBZ located on the northern side of the eastern Pontides. An influence factor is employed to control the relative influence of receiver function and surface-wave dispersion on the resultant velocity-depth profile. Radial- and transverse-component receiver functions at station TBZ exhibit an azimuthal amplitude and polarity pattern consistent with 2-D receiver structure that has a general dip direction towards approximately south. The radial-component receiver functions are least affected by the dipping structures along the strike direction and thereby we prefer teleseismic events sampling along-strike structures to alleviate the deflecting effect of dipping interfaces on the 1-D solution. The 1-D inversion effectively reveals the two-layer nature of the crust which is perturbed by high- and low-velocity layers, and serves as a provisional model for the 2-D forward modelling. Minor-to-moderate changes to the 1-D model, such as changing depth to and velocity contrast across an interface, are needed to achieve the results with the 2-D modelling. Dipping interfaces and seismic anisotropy are included in the 2-D modelling to fit both radial- and transverse-component receiver functions. The upper crust is characterized by a shear velocity of similar to3.5 km s(-1) and cut through by a 4 km thick high-velocity (i.e. similar to3.8 km s(-1)) layer. Overlying the upper crust, the sedimentary cover (i.e. the top 5 km) has velocities within the range similar to2.0-3.5 km s(-1). A mid-crustal velocity discontinuity between the upper granitic crust and the lower basaltic crust is identified at similar to16-km depth. This boundary is analogous to the mid-crustal discontinuity found under the Black Sea basin across which the shear velocity jumps from 3.5 to 4.1 km s(-1). A relatively thick (i.e. similar to12 km) low-velocity layer in the lower crust with a velocity reversal from 4.1 to 3.7 km s(-1) is needed to better explain reverberations off this depth range. We infer a 2-D Moho discontinuity placed at similar to35-km depth beneath the station. The proposed dip angle for the Moho is rather steep (i.e. similar to25degrees), although coincident with regional gravity studies. The associated Sn velocity (i.e. similar to4.4 km s(-1)) is rather low, indicating disturbed upper-mantle structure beneath the region. Initial amplitudes of transverse-component receiver functions are rather energetic, for which we propose substantial P and S velocity anisotropy (similar to12 per cent) for the topmost depths (<5 km).