Wide-angle seismic data reveal extensive overpressures in the Eastern Black Sea Basin

We present new data that explores the link between pore pressure and seismic velocity to estimate the magnitude of the overpressure within the deep sediments of the Eastern Black Sea basin. New wide-angle seismic data, combined with coincident reflection data, have been modelled simultaneously using the seismic tomography code, Jive3D, to provide a well-constrained seismic velocity model of the sediments. Our models reveal a widespread low-velocity zone at the depth of 5.5-8.5 km, which is characterized by a velocity decrease from 3.5 to ∼2.5 km s^-1. Using two separate methods that relate changes in seismic velocity to changes in effective stress, we estimate pore pressures of at least 160 MPa within the low-velocity zone. These pore pressures give λ * values of 0.8-0.9 within the centre of the basin and above the Mid-Black Sea High. The low-velocity zone occurs within the Maikop formation, an organic-rich mud layer identified as the source of mud volcanism in the Black Sea and South Caspian Sea.