Amplitude versus offset analyses of the deep sedimentary structures at the northern flank of the Porcupine Basin,SW of Ireland

This paper represents an attempt of analysing the amplitude versus offset (AVO) behaviour and specific seismic attributes of sedimentary structures from the Porcupine Basin, SW of Ireland. During the last decade, a huge number of carbonate mounds were investigated in this region in water depths of 600–1,000 m, but the genesis and growth of these mounds are still not clearly identified. The aim of this paper is to give a better understanding of the connection between fluid migration pathways in the deeper underground and surface expressions of their fluid expulsions like gas chimneys and pockmarks through which the mounds may generate themselves. The data used in this study to determine boundary conditions for the physical properties of the underlaying strata were gathered from the northern flank of the Porcupine Basin, where a huge amount of fluid and/or gas chimneys covers the seabed. Marine seismic reflection data contain information about the elastic properties of the underlying earth, mainly based on the observed variations in the seismic reflection amplitude at different shot–receiver offsets. To extract elastic parameters from the data, inversion techniques were used, which presume that input amplitudes are proportional to reflection coefficients for plane wave reflection. To calibrate the AVO analyses with the existing stratigraphy in the working area we have used the well logs from several bore holes in the region. The results of this study show clearly that the investigated and identified pockmarks on the seafloor are the surface expression of hydrocarbon seepage in the deeper sedimentary underground.