Abstract - The Porcupine Basin is a Mesozoic failed rift located in the North Atlantic margin, SW of Ireland, in which a postrift phase of extensional
faulting and reactivation of synrift faults occurred during the Mid–Late Eocene. Fault zones are known to act as either conduits or barriers for fluid flow and
to contribute to overpressure. Yet, little is known about the distribution of fluids and their relation to the tectono-stratigraphic architecture of the Porcupine
Basin. One way to tackle this aspect is byassessing seismic (Vp) and petrophysical (e.g., porosity) properties of the basins tratigraphy. Here, we use for the first
time in the Porcupine Basin 10-km long-streamer data to perform traveltime tomography of first arrivals and retrieve the 2D Vp structure of the postrift sequence
along a ~130km long E-W profile across the northern Porcupine Basin. A new Vp–density relationship is derived from the exploration wells tied to the seismic line to
estimate density and bulk porosity ofthe Cenozoic Postrift sequence from the tomographic result. The Vp model covers the shallowest 4 km of the basin and reveals a
steeper vertical velocity gradient in the centre of the basin than in the flanks. This variation together with a relatively thick Neogene and Quaternary sediment
accumulation in the centre of the basin suggests higher overburden pressure and compaction compared to the margins,implying fluid flow towards the edges of the
basin driven by differential compaction. The Vpmodel also reveals two prominent subvertical low-velocity bodies on the western margin of the basin. The tomographic
model in combination withthe time-migrated seismic section shows that whereas the first anomaly spatially coincides with the western basin-bounding fault, the second
body occurs within the hangingwall of the fault, where no major faulting is observed. Porosity estimates suggest that this latter anomaly indicates pore overpressure
of sandier Early–Mid Eocene units. Lithological well control together with fault displacement analysis suggests that the western basin-bounding fault can act as a
hydraulic barrier for fluids migrating from the centre of the basin towards its flanks, favouring fluid compartmentalization and overpressure of sandier units of its
hangingwall.
Basin Research, doi.org/10.1111/bre.12308, 2018.