Structure of the SW Iberian Margin from Combined Wide-angle and Multichannel Seismic Reflection Data (FRAME Project)

The SW Iberian Margin has a complex tectonic setting and crustal structure derived from a succession of rift events related to the opening of North Atlantic and Neotethys from the Mesozoic to the Lower Cretaceous, and to the subsequent convergence between Nubian and Eurasian plates from Lower Oligocene to present day. Neogene plate convergence led to the reactivation of pre-existing extensional faults originated during the Mesozoic rifting in a combination of thrust and strike-slip systems. Despite a slow convergence rate, these faults now represent a major regional seismological and tsunamigenic hazard, as demonstrated by the devastating 1755 Lisbon earthquake of M>8.5 and the ensuing tsunami. Thus, unveiling the lithospheric structure along the SW Iberian Margin is not only important to understand the different stages of rifting and compression, but also to characterize the distribution of major lithospheric-scale boundaries, currently active and potentially capable of generating great, destructive tsunamigenic earthquakes. To this end, we use here a spatially coincident wide-angle seismic (WAS) and multichannel seismic (MCS) data set collected along a NW-SE ~320 km transect SW of São Vicente cape during the FRAME survey in 2018. WAS data were recorded by 24 ocean bottom seismometers and hydrophones (OBS/H) while the MCS data were recorded by a 6 km long, 480 channel streamer. From NW to SE, the transect runs from the Tagus Abyssal plain to the westernmost extension of the Gulf of Cadiz across four major thrust faults, namely, the Tagus Abyssal Plain fault, Marquês de Pombal fault, São Vicente fault, and Horseshoe fault. We applied joint refraction and reflection travel-time tomography (TTT) using a combination of arrival times identified at both WAS and MCS recordings to invert for the 2D P-wave velocity (Vp) structure of the crust and uppermost mantle, as well as the geometry of the main structural boundaries identified as seismic reflectors: the top of the acou