Large earthquakes, submarine landslides and the tsunami they might originate are geohazards of great societal concern because they may impact world economies and struck coastal populations. Examples of these events are the 2004 northern Sumatra and 2011 Tohoku earthquakes and respective tsunamis. However, earthquakes of magnitude Mw > 8.0 in areas of relatively slow tectonic deformation and with long recurrence intervals, such as the external part of the Gulf of Cadiz, might also have a significant impact. The most relevant is the 1755 Lisbon earthquake, related submarine landslides and destructive tsunami. The occurrence of faults and landslides able to trigger a catastrophic tsunami reveals that the Gulf of Cadiz is one of the highest geohazard areas in Europe. Migration of sub-seafloor fluids has also been widely documented in the Gulf of Cadiz and such fluids are strongly related to the earthquake cycle and to the occurrence of submarine landslides. Understanding of these active processes can only be developed by using ultra-high-resolution tools able to map with unprecedented detail faults, submarine landslides and fluid escape structures. State-of-the-art techniques are used during INSIGHT-Leg 1, such as microbathymetry obtained from an autonomous underwater vehicle (AUV), sub-bottom profiles, HR multi-channel seismic data (MCS), and groundtruthing using sediment cores

We gratefully acknowledge financial support from Ministerio Economia y Competividad through national project INSIGHT “ImagiNg large SeismogenIc and tsunamiGenic structures of the Gulf of Cadiz with ultra-High resolution Technologies (INSIGHT-Leg1)” (CGL2011-30005-C02-02, PIs: Roger Urgeles and Eulàlia Gràcia) and Ocean Facilities Exchange Group (OFEG) for allowing us to use the AUVs “Abyss” from GEOMAR (Germany)

Cruise Report INSIGHT-Leg 1 R/V Sarmiento de Gamboa (SDG-68) 29th April - 18th May 2018.-- 139 pages, figures, tables, 2 annexes