Fluids, lithology and structure are known to play a major role in shallow fault slip modes but there is a major issue: Does one of them take precedence over the other two or are they linked? Are really fluids a key parameter? In recent years, studies in Japan, Costa Rica or New Zealand try to find the processes that control slip behaviours through marine campaigns and IODP drillings. The Ecuadorian margin is an exceptional laboratory to continue this international effort by adding a subduction zone to the list of those with contrasted slips at shallow depth. To go further in understanding a zone of the fault that could potentially participate to coseismic slip and create tsunami earthquakes, we need to estimate the in-situ scale of structure, fluids and lithology heterogeneities and identify their respective role. Thanks to three campaigns at sea and years of onshore/offshore data acquisition, this FLUID2SLIP project will participate to determine the exact role of fluids on slip behaviour around the updip part (0-15 km depth) of the seismogenic megathrust fault by localizing fluids and seismicity, imaging fault properties and deformation. To reach this ambitious objective, we designed 5 Tasks to : 1) quantify the fluid content and lithospheric structure by leading edge 2D and 3D seismic methods and heat flow mapping of physical properties of rocks, 2) characterize fluids flowing through the margin by analyzing their geochemical signature and relating fluid seepages to crustal deformation and interplate slip behaviour, 3) detect and locate seismic and transient signals activity with regard to fluids and slip behaviour using deep-learning techniques, 4) monitor seismic velocity time changes by ambient noise interferometry 5) model shear strength and slip processes in 4D onto two subduction zones in Ecuador and New Zealand and see if generic parameters/characteristics can be found. Our consortium gathers geoscientists and data sciences scientists from five French laboratories (Géoazur, I3S, Ifremer, ISTeP and Géosciences Rennes) and four international laboratories, covering thus a very broad range of expertise in seismic imaging, thermal structure, machine learning, seismicity, transient signals, marine tectonics and fluid seepage, and mechanics modelling. We can achieve our objectives in particular through a rare opportunity to have three planned cruises in 2022, each designed to reach specific goals. In addition to the deliverables to the scientific community (datasets, 3D geo-model, fluids database, 4D mechanical models), a science outreach sixth task, specifically addressed to the Youth, will be our contribution to the disaster risk reduction through the commitment of our Ecuadorian partner.