The objective of the ABYSS project is to probe the mechanical state of a fault zone prior to several large earthquakes (magnitude > 6) in order to identify systematic markers of the earthquake preparatory phase. The chosen target is one of the most active faults on Earth: the Chilean subduction zone. A promising technology will be used, the distributed acoustic measurement on optical fibers, which allows to detect earthquakes thanks to underwater telecommunication cables. ABYSS will rely on the GTD network along the Chilean coast. This unprecedented observation capability, combined with the development of real-time data stream processing, will strengthen the early warning system in Chile by improving the speed and accuracy of seismic warnings.