Itzhak Lior, The Hebrew University of Jerusalem Distributed Acoustic Sensing (DAS) is revolutionizing observational seismology by allowing for seismic measurement every few meters along tens-of-kilometers long optical fibers. One application bearing immense scientific and societal implications is the use of DAS for Earthquake Early Warning (EEW). For optimal warning times, seismic sensors should be installed as close as possible to expected earthquake sources. However, while the most hazardous earthquakes on Earth occur underwater, most seismic stations are located on-land; precious seconds may go by before these earthquakes are detected. In this work we harness optical fiber infrastructure, ubiquitously deployed across the world both on-land and off-shore, for EEW. We devised methods for real-time magnitude estimation and ground motion prediction and validated them using earthquakes recorded in France, Greece and Chile. The results demonstrate the potential of DAS-based EEW and the significant time-gains that can be achieved compared to the use of standard sensors, in particular for offshore earthquakes. Associated publication: https://www.nature.com/articles/s41598-023-27444-3