Scientists investigating a seismic fault off the U.S. West Coast have an unlikely new ally in their quest to create images of the Earth’s crust deep beneath the ocean: Fin whales. New research, published Thursday in Science, finds these calls’ sound waves can help create images of the seafloor subsurface down to 2.5 kilometers (1.6 miles). The sound waves penetrate the crust and bounce back to instruments on the seafloor, carrying information about the structures they travel through. This meant the signals were not coming directly from the whales, but were echoes bouncing back from within the crust. By comparing the arrival times of these two waves, Kuna could calculate the whales’ approximate locations.