In 1960 explosive shots off Perth, Australia were detected at Bermuda about 20,000 km away. The precise path the acoustic pulses need to take to get to Bermuda is complicated, but acoustic modes 1 and 2 appear to have unobstructed paths from source to receiver. This figure is from the book "Ocean Acoustic Tomography" by Munk, Worcester and Wunsch (1995), after Heaney, Kuperman, and McDonald (1991).