Northern Chile is an ideal natural laboratory to study the origin of earthquakes. Here, the Pacific Nazca plate slides underneath the South American continental plate with a speed of about 65 millimeters per year. This process, known as subduction, creates strain between the two plates and scientists thus expected a mega-earthquake here sooner or later, like the last one in 1877. But although northern Chile is one of the focal points of global earthquake research, until now there was no comprehensive data set on the structure of the marine subsurface—until nature itself stepped in to help.