Unlike conventional plate boundary earthquakes, which violently release pent-up energy for seconds or minutes at a time, slow earthquakes do not release seismic waves and can endure for many months. Although previous research suggests these slow-slip events occur in the region between an upper, brittle seismogenic zone and the more pliable underlying material, the physical mechanisms that generate slow earthquakes remain unclear.To better understand these puzzling aseismic events, Kano et al. scrutinized geodetic records from beneath the Yaeyama Islands, which sit along southwestern Japan’s Ryuku subduction zone. Using specially filtered Global Navigation Satellite System (GNSS) data from the GNSS Earth...