At mid-ocean ridges, the lithospheric plates drift apart, magma fills the gap to form new crust. This engine splutters at ultraslow speeds of less than 20 mm/y: Isolated volcanoes pierce the seafloor of ultraslow spreading ridges; between the volcanoes, there are long stretches without volcanism. The morphology and the mode of seafloor production at ultraslow spreading ridges differ fundamentally from all faster spreading ridges. The reasons for the uneven distribution of melts at ultraslow plate boundaries are still poorly understood as their main representatives, the Arctic ridge system and the Southwest Indian ridge, are difficult to access. We analysed the teleseismically recorded seismicity in 11 sections of ultraslow spreading ridges spanning altogether 7200 km. Epicentres located within 30–35 km of the rift axis were extracted from the catalogue of the International Seismological Centre for a time period of 35 years. The typical stripe-and-gap seismicity pattern of slow spreading ridges is not discernible at ultraslow spreading rates. Here, volcanic centres often have an increased seismicity rate relative to the background rather than appearing as seismic gap. In contrast, amagmatic segments of ultraslow spreading ridges are seismically only weakly active. Asymmetric accumulations of earthquakes at segment ends that are related to detachment faulting at slow spreading ridges do not exist at ultraslow spreading ridges. Local and teleseismic earthquakes at ultraslow spreading ridges occur down to depths of 20 km below seafloor, confirming the existence of a cold and brittle lithosphere. Underneath Logachev Seamount at Knipovich ridge, microearthquake hypocentre depths from a 10 days seismicity study with ocean bottom seismometers yield for the first time direct evidence for an undulating lithosphere-asthenosphere boundary which has often been postulated as one possible way to channel melts towards the centres of focussed magmatism.