At mid-ocean spreading ridges, tectonic plates drift apart and upwelling magma builds new seafloor and tectonic plates. Spreading ridges are grouped according to their spreading velocity. The slowest ridges among them work entirely different than their faster counterparts. They do not receive enough melt to close the gap between the diverging plates. Instead, there are widely spaced volcanic centers among magma-poor areas that exhibit rocks from the Earth’s mantle. In seismicity studies earthquakes give insights into the subsurface properties, for example temperature, and accompany any active spreading processes such as volcanic eruptions and tectonic extension. Because such studies require many ocean bottom seismometers, local seismicity studies of ultraslow spreading ridges until now have only covered either volcanoes or magma-poor areas. Our study collected for the first time earthquakes from several spreading segments to study the interplay between magma-rich and poor segments. The network of 26 ocean bottom seismometers covered around 160 km along axis of the ultraslow spreading Knipovich Ridge in the Greenland Sea and recorded earthquakes for about one year. We find seismicity varying distinctly along-axis. The maximum depth of earthquakes marking the thickness of the mechanically strong lithosphere shallows over distances of 70 km towards the Logachev volcanic center. Underneath the volcano, earthquake swarms and a seismicity gap indicate recent magmatic activity. Melts may thus be channeled towards major volcanic centers explaining the uneven along-axis melt distribution typical for ultraslow ridges. Presumably magma-poor regions exhibit deep earthquakes and a lack of shallow earthquakes. We think that the alteration of mantle rocks in these areas makes the lithosphere too soft to break in earthquakes.