Ultraslow spreading ridges represent the slowest divergent plate boundaries on Earth. Distinct spreading processes along ultraslow spreading ridges build magmatic segments that are volcanically active in between amagmatic segments that exhibit mantle rocks at the seafloor. Our local seismicity study along the ultraslow spreading Knipovich Ridge in the Greenland Sea gives insights into spreading processes of an entire ridge segment. The more than 8000 reliably located events exhibited an undulating brittle-ductile boundary shallowing towards the Logachev volcanic centre in the centre of the study area. Here, we observe a gap, where seismicity is absent apart from two earthquake swarms. Together with numerous earthquake swarms north of the seismicity gap, this indicates current activity of the volcanic centre. To further investigate the Logachev volcanic centre and its activity we perform a local earthquake tomography. The relevant part of the network of ocean bottom seismometers consisted of 14 stations, spaced by 10-20 km, deployed for one year approximately 60 km along the Knipovich Ridge. The tomography revealed a low velocity area underneath the Logachev volcanic centre at a depth of 10-12 km. This anomaly is robust when using different parameter sets and tomography algorithms. Together with the earthquake swarms and the presence of fresh basalts on the seafloor, this low velocity area could represent a magma chamber feeding the Logachev volcanic centre. From the magma chamber dikes rise to the surface thereby producing swarm activity and heating the surrounding area. The heated area does not allow background seismicity and thereby shows up as a seismicity gap.