From 2019 to 2024, we surrounded the Aurora, Jotul and Loki's Castle hydrothermal fields with ocean bottom seismometers and recorded microearthquakes for one year along with other geophysical parameters. The earthquakes show us faults where water can penetrate to depth. Heat sources as the motor of hydrothermal circulation are conspicuous by the absence of earthquakes or low velocities of seismic shear waves. The three investigated hydrothermal fields differ in the presumed location of faults and heat sources.