Seismicity and active tectonics at Coloumbo Reef (Aegean Sea, Greece): Monitoring an active volcano at Santorini Volcanic Center using a temporary seismic network

The high-resolution hypocentral relocations present a clear view of the volcanic submarine structure at the Coloumbo Reef, showing that the main seismic activity is located within a very narrow vertical column, mainly at depths between 6 and 9 km. The focal mechanisms of the best-located events show that the cluster at the Coloumbo Reef is associated with the “Kameni-Coloumbo Fracture Zone”, which corresponds to the western termination of the major ENE-WSW Santorini-Amorgos Fault Zone. Stress-tensor inversion of the available fault plane solutions from Coloumbo Reef, as well as existing neotectonic fault information from NE Santorini (Coloumbo peninsula), suggests that the NE Santorini-Coloumbo faults belong to a single rupture system, with a ~ 30° rotation of the local stress field with respect to the NNW-SSE regional extension field of the southern Aegean Sea. The observed change of the fault plane solutions shows that local conditions at the Coloumbo submarine volcano area control the observed faulting pattern.