According to the Ministry for Climate Crisis and Civil Protection, Greece, press release on 29 January, seismicity increased near Santorini, along the central Kameni fault in the N part of the caldera. Seismicity intensified and shifted NE to an area between the islands of Thira and Amorgos along a NE-SW-trending fault; during 31 January-1 February the largest earthquake was a M 4.3. The submarine Kolumbo volcano is located along that fault line, about 7 km NE of Santorini, though at the time scientists attributed the seismicity to tectonic activity. The Geodynamic Institute of the National Observatory of Athens reported more than 31,000 recorded earthquakes in that area, in a zone extending 15 km long, during 1-4 February, including 630 located events at depths of 2-18 km; events consisted of 155 at M 3.5-3.9, 48 at M 4-4.4, 21 at M 4.5-4.9, and one at M 5. During 4-5 February seismicity extended along an area about 30 km long. The seismicity was similar to a seismic crisis during 2010-2012 that did not lead to a volcanic eruption, though the previous activity was more intense and with larger average earthquake magnitudes.

According to news articles schools on islands including Santorini, Thira, Anafi, Ios, Amorgos, Mykonos, Leros, Syros, and Patmos were closed on 2 February through at least 4 February. Gatherings in enclosed spaces within Municipality of Thira were cancelled. By 3 February more than 11,000 people had left Santorini by ferry or plane, and additional flights to the islands were being scheduled to assist moving people to Athens.

Geological Summary. The submarine Kolumbo volcano is about 15 km NE of the center of the Santorini caldera. Although previously considered to be part of a volcanic field associated with Santorini along a fault zone, Klaver et al. (2016) concluded that Kolumbo was a distinct volcanic system with "a deep differentiation history" based on "a signature of high 208Pb/206Pb compared to Santorini". A strong eruption during September-November 1650 CE killed over 60 people, along with livestock, due to toxic gas emissions; ashfall reached mainland Turkey, and an island of pumice rose above sea level but was rapidly eroded. Klaver et al. (2016) describe the current crater as roughly oval-shaped with a diameter of ~1.7 km, with the crater floor at 500 m below sea level, and the highest point of the crater rim at -18 m. A chain of 19 smaller volcanic features extends ~10 km NE from this primary crater.

Sources: CNN, CBS News, BBC News, Greek City Times, National Observatory of Athens, Ministry for Climate Crisis and Civil Protection