Greece’s authorities has simply declared a state of emergency on the island of Santorini, as earthquakes shake the island a number of instances a day and typically solely minutes aside.
The “earthquake swarm” can be affecting different close by islands within the Aegean Sea. It started regularly with quite a few very minor (lower than magnitude 3) and principally imperceptible earthquakes in late January. Nevertheless, firstly of February, the seismic exercise intensified because the quakes grew to become bigger and extra frequent.
To this point, a number of thousand quakes have been recorded within the final two weeks. As many as 30 a day have been above magnitude 4.0 – most of them at lower than 10km depth, which is massive and shallow sufficient to be felt by individuals residing on native islands.
These bigger earthquakes have resulted in rock falls alongside the islands’ coastal cliffs, in addition to minor harm to susceptible buildings. The most important earthquake up to now was magnitude 5.1 on February 6, which was additionally felt within the capital metropolis, Athens, in addition to in Crete and in elements of Turkey greater than 240km away.
Often a well-liked vacationer vacation spot, Santorini is now nearly empty. Over the previous week, some 11,000 holidaymakers and locals have left the island, with many fearing the seismic exercise might presage a volcanic eruption.
So how precisely does an “earthquake swarm” occur? And what may occur within the coming days and weeks?
No stranger to earthquakes
This space of the world is not any stranger to earthquakes. Greece is likely one of the most seismically energetic areas in Europe.
The present seismic exercise is positioned close to Anydros, an uninhabited islet about 30km northeast of Santorini. This area lies throughout the volcanic arc of the “Hellenic subduction zone”, the place the African tectonic plate is slowly sliding beneath the Eurasian plate (and particularly the Aegean microplate). The area hosts volcanoes in addition to quite a few weak zones within the crust – what earth scientists typically name “faults”.
Santorini itself is a principally submerged caldera – a crater fashioned because of volcanic exercise over the previous 180,000 years, with its final eruption within the Nineteen Fifties. Earthquakes may be related to volcanic exercise – particularly, the motion of magma beneath the floor.
Nevertheless, this earthquake sequence shouldn’t be positioned beneath Santorini. And native scientists monitoring Santorini have reported no change to point the present seismic exercise is a forerunner of one other Santorini eruption. As an alternative, the earthquakes seem to align with faults mendacity between Santorini and the neighbouring island Amorgos.
Close by faults are identified to have produced earthquakes earlier than. For instance, in 1956, a 7.8 magnitude earthquake right here additionally produced a dangerous tsunami and was quickly adopted by a magnitude 7.2 aftershock. Greater than 53 individuals died because of this earthquake and the aftershock and tsunami. Many extra have been injured.
Earthquakes, proven as colored circles, of the January-February 2025 Anydros swarm, close to Santorini, Greece (Supply: seismo.auth.gr) and identified energetic faults, depicted as black traces (Supply: https://zenodo.org/information/13168947).
Dee Ninis & Konstantinos Michailos
No single stand-out occasion
Tectonic earthquakes happen when accumulating stress in Earth’s crust is immediately launched, inflicting a rupture alongside a fault and releasing vitality within the type of seismic waves.
Sometimes, reasonable to main earthquakes (often known as mainshocks) are adopted by smaller quakes (often known as aftershocks) that regularly diminish in magnitude and frequency over time. That is what seismologists name the mainshock–aftershock sequence.
Some sequences behave otherwise and don’t exhibit a single stand-out occasion. As an alternative, they contain a number of earthquakes of the same dimension that happen over days, weeks, and even months. A lot of these sequences are what seismologists name “earthquake swarms”.
The 1956 earthquake was a mainshock–aftershock sequence, with aftershocks lasting no less than eight months after the mainshock. Nevertheless, the present ongoing seismic exercise close to Santorini, no less than as of February 7, options hundreds of earthquakes, many with magnitudes ranging between 4.0 and 5.0.
This means it’s almost certainly an earthquake swarm.
Earthquake swarms are sometimes related to fluid motion within the earth’s crust and the ensuing seismic exercise is often much less dramatic than the sudden motion of a robust mainshock.
Seismologists are fascinated about distinguishing between mainshock–aftershock sequences and earthquake swarms as it could assist them higher perceive the processes that drive these phenomena.
Over the previous week, some 11,000 holidaymakers and locals have left Santorini.
Orestis Panagiotou/EPA
A bigger quake continues to be doable
We can not predict precisely what is going to come from the earthquake exercise close to Santorini. International observations of earthquakes inform us that solely a small fraction (about 5%) of earthquakes are foreshocks to bigger earthquakes.
That stated, there may nonetheless be a chance {that a} bigger and doubtlessly damaging earthquake may happen there quickly.
Though swarms sometimes contain earthquakes of decrease magnitudes, they’ll final for days to weeks, or persist for months. They will even decelerate, after which intensify once more, unsettling locals with intermittent floor shaking.
