Two earthquakes of 4.2 magnitude struck between Santorini and Amorgos in the early hours of Thursday morning, ocurring one shortly after the other- a significant phenomenon known as a double earthquake or ‘doublet earthquake’.
Given that experts have also recorded a 6-centimeter shift in the caldera since August, there is growing scientific consensus that the possibility of a volcanic eruption cannot be ruled out.
Meanwhile, due to the most recent seismic activity, authorities have also declared a state of emergency on the nearby island of Amorgos.
About the Double Earthquake
Around an hour after midnight, between Wednesday and Thursday, two 4.2-magnitude earthquakes struck within just one minute of each other—a phenomenon known as a doublet earthquake (DEQ).
The first quake occurred at 01:02 AM, with its epicenter located 23 kilometers southwest of Amorgos at a focal depth of 11.4 km. One minute later, according to the Revised Solution of the Geodynamic Institute, a second tremor was recorded at the same epicenter, this time with a focal depth of 12.8 km.
According to the Scientific Research Journal DEQs are defined as two seismic events where the magnitude difference does not exceed 0.2 units, the spatial separation is less than 100 km, and the time interval between them is minimal. DEQs are regarded as a significant seismic phenomenon due to their implications for fault stress redistribution and potential subsequent activity.
Santorini Caldera Has Shifted by 6 Centimeters
Meanwhile, in a statement, Thanasis Ganas, Director of Research at the Geodynamic Institute, reported that the Santorini caldera has experienced an uplift of up to 4 centimeters from August 2024 to the present. Additionally, experts have observed a horizontal eastward shift of approximately 6 centimeters.
“This is a result of the increased activity. I cannot say it is alarming at this moment because we observed the same phenomenon in 2011-2012, and no eruption followed. However, it is a significant change that needs to be closely monitored,” Ganas stated.
He explained that these changes are caused by magma rising from the mantle to the crust and then accumulating in the magma chamber, which is located beneath Nea Kameni and between Nea Kameni and Oia at a depth of 3 km.
“The initial measurements,” he noted, “show that magma volume has increased by 5 million cubic meters, whereas during the last volcanic crisis in 2011-2012, it had increased by 15 million cubic meters. However, since the phenomenon is ongoing, we must continue monitoring it to understand how it will develop.”
Ganas ruled out any immediate risk of activation of the Amorgos fault, which remains another key focus of scientific investigation. Seismologists warn that if the Amorgos fault—situated between Amorgos and Santorini—were to be activated, it could result in one of the most extreme scenarios, including an earthquake of over 6.0 magnitude and a tsunami.
“A Volcanic Eruption Cannot Be Ruled Out”
Meanwhile, Kostas Papazachos, Professor of Lithosphere Physics, Seismology, and Applied Geophysics at Aristotle University of Thessaloniki (AUTH) and a representative of the Special Committee of Experts, stated on ANT1’s main news bulletin that the volcano has been experiencing pre-volcanic activity since September, long before the recent seismic sequence of the past few weeks. He emphasized that this is a separate phenomenon under investigation.
Papazachos did not rule out the possibility of a volcanic eruption, stating that “the volcano is no longer in a dormant state.”
This opinion is increasingly shared among seismologists. Recently, during a separate televised interview, scientist Costas Synolakis stated that while he does not exclude the possibility of an eruption, he sought to calm public fears, reassuring that scientists would detect an impending eruption well in advance, allowing time for precautionary measures.
What Does it Mean?
The combination of DEQs, caldera movement, and magma accumulation raises concerns over potential volcanic unrest.
While similar activity in 2011-2012 did not lead to an eruption, experts are closely monitoring the situation for any signs of escalating seismic or magmatic activity.
