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Tens of thousands of earthquakes shook Santorini and its surroundings in January 2025. Researchers from the GFZ Helmholtz Centre for Geosciences and the GEOMAR Helmholtz Centre for Ocean Research Kiel, in collaboration with international partners, have now published their analysis in the journal Nature. The study reveals that ascending magma triggered the seismic crisis and points to a previously unknown connection between the magma reservoirs of Santorini and the Kolumbo submarine volcano.
- Joint press release by the GFZ Helmholtz Centre for Geosciences and GEOMAR Helmholtz Centre for Ocean Research Kiel -
Tens of thousands of earthquakes shook the Greek island of Santorini and the surrounding area at the beginning of the year. Now, researchers from GFZ Helmholtz Centre for Geosciences and GEOMAR Helmholtz Centre for Ocean Research Kiel, together with international colleagues, have published a comprehensive geological analysis of the seismic crisis in the journal Nature.
The researchers integrated data from earthquake stations and ocean bottom instruments deployed at the Kolumbo underwater volcano 7 km away from Santorini and used a newly developed AI-based method for locating earth-quakes. This enabled reconstructing the processes in the underground with unique detail, revealing that around 300 million cubic metres of magma rose from the deep crust and came to rest at a depth of around four kilometres below the ocean floor. During its ascent through the crust, the molten magma generated thousands of earthquakes and seismic tremors.
A seismically unstable region – geological background
Santorini is located in the eastern Mediterranean and forms part of the Hellenic volcanic arc, a highly active geological zone. This world-famous island group forms the rim of a caldera, which was created by a massive volcanic eruption around 3,600 years ago.
The active underwater volcano Kolumbo lies in the immediate vicinity. In addition, the region is crossed by several active geological fault zones, which is the result of the African Plate pushing north-east against the Hellenic Plate. The Earth's crust beneath the Mediterranean region has broken up into several microplates that shift against each other, and in some cases subduct and melt, thus, sourcing volcanic activity.
Santorini has produced multiple eruptions is historic times, most recently in 1950. In 1956, two severe earthquakes occurred in the southern Aegean Sea, only 13 minutes apart, between Santorini and the neighbouring island of Amorgos. These had magnitudes of 7.4 and 7.2 respectively, triggering a tsunami.
The earthquake swarm that initiated in late January 2025 took place in exactly this region. During the crisis, more than 28,000 earthquakes were recorded. The strongest of these reached magnitudes of over 5.0. The severe shaking caused great public concern during the seismic crisis, partly because the cause was initially unclear, being potentially either tectonic or volcanic.
What happened underground? – Findings from the current study
The new study now shows that the earthquake swarm was triggered by the deep transport of magma. The chain of events had already begun in July 2024, when magma rose into a shallow reservoir beneath Santorini. This initially led to a barely noticeable uplift of Santorini by a few centimetres. At the beginning of January 2025, seismic activity intensified, and from the end of January, magma began to rise from the depths, accompanied by intense seismic activity. However, the seismic activity shifted away from Santorini over a distance of more than 10 kilometres to the northeast. During this phase, the foci of the quakes moved in several pulses from a depth of 18 kilometres upwards to a depth of only 3 kilometres below the seafloor. The high-resolution temporal and spatial analysis of the earthquake distribution, combined with satellite radio interferometry (InSAR), GPS ground stations and seafloor stations, made it possible to model the events.
Dr Marius Isken, geophysicist at the GFZ and one of the two lead authors of the study, says: “The seismic activity was typical of magma ascending through the Earth's crust. The migrating magma breaks the rock and forms pathways, which causes intense earthquake activity. Our analysis enabled us to trace the path and dynamics of the magma ascent with a high degree of accuracy.”
As a result of the magma movement, the island of Santorini subsided again, which the authors interpret as evidence of a previously unknown hydraulic connection between the two volcanoes. Dr Jens Karstens, marine geophysicist at GEOMAR and also lead author of the study, explains: “Through close international cooperation and the combination of various geophysical methods, we were able to follow the development of the seismic crisis in near real time and even learn something about the interaction between the two volcanoes. This will help us to improve the monitoring of both volcanoes in the future.”
View from many perspectives – methods
Two factors in particular enabled the exceptionally detailed mapping of the subsurface. For one, an AI-driven method developed at the GFZ for the automatic evaluation of large seismic data sets. Secondly, GEOMAR had already deployed underwater sensors at the crater of the underwater volcano Kolumbo at the beginning of January as part of the MULTI-MAREX project. These sensors not only measured seismic signals directly above the reservoir, but also pressure changes resulting from the subsidence of the seabed by up to 30 centimetres during the intrusion of magma beneath Kolumbo.
Scientific research activity on Santorini is continuing despite the decline in seismic activity. The GFZ is conducting repeated gas and temperature measurements on Santorini, while GEOMAR currently has eight seabed sensor platforms in operation.
Prof. Dr Heidrun Kopp, Professor of Marine Geodesy at GEOMAR and project manager of MULTI-MAREX, says: “The joint findings were always shared with the Greek authorities in order to enable the fastest and most accurate assessment of the situation possible in the event of new earthquakes.” Co-author Prof. Dr Paraskevi Nomikou is Professor of Geological Oceanography at the University of Athens and works closely with the German partner institutes on the MULTI-MAREX project. She adds: “This long-standing cooperation made it possible to jointly manage the events at the beginning of the year and to analyse them so precisely from a scientific point of view. Understanding the dynamics in this geologically highly active region as accurately as possible is crucial for the safety and protection of the population.”
About: MULTI-MAREX
MULTI-MAREX is one of four projects in the research mission ‘Paths to improved risk management in the area of marine extreme events and natural hazards’ (mareXtreme), which is being implemented by the German Marine Research Alliance (DAM). It brings together ten partner institutions from six universities and the two Helmholtz Centres GFZ and GEOMAR in Germany. The aim is to develop a real-world laboratory for investigating geomarine extreme events such as earthquakes, volcanism and tsu-namis in the central Mediterranean region.
Isken, M., Karstens, J. et al. (2025). Volcanic crisis reveals coupled magma system at Santorini and Ko-lumbo. Nature. https://doi.org/10.1038/s41586-025-09525-7 (please note that the DOI link will not work before the embargo is lifted)
DOI: 10.1038/s41586-025-09525-7
https://www.marextreme.de/en Information on MULTI-MAREX joint project of the mareXtreme research mission
https://www.gfz.de/en/section/physics-of-earthquakes-and-volcanoes/overview Section Physics of Earthquakes and Volcanoes at GFZ
https://www.geomar.de/en/research/fb4/fb4-gdy/research-topics Research Unit Marine Geodynamics at GEOMAR
https://www.geomar.de/en/news images for download after the embargo has lifted
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