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janrinok [soylentnews.org] writes:

Magma displacement triggered tens of thousands of earthquakes, Santorini swarm study finds [phys.org]

Tens of thousands of earthquakes shook the Greek island of Santorini and the surrounding area at the beginning of the year. Now, researchers have published a comprehensive geological analysis of the seismic crisis in the journal Nature.

The researchers—from GFZ Helmholtz Center for Geosciences and GEOMAR Helmholtz Center for Ocean Research Kiel, together with international colleagues—integrated data from earthquake stations and ocean bottom instruments deployed at the Kolumbo underwater volcano seven kilometers away from Santorini and used a newly developed AI-based method for locating earthquakes.

This enabled reconstructing the processes in the underground with unique detail, revealing that around 300 million cubic meters of magma rose from the deep crust and came to rest at a depth of around four kilometers below the ocean floor. During its ascent through the crust, the molten magma generated thousands of earthquakes and seismic tremors.

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 are the result of the African Plate pushing northeast against the Hellenic Plate. 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 in 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 neighboring 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.

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 centimeters. 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 kilometers to the northeast. During this phase, the foci of the quakes moved in several pulses from a depth of 18 kilometers upwards to a depth of only 3 kilometers 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 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."

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 centimeters 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 analyze 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."

More information: Marius Isken can be reached via the GFZ press office, Volcanic crisis reveals coupled magma system at Santorini and Kolumbo, Nature (2025). DOI: 10.1038/s41586-025-09525-7 [doi.org]. www.nature.com/articles/s41586-025-09525-7 [nature.com]
       

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