Resolving the final phase of the 2025 Santorini-Amorgos seismic swarm using a local ocean bottom seismometer array

The Christiana-Santorini-Kolumbo volcanic field is the most volcanically active segment of the Aegean Arc, encompassing both the large, caldera system of Santorini, and the smaller, highly active submarine volcano Kolumbo to the northeast. In early 2025, the region experienced a strong seismic swarm, with activity concentrated in the Anydros area, between the islands of Santorini and Amorgos. The most widely accepted cause for the swarm so far is a dyke intrusion beneath the Anydros Ridge (e.g. 1, 2).

 

As part of the HYDROMOX project, the RRS Discovery conducted a multidisciplinary research cruise in March 2025, acquiring passive seismic data alongside heat flow measurements, hydrothermal fluid and gas samples, and ROV imagery across Santorini, Kolumbo, and the Anydros Ridge. Here, we present results from a local network of 25 short-period and broadband ocean bottom seismometers (OBS), deployed for approximately three weeks within the Santorini-Amorgos area during the waning phase of the seismic swarm in March 2025. Despite the swarm having peaked prior to deployment, the OBS array recorded over 140,000 seismic events across 23 days, resulting in ~20,000 well-located events. This local microseismic dataset allows the recording of smaller magnitude events with better spatial coverage than the land networks alone, particularly at shallow depths. Integrating these results with regional structural information and seismic velocity models allows us to further investigate the after-effects of the hypothesised dike intrusion and the activation of shallow fault networks. Our findings provide new insights into the post-peak dynamics of this complex volcano-tectonic seismic swarm in a densely populated and seismically active region of the Aegean.

 

References:

[1] Isken, M. P. et al. (2025). Volcanic crisis reveals coupled magma system at Santorini and Kolumbo. Nature 2025 645:8082, 645(8082), 939–945.

[2] Lomax, A. et al. (2025). The 2025 Santorini unrest unveiled: Rebounding magmatic dike intrusion with triggered seismicity. Science, 390(6775).