SantoArray: A dense hybrid temporary network in the Santorini volcanic complex for seismic monitoring and study of its crustal structure

SantoArray, a dense temporary land seismic network, was deployed in the Santorini volcanic complex from February 28 to March 23, 2025, in response to the 2024‑2025 Santorini‑Amorgos intense volcano‑tectonic unrest which included a significant earthquake sequence with more than 10 events with ML ≥ 5. The network consisted of 117 DATA‑CUBE 3‑component digitizers with 4.5 Hz geophones, complemented by 7 SmartSolo 5 Hz sensors and 12 permanent wideband and broadband stations. It operated in two phases with varying configurations, achieving an average ~0.6 km inter‑station spacing in Phase II, with more than 98% of data recovery during its operation. Preliminary analyses of P‑wave travel‑time mapping from intra‑caldera and regional earthquakes suggests that the network data can significantly improve hypocentral accuracy especially within the caldera. Moreover, ambient noise spectra, HVSR and cross‑correlation analysis reveals important information on the volcanic thickness variations above the metamorphic basement, resulting in high amplifications of strong ground motions. The analysis suggests that this large‑N array provides a robust dataset for advanced tomographic imaging, enhancing the resolution of Santorini’s shallow crustal structure and seismicity using ambient noise and earthquake waveform data. The retrieved information can offer critical insights into the 2025 unrest and Santorini’s subsurface dynamics, allowing us to improve seismic hazard assessment for the Santorini volcanic complex.