Syros island preserves pristine high-pressure metamorphic rocks and provides invaluable insight into subduction zone processes. Contrasting views on the structural history impede placing the island in a clear tectonic framework, limiting the broader impact of preserved information. We present a new geological map of Syros, based on field mapping and recent petrochronological evidence for sequential peak subduction metamorphism from 52 to 43 Ma for the Kampos, Chroussa and Posidonia subunits. Compiled P-T-t constraints show that retrograde metamorphism varies: cooling during decompression (Kampos subunit), isothermal decompression (Chroussa subunit) and warmer greenschist overprinting at lower pressures (Posidonia subunit). Phengite Rb/Sr and 40Ar/39Ar ages show a further downward trend of younger ages and wider age ranges. We present a tectonic model for exhumation that explains the contrasting kinematics recorded on the Kastri and Kini shear zones that separate these subunits. The brittle Kastri fault juxtaposed top-to-SW mylonites of the Kampos subunit against top-to-NE mylonites of the Chroussa subunit, which we interpret to reflect sequentially active extrusion wedges. The Kini shear zone records top-to-E deformation from eclogite to greenschist facies, reflecting wedge extrusion of the Posidonia subunit and Miocene reactivation as a detachment unroofing a core complex in South Syros. Low-angle brittle extension is also recorded on the Vari and Kastri shear zones, by reactivation of former subduction contacts. Based on similarities with Naxos and Sifnos, we call this the Central Cycladic Detachment system, which showcases a style of extension along parallel detachments causing thinning of the CBU, which may explain downward-increasing conditions of metamorphic overprinting. ... Read more

As underground hydrogen storage (UHS) is expected to play a key role in future renewable energy systems, understanding the potential geomechanical risks, such as induced seismicity, is essential. Therefore, this study aims to assess the probability of induced seismicity associated with the prospect of large-scale UHS plans. We commence by developing simulation models with increasing complexity, starting from the basic characteristics of the salt formation, salt cavern, and operational conditions, and progressing to the inclusion of structural features within the salt formation as well as in the overburden and sideburden. A 2D finite element simulator is used to incorporate deformation and simulate creep behaviour, which is subsequently coupled with a rate-and-state Coulomb threshold model to compute the seismicity rate from stress changes. The developed framework accounts for the geological and mechanical characteristics of the heterogeneities that influence local stress fields, allowing us to identify conditions that may increase seismic risk or enhance stability. ... Read more