Unveiling the 3D Hydrothermal Architecture of Nisyros Volcano (Greece) through Island-Wide Deep Electrical Resistivity Tomography (DERT)

The volcanic island of Nisyros, situated on the South Aegean Volcanic Arc, represents a critical site for studying the interactions between active magmatic-hydrothermal systems and structural tectonics. Following the 1998 seismic crisis and subsequent fumarolic activity, characterizing the island's subsurface has become essential for volcanic unrest monitoring. As part of the DEMETRA research line funded under the INGV ROSE infrastructure project, we present an unprecedented high-resolution 3D electrical resistivity model of Nisyros, reaching depths of 1.5 km.

To overcome the logistical and topographical constraints of this sensitive Geopark environment, we deployed a non-invasive 3D network of 34 IRIS V-Fullwaver receivers, ensuring island-wide coverage from the central Lakki caldera to the volcanic slopes.

Our 3D model provides a first-of-its-kind geophysical visualization of the island's hydrothermal system. Key findings include:

• Aquifer Identification: The detection of several hydrothermal aquifers, directly corroborated by historical geothermal boreholes (1983-1984).
• Structural Control: Precise imaging of the major NNW-SSE and NE-SW normal fault systems. These structures act as the primary conduits for fluid migration, establishing a definitive link between surface geothermal manifestations and deep aquifers.

The success of this study demonstrates that Deep Electrical Resistivity Tomography (DERT) is a powerful and socially accepted tool for investigating sensitive volcanic environments. This 3D model significantly improves our understanding of Nisyros’ first kilometer, providing a robust baseline for future hydrothermal modeling and hazard mitigation.