Near-surface anomalies within Solfatara Volcano, Campi Flegrei, Italy, revealed using magnetic gradient measurements and 3D electrical resistivity data

This paper presents a new high-resolution magnetic map of the Solfatara crater, derived from magnetic gradient measurements. Using the gradient of the magnetic tensor, rather than the gradient of the magnetic vector, enhances the spatial resolution of magnetic anomalies. This case study demonstrates the superior capability of magnetic tensor gradient measurements in accurately locating and interpreting near-surface anomalies compared to standard magnetic methods. The new magnetic map of the inner part of Solfatara reveals clear NE and NW trends that align with Apennine and anti-Apennine structural orientations. The total magnetic intensity field is characterized by numerous short-wavelength anomalies (10-20 m), which are associated with shallow petrophysical and structural heterogeneities near the crater surface. The significance of this high-resolution magnetic dataset lies in its potential to improve the understanding and interpretation of the shallow hydrothermal system and volcanic features of Solfatara, a key site of the recent unrest at Campi Flegrei. Finally, we present an example of the joint application of full magnetic gradient tensor measurements and 3D electrical resistivity data for anomaly characterization.