Bouguer Anomaly Re-Reduction and Interpretative Remarks of the Phlegraean Fields Caldera Structures (Southern Italy)

Abstract

Phlegraean Fields is a large, active caldera located in the densely populated westernmost sector of Naples’s Bay (Southern Italy). Several Bouguer anomaly surveys are available for this area with different resolution and accuracy; gravity data derive from the integration of stations placed below and above the sea level as the caldera develops both onshore and offshore. The comparison of these maps with the Digital Elevation Model shows a still remaining Terrain Effect hiding the shallower and deep caldera structure’s signal. This effect has an impact on the modelling of the gravity source’s depth and geometry. In this research, we apply a geologically constrained terrain correction method to the higher resolution Free Air dataset available for the study area to enhance the complete Bouguer reduction. The correlation analysis between the residual and the topography allows us to assess the quality of the outcomes. The results represent an improvement in the anomalies’ isolation and clearly show a continuous circular-like clustering of maxima related to the geometry of the caldera rim. The minima are associated with volcano-tectonic depression filled with pyroclastic and sediment. Furthermore, features alignments overlap the fault systems, along which the volcanic activity occurred.