Fault network geometries associated with the Campi Flegrei resurgence in the Gulf of Pozzuoli: an integrated analysis using 2D/3D high-resolution seismic reflection data

Abstract

Volcanic and hydrothermal activity, together with caldera floor uplift (resurgence), within the Neapolitan Yellow Tuff (NYT) caldera of Campi Flegrei (Gulf of Pozzuoli), have been the subject of extensive investigations aimed at delineating the structural architecture and geological evolution of the system (e.g., Sacchi et al., 2014; Corradino et al., 2021; Natale et al., 2022). Nevertheless, the intricate geometry of the fault network—particularly in the apical sector of the resurgent dome—remains insufficiently resolved at metre scale. This limitation is the result of the inherent constraints of 2D seismic data, which often lack the spatial resolution and areal coverage required to accurately resolve fine-scale fault geometries. Additionally, such datasets are frequently compromised by seismic artefacts—most notably out-of-plane reflections—that obscure or distort the true configuration of subsurface structures. Moreover, the interplay between fault architecture and fluid migration, which may influence local stress distribution and potentially induce seismicity, remains poorly understood. This study employs ultra-high-resolution 3D (UHR3D) seismic reflection data to investigate, at metre scale, the fault network geometry (including strikes, dips, and spatial extent) developed within the apical graben of the NYT resurgence. This new dataset is integrated with the analysis of 2D seismic reflection profiles, characterized by higher penetration depth, to enhance the understanding of the relationships between deep tectonic structures and shallow architectures. Seismic interpretation and attribute analyses reveal a complex fault network comprising more than 60 predominantly normal faults, organized into distinct strike domains. Collectively, these structures define a radial-shaped geometry converging toward a focal point located at the centre of the resurgence, within the onshore sector. From west to east, the fault network displays three principal strike orientations: NE–SW, NNE–SSW, and NNW–SSE, with a subordinate set of ENE-WSW-trending faults. Moreover, the presence of amplitude anomalies, bright spots, and localized velocity variations suggests that active fluid migration pathways sometimes exploit the fault network, crossing the main seismo-stratigraphic units. This research refines knowledge on understanding the processes responsible for the formation of complex fault-network geometry and their potential as fluid conduits within the resurgence apical graben. The new findings underscore the critical importance of a multiscale analysis to accurately identify relationship of deep and superficial resurgence structures for improving forecasts of caldera behaviour during periods of unrest.