Reprocessing and interpretation of vintage seisimc reflection profiles in the offshore Campi Flegrei caldera

In this study, we reprocessed and interpreted seven vintage deep-seismic profiles acquired offshore Campi Flegrei by OGS in the 1970s (Finetti and Morelli, 1974), whose potential could not be fully exploited at the time due to technological limitations. The reprocessing of vintage seismic reflection data represents a valuable scientific opportunity, particularly in geologically complex settings such as the Campi Flegrei area. Despite the complexity of the subsurface, deep geophysical exploration in the area has thus far relied mainly on potential-field methods and passive-source seismic tomography, both of which lack the resolution required to unravel the subsurface architecture at depth. Our main goal was to enhance the signal-to-noise ratio and improve depth imaging of these offset-limited datasets using the Common Reflection Surface (CRS; Zhang et al., 2001; Deidda, 2012) method alongside pre-stack migration techniques (Yilmaz, 2001).

The CRS technique improves subsurface imaging by increasing the signal-to-noise ratio, reflector continuity, and the visibility of dipping events. Unlike traditional common-depth-point (CDP) stacking, it accounts for lateral heterogeneities and dipping structures by using additional kinematic parameters and integrating information from adjacent CDP gathers (Deidda, 2012). By summing amplitudes along reflector segments, CRS produces higher-quality common-offset gathers suitable for the application of pre-stack migration methods (Garabito et al., 2012), particularly when the aim is to improve overall depth imaging rather than resolve subtle details. This is especially relevant because pre-stack depth migration (PSDM; Yilmaz, 2001) yields more reliable seismic images in volcanic environments, where strong vertical and lateral velocity variations and structurally complex subsurface conditions make the assumptions underlying post-stack migration unrealistic. On the other hand, PSDM requires robust and well-constrained velocity models.

The initial velocity model for PSDM was subsequently refined using the iterative Deregowski Loop approach (Deregowski, 1985, 1990). This method relies on common-offset binning of pre-stack data to identify velocity errors and suppress noise and unwanted lateral reflections, followed by Kirchhoff depth migration. Starting from an initial velocity model, refinement is carried out through the analysis of Common Image Gathers (CIGs), where residual moveout (RMO) is evaluated using semblance functions.

The combined use of CRS and PSDM in this work proved particularly effective in improving the imaging quality of the vintage profiles. This approach enabled the construction of a consistent velocity model and the effective use of seismic data for a better understanding of the geological and structural framework of the study area. The integration of CRS and PSDM also ensured coherent results and good comparability among the different seismic lines, providing a robust basis for geological interpretation. The reprocessed data support a reconstruction of the subsurface at considerable depth, allowing the identification of fault structures, volcanic edifices, explosive eruptive sequences, and preferential gas-leakage pathways. Reliable seismic imaging from reflection-seismic exploration data is essential to avoid interpretative ambiguities in the Campi Flegrei caldera, a highly complex volcanic system influenced by rising magmatic fluids, pervasive faulting, and intrusive bodies buried beneath younger volcaniclastic deposits.