First low-frequency 3D seismic investigation of the deep magmatic-hydrothermal system and architecture of the Campi Flegrei caldera to complement an amphibian ICDP/IODP drilling effort

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During the last decades, the partially submerged Campi Flegrei caldera (CFc) – one of the world’s highest volcanic risk areas – has received significant scientific and societal interest due to its history of catastrophic eruptions and ongoing volcanic unrest. Therefore, it has become subject to an amphibious ICDP-IODP approach. While the ICDP proposal (CFDDP) was approved and a first 500-m long pilot hole was successfully drilled (12/2012), the associated IODP initiative is still in the pre-proposal stage (#671) due to (at that point) limited availability of suitable seismic site surveys. Since then, two joint Italian-German expeditions dedicated to multichannel seismic (MCS) data acquisition were carried out to provide an appropriate database for the development of amphibious ICDP-IODP drilling campaign. Of particular importance is a 3D low-frequency MCS dataset (25 m line spacing; 20-200 Hz) collected in 2016, reaching a signal penetration in the range of the ICDP-IODP target depth of ~2-3 km. The acquisition of these new seismic datasets together with the active ICDP drilling as well as additional extensive research motivated to host another Magellan Workshop (02/2017), thereby revitalizing the amphibious drilling approach. While the original proposal aimed at the processing and interpretation of selected low-frequency MCS profiles to provide a robust site survey for the preparation of an amphibious ICDP-IODP drilling campaign, the here proposed 24-month project deals with a comprehensive analysis of the full 3D data (156 profiles). Such a 3D approach allows for an unprecedented examination of all facets of the deep caldera architecture and associated magmatic-hydrothermal system, thereby ultimately providing the unique opportunity to integrate and spatially extrapolate ICDP-IODP drilling results. This integrative strategy enables us to establish a 3D structural framework of the entire system, thereby holding the potential to revolutionize our understanding caldera volcanism.The aims and objectives of the proposed project follow recommendations from the 2017 Magellan Workshop and are closely linked to the ICDP-IODP effort. The main scientific focus lies on understanding (1) the eruption mechanisms of large-scale caldera forming eruptions, (2) the interconnectivity between shallow hydrothermal-magmatic features and the deep subsurface, and (3) the distinct difference between terrestrial and marine volcanic activity. To achieve that a careful 3D MCS data processing and analysis has to be implemented to allow for the identification and mapping of important features such as ignimbrite deposits, magmatic features (e.g. intrusions, feeder conduits), volcanic edifices, hydrothermally altered areas, escape pathways, fault zones, maximum caldera fill thickness, and undisturbed marine sedimentary successions. The results of the current proposal are essential for the final guidance of a planned diverted ICDP and positioning of IODP drill sites.