Fault systems in the offshore sector of the Campi Flegrei caldera (southern Italy): Implications for nested caldera structure, resurgent dome, and volcano-tectonic evolution.

The structure of a caldera may influence its activity, making its understanding crucial for hazard assessment. Here, we analysed high-resolution seismic profiles in the Campi Flegrei (southern Italy) offshore sector. We recognised two main fault systems, including those associated with the formation of the caldera and those affecting the resurgent dome. The former system comprises three broadly concentric fault zones (inner, medial and outer ring fault zones) depicting a nested caldera geometry. Considering the relations between faults and seismic units that represent the marine and volcaniclastic successions filling the caldera, all ring faults were formed during the Campanian Ignimbrite eruption (40 ka) and subsequently reactivated during the Neapolitan Yellow Tuff eruption (15 ka). In this last caldera-forming event, the inner and medial fault zones accommodated most of the collapse and were episodically reactivated during the younger volcano-tectonic activity. The second fault system occurs in the apical zone of the resurgent dome and comprises dominantly high-angle normal faults that are mainly related to the volcano-tectonic collapse that followed the Agnano-Monte Spina Plinian eruption (4.55 ka). Finally, we provide a volcano-tectonic evolutionary model of the last 40 kyr, considering the interplay among ring and dome faults activity, volcaniclastic sedimentation, ground deformation and sea-level changes. • A detailed structural map of the offshore sector of Campi Flegrei caldera is provided. • Two main fault zones have been identified associated with the caldera ring faults and the resurgent dome faults. • The Neapolitan Yellow Tuff eruption reactivated the 2.5 km wide caldera fault zone of the Campanian Ignimbrite eruption. • The dome fault zone accommodated volcano-tectonic collapse during the Agnano-Monte Spina eruption. • Mapped faults controlled caldera deformation, volcanism distribution and hydrothermal fluid uprise in the last 40 kyr. [ABSTRACT FROM AUTHOR]