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The volcano-tectonic seismicity occurring at Campi Flegrei caldera during its present unrest phase, started in 2005, is distributed into time-clustered events emerging from a background composed of earthquakes with higher inter-arrival times. Here, we show that clustered seismicity is cyclically recurrent at time scales from semidiurnal to annual, matching tidal and hydrological periodicities. These results suggest that volcano-tectonic seismicity at Campi Flegrei caldera is driven by both variations in the deep magmatic feeding system and exogenous phenomena, as rainfall or global inflation/deflation cycles of the Earth’s crust, controlled by the lunisolar interaction. Consequently, the role of exogenous triggers in the evolution of the present unrest phase should be properly considered in the elaboration of volcanic risk scenarios, presently limited to the study of surface indicators of deep phenomena.

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The joint application of different seismological techniques for seismic noise analysis, and the results of a volcanological and morphostructural survey, have allowed us to obtain a detailed and well constrained image of the shallow crustal structure of the Solfatara volcano (Campi Flegrei caldera, Italy). Horizontal‐to‐vertical spectral ratios, inversion of surface wave dispersion curves and polarization analysis provided resonance frequencies and peak amplitudes, shear wave velocity profiles and polarization pattern of coherent ambient noise. These results, combined in a unique framework, indicate that the volcanic edifice is characterized by lateral and vertical discontinuities and heterogeneities in terms of shear wave velocity, lithological contrasts and structural setting. The interpretation of the seismological results, with the volcanological and morphostructural constraints, supports the hypothesis that the volcano has been characterized by a complex and intense activity, with the alternation of constructive and destructive phases, during which magmatic and phreatomagmatic explosions built a complex tuff‐cone, later reworked by atmospheric agents and altered by hydrothermal activity. The differences in the velocity structure between the central and eastern parts of the crater have been interpreted as resulting from a possible eastward migration of the eruptive vent along the deformational features affecting the area, and to the presence of viscous lava and lithified tuff bodies within the feeding conduits, which are buried under a covering of reworked materials of variable thickness. The observed fault and fracture systems, partially inherited from regional structural setting and exhumed during volcanism and ground deformation episodes also seems to strongly control wave propagation, affecting the noise polarization properties.