Time evolution of medium and long-period ground tilting at Campi Flegrei caldera

摘要

We analyse tiltmeter time series recorded from April 2015 to March 2019 at three boreholeinstruments installed at Campi Flegrei caldera (Italy). We evaluate the crustal response in termsof ground tilting to external excitations of medium/long-period tidal constituents by applyinga?polarization analysis. The azimuths of the tilt vectors show well-defined polarizationdirections and the ground tilting planes oscillate with the periodicity of the corresponding tidalconstituents. For two of the three tiltmeters, the average ground oscillation pattern related tothe monthly Mm and fortnightly Mf constituents show seasonal variations, which can be ascribed torainfall-induced tilting. In addition, for the same two instruments, a?clear seasonal amplitudemodulation of the diurnal S1 constituent appears in the time series, revealing the occurrence ofsite thermoelastic effects. The results indicate that the tidal tilting is mainly controlled bythe local stress field distribution and rheology; in addition, seasonal exogenous factors likerainfalls play a?role in modulating the ground deformation.