Spectral analysis of the clinometric data at the Phlegraean Fields from 1992 to 1998

Ground deformation is one of the most important precursors for volcanic eruptions. In this respect, the surveillance of volcanoes has greatly benifited from the continuous recording of clinometric data, which represents an economical and reliable way to identify significant ground deformations. In this paper we analyze the clinometric data recorded at the Phlegraean Fields, Italy, in the period 1992-1998 through a classical time series analysis. We show that these techniques can be advantageously used to discriminate between the signals relative to the internal and external processes. In particular, we find that high-frequency fluctations are mainly due to thermal and atmospheric pressure variations, while at lower frequencies we highlight a constant subsidence, without any evidence of volcanic reactivation.