Abstract
Among geodetic methods used for monitoring ground deformation in volcanic areas, tiltmetry represents the most rapid technique and therefore it is used by almost all the volcanological observatories in the world. The deformation of volcanic building is not only the result of endogenous causes (i.e. dykes injection or magma rising), but also non-tectonic environmental factors. Such troubles cannot be removed completely but they can be reduce. This article outlines the main source of errors affecting the signals recorded by Phlegraean tilt, network, such as the dependence of the tilt response on temperature and to the thermoelastic effect on ground deformation. The analytical procedure used to evaluate about such errors and their reduction is explained. An application to data acquired from the tilt network during two distinct phases of ground uplift and subsidence of the Phlegraean Fields is reported.
Highlights
Tilt monitoring is a technique for the identification of some precursors of volcanic eruptions, but it is a useful tool for the study of the behaviour of volcanoes during post-eruptive phases
In April 1970, the Institute of Geodesy and Geophysics of the University of Trieste set up a network of four clinometric stations to study the ground deformation caused by the 1970-1972 Phlegraean Fields bradyseismic crisis (Manzoni, 1972)
The surface sensors Applied Geomechanics (AGI) have an angular range of ± 800 microradians in High Gain (HG) and of ± 8000 μrad in Low Gain (LG), a resolution of 0.1 μrad, a sensitivity of
Summary
Tilt monitoring is a technique for the identification of some precursors of volcanic eruptions, but it is a useful tool for the study of the behaviour of volcanoes during post-eruptive phases. Ground tilt measurements are very important because during an inflation episode the flanks of volcanoes deform themselves reaching variations of inclination in the order of about ten microradians. Such variations happen an almost constant way, but positive gradients of inclination followed by an inversion of the ground tilt recorded during the co-eruptive deflations are not rare (Bonaccorso and Gambino, 1997). The last eruption dates back to 1538, but major uplifts occurred in 1969-1972 and 1982-1984 when the ground displacements reached a maximum value of 174 cm and 179 cm respectively; these movements refer to the benchmarks (belonging to a Phlegraean levelling line) located in the town of Pozzuoli The subsidence phase, starting at the end of 1995 and interrupted by three small uplifts (fig. 2), is continuously monitored by the tilt network of the Osservatorio Vesuviano (OV)
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