Page 401 - Caldera Volcanism Analysis, Modelling and Response

376 Claudia Troise et al.

stress increase causes fracturing of the overlying rocks, magmatic fluids are injected in
shallower aquifers and generate large uplifts. This means that, given the common
magmatic origin, both small and large unrests contribute to the increase in pressure
of the magma chamber which, given sufficient magnitude, can cause fracturing of the
overburden and produce an eruption. In this paper, we show that the maximum
horizontal to vertical displacement ratio can be a powerful indicator of source changes,
and can give important information for volcanic eruption forecast.

1. Introduction
Campi Flegrei caldera (Figure 1) is a volcanic field located in the western
sector of larger Naples, and includes part of the city. About two million people are
heavily exposed to volcanic hazards from this area, and this makes hazard estimation
and eruption forecast crucial.
Campi Flegrei represents one of the most interesting examples of resurgent
caldera, having triggered the most intense episodes of caldera uplift observed in
recent times (Barberi et al., 1984). It is considered by several authors to be a nested

Figure 1 Sketch map of Campi Flegrei showing the main volcanological features, the perma-
nent GPS stations (yellow triangles), leveling network (red lines), and some peculiar leveling
benchmarks (blue closed circles). Leveling lines measured in the period May 2004--September
2006 are also shown (cyan lines).