b value enlightens different rheological behaviour in Campi Flegrei caldera

Abstract

The Campi Flegrei caldera is one of the most dangerous volcanoes in the world and since 2005 it is in unrest. Here we evaluate the 3D tomography of the b value at the Campi Flegrei volcanic area revealing a very good correlation with the structure of the hydrothermal system involved in the bradiseismic phenomenon. More precisely, we observe the smallest b-values where we expect the higher stress/strain concentration, namely in the caprock, and for the deepest seismicity. Conversely, the largest b values are observed where the porosity of the medium allows the passage of the volcanic gases toward the surface. Values of b close to typical tectonic ones are observed where the presence of faulting structures is well documented.

Investigating deformation and seismic data and their relationships during the ongoing unrest of Campi Flegrei caldera (Italy)

“…5-10% lower than those obtained by previous studies over different previous periods 19,45,58 evidencing a progressive decrease with time. This is also consistent with recent estimates of the b-value of the different volumes of the caldera showing a close relationship between this parameter and the physical and mechanical properties of the rocks and indicating lower b-values just at depths of 2.5-3 km where a caprock with brittle-fragile behavior is located 59 . All this represents further evidence of the overall progressive stress increase and medium weakening of the shallow crust of CFc as clearly observed in many experimental and volcanic systems 19,54,60 .…”