Observing Volcano Dynamics through Seismic and Deformation Patterns

Abstract Geophysical data provide the chance to investigate a volcano’s dynamics; in particular, considerable information can be gleaned on the stress and strain patterns accompanying the internal processes and the effect of magma ascent on the main structures triggering earthquakes. Here, we analysed in detail the seismicity recorded over the last two decades on Etna volcano, in central Mediterranean. We focused on earthquake and focal mechanism distribution and clustering; in addition, the ground deformation pattern affecting the volcanic edifice was considered to evaluate the inflation and deflation phases. Analysed data were compared in order to shed light on possible relationships with the volcanic activity and to better understand the internal dynamics of the volcano over time. Major steps during or shortly before major eruptions in the seismic strain release and ground deformation temporal series highlight a straightforward relationship between seismicity occurring at shallow level, inflation/deflation and volcanism. Furthermore, at depths greater than 5–7 km, down to about 20 km, the orientation of the P- and T-axes clearly indicate the existence of a pressure source in the central part of the volcano. All the results underline that the stress field related to the volcano plumbing system interferes with the regional field, partly overriding it.