Qp structure of Mount Etna: Constraints for the physics of the plumbing system

Abstract

In this study we present the three‐dimensional Qp structure of the Mount Etna volcano (Italy), obtained by using local earthquake data. The attenuation along ray paths (t*), computed from the high‐frequency decay of velocity spectra, is used to reconstruct the deep structure of the volcano down to 15 km depth. The tomographic images reveal two broad low‐Qp anomalies at 0 and 3 km depth, located to the south and southwest of the summit area and extending at depth to the west of a central high‐Qp anomaly located between 6 and 15 km depth. The joint analysis of P wave attenuation and velocity allows us to better constrain the physics of the plumbing system. The shallow low‐Qp anomalies are associated with high‐Vp anomalies beneath the top of the volcano and normal low Vp toward its western borders. We interpret the regions of low Qp and normal‐low Vp as shallow volumes where magmatic fluids are stored. Conversely, the low‐Qp, high‐Vp region may indicate intensely fractured rock volumes filled by fluids surrounding the magma branches. At depth, the low‐Qp anomaly defines the path of the magma ascent to the west of an extremely high‐Qp, high‐Vp volume located beneath the southeastern side of the summit area. The high‐Qp, high‐Vp body is interpreted to be the compact, solidified, high‐density intrusive body formed by nonerupted material during past volcano activity.

Geochemical evidence for mixing between fluids exsolved at different depths in the magmatic system of Mt Etna (Italy)

“…As mentioned in Section 1, geophysical studies have described the Etnean plumbing system in the form of interconnected dikes and sills, rather than as a chamber-like reservoir (Hirn et al, 1997;Chiarabba et al, 2000;De Gori et al, 2005;Aloisi et al, 2009). Such a structure strongly favors mechanisms of bubble segregation in dikes, similar to those investigated experimentally by Menand and Phillips (2007).…”

“…At these depths, the plumbing system would consist of the entirely crystallized main intrusive body, plus small volumes of melts (Chiarabba et al, 2000;Laigle et al, 2000). Investigations of the seismic tomography have also recently identified a vertically elongated zone of P-wave attenuation, which would be the main pathway via which magmas ascend from their source to shallower levels (De Gori et al, 2005).…”

“…The peculiar internal structure of this volcano makes it a natural laboratory for this topic, with the seismic tomography of Mt Etna volcano describing the plumbing system in the form of interconnected dikes and sills (Hirn et al, 1997;Chiarabba et al, 2000;De Gori et al, 2005;Aloisi et al, 2009). The discovery of CO 2 -rich melt inclusions in recent volcanites (Metrich et al, 2004;Spilliaert et al, 2006;Collins et al, 2009), as well as the observed enrichments of fluid mobile trace elements (Ferlito et al, 2007;Ferlito and Lanzafame, 2010) suggest that deep magmatic fluids can flush shallower magma bodies in such a complex geometry.…”

Gravity “steps” at Mt. Etna volcano (Italy): Instrumental effects or evidences of earthquake‐triggered magma density changes?

“…[27] Growing crystal mushes could also act as temporary blockages, locally limiting the magma flux within the plexus of dikes and sills which forms the shallower levels of Etna storage system [De Gori et al, 2005]. Removal of this blockage, once the accumulation of crystals is dislodged by the seismic waves, may lead to a sudden mass redistribution within the magma body.…”

“…[17] Etna's upper plumbing system is best envisioned as a plexus of dikes and sills, interconnecting the conduits below the four Summit Craters [e.g., De Gori et al, 2005]. In order to derive to a first order the density change that the medium should experience to produce the observed gravity changes, we approximate the plumbing system of Etna to a cylinder (see Figure 3).…”