Evidence of Fracture Reactivation integrating Volcanological, Structural, and Seismic Data Recorded at Mt. Etna, Italy

Abstract

We merge volcanological, structural, and volcanic tremor data to shed light on a fissure system opened on the upper SE flank of Mt. Etna, Italy, in 1989. The system propagates to about 6 km from the Southeast Crater (SEC), and although it is formed by dry (non-eruptive) NNW-SSE fissures, it was active throughout several eruptive episodes after 1989, such as in 1991-1993 and (at least in part) in 2001, 2004-2005, and 2006. Particularly, we focus our attention on a paroxysmal eruptive episode on 24 November 2006, which encompassed different eruptive styles, such as lava fountaining and effusion, and violent Strombolian explosions, involving several eruptive vents on and near the SEC. This event was documented by detailed field and aerial surveys and remote video cameras. The characteristics of the seismic radiation are analyzed considering: frequency content, wavefield properties, and centroid location of the volcanic tremor source. The synoptic analysis of volcanic phenomena and volcanic tremor data document that: i) an aborted intrusion of magma rose to ~2000 m above sea level in the late evening of 24 November, along the NNW-SSE direction from below the SEC towards the 1989 fracture system, ii) the fissures opened in 1989 strongly affected, approximately 17 years after their formation, the modality of propagation of the seismic energy radiation within the upper volcanic edifice. Besides the role played by the 1989 system on the properties of seismic radiation in 2006, the present study allows to postulate probable links between contiguous fault systems in the upper SE flank of Mt. Etna. Based on the structural framework on a volcano-wide scale, our results do indeed sketch out a hitherto unknown continuity of some faults affecting the southeastern flank, which might also shed some light onto the complex phenomenon of flank instability in the eastern sector of the volcano.