Abstract
In this paper we report seismological evidence regarding the emplacement of the dike that fed the July 18 - August 9, 2001 lateral eruption at Mt. Etna volcano. The shallow intrusion and the opening of the eruptive fracture system, which mostly occurred during July 12, and July 18, were accompanied by one of the most intense seismic swarms of the last 20 years. A total of 2694 earthquakes (1 £ Md £ 3.9) were recorded from the beginning of the swarm (July 12) to the end of the eruption (August 9). Seismicity shows the upward migration of the dike from the basement to the relatively thin volcanic pile. A clear hypocentral migration was observed, well constraining the upwards propagation of a near-vertical dike, oriented roughly N-S, and located a few kilometers south of the summit region. Earthquake distribution and orientation of the P-axes from focal mechanisms indicate that the swarm was caused by the local stress source related to the dike intrusion.
Highlights
The study of seismic activity is a powerful tool for understanding both the inner structure of a volcano and its eruptive behavior
The two eruptive fractures opened on the eastern side of the volcano, in Valle del Bove and Valle del Leone calderas, respectively
This paper focuses on the July 12-18, 2001 seismic swarm which was one of the strongest recorded in the last 20 years at Mt
Summary
Only the smallest and shallowest events have generally occurred close to the eruptive fissure, the largest shocks being spread over much larger areas than the eruptive ones (e.g., Gresta and Patanè, 1987). The strongest (Md = 4.5) earthquake, recorded during the swarm accompanying the onset of the 1991-1993 eruption, occurred several kilometers from the eruptive fissure (Ferrucci and Patanè, 1993; Bonaccorso et al, 1996) These case histories disclose that the seismic activation of fault systems at Mt. Etna often occurs as a response to accommodate deformations induced by the magma injection. It was suggested that an upward migration of magma along the NNW-SSE structural trend and its intrusion into the upper crust was responsible for the rotation of the local stress field observed from FPSs of shocks at depths less than 10 km (Bonaccorso et al, 1996; Barberi et al, 2000; Patanè and Privitera, 2001). The aim of this paper is to characterize and interpret the space-time evolution and kinematics of the seismicity preceding and accompanying the July 17 - August 9, 2001 lateral eruption
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