UNCORRECTED PROOF 1 2 Temporal evolution of long-period seismicity at Etna Volcano, Italy, 3 and its relationships with the 2004–2005 eruption 4 Ivan Lokmer a, ⁎ , Gilberto Saccorotti b , Bellina Di Lieto c , Christopher J. Bean a 5 a Seismology and Computational Rock Physics Laboratory, School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland 6 b Istituto Nazionale di Geofisica e Vulcanologia - Sezione di Pisa, Via della Faggiola, 32 - 56126 Pisa, Italy 7 c Dipartimento di Fisica “E. R. Caianiello”, Universita degli Studi di Salerno, Via S. Allende, I-84081 Baronissi (SA), Italy 8 9 Received 1 March 2007; received in revised form 30 October 2007; accepted 11 November 2007 10 11 Editor: C.P. Jaupart 12 Abstract 13 Between December 2004 and August 2005, more than 50,000 long-period events (LP) accompanied by very-long period pulses 14 (VLP) were recorded at Mt. Etna, encompassing the effusive eruption which started in September 2004. The observed activity can 15 be explained by the injection of a gas slug formed within the magmatic column into an overlying cavity filled by either magmatic 16 or hydrothermal fluids, thus triggering cavity resonance. Although a large number of LP events exhibit similar waveforms before 17 the eruption, they change significantly during and after the eruption. We study the temporal evolution of the LP-VLP activity in 18 terms of the source movement, change of the waveforms, temporal evolution of the dominant resonance frequencies and the source 19 Q factor and changes in the polarization of the signal. The LP source locations before and after the eruption, respectively, do not 20 move significantly, while a slight movement of the VLP source is found. The intensity of the LP events increases after the eruption 21 as well as their dominant frequency and Q factor, while the polarization of the signals changes from predominantly transversal to 22 pure radial motion. Although in previous studies a link between the observed LP activity and the eruption was not found, these 23 observations suggest that such a link was established at the latter end of the eruptive sequence, most likely as a consequence of a 24 reestablishment of the pressure balance in the plumbing system, after it was undermined due to discharge of large amounts of 25 resident magma during the eruption. Based on the polarization properties of the signal and geological setting of the area, a fluid- 26 filled crack is proposed as the most likely source geometry. The spectral analysis based on the autoregressive-models (SOMPI) is 27 applied to the signals in order to analyse the resonance frequencies and the source Q-factors. The results suggest water and basalt 28 with the low gas volume fraction as the most likely fluids involved in the source process. Using theoretical relations for the “slow 29 waves” radiated from the fluid-filled crack, we also estimate the crack size for both fluids, respectively. 30 © 2007 Elsevier B.V. All rights reserved. 31 32 Keywords: volcano seismology; long-period seismicity; Etna volcano; volcano monitoring 33 34 1. Introduction 35 The observation and modelling of seismic waves in 36 volcanic settings is of great importance to enhance our Available online at www.sciencedirect.com Earth and Planetary Science Letters xx (2007) xxx – xxx EPSL-09025; No of Pages 16 www.elsevier.com/locate/epsl ⁎ Corresponding author. Tel.: +353 1 7162079; fax: +353 1 2837733. E-mail address: ivan.lokmer@ucd.ie (I. Lokmer). 0012-821X/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2007.11.017 ARTICLE IN PRESS Please cite this article as: Lokmer, I., et al., Temporal evolution of long-period seismicity at Etna Volcano,Italy, and its relationships with the 2004–2005 eruption, Earth Planet. Sci. Lett. (2007), doi:10.1016/j.epsl.2007.11.017