In: Complex Monitoring of Volcanic Activity ISBN: 978-1-62417-985-3 Editor: Vyacheslav M. Zobin © 2013 Nova Science Publishers, Inc. Chapter 4 VOLCANO MONITORING AND EARLY W ARNING ON MT . ETNA, SICILY BASED ON VOLCANIC TREMOR: METHODS AND TECHNICAL ASPECTS M. D’Agostino 1, * , G. Di Grazia 1, §§ , F. Ferrari 1, † , H. Langer 1, ‡ , A. Messina 1,2, § , D. Reitano 1, ║ and S. Spampinato 1, ** 1 Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania, Italy 2 Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Roma 2, Italy ABSTRACT Eighteen paroxysmal episodes occurred on Mt Etna in 2011, and provided rich material for testing automatic procedures of data processing and alert systems in the context of volcano monitoring. The 2011 episodes represent a typical picture of activity of Mt Etna: in 2000 and 2001, before the 2001 flank eruption, more than one hundred lava fountains were encountered. Other major lava fountains occurred before the flank eruptions of 2002/03 and 2008. All these fountains, which are powerful but usually short lived phenomena, originated from the South-East Crater area and caused the formation of thick ash clouds, followed by the fallout of material with severe problems for the infrastructure of the metropolitan area of Catania. We focus on the seismic background radiation – volcanic tremor – which plays a key role in the surveillance of Mt Etna. Since 2006 a multi-station alert system has been established in the INGV operative centre of Catania exploiting STA/LTA ratios. Besides, it has been demonstrated that also the spectral characteristics of the signal changes correspondingly to the type of volcanic activity. The simultaneous application of Self Organizing Maps and Fuzzy Clustering offers an efficient way to visualize signal characteristics and its development with time, allowing to identify early stages of * marcello.dagostino@ct.ingv.it §§ giuseppe.digrazia@ct.ingv.it † ferruccio.ferrari@ct.ingv.it ‡ horst.langer@ct.ingv.it § alfio.messina@ct.ingv.it ║ danilo.reitano@ct.ingv.it ** salvatore.spampinato@ct.ingv.it No part of this digital document may be reproduced, stored in a retrieval system or transmitted commercially in any form or by any means. The publisher has taken reasonable care in the preparation of this digital document, but makes no expressed or implied warranty of any kind and assumes no responsibility for any errors or omissions. No liability is assumed for incidental or consequential damages in connection with or arising out of information contained herein. This digital document is sold with the clear understanding that the publisher is not engaged in rendering legal, medical or any other professional services.