Acoustic emission and seismicity: the case histories of Colfiorito, Molise, Cephalonia, with particular reference to the l’ Aquila earthquake • G. Paparo 1,2, G.P. Gregori1, M. Poscolieri1, C. Rafanelli1, S. De Simone1, V. Gallo1, G. Ventrice3 • 1 CNR–IDAC, Gruppo ICES, via del Fosso del Cavaliere, 100, Roma, Italia • 2 Ambasciata d’Italia a Buenos Aires, Calle Billinghurst, 2577 1425 Buenos Aires, Argentina • 3 P.M.E. Engineering, Via Tromello,32, 00135 Roma, Italia Correspondence to: M. Poscolieri (firstname.lastname@example.org) Abstract: Acoustic emission (AE) displays violent paroxysms preceding strong earthquakes, observed within some large area (several hundred kilometres wide) around the epicentre. We call them “storms of crustal stress” or, briefly “crustal storms”. A few case histories are discussed, all dealing with the Italian peninsula, and with the different behaviour shown by the AE records in the Cephalonia island (Greece), characterized by a different tectonic setting. AE is an effective tool for diagnosing the state of some wide slab of the Earth’s crust, and for monitoring its evolution, by means of AEat different frequencies. The same effect ought to be detected being time-delayed, when referring to progressively lower frequencies. This results into an effective check for validating the physical interpretation. A “crustal storm” typically involves some large slab of lithosphere and crust, but it cannot be easily reckoned to any specific seismic event. In fact, an earthquake responds to strictly local rheological features of the crust, which are eventually activated, and become crucial, on the occasion of a “crustal storm”, which in contrast involves a much wider region. A “crustal storm” lasts typically a few years, eventually involving several destructive earthquakes that hit at different times at different sites that lithospheric slab. The results of the present study, concerning AE time-series collected at 25 kHz (hereafter LF AE) and 150 kHz (hereafter HF AE), haves been submitted to Natural Hazards and Earth System Sciences.With regard to the case histories here discussed, one slab deals with the Italian peninsula. During 1996-1997 a “crustal storm” was on, maybe elapsing until 2002 (we lack information for the period 1998-2001). Fig 1: AE recordingsites, and epicentersof the earthquakesmentioned in the text Then, a quiet period occurred from 2002 until 26May 2008, when a new “crustal storm” started, and by the end of October 2009 it is still on. During the 1996-1997 “storm” two strong earthquakes occurred (Potenza and Colfiorito) and (maybe) in 2002 also the Molise earthquake can be reckoned to this “storm”. During the “storm” started in 2008 the l’Aquila earthquake occurred. Some basic additional logical analysis envisages the possibility of distinguishing some kind of “elementary” constituents of a ”crustal storm”, which can be briefly called “crustal substorms”. The concept of “storm” and “substorm” is a common logical aspect shared by several phenomena, depending on their lognormality and fractality. Compared to a “crustalstorm”, a “crustal substorm” is likely to be reckoned to some specific seismic event. Owing to brevity purposes, however, the discussion of “substorms” is given in Gregori et al. (2009). AE is an effective tool for monitoring these phenomena, and the processes that are ongoing inside the crust. Eventually they result to be precursors of some more or less violent earthquake. It should be stressed, however, that the target of AE monitoring is diagnosing the Earth’s crust. In contrast, earthquake prediction implies a much different perspective, which makes sense only by making reference to some more detailed multiparametric monitoring. An AE array can provide real physical information only about the processes that are objectively ongoing inside different large slabs of the crust. Figure 2 shows the weighted moving average values of the raw LF AE data at Orchi site (see fig. 1) for the 2002-2009 time lag, superposed with an offset, in order to distinguish the different years. One unique large peak appears, just a “crustal impulse” lasting 12 hours, displaying an intensity impressively larger than the signal implied by a “crustal storm”. It preceded the l’Aquila earthquake by 32 days. After this event the signal stabilized its intensity on a higher value (presumably because the acoustic impedance of the “natural probe” had changed). Figure 3 shows a detail of this peak from the raw AE LF data. It exhibits some internal structure, being the likely evidence of some lines of the tidal spectrum and/or by some free oscillation of the Earth (this item is to be investigated by means of the outlier series). Fig. 3 Fig. 2 Figure 4 shows the original database, with no rejection of outliers, and no smoothing, while the ordinate scale is limited to the range 0-0.1. The anomalous signals associated with the outliers can be recognized. These data were the objects of several papers (Gregori et al., 2005, 2007; Paparo et al., 2006; Poscolieri et al., 2006a). The vertical yellow rectangle indentifies the aforementioned “crustal impulse” (see figs. 2 and 3). The central vertical orange arrow in figure 4 indicates the beginning of an increasing trend, which occurred since June 2008, it elapsed until the end of 2008 (right vertical orange arrow), and it continued through 2009 (left vertical grey arrow). This is a “crustal storm”, as it better shown in figure 5 (raw input data), where the storm is monitored in HF AE and LF AE both at Orchi and at Valsinni. The storm appears to have started shortly before 26 May 2008, when the Valsinni station began to be operated. All four records, either HF-AE or LF-AE, either at Orchi or at Valsinni, seem to increase almost simultaneously . Figure 4 also displays a gentle seasonal modulation, which is much better evidenced in the HF AE (figure 6). Another peculiarity of figure 6 is concerned with the MFE’s (minor fracture events, i.e. abrupt discontinuities of the acoustic impedance of the natural probe underground). Whenever needed the data analysis was sometimes carried out separately over three subsets, upon selecting the data set referring to positive MFE’s, to negative MFE, and to “normal” AE records, respectively. Fig. 4 Fig. 5 Fig. 6 References Chiappini M., Gregori G.P., Paparo G., Bellecci C., Crisci G.M., De Natale G., Favali P., Marson I., Meloni A., Zolesi B., Boschi E.; 2002: Stromboli. A natural laboratory of environmental science. Journal of Volcanology and Geothermal Research, 113, 429-442 Cuomo V., Lapenna V., Macchiato M., Marson I., Paparo G., Patella D., Piscitelli S.; 2000: Geoelectrical and seismoacoustic anomalous signals jointly recorded close to an active fault system in Southern Apennines (Italy). Phys. Chem. Earth, 25 (3), 255-261. Diodati P., Falsaperla S., Paparo G., Scarpa R.; 1989: Esperimento AEGS: Attività Sismica ed Emissione Acustica al Vulcano Stomboli. Bollettino GNV, 1989-1, 209-226 Gregori G.P., Paparo G.; 2004: Acoustic emission (AE). A diagnostic tool for environmental sciences and for non destructive tests (with a potential application to gravitational antennas). In: W. Schroder, Meteorological and geophysical fluid dynamics, Arbeitkreis Geschichte der Geophysik und Kosmische Physik, Science Edition, Bremen, pp.166-204. Gregori, G.P., Paparo G.; 2006: The Stromboli crisis of 28÷30 December 2002. Acta Geod. Geophys. Hung., 41, 2, 273-287. Gregori G.P., Lupieri M., Paparo G., Poscolieri M., Ventrice G. e Zanini A.; 2007: Ultrasound monitoring of applied forcing, material ageing, and catastrophic yield of crustal structures. Natural Hazards Earth System Sci., 7, 723-731 Gregori, G. P., Paparo G., Coppa U., e. Marson I; 2002: Acoustic emission in geophysics: a reminder about the methods of analysis. Boll. Geofis. Teor. Appl., 43 (-2, 157-172. Gregori, G.P., Paparo, G., Poscolieri, M., e Zanini, A.; 2005: Acoustic emission and released seismic energy. Natural Hazards Earth System Sci., 5, 777-782. Gregori G.P., Paparo G., Coppa U. e Marson I.; 2002: Acoustic emission in geophysics: a reminder about the methods of analysis. Bollettino di Geofisica Teorica ed Applicata, 43, 1-2, 157-172 Gregori G.P., Paparo G., Coppa U., Marson I.; 2001: Acoustic Emission (AE) in geophysics. E-GLEA 2 - 10-14 Settembre 2001, Buenos Aires (Argentina), ISSN 1515-615X, 57-78 Gregori, G.P., Paparo, G., Poscolieri, M., Rafanelli, C., Ventrice, G., 2009. Acoustic emission (AE) for monitoring stress and ageing in materials. Time scales, lognormality, fractality, and precursors, submitted to Strain. Paparo G. e Gregori G.P.; 2001: Volcanoes and environment and the natural laboratory of Stromboli. In: Giovannelli F., The bridge between the Big Bang and biology. Stars, planetary systems, atmospheres, volcanoes: their link to life, Stromboli (Italy), 13-17 Settembre 1999, CNR, Roma, pp. 289-309 Paparo G., Gregori G.P.; 2003: Multifrequency acoustic emissions (AE) for monitoring the time evolution of microprocesses within solids. Reviews of Quantitative Nondestructive Evaluation, 22, (AIP Conference Proceedings, eds. D. O. Thompson e D. E. Chimenti), 1423-1430. Paparo G., Gregori G.P., Coppa U., De Ritis R., Taloni A.; 2002: Acoustic Emission (AE) as a diagnostic tool in geophysics, Annals of Geophysics, 45, 2, 401-416 Paparo G., Gregori G.P., Taloni A., e Coppa U.; 2004: Acoustic emissions (AE) and the energy supply to Vesuvius – ‘Inflation’ and ‘deflation’ times. Acta Geod. Geophys. Hung., 40, 4, 471-480. Paparo G., Gregori G. P., Poscolieri M., Marson I, Angelucci F., Glorioso G.; 2006: Crustal stress crises and seismic activity in the Italian peninsula investigated by fractal analysis of acoustic emission, soil exhalation and seismic data. In: G. Cello e B. D. Malamud, Fractal Analysis for Natural Hazards, Geological Society, London, Special Publications, 261, pp. 47- 61 Poscolieri M., Gregori G.P., Paparo G. e Zanini A.; 2006: Crustal deformation and AE monitoring: annual variation and stress-soliton propagation, Nat. Hazards Earth Syst. Sci., 6, 961-971 Poscolieri M., Lagios E., Gregori G. P., Paparo G., Sakkas V. A., Parcharidis I., Marson I., Soukis K., Vassilakis E., Angelucci F. E Vassilopoulou S.; 2006a: Crustal stress and seismic activity in the Ionian archipelago as inferred by combined satellite and ground-based observations, Kefallinia, Greece. In: G. Cello e B. D. Malamud, Fractal Analysis for Natural Hazards, Geological Society, London, Special Publications, 261, pp. 63–78 Ruzzante J. e Lòpez Pumarega M.I. (eds); 2008: Acoustic emission, Vol. 1, Microseismic, learning how to listen to the Earth, CNEA, Buenos Aires. ISBN 978-987-05-4116-5, 68 pp. Ruzzante J., Lòpez Pumarega M. I., Gregori G. P., Paparo G., Piotrkowski R., Poscolieri M., Zanini A.; 2008: Acoustic emission (AE), tides and degassing on the Peteroa volcano (Argentina). In: Ruzzante e Lòpez Pumarega (2008), pp. 37-68 Ruzzante J., Paparo G., Piotrkowski R., Armeite M., Gregori G.P., Lopez I.; 2005: Proyecto Peteroa, primiera estaciòn de emisiòn acustica en un volcàn de los Andes. Revista de la Uniòn Iberoamericana de Sociedades de Fìsica, 1, 1, 12-18.