GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 1.1 101 Priolo E., Romanelli M., Plasencia Linares M.P., Garbin M., Peruzza L., Romano M.A., Marotta P., Bernardi P., Moratto L., Zuliani D. and Fabris P.; 2015: Seismic monitoring of an underground natural gas storage facility: The Collalto Seismic Network. Seism. Res. Lett., 86 , 109–123. Romano M.A., Peruzza L., Garbin M., Priolo E. and Picotti V.; 2019: Microseismic Portrait of the Montello Thrust (Southeastern Alps, Italy) from a Dense, High-Quality Seismic Network. Seism. Res. Lett., 90 , 1502-1517. Stabile T.A., Giocoli A., Lapenna V., Perrone A., Piscitelli S. and Telesca L.; 2014: Evidence of Low-Magnitude Continued Reservoir-Induced Seismicity Associated with the Pertusillo Artificial Lake (Southern Italy). Bull. Seism. Soc. Am., 104 , 1820–1828. DETAILED STUDY OF THE 2010-2014 POLLINO SWARM-LIKE SEQUENCE (ITALY) AND IMAGING OF SURROUNDING AREA F. Napolitano 1 , A. Gervasi 2,3 , D. Galluzzo 2 , L. De Siena 4 , R. Scarpa 1 , M. La Rocca 3 1 Università degli Studi di Salerno, Fisciano (SA), Italy 2 INGV, Roma, Italy 3 Università della Calabria, Arcavacata di Rende (CS), Italy 4 JGU, Mainz, Germany Introduction. A sequence of almost 10.000 small-to-medium size ( M ≤5) earthquakes occurred between 2010 and 2014 in the western sector of the Pollino Range, Southern Italy. The seismic events were distributed in time as a swarm-like sequence rather than a classic mainshock-aftershock succession (Passarelli et al. , 2015, Totaro et al. , 2015). This behaviour is typical of slow strain areas like Mt.Pollino (Cheloni et al. , 2017). The abundance of earthquakes and the high number of seismic stations available during some periods of the sequence allowed for many detailed analyses of the local seismicity and geological structure. Here we describe the results of two different analyses: 1) a detailed imaging of the main seismogenic fault responsible for the 2010-2014 Pollino sequence; 2) a 2D attenuation and absorption tomography of the area. Some earthquakes of the sequence and seismic noise were also analyzed to assess site effects (Napolitano et al. , 2018). Here we focus our attention on the results obtained from relative location and attenuation analysis in the Pollino area in order to thoroughly image the source responsible for the swarm and confirm a physical evidence of the role that fluids may have had in driving the earthquake swarm. We also propose to apply the same analysis to other natural or induced swarm-like sequences to give new insights about the physical processes behind the swarms, still not fully understood. Such kind of applications would be useful to increase the interpretation of seismicity, especially in areas of exploitation of geo-resources. Relative location analysis. The idea is that detailed analysis of small earthquakes is the best way to image active faults. However, even in well instrumented regions the absolute hypocenter location is affected by errors from some hundreds of meters to kilometers, giving only a vague picture of the fault geometry. We applied a simple method of relative location based on the master-slave approach (Got et al. , 1994) to earthquakes of similar waveforms in order to reduce the error on the hypocenter relative location. This analysis allows for a high resolution imaging of some faults very active during the 2010-2014 Pollino seismic swarm. Applying an automatic picking algorithm to continuous recordings at a reference station (MMN, Fig.1), we selected 6261 events occurred during two periods of the seismic swarm: November 2011- April 2012 and September 2012–June 2013 (Fig.1A and 1B). During these time periods the number of seismic stations installed in the area was sufficient to perform the relative location. We performed the normalized cross-correlation for each pair of band-pass filtered waveforms, then we retained those couples whose cross-correlation was equal or higher than 0.8 and with an average RMS ≥1500 counts (roughly M>0.6). From this selection we collected 27 clusters (432