GNGTS 2013 - Atti del 32° Convegno Nazionale

They concentrated in a period of time of about 30 years close to the 2012 sequence, from July 1971 to January 2012. As such, this pattern may be an index of preseismic quiescence (e.g., Kanamori, 1981, Ellsworth, 1981, Scholz, 1988). Defining the length of the preseismic quiescence stage is not an easy task. One could assume the time frame going from year 1909 (occurrence of the Bassa Padana earthquake, M w 5.5) to 2012, corresponding to the “plateau” in Fig. 3b (dashed line). However, considering the average moment rate for the area under study (horizontal dashed line in Fig. 3a), it is not unreasonable to assume a wider period of time (which is not considered in the calculation due to catalog incompleteness), possibly extending from the 1570 Ferrara ( M w = 5.5) or 1688 Romagna ( M w = 5.9) earthquakes to 2012. To verify this second hypothesis, one should analyze the variation of the seismic moment release rate with time taking into consideration the contribution of the seismic activity since 1500 (despite the possible incompleteness of the catalog). Finally, comparing the results for site S1 and site S2, it is evident that the curves relevant at site S2 in Figs. 3a and 3b are influenced by the higher seismic activity characterizing the northeastern sector of the Apennine chain, at the border with the Po Plain. Concluding, this study has revealed that the 2012 Emilia seismic crisis occurred in an area characterized by a seismicity gap and was preceded by a quiescence period of at least 100 years (or possibly wider, going back to 1570) during which the moment rate and the cumulative moment trends indicate a deficit in the release of seismic deformation. Furthermore, the study has confirmed the effectiveness of the smoothed seismicity method of Barani et al. (2011) for the detection and analysis of peculiar seismicity patterns, such as seismic gaps and quiescence periods. This makes the method useful for the monitoring of the evolution of the seismic activity in a region, as it may help in inferring the areas of occurrence of future disastrous earthquakes. References Anderson, J. G.; 1979: Estimate the seismicity from geological structure for seismic-risk studies . Bull. Seism. Soc. Am., 69 , pp. 135-158. Barani. S. and Eva C.; 2011: Did the April 6, 2009 L’Aquila earthquake fill a seismic gap? J. Geophys. Res., 82 , pp. 645-653. Barani. S., Scafidi D. and Eva C.; 2010: Strain rates in northwestern Italy from spatially smoothed seismicity . J. Geophys. Res., 115 , B07302, doi: 10.1029/2009JB006637. Bignami C., Burrato P., Cannelli V., Chini M., Falcucci E., Ferretti A., Gori S., Kyriakopoulos C., Melini D., Moro M., Novali F., Saroli M., Stramondo S., Valensise G. and Vannoli P.; 2012: Coseismic deformation pattern of the Emilia 2012 seismic sequence imaged by Radarsat-1 interferometry . Annals Of Geophysics, 55 , pp. 789-795. Boccaletti M., Bonini M., Corti G., Gasperini P., Martelli L., Piccardi L., Tanini C. and Vannucci G.; 2004: Seismotectonic Map of the Emilia-Romagna Region, 1:250000 . Regione Emilia-Romagna – CNR. Boccaletti M., Corti G. and Martelli L.; 2011: Recent and active tectonics of the external zone of the northern Apennines (Italy) . Int. J. Earth Sci., 100 , pp. 1331-1348. Chen R.-Y., Kao H., Liang W.-T., Shin T.-C., Tsai Y.-B. and Huang B.-S.; 2009: Three-dimensional patterns of seismic deformation in the Taiwan region with special application from the 1999 Chi-Chi earthquake sequence . Tectonophysics, 466 , pp. 140-151. Chiarabba C., Jovane L. and Di Stefano R.; 2005: A new view of Italian seismicity using 20 years of instrumental recording . Tectonophysics, 395 , pp. 251-268. Ellsworth W. L., Lindh A. G., Prescott W. H. and Herd D. G.; 1981: The 1960 San Francisco earthquake and the seismic cycle . In: Simpson J. D. and Richards P. G. (ed), Earthquake Prediction: An International Review, Maurice Ewing Series 4, AGU, Washington, D.C., pp. 126-140. Frankel A.; 1995: Mapping seismic hazard in the Central and Eastern United States . Seism. Res. Lett., 66 , pp. 8-21. Gruppo di Lavoro CPTI; 2004: Catalogo Parametrico dei Terremoti Italiani, versione 2004 (CPTI04) . INGV, Bologna, http://emidius.mi.ingv.it/CPTI/. Kanamori H.; 1981: The nature of seismicity patterns before large earthquakes . In: Simpson J. D. and Richards P. G. (ed), Earthquake Prediction: An International Review, Maurice Ewing Series 4, AGU, Washington, D.C., pp. 1-19. Mirandola Earthquake Working Group (DPC, UniChieti, Uni Trieste, Regione Umbria); 2012: Report 2 (http://www. protezionecivile.gov.it/jcms/it/ran.wp) . Molli G., Crispini L., Mosca P., Piana F. and Federico L.; 2010: Geology of the western Alps-northern Apennine junction area: a regional review . In: M. Beltrando, A. Peccerillo, M. Mattei, S. Conticelli and C. Doglioni (eds.), The Geology of Italy, J. Virt. Explor., 36, paper 9 Patacca E., Sartori R. and Scandone P.; 1990: Tyrrhenian basin and Apenninic arcs: kinematic relation since Late Tortonian times . Memorie della Società Geologica Italiana, 45 , pp. 425-451. 214 GNGTS 2013 S essione 1.2