http://hdl.handle.net/2122/240 2013-05-21T06:18:42Z http://hdl.handle.net/2122/8619 Title: Quasi-synchronous multi-parameter anomalies associated with the 2010–2011 New Zealand earthquake sequence Authors: Qin, K.; College of Geosciences and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing, China; Wu, L. X.; Academy of Disaster Reduction and Emergency Management, Ministry of Civil Affairs/Ministry of Education of P.R. China (Beijing Normal University), Beijing, China; De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Meng, J.; College of Geosciences and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing, China; Ma, W. Y.; College of Geosciences and Surveying Engineering, China University of Mining and Technology (Beijing), Beijing, China; Cianchini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Positive thermal anomalies about one month before the 3 September 2010 Mw Combining double low line 7.1 New Zealand earthquake and " coincidental" quasi-synchronous fluctuations of GPS displacement were reported. Whether there were similar phenomena associated with the aftershocks? To answer it, the following was investigated: multiple parameters including surface and near-surface air temperature, surface latent heat flux, GPS displacement and soil moisture, using a long-term statistical analysis method. We found that local thermal and deformation anomalies appeared quasi-synchronously in three particular tectonic zones, not only about one month before the mainshock, but also tens of days before the 21 February 2011 Mw Combining double low line 6.3 aftershock, and that the time series of soil moisture on the epicenter pixel had obvious peaks on most of the anomalous days. Based on local tectonic geology, hydrology and meteorology, the particular lithosphere-coversphere-atmosphere coupling mode is interpreted and four mechanisms (magmatic-hydrothermal fluids upwelling, soil moisture increasing, underground pore gases leaking, and positive holes activating and recombining) are discussed. 2012-04-15T22:00:00Z http://hdl.handle.net/2122/8615 Title: Preliminary analysis of surface temperature anomalies that preceded the two major Emilia 2012 earthquakes (Italy) Authors: Qin, K.; China University of Mining and Technology, College of Geosciences and Surveying Engineering, Beijing, China; Wu, L. X.; China University of Mining and Technology, School of Environment Science and Spatial Informatics, Xuzhou, China; De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cianchini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: In the 1980's, from an analysis of satellite images, Russian scientists reported on a short-term thermal infrared radiation enhancement that occurred before some medium-to-large earthquakes in central Asia [Gorny et al. 1988]. Since then, many researchers have been studying earthquake thermal anomalies with satellite remote sensing data [Qiang et al. 1991, Tronin 1996, Tramutoli et al. 2001, Ouzounov and Freund 2004, Saraf and Choudhury 2004, Aliano et al. 2008, Blackett et al. 2011]. Recently, abnormal surface latent heat flux [Dey and Singh 2003, Cervone et al. 2005, Qin et al. 2009, Qin et al. 2011, Qin et al. 2012], outgoing long-wave radiation [Ouzounov et al. 2007] and microwave radiation [Takashi and Tadashi 2010] have also been shown to precede earthquakes. To investigate the possible physical mechanisms of such satellite thermal anomalies, some studies conducted a series of detecting experiments on rock loaded to fracturing [Wu et al. 2000, Freund 2002, Wu et al. 2002, Wu et al. 2006a, Wu et al. 2006b, Freund et al. 2007], and some hypotheses have been proposed. These have included: leaking of pore-gas, and hence the resulting greenhouse effect [Qiang et al. 1995]; activating and recombining of p-holes during rock deformation [Freund 2002]; release of latent heat due to near-surface air ionization [Pulinets et al. 2006], and stress-induced thermal effects due to friction and fluids [Wu and Liu 2009]. According to the Istituto Nazionale di Geofisica e Vulcanologia (INGV; National Institute of Geophysics and Volcanology), two major earthquakes with almost the same large magnitudes struck northern Italy, on the Po Plain in the Emilia Region. The first hit on May 20, 2012, at 02:03 UTC, with ML 5.9 (44.89 °N, 11.23 °E; 6 km in depth), and the second on May 29, 2012, at 07:00 UTC, with ML 5.8 (44.85 °N, 11.09 °E; 10 km in depth). These caused a total of 27 deaths and widespread damage. In this study, the long-term temperature data from both satellite and ground (with greater emphasis on the satellite data) have been used to determine whether there were thermal anomalies associated with this Emilia 2012 seismic sequence. In particular, the next section will be dedicated to describing both the data and the method of analysis. In Section 3, we provide the more significant results, which we discuss in Section 4, together with the main conclusions. We acknowledge that this work cannot be exhaustive, as it will require more data and analyses. However, although further studies will be welcome, we are confident that we have done the best with the data at our disposal. 2011-12-31T23:00:00Z http://hdl.handle.net/2122/8614 Title: Magnetic transfer function entropy and the 2009 Mw = 6.3 L’Aquila earthquake (Central Italy) Authors: Cianchini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Barraclough, D. R.; British Geological Survey, Edinburgh, UK; Wu, L. X.; Academy of Disaster Reduction and Emergency Management, Beijing Normal University, China; Qin, K.; China University of Mining and Technology, Beijing, China Abstract: With the aim of obtaining a deeper knowledge of the physical phenomena associated with the 2009 L’Aquila (Central Italy) seismic sequence, culminating with a Mw = 6.3 earthquake on 6 April 2009, and possibly of identifying some kind of earthquake-related magnetic or geoelectric anomaly, we analyse the geomagnetic field components measured at the magnetic observatory of L’Aquila and their variations in time. In particular, trends of magnetic transfer functions in the years 2006–2010 are inspected. They are calculated from the horizontal to vertical magnetic component ratio in the frequency domain, and are very sensitive to deep and lateral geoelectric characteristics of the measurement site. Entropy analysis, carried out from the transfer functions with the so called transfer function entropy, points out clear temporal burst regimes of a few distinct harmonics preceding the main shock of the seismic sequence. A possible explanation is that they could be related to deep fluid migrations and/or to variations in the micro-/meso-fracturing that affected significantly the conductivity (ordered/disordered) distribution in a large lithospheric volume under the seismogenic layer below L’Aquila area. This interpretation is also supported by the analysis of hypocentres depths before the main shock occurrence. 2012-07-22T22:00:00Z http://hdl.handle.net/2122/8554 Title: GPS observations of coseismic deformation following the May 20 and 29, 2012, Emilia seismic events (northern Italy): data, analysis and preliminary models Authors: Serpelloni, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Anderlini, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Avallone, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Cannelli, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Cavaliere, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Cheloni, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; D'Ambrosio, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; D'Anastasio, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Esposito, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Pietrantonio, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Pisani, A. R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Anzidei, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Cecere, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; D'Agostino, N.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Del Mese, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Devoti, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Galvani, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Massucci, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Melini, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Riguzzi, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Selvaggi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Sepe, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia Abstract: In May-July 2012, a seismic sequence struck a broad area of the Po Plain Region in northern Italy. The sequence in- cluded two ML >5.5 mainshocks. The first one (ML 5.9) oc- curred near the city of Finale Emilia (ca. 30 km west of Ferrara) on May 20 at 02:03:53 (UTC), and the second (ML 5.8) occurred on May 29 at 7:00:03 (UTC), about 12 km south- west of the May 20 mainshock (Figure 1), near the city of Mirandola. The seismic sequence involved an area that ex- tended in an E-W direction for more than 50 km, and in- cluded seven ML ≥5.0 events and more than 2,300 ML >1.5 events (http://iside.rm.ingv.it). The focal mechanisms of the main events [Pondrelli et al. 2012, Scognamiglio et al. 2012, this volume] consistently showed compressional kinematics with E-W oriented reverse nodal planes. This sector of the Po Plain is known as a region charac- terized by slow deformation rates due to the northwards mo- tion of the northern Apennines fold-and-thrust belt, which is buried beneath the sedimentary cover of the Po Plain [Pi- cotti and Pazzaglia 2008, Toscani et al. 2009]. Early global po- sitioning system (GPS) measurements [Serpelloni et al. 2006] and the most recent updates [Devoti et al. 2011, Bennett et al. 2012] recognized that less than 2 mm/yr of SW-NE short- ening are accommodated across this sector of the Po Plain, in agreement with other present-day stress indicators [Mon- tone et al. 2012] and known active faults [Basili et al. 2008]. In the present study, we describe the GPS data used to study the coseismic deformation related to the May 20 and 29 mainshocks, and provide preliminary models of the two seismic sources, as inverted from consensus GPS coseismic deformation fields. 2011-12-31T23:00:00Z http://hdl.handle.net/2122/8552 Title: Coseismic deformation and source modeling of the May 2012 Emilia (Northern Italy) earthquakes Authors: Pezzo, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Merryman Boncori, J. P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Tolomei, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Salvi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Atzori, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Antonioli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Trasatti, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Novali, F.; Tele-Rilevamento Europa - T.R.E. srl; Serpelloni, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Candela, L.; Agenzia Spaziale Italiana, Unità Osservazione della Terra; Giuliani, R.; Dipartimento della Protezione Civile, Ufficio Rischio Sismico Abstract: On May 20th, 2012, an ML 5.9 earthquake (Table 1) occurred near the town of Finale Emilia, in the Central Po Plain, Northern Italy (Figure 1). The mainshock caused 7 casualties and the collapse of several historical buildings and industrial sheds. The earthquake sequence continued with diminishing aftershock magnitudes until May 29th, when an ML 5.8 earthquake occurred near the town of Mirandola, ~12 km WSW of the mainshock (Scognamiglio et al., 2012). This second mainshock started a new aftershock sequence in this area, and increased structural damage and collapses, causing 19 more casualties and increasing to 15.000 the number of evacuees. Shortly after the first mainshock, the Department of Civil Protection (DPC) activated the Italian Space Agency (ASI), which provided post-seismic SAR Interferometry data coverage with all 4 COSMO-SkyMed SAR satellites. Within the next two weeks, several SAR Interferometry (InSAR) image pairs were processed by the INGV-SIGRIS system (Salvi et al., 2012), to generate displacement maps and preliminary source models for the emergency management. These results included continuous GPS site displacement data, from private and public sources, located in and around the epicentral area. In this paper we present the results of the geodetic data modeling, identifying two main fault planes for the Emilia seismic sequence and computing the corresponding slip distributions. We discuss the implication of this seismic sequence on the activity of the frontal part of the Northern Apennine accretionary wedge by comparing the co-seismic data with the long term (geological) and present day (GPS) velocity fields. 2012-12-31T23:00:00Z http://hdl.handle.net/2122/8514 Title: A multidisciplinary study of an active fault crossing urban areas: The Trecastagni Fault at Mt. Etna (Italy) Authors: Bonforte, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Carnazzo, A.; Provincia Regionale di Catania; Gambino, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Guglielmino, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Obrizzo, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; Puglisi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia Abstract: The Trecastagni Fault is a NNW–SSE tectonic structure in the densely inhabited southern flank of Mt. Etna, characterised by evident morphological scarps and movements of normal and right-lateral type that directly affect roads and buildings. The fault is affected by continuous dynamics with intermittent accelerations accompanied with shallow seismicity. It has an important role in the instability affecting Mt. Etna's south-eastern flank and represents part of the southern boundary of the unstable sector. The motion of the fault between 2005 and 2011 has been analysed by using a multi-disciplinary approach involving terrestrial and satellite ground deformation data. Active monitoring systems able to investigate the fault in detail are extensometers, a levelling network and InSAR. Two episodes of acceleration were recorded at the end of 2009 and during 2010. Data evidences that the acceleration episodes affected only portions of the fault and that stress may accumulate and be periodically released. Although bothmagmatic processes (inflation or intrusive episodes) and flank dynamics influence the occurrence of the TF acceleration episodes, the dragging effect of the overall seaward sliding of the south-eastern flank is evident and it causes the subsidence of the hangingwall, accumulating stress on the fault that is periodically seismically released. 2012-12-31T23:00:00Z http://hdl.handle.net/2122/8501 Title: Mazara del Vallo tide gauge observations (1906-1916): land subsidence or sea level rise? Authors: Olivieri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; Spada, G.; Dipartimento di Scienze di Base e Fondamenti, Urbino University “Carlo Bo”; Antonioli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Galassi, G.; Dipartimento di Scienze di Base e Fondamenti, Urbino University “Carlo Bo” Abstract: Tide gauge data constitute an invaluable tool for the interpretation of short and long-term sea level changes occurring in the Mediterranean Sea. The complex geophysical environment and the limited amount of sufficiently long records make the interpretation of local signals problematic, since these are often affected by interlacing processes. Starting from newly disclosed tide gauge records from the site of Mazara del Vallo (SW Sicily), we analyze simultaneously the time series available from other locations in Sicily across the beginning of the 20th century (Messina and Palermo). Despite the limited record length, we show that these observations provide new perspectives on the causes of the observed sea level variations in the central Mediterranean region, and in particular they challenge previous tenets regarding the extent of land movements caused by the 1908 Messina Straits earthquake. 2012-12-31T23:00:00Z http://hdl.handle.net/2122/8478 Title: Integrating new and traditional approaches for the estimate of slip-rates of active faults: examples from the Mw 6.3, 2009 L’Aquila earthquake area, Central Italy Authors: Civico, Riccardo; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia Abstract: This thesis developed a multidisciplinary and multi-scale investigation strategy based on the integration of traditional and innovative approaches aimed at improving the normal faults seismogenic identification and characterization, focusing mainly on slip-rate estimate as a measure of the fault activity. The L’Aquila Mw 6.3 April 6, 2009 earthquake causative fault was used as a test site for the application, testing, and refinement of traditional and/or innovative approaches, with the aim to 1) evaluate their strength or limitations 2) develop a reference approach useful for extending the investigation to other active faults in the area and 3) translate the results of the methodological approaches into new inputs to local seismic hazard. The April 6, 2009 L’Aquila earthquake occurred on a so far poorly known tectonic structure, considered having a limited seismic potential, the Paganica - San Demetrio fault system (PSDFS), and thus has highlighted the need for a detailed knowledge in terms of location, geometry, and characterization of the active faults that are the potential sources for future earthquakes. To fill the gap of knowledge enhanced by the occurrence of the 2009 L’Aquila earthquake, we developed a multidisciplinary and multiscale‐based strategy consisting of paleoseismological investigations, detailed geomorphological and geological field studies, as well as shallow geophysical imaging and an innovative methodology that uses, as an alternative paleoseismological tool, core sampling and laboratory analyses but also in situ measurements of physical properties. The integration of geomorphology, geology as well as shallow geophysics, was essential to produce a new detailed geomorphological and geological map of the PSDFS and to define its tectonic style, arrangement, kinematics, extent, geometry and internal complexities. Our investigations highlighted that the PSDFS is a 19 km-long tectonic structure characterized by a complex structural setting at the surface and that is arranged in two main sectors: the Paganica sector to the NW and the San Demetrio sector to SE. The Paganica sector is characterized by a narrow deformation zone, with a relatively small (but deep) Quaternary basin affected by few fault splays. The San Demetrio sector is characterized by a strain distribution at the surface that is accommodated by several tectonic structures, with the system opening into a set of parallel, km-spaced fault traces that exhume and dissect the Quaternary basin. The integration of all the fault displacement data and age constraints (radiocarbon dating, optically stimulated luminescence (OSL) and tephrochronology) resulting from paleoseismological, geomorphological, geophysical and geological investigations played a primary role in the estimate of the slip-rate of the PSDFS. Slip-rates were estimated for different time intervals in the Quaternary, from Early Pleistocene (1.8 Ma) to Late Holocene (last 5 ka), yielding values ranging between 0.09 and 0.58 mm/yr and providing an average Quaternary slip-rate representative for the PSDFS of 0.27 - 0.48 mm/yr. We contributed also to the understanding of the PSDFS seismic behavior and of the local seismic hazard by estimating the max expected magnitude for this fault on the basis of its length (ca. 20 km) and slip per event (up to 0.8 m), and identifying the two most active fault splays at present. Our multidisciplinary results converge toward the possibility of the occurrence of past surface faulting earthquakes characterized by a moment magnitude between 6.3 and 6.8, notably larger than the 2009 event, but compatible with the M range observed in historical earthquakes in the area. The slip-rate distribution over time and space and the tectonic style of the PSDFS suggested the occurrence of strain migration through time in the southern sector, from the easternmost basin-bounding fault splay toward the southwestern splays. This topic has a significant implication in terms of surface faulting hazard in the area, because it can contribute defining the fault splays that have a higher potential to slip during future earthquakes along the PSDFS. By a methodological point of view, the multidisciplinary and multiscale‐based investigation strategy emphasizes the advantages of the joint application of different approaches and methodologies for active faults identification and characterization. Our work suggests that each approach alone may provide sufficient information but only the application of a multidisciplinary strategy is effective in providing robust results and in defining a proper framework of active faults. 2011-12-31T23:00:00Z http://hdl.handle.net/2122/8477 Title: Heterogeneities along the 2009 L’Aquila normal fault inferred by the b-value distribution Authors: De Gori, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Lucente, F. P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Lombardi, A. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Chiarabba, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Montuori, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: In this study we map the distribution of the b-value of the Gutenberg-Richter law—as well as complementary seismicity parameters—along the fault responsible for the 2009 MW 6.1 L'Aquila earthquake. We perform the calculations for two independent aftershock sub-catalogs, before and after a stable magnitude of completeness is reached. We find a substantial spatial variability of the b-values, which range from 0.6 to 1.3 over the fault plane. The comparison between the spatial distribution of the b-values and the main-shock slip pattern shows that the largest slip occurs in normal-to-high b-values portion of the fault plane, while low b-value is observed close to the main-shock nucleation. No substantial differences are found in the b-value computed before and after the main-shock struck in the small region of the fault plane populated by foreshocks. 2012-08-03T22:00:00Z http://hdl.handle.net/2122/8475 Title: Very detailed seismic pattern and migration inferred from the April 2010 Pietralunga (northern Italian Apennines) micro-earthquake sequence Authors: Marzorati, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Massa, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia; Cattaneo, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Monachesi, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia; Frapiccini, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia Abstract: We propose a very detailed picture of the seismicity occurring in the proximity of the Alto Tiberina Low Angle Normal Fault (ATF, Northern Italian Apennines) by presenting the pattern and evolution of a seismic sequence that occurred on the hanging wall of the ATF in the first months of 2010 and that was characterized by about 1000 events with ML ranging from -0.7 to 3.8. In order to capture the rupture kinematics of the investigated area, a cross-correlation technique was at first applied to calculate very accurate time shifts among the events of the sequence and then to relocate them. Considering the many factors that can affect the accuracy of a routine event location, the whole sequence was relocated with the double-difference method, including both absolute travel-time measurements and cross-correlation differential travel-times. The new locations confirm that seismic activity is mainly arranged along a NW-SE oriented structure, ranging in depth from 4 to 6 km and dipping towards North East with an angle of about 65°. A further analysis of waveforms similarity was performed at a reference station by merging the capability of the cross-correlation technique and the bridging algorithm. The analysis allows us to group events into several earthquake families (from now on multiplets), 11 of which include at least 10 events with a cross-correlation value higher than 0.9. The detected mutiplets allow us to emphasize the spatial and temporal migration of the sequence occurred along a 307°N strike direction with an averaged propagation velocity of about 0.4 km/day. The normal focal mechanisms obtained from the events with ML≥2 validate the supposed extensional tectonic regime of the investigated area. The main nodal planes, characterized by strikes ranging in 312°±12 and dips about -90°, are consistent with the spatial evolution of the aftershocks. 2011-12-31T23:00:00Z