GNGTS 2018 - 37° Convegno Nazionale

158 GNGTS 2018 S essione 1.1 Observations on ˜150 faults at more than 30 sites have shown a complex structural frame, where the major faults are composed of NW-SE and E-W striking major fault segments, accompanied by NNE-SSW striking minor faults. Slip superposition analysis revealed the existence of up to three sets of differently oriented slip lineations on the same fault surface. These observations served as a base to distinguish three different sets of fault motions. The most recurrent set is associated to normal and right- transtensional slip on the NW-SE and E-W striking major faults. This lineation set defines an extensional axis which trends NNE-SSW to NE-SW. A second slip lineation set with the NW- SE faults moving as left-transtentional is observed and defines a T axis trending ~NNW-SSE to NW-SE. Preliminary data on slip superposition suggests that the latter motion is the oldest. Finally, a third set is occasionally found and is associated to an ˜E-W trending T axis. Data are still limited to assess whether this latter fault set has a regional extent or represents a local strain imparted by the changing strike of faults. Notwithstanding these limitations, our observations indicate that the major border faults have a multiphase kinematics, and generally slipped as transtensional. The main resolved extension axis (˜NE-SW) is however in agreement with the active strain axis in the Apennines (Montone and Mariucci, 2016). Regarding the analysis of background seismicity, we performed a re-picking of the seismic events occured in and around the Campanian Plain with the exception of the local seismicity of Vesuvio and Campi Flegrei volcanic areas, in order to have well constrained hypocentral parameters and to obtain a P-wave data set to compute fault plane solutions. Preliminary relocation is characterized by few single and/or swarm-type events of low energy (M<2.5). Background seismicity localizes along the transition area between the Plain and the foothills of the Apennines and is less present in the Plain. The fault plane solutions of low magnitude events (M < 2.5 and depth between 7 and 9 km), localized between Sarno and Avella ridges, and around Caserta area show kinematics that seem compatible with transtensional motion. Differently, the kinematics of an event at the northern border of the plain (Roccamonfina area) is characterized by almost extensional motion. All these events have T axis in agreement with the regional extensional strain axis (Montone and Mariucci, 2016), but the kinematics changes from almost normal to transtensional moving from north to south. It is interesting to note that the NW-SE to E-W nodal planes of events between Sarno and Avella ridges are characterized by right transtension, in accordance with the major and possibly more recent kinematics observed along the main faults. Future work will elucidate whether these seismic events, and other events for which we are perfoming a re-picking, might be connected with the major faults analysed in the field. References Acocella, V., Funiciello, R.; 2006: Transverse systems along the extensional Tyrrhenian margin of central Italy and their influence on volcanism. Tectonics, Vol. 25, TC2003, doi:10.1029/2005TC001845. Aprile F., Toccaceli R.M., Sbrana A.; 2004: Il ruolo dei depositi piroclastici nell’analisi cronostratigrafica dei terreni quaternary del sottosuolo della Piana Campana. Il Quaternario, 17, 547-554. Bellucci F.,Santangelo N., Santo A.; 2004: Segnalazione di nuovi depositi piroclastici intercalati alle successioni continentali del Pleistocene Superiore-Olocene della porzione nord-orientale della Piana campana. Il Quaternario, 16(2), 279-287. Brancaccio G., Cinque A., Romano P., Rosskopf C., Russo F., Santangelo N., Santo A.; 1991: Geomorphology and neotectonic evolution of a sector of the Tyrrhenian flank of the southern Apennines (region of Naples, Italy). In Z. Geomorph. N. F., Suppl. -Bd., vol. 82: 47-58. Bruno, P.P., Di Fiore, V., Ventura, G.; 2000: Seismic study of the ’41 st Parallel’ Fault System offshore the Campanian- Latial continental margin, Italy. Tectonophysics 324, 37-55. Ferranti, L., Palano, M., Cannavò, F., Mazzella, M.E., Oldow, J.S., Gueguen, E., Mattia, M., Monaco, C.; 2014: Rates of geodetic deformation across active fault in southern Italy. Tectonophysics 621, 101-122. Florio G., Fedi M., Cella F., Rapolla A.; 1999: The Campanian Plain and Phlegrean Fields: structural setting from potential field data. Journal of Volcanology and Geothermal Research 91 _1999. 361–379.