GNGTS 2018 - 37° Convegno Nazionale

GNGTS 2018 S essione 1.1 135 the recorded seismic signals also allow the reliable location of low magnitude (M≤2.0) seismic events. We used seismic data recorded by the seismic stations of the Centralized National Seismic Network (RSNC) operated by INGV in the area. The waveforms of all seismic events have been collected and analyzed to perform a manual re-picking of the P- and S-wave arrival times, focusing the attention on S-phase for the reliability of the focal depth, to obtain reliable hypocentral location and a P-wave polarity data-set to compute constrained fault plane solutions. The spatial distribution of the preliminary relocation of the seismicity in the study area, delimited by a red square in Fig. 1, although relative to the limited analyzed time span, mainly consists of single eventswithmagnitudeM L ≤2.5. Only 3 events had 3.0≤M L ≤3.5 and no particular alignment of the background seismicity can be recognized. In the analyzed time period, two low magnitude seismic swarms occurred. The first one occurred at the end of May 2010 and it was triggered by an earthquake of M L 3.3. About 120 events, with magnitude ranging between 0.8 and 2.5, took place within the next 48 hours from the main event. The epicentral distribution shows a roughly WNW-ESE alignment and the hypocenters, confined in the range 5-15 km depth, roughly show a SW dipping plane. The fault plane solution of the very few events with M L > 2.0 show both normal dip slip solutions with a minor strike component, and strike-slip solutions with a minor dip component. However, the common element of the computed fault plane solutions is the presence of a SW dipping plane striking from NW-SE to NNW-SSE. The second swarm is constituted by less than 20 events, with magnitude ranging between 1.5 and 2.5, and occurred at the beginning of October 2011. Although limited to a short time interval, the seismicity observed might be consistent with a high fractured medium in which the release of seismic energy occurs in a diffused way and with the occurrence of seismic swarms on faults with very small dimension. The seismological results obtaining by the integration of the present data set, jointly discussed with geological and other geophysical data, will allow to deepening the seismotectonics knowledge in the area of the 1349 earthquake. References CNR-PFG, 1983. Neotectonic map of Italy . Sottoprogetto Neotettonica, Dir. Barberi, Coor. Bosi, Scale 1:500,000, Sheet 4. Convertito V., Pino N. A. and Di Luccio F.; 2016: Investigating source directivity of moderate earthquakes by multiple approach: the 2013 Matese (southern Italy) Mw = 5 event . Geophys. J. Int., 207 , 1513–1528. DISS Working Group (2018). Database of Individual Seismogenic Sources (DISS), Version 3.2.1: A compilation of potential sources for earthquakes larger than M 5.5 in Italy and surrounding areas.  Istituto Nazionale di Geofisica e Vulcanologia; DOI:10.6092 /INGV.IT -DISS3.2.1 <http://diss.rm.ingv.it/diss/> Ferranti L., Milano G., Burrato P., Palano M. and Cannavo, F.; 2015: The seismogenic structure of the 2013–2014 Matese seismic sequence, Southern Italy: implication for the geometry of the Apennines active extensional belt . Geophys. J. Int., 201 (2), 823–837. Galli P. and Naso G.; 2009: Unmasking the 1349 earthquake source (southern Italy): palaeoseismological and archaeoseismological indications from the Aquae Iuliae fault . J. Struct. Geol., 31 , 128–149. Milano G., Di Giovambattista R. and Ventura, G.; 2008: Seismic activity in the transition zone between Southern and Central Apennines (Italy): evidences of longitudinal extension inside the Ortona-Roccamonfina tectonic line. Tectonophysics, 457 (1–2), 102–110. Milano G.; 2014: Seismological investigation of the 2013–2014 seismic sequence of the Matese Massif (Southern Apennines, Italy) . Atti del 33° Convegno Nazionale GNGTS, Tema Geodinamica, 79-84. Volume: ISBN 978-88- 940442-1-8; Raccolta: ISBN 978-88-940442-0-1. Milano G.; 2016: Seismological investigation of the 2016 low-magnitude seismic sequence near Baranello (Sannio- Matese area, Southern Apennines - Italy): first results. VolumeAtti del 35° ConvegnoAnnuale GNGTS, pp 149-151. Moretti M., Margheriti L., Basili A., Baccheschi P., Villani F., Cecere G., D’Ambrosio C., Di Stefano R., Falco L., Memmolo A., De Luca G., Migliari F., Minichiello F., Scognamiglio L.; 2017: Il terremoto a Campobasso del 16 gennaio 2016. L’evento di M W 4.3 e la sequenza sismica associata . Quaderni di Geofisica INGV, No 140 , Febbraio 2017.