GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 1.3 GNGTS 2024 The coda atenuaton method reveals a very high atenuatng crust in the High Agri Valley (Southern Italy) S. Lucente (a) , V. Serlenga (b) , S. de Lorenzo (a) , E. del Pezzo (c,d) , M. Filippucci (a,c) , T. Ninivaggi (e) , T.A. Stabile (b) , A. Tallarico (a,c) (a) Università degli Studi di Bari Aldo Moro, Dipartmento di Scienze della Terra e Geoambientali, Bari, Italy (b) CNR Insttute of Methodologies for Environmental Analysis, IMAA, Tito Scalo, Italy (c) Isttuto Nazionale di Geofsica e Vulcanologia, Sezione di Napoli “Osservatorio Vesuviano”, Napoli, Italy (d) Insttuto Andaluz de Geofsica, Universidad de Granada, Granada, Spain (e) Isttuto Nazionale di Geofsica e Vulcanologia, Sezione Irpinia, Grotaminarda, Italy High Agri Valley is an intermontane basin located in the axial porton of Southern Apennines, a fold and thrust chain originated startng from the late Oligocene (Patacca & Scandone, 2007). The investgated area is characterized by a very strong seismogenic potental as testfed by the Mw=7.0 1857 earthquake. In the last decades, a low magnitude natural seismicity has been recorded by the statons belonging to both the trigger-mode monitoring network managed by ENI Oil Company and the Italian Natonal Seismic Network managed by INGV. In additon to the natural seismicity, two anthropogenic seismicity clusters are documented (Stabile et al., 2014; Improta et al., 2017 among the others), located NE and SW of the artfcial Pertusillo lake, respectvely: a) fuid-induced microseismic swarms due to the injecton, through the Costa Molina 2 well, of the wastewater produced by the exploitaton of the Val d’Agri oilfeld; b) protracted reservoir induced seismicity (RIS) caused by the combined efects of the water table oscillatons of the Pertusillo lake, the regional tectonics and likely the poroelastc/elastc stress due to aquifers in the carbonate rocks (Picozzi et al., 2022). In order to gain insights on the atenuaton propertes of the crust of this region, we selected a dataset of about 1800 events acquired from 2001 to 2015 by the two above mentoned seismic networks, with local magnitude (ML) ranging from 0 to 3.3. The dataset is composed of triaxial recordings acquired by an average number of 14 statons. We estmated the atenuaton of S-coda waves Qc -1 from a linear regression analysis of the envelope of the amplitude decay curve (Sato, 1977). This parameter can give informaton about the physical state of the crust (possible presence of fuids, or thermal anomalies, or ductle rock volumes) and in tectonic context it is widely accepted that Q c , estmated with the single scatering model at long lapse tme, is representatve of the intrinsic atenuaton Q i (Mayor et al. 2016). The method consists in the linear ftng of the decreasing trend on the envelopes of S coda waves in a selected tme window. Moreover, we developed a method aimed at automatcally fnding the end- tme (T 2 ) of the coda envelope, avoiding the manual and subjectve criterion of selecton of the end of coda. This method was tested on a signifcant sample of real data before of its applicaton to the entre dataset. Only the components, for which the conditon T 1 <T L <T 2 was fulflled, were considered for the linear regression. The Qc estmates were performed by using diferent tme windows for the envelope ftng, startng from the tme T 1 to the tme T L (the lapse tme). In detail, we adopted, as T 1, 1.0*Ts, 1.5*Ts and 2.0*Ts (being Ts the S wave arrival tme), and as T L 10s, 15s, 20s, 25s and 30 s from the event origin