GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 3.2 717 Theseismic faciesLs isevidencedby inclinedslopingreflectors, characterizedbydiscontinuous to chaotic low-amplitude reflections, generally terminating against each other. This reflectors arrangement looks like the typical pattern of the Lateral Accretion Package (LAP) (Posamentier, 2002). The high-amplitude reflections mark the bounding surfaces of these features giving to this facies a “U-shaped” geometry. This facies is scattered and is always contained within the seismic facies L. The facies Ls probably corresponds to channelized bodies of coarse-grained deposits within the generally finer MDS. These channels, defined as channel-point bars, were formed by dunes and ripple migration lateral to the currents, and are encased in floodplain pelite. The facies R is always located in the lower sector of the Corso section and is characterized by high reflectivity and amplitude, with disturbed or semi-continuous reflectors. The faintly continuous reflectors show a divergent internal configuration, typical of wedge-shaped geometries. The boundary between the facies R and S is irregular, probably because of the extremely disturbed signal. The irregularly-fringed and high-amplitude reflectors of the facies R probably can be referable to the late Piacenzian-Gelasian coarse-grained deposit (CCF). At last, the seismic facies S is composed by chaotic shape, with low-amplitude dipping reflective pattern, and discontinuous reflectors. It is located on the deepest sector of the basin fill. The poor diffusion of this facies, related to the low-resolution signal and discontinuity of reflectors, points to the acoustic bedrock of the Western L’Aquila Basin. The facies S is referable to the Meso-Cenozoic bedrock that, below the Corso section, could be represented by Miocene carbonate-ramp as testified by a deep borehole. In the Corso section, several normal faults can be recognised, which mostly displace MDS and the underlying units (CCF and theMeso-Cenozoic bedrock). The principal one, called Piazza Duomo Fault (PDF) is a growth-fault characterised by a SW-dipping sub-planar geometry. The resolution of the Corso section does not permit to evidence the displacement of the COM/CMA boundary due to PDF. Although, the COM thickness in the PDF hangingwall is higher than in the footwall, denoting a possible tectonic activity of PDF during the Late Pleistocene. Conclusion. The interpretation of the 1000 m-long high-resolution seismic reflection profile (Corso section), accompanied by deep boreholes, detailed survey data, and seismic refraction tomography, permitted us at updating the subsoil model of L’Aquila historical centre (Fig. 1). The results, within the scope of seismic microzonation mapping, are useful to refine a detailed geological subsoil model at an urban scale, and thus to provide evidence of both seismic site effects and the activity of buried faults. This information, for Italian towns with rich cultural heritage, such as L’Aquila historical centre, was crucial to design an urban masterplan specifically devoted to the seismic hazard. References Cosentino D., Asti R., Nocentini M., Gliozzi E., Kotsakis T., Mattei M., Esu D., Spadi M., Tallini M., Cifelli F., Pennacchioni M., Cavuoto G. and Di Fiore V.; 2017: New insights into the onset and evolution of the central Apennine extensional intermontane basins based on the tectonically active L’Aquila Basin (central Italy) . Bull. Geol. Soc. Am., 129 , 1314–1336. Del Monaco F., Tallini M., De Rose C. and Durante F.; 2013: HVNSR survey in historical downtown L’Aquila (central Italy): site resonance properties vs. subsoil model . Engineering Geology, 158, 34-47. Nocentini M., Asti R., Cosentino D., Durante F., Gliozzi E., Macerola L. and Tallini M.; 2017: Plio-Quaternary geology of L’Aquila–Scoppito Basin (Central Italy) . J. Maps, 13 , 563–574. Nocentini M., Cosentino D., Spadi M. and Tallini M.; 2018: Plio-Quaternary geology of the Paganica- San Demetrio-Castelnuovo Basin (Central Italy) . J. Maps, 14 , 411–420. Posamentier H.W.; 2002: Ancient shelf ridges—a potentially significant component of the transgressive systems tract: case study from offshore northwest Java . Am. Assoc. Pet. Geol. Bull., 86 , 75–106. Tallini M., Cavuoto G., Del Monaco F., Di Fiore V., Mancini M., Caielli G., Cavinato G.P., De Franco R., Pelosi N. and Rapolla A.; 2012: Seismic surveys integrated with geological data for in-depth investigation of Mt. Pettino active fault area (Western L’Aquila Basin) . Ital. J. Geosci. (Boll. Soc. Geol. It.), 131 , 389-402. Tallini M., Spadi M., Cosentino D., Nocentini M., Cavuoto G. and Di Fiore V.; 2019: High-resolution seismic reflection exploration for evaluating the seismic hazard in a Plio-Quaternary intermontane basin (L’Aquila downtown, central Italy) . Quaternary International, https://doi.org/10.1016/j.quaint.2019.09.016.