GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.2 GNGTS 2024 P-and S-velocity 3D model for the characterisaton of the subsurface beneath the village of Arquata del Tronto G. Böhm 1 , A. Afatato 1 , L. Baradello 1 , G. Brancatelli 1 , E. Forlin 1 , F. Meneghini 1 1 Natonal Insttute of Oceanography and Applied Geophysics – OGS (Italy) 1. Introducton The 2016-2017 seismic sequence in the Central Apennines has, once again, demonstrated the importance of diferent seismic efects in complex geological contexts at short distances (e.g., valleys flled with sof sediments, hilltops, complex buried geometries). The severe damage reported by ancient setlements located on the top of a rocky hill, as in the case of Arquata del Tronto, has underlined the need to defne an accurate three-dimensional numerical model (topography, seismo-stratgraphic, geomechanical, geotechnical characteristcs, etc.) in order to best model the local seismic response through appropriate numerical simulatons. This work describes the results of a high-resoluton refecton seismic acquisiton (P-wave and S- wave) carried out at the Arquata del Tronto (AP) site for the geophysical characterizaton of the subsurface, as part of the public interventon "Progeto di suolo (terrazzament)" in the historic centre of Arquata del Tronto (AP). The fnal product of this study was a 3D velocity model obtained by the travel tme tomography of the picked frst break from the acquired seismic survey. 2. Seismic acquisiton The seismic survey made at this site consists of 3 separate lines (Fig. 1). The acquisiton of Line 1 (source spacing 4 m, group spacing 2 m), was carried out in 3 phases, using the electrodynamic vibrator (ELVIS VII) with 20-220 Hz, 10 seconds sweep as the source: - with the P source and P geophones (10 Hz); - with the S source oriented at an angle of 5° N (corresponding to the average strike directon of the outcropping formatons) and the S geophones ( 14 Hz single component geophones oriented at the same angle of 5° N), called SA; - with the S source oriented at an angle of 95° N (perpendicular to the strike directon) and the S geophones (single component geophones oriented at the same angle of 95° N), called SB. Line 2 (source spacing 4 m, group spacing 2 m), was acquired with the shotgun as the source and the P geophones. Line 3 (source spacing 8 m, group spacing 4 m), was acquired in 2 stages using the P-source ELVIS VII ( 20-220 Hz, 10 s sweep) and S-source MiniVib IVI T-2500 (20-200 Hz, 10 s sweep ): - with the P source and P geophones; - with the S source aligned perpendicular to the local directon of the line and the S geophones (single component geophones, all oriented at an angle of 5° N);