A geology-based 3D velocity model of the Amatrice Basin (Central Italy).

The Amatrice area has historically been affected by moderate to large earthquakes, which caused extensive damage and many casualties, like the 1639 and the 2016-2017 seismic sequences. For this reason, this area was extensively studied and, consequently, a large amount of seismological, geological and geophysical data is available. Due to this large amount of data, the Amatrice area represents a remarkably interesting case study for reconstructing a 3D geological and geophysical model, however, to date a detailed geology-based 3D velocity model of the Amatrice subsoil is still missing. Consequently, the local seismic response evaluation of the area can be based only on the geological and geotechnical characteristics and the available low-resolution large-scale models. We present a new methodological approach which integrates geological and geophysical data for reconstructing accurate and more realistic 3D geological and geophysical models exploitable, for example, in the seismic hazard assessment of seismic areas. As a case study, we propose the reconstruction of a geology-based 3D velocity model of the uppermost hundreds of meters of the Amatrice high-seismic-hazard area. The Amatrice area model integrates geological (e.g., maps, cross-sections and core-wells) and geophysical (e.g., down-hole, MASW, refraction, and seismic noise measurements) data, which were georeferenced and uploaded into 3D geological modeling software, where faults, stratigraphic boundaries, and geophysical attributes were digitized, checked, hierarchized, and modelled. First we have reconstructed the 3D geological model of the area and then we have parameterized it with the Vs and Vp velocities values. Finally, the reconstructed 3D geology-based velocity model has been verified by comparing the environmental noise (i.e., horizontal-to-vertical spectral ratio analysis, HVSR) recorded at some seismic stations with the seismic responses modelled at some nearby control points. The proposed model is the first geology-based 3D velocity model of the Amatrice area and represents a new potential geophysical prediction tool for areas devoid of geophysical measurements (i.e. HVSR curves), as well as a potential input-model for future ground-motion and seismic-wave-propagation simulations aimed at a more precise local seismic response assessment and, consequently, at the development of more realistic seismic hazard scenarios. This model is intended as a work in progress since it will be improved as soon as new data and more advanced algorithms became available.