The Ivrea Verbano Zone (IVZ) is one of the most complete crust–upper mantle geological references in the world, and the Drilling the Ivrea-Verbano zone project (DIVE) aims to resolve the uncertainties below this area. Geophysical anomalies detected across the IVZ indicate that dense, mantle-like rocks are located at depths as shallow as ca. 1-3 km (Scarponi et al., 2020, 2021). Thus, within DIVE several geological, geochemical and geophysical studies are planned, including the drilling of a 4 km deep borehole that will penetrate the Balmuccia Peridotite (Val Sesia, Italy) to approach, and possibly cross, the crust–mantle transition zone, and provide for the first time geophysical in-situ measurements of the deepest rocks of the IVZ.

One of the primary requirements before drilling is a seismic site characterization, to define with precision the correct positioning and orientation of the borehole, to assess potential drilling hazards and to allow for the spatial extrapolation of the borehole logs. For that goal, two joint geophysical surveys were performed in October 2020 in a collaboration between GFZ Potsdam, Université de Lausanne and Montanuniversität Leoben: (1) a deep seismic survey performed by GFZ Potsdam, entitled SEismic imaging of the Ivrea ZonE (SEIZE), consisting of two approximately orthogonal 15 km-long seismic lines, that aim to resolve the deeper structure of the IVZ in the area, and (2) a smaller seismic survey at the proposed drill site, entitled High-resolution SEismic imaging of the Ivrea ZonE (HiSEIZE), geared towards providing high-resolution seismic images of the uppermost few km at the proposed drill site.

The HiSEIZE survey (Figure 1), the subject of this study, was performed with a fixed spread of 200 vertical geophones and 160 3C-sensors, spaced at ca. 11m along three sub-parallel lines spaced 50-80 m apart. A 17’000 kg Vibroseis was utilized as a source at 22 m spacing along a 2.4 km line emitting a 10 s linear sweep (from 12 to 140 Hz) with 3 s listening time.

The presence of high-velocity crystalline rocks and sub-vertical structures throughout the study area (Liu et al., 2021) make seismic processing challenging. Important processing steps applied include:
• P- and S-wavefield separation,
• Generation of a high-resolution near-surface velocity model through refraction tomography. Merging with low-resolution velocity model from the SEIZE survey,
• Pre-Stack Depth Migration (PSDM).

This project will not only provide site characterization for the DIVE project, but also contribute to understanding the structure of the Balmuccia Peridotite, its changes in depth and its relationship with the crustal-mantle transition.

In this contribution, we will present the newly acquired data and first results.