Overview of geophysical surveys conducted during ICDP-DIVE phase 1 in Val d’Ossola, Italy.

Since the inception of the ICDP expedition 5071, the Drilling the Ivrea-Verbano zonE (DIVE) project, geophysical surveys have played a key role in the planning and operational stages of phase 1. DIVE aims to investigate the continental lower crust with a focus on the physical and petrological transition towards the crust–mantle boundary at key sites in the Ivrea Zone of the Italian Alps. Phase 1 drilling site selection was strengthened with several 2D seismic profiles in the Ornavasso, Megolo and Premosello municipalities of Val d’Ossola, characterizing the complexity of the underlying lower crustal rock of interest and the overlying sedimentary cover. Preliminary site surveys identified near surface features deemed either disadvantageous or advantageous to drilling, subsequently refining the exact drill collar locations for the 5071_1_B and 1_A drill holes. During drilling pauses of 1_A and 1_B, dominant fracture orientations were determined with borehole acoustic methods, which influenced drilling decisions and the strategic termination of 1_B. Physical rock properties, magnetic susceptibility, and natural gamma radiation, were measured on rock cores as part of the on-site core characterization process. Additionally, seismic activity during the drilling periods was monitored through three approaches: seismic-while-drilling arrays located immediately around the drilling sites; a buried fiber optic cable in the nearby area; and a seismic monitoring network (DIVEnet) of a broader area covering the northeastern part of the Ivrea-Verbano Zone.  

Physical rock properties have been determined along the length of each borehole through open-hole wireline logging, during and at the end of the drilling, establishing clear relationships between the different core-lithologies. Vertical seismic profiles (VSP), and reverse VSP check shot surveys have been conducted at the conclusion of drilling, including the use of a novel bare-fiber optic cable deployed in 5071_1_A, to determine the seismic velocity structure and seismic reflectivity. Additionally, gamma-gamma density measurements have been acquired at 10 cm intervals on all the recovered core using a multi-sensor-core-logger allowing the computation of elastic rock properties. Further rock physics experiments are ongoing and nearing completion and, together with a wealth of chemical analyses, start to reveal the fine details of lower crustal variability.  

All the above surveys have contributed to an extensive geophysical data set across all scales that will be analyzed in the coming years. These data sets will briefly be introduced in the presentation.