High-resolution seismic reflection survey crossing the Insubric Line into the Ivrea-Verbano Zone: Novel approaches for interpreting the seismic response of steeply dipping structures

A high-resolution seismic reflection survey has been conducted across the Insubric Line from the Sesia Zone into the Ivrea-Verbano Zone (IVZ), where a remarkably complete cross-section of lower continental crust is exposed. The survey was carried out in preparation for the DIVE (Drilling the Ivrea-Verbano zonE) project, which was recently approved by the International Continental Scientific Drilling Program (ICDP). DIVE aims to gain new insights into the characteristics of the lower continental crust through targeted drilling, sampling, and borehole logging. A key borehole is planned near the Insubric Line at Balmuccia, where the deepest parts of the lower continental crust are exposed. As such, the primary objective of this seismic survey was to explore whether the sub-vertical structures prevailing at the surface can be expected to continue at depth or whether there are any indications for major flattening or fault-related offsets. Correspondingly, the acquisition and processing of the seismic reflection data were geared towards revealing weak backscattered events from local heterogeneities associated with the prevailing sub-vertical structural grain. The migrated sections, contain coherent backscattered events to a depth of ~1 km, which form numerous short lineaments that seem to align sub-vertically. To substantiate this observation, we have generated synthetic seismic reflection surveys for canonical models of sub-vertical structures associated with Gaussian- and binary-distributed heterogeneities. Both the observed and synthetic seismic data were then subjected to energy-based attribute analysis as well as geostatistical estimations of the structural aspect ratios and the associated dips. The results of these quantitative interpretation approaches are indicative of the overall consistency between the synthetic and the observed seismic data and, hence, support the original qualitative interpretation of the latter in that the sub-vertical structural grain evident at the surface seems to prevail throughout the imaged part of the upper crust.