MACIV: a new project on multiscale seismic imaging of Massif Central (France) focusing on recent intraplate volcanism

Volcanic hazard is still an issue in the French Massif Central (FMC) because the last eruptions are dated 6700 yrs BP. Indeed, seismic bursts and geodetic uplift related to volcano-magmatic activity have recently been detected in the Eifel region (Germany), which belongs to the same European Cenozoic rift system as the FMC. However, geophysical knowledge of the sources of FMC volcanism is limited to the mantle-plume hypothesis, which dates from the last seismological experiment performed >30 years ago. To improve our knowledge on the deep structures of the FMC and the sources of volcanism, a multidisciplinary team of geophysicists, geologists, and volcanologists has set up the MACIV project, in a context of solid synergy with ongoing and future research initiatives in France and Europe (e.g. AdriaArray). Between 2023-2026, we will deploy several hundreds of seismic instruments in a multiscale configuration to probe the different scales and depths of the FMC volcanic systems with optimal spatial resolution. The entire FMC will be covered with broadband seismic stations in a 2-D array (spacing ~35 km) and three transverse profiles (spacing 5-20 km) for durations of 1.5-3 yrs. These arrays will provide information on the causes of mantle melting at depth, their links with the expression of volcanism at the surface, and the influence of Variscan and Cenozoic lithospheric structures. On a smaller scale, dense large-N arrays of ~650 short-period stations will provide images of the upper crust below the volcanoes and illuminate their plumbing systems. The enhanced earthquake detection power of the dense arrays will illuminate active faults and possible plumbing systems of the youngest volcanoes. The MACIV project will help better evaluate the volcanic hazard and provide a framework for a monitoring strategy scaled to a currently dormant volcanic province. The resulting seismological dataset will be used for years to come to yield essential information on intraplate volcanism.