The DIVEnet: a local seismographic network monitoring the lower continental crust drillings for the ICDP-DIVE project

<p><span>The ICDP DIVE project (www.dive2ivrea.org) is aimed at addressing fundamental questions on the nature of the lower continental crust and its transition to the mantle, in a first phase through two drillings in the Ivrea Verbano zone (IVZ). The IVZ, considered the world's best outcrop of lower crustal continental rocks, is the exposed part of the Ivrea Geophysical Body (IGB), a major high gravity and high seismic velocity anomaly studied since the 1960s and strongly related to Western Alps structural and tectonic history. Beneath the IVZ the Moho possibly reaches very shallow depth (locally ~1&#177;1 km b.s.l.), making this site unique all over the World.</span></p><p><span>The two proposed drillings will start in the 2022 in Val D&#8217;Ossola: the first in Ornavasso and the second in Megolo, 7 km apart from each other. The assemblage of the two will constitute the most complete record of lower continental crust. Physical and chemical data systematically collected downhole as well as along drill cores will be combined and compared with local/regional geophysical and geological surveys. Within this frame and scope, a dedicated seismographic network named DIVEnet has been planned to monitor local earthquakes and operation-related seismic activity.</span></p><p><span>Starting from summer 2021 the survey and seismic station deployment started to have all stations running by January 2022. So far 10 seismographic stations provided by INGV and University of Lausanne have been installed within a 15 km maximum distance from the mid-point between the two drilling sites and recording in continuous mode (100 sps). One of the seismometers will be housed in the first completed borehole while the second one is being drilled. Given that the area is characterized by low natural local seismicity and low seismic stations density, having a long time record of background activity and background noise, including the period before and after the drilling activities&#8217; initiation, is of crucial importance. The acquisition and first elaboration of seismic data have been actively included in the routine work at INGV.</span></p>