Imaging the uppermost layers of the Eifel volcanic system (Germany) using ambient microseismic noise

The Eifel region is a large volcanic system in the middle of European continent. From the Eifel teleseismic tomography experiment (8 months in 1997-1998), a mantle plume beneath the volcanic fields (down to 400 km depth) has been identified and further confirmed by receiver function and teleseismic surface wave dispersion analyses. A study in 2020 using dense geodetic observations leads to the conclusion that the Eifel region experiences a pronounced uplift encompassing the neighbouring countries Netherlands, Belgium, Luxembourg and France, which is attributed to the same buoyant mantle plume.

A detailed focus on the uppermost 30 km above the Moho has been missing until recently. However, a noteworthy recent seismological investigation showed the evidence of a deep magmatic recharge beneath the Laacher See Volcano in East Eifel between 2013 and 2018. Located at depth roughly between 40 and 10 km, low-frequency seismic swarms, which are typical of volcanic environment, convey the presence of magma movements and potential storage zones in the crust.  

The present study aims to bring additional information on this shallow active magmatic system using an Ambient Noise Tomography (ANT). Thanks to theoretical and technical developments over the two last decades, this approach has been increasingly popular for imaging Earth structure worldwide at different scales. We use here ambient noise data from archives of the 1997-1998 Eifel experiment and more recent (2019-2020) continuous seismic record. The group velocity dispersion of Rayleigh waves are estimated between station pairs from Noise Cross-correlation Functions (NCF) covering the secondary microseismic frequency band, which allows to sample the uppermost 10-20 km of the crust. Our contribution includes a complete description of the ANT/NCF processing (e.g., directivity of the noise sources, sensitivity tests) in order to better constrain the velocity anomalies observed in the Eifel region and around.