Moho and LAB Across the Western Alps (Europe) From P and S Receiver Function Analysis

In spite of numerous active and passive seismological investigations, the existence of continuous or interrupted continental subduction below the Western Alps is still open to debate. Many of the observations focus on the Moho or the deeper part of the mantle, while reliable information on the Lithosphere‐Asthenosphere Boundary (LAB) below the Alpine region is scarce. Exploiting the data from the dense, broadband AlpArray Seismic Network we present a set of Receiver Function (RF) measurements on the Moho and LAB of a region encompassing the Western Alps, which includes the Ivrea Geophysical Body (IGB), a fragment of mantle placed at a few kilometers depth at the collision margin between Eurasia and Adria plates. We derive seismic velocity profiles of the crust‐uppermost mantle below each station down to about 250 km, through the joint inversion of P and S RF. We constrain the lateral variations of the Moho and LAB topographies across the colliding plates, and quantify the errors related to our measurements. Our results allow us to considerably expand the published data of the Moho depth and to add a unique set of new measurements of the LAB. Our observations show that Eurasia and Adria lithospheres have a comparable thickness (on average 90–100 km), and are colliding below the IGB, and that Eurasia is not presently continuously subducting below Adria. These observations suggest that there is a gap between the superficial (continental) European lithosphere and the deep (oceanic) lithosphere, confirming the discontinuous structure imaged by some seismic tomography models. Plain Language Summary The Alps are one of the most studied orogenic systems but a number of questions remain unanswered, such as the existence of continuous or interrupted subduction of the Eurasian plate below the Adria plate in the Western Alps. To answer this question, it is necessary to assess the geometry (such as thickness and position) of the two lithospheric plates that are involved. We use the receiver function technique on seismometer data coming from the dense AlpArray Seismic Network to explore the interfaces that delimit the shallow Earth layers: the Moho and the Lithosphere‐Asthenosphere Boundary. Thanks to these measurements we were able to define the plate geometries below the Western Alps. Our observations show that Eurasia and Adria lithospheres have comparable (on average 90–100 km), that the plates are colliding, and that Eurasia is not presently continuously subducting