New data on the crustal structure of the Cantabrian Mountains in the western continuation of the Pyrenees: receiver function results from the CANALAB project

Seismic profiling has revealed since the 1990s that the Iberian Moho deepens towards the north in the Cantabrian Mountains, as it does in the Pyrenees to the east. However, the crustal root is only robustly imaged by deep seismic sounding beneath the central part of the Cantabrian Mountains, and its maximum extent has only been inferred from unreversed wide-angle reflection data in ocean–land seismic experiments (ESCIN and MARCONI projects). This lack of strong constraints has opened the door to a wide variety of interpretations of Moho depths beneath the northern boundary of the Cantabrian Mountains, along the shoreline of the Bay of Biscay, ranging from ~14 to ~55 km.

One of the main objectives of the ongoing CANALAB project (PID2020-118228RB-C21, funded by MCIN/AEI/10.13039/501100011033) is to add more robust constraints on the lithospheric structure of the Pyrenean–Cantabrian mountain belt using passive seismic techniques. These techniques were applied in two successive deployments of broadband seismic stations: one following a N–S transect along the central Cantabrian Mountains (eastern border of the Asturian Paleozoic massif), and another following a NNE–SSW transect through the eastern Cantabrian Mountains (the Basque–Cantabrian Zone). This work presents the results from the first deployment, extending northwards and southwards the area imaged by the ESCIN-2 seismic reflection profile, in which the deepening of the Iberian Moho beneath the mountain range was previously identified. The new high-resolution passive seismic profile was obtained using 29 stations between the Cantabrian coast and the Duero Foreland Basin, with spacings of 2.2 to 5.5 km. The analysis of teleseismic receiver functions shows that the Iberian Moho sinks into the mantle towards the north to depths of at least 52 km below the coastline, an observation with important implications for the quantification of Alpine shortening and for the validation of the various tectonic models proposed for the area.