Mapping the basement of the Cerdanya Basin (eastern Pyrenees) using seismicambient noise

Ambient seismic noise acquired in the Cerdanya Basin (easternPyrenees) is used to assess the capability of different methodologies to mapthe geometry of a small-scale sedimentary basin. We present results based ona 1-year-long broad-band deployment covering a large part of the easternPyrenees and a 2-month-long high-density deployment covering the basin withinterstation distances around 1.5 km. The explored techniques includeautocorrelations, ambient noise Rayleigh wave tomography, horizontal-to-vertical-spectra ratio (HVSR) and band-pass-filtered ambient noise amplitudemapping. The basement depth estimations retrieved from each of theseapproaches, based on independent datasets and different implicitassumptions, are consistent, showing that the deeper part of the basin islocated in its central part, reaching depths of 600-700 m close to theTet fault trace bounding the Cerdanya Basin to the NE. The overallconsistency between the results from all the methodologies provides solid constraints to our basement depth estimation, although significantdifferences arise in some areas. The results also show that, whenhigh-density seismic data are available, HVSR and ambient noise amplitudeanalysis in a selected frequency band are useful tools to quickly map thesedimentary 3D geometry. Beside this methodological aspect, our results helpto improve the geological characterization of the Cerdanya Basin and willprovide further constraints to refine the seismic risk maps of an area ofrelevant touristic and economic activity.