Magnetotelluric and Seismic Noise Techniques Combination for the Cerdanya Basin Characterization (Eastern Pyrenees)

A sedimentary Tertiary basin filled with unconsolidated sediments located in eastern Pyrenees has been subjected to a combine passive geophysical survey in order to increase knowledge of bedrock geometry and sediment properties. The methodology consists of combining and integrating both seismic noise techniques (H/V and array) and audio-magnetotelluric (AMT) and magnetotelluric (MT) data. AMT and MT data have been recorded along a NW-SE profile crossing the basin. Four 2D seismic noise arrays and 79 single station measurements were deployed at this profile. H/V technique has been suitable to obtain a soil fundamental frequency. Bedrock depth assessment can be obtained using S-wave velocity profiles derived from seismic noise array analysis. This information will allow establishing a soil fundamental frequency-bedrock depth relationship suitable for this basin. On the other hand, interpretation of the electrical resistivity model obtained from an AMT- MT survey will be constrained by the seismic results. This electrical resistivity model provides a detailed imaging of structural features such as the Cerdanya fault. This methodology, based on sediment characterization from shear-wave velocity and resistivity information, can be an attractive option for basin characterization essential for projects such as reservoir imaging.