The Seismic Response of Faroe Basalts from Integrated Borehole and Wide-Angle Seismic Data

We study the seismic response of layered basalts in the Faroe Islands using borehole data and vertical seismic profiles from the Vestmanna borehole, combined with reflection and wide-angle seismic data recorded into arrays of both borehole and land multicomponent receivers. Imaging through the basalt cover in the Faroe-Shetland Basin is a challenge for conventional seismic surveys: scattering caused by the high reflectivity of the basalt as well as intra-basalt multiples and high attenuation from the layered sequence make it difficult to image within and beneath the basalts. This project allows us to correlate ultrasonic-scale velocity and density measurements from the borehole together with ground-truthing from borehole logs and core samples with the seismic-scale velocities and reflection images derived from VSP and surface data. We find a good match of observed travel-times of borehole and wide-angle P-wave data with those predicted from the borehole measurements, suggesting lateral homogeneity over horizontal distances on the kilometre scale, and restricted transverse anisotropy of the layered basalts. A pronounced intra-basalt reflector identified on the multichannel surface seismic can be correlated with lithostratigraphic interpretation of the borehole logs as caused by thick flows near the top of the Lower Basalt formation.