Low frequency passive seismic tomography using Valhall LoFS

We used 6 hours of vertical component continuous data recorded from more than 2400 receivers of the Valhall LoFS for passive seismic interferometry. The Correlation Functions contain symmetrical Scholte-waves in the 0.1-2 Hz frequency range and we showed by beamforming that the sources of these waves were homogeneously distributed around the array. We constructed group velocity dispersion curves of the extracted Scholte-waves and inverted them to produce a group velocity map of the Valhall field subsurface. We found that seismic velocities were higher in the center of the array than at its edge. It is in good agreement with geomechanical models based on the sea-floor subsidence due to the reservoir production.