Spatial variation in seismic velocity change in the shallow subsurface of Groningen, the Netherlands

We previously developed a physics-based model relating changes in pore pressure and vertical stress to seismic velocity variations and validated the model in a small area of Groningen gas field. Using the entire Groningen seismic network, near-surface velocity changes are estimated over a three-year period, using passive image interferometry. For the South-East region of Groningen we predict the observed velocity changes by applying the newly derived theory to pressure-head recordings. Towards the North-West, where pressure-head measurements are absent, we observe that the amplitudes of the measured velocity variations increase gradually, while their phases remain the same. We attempt to explain spatial differences in seismic velocity variations in the light of our previously developed model.