A Regional Site-Response Model for the Groningen Gas Field

A key element in the assessment of seismic hazard and risk due to induced earthquakes in the Groningen gas field is a model for the prediction of ground motions. Rather than using ground-motion prediction equations with generic site amplification factors conditioned on proxy parameters such as VS30, a field-wide zonation of frequency-dependent nonlinear amplification factors has been developed. Each amplification factor is associated with a measure of site-to-site variability that captures the variation of VS profiles and hence amplification factors across each zone, as well as the influence of the uncertainty in the modulus reduction and damping functions for each soil layer. This model can be used in conjunction with the predictions of response spectral accelerations at a reference rock horizon at a depth of about 800 m to calculate fully probabilistic estimates of the hazard in terms of ground shaking at the surface for a large region potentially affected by induced earthquakes.