Presented by
Adrian Rodriguez-Marek, Virginia Tech, USA.
Gas extraction in the Groningen Gas field has led to the occurrence of small earthquakes over the last couple of decades. While these events have been relatively small (the largest recorded to date is a ML 3.6 earthquake), they have led to a large effort to evaluate the hazards and risks associated with induced seismicity associated with gas production in the field. As part of these efforts, a site response model was developed to predict amplification factors over the entire 40×50 km extent of the field. The Groningen region has unique characteristics due to the presence of very soft clays and peats and due to the deep extent of sedimentary deposits at the site. Rather than use generic site amplification factors conditioned on proxy parameters such as VS30, a field-wide zonation of frequency-dependent non-linear amplification factors has been developed. Each amplification factor is associated with a measure of site-to-site variability that captures the variation of shear-wave velocity profiles and hence amplification factors across each zone, as well as the influence of uncertainty in the modulus reduction and damping functions for each soil layer.