We have built two geological models that serve as input for the seismic hazard and risk analysis of the onshore gas field of the Groningen region, the Netherlands. The first model describes the liquefaction potential indicators and the second model consists of the characterisation and layer model for site response calculations. The models have a regional coverage spanning an area of more than 1,000 km2. ... Read more

A regional shear-wave velocity (V_S) model has been developed for the Groningen gas field in the Netherlands as the basis for seismic microzonation of an area of more than 1000 km². The V_S model, extending to a depth of almost 1 km, is an essential input to the modelling of hazard and risk due to induced earthquakes in the region. The detailed V_S profiles are constructed from a novel combination of three data sets covering different, partially overlapping depth ranges. The uppermost 50 m of the V_S profiles are obtained from a high-resolution geological model with representative V_S values assigned to the sediments. Field measurements of V_S were used to derive representative V_S values for the different types of sediments. The profiles from 50 to 120 m are obtained from inversion of surface waves recorded (as noise) during deep seismic reflection profiling of the gas reservoir. The deepest part of the profiles is obtained from sonic logging and V_P–V_S relationships based on measurements in deep boreholes. Criteria were established for the splicing of the three portions to generate continuous models over the entire depth range for use in site response calculations, for which an elastic half-space is assumed to exist below a clear stratigraphic boundary and impedance contrast encountered at about 800 m depth. In order to facilitate fully probabilistic site response analyses, a scheme for the randomisation of the V_S profiles is implemented. ... Read more

The surface movement in the Krimpenerwaard polder in The Netherlands results from primary or hydrodynamic settlement/swelling, secondary or creep settlement/swelling, and peat oxidation. We used surface movement measurements in a Bayesian inversion scheme to disentangle the contribution of these three processes to the subsidence. The prior information, including spatial correlations, appeared to be crucial in our procedure. This prior information was derived from geological modeling incorporating the most important uncertainties. The inversion procedure allowed us to quantify the contributions of the three processes with unprecedented accuracy. Surface rise in the data was related to swelling of the clay layers, even though swelling was considered infeasible in the prior information. Despite this, the irreversible nature of peat oxidation was preserved. The improved subsurface description offers prospects for identification of incorrect information and for better assessments of the effects of water management. ... Read more