Abstract
A regional shear-wave velocity (VS) 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 VS 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 VS profiles are constructed from a novel combination of three data sets covering different, partially overlapping depth ranges. The uppermost 50 m of the VS profiles are obtained from a high-resolution geological model with representative VS values assigned to the sediments. Field measurements of VS were used to derive representative VS 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 VP–VS 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 VS profiles is implemented.
Highlights
The province of Groningen in the Netherlands (Fig. 1) is experiencing induced earthquakes due to the exploitation of a large onshore gas field
This paper describes the development of the VS model for the Groningen field
The combination of three different VS models resulted in a model that is unique on this scale
Summary
The province of Groningen in the Netherlands (Fig. 1) is experiencing induced earthquakes due to the exploitation of a large onshore gas field. Rather than using proxy parameters such as the time-averaged 30 m shear-wave velocity, VS30, to capture site effects, the aim has been to more faithfully model the dynamic effects of the specific profiles in the field, which are overlain by a thick deposit of soft soils. To this end, a seismic microzonation of the field has been developed, the starting point of which is the model of shear-wave velocity (VS) profiles described . The paper concludes with a discussion of potential improvements to the VS model that may be addressed in future work
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