Abstract
In order to inform decision-making regarding measures to mitigate the impact of induced seismicity in the Groningen gas field in the Netherlands, a comprehensive seismic risk model has been developed. Starting with gas production scenarios and the consequent reservoir compaction, the model generates synthetic earthquake catalogues which are deployed in Monte Carlo analyses, predicting ground motions at a buried reference rock horizon that are combined with nonlinear amplification factors to estimate response spectral accelerations at the surface. These motions are combined with fragility functions defined for the exposed buildings throughout the region to estimate damage levels, which in turn are transformed to risk in terms of injury through consequence functions. Several older and potentially vulnerable buildings are located on dwelling mounds that were constructed from soils and organic material as a flood defence. These anthropogenic structures are not included in the soil profile models used to develop the amplification factors and hence their influence has not been included in the risk analyses to date. To address this gap in the model, concerted studies have been identified to characterize the dwelling mounds. These include new shear-wave velocity measurements that have enabled dynamic site response analyses to determine the modification of ground shaking due to the presence of the mound. A scheme has then been developed to incorporate the dwelling mounds into the risk calculations, which included an assessment of whether the soil-structure interaction effects for buildings founded on the mounds required modification of the seismic fragility functions.
Highlights
Gas production in the Groningen field in the northern Netherlands began in 1963 and since 1991 the consequent compaction of the sandstone formation where the reservoir resides has been generating induced seismicity.The largest earthquake to date was the ML 3.6 (M 3.5, Dost et al 2019) Huizinge earthquake of August 2012, following which the field operator initiated an extensive data acquisition and modelling programme to quantify the resulting seismic hazard and risk (van Elk et al 2017)
The near-surface VS profiles are based on the GeoTOP model that defines the lithological profiles across the Netherlands (Stafleu and Dubelaar 2016); the resulting VS profiles have been validated by site-specific measurements using both borehole and non-invasive techniques (Noorlandt et al 2018)
A bespoke seismic risk model has been developed as a tool for the management of induced earthquakes in the Groningen gas field in the Netherlands
Summary
Gas production in the Groningen field in the northern Netherlands began in 1963 and since 1991 the consequent compaction of the sandstone formation where the reservoir resides has been generating induced seismicity (van Thienen-Visser et al 2015; Bourne et al 2018).The largest earthquake to date was the ML 3.6 (M 3.5, Dost et al 2019) Huizinge earthquake of August 2012, following which the field operator initiated an extensive data acquisition and modelling programme to quantify the resulting seismic hazard and risk (van Elk et al 2017). While only a very small proportion of the exposed buildings in the Groningen region are founded on these dwelling mounds, it has been a long-term objective to include the wierden into the risk modelling for completeness. In order to be able to model the dynamic response of the wierden, VS p measurements were made at a number of selected mounds across the region For the building types located on these geotechnical structures, the risk model needs to consider both the modification of the ground shaking due to the presence of the mound and the possible modification of the
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