Ground-motion prediction models for induced earthquakes in the Groningen gas field, the Netherlands

Abstract

Small-magnitude earthquakes induced by gas production in the Groningen field in the Netherlands have prompted the development of seismic risk models that serve both to estimate the impact of these events and to explore the efficacy of different risk mitigation strategies. A core element of the risk modelling is ground-motion prediction models (GMPM) derived from an extensive database of recordings obtained from a dense network of accelerographs installed in the field. For the verification of damage claims, an empirical GMPM for peak ground velocity (PGV) has been developed, which predicts horizontal PGV as a function of local magnitude, ML; hypocentral distance, Rhyp; and the time-averaged shear-wave velocity over the upper 30 m, VS30. For modelling the risk due to potential induced and triggered earthquakes of larger magnitude, a GMPM for response spectral accelerations has been developed from regressions on the outputs from finite-rupture simulations of motions at a deeply buried rock horizon. The GMPM for rock motions is coupled with a zonation map defining frequency-dependent non-linear amplification factors to obtain estimates of surface motions in the region of thick deposits of soft soils. The GMPM for spectral accelerations is formulated within a logic-tree framework to capture the epistemic uncertainty associated with extrapolation from recordings of events of ML ≤ 3.6 to much larger magnitudes.

A database of ground motion recordings, site profiles, and amplification factors from the Groningen gas field in the Netherlands

“…The ground motion database also contains a table with horizontal component pseudo-spectral accelerations after deconvolution from the surface to the reference baserock used in the Groningen GMMs (Bommer et al, 2022a), the base of the North Sea formation (NS_B) at a depth of ∼800 m. The site profiles at the recording stations were used to compute transfer functions (TFs) and amplification factors (AFs) to transfer the FAS and pseudo-acceleration response spectra, respectively, to the reference rock horizon.…”

“…to apply the model to R = 40 km, R should be replaced by 35 km). An extensive discussion of AF and TF derivation is given in Bommer et al (2022a).…”

“…A vital element of the risk analysis is a model for the prediction of ground motion parameters due to the induced earthquakes and possible triggered earthquakes of larger magnitude (Bommer and van Elk, 2017). An analysis of recordings from the small accelerograph network that has been operated in the region for many years by the national seismological service of the Netherlands, the KNMI (Koninklijk Nederlands Meteorologisch Instituut-Royal Netherlands Meteorological Institute) suggested systematic differences even with ground motions from induced earthquakes in other Dutch gas fields (Bommer et al, 2017a(Bommer et al, , 2022b, prompting the decision to develop a bespoke ground motion model (GMM) for Groningen (Bommer et al, 2016). Toward this end, the ground motion recording networks in the field were expanded and field measurements were undertaken to characterize the dynamic properties of the near-surface profiles at the recording sites.…”

“…The GMM for response spectral accelerations has evolved through numerous iterations and extensive review by an international panel of experts (see “Acknowledgments” section), incorporating the results of simulations (Edwards et al, 2019), derivation of a field-specific model of soil damping (Ruigrok et al, 2022), and inclusion of scenario-dependence in the linear amplification factors at short periods (Stafford et al, 2017). The final GMM (Bommer et al, 2022a) is now available at the NAM website (see “References” section). In addition to the GMM for spectral accelerations required for the risk calculations over a broad range of earthquake magnitudes, an empirical GMM for peak ground velocity (PGV), applicable only in the magnitude range of the data, has been developed for applications related to damage assessment (Bommer et al, 2021); the PGV model is also available for download from the NAM website (see “References” section).…”

“…In addition to the GMM for spectral accelerations required for the risk calculations over a broad range of earthquake magnitudes, an empirical GMM for peak ground velocity (PGV), applicable only in the magnitude range of the data, has been developed for applications related to damage assessment (Bommer et al, 2021); the PGV model is also available for download from the NAM website (see “References” section). Both models are summarized by Bommer et al (2022b).…”