Abstract
We present simulations performed for the development of a ground motion model for induced earthquakes in the Groningen gas field. The largest recorded event, with M3.5, occurred in 2012 and, more recently, a M3.4 event in 2018 led to recorded ground accelerations exceeding 0.1 g. As part of an extensive hazard and risk study, it has been necessary to predict ground motions for scenario earthquakes up to M7. In order to achieve this, while accounting for the unique local geology, a range of simulations have been performed using both stochastic and full-waveform finite-difference simulations. Due to frequency limitations and lack of empirical calibration of the latter approach, input simulations for the ground motion model used in the hazard and risk analyses have been performed with a finite-fault stochastic method. However, in parallel, extensive studies using the finite-difference simulations have guided inputs and modelling considerations for these simulations. Three approaches are used: (1) the finite-fault stochastic method, (2) elastic point- and (3) finite-source 3D finite-difference simulations. We present a summary of the methods and their synthesis, including both amplitudes and durations within the context of the hazard and risk model. A unique form of wave-propagation with strong lateral focusing and defocusing is evident in both peak amplitudes and durations. The results clearly demonstrate the need for a locally derived ground motion model and the potential for reduction in aleatory variability in moving toward a path-specific fully non-ergodic model.
Highlights
The Groningen gas field, located in the north-east of the Netherlands, is the largest known source of natural gas in Europe and has been in production since 1963
In an effort to mitigate the effects of these earthquakes the field operator, Nederlandse Aardolie Maatschappij B.V. (NAM), commissioned a comprehensive data collection, monitoring and hazard and risk study (Bommer et al 2017a; van Elk et al 2017) that has been ongoing since 2013
The Groningen GMM has evolved from an adjusted European empirical GMPE, to a GMM logic-tree based on finite-fault stochastic simulations
Summary
The Groningen gas field, located in the north-east of the Netherlands, is the largest known source of natural gas in Europe and has been in production since 1963. The GMPE was shown by Bourne et al (2015) to significantly over-predict both peak ground acceleration and velocity (PGA and PGV) This was interpreted as being mainly due to the fact that in Groningen the high-velocity Zechstein salt layer lies above the gas reservoir, whereas in the Roswinkel field the gas reservoir is above the Zechstein (Kraaijpoel and Dost 2013). The Groningen GMM has evolved from an adjusted European empirical GMPE, to a GMM logic-tree based on finite-fault stochastic simulations These simulations have been guided by full-waveform finite-difference simulations and account for source and path characteristics based on locally recorded events, along with transitions of material properties as ruptures penetrate the Carboniferous. Non-linear site response analysis through the upper ~ 800 m of overburden brings the simulations from the reference rock horizon to the surface (Bahrampouri et al 2018; Bommer et al 2017a, b; Kruiver et al 2017; Noorlandt et al 2018; Rodriguez-Marek et al 2017; Stafford et al 2017)
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