Defining the usable bandwidth of weak-motion records: application to induced seismicity in the Groningen Gas Field, the Netherlands

Seismic hazard and risk analyses are increasingly tapping into the previously underused resource of local weak-motion records. This is facilitating the development of local- or even application-specific models for the characterisation of earthquake ground motion. In turn, this offers the opportunity to derive non- or partially non-ergodic models and significantly reduce bias and uncertainty. However, weak-motion data, while carrying important information about local earthquake source, path and site effects, are susceptible to noise. We show that high-frequency noise has a record-, or region-specific, impact on pseudo-spectral acceleration (PSA). This impact depends on the shape of the records’ Fourier amplitude spectrum (FAS): PSA from moderately to highly damped ‘soil’ records (e.g. Groningen, the Netherlands) is much less susceptible to high-frequency noise than PSA from weakly damped ‘rock’ records (e.g. Eastern North America). We make use of simulated ground motion records to develop a parametric model for the lower usable period of PSA (Tmin). The model accounts for the impact of high-frequency noise on PSA, conditional on easily measured parameters characterising the shape of a record’s FAS. We then present a workflow, describing processing undertaken for records of induced seismicity from the Groningen gas field. The workflow includes the definition of maximum and minimum usable frequencies and periods of FAS and PSA, respectively. As part of the workflow, we present an approach that considers multiple estimates of Tmin. These include the parametric model and, additionally, record-specific hybrid simulations that artificially extend or modify time series’ FAS beyond the noise floor to assess subsequent impacts on PSA.