KEM-04 Data driven study on seismic 3D structural features of Groningen ground motions

The objective of the project is to better understand characteristics of induced earthquakes and espcially the non uniform propagation of seismic waves and their effects on seismic structural response at the surface in Groningen and to identify possible modelling improvement strategies.

The study should employ empirical analysis based especially on the 3D seismological data from the new seismic surface networks and possibly 3D numerical simulations of wave propagation through complex media to identify distinctive features,. This should provide for a better understanding of the varying horizontal and vertical ground motions in Groningen due to induced seismicity.

The output of the project will be used to validate and/or improve the existing Ground motion prediction model (GMPE) of Groningen gas field operator NAM and for deriving relevant time series for earthquake engineering related questions, that is Groningen seismic risk assessment.

RESEARCH REQUEST FULL TEXT
 

The project resulted in a final report with 4 annexes:

FINAL REPORT KEM-04 PROJECT and annexes REPORT B met ANNEX, REPORT C, REPORT D and REPORT E.

The KEM-04 project addresses a number of highly important issues related to the Groningen seismic risk assessment. Ground motion modelling (GMM) is a major contribution to the uncertainty in the final hazard and risk results and observed inconsistencies between observed ground motions and GMM used in V5 are concerning. Results of KEM-04 are highly relevant for better understanding observations, for constraining uncertainties and for characterising spatial variability in ground motion fields.
Importantly, KEM-04 has shown convincingly that 3D physics-based numerical approaches to characterize earthquake ground motion are feasible and can be a diagnostic tool to understand the relevance of specific geologic conditions. Empirical Green Functions and 3D simulations can thus complement existing 1D approaches and should be considered in the Groningen GMM V6 and V7. The KEM-04 model comparisons and calibrated ground motion simulations presented are one of the most advanced studies of this kind conducted worldwide. It is now conceivable that physics-based simulations are a superior alternative for GMM in areas with very detailed geological/geophysical models, potentially reducing the uncertainties in GMM. Physics-based simulation may be superior in upscaling to larger magnitudes, as well as to shorter distances, and KEM-04 results in this respect are encouraging; however, it will take significant additional research and also computational power to build a full probabilistic GMM that adequate captures uncertainties. More focus on the effect of non-linear ground motions would be needed also to understand upscaling.

KEM-04 has highlighted the importance of heterogeneities as salt domes -occurring in the southern part of the Groningen field - in shaping and amplifying ground motion fields, and the relatively lower importance of Peelo valleys, both are important findings. The effect of both geological heterogeneities cannot explain different responses at short (<500 m) distances.

Based on their analsysis KEM-04 also delivered a large set of recommendations, including priorities and assessment of efforts. These are important suggestions that will help to structure future research needs and the larger context of the HRA and model train. A broader sensitivity analysis can help to set overarching priorities before additional KEM research and HRA developments is assigned.
In summary, KEM-04 is an important contribution to enhancing the understanding of GMM in Groningen and represents a positive example of KEM-related applied research.

The project and its results have been evaluated by the KEM scientific expert panel. Overall, KEM-04 project team delivered high quality results that addressed the research questions posed in great detail and - in selected places - substantially exceeded the expectations.
The practical outcome of the project has provided for:
- improved insight into the potential and limitations of 3D full waveform-based modelling approaches for understanding observed - and modelling future – earthquake ground motions. Given detailed geological and geophysical knowledge of the area, KEM-04 has demonstrated that these emerging techniques represents a viable alternative approach to better understand near source effects and larger magnitude events.
- the quantification of effects of salt domes and Peelo structures on the 3D seismic wave field and on the PGA or PGV values at ground surface, indicating these geological heterogeneities do not explain local (<500m) variations of anomalies in PGA.

Two scientific papers about the KEM-04 research have been submitted for publication, as well as the answers to specific questions raised by the public in Groningen.

January 28, 2021 a joint KEM - DeepNL colloquium was held. Two presentations of the KEM-04 team can be viewed by using the respective links:
Prof. Roberto Paolucci (KEM-04 results of 3D numerical simulations of earthquake ground motions in Groningen),
Dr. Gabriele Ameri (Selected results of KEM-04 focused on 3D ground motion effects).