04 Sep 2023
 | 04 Sep 2023
Status: this preprint is currently under review for the journal NHESS.

Modelling seismic ground motion and its uncertainty in different tectonic contexts: Challenges and application to the 2020 European Seismic Hazard Model (ESHM20)

Graeme Weatherill, Sreeram Reddy Kotha, Laurentiu Danciu, Susana Vilanova, and Fabrice Cotton

Abstract. Current practice in strong ground motion modelling for probabilistic seismic hazard analysis (PSHA) requires the identification and calibration of empirical models appropriate to the tectonic regimes within the region of application, along with quantification of both their aleatory and epistemic uncertainties. For the development of the 2020 European Seismic Hazard Model (ESHM20) a novel approach for ground motion characterization was adopted based on the concept of a regionalized scaled backbone model, wherein a single appropriate ground motion model (GMM) is identified for use in PSHA, to which adjustments or scaling factors are then applied to account for epistemic uncertainty in the underlying seismological properties of the region of interest. While the theory and development of the regionalized scaled backbone GMM concept has been discussed in earlier publications, implementation in the final ESHM20 required further refinements to the shallow seismicity GMM in three regions, which were undertaken considering new data and insights gained from the feedback provided by experts in several regions of Europe: France, Portugal and Iceland. Exploration of the geophysical characteristics of these regions and analysis of additional ground motion records prompted re-calibrations of the GMM logic tree and/or modifications to the proposed regionalization. These modifications illustrate how the ESHM20 GMM logic tree can still be refined and adapted to different regions based on new ground motion data and/or expert judgement, without diverging from the proposed regionalized scaled backbone GMM framework.

In addition to the regions of crustal seismicity, the scaled backbone approach needed to be adapted to earthquakes occurring in Europe’s subduction zones and to the Vrancea deep seismogenic source region. Using a novel fuzzy methodology to classify earthquakes to according to different seismic regimes within the subduction system, we compare ground motion records from non-crustal earthquakes to existing subduction GMMs and identify a suitable backbone GMM for application to subduction and deep seismic sources in Europe. The observed ground motion records from moderate and small magnitude earthquakes allow us to calibrate the anelastic attenuation of the backbone GMM specifically for the Eastern Mediterranean region. Epistemic uncertainty is then calibrated based on the global variability in source and attenuation characteristics of subduction GMMs.

With the ESHM20 now completed, we reflect on the lessons learned from implementing this new approach in regional scale PSHA and highlight where we hope to see new developments and improvements to the characterization of ground motion in future generations of the European Seismic Hazard Model.

Graeme Weatherill et al.

Status: open (until 17 Oct 2023)

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Graeme Weatherill et al.

Graeme Weatherill et al.


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Short summary
The ground motion models (GMMs) selected for the 2020 European Seismic Hazard Model (ESHM20), and their uncertainties require adaptation to different tectonic environments. Using insights from new data, local experts and developments in the scientific literature, we further calibrate the ESHM20 GMM logic tree to capture previously unmodelled regional variation. We also propose a new scaled backbone logic tree for application to Europe’s subduction zones and the Vrancea deep seismic source.