A regionally-adaptable “scaled backbone” ground motion logic tree for shallow seismicity in Europe: application to the 2020 European seismic hazard model

Abstract

The selection of ground motion models, and the representation of their epistemic uncertainty in the form of a logic tree, is one of the fundamental components of probabilistic seismic hazard and risk analysis. A new ground motion model (GMM) logic tree has been developed for the 2020 European seismic hazard model, which develops upon recently compiled ground motion data sets in Europe. In contrast to previous European seismic hazard models, the new ground model logic tree is built around the scaled backbone concept. Epistemic uncertainties are represented as calibrations to a reference model and aim to characterise the potential distributions of median ground motions resulting from variability in source scaling and attenuation. These scaled backbone logic trees are developed and presented for shallow crustal seismic sources in Europe. Using the new European strong motion flatfile, and capitalising on recent perspectives in ground motion modelling in the scientific literature, a general and transferable procedure is presented for the construction of a backbone model and the regionalisation of epistemic uncertainty. This innovative approach forms a general framework for revising and updating the GMM logic tree at national and European scale as new strong motion data emerge in the future.

A ground motion logic tree for seismic hazard analysis in the stable cratonic region of Europe: regionalisation, model selection and development of a scaled backbone approach

“…The conceptual framework of the scaled backbone logic tree that is being adopted within the ESHM20 and its data-driven regionalisation is outlined by Weatherill et al (2020), who adapt the strategy initially proposed by Douglas (2018a). In the construction of the scaled backbone GMM logic tree for general crustal seismicity Europe, Kotha et al (2020) derive a new GMM that capitalises on the wealth of strong motion data available within the European Strong Motion (ESM) flatfile (Lanzano et al 2019).…”

“…Where the data are absent or insufficient to constrain the region-specific random effects, however, the full distributions of L2L and C 3 are used. As explained by Weatherill et al (2020), the spatial variation in L2L l is complex and potentially poorly constrained, thus we retain the full uncertainty ( L2L ) across Europe. For C 3,R , however, regions of similar residual attenuation characteristics are grouped into clusters that capture the broader scale regional attenuation variation and permit characterisation of a region-specific distribution of attenuation properties.…”

“…The critical question then is whether it can be determined that a region of shallow seismicity in Europe is of a fundamentally different nature in terms of its ground motion characteristics, compared to the range of properties represented in ESM dataset, such that the centre, body and range of median ground motion scaling described by the 'general crustal seismicity' logic tree is not sufficiently representative. Ground motion model regionalisation of the ESHM20, with the craton zones highlighted in purple, the default shallow crustal logic tree region in white, and the different cluster-analysis defined regionalisation of shallow crustal seismicity in the coloured zones labelled from 1 to 5 (Weatherill et al 2020) 1 3…”

“…This concept aims to represent epistemic uncertainty in the ground motion model not by means of selecting multiple independent models, but rather by taking a core model or models (the backbone) and applying to this model(s) scaling factors to account for the uncertainty in the seismological properties of the target region. A more comprehensive exposition of this approach and its advantages with respect to the multi-model approach can be found in Atkinson et al (2014), Douglas (2018a) and Weatherill et al (2020).…”

“…The general framework for the scaled backbone GMM logic tree for use in regions of shallow crustal seismic activity within the ESHM20 is presented by Weatherill et al (2020), which describes the construction and regionalisation of the scaling factors built around the recent European backbone GMM of Kotha et al (2020). As this model illustrates the philosophy and approach behind the ESHM20 strategy for ground motion modelling that will be adapted to application in northeastern Europe, the key aspects will be summarised in Sect.…”