Search

Earthquake hazard analyses rely on seismogenic source models. These are designed in various fashions, such as point sources or area sources, but the most effective is the three-dimensional representation of geological faults. We here refer to such models as fault sources. This study presents the European Fault-Source Model 2020 (EFSM20), which was one of the primary input datasets of the recently released European Seismic Hazard Model 2020. The EFSM20 compilation was entirely based on reusable data from existing active fault regional compilations that were first blended and harmonized and then augmented by a set of derived parameters. These additional parameters were devised to enable users to formulate earthquake rate forecasts based on a seismic-moment balancing approach. EFSM20 considers two main categories of seismogenic faults: crustal faults and subduction systems, which include the subduction interface and intraslab faults. The compiled dataset covers an area from the Mid-Atlantic Ridge to the Caucasus and from northern Africa to Iceland. It includes 1248 crustal faults spanning a total length of ∼95100 km and four subduction systems, namely the Gibraltar, Calabrian, Hellenic, and Cyprus arcs, for a total length of ∼2120 km. The model focuses on an area encompassing a buffer of 300 km around all European countries (except for Overseas Countries and Territories) and a maximum of 300 km depth for the subducting slabs. All the parameters required to develop a seismic source model for earthquake hazard analysis were determined for crustal faults and subduction systems. A statistical distribution of relevant seismotectonic parameters, such as faulting mechanisms, slip rates, moment rates, and prospective maximum magnitudes, is presented and discussed to address unsettled points in view of future updates and improvements. The dataset, identified by the DOI https://doi.org/10.13127/efsm20 (Basili et al., 2022), is distributed as machine-readable files using open standards (Open Geospatial Consortium). [ABSTRACT FROM AUTHOR]

The 2020 update of the European Seismic Hazard Model (ESHM20) is the most recent and up-to-date assessment of seismic hazard for the Euro-Mediterranean region. The new model, publicly released in May 2022, incorporates refined and cross-border harmonized earthquake catalogues, homogeneous tectonic zonation, updated active fault datasets and geological information, complex subduction sources, updated area source models, a smoothed seismicity model with an adaptive kernel optimized within each tectonic region, and a novel ground motion characteristic model. ESHM20 supersedes the 2013 European Seismic Hazard Model (ESHM13; Woessner et al., 2015) and provides full sets of hazard outputs such as hazard curves, maps, and uniform hazard spectra for the Euro-Mediterranean region. The model provides two informative hazard maps that will serve as a reference for the forthcoming revision of the European Seismic Design Code (CEN EC8) and provides input to the first earthquake risk model for Europe (Crowley et al., 2021). ESHM20 will continue to evolve and act as a key resource for supporting earthquake preparedness and resilience throughout the Euro-Mediterranean region under the umbrella of the European Facilities for Seismic Hazard and Risk consortium (EFEHR Consortium). [ABSTRACT FROM AUTHOR]

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 characterisation was adopted based on the concept of a regionalised 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 regionalised scaled-backbone GMM concept have 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 recalibrations of the GMM logic tree and/or modifications to the proposed regionalisation. 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 regionalised 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 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 characterisation of ground motion in future generations of the European Seismic Hazard Model. [ABSTRACT FROM AUTHOR]

Earthquake hazard analyses rely on the availability of seismogenic source models. These are designed in different fashions, such as point sources or area sources, but the most effective is the three-dimensional representation of geological faults. We here refer to such models as fault sources. This study presents the European Fault-Source Model 2020 (EFSM20), which formed the basis for one of the primary input datasets of the recently released European Seismic Hazard Model 2020. The EFSM20 compilation was entirely based on reusable data from existing active fault regional compilations that were first blended and harmonized and then augmented by a set of derived parameters. These additional parameters were devised to enable users to formulate earthquake rate forecasts based on a seismic-moment balancing approach. EFSM20 considers two main categories of seismogenic faults: crustal faults and subduction systems. The compiled dataset covers an area from the Mid-Atlantic Ridge to the Caucasus and from northern Africa to Iceland. It includes 1,248 crustal faults spanning a total length of ~95,100 km and four subduction systems, namely the Gibraltar, Calabrian, Hellenic, and Cyprus Arcs. The model focuses on an area encompassing a buffer of 300 km around all European countries (except for Overseas Countries and Territories, OTCs) and a maximum of 300 km depth for the subducting slabs. All the parameters required to develop a seismic source model for earthquake hazard analysis were determined for crustal faults and subduction systems. A statistical distribution of relevant seismotectonic parameters, such as faulting mechanisms, slip rates, moment rates, and prospective maximum magnitudes, is presented and discussed to address unsettled points in view of future updates and improvements. The dataset, identified by the DOI https://doi.org/10.13127/efsm20, is distributed as machine-readable files using open standards (Open Geospatial Consortium). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Historical earthquakes are of major importance in the analysis of seismic hazards, in particular for stable continental regions. In this article, we propose a methodology that uses seismic scenarios to provide constraints on the location of the seismic source of historical earthquakes. Our methodology involves generating seismic scenarios for the proposed seismic sources and comparing the results to the observed intensity field of the earthquake. To avoid the bias related to strongly heterogeneously distributed datasets, we focus on data points that are useful in discriminating between competing ruptures. These data are identified by the spatial patterns of residuals between seismic scenarios produced for each source. We apply this methodology to a test event--the 1999 Athens earthquake--for which both the magnitude and location are constrained by independent data, and to the 1909 Benavente earthquake, for which the magnitude is constrained by seismological studies, but the location is uncertain due to the very poor azimuthal coverage available. Within its application limits, the proposed methodology was capable of identifying the source of the Athens earthquake amongst different ruptures located few kilometers apart. The analysis performed for the 1909 Benavente earthquake suggests that the eastern strand of the lower Tagus Valley fault zone is the most likely seismic source for earthquake, amongst those proposed in the literature. [ABSTRACT FROM AUTHOR]

The inclusion of site-specific conditions is essential to adequately represent the seismic hazard and the seismic risk for a region. We acquired, gathered, and organized a near-surface shear-wave velocity database for Portugal and applied a three-step methodological approach for developing a VS30 site-condition map using extrapolation based on surface geology. The methodology includes (1) defining a preliminary set of geologically defined units, (2) calculating the probability distribution of logVS30 for each unit, and (3) merging the units according to the results of statistical tests. The final model comprises three geologically defined units characterized by logVS30 distributions that are statistically significantly different from each other: F1, igneous, metamorphic, and old sedimentary rocks; F2, Neogene and Pleistocene formations; and F3, Holocene formations. The site conditions for the F3 unit may be further refined using correlations with topographic slope based on the Shuttle Radar Topography Mission at 3 arcsec resolution (SRTM3) dataset. We analyzed the performance site-condition models based on correlations with exogenous data (topographic slope and surface-geology analogs). The results show that the residual distributions between logVS30 values measured and estimated from those proxies are strongly biased for some geological units, emphasizing the need for acquiring regional VS data. [ABSTRACT FROM AUTHOR]

The lack of constraints regarding ground-motion propagation characteristics in western Iberia remains one of the major hindrances to accurate seismic-hazard and seismic-risk assessment in the region. The fact that western Iberia is geographically located near the confluence of oceanic crust, active continental crust, and stable continental crust further complicates the selection of appropriate ground-motion models. To address this question we compare, through visual inspection and residual analysis, the regional ground-motion data for moderate magnitude earthquakes with a set of six ground-motion prediction equations, some of which were developed for active tectonic regions and the others for stable continental regions. Although the available data pertain mostly to offshore moderate magnitude earthquakes (M 4.8-6.0) at large distances (100-400 km), the few records from an onshore M 4.0 earthquake and from the 1969 M 7.8 earthquake display similar trends. The results show that the performance of the models is period-dependent, with shorter spectral periods (0.01 s, 0.1 s, 0.2 s, and 0.5 s) being strongly underpredicted by models developed for shallow active tectonic regions. More interestingly, the performance of the models for stable continental regions seems to be magnitude-dependent, with response spectra amplitudes for magnitudes of engineering interest being accurately estimated by the models. The inspection of the residual distributions of intensity observations leads to similar conclusions for the offshore data, while highlighting the extent of epistemic uncertainty in predicting the ground motions for moderate magnitude earthquakes at short to moderate distances. [ABSTRACT FROM AUTHOR]

The probabilistic seismic hazard of Portugal is analyzed with a logic tree approach. A critical part of the work was the review of the seismic catalog and the moment magnitude (M) estimation for historical earthquakes. To produce a catalog with a uniform magnitude scale, the instrumental magnitudes were converted to M through empirical relations. Two seismic zonations were considered, each including two broad tectonic zones and a set of smaller seismicity zones. Catalog completeness and the b-value for the truncated exponential recurrence model were calculated for the broad sources defined by tectonic criteria. The smaller seismicity sources were used to calculate the a-value using the fixed b-value of the corresponding tectonic zone. This approach allows for a larger amount of data to estimate the most critical parameters by statistical methods, without compromising the spatial detail of hazard results. Three published attenuation relations were used in the logic tree, with weights that were based on tectonic considerations and on the comparison with macroseismic data converted to horizontal peak ground acceleration (PGA). The Ambraseys et al. (1996) attenuation model for PGA, used by most previous hazard studies of the region, seems to underestimate considerably the ground motion for mainland Portugal. A total of 96 hazard curves were calculated with SEISRISK III for each point of the map. The resulting mean hazard map for 10% exceedence probability in 50 years displays PGA values that range from 0.05g to 0.20g. These mean values are slightly higher than in previous PGA studies. The hazard patterns obtained display a maximum related to intraplate onshore seismicity, whereas previous studies using intensities highlighted the southwest offshore contribution. Further work on ground-motion attenuation in western Iberia is necessary to improve the seismic-hazard assessment. [ABSTRACT FROM AUTHOR]

This section presents a response by Susana P. Vilanova et al to a commentary on their article "Lisbon 1755: A Case of Triggered Onshore Rupture?" by L. Matias et al that was published in a 2003 issue of the "Bulletin of the Seismological Society of America." It answers a question regarding the suitability of using maps drawn before and after the 1755 earthquake.