Céline Beauval’s research while affiliated with Institute of Research for Development and other places

This study presents a numerical approach for probabilistic fault displacement hazard analysis (PFDHA), aimed at addressing an alternative solution to commonly used empirical methodologies. Our model utilizes probability distributions to compute the conditional probability of surface rupture (CPSR). Leveraging earthquake catalogs, we derived the hypocentral depth distribution (HDD) across eight globally distributed seismotectonic regions categorized by faulting kinematics (normal, reverse, strike-slip). We calculated the hypocentral depth ratio (HDR) distribution, to model rupture position from the hypocenter. Rupture widths are estimated as a function of magnitude based on previously published scaling relations. User-input parameters, including fault style, average dip angle, and seismogenic depth, with associated uncertainties, derive the CPSR estimation of surface rupture occurrences. Our findings highlight seismogenic depth as the most influential parameter and reveal correspondences between empirical curves derived for specific regions. These findings support the use of source-specific surface rupture probability assessments over approaches based on global datasets, and underscore the importance of considering the local seismotectonic setting when evaluating fault displacement hazard. The numerical code for CPSR calculation has been developed and is openly accessible on GitHub.

The Levant Fault System (LFS), a 1200 km-long left-lateral strike-slip fault connecting the Red Sea to the East Anatolian fault, is a major source of seismic hazard in the Levant. In this study, we focus on improving regional Probabilistic Seismic Hazard Assessment (PSHA) models by considering the interconnected nature of the LFS, which challenges the traditional approach of treating faults as isolated segments. We analyze the segmentation of the fault system and identify 43 sections with lengths varying from 5 to 39 km along the main and secondary strands. Applying the SHERIFS (Seismic Hazard and Earthquake Rate In Fault Systems) algorithm, we develop an interconnected fault model that allows for complex ruptures, making assumptions on which sections can break together. At first, using a maximum magnitude of 7.5 for the system and considering that ruptures cannot pass major discontinuities, we compare the classical and interconnected fault models through the seismic rates and associated hazard results. We show that the interconnected fault model leads on average to increased hazard along the secondary faults, and lower hazard along the main strand, with respect to the classical implementation. Next, we show that in order for the maximum magnitude earthquake to be more realistic (~7.9), the connectivity of the LFS fault system must be fully released. At a 475-year return period, hazard levels obtained at the PGA are above 0.3 g for all sites within ~20 km of faults, with peak values around 0.5 g along specific sections. At 0.2 s spectral acceleration, hazard values exceed 0.8 g along all fault segments. This study highlights the importance of incorporating complex fault interactions into seismic hazard models.

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).

Seismic hazard assessment in low-to-moderate seismicity regions can benefit from the knowledge of surface deformation rates to better constrain earthquake recurrence models. This, however, amounts to assuming that the known seismicity rate, generally observed over historical times (i.e., up to a few centuries in Europe), provides a representative sample of the underlying long-term activity. We here investigate how this limited sampling can affect the estimated seismic hazard and whether it can explain the disagreement between the seismic moment loading rate as seen by nowadays Global Navigation Satellite Systems (GNSS) measurements and the seismic moment release rate by past earthquakes, as is sometimes observed in regions with limited activity. We approach this issue by running simulations of earthquake time series over very long timescales that account for temporal clustering and the known magnitude–frequency distribution in such regions, and that those are constrained to a seismic moment rate balance between geodetic and seismicity estimates at very long timescales. We show that, in the example of southeastern Switzerland, taken here as a case study, this sampling issue can indeed explain this disagreement, although it is likely that other phenomena, including aseismic deformation and changes in strain rate due to erosional and/or glacial rebound, may also play a significant role in this mismatch.

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).

The primary aim of this research is to investigate how geodetic monitoring can offer valuable constraints to enhance the accuracy of the source model in probabilistic seismic hazard assessment. We leverage the release of geodetic strain rate maps for Europe, as derived by Piña-Valdès et al. (2022), and the ESHM20 source model by Danciu et al. (2024) to compare geodetic and seismic moment rates across Europe, a geographically extensive region characterized by heterogeneous seismic activity. Seismic moment computation relies on the magnitude-frequency distribution proposed in the ESHM20 source model logic tree, which is based on earthquake catalogs and fault datasets. This approach allows us to account for epistemic uncertainties proposed in ESHM20. On the geodesy side, we meticulously calculate the geodetic moment for each zone, considering associated epistemic uncertainties. Comparing the distributions of geodetic and seismic moments rates at different scales allows us to assess compatibility. The geodetic moment rate linearly depends of the seismogenic thickness, that is therefore a pivotal parameter contributing to the uncertainty. In high-activity zones, such as the Apennines, Greece, the Balkans, and the Betics, primary compatibility between seismic and geodetic moment rates is evident. However, local disparities underscore the importance of source zone scale; broader zones enhance the overlap between geodetic and seismic moment rate distributions. Discrepancies emerge in low-to-moderate activity zones, particularly in areas affected by Scandinavian Glacial Isostatic Adjustment, where geodetic moment rates exceed seismic moment rates significantly. Nevertheless, in some zones where ESHM20 recurrence models are well-constrained, by either enough seismic events in the catalogue or mapped active faults, we observe an overlap in the distributions of seismic and geodetic moments, suggesting the potential for integrating geodetic data even in regions with low deformation.

To design user-centred and scientifically high-quality outreach products to inform about earthquake-related hazards and the associated risk, a close collaboration between the model developers and communication experts is needed. In this contribution, we present the communication strategy developed to support the public release of the first openly available European Seismic Risk Model and the updated European Seismic Hazard Model. The backbone of the strategy was the communication concept in which the overall vision, communication principles, target audiences (including personas), key messages, and products were defined. To fulfil the end-users' needs, we conducted two user testing surveys: one for the interactive risk map viewer and one for the risk poster with a special emphasis on the European earthquake risk map. To further ensure that the outreach products are not only understandable and attractive for different target groups but also adequate from a scientific point of view, a two-fold feedback mechanism involving experts in the field was implemented. Through a close collaboration with a network of communication specialists from other institutions supporting the release, additional feedback and exchange of knowledge was enabled. Our insights, gained as part of the release process, can support others in developing user-centred products reviewed by experts in the field to inform about hazard and risk models.

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 harmonised earthquake catalogues, homogeneous tectonic zonation, updated active faults datasets and geological information, complex subduction sources, updated area source models, a smoothed seismicity model with an adaptive kernel optimised within each tectonic region and a novel ground motion characteristic model. ESHM20 supersedes the 2013 European Seismic Hazard Model (ESHM13, Wössner 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 Euro-Mediterranean region under the umbrella of the European Facilities for Seismic Hazard and Risk Consortium (EFEHR Consortium).

We explore how variation of slip rates in fault source models affect computed earthquake rates of the Pallatanga–Puna fault system in Ecuador. Determining which slip rates best represent fault-zone seismicity is vital for use in probabilistic seismic hazard assessment (PSHA). However, given the variable spatial and temporal scales slip rates are measured over, significantly different rates can be observed along the same fault. The Pallatanga–Puna fault in southern Ecuador exemplifies a fault where different slip rates have been measured using methods spanning different spatial and temporal scales, and in which historical data and paleoseismic studies provide a record of large earthquakes over a relatively long time span. We use fault source models to calculate earthquake rates using different slip rates and geometries for the Pallatanga–Puna fault, and compare the computed magnitude–frequency distributions (MFDs) to earthquake catalog MFDs from the fault zone. We show that slip rates measured across the entire width of the fault zone, either based on geodesy or long-term geomorphic offsets, produce computed MFDs that compare more favorably with the catalog data. Moreover, we show that the computed MFDs fit the earthquake catalog data best when they follow a hybrid-characteristic MFD shape. These results support hypotheses that slip rates derived from a single fault strand of a fault system do not represent seismicity produced by the entire fault zone.

Seismic hazard levels used as reference for the French Lesser Antilles are derived from probabilistic seismic hazard assessment studies performed in 2002. However, scientific knowledge has greatly increased over the past 20 years in this area, warranting an update of the seismic hazard models. As part of a project linking the French Ministry of Ecological Transition and Territory Cohesion, and the Seismicity Transverse Action of RESIF-EPOS (French seismological and geodetic network), we developed a new seismotectonic zoning model of the Lesser Antilles. The Lesser Antilles tectonic system results from the subduction of the North and South American plates beneath the Caribbean plate since the Eocene. The boundary extends along 850 km with a convergence of 18-20 mm/yr oriented ENE-WSW. Significant north south variations in tectonics, seismic and volcanic activities highlight the lateral variability of the undergoing geodynamic processes. Oceanic fractures and ridges entering into the subduction zone impact the trench, the subduction interface, and upper plate tectonics, adding seismotectonic complexities. Several controversial questions remain, such as the origins of the 1839 (Mw=7.5-8) and 1843 (Mw=8-8.5) earthquakes or the state of interseismic coupling of the subduction interface (potentially very low compared to other subduction systems). In this study, we propose new seismotectonic models and associated seismotectonic zoning for seismic hazard. We treat all components of the Lesser Antilles system: subducted oceanic plate, subduction interface, mantle wedge, upper plate crust and associated volcanisms. Our work is based on a compilation of up-to-date seismicity and fault catalogs as well as research-based active tectonic hypotheses, completed by an analysis of focal mechanisms rupture styles and strain tensor derived from geodetic data. Compared to previously published models, our new seismotectonic zoning model provides better depth resolution, a fully revised zoning around Guadeloupe, new mantle wedge and volcanic zones, and a complete redefinition of the subduction interface and slab. Our results also highlight specific needs for better seismic hazard assessment in this region.