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Reducing the standard deviation of ground motion models (GMMs) is a challenge that has engaged the seismic hazard scientific community for many years with results that unfortunately do not match the dedicated efforts. The work of the last few years, allowing the processing of an ever-increasing amount of data with machine learning approaches, has allowed great progress towards the reduction of these uncertainties, nevertheless, the high frequency uncertainty remains large, especially for GMMs developed in the Fourier domain.While these machine learning approaches are particularly promising, it is nevertheless necessary for the seismologist to provide them with the relevant parameters to test. In this work, we inventory a set of phenomena that disturb high frequency signals and that are not or rarely taken into account. We present a synthesis of recent results on different phenomena: small-scale soil-structure interaction generated by slabs or pillars often used to couple seismometers and accelerometers, depth effect, small-scale topography effect, seasonal variations. We discuss the interest of a better documentation of the installation conditions within the metadata associated to seismic motion databases., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

Recording ground motions is essential to estimate the seismic hazard. Signals from the databases are often considered to be in free-field, i.e. at the natural surface of the ground, without disturbances due to buildings or neighbouring structures. Nevertheless, the analysis of seismological networks has highlighted many installation modalities, including the coupling of seismometers, coexist. Recent studies have also shown that the installation conditions of these seismological stations can have a significant impact on the recorded motion, compared to true free-field measurements. Similarly, the effects of topography on a metric or decametric scale are poorly studied but also impact on the measurement at high frequency.This study focuses on a qualification of the effects of installation of seismometers, through several experiments that have been set up in Greece, mainly in Cephalonia Island, chosen for its high seismicity. The influence of the coupling methods of the seismometers is studied using the experiment called "ArgoSlab", where around thirty seismometers have been installed on slab or on seismic pillar of different size and shape, outdoor or sheltered, and compared to the recordings obtained by free-field sensors. The effect of topography at the metric and decametric scale is addressed by the analysis of about fifteen seismometers installed in the hill of Krani, near Argostoli («ArgoScarp» experiment). Finally, the analysis of soil-structure interaction is carried out by the comparison of sets of sensors in free-field (several tens of metres from the building), very close to buildings and inside buildings (basement and top floor)., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

We present the status of ShakeMap-EU, an initiative initially proposed in 2018 to: (i) provide an integrated archive of ShakeMaps at the European level built on EPOS Seismology (www.epos-eu.org/tcs/seismology) services & data products and modern community software; (ii) serve as a backup to authoritative ShakeMap implementations; (iii) deliver ShakeMaps for regions where no local capability is yet available.ShakeMap-EU is accessible at the shakemapeu.ingv.it web portal since 2020, and is jointly governed by participating institutions through voluntary contributions and EC-funded projects. It has become a reliable European seismological service, integrating authoritative models and workflows consistently. The system is based on: (a) the latest version of ShakeMap®; (b) the earthquake information delivered by the EMSC (www.emsc-csem.org); (c) the earthquake shaking data distributed by ORFEUS (orfeus-eu.org/data/strong); (d) the ground motion models adopted within EFEHR (www.efehr.org) for mapping seismic hazard across Europe; (d) the official ShakeMap configurations of some of the most hazardous countries in Europe. Configuration of, and input to the system are managed via a GitHub repository that allows automatic/manual triggering and interaction by authorized users. ShakeMap-EU provides a collaboration framework and laboratory for seismological agencies to address the challenges posed by the heterogeneity of ground-shaking mapping strategies across Europe and the need to promote homogenization and best practices in this domain. ShakeMap-EU is used in research projects as the test platform for novel international collaborative research: among recent examples are the ongoing enhancements towards an evolutionary hazard information system including real-time seismicity characterization and information on earthquake-induced phenomena., The 28th IUGG General Assembly (IUGG2023) (Berlin 2023)

We present a dataset of 77 strong ground motion records within 200 km epicentral distance from the 30 October 2020, M7.0 Samos Island (Aegean Sea) earthquake, which affected Greece and Turkey. Accelerograms from National Networks of both countries have been merged into a single dataset, including metadata that have been uniformly derived using a common preliminary source model. Initial findings from the analysis and comparative examination of acceleration time histories, Fourier amplitude spectra and 5%-damped response spectra are discussed along with significant source, propagation path and site effects. The long-period amplifications observed in most records in Izmir bay triggered failures and severe damages in weak structures. Yet, the spectral accelerations are observed to lie below the current and previous design spectra corresponding to the damaged regions. Peak ground motions are used to construct a purely instrumental-based macroseismic intensity map, which is capable of reflecting the actual earthquake damage caused by this considerably large event. Finally, peak ground motions are compared to various ground motion models (GMMs) and deviations are highlighted. Our overall preliminary analysis reveals a strong energy signature of the Samos earthquake in the period range 0.5-1.5 s at many sites, both on rock and soil, whereas records in the heavily hit Izmir city, at an epicentral distance circa 70 km, provide strong indication for additional amplification due to basin effects. At relatively large distance from the earthquake source (> 120 km), several recorded amplitudes are significantly lower than those predicted by many GMMs, implying that further studies are necessary toward the improvement of regional attenuation models.

International audience; The Cephalonia Island (Greece) area is located in the north-western end of the Aegean subduction frontal thrust that is linked to the dextral Cephalonia Transform Fault (west of Cephalonia). As the mean slip rate and the length of the Cephalonia Transform Fault are large, the seismic hazard is high in terms of earthquake frequency and magnitude. The Plio-Quaternary Koutavos-Argostoli basin site was selected within the French Research Agency PIA SINAPS@ project (www.institut-seism.fr/projets/sinaps/) to host a vertical accelerometer array. The long-term goal is to validate three-dimensional nonlinear numerical simulation codes to assess the site¬specific amplification and nonlinearity in the framework of seismic hazard assessment. Geological and geophysical surveys were carried out from 2011 to 2017. The aim of this work is to present i) the geological and structural context, ii) the complementary geological, geotechnical, and iii) the geophysical investigations that led to the identification of the main geotechnical bodies and their structures. The characterization of the three-dimensional structure of the stratigraphic units was achieved by coupling geological cross-sections (i.e., depth geometry) and HVSR/AVA geophysical surveys that were designed to identify the sedimentary body thickness. The data gathered allowed to build a three-dimensional geological model of the Argostoli basin. Starting from this point, a 3D numerical model on the same area was constructed using spectral element code known as SEM3D. Several simulations of seismic scenarios were performed, for the purpose of highlighting the importance of the use a representative model of the complexity of the wave path on the hazard assessment.

An updated Hellenic database of strong ground motion recordings together with the earthquake source properties and the site characterization of the recording stations are described here. The strong motion database consists of 2751 corrected recordings from 497earthquakes of focal depths h4.5and a number of finite fault plane solutions corresponding to earthquakes with M>6.0. The data is compiled from existing catalogs published by Hellenic and international seismological centers. The properties for each recording station include surface geology, a measured or estimated time-averaged shear wave velocity in the upper 30m (VS30), and information on instrument housing. Out of the 338sites, 75 have in-situ shear wave velocity measurements while for the rest VS30 values are derived from proxy-based relationships based on terrain or geology combined with surface gradient.