Articles | Volume 26, issue 1
https://doi.org/10.5194/nhess-26-41-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Special issue:
https://doi.org/10.5194/nhess-26-41-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
13 Jan 2026
Research article |
| 13 Jan 2026
| 13 Jan 2026
The quest for reference stations at the National Observatory of Athens, Greece
Institute of Geodynamics, National Observatory of Athens, Lofos Nymfon-Thiseion, Athens, 11850, Greece
Erion-Vasilis Pikoulis
Institute of Geodynamics, National Observatory of Athens, Lofos Nymfon-Thiseion, Athens, 11850, Greece
Antonia Papageorgiou
Institute of Geodynamics, National Observatory of Athens, Lofos Nymfon-Thiseion, Athens, 11850, Greece
Department of Geology, University of Patras, Patras, 26504, Greece
Fevronia Gkika
Institute of Geodynamics, National Observatory of Athens, Lofos Nymfon-Thiseion, Athens, 11850, Greece
Spyros Liakopoulos
Institute of Geodynamics, National Observatory of Athens, Lofos Nymfon-Thiseion, Athens, 11850, Greece
Ziya Cekinmez
Institute of Geodynamics, National Observatory of Athens, Lofos Nymfon-Thiseion, Athens, 11850, Greece
School of Civil Engineering, National Technical University of Athens, Athens, 15780, Greece
Panagiotis Savvaidis
Institute of Geodynamics, National Observatory of Athens, Lofos Nymfon-Thiseion, Athens, 11850, Greece
Department of Geology, Aristotle University of Thessaloniki, Thessaloniki, 54124, Greece
Kalliopi-Elli Fragouli
Institute of Geodynamics, National Observatory of Athens, Lofos Nymfon-Thiseion, Athens, 11850, Greece
Fanis Chalaris
Institute of Geodynamics, National Observatory of Athens, Lofos Nymfon-Thiseion, Athens, 11850, Greece
Christos P. Evangelidis
Institute of Geodynamics, National Observatory of Athens, Lofos Nymfon-Thiseion, Athens, 11850, Greece
Related authors
Irina Dallo, Michèle Marti, Nadja Valenzuela, Helen Crowley, Jamal Dabbeek, Laurentiu Danciu, Simone Zaugg, Fabrice Cotton, Domenico Giardini, Rui Pinho, John F. Schneider, Céline Beauval, António A. Correia, Olga-Joan Ktenidou, Päivi Mäntyniemi, Marco Pagani, Vitor Silva, Graeme Weatherill, and Stefan Wiemer
Nat. Hazards Earth Syst. Sci., 24, 291–307, https://doi.org/10.5194/nhess-24-291-2024, https://doi.org/10.5194/nhess-24-291-2024, 2024
Short summary
Short summary
For the release of cross-country harmonised hazard and risk models, a communication strategy co-defined by the model developers and communication experts is needed. The strategy should consist of a communication concept, user testing, expert feedback mechanisms, and the establishment of a network with outreach specialists. Here we present our approach for the release of the European Seismic Hazard Model and European Seismic Risk Model and provide practical recommendations for similar efforts.
Irina Dallo, Michèle Marti, Nadja Valenzuela, Helen Crowley, Jamal Dabbeek, Laurentiu Danciu, Simone Zaugg, Fabrice Cotton, Domenico Giardini, Rui Pinho, John F. Schneider, Céline Beauval, António A. Correia, Olga-Joan Ktenidou, Päivi Mäntyniemi, Marco Pagani, Vitor Silva, Graeme Weatherill, and Stefan Wiemer
Nat. Hazards Earth Syst. Sci., 24, 291–307, https://doi.org/10.5194/nhess-24-291-2024, https://doi.org/10.5194/nhess-24-291-2024, 2024
Short summary
Short summary
For the release of cross-country harmonised hazard and risk models, a communication strategy co-defined by the model developers and communication experts is needed. The strategy should consist of a communication concept, user testing, expert feedback mechanisms, and the establishment of a network with outreach specialists. Here we present our approach for the release of the European Seismic Hazard Model and European Seismic Risk Model and provide practical recommendations for similar efforts.
Cited articles
Ancheta, T. D., Darragh, R. B., Stewart, J. P., Seyhan, E., Silva, W. J., Chiou, B. S. J., Wooddell, K. E., Graves, R. W., Kottke, A. R., Boore, D. M., Kishida, T. and Donahue, J. L.: NGA-West2 Database, Earthquake Spectra, 30, 989–1005, https://doi.org/10.1193/070913EQS197M , 2014.
Anderson, J. G. and Hough, S. E.: A model for the shape of the fourier amplitude spectrum of acceleration at high frequencies, B. Seismol. Soc. Am., 74, 1969–1993, https://doi.org/10.1785/BSSA0740051969, 1984.
Ashford, S. A. and Sitar, N.: Analysis of Topographic Amplification of Inclined Shear Waves in a Steep Coastal Bluff, B. Seism. Soc. Am., 87, 692–700, https://doi.org/10.1785/BSSA0870030692, 1997.
Borcherdt, R. D.: Effects of local geology on ground motion near San Francisco Bay, B. Seismol. Soc. Am., 60, 29–61, 1970.
Brune, J. N.: Tectonic stress and the spectra of seismic shear waves from earthquakes, J. Geoph. Res., 75, 4997–5002, 1970.
Brune, J. N.: Correction to Tectonic stress and the spectra, of seismic shear waves from earthquakes, J. Geophys. Res., 76, 5002, https://doi.org/10.1029/JB076i020p05002, 1971.
Castellaro, S., Alessandrini, G., and Musinu, G.: Seismic station installations and their impact on the recorded signals and derived quantities, Seis. Res. Lett., 93, 3348–3362, https://doi.org/10.1785/0220220029, 2022.
CEN (Comité Européen de Normalisation): Eurocode 8: Design of structures for earthquake resistance. Part 1: general rules, seismic actions and rules for buildings (EN 1998–1: 2004), Brussels, Belgium, 229 pp., 2004.
Cranswick, E., Wetmiller, R., and Boatwright, J.: High-frequency observations and source parameters of microearthquakes recorded at hard-rock sites, Bull. Seismol. Soc. Am., 75, 1535–1567, https://doi.org/10.1785/BSSA0750061535, 1985.
Crowley, H., Dabbeek, J., Despotaki, V., Rodrigues, D., Martins, L., Silva, V., Romão, X., Pereira, N., Weatherill, G., and Danciu, L.: European Seismic Risk Model (ESRM20), EFEHR Technical Report 002, V1.0.0, https://doi.org/10.7414/EUC-EFEHR-TR002-ESRM20, 2021.
Cultrera, G., Cornou, C., Di Giulio, G., and Bard, P. Y.: Indicators for site characterization at seismic station: recommendation from a dedicated survey, Bull. Earth. Eng. 19, 4171–4195, https://doi.org/10.1007/s10518-021-01136-7, 2021.
Danciu, L., Nandan, S., Reyes, C., Basili, R., Weatherill, G., Beauval, C., Rovida, A., Vilanova, S., Sesetyan, K., Bard, P.Y., Cotton, F., Wiemer, S., and Giardini, D.: The 2020 update of the European Seismic Hazard Model: Model Overview, EFEHR Technical Report 001, https://doi.org/10.12686/a15, 2021.
Di Giulio, G., Cultrera, G., Cornou, C., Bard, P. Y., and Tfaily, B. Al.: Quality assessment for site characterization at seismic stations, B. Earth. Eng., 19, 4643–4691, https://doi.org/10.1007/s10518-021-01137-6, 2021.
Evangelidis, C. P., Triantafyllis, N., Samios, M., Boukouras, K., Kontakos, K., Ktenidou, O.-J., Fountoulakis, I., Kalogeras, I., Melis, N. S., Galanis, O., Papazachos, C. B., Hatzidimitriou, P., Scordilis, E., Sokos, E.,Paraskevopoulos, P., Serpetsidaki, A., Kaviris, G., Kapetanidis, V., Papadimitriou, P., Voulgaris, N., Kassaras, I., Chatzopoulos, G., Makris, I., Vallianatos, F., Kostantinidou, K., Papaioannou, C., Theodoulidis, N., Margaris, B., Pilidou, S., Dimitriadis, I., Iosif, P., Manakou, M., Roumelioti, Z., Pitilakis, K., Riga, E., Drakatos, G., Kiratzi, A., and Tselentis, G. A.: Seismic waveform data from Greece and Cyprus: Integration, archival and open access, Seismol. Res. Letts., 92, 1672–1684, https://doi.org/10.1785/0220200408, 2021.
Geli, L., Bard, P. Y., and Jullien, B.: The effect of topography on earthquake ground motion: a review and new results, B. Seism. Soc. Am., 78, 42–63, 1988.
Goulet, C. A., Bozorgnia, Y., Kuehn, N., Alatik, L., Youngs, R. R., Graves, R. W., and Atkinson, G. M.: NGA-East Ground-Motion Characterization model part I: Summary of products and model development, Earthquake Spectra, 37, 1231–1282, https://doi.org/10.1177/87552930211018723, 2021.
Grendas, I., Theodoulidis, N., Hatzidimitriou, P., Margaris, B., and Drouet, S.: Determination of source, path and site parameters based on non-linear inversion of accelerometric data in Greece, Bull. Earth. Engin., https://doi.org/10.1007/s10518-018-0379-8, 2018.
Hollender, F., Roumelioti, Z., Maufroy, E., Traversa, P., and Mariscal, A.: Can we trust high-frequency content in strong-motion database signals? Impact of housing, coupling, and installation depth of seismic sensors, Seis. Res. Lett., 91, 2192–2205, https://doi.org/10.1785/0220190163, 2020.
ITSAK (Institute of Engineering Seimology Earthquake Engineering): ITSAK Strong Motion Network, International Federation of Digital Seismograph Networks [data set], https://doi.org/10.7914/SN/HI, 1981.
Institute of Geodynamics of the National Observatory of Athens: Regional EIDA node for Greece and the southeastern Mediterranean, Institute of Geodynamics, https://eida.gein.noa.gr/ (last access: 1 April 2025), 2023a.
Institute of Geodynamics of the National Observatory of Athens: Regional EIDA node for Greece and the southeastern Mediterranean: FDSNWS-availability, Institute of Geodynamics, https://eida.gein.noa.gr/fdsnws/availability/1 (last access: 1 April 2025), 2023b.
Institute of Geodynamics of the National Observatory of Athens: NOA catalogue: Database of revised events since 01/01/2008, European Commission [data set], http://bbnet.gein.noa.gr/HL/databases/database (last access: 1 April 2025), 2023c.
Ito, E., Nakano, K., Nagashima, F., and Kawase H.: A Method to Directly Estimate S-Wave Site Amplification Factor from Horizontal-to-Vertical Spectral Ratio of Earthquakes (eHVSRs), B. Seismol. Soc. Am., 110, 2892–2911, https://doi.org/10.1785/0120190315, 2020.
Kishida, T., Ktenidou, O.-J., Darragh, R., and Silva, W.: Semi-automated procedure for windowing time series and computing Fourier Amplitude Spectra (FAS) for the NGA-west2 database. PEER report 2016/02, Berkeley, CA: Pacific Earthquake Engineering Research Center, 63 pp., https://peer.berkeley.edu/sites/default/files/publications/webpeer-2016-02_tadahiro_kishida_olga-joan_ktenidou_robert_b._darragh_walter_j._silva.pdf (last access: 31 December 2023), 2016.
Konno, K. and Ohmachi, T.: Ground-motion characteristics estimated from spectral ratio between horizontal and vertical components of microtremor, B. Seismol. Soc. Am., 88, 228–241, https://doi.org/10.1785/BSSA0880010228, 1998.
Ktenidou O.-J., Chávez-García, F. J., and Pitilakis, K.: Variance reduction and signal-to-noise ratio: reducing uncertainty in spectral ratios, Bull. Seismol. Soc. Am., 101, 619–634, https://doi.org/10.1785/0120100036, 2011.
Ktenidou, O.-J.: Hard as a rock? Reconsidering rock-site seismic response and reference ground motions, in: Progresses in European Earthquake Engineering and Seismology - Third European Conference on Earthquake Engineering and Seismology – Bucharest, 2022, edited by: Vacareanu, R. and Ionescu, C., Springer Proceedings in Earth and Environmental Sciences, https://doi.org/10.1007/978-3-031-15104-0_3, 2022.
Ktenidou, O.-J., Cotton, F., Abrahamson, N. A., and Anderson, J. G.: Taxonomy of κ: A Review of Definitions and Estimation Approaches Targeted to Applications, Seismol. Res. Lett., 85, 135–146, https://doi.org/10.1785/0220130027, 2014.
Ktenidou, O.-J. and Abrahamson, N.: Empirical estimation of high-frequency ground motion on hard rock, Seismol. Res. Lett., 87, 1465–1478, https://doi.org/10.1785/0220160075, 2016.
Ktenidou, O.-J. and Kalogeras, I.: The accelerographic network of the National Observatory of Athens, Greece: improving site characterisation using strong motion recordings, 2nd International Conference on Natural Hazards & Infrastructure (ICONHIC), Chania, 23–26 June, 9 pp., 2019.
Ktenidou, O.-J., Chávez-García, F. J., Raptakis, D., and Pitilakis, K. D.: Directional dependence of site effects observed near a basin edge at Aegion, Greece, B. Earth. Eng., 14, 623–645, https://doi.org/10.1007/s10518-015-9843-x, 2016.
Ktenidou, O.-J., Gkika, F., and Evangelidis, C.: The Quest for Rock Site Characterization for the Greek National Seismic Network, EUROENGEO: 3rd European Regional Conference of IAEG, Athens/online, 6–9 October, https://iaeg.info/wp-content/uploads/2024/01/PROCEEDINGS-ABSTRACTS_20211004.pdf (last access: 31 December 2023), 2021a.
Ktenidou, O.-J., Gkika, F., Pikoulis, E.-V., and Evangelidis, C.: Hard as a rock? Looking for typical and atypical reference sites in the Greek network, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13659, https://doi.org/10.5194/egusphere-egu21-13659, 2021b.
Ktenidou, O.-J., Pikoulis, E.-V., Papageorgiou, A., Gkika, F., Liakopoulos, S., Cekinmez, Z., Savvaidis, P., Fragouli, K. E., Chalaris, F., and Evangelidis, C.: Supplemental material and full station flatfile to accompany “The quest for reference stations at the National Observatory of Athens, Greece”, Zenodo [data set], https://zenodo.org/records/14773307, 2025.
Labbé, P. and Paolucci, R.: Developments Relating to Seismic Action in the Eurocode 8 of Next Generation, in: Progresses in European Earthquake Engineering and Seismology – Third European Conference on Earthquake Engineering and Seismology – Bucharest, 2022, edited by: Vacareanu, R. and Ionescu, C., Springer Proceedings in Earth and Environmental Sciences, 1st Edn., ISBN-10 3031151038, 2022.
Lanzano, G., Felicetta, C., Pacor, F., Spallarossa, D., and Traversa, P.: Methodology to identify the reference rock sites in regions of medium-to-high seismicity: An application in Central Italy, Geophys. J. Int., 222, 2053–2067, https://doi.org/10.1093/gji/ggaS261, 2020.
Lanzano, G., Luzi, L., Cauzzi, C., Bienkowski, J., Bindi, D., Clinton, J., Cocco, M., D’Amico, M., Douglas, J., Faenza, L., Felicetta, C., Gallovic, F., Giardini, D., Ktenidou, O.-J., Lauciani, V., Manakou, M., Marmureanu, A., Maufroy, E., Michelini, A., Özener, H., Puglia, R., Rupakhety, R., Russo, E., Shahvar, M., Sleeman, R., and Theodoulidis, N.: Accessing European Strong-Motion Data: An Update on ORFEUS Coordinated Services, Seismol. Res. Lett., 92, 1642–1658, https://doi.org/10.1785/0220200398, 2021.
Lermo, J. and Chávez-García, F. G.: Site effect evaluation using spectral ratios with only one station, B. Seismol. Soc. Am., 83, 1574–1594, 1993.
Luzi, L., Puglia, R., Russo, E., D'Amico, M., Felicetta, C., Pacor, F., Lanzano, G., Çeken, U., Clinton, J., Costa, G., Duni, L., Farzanegan, E., Gueguen, P., Ionescu, C., Kalogeras, I., Özener, H., Pesaresi, D., Sleeman, R., Strollo, A., and Zare, M.: The engineering strong motion database: A platform to access pan-European accelerometric data, Seismol. Res. Lett., 87, 987–99, https://doi.org/10.1785/0220150278, 2016.
Luzi, L., Lanzano, G., Felicetta, C., D’Amico, M. C., Russo, E., Sgobba, S., Pacor, F., and ORFEUS Working Group 5: Engineering Strong Motion Database (ESM) (Version 2.0), Istituto Nazionale di Geofisica e Vulcanologia (INGV), https://doi.org/10.13127/ESM.2, 2020.
Margaris, B., Kalogeras, I., Papaioannou, Ch., Savvaidis, A., and Theodoulidis, N.: Evaluation of the national strong motion network in Greece: Deployment, data processing and site characterization, B. Earth. Engin., 12, 237–254, https://doi.org/10.1007/s10518-013-9580-y, 2014.
Margaris, B. E., Scordilis, M., Stewart, J. P., Boore, D. M., Theodulidis, N., Kalogeras, I., Melis, N., Skarlatoudis, A., Klimis, N., and Seyhan, E.: Hellenic strong-motion database with uniformly assigned source and site metadata for period of 1972–2015, Seismol. Res. Lett., 92, 2065–2080, https://doi.org/10.1785/0220190337, 2021.
Meinhold, G., Kostopoulos, D., and Reischmann, T.: Geochemical constraints on the provenance and depositional setting of sedimentary rocks from the islands of Chios, Inousses and Psara, Aegean Sea, Greece: implications for the evolution of Palaeotethys, J. Geol. Soc., 164, 1145–1163, https://doi.org/10.1144/0016-76492006-111, 2007.
Morasca, P., D'Amico, M., Sgobba, S., Lanzano, G., Colavitti, L., Pacor, F., and Spallarossa, D.: Empirical correlations between an FAS non-ergodic ground motion model and a GIT derived model for Central Italy, Geophys. J. Int., 233, 51–68, https://doi.org/10.1093/gji/ggac445, 2023.
NOA-GI (National Observatory of Athens, Institute of Geodynamics, Athens): National Observatory of Athens Seismic Network, International Federation of Digital Seismograph Networks [data set], https://doi.org/10.7914/SN/HL, 1975.
Pilz, M., Cotton, F., and Reddy Kotha, S.: Data-driven and machine learning identification of seismic reference stations in Europe, Geoph. J. Int., 222, 861–873, https://doi.org/10.1093/gji/ggaa199, 2020.
Pitilakis, K., Riga, E., Apostolaki, S., and Danciu, L.: Seismic hazard zonation map and definition of seismic actions for Greece in the context of the ongoing revision of EC8, B. Earthq. Eng., 22, 3753–3792, https://doi.org/10.1007/s10518-024-01919-8, 2024.
Puglia, R., Albarello, D., Gorini, A., Luzi, L., Marcucci, S., and Pacor, F.: Extensive characterization of Italian accelerometric stations from single-station ambient-vibration measurements, Bull. Earthq. Eng., 9, 1821–1838, https://doi.org/10.1007/s10518-011-9305-z, 2011.
Silva, W. J. and Darragh, R.: Engineering Characterization of Earthquake Strong Ground Motion Recorded at Rock Sites (TR-102261), Palo Alto, CA: Electric Power Research Institute, https://www.epri.com/research/products/TR-102262 (last access: 31 December 2023), 1995.
Steidl, J. H., Tumarkin, A. G., and Archuleta, R. J.: What is a reference site?, B. Seism. Soc. Am., 86, 1733–1748, https://doi.org/10.1785/BSSA0860061733, 1996.
Stewart, J. P., Klimis, N., Savvaidis, A., Theodoulidis, N., Zargli, E., Athanasopoulos, G., Pelekis, P., Mylonakis, G., and Margaris, B.: Compilation of a local VS profile database and its application for inference of VS30 from geologic and terrain-based proxies, B. Seism. Soc. Am., 104, 2827–2841, https://doi.org/10.1785/0120130331, 2014.
Theodoulidis, N., Kalogeras, I., Papazachos, C. B., Karastathis, V., Margaris, B. N., Papaioannou, Ch., and Skarlatoudis, A. A.: HEAD v1.0: A unified Hellenic Accellerogram Database, Seis. Res. Lett., 75, 36–45, 2004.
Trikolas, K.: Geological study of the wider area od Aegialia and Kalavryta, Ph.D. thesis, School of Mining and Metallurgical Engineering, National Technical University of Athens, Greece, 602 pp., https://doi.org/10.12681/eadd/16208, 2006.
Van Houtte, C., Ktenidou, O.-J., Larkin, T., and Kaiser, A.: Reference stations for Christchurch, B. New Zealand Soc. Earth. Eng., 45, 184–195, https://doi.org/10.5459/bnzsee.45.4.184-195, 2012.
Ward, J. H.: Hierarchical Grouping to Optimize an Objective Function, J. Am. Stat. Assoc., 58, 236–244, 1963.
Wessel, P., Smith, W., Scharroo, R., Luis, J., and Wobbe, F.: Generic mapping tools: improved version released, Eos Trans. AGU, 94, 409–410, 2013.
Weatherill, G., Crowley, H., Roullé, A., Tourlière, B., Lemoine, A., Gracianne, C., Reddy Kotha, S., and Cotton, F.: Modelling site response at regional scale for the 2020 European Seismic Risk Model (ESRM20), B. Earthquake Eng., 21, 665–714, https://doi.org/10.1007/s10518-022-01526-5, 2023.
Zhu, C., Cotton, F., and Pilz, M.: Detecting Site Resonant Frequency Using HVSR: Fourier versus Response Spectrum and the First versus the Highest Peak Frequency, B. Seismol. Soc. Am., 110, 427–440, https://doi.org/10.1785/0120190186, 2020.
Short summary
Greek seismic data are invaluable to global databases. Recordings from stations on rock (i.e. not soft deposits) are needed in seismology in order to define reference ground conditions and ground motions, which serve as the basis for all hazard calculations. However, very little knowledge exists on how rock stations in Greece behave. This is the first time the network of the National Observatory is studied systematically and multiparametrically to reveal the most adequate reference stations.
Greek seismic data are invaluable to global databases. Recordings from stations on rock (i.e....
Special issue
Altmetrics
Final-revised paper
Preprint