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The role of site effects on elevated seismic demands and corollary structural damage during the October 30, 2020, M7.0 Samos Island (Aegean Sea) Earthquake

  • S.I. : The M7.0 Samos Island (Aegean Sea) Earthquake of 30th October 2020
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Abstract

On October 30, 2020 14:51 (UTC), a moment magnitude (M) 7.0 (USGS, EMSC) earthquake occurred in the Aegean Sea. This paper presents the reconnaissance findings regarding the site effects on recorded strong ground motion intensities and duration, along with the resulting induced-structural damage in Izmir Bay and Samos Island, respectively. In all rock records, relatively high intensity long period rock spectral accelerations were observed in the mid to long period range of 0.5–1.5 s, which are attributed to the source, more specifically, to the slower rupture-mechanism of the event. These rich spectral intensities were further amplified by soil site effects and soil-superstructure resonance, leading to two to six times amplified overall responses and prolonged seismic shaking durations, more pronounced in Bayrakli and other Izmir Bay sites in Turkey. However, these amplified and prolonged excitations are still below design basis earthquake levels, which addresses the lack of proper structural design and construction deficiencies, as the underlying causes for the collapse to heavy damage performance of 795 buildings. On the other hand, although located only about 10 km from the rupture (22 km from the epicenter) and within the near fault zone, the town of Vathy on Samos Island (Greece) was rather lightly affected by the earthquake, with relatively few collapsed or heavily damaged buildings, partially attributed to the low height/low weight of structures in the area. However, a concentration of damage in low-rise buildings in Ano Vathy hill is considered indicative of a combination of coupled valley and topography effects on the strong motion. This event once again addressed the need to develop region-specific zonation and provisions, when more general code practices are proven to be inadequate to assess these extreme site effects.

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Acknowledgements

The authors are indebted to Professor George Bouckovalas of the National Technical University of Athens, Prof. Dr. Atilla Ansal of Ozyegin University, Istanbul, Prof. Dr. Ayfer Erkin of Istanbul Technical University, Prof. Dr. Bilge Siyahi of Gebze Technical University, Istanbul for their valuable review of the paper, and their insightful comments that significantly improved many of the discussions presented herein, particularly those pertaining to site effects in the town of Vathy and city Izmir. The authors would also like to deeply thank external contributors who kindly provided data and assistance with carrying out field measurements included in this paper. In this regard, George Milionis, Geologist, provided the boreholes log data for BH1, BH2, BH3 and BH4 shown in Fig. 20 and Fig. 24, while the borehole log data for BH5 shown in Fig. 20 was provided by Peggy Sechioti, employee of the Greek Ministry of Infrastructure and Transport. A number of photographs and information about structural damage in Ano Vathy were provided by HAEE/ETAM members Christos Giarlelis and Prof. A. Sextos, respectively. Information about the orientation and polarity of the strong motion instruments at Vathy was provided by Drs Ioannis Kalogeras, Vassilis Margaris and Nikos Theodulidis of NOA and ITSAK-EPPO. MASW and HVSR field measurements by Prof. P. Pelekis were supported by Vasilis Christopoulos, laboratory member, and Paraskevi Paliatsa, postgraduate student, of the Civil Engineering Department, University of Patras. Additionally, a number of photographs and information about structural damage in Izmir Bayrakli were provided by Ali Aksoyer. Their valuable contribution is gratefully acknowledged. The members of Middle East Technical University, Ankara, were partially funded by reconnaissance funds of METU, which is greatly appreciated. Financial support to the U-Patras team was provided by HAEE/ETAM. Prof Katerina Ziotopoulou’s field reconnaissance and participation was supported by the NSF-sponsored Geotechnical Extreme Events Reconnaissance (GEER) association. The work of the GEER Association, in general, is based upon work supported in part by the National Science Foundation through the Geotechnical Engineering Program under Grant No. CMMI-1826118. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NSF. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. The GEER Association is made possible by the vision and support of the NSF Geotechnical Engineering Program Directors: Dr. Richard Fragaszy and the late Dr. Cliff Astill. GEER members also donate their time, talent, and resources to collect time-sensitive field observations of the effects of extreme events. Last but not least, thanks to EduPro Civil Systems Inc., the ProShake software license was freely provided for assessing site response analyses, which is acknowledged.

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Authors and Affiliations

  1. Middle East Technical University, Universiteler Mah, Dumlupınar Bulv, 06800, Cankaya-Ankara, Turkey

    Kemal Onder Cetin, Aysegul Askan, Makbule Ilgac, Gizem Can, Elife Cakir, Berkan Soylemez, Ahmed Al-Suhaily, Alaa Elsaid & Moutasem Zarzour

  2. National Technical University of Athens, Athens, Greece

    Achilleas G. Papadimitriou

  3. Ege University, Izmir, Turkey

    Selim Altun & Alper Sezer

  4. University of Patras, Patras, Greece

    Panagiotis Pelekis

  5. Hacettepe University, Ankara, Turkey

    Berna Unutmaz

  6. Institute of Engineering Seismology and Earthquake Engineering, Thessaloniki, Greece

    Emmanouil Rovithis

  7. Dokuz Eylül University, Izmir, Turkey

    Mustafa Akgun & Cem Kincal

  8. Democritus University of Thrace, Komotiny, Greece

    Nikolaos Klimis

  9. University of California Davis, Davis, USA

    Katerina Ziotopoulou

  10. University of California, Los Angeles, USA

    Jonathan Stewart & George Mylonakis

  11. Khalifa University, Abu Dhabi, UAE

    George Mylonakis

  12. University of Bristol, Bristol, UK

    George Mylonakis

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  1. Kemal Onder Cetin
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Correspondence to Kemal Onder Cetin.

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Cetin, K.O., Papadimitriou, A.G., Altun, S. et al. The role of site effects on elevated seismic demands and corollary structural damage during the October 30, 2020, M7.0 Samos Island (Aegean Sea) Earthquake. Bull Earthquake Eng 20, 7763–7792 (2022). https://doi.org/10.1007/s10518-021-01265-z

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