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Reassessing Eastern Mediterranean tectonics and earthquake hazard from the AD 365 earthquake

R. Ott,K. Wegmann,S. Gallen,F. Pazzaglia,M. Brandon,K. Ueda,C. Fassoulas

Published 2021 in Unknown venue

ABSTRACT

The hallmark of great earthquakes (Mw ≈ 8,3-8.5) in the Mediterranean is the 21 July AD 365 earthquake and tsunami that destroyed cities and killed thousands of people throughout the Eastern Mediterranean. This event is intriguing because most Mediterranean subduction forearcs exhibit pervasive crustal extension and minimal definitive evidence exists for great subduction megathrust earthquakes, consistent with weak seismic coupling. This conundrum has led many to favor rupture of a previously unrecognized upper plate splay fault south of Crete in an Mw 8.38.5 earthquake, uplifting a Holocene paleoshoreline on Crete by up to 9 m. Similar source mechanisms have been adapted and commonly used for seismic and tsunami hazard estimation in the region. We present an alternative model for the uplift of the Cretan paleoshoreline and the AD 365 tsunami that centers on known active normal fault systems offshore of western and southwestern Crete. We use new and published radiocarbon dates, together with historical records, to show that uplift of the Cretan paleoshoreline likely occurred during two or more earthquakes within 2 to 3 centuries. Visco-elastic dislocation modeling demonstrates that the rupture of these normal faults fits observed data equally as well as reverse fault models but requires less slip. Tsunami modeling shows that normal-fault ruptures produce strong tsunamis that better match historical reports than a hypothetical reverse fault. Our findings collectively favor the interpretation that damaging earthquakes and tsunamis in the Eastern Mediterranean originate on normal faults and highlight the potential hazard from tsunamigenic upper plate normal fault earthquakes. Plain Language Summary Most people living and vacationing near the Mediterranean Sea coast are not fully aware of the region's earthquake and tsunami hazard. Here we contribute to understanding the mechanisms for major earthquakes and tsunamis in the Mediterranean by investigating the region’s largest historically documented earthquake. The record of this event is thought to be preserved in part as a fossil beach uplifted by up to 9 m on the island of Crete, Greece. Previous studies assumed that the fossil beach was uplifted during a single earthquake in AD 365. However, our results from the dating of marine fossils that died due to sudden emergence above sea level and an assessment of existing historical and archeological records suggest that there were a series of earthquakes that might have incrementally uplifted the fossil beach. We identify manuscript submitted to AGU Advances and model a previously overlooked source for these earthquakes (normal faults) and tsunamis and find that these sources perform as well as or better than the traditionally assumed earthquake sources when compared to observations. These results highlight the potential importance of considering normal-fault earthquake sources in regions where tectonic plates converge and identify future research directions for more comprehensive hazard characterization.

PUBLICATION RECORD

  • Publication year

    2021

  • Venue

    Unknown venue

  • Publication date

    Unknown publication date

  • Fields of study

    Not labeled

  • Identifiers
    DOI 10.31223/x5h036
  • External record

    Open on Semantic Scholar

  • Source metadata

    Semantic Scholar

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