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Earthquake-swarms, slow-slip and fault-interactions at the western-end of the Hellenic Subduction System precede the Mw 6.9 Zakynthos Earthquake, Greece
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  • Vasiliki Mouslopoulou,
  • Gian Maria Bocchini,
  • Simone Cesca,
  • Vasso Saltogianni,
  • Jonathan R Bedford,
  • Gesa Maria Petersen,
  • Michael Gianniou,
  • Onno Oncken
Vasiliki Mouslopoulou
Institute of Geodynamics, National Observatory of Athens

Corresponding Author:[email protected]

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Gian Maria Bocchini
Ruhr University Bochum
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Simone Cesca
GFZ German Research Centre for Geosciences
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Vasso Saltogianni
GFZ German Research Centre for Geosciences
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Jonathan R Bedford
GFZ German Research Centre for Geosciences
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Gesa Maria Petersen
GFZ German Research Centre for Geosciences
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Michael Gianniou
University of West Attica
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Onno Oncken
GFZ German Research Centre for Geosciences
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Abstract

The month-to-year-long deformation of the Earth’s crust where active subduction zones terminate is poorly explored. Here we report on a multidisciplinary dataset that captures the synergy of slow-slip events, earthquake swarms and fault-interactions during the ~5 years leading up to the 2018 M 6.9 Zakynthos Earthquake at the western termination of the Hellenic Subduction System (HSS). It appears that this long-lasting preparatory phase initiated due to a slow-slip event that lasted ~4 months and released strain equivalent to a ~M 6.3 earthquake. We propose that the slow-slip event, which is the first to be reported in the HSS, tectonically destabilised the upper 20-40 km of the crust, producing alternating phases of seismic and aseismic deformation, including intense microseismicity (M<4) on neighbouring faults, earthquake swarms in the epicentral area of the M 6.9 earthquake ~1.5 years before the main event, another episode of slow-slip immediately preceding the mainshock and, eventually, the large (M6.9) Zakynthos Earthquake. Tectonic instability in the area is evidenced by a prolonged (~4 years) period of overall suppressed b-values (<1) and strong earthquake interactions on discrete strike-slip, thrust and normal faults. We propose that composite faulting patterns accompanied by alternating (seismic/aseismic) deformation styles may characterise multi-fault subduction-termination zones and may operate over a range of timescales (from individual earthquakes to millions of years).
Dec 2020Published in Geochemistry, Geophysics, Geosystems volume 21 issue 12. 10.1029/2020GC009243