Earthquake Swarms, Slow Slip and Fault Interactions at the Western‐End of the Hellenic Subduction System Precede the Mw 6.9 Zakynthos Earthquake, Greece. (14th December 2020)

• Record Type: Journal Article
• Authors: Mouslopoulou, Vasiliki; Bocchini, Gian Maria; Cesca, Simone; Saltogianni, Vasso; Bedford, Jonathan; Petersen, Gesa; Gianniou, Michael; Oncken, Onno
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 21:Number 12(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-12-14
• Subjects: Hellenic subduction -- microseismicity -- plate‐interface -- slow slip events -- upper‐plate -- Zakynthos Earthquake; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2020GC009243
• Languages: English
• ISSNs: 1525-2027

Abstract

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 data set that captures the synergy of slow‐slip events, earthquake swarms and fault interactions during the ∼5 years leading up to the 2018 Mw 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 ∼Mw 6.3 earthquake. We propose that the slow‐slip event, which is the first to be reported in the HSS, tectonically destabilized the upper 20–40 km of the crust, producing alternating phases of seismic and aseismic deformation, including intense microseismicity (Mw < 4) on neighboring faults, earthquake swarms in the epicentral area of the Mw 6.9 earthquake ∼1.5 years before the main event, another episode of slow slip immediately preceding the mainshock and, eventually, the large (Mw 6.9) 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 characterize multifault subduction‐termination zones and may operate over a range of timescales (from individual earthquakes to millions of years). Key Points: First ever report of slow‐slip event in the Hellenic Subduction System (HSS) prior to a large‐magnitude earthquake Synergy of upper‐plate faulting, slow slip and earthquake swarms tectonically destabilize a subduction‐termination prior to the mainshock Plate‐motion at the western HSS is accommodated by alternating phases of seismic and aseismic slip operating at various depths