The 25 October 2018 Mw = 6.7 Zakynthos earthquake (Ionian Sea, Greece): A low-angle fault model based on GNSS data, relocated seismicity, small tsunami and implications for the seismic hazard in the west Hellenic Arc

Ganas, Athanassios; Briole, Pierre; Bozionelos, George; Barberopoulou, A.; Elias, Panagiotis; Tsironi, Varvara; Valkaniotis, Sotiris; Moshou, Alexandra; Mintourakis, I.

doi:10.1016/j.jog.2020.101731

Cited by 34 publications

(29 citation statements)

References 63 publications

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“…(2020) and Ganas et al. (2020), which is more compatible with the plate‐interface. Repeating our MT decomposition and forcing the thrust and strike‐slip subevents to have the geometry proposed by Sokos et al.…”

Section: The 2014–2019 Zakynthos Earthquake Sequence (Zes)mentioning

confidence: 97%

Earthquake Swarms, Slow Slip and Fault Interactions at the Western‐End of the Hellenic Subduction System Precede the M_w 6.9 Zakynthos Earthquake, Greece

Mouslopoulou

Bocchini

Cesca

et al. 2020

Geochem Geophys Geosyst

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Section: The 2014–2019 Zakynthos Earthquake Sequence (Zes)mentioning

confidence: 97%

Earthquake Swarms, Slow Slip and Fault Interactions at the Western‐End of the Hellenic Subduction System Precede the M_w 6.9 Zakynthos Earthquake, Greece

Mouslopoulou

Bocchini

Cesca

et al. 2020

Geochem Geophys Geosyst

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“…It has a similar orientation as the fault planes that Cirella et al (2020) and Ganas et al (2020) inferred for the main shock by jointly considering geodetic and seismic data. However, in contrast to our representative MT of cluster 3, the main shock mechanism has a large strike-slip component (Cirella et al 2020;Ganas et al 2020;Mouslopoulou et al 2020;Sokos et al 2020). The PCA supports the identification of the causative plane, as both PCA axes have a similar length, which indicates a low dip angle.…”

Section: Discussion Part I: On the Methodological Implementationmentioning

confidence: 77%

“…The study region is characterized by intense seismic activity and strong main shocks (M > 6, Papazachos & Papazachou 2003). On 25 October 2018, a magnitude M w 6.9 earthquake struck southwest of Zakynthos (Chousianitis & Konca 2019;Cirella et al 2020;Ganas et al 2020;Karakostas et al 2020;Mouslopoulou et al 2020;Sokos et al 2020). It occurred after a 4-yr-long phase of seismic unrest which was probably triggered by a slow-slip event (Mouslopoulou et al 2020) and was followed by strong aftershock activity, which is still ongoing (Mouslopoulou et al 2020;Sokos et al 2020).…”

Section: )mentioning

confidence: 99%

“…In this study we apply the clustering toolbox to the aftershock sequence of the 25 October 2018 M w 6.9 Zakynthos (Greece) earthquake (Chousianitis & Konca 2019;Cirella et al 2020;Ganas et al 2020;Karakostas et al 2020;Mouslopoulou et al 2020;Sokos et al 2020). The data set includes >2300 events with M ≥ 2.8 recorded at 33 stations from 25/10/2018 to 14/11/2019.…”

Section: Introductionmentioning

confidence: 99%

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Clusty, the waveform-based network similarity clustering toolbox: concept and application to image complex faulting offshore Zakynthos (Greece)

Petersen

Niemz

Cesca

et al. 2020

Geophysical Journal International

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Summary Clusty is a new open source toolbox dedicated to earthquake clustering based on waveforms recorded across a network of seismic stations. Its main application is the study of active faults and the detection and characterization of faults and fault networks. By using a density-based clustering approach, earthquakes pertaining to a common fault can be recognised even over long fault segments, and the first-order geometry and extent of active faults can be inferred. Clusty implements multiple techniques to compute a waveform based network similarity from maximum cross-correlation coefficients at multiple stations. The clustering procedure is designed to be transparent and parameters can be easily tuned. It is supported by a number of analysis visualisation tools which help to assess the homogeneity within each cluster and the differences among distinct clusters. The toolbox returns graphical representations of the results. A list of representative events and stacked waveforms facilitate further analyses like moment tensor inversion. Results obtained in various frequency bands can be combined to account for large magnitude ranges. Thanks to the simple configuration, the toolbox is easily adaptable to new datasets and to large magnitude ranges. To show the potential of our new toolbox, we apply Clusty to the aftershock sequence of the Mw 6.9 October 25, 2018 Zakynthos (Greece) Earthquake. Thanks to the complex tectonic setting at the western termination of the Hellenic Subduction System where multiple faults and faulting styles operate simultaneously, the Zakynthos dataset provides an ideal case-study for our clustering analysis toolbox. Our results support the activation of several faults and provide insight into the geometry of faults or fault segments. We identify two large thrust faulting clusters in the vicinity of the mainshock and multiple strike-slip clusters to the east, west and south of these clusters. Despite its location within the largest thrust cluster, the mainshock does not show a high waveform similarity to any of the clusters. This is consistent with the results of other studies suggesting a complex failure mechanism for the mainshock. We propose the existence of conjugated strike-slip faults in the south of the study area. Our waveform similarity based clustering toolbox is able to reveal distinct event clusters which cannot be discriminated based on locations and/or timing only. Additionally, the clustering results allows distinction between fault and auxiliary planes of focal mechanisms and to associate them to known active faults.

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“…However, no consistent results were obtained. One approach [ 50 ] indicated that the inverted slip distribution is characterized by two asperities with peak slip of 1.4 m at depth 17 km. The rupture propagated unilaterally but mainly towards N-NE and with a down-dip extent up to 38 km, indicating that this event broke the entire underthrust Ionian oceanic crust beneath the megathrust.…”

Section: Methodsmentioning

confidence: 99%

Short-Term Foreshocks as Key Information for Mainshock Timing and Rupture: The Mw6.8 25 October 2018 Zakynthos Earthquake, Hellenic Subduction Zone

Papadopoulos

Agalos

Minadakis

et al. 2020

Sensors

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Significant seismicity anomalies preceded the 25 October 2018 mainshock (Mw = 6.8), NW Hellenic Arc: a transient intermediate-term (~2 yrs) swarm and a short-term (last 6 months) cluster with typical time-size-space foreshock patterns: activity increase, b-value drop, foreshocks move towards mainshock epicenter. The anomalies were identified with both a standard earthquake catalogue and a catalogue relocated with the Non-Linear Location (NLLoc) algorithm. Teleseismic P-waveforms inversion showed oblique-slip rupture with strike 10°, dip 24°, length ~70 km, faulting depth ~24 km, velocity 3.2 km/s, duration 18 s, slip 1.8 m within the asperity, seismic moment 2.0 × 1026 dyne*cm. The two largest imminent foreshocks (Mw = 4.1, Mw = 4.8) occurred very close to the mainshock hypocenter. The asperity bounded up-dip by the foreshocks area and at the north by the foreshocks/swarm area. The accelerated foreshocks very likely promoted slip accumulation contributing to unlocking the asperity and breaking with the mainshock. The rupture initially propagated northwards, but after 6 s stopped at the north bound and turned southwards. Most early aftershocks concentrated in the foreshocks/swarm area. This distribution was controlled not only by stress transfer from the mainshock but also by pre-existing stress. In the frame of a program for regular monitoring and near real-time identification of seismicity anomalies, foreshock patterns would be detectable at least three months prior the mainshock, thus demonstrating the significant predictive value of foreshocks.

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The 25 October 2018 Mw = 6.7 Zakynthos earthquake (Ionian Sea, Greece): A low-angle fault model based on GNSS data, relocated seismicity, small tsunami and implications for the seismic hazard in the west Hellenic Arc

Cited by 34 publications

References 63 publications

Earthquake Swarms, Slow Slip and Fault Interactions at the Western‐End of the Hellenic Subduction System Precede the M_w 6.9 Zakynthos Earthquake, Greece

Earthquake Swarms, Slow Slip and Fault Interactions at the Western‐End of the Hellenic Subduction System Precede the M_w 6.9 Zakynthos Earthquake, Greece

Clusty, the waveform-based network similarity clustering toolbox: concept and application to image complex faulting offshore Zakynthos (Greece)

Short-Term Foreshocks as Key Information for Mainshock Timing and Rupture: The Mw6.8 25 October 2018 Zakynthos Earthquake, Hellenic Subduction Zone

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The 25 October 2018 Mw = 6.7 Zakynthos earthquake (Ionian Sea, Greece): A low-angle fault model based on GNSS data, relocated seismicity, small tsunami and implications for the seismic hazard in the west Hellenic Arc

Cited by 34 publications

References 63 publications

Earthquake Swarms, Slow Slip and Fault Interactions at the Western‐End of the Hellenic Subduction System Precede the Mw 6.9 Zakynthos Earthquake, Greece

Earthquake Swarms, Slow Slip and Fault Interactions at the Western‐End of the Hellenic Subduction System Precede the Mw 6.9 Zakynthos Earthquake, Greece

Clusty, the waveform-based network similarity clustering toolbox: concept and application to image complex faulting offshore Zakynthos (Greece)

Short-Term Foreshocks as Key Information for Mainshock Timing and Rupture: The Mw6.8 25 October 2018 Zakynthos Earthquake, Hellenic Subduction Zone

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Earthquake Swarms, Slow Slip and Fault Interactions at the Western‐End of the Hellenic Subduction System Precede the M_w 6.9 Zakynthos Earthquake, Greece

Earthquake Swarms, Slow Slip and Fault Interactions at the Western‐End of the Hellenic Subduction System Precede the M_w 6.9 Zakynthos Earthquake, Greece