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Seismotectonic implications of the 2020 Samos, Greece, Mw 7.0 mainshock based on high resolution aftershock relocation and source slip model

Karakostas V., Tan O., Kostoglou A., Papadimitriou E., Bonatis P.

Acta Geophysica

2021

Vol. 69, no. 3

979--996

The 30 October 2020, Mw 7.0 Samos mainshock took place in the ofshore north of Samos Island in eastern Aegean area, previously struck in 1904 with a comparable magnitude earthquake ofshore the southern coastline. The investigation of the aftershock seismicity evolution and the properties of the activated fault network was accomplished with aftershock relocation performed with the double-diference and cross-correlation techniques. The highly accurate relocated seismicity illustrates a well-defned E–W activated structure located deeper than 5 km with an average depth of~12 km. Moment tensor solutions indicate mostly normal faulting with an average T-axis~ 185ο . Strong-motion waveform modeling revealed a N-dipping fault plane with a coseismic slip patch of 36 km × 22 km and a maximum slip equal to 1 m at 12 km depth. The slip is mainly concentrated in a single asperity implying a rupture mode of asperities breaking in isolated earthquakes rather than to cooperate to produce a larger rupture. Coulomb stress calculations unveil increased positive static stress changes values at the locations of the majority of the aftershocks and activation of minor fault segments by stress transfer.

Relocation of the 2018 Zakynthos, Greece, aftershock sequence: spatiotemporal analysis deciphering mechanism diversity and aftershock statistics

Karakostas V., Kostoglou A., Chorozoglou D., Papadimitriou E.

Acta Geophysica

2020

Vol. 68, no. 5

1263--1294

An Mw 6.8 earthquake occurred on October 25, 2018, 35 km ofshore from the southwest coastlines of Zakynthos Island. The aftershock sequence appeared remarkably productive with six aftershocks of M≥5.0 in the frst month and tens of aftershocks with M≥4.0 during the study period. The GCMT solution for the main shock suggests a very low angle plane (dip=24°) for a dextral strike–slip faulting (rake=165°). A similar solution is suggested for the largest aftershock (Mw 5.9) that occurred 5 days afterward. The proximity of the main shock location with the dextral active boundary of Kefalonia Transform Fault Zone (KTFZ) along with the Hellenic Subduction front supports this oblique faulting. The aftershock activity is comprised mostly in depths 5–12 km and forms eight distinctive clusters that accommodate regional strain and evidence strain partitioning. The role of stress transfer and statistical analysis are combined for detailing the highly productive aftershock sequence. Earthquake networks analysis reveals their random structure soon after the main shock, which became small-world structure after the frst 200 days. Time series analysis constructed from the aftershock frequency and seismic moment release and manifested signifcant correlation among the eight seismicity clusters.