Early preliminary results on co-seismic deformation of the island of Samos associated with co-seismic slip following the October 2020 M-w 6.9 Samos earthquake (Greece)


Toker M. , ŞENTÜRK E., Bayik C.

ARABIAN JOURNAL OF GEOSCIENCES, vol.14, no.23, 2021 (Journal Indexed in SCI) identifier

  • Publication Type: Article / Article
  • Volume: 14 Issue: 23
  • Publication Date: 2021
  • Doi Number: 10.1007/s12517-021-08951-x
  • Title of Journal : ARABIAN JOURNAL OF GEOSCIENCES
  • Keywords: Samos earthquake, Samos island, Co-seismic slip distribution, Coulomb stress change, InSAR data, HELLENIC SUBDUCTION ZONE, FAULT-PLANE SOLUTIONS, FOCAL MECHANISMS, AEGEAN SEA, SOURCE PARAMETERS, CRUSTAL MOTION, STRESS-FIELD, LITHOSPHERE, MICROSEISMICITY, SEISMICITY

Abstract

On 30 October 2020, an M-w 6.9 normal faulting earthquake to the north and offshore from the island of Samos, very close to the south west coast of Turkey, occurred at 14:51 local time (11:51:34.8 UTC). In this study, the stress change features of the rupture process and the co-seismic surface deformation of the island of Samos during this event are analyzed. The co-seismic slip distribution model of the causative fault was initially adopted, inverted from the Global Centroid Moment Tensor (GCMT) solution for the M-w 6.9 Samos 2020 earthquake. Then, this GCMT-inverted fault source model (uniform-slip) was used to compute the co-seismic Coulomb stress changes in the crustal volume affected by the early seismicity and to analyze the Coulomb stress change characteristics of the mainshock in terms of early aftershocks, stress state of the causative fault, and of the adjacent Samos island. Lastly, interferometric synthetic aperture radar (InSAR) interferograms (Sentinel-1 satellites) were used to measure the co-seismic surface displacements of the adjacent island of Samos and to evaluate stress transfer of the causative fault. Finally, the results obtained from the Coulomb stress changes associated with the co-seismic slip distribution and InSAR observations were compared. The Coulomb stress change features caused by the uniform-slip for the causative fault were in good agreement with the pattern of aftershock distributions in the first week following the mainshock. It was found that most of the aftershocks occurred in end-fault and off-fault lobes, as areas of Coulomb stress increase of 2-5 bar, and in the stress shadow zone near the rupture, as an area of Coulomb stress decreases of between -4 and -5 bar, corresponding to the largest slip patch (similar to 2.7 m) according to the uniform-slip. A rupture propagation direction from E (similar to. 2.7 m max. slip) to W (similar to 30 cm min. slip) and asymmetric deepening of the slip distribution down to a depth > 10 km in the fault plane, in agreement with our uniform-slip model, explained the Samos mainshock, Coulomb stress changes, and co-seismic deformation of Samos island. The best constraints on the early deformation pattern of Samos island, in the absence of near-mainshock seismic stations, obtained from InSAR data revealed maximum displacement (+/- similar to 10 cm) of the island from E to W and from SE (subsidence) to NW (uplift). Finally, based on the Coulomb stress change and InSAR computation, it is concluded that the 2020 Samos mainshock increased the stress level of the assumed faults and/or possible fault segments in the N and adjacent to Samos island in the S as a result of end-fault and off-fault lobes.