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Ganas A.,Institute of Geodynamics | Karastathis V.,Institute of Geodynamics | Moshou A.,Institute of Geodynamics | Valkaniotis S.,9 Koronidos Str. | And 2 more authors.
Tectonophysics | Year: 2014

On August 7, 2013 a moderate earthquake (NOA ML=5.1, NOA Mw=5.4) occurred in central Kallidromon Mountain, in the Pthiotis region of central Greece. 2270 aftershocks were relocated using a modified 1-D velocity model for this area. The b-value of the aftershock sequence was b=0.85 for a completeness magnitude of Mc=1.7. The rate of aftershock decay was determined at p=0.63. The spatial distribution of the aftershock sequence points towards the reactivation of a N70°±10°E striking normal fault at crustal depths between 8 and 13km. A NNW-SSE cross-section imaged the activation of a steep, south dipping normal fault. A stress inversion analysis of 12 focal mechanisms showed that the minimum horizontal stress is extensional at N173°E. No primary surface ruptures were observed in the field; however, the earthquake caused severe damage in the villages of the Kallidromon area. The imaged fault strike and the orientation of the long-axis of the aftershock sequence distribution are both at a high-angle to the strike of known active faults in this area of central Greece. We interpret the Kallidromon seismic sequence as release of extensional seismic strain on secondary, steep faults inside the Fokida-Viotia crustal block. © 2014 Elsevier B.V.


Valkaniotis S.,9 Koronidos Str. | Ganas A.,Institute of Geodynamics | Papathanassiou G.,Aristotle University of Thessaloniki | Papanikolaou M.,Institute of Geodynamics
Tectonophysics | Year: 2014

On Jan. 26 and Feb 3, 2014 Cephalonia Island, Ionian Sea, Greece, was struck by two strong, shallow earthquakes (NOA local magnitudes ML5.8 and ML5.7, respectively). The earthquakes ruptured two sub-parallel, strike-slip faults, with right-lateral kinematics. During both earthquakes, ground-shaking phenomena such as liquefaction, road failures, rock falls, small/medium size landslides and stonewall failures were widespread all over the western part of the island. No primary fault surface ruptures were observed, however one patch of the rupture of the second event may have nearly reached the surface, because of the abundance of surface cracks with cm-size offsets mapped in the field in north Paliki Peninsula. Liquefaction phenomena were mainly triggered in reclaimed lands in the waterfront areas of Argostoli and Lixouri inducing structural damages to quays, sidewalks and piers. We also present evidence for liquefaction-induced ground disruption in the recently constructed marina of Argostoli, which is situated at the opposite (eastern) shore to the town. © 2014 Elsevier B.V.

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