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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.

A detailed analysis of microseismicity in Samos and Kusadasi (Eastern Aegean Sea) areas

Tan O., Papadimitriou E. E., Pabuccu Z., Karakostas V., Yoruk A., Leptokaropoulos K.

Acta Geophysica

2014

Vol. 62, no. 6

1283--1309

A detailed investigation of microseismicity and fault plane solutions are used to determine the current tectonic activity of the prominent zone of seismicity near Samos Island and Kusadasi Bay. The activation of fault populations in this complex strike-slip and normal faulting system was investigated by using several thousand accurate earthquake locations obtained by applying a double-difference location method and waveform cross-correlation, appropriate for areas with relatively small seismogenic structures. The fault plane solutions, determined by both moment tensor waveform inversions and P-wave first motion polarities, reveal a clear NS trending extension direction, for strike slip, oblique normal and normal faults. The geometry of each segment is quite simple and indicates planar dislocations gently dipping with an average dip of 40-45°, maintaining a constant dip through the entire seismogenic layer, down to 15 km depth.

Multi-disciplinary earthquake researches in Western Turkey: Hints to select sites to study geochemical transients associated to seismicity

Inan S., Ertekin K., Seyis C., Simsek S, Kulak F., Dikbas A., Tan O., Ergintav S., Cakmak R., Yoruk A., Cergel M., Yakan H., Karakus H., Saatcilar R., Akcig Z., Iravul Y., Tuzel B.

Acta Geophysica

2010

Vol. 58, no. 5

767-813

Warm and hot spring water as well as soil gas radon release patterns have been monitored in the Aegean Extensional Province of Western Turkey, alongside regional seismic events, providing a multidisciplinary approach. In the study period of 20 months, seven moderate earthquakes with ML between 4.0 and 4.7 occurred in this seismically very active region; two earthquakes with magnitude 5.0 also occurred near the study area. Seismic monitoring showed no foreshock activity. By contrast, hydro-geochemical anomalies were found prior to these seismic events, each lasting for weeks. The anomalies occurred foremost in conjunction with dip-slip events and seem to support the dilatancy and water diffusion hypothesis. Increased soil gas radon release was recorded before earthquakes associated with strike-slip faults, but no soil radon anomalies were seen before earthquakes associated with dip-slip faults. Geochemical anomalies were also noticeably absent at some springs throughout the postulated deformation zones of impending earthquakes. The reason for this discrepancy might be due to stress/strain anisotropies.