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Fault modelling, seismic sequence evolution and stress transfer scenarios for the July 20, 2017 (MW 6.6) Kos–Gökova Gulf earthquake, SE Aegean

Sboras Sotirios, Lazos Ilias, Mouzakiotis Evaggelos, Karastathis Vassilios, Pavlides Spyros, Chatzipetros Alexandros

Acta Geophysica

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2020

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Vol. 68, no. 5

1245--1261

EN

The July 20, 2017, MW 6.6 Kos–Gökova Gulf earthquake occurred ofshore, near Bodrum of Turkey and Kos of Greece. It was one of the strongest in the broader area during the last many decades causing two deaths, many injuries and extensive damages. We investigated the evolution of the seismic sequence using seismological and geological tools. The aftershock sequence was relocated mainly in order to defne the geometry of the main seismic source, depicting a NNW-dipping fault plane. It also revealed signifcant clustering, associated with other nearby faults, and asymmetric spatio-temporal evolution. Along with morphotectonic analysis on Kos Island, and other published seismological information (e.g. focal mechanisms), we modelled the seismic source of the mainshock, as well as the one of the strongest aftershocks (August 8, MW 5.3). We applied the Coulomb failure criterion in order to investigate the efect of the mainshock on the strongest aftershock, and the rest of the sequence as well. Using the same method, we also investigated the stress changes of both strongest shocks for the prevailing E–W-trending normal faults in this area. Among other conclusions and implications, we deduce that the prevailing tectonic setting of the Gökova Gulf consists of roughly E–W-striking normal faults forming inner horsts and grabens.

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Stress release during earthquake sequences

Gibowicz S.

Acta Geophysica Polonica

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2004

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Vol. 52, nr 3

271-299

EN

The average stress drop and apparent stress released during 65 complex earthquake sequences from all over the world are estimated separately for foreshocks, main shocks and aftershocks. All of them but one occurred between 1977 and 1997. The Harvard CMT solutions are available for 60 main shocks, 38 foreshocks and 218 aftershocks. The stress drop is estimated using the values of seismic moment and source half duration and the scaling relations between various source parameters: seismic moment, source half duration, fault surface and fault length, taken from Harvard catalogues and other publications. The average stress drop is the highest during foreshocks (1.8 MPa), middle during main shocks (1.1 MPa) and the lowest during aftershocks (0.4 MPa). Similarly, the apparent stress, estimated from seismic moment and radiated energy taken from PDE-NEIC bulletins and other publications, is also the highest for foreshocks (0.6 MPa), middle for main shocks (0.4 MPa) and the lowest for aftershocks (0.2 MPa).

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Temporal distribution, source parameters, and depth discrimination of earthquakes from the Abu Dabbab region, Egypt

Hassoup A., Niewiadomski J., Gibowicz S.

Acta Geophysica Polonica

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2003

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Vol. 51, nr 2

135-146

EN

Records of earthquakes from the Abu Dabbab region in Egypt, situated about 25 km west of the Red Sea coast, were collected from the Aswan Seismograph Network (ASN). The temporal distribution of these events shows several sequences of the foreshock-main shock-aftershock type. Four such sequence occurred in 1984 and 1985. the slope of the frequency-amplitude relation (b-value) for the four sequences ranges form 1.8 to 2.4, reflecting co-seismic deformation with time in the vicinity of the source area. Source parameters were estimated for ten events from the same area, which occurred between 1998 and 2001 and had magnitude ranging from 3.0 to 4.2.the spectral plateau, corner frequency, seismic moment, source dimension, and stress drop were calculated. A good correlation is found between the logarithm of seismic moment and the local duration magnitude determined by the ASN. The stress drop is not uniform and ranges between 0.1 and 6.8 MPa. In addition, the relative decay of the amplitude of S waves from the Abu Dabbab earthquakes with the epicentral distance is examined from the records of various stations of the ASN. It was found the rater of decay can be divided into two distinct types, related to different paths between the hypocenters and the stations, which in turn indicate different depths of the studied events.