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Ayvacık district of Çanakkale province was hit by four moderate size earthquakes on 6 February 2017 03:51 Mw 5.2, 6 February 2017 10:58 Mw 5.1, 7 February 2017 02:24 Mw 5.2, 12 February 2017 13:48 Mw 5.3. Centroid moment tensor solutions for 60 events with moment magnitudes (Mw) between 3.4 and 5.3 are computed by applying a waveform inversion method on data from the Turkish and Greek broadband seismic networks. The time span of data covers the period between 1 January and 28 February 2017. The mainshock is a shallow focus normal event with strike-slip component at a depth of 10 km. Focal depths of aftershocks range from 3 to 24 km. The seismic moment (Mo) of the mainshock is estimated as 7.62 × 1016 Nm. The calculated rupture duration of the Ayvacık mainshock is 3 s. The focal mechanisms of the aftershocks are mainly normal faulting with a minor strike-slip component. The geometry of focal mechanisms reveals a normal faulting regime with NE-SW trending direction of T-axis in the entire activated region. We perform stress tensor inversion to acquire more accurate picture for the regional stress field. The stress tensor inversion results indicate a predominant normal stress regime with a WNW-ESE oriented maximum horizontal compressive stress (SH). With respect the newly determined focal mechanisms, the effect of the propagation of the North Anatolian Fault into Aegean Sea is very clearly pronounced. According to the double-difference relocation algorithm for the 2017 Ayvacık seismic sequence, ten clusters are revealed. In order to find these clusters, we use HypoDD software. According to the relative relocations from HypoDD, we define 10 clusters along the five profiles. The aftershock activity in the observation period between 1 January and 28 February 2017 extends from W to E direction. Seismic cross-sections indicate that a complex pattern of the hypocenter distribution with the ruptured segments. The western cluster is associated with a fault plane trending mainly N- S and dipping vertical, while the eastern is related to a fault plane trending NE-SW and dipping towards NW. The best constrained focal depths operate in the approximate depth range from 3 to 24 km. Coulomb stress analysis is performed to calculate the cumulative effect of all the earthquakes of the swarm and correlate it with the activated region. Positive lobes with stress more than 3 bars are obtained, these values are large enough to trigger failure towards NW-SE of the swarm activity.
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