Source Mechanisms and Stress Fields of the 15–16 June 2013 Crete Earthquake Sequence Along Hellenic Subduction Zone
15 June 2013 M w 6.1 off-shore southern Crete earthquake and its aftershock sequence along Hellenic Subduction Zone are examined. Centroid moment tensors (CMTs) for 40 earthquakes with moment magnitudes (M w) between 3.5 and 6.1 are determined by applying a waveform inversion method. The mainshock is shallow focus thrust event with a minor strike-slip component at a depth of 20 km. The seismic moment (M o) of the mainshock is estimated as 2.07 × 1018 Nm, and rupture duration of the mainshock is 4 s. The focal mechanisms of aftershocks are mainly thrust faulting with a strike-slip component. The geometry of the moment tensors (M w ≥ 3.5) reveals a thrust faulting regime with N–S trending direction of P axis in the entire activated region. According to high-resolution CMT solutions of the off-shore southern Crete earthquake sequence, one main cluster consisting of 40 events is revealed. The aftershock activity in the observation period between 15 June and 15 July 2013 extends from N to S and NW to SE directions. Seismic cross sections indicate a complex pattern of the hypocenter distribution with the activation of two segments. The subduction interface is clearly revealed with high-resolution hypocenter source relocation and moment tensor solution. The best-constrained focal depths indicate that the aftershock sequence is mainly confined in the upper plate (depth < 30 km) and is ranging from about 5–28 km depth. A stress tensor inversion of focal mechanism data is performed to obtain a more precise picture of the off-shore southern Crete stress field. The stress tensor inversion results indicate a predominant thrust stress regime with a NE–SW-oriented maximum horizontal compressive stress (S H). According to variance of the stress tensor inversion, to first order, the southern Crete region is characterized by a homogeneous interplate stress field. We also investigate the Coulomb stress change associated with the mainshock to evaluate any significant enhancement of stresses along southern Crete and surrounding regions. Positive lobes with stress more than 0.3 bars are obtained for the mainshock, indicating that these values are large enough to increase the Coulomb stress failure toward WNW–ESE direction.
KeywordsAftershock Coulomb stress analysis Crete earthquake focal mechanism moment tensor inversion stress tensor inversion
Author thanks all members of the GeoForschungsZentrum Potsdam GEOFON for providing the continuous seismological data used in this study. The author is also grateful to Dr. Masaru Nakano for providing the waveform inversion code. I would like to thank Adrien Oth (Solid Earth Sciences Editor) and two anonymous reviewers for their constructive comments and suggestions which improved the manuscript. All figures are generated by Generic Mapping Tools (GMT) code developed by Wessel and Smith (1998).
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