The 24 May 2014 Mw 6.9 Gokceada, North Aegean Sea Earthquake and Its Aftershocks

Abstract:

On 2014 May 24, the Gokceada Island in northern Aegean Sea region was hit by an M_w = 6.9 earthquake. The Gokceada earthquake occurred 43 km SW of Gokceada Island. Centroid moment tensors for 42 events with M_w between 3.5 and 6.9 are computed by applying a waveform inversion method. The time span of data covers the period between 2014 May 24 - June 26. The mainshock is a shallow focus strike-slip event at a depth of 15 km. Focal depths of aftershocks range from 5 to 25 km. The seismic moment (M₀) of the mainshock is estimated 2.53 × 10¹⁹ Nm. The focal mechanisms of the aftershocks are mainly strike-slip faulting with a variable and sometimes significant normal component. This geometry indicates a strike-slip faulting regime with NE-SW trending direction of T-axis in the entire activated region. A Stress tensor inversion of focal mechanism data is performed to obtain a more accurate picture of the Gokceada earthquake stress field. The stress tensor inversion results show a predominant strike-slip stress regime with a NW-SE to NNE-SSW oriented maximum horizontal compressive stress (S_H). The secondary fault system striking mostly E-W is activated generally with normal faulting in the east of the mainshock. This difference in mechanism suggests that towards the east, a different fault system is activated with respect to the NE-SW trending strike-slip faults beneath Gokceada Island and more to the west. Thus, to first order, the Gokceada Island earthquake region is characterized by a homogeneous intraplate stress field.