Stress Inversion of Regional Seismicity in the Sea of Marmara Region, Turkey

In this study we derive the stress tensor and its local variations throughout the Marmara region, Turkey. Based on a recently compiled 10-year earthquake catalogue, we directly invert first-motion polarity data and quantify confidence intervals for the principal stress orientations. We find a combined strike-slip and normal faulting stress field for the Marmara region generally reflecting the overall transtensional setting. However, the results clearly show moderate local variations of the stress field. The largest (${\sigma }_1$) and intermediate (${\sigma }_2$) principal stresses show an average regional trend of N$125{}^{\circ }$E and locally varying plunges. The least principal stress (${\sigma }_3$) is well resolved in its confidence interval and consistent throughout the region with an average trend of $\sim$ N$35{}^{\circ }$E and a subhorizontal plunge. The eastern Sea of Marmara shows local stress field orientations with pronounced strike-slip (northern part) and normal faulting (southern part) components. Along the central Marmara region, normal faulting tends to dominate, while a well resolved strike-slip stress regime is found in the western Sea of Marmara region. Regarding the faulting mechanism of an earthquake with magnitude up to 7.4 which is expected in this area in direct vicinity of the Istanbul metropolitan region, our results imply that neither strike-slip nor normal faulting kinematics can be excluded.