Moment tensor inversion of recent small to moderate sized earthquakes: implications for seismic hazard and active tectonics beneath the Sea of Marmara

Abstract

We retrieve the moment tensors of 64 small to moderate sized events that occurred mostly beneath the Sea of Marmara using near-field data recorded at strong-motion and broad-band seismic stations. The near-field displacement records are inverted to their sources utilizing Kuge's method where the best fit between the synthetic and observed seismograms is achieved through searching a centroid moment tensor (CMT) point in a grid scheme. We also analyse the stress fields acting in the eastern and western parts of the Sea of Marmara by inverting the P - and T -axes of the focal mechanisms obtained. Significant biases in the stress tensors are obtained. The nearly horizontal maximum compressive axis sigma(1) in the western part is rotated 16degrees counter-clockwise compared with sigma(1) in the eastern part. The sigma(2) -axis is close to vertical (shear tectonic regime) in the east and the plunge of sigma(2)-axis in the west is 36degrees (transpressive tectonic regime). Changes in the sigma(3) -axis are also observed, that is, it is close to horizontal in the east and dips 49degrees in the west.