THE ANALYSIS OF SEISMIC STRESS REGIME IN AHAR- VARZEGHAN REGION, NORTHWESTERN IRAN

We analyze stress state in northwestern Iran which includes Ahar-Varzeghan region by determining the focal mechanisms of 15 earthquakes using the moment tensor inversion method of ISOLA and also by focal mechanisms of other large and moderate earthquakes determined by GCMT. The events have moment magnitudes higher than 4 and encompass latitudes between 34- 40° N, and longitudes between 43- 51° E, during the period 1976-2013. We calculate the principal orientations of stresses in the region by multiple inverse method. The result shows the stress model with σ1 direction equal to 136.7 degree. In contrast, the direction of the principal stress is almost north-south in eastern Anatolia and east-west in western Caspian sea. This difference in geodynamic regimes in the study area may be attributed to the north Tabriz fault.

Keywords:

Stress , Focal Mechanism , ISOLA , Multiple Inverse Method , Ahar-Varzeghan