State of stress induced by plate convergence and stress partitioning in northeastern Iran, as indicated by focal mechanisms of earthquakes

Behzad Zamani G., Jacques Angelier and Ahmad Zamani

Abstract

We analyse the state of stress in northeastern Iran, based on systematic inversion of available focal mechanisms of earthquakes. The calculated average stress regimes in this area indicates major N32°E trending compression expressed in reverse and strike-slip focal mechanisms, consistent with the plate convergence in Iran that shows clockwise deflection with respect to Arabia-Eurasia convergence. A secondary stress regime is reliably characterised from our stress inversion, with a N172°E trending compression expressed in focal mechanisms of predominant strike-slip type. Whereas the NNE–SSW and N–S compressions coexist in the western Kopet Dagh, East Alborz and the northwestern Doruneh fault zone, where the structural grain trends ENE–WSW, the N–S compression is absent in the eastern and central Kopet Dagh, Binalud and northeastern Doruneh fault zone, where the structural grain trends ESE–WNW, perpendicular to relative motion. This configuration reveals stress partitioning involving oblique compression with significant along-belt component of left-lateral shear to the west, in contrast to typical belt-perpendicular compression in the eastern sub-area.