Stress field and tectonic regime of Central Iran from inversion of the earthquake focal mechanisms.

This paper provides a latest compilation of data on the present-day stress pattern in Central Iran and its tectonic regime. We compiled 103 focal mechanism data collected from the Global Centroid Moment Tensor Project (GCMT) including data from Harvard University (HRVD) and the International Seismological Center (ISC). Stress inversion of all shallow focal depths provides a first order stress field with a N029°E maximum horizontal compressive stress (SH max) direction corresponding to a general compressive tectonic regime. In order to reconstruct the second and third order stress fields, we subdivided the study area into eight zones on the basis of their structures, relatively similar focal mechanisms and relatively homogeneous deformation. For each zone and for the same data set, reduced stress tensors have been obtained by formal stress inversion using the Win-Tensor program and modified SLICK method. Both inversion methods show similar results for horizontal stress axes orientations and for the tectonic regimes. The obtained NE-SW direction of the first order stress field is related to Arabia-Eurasia convergence as confirmed by the geodetic measurements. This stress field is responsible for accommodation of shortening within Central Iran and right-lateral movement along the N-S faults as well as left-lateral movement along the E -W faults. Solid block rotation between strike-slip and thrust faults, vertical rotation of the fault bounded blocks, escape tectonics, block extrusion and strain partitioning occurred due to second and third order stress fields with variable SH max directions from N006° to N081° and in different tectonic regimes. [Display omitted] • Inversion of crustal focal mechanisms detects stress field orders in Central Iran. • The first order SH max is N029°E corresponding to a compressive tectonic regime. • The second and third order SH max vary from N006° to N081° related to variable tectonic regimes. [ABSTRACT FROM AUTHOR]