The focal mechanisms in Iran and their relations to tectonics

Abstract

Data from focal mechanism solutions obtained by different authors and those of 8 fault-plane solutions found in this study have been used to search for the distribution of the main stress axes in Iran. For this purpose, the area has been divided into three regions as southern, central and northern Iran. The results indicate that the characteristics of the motion at the foci are different in each of the three regions. — By examining the B axes in south Iranian earthquakes, direction of tectonic motion has been obtained as N 66°E. Since the maximum and intermediate stress axes are nearly horizontal, it is concluded that focal movements in this region are of reverse fault type. Thus, there is a similarity between recent crustal movements and those occurring during Alpine orogeny which is in the form of an overthrusting to the southwest. — In central Iran earthquakes however, tension is predominant, and, therefore, in this region faultings are dip-slip normal or strike-slip, and the horizontal components of displacements are dextral. The mean direction of maximum tension axes is nearly perpendicular to the central Iranian complexes. — It is deduced from north Iranian shocks that, in this region, the earthquakes studied are of nearly almost pressural type, and horizontal components of the oblique displacements in foci are sinistral.