Determination of directions of principal stresses causer of south Marzan abad faults (Karaj - Chalus road)

Category Tectonic & Seismotectonic
Group GSI.IR
Location The 25 Symposium of Geosciences
Author A.Tavakouli
Holding Date 01 July 2007



Alborz mountain range, that is located in north Iran, is part of Alps-Himalaya orogenic belt. This mountain range is created by Cimmerian and Alpide Orogeny and affected with several tectonic events from late Triassic time to the present day. In fact, Alborz is caused of convergence and compressional movements between Central Iranian Block and South Caspian Basin.

In this investigation, we try to find stress field orientation at the time of faulting in study area based on its faults geometry and movement directions. Thus, with individual analyze of fault plane solution of 21 main faults, the orientation of pressure axis (P), which reflects the maximum compressive stress, and tension axis (T), which reflects the minimum compressive stress, for everyone of faults is determined. Then the orientations of principal stresses axis, at the time of faulting in study area, are determined from contour diagrams for each axis and Aleksandrowski method(1985).

The orientation of s1, s2 and s3 axis are 12/360, 16/093 and 70/235, respectively. Compare of calculated principal compressive axis with the same parameters of Baladeh earthquake (2004/05/28, Mw=6.2) shows that perhaps these axis (P, b and T) are rotated 30 degree clockwise around 81/120, axis of rotation, to the present time. On the other hand, according to the orientation of movement plane and s1, it is possible that the most of faults in study area are generated (or inverted) before Plio-quaternary time and maybe in Miocene.