Separation of paleostress phases using fault slip data in the Khalkhal region

In this study, separation of paleostress phases in the Khalkhal region has been doneusing paleostress analysis based on heterogeneous fault slip data and related slip lineations.The data have been measured and collected from the Jurassic, Cretaceous and Eocene units.To determine the sense of shear or slip, indices such as stratigraphic separation across the faults, kinematic indicators on fault surfaces, conjugate fractures, and tensile cracks were used.The data were analyzed with the help of inversion method. The results indicate that strike-slip regime is dominant in the region. Constraining the stress phases and comparison with the field and seismic data revealed that the third stress regime is characterized by avertical σ2and a NE-SW extension related to the modern stress regime, which is also compatible with the seismic data. The first and second phases of stress prevailed along NW-SE and N-S directions related to the paleostress regimes.Various investigations, including rose diagram analysis of faults and arrangement of structures show that the faults in the region are dominantly strike-slip and strike-slip with normal component, and the shape of the stress field in the region is prolate.