الگوي دگرريختي و هندسه پهنه گسله شمال البرز (بين طولهاي جغرافيايي 52 تا 54 درجه خاوري )

Deformation Pattern and Geometry of North Alborz Fault Zone (Between Longitudes 52 0 - 54 0 E)

The northern flank of East - Central Alborz located between 52ʹ - 54 o E is characterized by an abrupt change of trends. The study area covers the eastern and western part of the mentioned change of trends. In this article and attempt has been made to determine the geometry and mechanism of the North Alborz Fault Zone, in eastern and central part of the study area.In order to achieve this purpose, statistical analysis of the prevailing fault mechanisms has been made and stress direction arc determined.According to statistical investigations, it is possible to distinguish four fault trends similar to the fault patterns of the other parts of Iran. The main trends are as follows: " NW-SE, NE-SW, N-S, E-W " . These trends of faults appear in well defined zones. The presence of the high angle reverse fault dipping to the south indicates a compressive tectonic regime. In general , two: different fault trends can be separated among the four mentioned trends according to the compressional regime affecting the North Alborz Fault zone. The deviation of two trends of faults are located between 52 ° , 50ʹ to 53 ° E.Although, the main sense of motion on these two trends is reverse, they differ by opposite horizontal components of small magnitude.The stress analysis based on inversion of fault-slip data has been carried out in North Alborz Fault Zone in order to characterize the direction of contemporary stress. Two different directions of compression have been recognized. Both the geological and geomorphological evidences confirm recent activity which are in good agreement with seismic data. However, the few available focal mechanisms in this area accord with geological data.