Investigation of stress and strain rate variations in the Central Alborz by using earthquake focal mechanisms and GPS velocity vector data

The Alborz, as one of the important seismotectonic provinces in Iran, has a great vulnerability from natural disasters, especially seismic risk point of view, because of the existence of Tehran megacity in its southern edge. The importance of this area has caused a relatively dense GPS network around it. In this study, the earthquake focal mechanism data obtained from different resources was used for stress tensor inversion in the Central Alborz. On the other hand, interpolation of the GPS vectors in rectangular grids and differentiation in the center of each grid cell was used for the study of strain rate in this area. The results showed special variation in principal axes of stress and strain rate, and also the changes in areal and maximum shear strain rates in different parts of the Central Alborz, which shows the geodynamic complexity of the study area. Finally, the angular differences between the maximum horizontal stress and strain rate compressive axis directions were calculated in the location of the clusters of the earthquakes. These calculations showed that the extent of the strain partitioning in the middle parts of the mountain range, where strike-slip motions on Mosha and Firuzkuh faults are observed, has more significant effect on the current deformation processes in the Central Alborz. Meanwhile, in the Northern parts of the range, where dominantly sip slip motions on Khazar Thrust and North Alborz fault occurs, deformation partitioning plays a minor role in the region