Tehran is situated in the northern margin of the morphotectonic zones of the central Iran and on the border of the southern mountain bases of the morphotectanic unit of the central Alborz. The location of the city between these two has made it vulnerable to direct and indirect impacts from both. The substratum of Tehran is formed by Alborz mountain-based alluvial fans. The fans are settled on the volcanic-sedimentary base stones of the Mesozoic era and have constantly changed under the influence of the recent tectonic activities in the Quaternary , making the present morphology of Tehran. Geomorphologically, Tehran is divided into 4 sections and a number of subsections as follows:
1. The mountainous part of Alborz: The mountainous part of Alborz in the north of Tehran consists of the heights surrounding Tochal mountain and the southern slopes overlooking Tehran. Tochal peak has a height of 3900 meters and its main ridges overlooks the southern slopes and Tehran plain, and forms small drainage basins. The rivers flowing in these basins are the life veins of the city. Water constantly flows in these basins and probably the main reason why Tehran developed is its hydromorphological conditions influenced by its northern heights. The most important basin which cover the southern slopes of the northern heights of the city include: Kan, Farahzad, Darakeh and Darband basins. The northern fault of Tehran is the border of the mountainous part of the city in the north and its mountain-based alluvial fans.
Geomorphologic overview map of the area of Tehran and its surroundings
Figure 1.3 Block diagram of geomorphology within Tehran limits